A method of welding by on-line vapor phase welding

Abstract

This application provides an online vapor phase welding method, relating to the field of vapor phase welding technology, implemented by a vapor phase welding device comprising a preheating chamber, a reduction chamber, a welding chamber, and a cooling chamber. The preheating chamber and welding chamber have independent heating elements and vapor phase liquid injection pipelines on their inner walls. The reduction chamber has a liftable heating plate at its bottom connected to a nitrogen-formic acid mixed gas pipeline. The workpiece first enters the preheating chamber, where, under vacuum and stable pressure, the vapor phase liquid is uniformly preheated by the wall heating field to form saturated vapor. Residual heat vapor is evacuated and condensed for recovery. The workpiece is then sent to the reduction chamber, where it undergoes vacuum pressure holding, contact heating with the heating plate, and reduction treatment with a nitrogen-formic acid mixed gas. After the reaction byproducts and flux volatiles are evacuated, nitrogen is purged and the workpiece is repressurized for transfer. The welding chamber is similarly heated by vacuum saturated steam to melt the solder and complete the welding. The steam is recovered and sent to the cooling chamber. Nitrogen is introduced into the cooling chamber under vacuum to cool the workpiece before it is sent out. This method enables continuous vapor phase welding of workpieces, with a uniform temperature field and thorough reduction, significantly improving welding quality and process stability.

Description

Technical Field

[0001] This invention belongs to the field of vapor phase welding technology, and specifically relates to an online vapor phase welding method. Background Technology

[0002] In current vapor phase welding processes, to complete preheating, welding, and cooling within a single production cycle, a single-chamber or double-chamber structure is typically used, repeatedly performing vacuuming, heating, and cooling operations within a single chamber. The large heat capacity of a single chamber itself leads to severe thermal inertia hysteresis during wide temperature cycling. Specifically, each process cycle requires a significant amount of time and energy to repeatedly heat and cool the chamber body, rather than directly and efficiently applying heat to the workpiece. This fundamentally limits production cycle time and becomes the core bottleneck preventing vapor phase welding technology from efficiently integrating with automated production lines and achieving large-scale mass production. Summary of the Invention

[0003] In view of the above-mentioned defects or deficiencies in the prior art, a controller-based online vapor phase welding device is provided. The device includes a preheating chamber, a reduction chamber, a welding chamber, and a cooling chamber arranged sequentially along the workpiece conveying direction. Heating elements are installed on the inner top wall, inner bottom wall, and inner side wall of both the preheating chamber and the welding chamber, each independently connected to a vapor phase liquid injection pipeline. A liftable heating plate is installed at the bottom of the reduction chamber and connected to a nitrogen and formic acid mixed gas supply pipeline. The controller is configured to: The system receives a signal that the workpiece has entered the preheating chamber, controls the preheating chamber to be evacuated to a preset vacuum range and maintains a stable pressure. The heating field formed by the heating elements on each wall causes the injected liquid vapor phase to evaporate into a saturated vapor atmosphere, which uniformly preheats the workpiece. After the preheating is completed, the uncondensed vapor is evacuated, condensed and recovered, and the workpiece is transferred to the reduction chamber. Upon receiving a signal that the workpiece has entered the reduction chamber, the first reduction operation is executed: the reduction chamber is first evacuated to a set vacuum level and then sealed and pressurized; then the heating plate is raised to contact the bottom surface of the tray carrying the workpiece for contact heating; and a mixture of nitrogen and formic acid is quantitatively introduced into the chamber to a slightly positive pressure to reduce the workpiece. After the preset reduction time is met, the second reduction operation is executed: the reduction chamber is evacuated to remove the gaseous byproducts and flux volatiles generated by the reduction reaction; after evacuation, nitrogen is introduced to restore atmospheric pressure, and the workpiece is transferred into the welding chamber. Upon receiving a signal that the workpiece has entered the welding chamber, the welding chamber is evacuated to a preset vacuum level and maintained under stable pressure. The heating field formed by the heating elements on each wall causes the injected liquid vapor phase to evaporate into a saturated steam atmosphere, which uniformly heats the workpiece until the solder melts and welding is completed. After welding is completed, the uncondensed steam is evacuated, condensed and recovered, and the workpiece is transferred to the cooling chamber. The system receives a signal that the workpiece has entered the cooling chamber, controls the cooling chamber to circulate nitrogen gas under vacuum to cool the welded workpiece, and then transmits the signal out.

[0004] According to the technical solution provided in this application, the liquid medium recovered by evacuation and condensation in the preheating chamber and the welding chamber is respectively returned to a common storage tank. The common storage tank is provided with a partition structure to divide the space inside the tank into a first storage area and a second storage area. The condensate recovered from the preheating chamber flows into the first storage area, and the condensate recovered from the welding chamber flows into the second storage area. The liquid medium in the two areas is not interconnected. The controller is also configured to: When performing the process of the preheating chamber, liquid medium is preferentially drawn from the first liquid storage area and injected into the preheating chamber. When the liquid level in the first liquid storage area is lower than the preset minimum liquid level threshold, fresh vapor-phase liquid is injected into the preheating chamber from the second liquid storage area or externally. During the process of the welding chamber, only fresh vapor phase liquid replenished from the second liquid storage area or externally is injected into the welding chamber.

[0005] According to the technical solution provided in this application, the nitrogen and formic acid mixed gas supply pipeline includes a mass flow controller for independently adjusting the flow rates of nitrogen and formic acid respectively. The process of quantitatively filling the chamber with a mixture of nitrogen and formic acid to a slightly positive pressure includes the following steps: The first mixed gas with a formic acid volume concentration in the first preset concentration range is controlled to be introduced into the chamber, so that the pressure in the chamber reaches the first preset micro-positive pressure value and is maintained for the first preset time, so as to form an initial reducing and wetting atmosphere rich in formic acid on the surface of the workpiece. After the first inflation sub-stage is completed, nitrogen is injected to increase the pressure inside the chamber from the first preset micro-positive pressure value to the second preset micro-positive pressure value. At the same time, the formic acid flow rate is adjusted by the mass flow controller to reduce the volume concentration of formic acid inside the chamber from the first preset concentration range to the second preset concentration range. During or after the second inflation sub-stage, at least one pressure oscillation cycle is performed, the pressure oscillation cycle comprising: partially or completely extracting the gas in the chamber until the pressure in the chamber drops to a preset lower limit pressure for oscillation, and then re-injecting the mixed gas or nitrogen into the chamber to restore the pressure in the chamber to the second preset micro-positive pressure value.

[0006] According to the technical solution provided in this application, a temperature measuring device is provided inside the preheating chamber and / or the welding chamber, and the temperature measuring device includes: A temperature measuring bracket is fixedly installed on the inner bottom wall of the cabin. A temperature measuring base is installed on the temperature measuring bracket; A temperature-sensing contact copper block is movably mounted on the temperature-sensing base via a guide portion. A high-temperature spring is fitted on the guide portion so that the temperature-sensing contact copper block can elastically float along the axial direction of the guide portion. A temperature-sensing thermocouple is installed at the bottom of the temperature-sensing contact copper block; The temperature-measuring contact copper block has a flat middle section and beveled ends. When the workpiece tray passes by, the beveled ends guide the tray to gradually compress the high-temperature spring, eventually making it tightly fit against the flat middle section.

[0007] According to the technical solution provided in this application, the controller is further configured such that: the preheating stage of the preheating chamber includes a radiant preheating section and a steam heating section; the controller is further configured such that: In the radiation preheating section, after the workpiece enters the preheating chamber, without the injection of liquid vapor phase liquid, the upper heating element in the preheating chamber is controlled to operate at the first upper radiation power, the lower heating element at the first lower radiation power, and the side heating element at the first side radiation power, so as to preheat the workpiece by pure thermal radiation. The workpiece surface temperature is obtained through the temperature measuring device. When the workpiece surface temperature reaches above the preset steam dew point temperature, the radiation preheating section is terminated and the steam heating section begins. In the steam heating section, the power of the lower heating element is increased to an evaporation power higher than the first lower radiation power, and the power of the upper heating element is decreased to a heat preservation power lower than the first upper radiation power. Liquid vapor phase is injected into the chamber, and the liquid vapor phase is evaporated by the lower heating element to form a steam atmosphere, while the upper heating element maintains the steam in a saturated state.

[0008] According to the technical solution provided in this application, obtaining the workpiece surface temperature through the temperature measuring device includes the following steps: In the radiation preheating section, when the workpiece tray passes the temperature measuring device, the temperature response curve of the temperature measuring thermocouple is recorded throughout the entire process from the tray contacting the inlet end slope of the temperature measuring contact copper block to the tray leaving the outlet end slope. Extract the duration of the temperature stability segment corresponding to the planar contact stage in the middle section of the temperature-measuring copper block from the temperature response curve; If the duration is greater than or equal to a preset duration threshold, the surface temperature of the workpiece is obtained based on the temperature value of the temperature stabilization segment. If the duration is less than the duration threshold, then the temperature decrease rate of the temperature response curve at the corresponding stage of the outlet slope is extracted. If the deviation between the temperature drop rate and the normal temperature drop rate is within a preset range, it is determined that the insufficient duration is caused by the attenuation of the elastic force of the high-temperature spring, a spring maintenance reminder is generated, and the temperature value of the temperature stabilization segment is corrected by a preset compensation and used as the surface temperature of the workpiece. If the deviation between the temperature drop rate and the normal detachment drop rate exceeds the preset range, it is determined that the insufficient duration is caused by an abnormality on the bottom surface of the workpiece tray, and a tray abnormality prompt is generated.

[0009] According to the technical solution provided in this application, in the steam heating section, the controller is further configured to perform temperature field self-balancing control on the side heating element, including the following steps: Before injecting the liquid vapor phase, the side heating element is controlled to be turned on in advance with the first side heat preservation power to preheat the inner side wall of the chamber to a temperature not lower than the saturation temperature of the vapor phase to be injected under the current pressure. After the liquid vapor phase is injected, the temperature of at least two different measurement points on the surface of the workpiece is continuously obtained by the temperature measuring device. The measurement points include an edge area measurement point near the side wall of the chamber and a center area measurement point away from the side wall. If the temperature at the edge region measurement point is lower than the temperature at the center region measurement point, and the temperature difference between the two exceeds a preset edge temperature difference threshold, then the power of the side heating element is increased to increase radiative heating compensation for the workpiece edge region. If the temperature at the edge region measurement point is higher than the temperature at the center region measurement point, and the temperature difference between the two exceeds a preset center temperature difference threshold, then the power of the side heating element is reduced to reduce radiant heating of the workpiece edge region. If the temperature difference between the measurement point in the edge region and the measurement point in the center region remains within the allowable deviation range, then the current power of the side heating element is maintained.

[0010] According to the technical solution provided in this application, the insulation power of the first side is dynamically determined by the controller during the process of a single batch, including the following steps: During the radiation preheating phase, the side heating element is operated with the first side radiation power, and the real-time temperature of the inner sidewall of the cabin is recorded at the end of this phase. As the liquid to be injected approaches the steam heating section, the saturation temperature of the vapor phase liquid at that pressure is obtained based on the current chamber pressure. The saturation temperature is compared with the real-time temperature of the sidewall: if the saturation temperature is higher than the real-time temperature of the sidewall, the first side insulation power is set to be higher than the first side radiation power to compensate for the heating demand of the sidewall before entering the steam heating section; if the saturation temperature is lower than the real-time temperature of the sidewall, the first side insulation power is set to be lower than the first side radiation power to avoid overheating of the sidewall. The adjustment range of the first side insulation power is positively correlated with the difference between the saturation temperature and the real-time temperature of the side wall, and the adjustment range is determined by the built-in thermal balance formula, which is based on the heating efficiency of the side heating element, the heat capacity of the cabin side wall and the heat dissipation characteristics pre-calibrated.

