Method and system for determining heat transfer coefficient in continuous heating process

Abstract

The present application discloses a method and system for determining the heat transfer coefficient in a continuous heating process. Aiming at the problem that the heat transfer parameters in the temperature model of the reflow soldering furnace during the continuous heating process have a great influence on the calculation results and are difficult to directly measure, first, a temperature simulation model of the reflow soldering furnace is established according to Fourier's heat transfer theorem, and the workpiece temperature data is collected through a constant temperature experiment on the reflow soldering furnace; then, the heat transfer parameters are calculated based on the experimental data; finally, the linear equation parameters are calculated according to the least square method to determine the relationship between the heat transfer parameters and the fan speed. The present invention aims at the calculation problem of the heat transfer parameters in the temperature model of the continuous heating process, calculates the relationship between the heat transfer parameters and the fan speed through the least square method, realizes the dynamic setting of the heat transfer parameters, is conducive to quickly determining the changing heat transfer parameters during the continuous heating process, and improves the accuracy and operation efficiency of the simulation.

Description

Technical Field

[0001] The present invention relates to the technical fields of heat transfer and automatic control, and particularly to a method and system for determining the heat transfer coefficient in a continuous heating process. Background Art

[0002] With the continuous in-depth development of advanced manufacturing and the theory of integrated systems, embedded systems based on printed circuit boards have developed rapidly and are widely used in various industries such as aerospace, industrial robots, electronic products, and new energy vehicles. In the manufacturing process of printed circuit boards, the batch spot welding process of various small components is involved. Due to its large workload and high requirements for temperature accuracy, traditional welding methods are difficult to meet its needs. In this context, reflow soldering furnaces have been widely used due to their high efficiency and strong controllability. The reflow soldering technology, which develops in the direction of high efficiency, multi-function, and intelligence, has gradually become the core technology in the processing of printed circuit boards.

[0003] As a key device in the production of printed circuit boards, accurate temperature control is the core function of the performance of this device. Due to the strong coupling and non-linear characteristics of the reflow soldering furnace, it is difficult to obtain accurate control parameters of the system through manual attempts. Therefore, there is a requirement for analyzing the temperature field of the reflow soldering furnace and establishing a temperature model of the reflow soldering furnace for auxiliary control. According to Fourier's law of heat conduction, a temperature simulation model of the reflow soldering furnace can be established by combining the continuous heating process of the reflow soldering furnace. The internal working process of the reflow soldering furnace is a continuous heating process in multiple temperature zones, which involves heat transfer processes at different temperatures and different wind speeds between different temperature zones, and these processes have different heat transfer rates. Finding the relationship between temperature difference, wind speed, and heat transfer rate is the key to establishing an accurate temperature model to guide temperature control.

[0004] The least squares method is a classical linear regression method and a commonly used algorithm in the fitting of linear relationships, and is widely used in parameter identification. In the least squares method, first, several data points including the function mapping to be solved are obtained, and then the slope and solution of the fitted linear mapping are obtained through the least squares formula, so as to achieve the solution of the linear relationship. With the advantages of simple operation and fast operation speed, the least squares method has been widely used in fields such as system identification. However, it has not been applied in the determination of heat transfer parameters in continuous heating processes such as reflow soldering furnaces. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and system for determining the heat transfer coefficient in a continuous heating process, so as to solve the problem that the heat transfer parameters in the temperature model of the continuous heating process of the reflow soldering furnace have a great influence on the calculation results and are difficult to directly measure.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] The first aspect of the present application provides a method for determining the heat transfer coefficient in a continuous heating process, including:

[0008] S1. Conduct temperature simulation modeling on the reflow soldering furnace according to Fourier's law of heat conduction. The heat transfer formula for its continuous heating process is:

[0009]

[0010] where α is the heat transfer parameter, T(t) is the temperature of the workpiece in the reflow soldering furnace at time t, is the temperature inside the reflow soldering furnace at time t, and Δt is the preset time interval;

[0011] S2. Set experimental parameters, including chain speed, zone temperature, and fan speed, conduct a constant temperature experiment in the reflow soldering furnace, obtain multiple groups of constant temperature experiment data, and calculate the corresponding heat transfer parameter α according to each group of constant temperature experiment data i ;

[0012] S3. Establish a linear function between the heat transfer parameter α and the fan speed . The linear relationship is:

[0013]

[0014] Use each group of constant temperature experiment data and the calculated heat transfer parameter α i , and calculate k and b by the least square method to determine the linear relationship between the heat transfer parameter α and the fan speed ;

[0015] S4. Combine the obtained linear relationship between the heat transfer parameter α and the fan speed with the Fourier heat conduction formula for the continuous heating process in step S1 to calculate the simulated heat transfer curve.

[0016] Preferably, in step S1, the preset time interval Δt is 0.25 s.

[0017] Preferably, step S2 specifically includes the following steps:

[0018] Place the workpiece in the reflow soldering furnace, select at least three combinations from zone temperatures of 150 °C, 200 °C, and 250 °C and a constant fan speed for experiments, record the workpiece temperature, and calculate the heat transfer parameter α according to three groups of temperature data i . The calculation formula is as follows:

[0019]

[0020] Preferably, step S3 specifically includes the following steps:

[0021] Using multiple sets of fan speeds set in the constant temperature experiment and multiple sets of heat transfer parameters α calculated in step S2 i , calculate k and b by the least squares method, and the calculation formula is:

[0022]

[0023]

[0024] wherein, represents the i-th set of fan speeds, and α i represents the i-th set of heat transfer parameters, and i = 1, 2, 3; represents the average value of multiple sets of fan speeds, represents the average value of multiple sets of heat transfer parameters.

[0025] Preferably, after step S4, the method further includes the following steps:

[0026] S5. Conduct an experiment in a reflow soldering furnace using the same experimental parameters as the simulated heat transfer curve to verify the accuracy of k and b.

[0027] Preferably, after step S4, the method further includes the following steps:

[0028] If the workpiece type is changed or the internal temperature field of the reflow soldering furnace is changed, return to step S2 to re-conduct the constant temperature experiment, and calculate the heat transfer parameters α, k, and b.

[0029] The second aspect of the present application provides a heat transfer coefficient determination system for a continuous heating process, including:

[0030] A simulation model establishment module configured to perform temperature simulation modeling on a reflow soldering furnace according to Fourier's law of heat conduction, and the heat transfer formula for its continuous heating process is:

[0031]

[0032] wherein, α is the heat transfer parameter, T(t) is the temperature of the workpiece in the reflow soldering furnace at time t, is the temperature inside the reflow soldering furnace at time t, and Δt is a preset time interval;

[0033] A heat transfer parameter determination module configured to set experimental parameters, conduct a constant temperature experiment in a reflow soldering furnace, obtain multiple sets of constant temperature experiment data, and calculate the corresponding heat transfer parameter α according to the multiple sets of constant temperature experiment data i , wherein the experimental parameters include chain speed, zone temperature, and fan