[0011] According to the technical solution provided in this application, the pre-calibration of the thermal equilibrium relationship includes the following steps: In the calibration mode after initial equipment commissioning or maintenance, the side heating element is controlled to operate sequentially at multiple different calibration power values, and the real-time temperature of the inner side wall of the cabin is monitored until the side wall temperature reaches a steady state under each calibration power value. Record the steady-state sidewall temperature and the current ambient temperature corresponding to each calibration power value, and construct a calibration data set that characterizes the relationship between heating input power and net sidewall temperature rise; Based on the calibration data set, a first characteristic coefficient corresponding to the electrothermal conversion efficiency of the side heating element and a second characteristic coefficient corresponding to the heat dissipation capacity of the cabin sidewall to the environment are determined by numerical fitting. The first characteristic coefficient and the second characteristic coefficient together constitute the heat balance relationship.

[0012] According to the technical solution provided in this application, the following steps are also included: At the end of the radiation preheating section of each process batch, the average actual operating power of the side heating element in this radiation preheating section, the real-time side wall temperature at that moment, and the current ambient temperature are obtained as a set of online correction sample data. The consistency of the online corrected sample data with the currently valid heat balance relationship is compared to generate a deviation quantity characterizing the degree of deviation of the relationship at the current operating point; If the deviation exceeds a preset correction trigger threshold, a recursive fitting algorithm with a forgetting factor is triggered to incorporate the online correction sample data and correct the first feature coefficient and the second feature coefficient.

[0013] Compared with the prior art, the beneficial effects of this application are as follows: By configuring a preheating chamber, a reduction chamber, a welding chamber, and a cooling chamber, and ensuring that each chamber independently maintains its own stable process atmosphere, the following beneficial effects are achieved: I. Eliminating the constraints of chamber thermal inertia on production cycle time, enabling continuous production. Once activated, each functional compartment can maintain its required steady-state temperature and pressure environment without repeated heating and cooling. Workpieces flow sequentially between compartments, eliminating the wasted time and energy spent on repeated heating and cooling of chambers in traditional processes. This allows vapor phase welding to operate continuously in an assembly line manner, significantly improving production efficiency and enabling seamless integration with automated production lines.

[0014] II. Significantly Reduced Equipment Energy Consumption and Thermal Shock Losses. The preheating and welding chambers maintain continuous temperature, and the heating elements operate under steady-state conditions, avoiding the repeated peak power surges required to compensate for chamber cooling in batch processing modes, resulting in a substantial reduction in overall energy consumption. Simultaneously, the structure of each chamber and its seals are freed from the thermal fatigue cycle caused by repeated and severe thermal expansion and contraction, fundamentally improving equipment lifespan and long-term process stability. Attached Figure Description

[0015] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 A flowchart illustrating the steps of the online vapor phase welding method provided in this application; Figure 2 A schematic diagram of the online vapor phase welding equipment provided in this application; Figure 3 A schematic diagram showing the installation location of the temperature measuring device provided in this application; Figure 4 A schematic diagram of the temperature measuring device provided in this application.

[0016] The text labels in the image represent: 1. Installation platform; 2. Preheating chamber; 3. Reduction chamber; 4. Welding chamber; 42. Upper heating element; 43. Side heating element; 44. Lower heating element; 5. Cooling chamber; 6. Temperature measuring device; 61. Temperature measuring contact copper block; 62. High temperature spring; 63. Guide part; 64. Temperature measuring base; 65. Temperature measuring thermocouple; 66. Temperature measuring bracket. Detailed Implementation

[0017] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0019] As mentioned in the background section, this application proposes a controller-based online vapor phase welding device. The device includes a preheating chamber 2, a reduction chamber 3, a welding chamber 4, and a cooling chamber 5 arranged sequentially along the workpiece conveying direction. The preheating chamber 2 and the welding chamber 4 each have heating elements located on their inner top, bottom, and side walls, respectively, and are independently connected to vapor phase liquid injection pipelines. The reduction chamber 3 has a liftable heating plate at its bottom and is connected to a nitrogen and formic acid mixed gas supply pipeline. The controller is configured to: Upon receiving a signal that the workpiece has entered the preheating chamber 2, the preheating chamber 2 is evacuated to a preset vacuum level and maintained under stable pressure. The heating field formed by the heating elements on each wall causes the injected liquid vapor phase to evaporate into a saturated vapor atmosphere, which uniformly preheats the workpiece. After preheating, the uncondensed vapor is evacuated, condensed, and recovered before the workpiece is transferred to the reduction chamber 3. Upon receiving a signal that the workpiece has entered the reduction chamber 3, the first reduction operation is executed: the reduction chamber 3 is first evacuated to a set vacuum level and then sealed and pressurized; then the heating plate is raised to contact the bottom surface of the tray carrying the workpiece for contact heating; and a mixture of nitrogen and formic acid is quantitatively introduced into the chamber to a slightly positive pressure to reduce the workpiece. After the preset reduction time is met, the second reduction operation is executed: the reduction chamber 3 is evacuated to remove the gaseous byproducts and flux volatiles generated by the reduction reaction; after evacuation, nitrogen is introduced to restore normal pressure, and the workpiece is transferred to the welding chamber 4. Upon receiving a signal that the workpiece has entered the welding chamber 4, the welding chamber 4 is evacuated to a preset vacuum level and maintained under stable pressure. The heating field formed by the heating elements on each wall causes the injected liquid vapor phase to evaporate into a saturated steam atmosphere, which uniformly heats the workpiece until the solder melts and welding is completed. After welding is completed, the uncondensed steam is evacuated, condensed and recovered, and the workpiece is transferred to the cooling chamber 5. Upon receiving a signal that the workpiece has entered the cooling chamber 5, the system controls the cooling chamber 5 to introduce nitrogen gas into the vacuum state to cool the welded workpiece before it exits.

[0020] Specifically, before implementing this method, the hardware setup of the equipment must be completed. Four independent chambers—preheating chamber 2, reduction chamber 3, welding chamber 4, and cooling chamber 5—are installed sequentially along the linear conveying direction. These chambers are connected in series via pneumatic or electric isolation valves. The conveying system uses a high-temperature resistant roller conveyor or chain conveyor mechanism. Workpieces are placed on metal trays and driven by the conveying mechanism to move between the chambers in a rhythmic manner. The controller is a programmable logic controller (PLC) with analog and digital input / output modules; alternatively, an industrial control computer with a data acquisition card can be used. The controller's inputs are connected to the vacuum gauge signals, temperature sensor signals, valve position sensor signals, and workpiece arrival detection sensor signals from each chamber. The controller's output is connected to the vacuum pump start / stop control relays of each chamber, the opening control signal of the vacuum regulating valve, the switching or analog input signal of the heating element power regulator, the start / stop and dosage signals of the solenoid valves or injection pumps on the vapor-liquid injection pipeline, the setpoint signals of the mass flow controllers on each gas pipeline, the forward / reverse control signals of the heating plate lifting mechanism, and the opening / closing control signals of all isolation valves. The controller is pre-programmed with process parameter tables, including vacuum thresholds, temperature setpoints, injection volume, and duration for each step, which can be modified via the human-machine interface. Before formal production, the preheating chamber 2 and welding chamber 4 are heated and maintained at a constant temperature under no-load conditions to ensure the heating elements of each chamber wall reach a basic insulation state, while the reduction chamber 3 and cooling chamber 5 can remain in standby mode at room temperature.

[0021] The process of the workpiece entering the preheating chamber 2 is as follows. When the conveying mechanism sends the pallet carrying the workpiece into the preheating chamber 2 and triggers the positioning sensor, the sensor sends a switching signal to the controller. Upon receiving this signal, the controller first sends a closing command to the actuators of the inlet and outlet valves of the preheating chamber 2. After confirming that the valves are closed, it sends a start command to the vacuum pump connected to the preheating chamber 2 and simultaneously sends a fully open command to the proportional control valve in the vacuum pipeline to begin vacuuming. The controller reads the analog signal returned by the vacuum gauge on the preheating chamber 2 in real time and converts it into an actual pressure value. When the actual pressure value drops to the lower limit of the preset vacuum range, such as 50 Pascals, the controller sends a control command to the proportional control valve to reduce the valve opening, thereby reducing the pumping speed and stabilizing the pressure within that range. Pressure stabilization can be achieved through PID closed-loop control. The controller uses the real-time pressure of the vacuum gauge as the process variable and the intermediate value of the preset vacuum level as the setpoint, calculates the value, and outputs a control quantity to the control valve.

[0022] While the pressure stabilizes, the controller sends a given signal to the power regulators of the heating elements on each wall of the preheating chamber 2. The upper heating element 42, lower heating element 44, and side heating element 43 can be given the same power, or different given values ​​can be assigned according to process requirements. The given signal is a 4 to 20 mA analog quantity or digital communication command, which the power regulator uses to adjust the current or duty cycle output to the heating elements. After each heating element is energized, its temperature rises, heating the chamber space through thermal radiation and natural convection. When the temperature inside the chamber reaches above the boiling point of the vapor phase liquid, the controller sends a pulse command to the injection metering pump in the vapor phase liquid injection pipeline. The metering pump then extracts the liquid vapor phase liquid from the storage tank and injects it into the chamber according to the set single injection volume, such as 15 ml. The liquid vapor phase liquid can be perfluorotributylamine or perfluoropolyether, with a boiling point in the temperature range of 150 to 240 degrees Celsius. After entering the high-temperature chamber, the liquid rapidly boils and evaporates upon contact with the bottom wall of the chamber. The controller does not directly control the evaporation process. Instead, it maintains the power supply and pressure stability of the heating elements to keep the steam in a saturated state, thus creating a saturated steam atmosphere. The saturated steam atmosphere can be determined by comparing the steam temperature with the boiling point at the current pressure. When the difference between the two is within 2 degrees Celsius, it is considered saturated.

[0023] After the workpiece is continuously heated in saturated steam for a preset time, such as 60 seconds, the controller executes the evacuation and recovery process. The controller sends a start command to the vacuum pump, switching the evacuation pipeline to the condensation recovery branch. The condensation recovery branch consists of a water-cooled or air-cooled condenser and a gas-liquid separator. The steam is cooled and liquefied as it flows through the condenser and flows into the recovery storage tank. After evacuation until the pressure inside the chamber is below a certain recovery end threshold, such as 200 Pascals, the controller shuts off the vacuum pump and fills the chamber with nitrogen. The nitrogen pipeline is equipped with a solenoid valve and a mass flow controller. The controller sends an open command to the solenoid valve and simultaneously sends a set flow rate value, such as 10 liters per minute, to the mass flow controller. Nitrogen is filled into the chamber until the pressure sensor reports atmospheric pressure, at which point the controller closes the solenoid valve. Then, the controller sends open commands to the outlet valve of preheating chamber 2 and the inlet valve of reduction chamber 3, activating the conveyor mechanism to transfer the workpiece out of preheating chamber 2 and into reduction chamber 3.

[0024] The process of the workpiece entering the reduction chamber 3 is as follows. After the position sensor of the reduction chamber 3 is triggered, the controller executes the first reduction operation. First, the inlet valve of the reduction chamber 3 is closed, the vacuum pump is started, and the evacuation valve is opened to evacuate the reduction chamber 3. The controller reads the vacuum gauge, and when the pressure drops to the set vacuum level, such as 80 Pascals, the evacuation valve and vacuum pump are closed, and the chamber is sealed and pressurized. Then, the controller sends a lifting command to the heating plate lifting mechanism. The lifting mechanism is driven by a servo motor and a lead screw nut or by a cylinder. The controller controls the motor to rotate forward or the cylinder to intake air by outputting a switch quantity or pulse signal. During the rising process of the heating plate, its internal heating element has been pre-energized to a preset temperature, such as 200 degrees Celsius. The determination of when the heating plate rises to contact the bottom surface of the tray can be achieved by a current sensor. When the motor load current jumps above the threshold, the controller determines that contact has been made and stops the rising. Alternatively, it can be achieved by a position sensor, stopping when the encoder feedback reaches the preset height value. After contact, the heat of the heating plate is conducted to the tray and the workpiece through the contact surface.

[0025] After the heating plate makes contact, the controller sends an opening command to the solenoid valve on the nitrogen and formic acid mixture supply line. This line has two mass flow controllers, one for nitrogen and one formic acid, controlling the flow rate respectively. The controller sends a first setpoint to the nitrogen mass flow controller and a second setpoint to the formic acid mass flow controller; the mixture is then introduced into the chamber. During the filling process, the controller continuously reads the feedback value from the chamber pressure sensor. When the pressure reaches a slightly positive pressure setpoint, such as 1.1 times atmospheric pressure, the solenoid valve on the supply line is closed, maintaining a sealed state. Under heating conditions, the formic acid gas undergoes a reduction reaction with the oxides on the workpiece surface. The controller starts an internal timer; after the preset reduction duration, such as 45 seconds, the second reduction operation is executed. The controller opens the vacuum pump and evacuation valve to expel the reacted gas mixture from the chamber. After evacuating to the preset pressure, the evacuation valve is closed, and nitrogen is introduced into the nitrogen line to reach atmospheric pressure. Then, the outlet valve of reduction chamber 3 and the inlet valve of welding chamber 4 are opened, allowing the workpiece to be transferred into welding chamber 4.

[0026] The process of the workpiece entering welding chamber 4 is similar to that of preheating chamber 2, but with different parameters. The controller evacuates welding chamber 4 to a preset vacuum range, such as 80 to 150 Pascals, and maintains a stable pressure. Power commands are sent to the heating elements on each wall, and the heating temperature is set above the melting point of the solder, such as 220 to 260 degrees Celsius. Liquid vapor phase is injected into the chamber, for example, at a dosage of 20 ml. The vapor phase evaporates to form a saturated vapor atmosphere, and the workpiece is heated in the vapor until the solder melts. After welding is held for, for example, 60 seconds, evacuation, condensation recovery, and nitrogen purging are performed to restore atmospheric pressure, and then the workpiece is transferred to cooling chamber 5.

[0027] The process for the workpiece entering cooling chamber 5 is as follows: The controller closes the inlet valve of cooling chamber 5 and starts the vacuum pump to evacuate to a preset value, such as 100 Pascals. Under vacuum, the controller opens the solenoid valve of the nitrogen supply pipeline inside cooling chamber 5, and the cryogenic nitrogen is evenly diffused through the gas distribution plate and blown onto the surface of the workpiece. The temperature of the cooling nitrogen can be pre-cooled to 5 to 15 degrees Celsius by a liquid nitrogen vaporization heat exchanger or a refrigeration unit. The controller monitors the temperature sensor inside cooling chamber 5. When the workpiece temperature drops to the preset range of 20 to 30 degrees Celsius, the nitrogen supply is shut off, nitrogen is purged or the atmosphere is purged to atmospheric pressure, the outlet valve is opened, and the workpiece is transferred to the downstream docking station.

[0028] Through the above-described implementation method of four compartments operating independently in sequence, each compartment operates under its own constant temperature and pressure window, without undergoing repeated heating and cooling cycles. The workpieces flow continuously through each functional station under the drive of the conveyor cycle, realizing online continuous production.

[0029] In a preferred embodiment, the liquid medium evacuated and condensed from the preheating chamber 2 and the welding chamber 4 is returned to a common storage tank. The common storage tank is equipped with a partition structure to divide the space inside the tank into a first storage area and a second storage area. The condensate recovery liquid from the preheating chamber 2 flows into the first storage area, and the condensate recovery liquid from the welding chamber 4 flows into the second storage area. The liquid medium in the two areas is not interconnected. The controller is also configured to: When performing the process of the preheating chamber 2, liquid medium is preferentially drawn from the first liquid storage area and injected into the preheating chamber 2. When the liquid level in the first liquid storage area is lower than the preset minimum liquid level threshold, fresh vapor phase liquid is injected into the preheating chamber 2 from the second liquid storage area or externally. When performing the process in the welding chamber 4, only fresh vapor phase liquid replenished from the second liquid storage area or externally is injected into the welding chamber 4.

[0030] Specifically, a shared storage tank with a partition structure needs to be constructed first. This storage tank is made of welded stainless steel. The partition structure is implemented by welding a vertical partition inside the tank, with the partition height matching the inner cavity height of the tank, dividing the internal space into two independent chambers, serving as the first and second storage zones respectively. Each zone has a liquid outlet at the bottom and a liquid return and venting interface at the top. The partition weld must be airtight to ensure that the liquid media in the two zones do not communicate during storage. Each zone is equipped with a level sensor, which can be a float-type level switch or a submersible level transmitter, outputting a digital or analog signal to the controller.

[0031] The pipeline connections are as follows: The outlet of the condensate recovery device in preheating chamber 2 is connected to the return interface of the first storage area of ​​the shared storage tank via a first recovery pipeline. The outlet of the condensate recovery device in welding chamber 4 is connected to the return interface of the second storage area via a second recovery pipeline. The two recovery pipelines are independent and do not have connecting valves. The liquid extraction pipelines are arranged as follows: the outlet of the first storage area is connected to the inlet of the vapor-liquid injection pipeline in preheating chamber 2 via a first extraction pump; the outlet of the second storage area is connected to the inlet of the vapor-liquid injection pipeline in welding chamber 4 via a second extraction pump. Furthermore, the outlets of the two areas are connected by a connecting pipe equipped with a check valve and a solenoid valve. The check valve allows liquid medium to flow from the second storage area to the first storage area, but not vice versa. External fresh vapor-liquid replenishment pipelines are connected to the replenishment interfaces above the two areas, and solenoid valves are installed on the replenishment pipelines.

[0032] The specific steps of the controller implementing the differentiated liquid extraction strategy are as follows. When preheating chamber 2 needs to be injected with vapor-phase liquid, the controller first reads the feedback value of the liquid level sensor in the first storage area. If the liquid level is higher than the preset minimum liquid level threshold, such as 10% of the total height of the tank, the controller starts the first liquid extraction pump to extract liquid from the first storage area and inject it into preheating chamber 2. The running time of the liquid extraction pump is calculated by the controller based on the preset injection volume, such as 0.2 seconds of pump operation per milliliter. The controller quantitatively extracts liquid by controlling the relay closing time of the pump motor. If the liquid level in the first storage area is lower than the preset minimum liquid level threshold, the controller will not immediately start the first liquid extraction pump, but will first determine whether the liquid level in the second storage area is higher than its own minimum liquid level threshold. If there is a surplus in the second storage area, the controller opens the solenoid valve on the connecting pipe and starts the second liquid extraction pump to pump the liquid medium in the second storage area into the first storage area through the connecting pipe, and then switches back to the first liquid extraction pump to extract liquid from the first storage area and inject it into preheating chamber 2. If the liquid level in the second storage zone is also insufficient, the controller will open the solenoid valve of the external fresh vapor-liquid replenishment pipeline to directly replenish fresh liquid to the first storage zone, and then perform the liquid extraction action.

[0033] When welding chamber 4 requires the injection of vapor phase liquid, the controller executes a more stringent extraction logic. The controller reads the feedback value from the level sensor in the second storage area. If the level is sufficient, it activates the second extraction pump to extract liquid from the second storage area and inject it into welding chamber 4. If the level in the second storage area is insufficient, the controller directly opens the solenoid valve of the external fresh vapor phase liquid replenishment pipeline to replenish fresh liquid to the second storage area before extraction. Throughout the entire extraction logic for welding chamber 4, the controller will not open the connecting pipe to extract liquid from the first storage area, nor will it activate the first extraction pump. This logic is achieved by setting interlock conditions in the controller program; that is, the extraction trigger signal for welding chamber 4 is hard-coded in the program to only activate the second extraction pump or the replenishment valve, and cannot activate the first extraction pump or the connecting valve.

[0034] The principle behind the aforementioned zoned recycling and tiered utilization scheme is that the recycled liquid in preheating chamber 2, due to its lower operating temperature, is only slightly contaminated by low-boiling-point volatiles of flux, and its cleanliness is acceptable for reuse in preheating. The recycled liquid in welding chamber 4, having experienced the high temperatures of solder melting, is mixed with flux decomposition products and possible metal ions, resulting in lower cleanliness. Mixing the two would lower the overall liquid quality; therefore, physical zoning is used for separate storage. The retrieval strategy is matched to the cleanliness level: the preheating stage uses recycled liquid with lower cleanliness requirements, while the welding stage uses relatively clean recycled liquid or fresh liquid to ensure quality. The technical effect is to reduce the consumption of fresh vapor-liquid phase while preventing cross-contamination from affecting welding quality.

[0035] In a preferred embodiment, the nitrogen and formic acid mixed gas supply pipeline includes a mass flow controller for independently adjusting the flow rates of nitrogen and formic acid respectively; The process of quantitatively filling the chamber with a mixture of nitrogen and formic acid to a slightly positive pressure includes the following steps: The first mixed gas with a formic acid volume concentration in the first preset concentration range is controlled to be introduced into the chamber, so that the pressure in the chamber reaches the first preset micro-positive pressure value and is maintained for the first preset time, so as to form an initial reducing and wetting atmosphere rich in formic acid on the surface of the workpiece. After the first inflation sub-stage is completed, nitrogen is injected to increase the pressure inside the chamber from the first preset micro-positive pressure value to the second preset micro-positive pressure value. At the same time, the formic acid flow rate is adjusted by the mass flow controller to reduce the volume concentration of formic acid inside the chamber from the first preset concentration range to the second preset concentration range. During or after the second inflation sub-stage, at least one pressure oscillation cycle is performed, the pressure oscillation cycle comprising: partially or completely extracting the gas in the chamber until the pressure in the chamber drops to a preset lower limit pressure for oscillation, and then re-injecting the mixed gas or nitrogen into the chamber to restore the pressure in the chamber to the second preset micro-positive pressure value.

[0036] Specifically, in terms of hardware configuration, the nitrogen and formic acid mixed gas supply pipeline is formed by the convergence of the nitrogen branch and the formic acid branch. The nitrogen branch is drawn from the nitrogen source and connected in series with a pressure reducing valve, a first mass flow controller, and a first check valve. The formic acid branch is drawn from the liquid formic acid storage tank, which needs to be equipped with a heating jacket or placed in a constant temperature water bath to maintain sufficient saturated vapor pressure of formic acid. A gas phase pipeline is drawn from the top of the storage tank and connected in series with a second mass flow controller and a second check valve. The two branches converge after the check valve, and the converged main pipeline is connected to the gas filling port of the reduction chamber 3. A shut-off solenoid valve is installed on the main pipeline. The setpoint signal input terminals of the first and second mass flow controllers are respectively connected to the analog output module of the controller. The controller can adjust the gas flow of each branch in real time by changing the output current or voltage value.

[0037] The controller performs the phased inflation process as follows. In the first inflation sub-stage, the controller sets the nitrogen flow rate of the first mass flow controller to a first nitrogen value, for example, 0.5 liters per minute. The formic acid flow rate of the second mass flow controller is set to a first formic acid value, for example, 0.2 liters per minute. The volume concentration of formic acid after mixing can be calculated from the flow rate ratio, which in this example is approximately 28.6%, falling within a first preset concentration range, for example, between 20% and 40%. The controller opens the shut-off solenoid valve on the main inflation pipeline, and the mixed gas begins to be injected into the reduction chamber 3. The controller continuously reads the pressure sensor signal of the reduction chamber 3. When the pressure rises to a first preset micro-positive pressure value, for example, 1.05 times atmospheric pressure, the shut-off solenoid valve is closed, and inflation stops. Simultaneously, the controller starts a timer for a first preset duration, for example, 30 seconds. During these 30 seconds, the chamber is sealed, and the high-concentration formic acid gas diffuses and adsorbs onto the workpiece surface under micro-positive pressure, forming a formic acid-rich wetting layer. During implementation, this state can be named the immersion stage in the industrial control computer program, and it will automatically switch to the next stage after the timer expires.

[0038] After the first preset duration, the controller executes the second inflation sub-stage. The controller maintains the formic acid flow rate of the second mass flow controller constant or reduces it, while simultaneously increasing the nitrogen flow rate setpoint of the first mass flow controller to the second nitrogen value, for example, 2 liters per minute. The formic acid concentration in the inflation gas decreases significantly due to the substantial increase in the nitrogen content, reaching the second preset concentration range, for example, 5% to 10%. The controller reopens the main inflation line shut-off solenoid valve and continues inflation. As a large amount of nitrogen is injected, the chamber pressure continuously rises from the first preset micro-positive pressure value. The controller monitors the pressure sensor, and when the pressure reaches the second preset micro-positive pressure value, for example, 1.15 times atmospheric pressure, it closes the shut-off solenoid valve again. In this stage, the increase in total pressure further forces the previously adsorbed formic acid gas into the deep pores and narrow gaps, while the reduced formic acid concentration prevents excessive formic acid from condensing and remaining on the surface.

[0039] There are two execution methods for the pressure oscillation cycle. The first method involves embedding oscillation within the second inflation sub-stage. After the chamber pressure reaches the second preset micro-positive pressure value, the controller maintains pressure for a short period, such as 10 seconds. Then, it opens the evacuation valve of the reduction chamber 3 and starts the vacuum pump to extract a portion of the gas from the chamber. During evacuation, the controller monitors the pressure sensor. When the pressure drops to the preset oscillation lower limit pressure, such as 0.8 times atmospheric pressure, it closes the evacuation valve and vacuum pump. Then, it reopens the inflation line, injecting the aforementioned second-ratio mixed gas or only nitrogen to restore the pressure to the second preset micro-positive pressure value. This evacuation and inflation constitutes one oscillation cycle, with a preset number of oscillations of 2 to 3. The second method involves executing the evacuation-gas replenishment oscillation as an independent stage after the second inflation sub-stage is completed. After completing the inflation and pressure maintenance of the second sub-stage, the controller executes several pressure oscillations as described above. During oscillation, the gas component injected can be pure nitrogen to gradually replace and remove residual formic acid during the oscillation process.

[0040] The specific pumping amplitude and rate of pressure oscillation are controlled by adjusting the vacuum valve opening. The controller outputs a control signal to the proportional regulator of the evacuation valve, controlling the valve opening to regulate the pumping speed. The relatively slow pumping avoids rapid pressure drops that could cause the liquid flux to boil and splash. The replenishment rate is determined by the setpoint of the mass flow controller.

[0041] This phased variable ratio and pressure oscillation scheme achieves precise control of the mass transfer process in the reduction reaction by programming three variables—gas composition, total pressure, and flow state—in segments along the time axis. The wetting stage utilizes a high concentration to establish a reactant concentration gradient; the pressurization stage uses total pressure to force the gas into the micro-slit; and the oscillation stage uses pressure difference to drive the gas in and out, achieving the removal of reaction products and the replenishment of fresh reactants. The technical effect is to achieve thorough and uniform reduction of complex-shaped workpieces, reducing welding defects and voids caused by insufficient reduction.

[0042] In a preferred embodiment, a temperature measuring device 6 is provided inside the preheating chamber 2 and / or the welding chamber 4, the temperature measuring device 6 comprising: Temperature measuring bracket 66 is fixedly installed on the inner bottom wall of the cabin; Temperature measuring base 64 is installed on temperature measuring bracket 66; The temperature-sensing contact copper block 61 is movably mounted on the temperature-sensing base 64 via the guide part 63. A high-temperature spring 62 is sleeved on the guide part 63 so that the temperature-sensing contact copper block 61 can elastically float along the axial direction of the guide part 63. A temperature-measuring thermocouple 65 is installed at the bottom of the temperature-measuring contact copper block 61; The temperature-measuring contact copper block 61 has a flat middle section and beveled ends. When the workpiece tray passes by, the beveled ends guide the tray to gradually compress the high-temperature spring 62, eventually making it tightly fit against the flat middle section.

[0043] Specifically, the temperature measuring device 6 is installed on the inner bottom wall of the chamber and is used to perform real-time contact measurement of the temperature of the workpiece pallet and the workpiece during the process of the workpiece pallet entering the chamber and moving along the conveying direction.

[0044] The temperature measuring bracket 66 is the mounting base for the temperature measuring device 6. It is made of sheet metal and is bolted to a predetermined position on the bottom wall of the chamber. The upper part of the temperature measuring bracket 66 has an elongated hole extending vertically to adjust the installation height of the temperature measuring base 64. The temperature measuring base 64 is a block-shaped component, fixed to the temperature measuring bracket 66 by bolts or screws passing through the elongated hole. Because the elongated hole provides vertical adjustment, the temperature measuring base 64 can be moved up and down to a suitable height after loosening the fasteners and then re-locked, thereby adjusting the height of the entire temperature measuring device 6 relative to the workpiece tray feeding plane.

[0045] A vertically oriented guide portion 63 is installed on the temperature measuring base 64. In this embodiment, the guide portion 63 is specifically a temperature measuring block guide screw, the lower end of which is screwed into a threaded hole on the top surface of the temperature measuring base 64 for fixation, and the upper end extends upward. A high-temperature spring 62 is sleeved on the outside of the guide screw, with its lower end supported on the top surface of the temperature measuring base 64 and its upper end being a free end. The temperature measuring contact copper block 61 is a block-shaped metal component with a through hole at its bottom that mates with the guide screw. The temperature measuring contact copper block 61 is sleeved on the guide screw through this through hole and sits on the upper end face of the high-temperature spring 62. Thus, the temperature measuring contact copper block 61 can float up and down along the axial direction of the guide screw, and the high-temperature spring 62 provides it with an upward elastic support force.

[0046] The temperature-sensing contact copper block 61 has specific geometric features. The top surface of the copper block is the working surface that contacts the workpiece tray, and this working surface is divided into three areas: a middle section and two ends. The middle section is a horizontal plane, and each end is machined into a slope, which gradually slopes downwards from the middle section to the ends. The slopes of the two slopes are gentle; in this embodiment, they are trapezoidal slopes with rounded edges. A temperature-sensing thermocouple 65 is installed at the bottom of the temperature-sensing contact copper block 61, and the temperature probe of the thermocouple is tightly fitted into a blind hole or channel on the bottom surface of the copper block, sensing the temperature through thermal conduction.

[0047] During operation, the workpiece pallet enters the preheating chamber 2 horizontally along the conveying direction, with its bottom surface gradually approaching the temperature measuring device 6. The lower front surface of the pallet first contacts the inclined surface at the entrance of the temperature measuring contact copper block 61. As the pallet continues to advance, the inclined surface converts the horizontal movement of the pallet into a vertical compressive force on the copper block. The copper block overcomes the elastic force of the high-temperature spring 62 and gradually moves downward along the guide screw, compressing the spring. When the pallet reaches the middle plane area of ​​the temperature measuring contact copper block 61, the bottom surface of the pallet completely adheres to the middle plane, forming a tight surface contact between the two. At this time, the compression of the spring reaches its maximum, and the spring reaction force acts on the bottom surface of the pallet through the copper block, ensuring a tight, gapless contact. The temperature measured by the thermocouple accurately reflects the true temperature of the pallet and the workpiece.

[0048] The technical problem solved by this temperature measuring device 6 is that in existing online vapor phase welding equipment, the temperature measuring thermocouple 65 usually requires an independent lifting mechanism to drive its ascent to contact the tray and its descent to detach, resulting in a complex structure and the lifting mechanism being prone to failure in high-temperature steam environments. This invention eliminates the lifting mechanism, fixing the temperature measuring device 6 at the bottom of the chamber. The horizontal conveying motion of the tray itself completes the temperature measurement contact action. Through the inclined guidance of the temperature-contacting copper block 61 and the spring-floating adaptive structure, reliable, automated temperature measurement is achieved without power. The technical advantages of this structure are: the temperature measuring device 6 has a simplified structure and high reliability during long-term operation in high-temperature steam and vacuum environments. The spring elastic support and inclined guidance design ensure smooth, impact-free tray movement, tight contact, and high measurement accuracy; when the tray leaves, the spring automatically resets, without affecting subsequent measurements on subsequent trays.

[0049] In a preferred embodiment, the controller is further configured such that the preheating stage of the preheating chamber 2 includes a radiant preheating section and a steam heating section; the controller is further configured to: In the radiation preheating section, after the workpiece enters the preheating chamber 2, without the injection of liquid vapor phase liquid, the upper heating element 42 in the preheating chamber 2 is controlled to operate at the first upper radiation power, the lower heating element 44 is controlled to operate at the first lower radiation power, and the side heating element 43 is controlled to operate at the first side radiation power, so as to preheat the workpiece by pure thermal radiation. The workpiece surface temperature is obtained by the temperature measuring device 6. When the workpiece surface temperature reaches above the preset steam dew point temperature, the radiation preheating section is terminated and the steam heating section is entered. In the steam heating section, the power of the lower heating element 44 is increased to an evaporation power higher than the first lower radiation power, and the power of the upper heating element 42 is decreased to a heat preservation power lower than the first upper radiation power. Liquid vapor phase is injected into the chamber, and the liquid vapor phase is evaporated by the lower heating element 44 to form a steam atmosphere, while the upper heating element 42 maintains the steam in a saturated state.

[0050] Specifically, before entering the preheating program, the controller needs to obtain the power values ​​of each heating element required for the radiant preheating section, namely the first upper radiant power, the first lower radiant power, and the first side radiant power. These power values ​​are determined as follows: During the equipment commissioning phase, for a specific workpiece and tray combination, a workpiece temperature response curve is established through multiple experiments. During the experiment, the test workpiece with a temperature sensor is placed in the preheating chamber 2, and each wall heating element is operated individually in pure radiant mode. The rate of temperature rise of the workpiece surface per unit time at different power levels is recorded. Based on the radiant preheating section duration allowed by the production cycle, the total heat input required to raise the workpiece temperature from room temperature to above the steam dew point temperature is calculated. Then, the total heat is proportionally allocated to each wall heating element. The allocation principle is as follows: the lower heating element 44, due to the upward effect of the hot airflow, undertakes the main heating, typically receiving 40% to 60% of the total heating power; the upper heating element 42 undertakes auxiliary heating, receiving 20% ​​to 30%; and the side heating element 43 receives 20% to 30%. The rated power of each heating element is known, and the actual power to be allocated divided by the rated power is the power percentage given value. After the test results are confirmed, the given values ​​of the first upper radiation power, the first lower radiation power, and the first side radiation power are recorded in the formula parameter table of the controller, bound to the workpiece model, and called up during production.

[0051] The steam dew point temperature is determined as follows: Based on the saturated vapor pressure curve of the selected vapor-phase liquid, provided by the vapor-phase liquid supplier in the form of a data table, the boiling point temperature of the vapor-phase liquid at different pressures is given. This data table is pre-stored in the controller's memory. Using the current chamber pressure as the input variable, the controller retrieves the saturation temperature corresponding to that pressure through table lookup or linear interpolation. This saturation temperature is the dew point temperature at which steam begins to condense after the vapor-phase liquid is injected. For example, if the pressure in preheating chamber 2 is maintained at 100 Pascals, and the boiling point of the used vapor-phase liquid at that pressure is 170 degrees Celsius, then the steam dew point temperature is 170 degrees Celsius. The controller uses this value as the termination threshold for the radiant preheating section.

[0052] Once the workpiece enters preheating chamber 2, the controller executes the radiation preheating phase. The controller reads the set values ​​of the first upper radiation power, first lower radiation power, and first side radiation power from the recipe parameter table, converts them into 4 to 20 mA current signals or digital communication commands, and sends them to the corresponding power regulators. The power regulators adjust the duty cycle of the solid-state relays or the conduction angle of the thyristors to ensure the heating elements operate at the given power. Each heating element simultaneously radiates heat to both the chamber space and the workpiece.

[0053] During radiant heating, the workpiece tray moves along the conveying direction and passes the temperature measuring device 6. The controller acquires the workpiece surface temperature through the temperature measuring device 6. The controller compares the acquired workpiece surface temperature with the steam dew point temperature in real time. When the workpiece surface temperature reaches or exceeds the steam dew point temperature, the controller determines that there are no cold spots on the workpiece that would cause steam condensation, and it is safe to inject the gaseous liquid. At this time, the controller records the actual time consumed in the radiant preheating section for subsequent production cycle optimization, and then switches the program state to the steam heating section.

[0054] Upon entering the steam heating section, the controller needs to adjust the power of the heating element. The evaporation power is determined as follows: the evaporation power must be sufficient to completely evaporate the injected liquid-gas phase within a predetermined time and maintain it at saturation. This value is obtained by calculating the total heat required for the vaporization of the liquid-gas phase. Given the mass of the injected liquid-gas phase, the latent heat of vaporization of the liquid, and the desired evaporation completion time, the minimum required heating power can be calculated. The heat transfer efficiency between the lower heating element 44 and the liquid-gas phase is considered during the calculation, typically taken as 1.2 to 1.5 times the calculated value to allow for a margin. For example, with an injection volume of 15 ml, a latent heat of vaporization of 80 kJ / kg, and a liquid density of 1.8 g / ml, the mass is 27 g, and the required heat of vaporization is approximately 2160 joules. If evaporation is required within 5 seconds, the theoretical power would be 432 watts; considering efficiency and margin, 600 watts is used. If the rated power of the lower heating element 44 is 1000 watts, the evaporation power is given as 60% of the rated power, higher than the first lower radiant power. The controller sends the given value to the power regulator of the lower heating element 44.

[0055] The insulation power is determined as follows: The main function of the upper heating element 42 in the steam heating section is to maintain the temperature of the top space at or above the steam saturation temperature to prevent steam condensation on the top wall. The insulation power is calculated through heat balance, taking into account the heat dissipation rate from the top wall to the external environment, the convective heat transfer from the steam to the top wall, and the thermal radiation efficiency of the upper heating element 42 itself. During equipment calibration, the steady-state power required to maintain the top wall temperature equal to the saturation temperature is experimentally determined under different ambient temperatures, and a correspondence table between ambient temperature and insulation power is established. During production, the controller looks up the insulation power setpoint from the table based on the current ambient temperature and sends it to the power regulator of the upper heating element 42. The insulation power is usually lower than the first upper radiation power because the chamber is already filled with high-temperature steam at this point, and the heat loss from the top wall is compensated by the latent heat of steam condensation; the upper heating element 42 only needs to compensate for the difference.

[0056] After power adjustment, the controller sends a command to the gas-liquid injection pipeline to inject a preset amount of liquid gas-liquid. Upon contact with the high-temperature wall surface and lower heating element 44, the liquid gas-liquid rapidly evaporates, forming steam. The lower heating element 44 continues to supply heat at high power to maintain steam generation. The upper heating element 42 operates at a heat preservation power to maintain the temperature of the top space. After the preset heat preservation time in this steam heating section, the controller switches to the evacuation and condensation recovery process.

[0057] The technical principle is as follows: If a workpiece is in direct contact with gaseous liquid vapor in a cold state, the vapor will condense on the cold surface of the workpiece, releasing latent heat. This leads to excessively rapid local heating and drastic temperature differences between different parts of the workpiece, creating thermal stress and potentially causing solder paste splattering or uneven evaporation. By first uniformly heating the workpiece above its dew point through pure radiation, the temperature of all parts of the workpiece surface is higher than the vapor dew point. The vapor will no longer condense but will instead circulate and transfer heat uniformly in a gaseous state, thus achieving truly uniform heating. The resulting effect is a uniform temperature distribution on the workpiece, laying the foundation for consistent solder melting in the subsequent process.

[0058] In a preferred embodiment, obtaining the workpiece surface temperature through the temperature measuring device 6 includes the following steps: In the radiation preheating section, when the workpiece tray passes the temperature measuring device 6, the temperature response curve of the temperature measuring thermocouple 65 is recorded throughout the entire process from the tray contacting the inlet end slope of the temperature measuring contact copper block 61 to the tray leaving the outlet end slope. Extract the duration of the temperature stability segment corresponding to the planar contact stage in the middle section of the temperature-measuring copper block 61 from the temperature response curve; If the duration is greater than or equal to a preset duration threshold, the surface temperature of the workpiece is obtained based on the temperature value of the temperature stabilization segment. If the duration is less than the duration threshold, then the temperature decrease rate of the temperature response curve at the corresponding stage of the outlet slope is extracted. If the deviation between the temperature drop rate and the normal temperature drop rate is within a preset range, it is determined that the insufficient duration is caused by the attenuation of the elastic force of the high temperature spring 62, a spring maintenance prompt is generated, and the temperature value of the temperature stabilization segment is used as the workpiece surface temperature after preset compensation correction. If the deviation between the temperature drop rate and the normal detachment drop rate exceeds the preset range, it is determined that the insufficient duration is caused by an abnormality on the bottom surface of the workpiece tray, and a tray abnormality prompt is generated.

[0059] Specifically, a set of benchmark parameters needs to be pre-calibrated, including a preset duration threshold, a normal detachment descent rate, and a preset compensation correction value. These parameters are calibrated after factory testing or after replacing springs and pallets. During calibration, a standard workpiece with a known temperature is heated to a known uniform temperature and then fed into the preheating chamber 2, allowing the pallet to pass through the temperature measuring device 6 at normal production speed. The controller records the complete temperature response curve, extracts the duration of the mid-section planar contact stage, and calculates the average value as the preset duration threshold, storing it in the controller. Simultaneously, the temperature descent rate at the exit end inclined plane stage is extracted, and the average value is calculated as the normal detachment descent rate, storing it in the controller. If a compensation correction value needs to be determined, different degrees of spring attenuation can be artificially simulated, for example, replacing springs with springs whose elastic coefficient decreases by 10% or 20%. The deviation between the temperature value in the stable temperature range and the standard value is recorded, and a correspondence table between the attenuation amount and the compensation value is established and stored in the controller.

[0060] In actual production, when the workpiece pallet passes the temperature measuring device 6, the controller continuously collects the temperature value of the temperature measuring thermocouple 65 at a fixed sampling period (e.g., 10 milliseconds). When the temperature value rises continuously from the environmental reference and exceeds a start-up threshold (e.g., 10 degrees Celsius above the ambient temperature), the controller determines that the pallet has contacted the inlet end slope and begins recording temperature data. When the temperature value falls back to near the reference from the platform, recording stops, obtaining the temperature response curve of the entire process from inlet to outlet.

[0061] The method for extracting temperature stability segments involves performing a moving average on the recorded curves to reduce noise, and then identifying intervals where the rate of temperature change is close to zero for multiple consecutive sampling points. Specifically, a fluctuation tolerance value is set, such as ±0.5 degrees Celsius. If the difference between the maximum and minimum temperature values ​​for 100 consecutive sampling points (corresponding to 1 second) is less than this tolerance value, then this time period is considered a temperature stability segment, and its duration and the average temperature of this segment are recorded.

[0062] The controller compares the duration with a preset duration threshold. If the duration is greater than or equal to the duration threshold, it indicates that the contact process is complete and the spring and tray are in normal condition. The average temperature of the stable temperature range is then used as the workpiece surface temperature output.

[0063] If the duration is less than the duration threshold, it indicates an abnormally shortened contact process, requiring diagnosis. The controller extracts the descent phase from the end of the temperature stability segment to the temperature regression baseline point from the temperature response curve, as the exit slope phase data. Linear regression is performed on this phase data to calculate the slope of temperature decrease over time, i.e., the temperature decrease rate. This decrease rate is compared with the pre-stored normal detachment decrease rate to calculate the deviation. The deviation can be calculated as an absolute value difference or a relative percentage difference.

[0064] If the deviation is within the preset range (e.g., the absolute value of the deviation is less than 20% of the normal value), the controller determines that the elastic force of the high-temperature spring 62 has weakened. The mechanism is as follows: due to long-term high-temperature use, the spring experiences stress relaxation, resulting in a decrease in the elastic coefficient. When the tray detaches, the rebound speed of the copper block slows down, causing the mid-section planar contact phase to end prematurely and its duration to shorten. However, the sliding friction state during the detachment process remains similar to that of a normal spring, and the temperature drop curve is basically the same. The controller then generates a spring maintenance prompt, displays an alarm code on the human-machine interface, or triggers a maintenance indicator light. The workpiece surface temperature is output after adding a preset compensation correction value to the temperature value of the stable temperature range. The compensation correction value is obtained by interpolation from a pre-stored attenuation compensation table based on the shortening ratio of the duration.

[0065] If the temperature drop rate deviates from the normal detachment rate beyond the preset range, the controller determines that the bottom surface of the workpiece tray is abnormal. Possible causes include thermal deformation and warping of the tray bottom surface, weld spatter adhesion, or severe wear of the tray bottom surface. These defects cause irregular scraping or partial detachment of the tray from the copper block during detachment, resulting in abnormal changes in the temperature drop curve, such as abrupt changes or excessively rapid or slow temperature drops. The controller generates a tray abnormality alert, requiring the operator to check the tray's condition.

[0066] Technical Principle: This solution utilizes the correlation between the dynamic characteristics and mechanical state of the temperature measuring device 6 during the contact temperature measurement process. The states of the spring and the tray directly affect the contact time and dynamic behavior of the copper block and the tray during the separation process, which are reflected in the time-domain characteristics of the temperature curve in real time. Through multi-feature analysis and comparison of the curve, the temperature measuring device 6 is essentially endowed with self-diagnostic capabilities without adding any additional sensors. The technical effect is that while accurately measuring the temperature, it can promptly detect performance degradation of key components or tray defects, avoiding batch welding defects caused by inaccurate temperature measurement and reducing unplanned downtime.

[0067] In a preferred embodiment, in the steam heating section, the controller is further configured to perform temperature field self-balancing control on the side heating element 43, including the following steps: Before injecting the liquid vapor phase, the side heating element 43 is controlled to be turned on in advance with the first side heat preservation power to preheat the inner side wall of the chamber to a temperature not lower than the saturation temperature of the vapor phase to be injected under the current pressure. After the liquid vapor phase is injected, the temperature measuring device 6 continuously acquires the temperature of at least two different measuring points on the surface of the workpiece. The measuring points include an edge area measuring point near the side wall of the chamber and a center area measuring point away from the side wall. If the temperature of the measurement point in the edge region is lower than the temperature of the measurement point in the center region, and the temperature difference between the two exceeds the preset edge temperature difference threshold, then the power of the side heating element 43 is increased to increase the radiative heating compensation for the edge region of the workpiece. If the temperature of the edge region measurement point is higher than the temperature of the center region measurement point, and the temperature difference between the two exceeds the preset center temperature difference threshold, then the power of the side heating element 43 is reduced to reduce radiative heating of the workpiece edge region. If the temperature difference between the edge region measurement point and the center region measurement point is maintained within the allowable deviation range, the current power of the side heating element 43 is maintained.

[0068] Specifically, on the bottom surface of the tray, the edge area near the sidewall of the cabin and the central area away from the sidewall are related in the direction of transport. As the tray moves forward, a point in the edge area and a point in the central area will successively pass directly above the temperature-sensing contact copper block 61. The controller continuously collects temperature data from the temperature-sensing thermocouple 65 at a fixed sampling frequency, forming a complete temperature response curve. This curve does not have only one stable temperature segment. If there is a temperature difference between the edge and central areas of the tray bottom, the first stable temperature segment will occur when the corresponding point in the edge area passes the central plane of the copper block, and the second stable temperature segment will occur when the corresponding point in the central area passes the central plane of the copper block. The controller extracts the temperature values ​​of these two stable temperature segments from the temperature response curve in chronological order, using them as the temperatures of the measurement points in the edge and central areas, respectively. Assuming the bottom surface of the tray is flat, the length of the central plane of the copper block ensures sufficient contact time for each measurement point to form a recognizable stable temperature reading. The specific locations of the measurement points on the bottom of the tray corresponding to the edge area measurement points and the center area measurement points are determined by actual measurement and calibration during the equipment commissioning phase. The calibration method is to attach temporary thermocouples at the corresponding positions on the bottom of the tray, verify the consistency between the temperature value obtained by the temperature measuring device at 6 minutes and the actual measured value of the temporary thermocouples, and record the coordinate positions of the two measurement points on the bottom of the tray in the controller parameter table after confirmation.

[0069] The temperature difference threshold required for self-balancing temperature field control was also determined through multi-channel temperature measurement tray tests during equipment commissioning. During commissioning, a dedicated test tray equipped with multiple surface thermocouples was used to run the entire steam heating section under typical process conditions, recording the temperature distribution at various locations on the tray throughout the heating section. The maximum allowable difference between the temperature at a measurement point 10 to 15 mm from the sidewall and the temperature at the geometric center of the tray was taken as the edge temperature difference threshold, typically set to 3 to 5 degrees Celsius. The center temperature difference threshold and the edge temperature difference threshold can be the same, or they can be set separately.

[0070] Before the steam heating phase begins, the controller performs a sidewall preheating operation. The controller reads the real-time value of the current chamber pressure and uses this pressure to query the pre-stored gas-liquid saturation temperature curve table. Through linear interpolation, the saturation temperature of the gas-liquid phase at the current pressure is obtained. The controller sends a first side insulation power setpoint to the power regulator of the side heating element 43, causing the side heating element 43 to begin heating. The controller continuously reads the sidewall temperature sensors installed on the inner sidewall of the chamber. When the sidewall temperature reaches or exceeds the saturation temperature, the sidewall preheating phase is complete.

[0071] After the liquid gas phase is injected, the controller enters the main cycle of temperature field self-balancing control. The execution cycle of the control cycle can be set to 1 to 2 seconds. Within each cycle, the controller performs two temperature data acquisitions. The first acquisition is completed when the measuring point in the edge area of ​​the tray passes the temperature measuring device 6, obtaining the temperature of the edge area measuring point. The second acquisition is completed when the measuring point in the center area of ​​the tray passes the temperature measuring device 6, obtaining the temperature of the center area measuring point. If the tray only passes the temperature measuring device 6 once in one transfer, the temperature is extracted from the temperature curve by taking advantage of the multiple reciprocating or slow movements that the tray may make in the steam heating section, or by taking advantage of the continuous contact between the temperature measuring contact copper block 61 and the bottom surface of the tray for a period of time.

[0072] The controller calculates the temperature difference between the edge and the center, comparing it to preset edge and center temperature difference thresholds. When the edge temperature is lower than the center temperature, and the absolute value of the difference exceeds the edge temperature difference threshold, it indicates that insufficient heat is being received by the workpiece edge area due to sidewall heat dissipation. The controller calculates the increase in power for the side heating element 43, with the power increment proportional to the portion of the temperature difference exceeding the threshold. The proportionality coefficient is obtained through experimental tuning. The tuning method involves artificially increasing sidewall heat dissipation during debugging to create a known temperature difference, gradually increasing the power of the side heating element 43 until the temperature difference returns to within the threshold, recording the correspondence between the power increment and the temperature difference, and obtaining the proportionality coefficient. The controller adds the calculated power increment to the current setpoint of the side heating element 43, limiting it within the rated power, and outputs it to the power regulator.

[0073] When the edge temperature is higher than the center temperature, and the difference exceeds the center temperature difference threshold, it indicates that the sidewall is overheating, causing the workpiece edge area to receive additional radiant heating. The controller calculates the power reduction, which is proportional to the portion of the temperature difference exceeding the threshold. This reduction is subtracted from the current given value and output after limiting.

[0074] When the difference between the edge temperature and the center temperature is within the allowable deviation range, the controller maintains the current power of the side heating element 43 unchanged.

[0075] Measures to avoid frequent adjustments include: setting a confirmation counter in the controller program; power adjustment is only performed if the temperature difference judgment result is consistently out of tolerance for several consecutive control cycles. A minimum interval is set between two power adjustment operations to allow the heating element sufficient time to respond to power changes and reflect the temperature response on the workpiece.

[0076] Technical Principle: This solution utilizes the characteristic that different areas of the tray bottom surface sequentially pass through fixed temperature measurement points during the conveying process. It converts the signals from a single temperature measurement point, separated along the time axis, into temperature information at different spatial locations of the workpiece. This is equivalent to upgrading a fixed single-point temperature measurement device 6 into a temperature measurement system with spatial scanning capabilities, without requiring any additional temperature measurement hardware. Based on the temperature difference between the workpiece edge and center, a side heating element 43 is used as a compensation actuator to actively eliminate radial temperature differences in the workpiece caused by heat dissipation or overheating from the side walls. The technical effect is that, while meeting the structural limitations of the temperature measurement device 6, it achieves uniform control of the workpiece temperature field in the steam-heated section across a cross-section perpendicular to the conveying direction, suppressing asynchronous solder melting caused by temperature differences, thereby improving welding consistency.

[0077] In a preferred embodiment, the insulation power of the first side is dynamically determined by the controller during a single batch of the process, including the following steps: During the radiation preheating phase, the side heating element 43 is operated with the first side radiation power, and the real-time temperature of the inner sidewall of the cabin is recorded at the end of this phase. As the liquid to be injected approaches the steam heating section, the saturation temperature of the vapor phase liquid at that pressure is obtained based on the current chamber pressure. The saturation temperature is compared with the real-time temperature of the sidewall: if the saturation temperature is higher than the real-time temperature of the sidewall, the first side insulation power is set to be higher than the first side radiation power to compensate for the heating demand of the sidewall before entering the steam heating section; if the saturation temperature is lower than the real-time temperature of the sidewall, the first side insulation power is set to be lower than the first side radiation power to avoid overheating of the sidewall. The adjustment range of the first side insulation power is positively correlated with the difference between the saturation temperature and the real-time temperature of the side wall, and the adjustment range is determined by the built-in thermal balance formula, which is based on the heating efficiency of the side heating element 43, the heat capacity of the cabin side wall and the heat dissipation characteristics pre-calibrated.

[0078] Specifically, the first step is to establish a thermal balance equation. This equation is a mathematical expression describing the quantitative relationship between the input electrical power of the side heating element 43, the change in sidewall temperature, and the heat dissipation from the sidewall to the environment. The pre-calibration process for this equation will be described later; here, we will first explain the form the equation takes in the controller after calibration. After calibration, the controller's memory stores two characteristic coefficients: the first coefficient corresponds to the combined effect of the electrothermal conversion efficiency of the side heating element 43 and the effective heat capacity of the sidewall; the second coefficient corresponds to the equivalent heat dissipation coefficient of the cabin sidewall to the environment. The controller also stores the available heating preparation time for the current batch. This time is a fixed duration reserved between the end of the radiation preheating phase and the actual injection of the liquid gas phase, determined by the equipment's transmission cycle, for example, 5 seconds or 8 seconds.

[0079] During the radiant preheating phase, the controller operates the side heating element 43 at the first side radiant power. This first side radiant power is a value pre-determined experimentally and stored in the formula parameter table as a process parameter for the radiant preheating phase. Throughout the radiant preheating phase, the controller continuously collects the side wall temperature via a side wall temperature sensor installed on the inner side wall of the cabin. The side wall temperature sensor can be a type K thermocouple or a Pt100 platinum resistance thermometer; its measuring end is fixed to the inner side of the outer wall of the cabin by welding or clamping, and the lead wire passes through the cabin wall sealing joint to connect to the controller's temperature acquisition module. The controller reads the side wall temperature value at a fixed sampling period, such as once per second, and updates it cyclically in memory. When the controller determines that the termination conditions of the radiant preheating phase are met, it reads the latest value from the side wall temperature sensor at that moment and records it as the real-time side wall temperature.

[0080] The controller then enters the insulation power calculation subroutine. The first step of this subroutine is to obtain the saturation temperature of the gaseous liquid to be injected at the current pressure. The controller reads the current pressure reading of the vacuum gauge in preheating chamber 2, uses this pressure value as input, and searches for it in a pre-stored gaseous liquid property parameter table. The property parameter table uses pressure as the row index and saturation temperature as the column value, and the data comes from the property data sheet provided by the gaseous liquid supplier. If the current pressure value is exactly equal to a record point in the table, the corresponding saturation temperature is directly taken. If the pressure value falls between two record points, linear interpolation is used for calculation. For example, if the table records 80 Pascals corresponding to 165 degrees Celsius and 100 Pascals corresponding to 170 degrees Celsius, and the current pressure is 90 Pascals, then the saturation temperature is taken as 167.5 degrees Celsius.

[0081] The controller compares the calculated saturation temperature with the real-time sidewall temperature at the end of the radiation preheating section and handles two cases.

[0082] Scenario 1: The saturation temperature is higher than the real-time sidewall temperature. This indicates that the current sidewall temperature is too low. Without additional heating, after the vapor-liquid phase is injected, the vapor will condense upon contact with the cooler sidewall surface. Condensation not only consumes steam but also forms a liquid film on the sidewall surface. When this liquid film evaporates, it absorbs heat from the workpiece edge region near the sidewall, causing the edge temperature to drop. The controller needs to set the first-side insulation power higher than the first-side radiation power to compensate for the sidewall temperature and raise it above the saturation temperature within a short period before steam injection. The temperature rise is the difference between the saturation temperature and the real-time sidewall temperature. The controller uses this temperature difference as input, calls the heat balance formula, and, combined with the current ambient temperature and available heating time, calculates the heating power required by the side heating element 43. This calculated value is usually higher than the first-side radiation power. The controller compares the calculation result with the rated power of the side heating element 43; if it exceeds the rated value, it limits the power to the rated power.

[0083] Scenario 2: The saturation temperature is lower than or equal to the real-time sidewall temperature. This indicates that the current sidewall temperature is already high enough, requiring no additional heating, and may even be overheated. Continuing to heat the sidewall at a higher power would cause its temperature to exceed the steam temperature, and the thermal radiation from the sidewall would cause the workpiece edge area to receive additional heat, resulting in edge overheating. In this case, the controller sets the first-side insulation power lower than the first-side radiation power. The insulation power is set based on the heat dissipation loss of the sidewall at the current ambient temperature, ensuring that the sidewall temperature neither continues to rise nor drops rapidly during the steam heating phase, maintaining it near the saturation temperature. The controller calls the heat balance equation to calculate the minimum sustaining power required only to compensate for heat dissipation, multiplies it by a derating factor less than 1, and outputs the result.

[0084] The positive correlation between the temperature difference and the power adjustment range is quantitatively described by the heat balance equation. In this equation, the required power adjustment equals the effective heat capacity of the sidewall multiplied by the temperature difference divided by the available heating time, plus the equivalent heat dissipation coefficient multiplied by the difference between the sidewall temperature and the ambient temperature. The controller substitutes the saturation temperature and the real-time sidewall temperature into the temperature difference term, and the ambient temperature into the heat dissipation term, to calculate the value of the first side insulation power. This value is then sent to the power regulator of the side heating element 43 via an analog output module or a digital communication interface. The power regulator adjusts the operating power of the side heating element 43 accordingly before and during the steam heating phase.

[0085] The technical principle of this solution lies in treating the radiative preheating stage as a natural pre-regulation process for the thermal state of the sidewall. At the end of the radiative preheating stage, the sidewall has been heated to a certain temperature by the first side radiative power. This temperature depends on the previous operating time, ambient temperature, and the magnitude of the first side radiative power. The controller does not reset the sidewall temperature to zero; instead, it accepts this existing temperature as the initial condition and uses the gas-liquid saturation temperature as the target, calculating the power required to reach the target state from the current state using the heat balance formula. This avoids insufficient or excessive preheating caused by different initial states, as is common in traditional fixed-power methods. The achieved technical effect is that the side insulation power can be automatically matched to different ambient temperatures, seasons, and different equipment operating conditions (hot or cold), ensuring that steam does not condense on the sidewall to maintain a uniform temperature field, while also preventing overheating of the sidewall that could lead to overheating of the workpiece edges or energy waste.

[0086] In a preferred embodiment, the pre-calibration of the heat balance equation includes the following steps: In the calibration mode after initial equipment commissioning or maintenance, the side heating element 43 is controlled to operate at multiple different calibration power values ​​in sequence, and the real-time temperature of the inner side wall of the cabin is monitored until the side wall temperature reaches a steady state under each calibration power value. Record the steady-state sidewall temperature and the current ambient temperature corresponding to each calibration power value, and construct a calibration data set that characterizes the relationship between heating input power and net sidewall temperature rise; Based on the calibration data set, a first characteristic coefficient corresponding to the electrothermal conversion efficiency of the side heating element 43 and a second characteristic coefficient corresponding to the heat dissipation capacity of the cabin sidewall to the environment are determined by numerical fitting. The first characteristic coefficient and the second characteristic coefficient together constitute the heat balance relationship.

[0087] Specifically, before calibration, it is necessary to ensure that the equipment is in a relatively constant ambient temperature, all chamber valves are closed, and the preheating chamber 2 is not evacuated, maintaining a normal atmospheric pressure atmosphere. The controller can enter calibration mode through the calibration menu on the human-machine interface, and is started after entering administrator privileges. In calibration mode, the controller automatically executes the preset calibration sequence without manual intervention.

[0088] The first step in the calibration sequence is to determine the test power point. The controller internally presets a set of suitable calibration power values ​​that cover the typical range of the actual operating power of the side heating element 43, evenly distributed from lower to higher power. For example, four calibration power values ​​are preset, representing 20%, 40%, 60%, and 80% of the rated power of the side heating element 43. The selection of calibration power values ​​must avoid ineffective ranges where the sidewalls barely heat up, and also avoid overheating ranges exceeding the requirements for normal insulation.

[0089] The controller starts with the lowest rated power value and sends the power setpoint to the power regulator of the side heating element 43 via the output module. The side heating element 43 operates continuously at this power. The controller continuously reads the temperature value from the side wall temperature sensor at a fixed sampling period. After each reading, the controller compares the current temperature value with the previously read temperature value. If the absolute value of the difference between the two temperature values ​​is less than a preset steady-state determination threshold, such as 0.3 degrees Celsius, and this state is maintained continuously for a sufficiently long time, such as 15 minutes, the controller determines that the side wall temperature has reached a steady state at this power level. The steady-state determination threshold is selected based on the measurement noise level of the temperature sensor and the amplitude of small temperature fluctuations caused by natural convection in the cabin, and can be set by observing the fluctuation range of the temperature readings under constant power during commissioning.

[0090] Once steady state is reached, the controller records the calibration data, including the current calibrated power value, the current steady-state sidewall temperature value, and the current ambient temperature value. The ambient temperature value is read from an ambient temperature sensor mounted on the equipment frame. After recording, the controller automatically switches to the next calibrated power value and repeats the above process of heating, waiting for steady state, and recording data until all preset calibrated power values ​​have been tested. Finally, the controller's memory obtains a set of calibration data containing multiple operating points, each operating point containing three data points: heating power, steady-state sidewall temperature, and ambient temperature.

[0091] The controller performs numerical fitting on the calibration data set. The goal of the fitting is to determine the first characteristic coefficient corresponding to the electrothermal conversion efficiency of the side heating element 43, and the second characteristic coefficient corresponding to the heat dissipation capacity of the cabin sidewall to the environment. The physical meaning of the two characteristic coefficients can be defined by engineers before calibration. In this embodiment, the thermal balance relationship of the sidewall under steady state is approximated as follows: the effective heating power output by the side heating element 43 is equal to the heat dissipation power of the sidewall to the environment. Under the heat transfer mode dominated by natural convection and radiation, the heat dissipation power can be approximately considered to be proportional to the difference between the sidewall temperature and the ambient temperature. Therefore, the heating power under steady state is approximately proportional to the difference between the sidewall temperature and the ambient temperature, and the proportionality coefficient is the equivalent heat dissipation coefficient, which is the second characteristic coefficient. The effective heating power is equal to the input electrical power of the side heating element 43 multiplied by the electrothermal conversion efficiency, which is the first characteristic coefficient. Therefore, under steady state, there exists a relationship that the input electrical power multiplied by the first characteristic coefficient is approximately equal to the second characteristic coefficient multiplied by the temperature difference.

[0092] The controller processes each set of recorded data, using the input electrical power as the independent variable and the temperature difference as part of the dependent variable. Numerical fitting employs a linear regression method. The controller substitutes the electrical power and temperature difference data from multiple calibration points into a least-squares calculation program, a built-in numerical calculation subroutine, to fit an optimal straight line passing through or not passing through the origin. The slope of the line contains the ratio of the first and second characteristic coefficients. Then, using the known typical range of electrothermal conversion efficiency as constraints, the specific values ​​of the first and second characteristic coefficients are separated. Alternatively, additional dynamic testing, such as applying a step power and recording the temperature rise curve, combined with the temperature rise time constant, can simultaneously solve for the heat capacity and heat dissipation coefficient, further decoupling the two characteristic coefficients. After fitting, the controller writes the obtained values ​​of the first and second characteristic coefficients into non-volatile memory as formal parameters for subsequent thermal balance equations.

[0093] After calibration, the controller displays a message on the human-machine interface indicating that calibration is complete, along with the fitted characteristic coefficients and fitting error. If the fitting error exceeds a preset acceptable range, such as a relative deviation of the fitted line from each data point exceeding 5%, the controller issues a calibration abnormality alarm, prompting the operator to check the installation of the side wall temperature sensor, the integrity of the insulation layer, or whether the ambient temperature sensor readings are normal.

[0094] The technical principle lies in the fact that calibration utilizes the deterministic relationship between heating power and temperature difference under steady-state thermal equilibrium conditions. This parameterizes the thermal characteristics of the actual equipment, extracting them as two constant coefficients stored in the controller. These two coefficients comprehensively reflect practical engineering factors that are difficult to obtain through theoretical calculations, such as manufacturing deviations of the side heating element 43 itself, installation contact thermal resistance, the actual insulation effect of the side wall insulation layer, and the specific path of heat dissipation from the cabin structure. After calibration, the thermal equilibrium formula is transformed from a general theoretical formula into a precise model of the equipment under its current state. The technical effect is that when subsequently using this formula to calculate the insulation power, the calculation results highly match the actual thermal response of the equipment, improving the accuracy of dynamic calculation of insulation power. Furthermore, the calibration process can be repeated to adapt to characteristic drift after equipment aging.

[0095] In a preferred embodiment, the following steps are also included: At the end of the radiation preheating section of each process batch, the average actual operating power of the side heating element 43 in this radiation preheating section, the real-time side wall temperature at that moment, and the current ambient temperature are obtained as a set of online correction sample data. The consistency of the online corrected sample data with the currently valid heat balance relationship is compared to generate a deviation quantity characterizing the degree of deviation of the relationship at the current operating point; If the deviation exceeds a preset correction trigger threshold, a recursive fitting algorithm with a forgetting factor is triggered to incorporate the online correction sample data and correct the first feature coefficient and the second feature coefficient.

[0096] Specifically, this embodiment provides a concrete implementation method for online adaptive updating of the heat balance formula during continuous production. After long-term operation of the equipment, the side heating element 43 may experience a decrease in electrothermal conversion efficiency due to aging, and the heat dissipation characteristics of the outer insulation layer of the side wall may change due to scale buildup or moisture. Ambient temperature also fluctuates significantly with seasonal changes. These slow drifts will cause the aforementioned calibrated heat balance formula to gradually deviate from the actual situation, resulting in a systematic deviation in the calculation of the first side insulation power. The online adaptive update mechanism enables the formula to automatically track these changes.

[0097] The online update data source is the naturally generated operating data for each process batch, eliminating the need for a dedicated calibration period. During the radiant preheating phase of each process batch, the side heating element 43 operates at a first side radiant power, determined by the recipe parameters and remaining constant or varying according to a preset curve throughout the preheating phase. The controller records the actual operating power of the side heating element 43 at fixed intervals throughout the preheating phase. The actual operating power can be calculated by reading the effective values ​​of the output current and voltage of the power regulator, or by reading the power setpoint sent by the controller combined with the feedback signal from the power regulator. At the end of the preheating phase, the controller calculates the average power of the side heating element 43 for this phase, i.e., the arithmetic mean of the power values ​​recorded over all sampling periods, recording this as the average actual operating power. Simultaneously, the controller reads the current temperature value from the sidewall temperature sensor as the real-time sidewall temperature and the current temperature value from the ambient temperature sensor as the current ambient temperature. These three data points constitute a set of online correction sample data.

[0098] The controller compares this set of online correction sample data with the currently valid thermal balance formula. Specifically, it substitutes the real-time sidewall temperature and ambient temperature from the sample data into the current thermal balance formula to calculate the power output of the side heating element 43 predicted by the formula under those temperature and heat dissipation conditions, or to calculate the sidewall temperature predicted by the formula at that power level. The predicted value is then compared with the measured value in the sample data; the difference between the two is the deviation. The deviation can be a signed value; a positive value indicates that the measured power is higher than the predicted power, and a negative value indicates that the measured power is lower than the predicted power.

[0099] The controller compares the absolute value of the deviation with a preset correction trigger threshold. The correction trigger threshold must be set to balance sensitivity to actual drift with insensitivity to random fluctuations. The threshold can be set to 5% to 10% of the measured power, or the power deviation corresponding to a temperature deviation of 2 to 3 degrees Celsius. If the deviation does not exceed the correction trigger threshold, it indicates that the current thermal equilibrium relationship is still accurate, the sample data is consistent with the model prediction, the controller does not trigger correction, and the current relationship parameters remain unchanged.

[0100] If the deviation exceeds the correction trigger threshold, the controller determines that the thermal balance relationship has undergone a non-negligible drift and triggers the correction procedure. The correction procedure employs a recursive fitting algorithm with a forgetting factor. This algorithm is an online algorithm that can progressively update existing model parameters based on new data. The forgetting factor is a constant between 0.9 and 1.0, for example, 0.95. Its function is to make the influence of historical data on the model decay exponentially over time, giving new data a higher weight. The specific value of the forgetting factor is preset in the controller parameters. The closer the forgetting factor is to 1, the longer the old data is retained, the smoother the model update, but the slower the response drift. A smaller forgetting factor allows the model to track drift faster but is more sensitive to random fluctuations, requiring a trade-off selection based on the stability of the equipment's thermal response.

[0101] The recursive fitting algorithm is executed as follows: the controller takes the current online corrected sample data and the current first and second feature coefficients as input to the algorithm, and calculates the updated estimates of the first and second feature coefficients. The calculation process is based on the least squares recursive formula, where the old estimate is added to a correction term, which is equal to the gain factor multiplied by the prediction bias. The gain factor is calculated from the historical data covariance matrix, the forgetting factor, and the vector form of the current sample data. The controller's built-in numerical calculation subroutine performs these matrix operations, and the results yield the new first and second feature coefficients.

[0102] The controller writes the new characteristic coefficients to non-volatile memory, replacing the old values, thus completing the online update. After the update, the controller can choose to register an update log in the event log of the human-machine interface, including the update time, old coefficient value, new coefficient value, and the deviation when the update was triggered, for maintenance personnel to trace.

[0103] To ensure the stability and security of online updates, the controller also incorporates protection logic. If multiple consecutive online corrections of sample data trigger updates, and the direction of change in the characteristic coefficients is inconsistent after each update (i.e., the coefficient values ​​fluctuate rather than drift trend-like), the controller will suspend the online update function and issue an alarm, indicating possible abnormalities such as intermittent failure of the side wall temperature sensor or interference with the ambient temperature sensor. Furthermore, upper and lower limits are set for the range of change in the updated characteristic coefficients. If the new coefficients exceed ±30% of the initial calibration value, the controller will not update and will issue an alarm, assuming that excessive drift may be due to hardware failure rather than natural aging.

[0104] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A welding method for online vapor phase welding, characterized in that, Executed by a controller, this is achieved using an online vapor phase welding device. The device includes a preheating chamber (2), a reduction chamber (3), a welding chamber (4), and a cooling chamber (5) arranged sequentially along the workpiece conveying direction. The preheating chamber (2) and the welding chamber (4) each have heating elements located on their inner top, bottom, and side walls, each independently connected to a vapor phase liquid injection pipeline. The reduction chamber (3) has a liftable heating plate at its bottom, connected to a nitrogen and formic acid mixed gas supply pipeline. The controller is configured to: The signal that the workpiece has entered the preheating chamber (2) is received, and the preheating chamber (2) is evacuated to a preset vacuum range and maintained in a stable pressure state. The heating field formed by the heating elements on each wall causes the injected liquid vapor phase to evaporate into a saturated steam atmosphere, and the workpiece is preheated uniformly. After the preheating is completed, the uncondensed steam is evacuated, condensed and recovered, and the workpiece is transferred to the reduction chamber (3). Upon receiving a signal that the workpiece has entered the reduction chamber (3), the first reduction operation is executed: the reduction chamber (3) is first evacuated to a set vacuum level and then sealed and pressurized. The heating plate is then raised to contact the bottom surface of the tray carrying the workpiece for contact heating. A mixture of nitrogen and formic acid is quantitatively introduced into the chamber to a slightly positive pressure to reduce the workpiece. After the preset reduction time is met, the second reduction operation is executed: the reduction chamber (3) is evacuated to discharge the gaseous byproducts and flux volatiles generated by the reduction reaction. After evacuation, nitrogen is introduced to restore normal pressure, and the workpiece is transferred to the welding chamber (4). The signal that the workpiece has entered the welding chamber (4) is received, and the welding chamber (4) is controlled to be evacuated to a preset vacuum range and maintained in a stable pressure state. The heating field formed by the heating elements on each wall surface causes the injected liquid vapor phase to evaporate into a saturated steam atmosphere, and the workpiece is uniformly heated until the solder melts and the welding is completed. After the welding is completed, the uncondensed steam is evacuated, condensed and recovered, and the workpiece is transferred to the cooling chamber (5). The system receives a signal that the workpiece has entered the cooling chamber (5), controls the cooling chamber (5) to introduce nitrogen gas into the vacuum state to cool the welded workpiece, and then transmits it out. The preheating chamber (2) and / or the welding chamber (4) are equipped with a temperature measuring device (6), the temperature measuring device (6) comprising: Temperature measuring bracket (66) is fixedly installed on the inner bottom wall of the cabin; Temperature measuring base (64) is installed on the temperature measuring bracket (66); The temperature-measuring contact copper block (61) is movably mounted on the temperature-measuring base (64) via the guide part (63). A high-temperature spring (62) is sleeved on the guide part (63) so that the temperature-measuring contact copper block (61) can elastically float along the axial direction of the guide part (63). A temperature-measuring thermocouple (65) is installed at the bottom of the temperature-measuring contact copper block (61); The temperature-measuring contact copper block (61) has a flat middle section and inclined ends, so that when the workpiece tray passes by, the inclined ends guide the tray to gradually compress the high-temperature spring (62) and finally fit tightly against the flat middle section. Among them, the temperature measuring device (6) is fixedly installed at the bottom of the cabin, and the temperature measuring and bonding action is completed by the horizontal transmission movement of the tray itself. The temperature measuring contact copper block (61) is guided by the inclined surface and the spring floating adaptive structure to achieve reliable temperature measurement without power and in an automated manner. The preheating stage of the preheating chamber (2) includes a radiation preheating section and a steam heating section; the controller is also configured to: In the radiation preheating section, after the workpiece enters the preheating chamber (2), without the injection of liquid vapor phase liquid, the upper heating element (42) in the preheating chamber (2) is controlled to operate with the first upper radiation power, the lower heating element (44) operates with the first lower radiation power, and the side heating element (43) operates with the first side radiation power, so as to preheat the workpiece by pure thermal radiation. The surface temperature of the workpiece is obtained by the temperature measuring device (6). When the surface temperature of the workpiece reaches above the preset steam dew point temperature, the radiation preheating section is terminated and the steam heating section is entered. In the steam heating section, the power of the lower heating element (44) is increased to an evaporation power higher than the first lower radiation power, and the power of the upper heating element (42) is decreased to a heat preservation power lower than the first upper radiation power. Liquid vapor phase liquid is injected into the chamber, and the liquid vapor phase liquid is evaporated by the lower heating element (44) to form a steam atmosphere. The steam is maintained in a saturated state by the upper heating element (42). The process of obtaining the workpiece surface temperature through the temperature measuring device (6) includes the following steps: In the radiation preheating section, when the workpiece tray passes the temperature measuring device (6), the temperature response curve of the temperature measuring thermocouple (65) is recorded from the inlet end slope of the tray from contact with the temperature measuring contact copper block (61) to the outlet end slope. Extract the duration of the temperature stability segment corresponding to the planar contact stage in the middle section of the temperature-measuring copper block (61) from the temperature response curve; If the duration is greater than or equal to a preset duration threshold, the surface temperature of the workpiece is obtained based on the temperature value of the temperature stabilization segment. If the duration is less than the duration threshold, then the temperature decrease rate of the temperature response curve at the corresponding stage of the outlet slope is extracted. If the deviation between the temperature drop rate and the normal temperature drop rate is within a preset range, it is determined that the insufficient duration is caused by the attenuation of the elastic force of the high temperature spring (62), a spring maintenance prompt is generated, and the temperature value of the temperature stabilization segment is corrected by a preset compensation and used as the surface temperature of the workpiece. If the deviation between the temperature drop rate and the normal detachment drop rate exceeds the preset range, it is determined that the insufficient duration is caused by an abnormality on the bottom surface of the workpiece tray, and a tray abnormality prompt is generated.

2. The online vapor phase welding method according to claim 1, characterized in that, The liquid medium evacuated and condensed from the preheating chamber (2) and the welding chamber (4) is returned to a common storage tank. The common storage tank is equipped with a partition structure to divide the space inside the tank into a first storage area and a second storage area. The condensate recovery liquid from the preheating chamber (2) flows into the first storage area, and the condensate recovery liquid from the welding chamber (4) flows into the second storage area. The liquid medium in the two areas is not interconnected. The controller is also configured to: When performing the process of the preheating chamber (2), liquid medium is preferentially extracted from the first liquid storage area and injected into the preheating chamber (2). When the liquid level in the first liquid storage area is lower than the preset minimum liquid level threshold, fresh vapor phase liquid is injected into the preheating chamber (2) from the second liquid storage area or externally. When performing the process of the welding chamber (4), only fresh vapor phase liquid replenished from the second liquid storage area or externally is injected into the welding chamber (4).

3. The online vapor phase welding method according to claim 1, characterized in that, The nitrogen and formic acid mixed gas supply pipeline includes a mass flow controller for independently adjusting the flow rates of nitrogen and formic acid respectively. The process of quantitatively filling the chamber with a mixture of nitrogen and formic acid to a slightly positive pressure includes the following steps: The first mixed gas with a formic acid volume concentration in the first preset concentration range is controlled to be introduced into the chamber, so that the pressure in the chamber reaches the first preset micro-positive pressure value and is maintained for the first preset time, so as to form an initial reducing and wetting atmosphere rich in formic acid on the surface of the workpiece. After the first inflation stage is completed, nitrogen is injected to increase the pressure inside the chamber from the first preset micro-positive pressure value to the second preset micro-positive pressure value. At the same time, the formic acid flow rate is adjusted by the mass flow controller to reduce the volume concentration of formic acid inside the chamber from the first preset concentration range to the second preset concentration range. During or after the second inflation sub-stage, at least one pressure oscillation cycle is performed, which includes: partially or completely extracting the gas in the chamber until the pressure in the chamber drops to a preset lower limit pressure for oscillation, and then re-injecting the mixed gas or nitrogen into the chamber to restore the pressure in the chamber to the second preset micro-positive pressure value.

4. The online vapor phase welding method according to claim 1, characterized in that, In the steam heating section, the controller is also configured to perform temperature field self-balancing control on the side heating element (43). Includes the following steps: Before injecting the liquid vapor phase, the side heating element (43) is controlled to be turned on in advance with the first side heat preservation power to preheat the inner side wall of the chamber to a temperature not lower than the saturation temperature of the vapor phase to be injected under the current pressure; After the liquid vapor phase is injected, the temperature of at least two different measurement points on the surface of the workpiece is continuously obtained by the temperature measuring device (6). The measurement points include the edge area measurement point near the side wall of the chamber and the center area measurement point away from the side wall. If the temperature of the edge region measurement point is lower than the temperature of the center region measurement point, and the temperature difference between the two exceeds the preset edge temperature difference threshold, then the power of the side heating element (43) is increased to increase the radiative heating compensation for the edge region of the workpiece. If the temperature of the edge region measurement point is higher than the temperature of the center region measurement point, and the temperature difference between the two exceeds the preset center temperature difference threshold, then the power of the side heating element (43) is reduced to reduce radiative heating of the workpiece edge region. If the temperature difference between the edge region measurement point and the center region measurement point is maintained within the allowable deviation range, the current power of the side heating element (43) is maintained.

5. The online vapor phase welding method according to claim 4, characterized in that, The insulation power on the first side is dynamically determined by the controller during a single batch of the process, including the following steps: During the radiation preheating phase, the side heating element (43) is operated with the first side radiation power, and the real-time temperature of the inner sidewall of the cabin is recorded at the end of the phase. As the liquid to be injected approaches the steam heating section, the saturation temperature of the vapor phase liquid at that pressure is obtained based on the current chamber pressure. The saturation temperature is compared with the real-time temperature of the sidewall: if the saturation temperature is higher than the real-time temperature of the sidewall, the first side insulation power is set to be higher than the first side radiation power to compensate for the heating demand of the sidewall before entering the steam heating section; if the saturation temperature is lower than the real-time temperature of the sidewall, the first side insulation power is set to be lower than the first side radiation power to avoid overheating of the sidewall. The adjustment range of the first side insulation power is positively correlated with the difference between the saturation temperature and the real-time temperature of the side wall, and the adjustment range is determined by the built-in thermal balance formula, which is based on the heating efficiency of the side heating element (43), the heat capacity of the cabin side wall and the heat dissipation characteristics pre-calibrated.

6. The online vapor phase welding method according to claim 5, characterized in that, The pre-calibration of the heat balance equation includes the following steps: In the calibration mode after the initial debugging or maintenance of the equipment, the side heating element (43) is controlled to operate at multiple different calibration power values ​​in sequence, and the real-time temperature of the inner side wall of the cabin is monitored until the side wall temperature reaches a steady state under each calibration power value. Record the steady-state sidewall temperature and the current ambient temperature corresponding to each calibration power value, and construct a calibration data set that characterizes the relationship between heating input power and net sidewall temperature rise; Based on the calibration data set, the first characteristic coefficient corresponding to the electrothermal conversion efficiency of the side heating element (43) and the second characteristic coefficient corresponding to the heat dissipation capacity of the cabin sidewall to the environment are determined by numerical fitting. The first characteristic coefficient and the second characteristic coefficient together constitute the heat balance relationship.

7. The online vapor phase welding method according to claim 6, characterized in that, It also includes the following steps: At the end of the radiation preheating section of each process batch, the average actual operating power of the side heating element (43) in this radiation preheating section, the real-time side wall temperature at that moment, and the current ambient temperature are obtained as a set of online correction sample data. The consistency of the online corrected sample data with the currently valid heat balance relationship is compared to generate a deviation quantity characterizing the degree of deviation of the relationship at the current operating point; If the deviation exceeds a preset correction trigger threshold, a recursive fitting algorithm with a forgetting factor is triggered to incorporate the online correction sample data and correct the first feature coefficient and the second feature coefficient.

Images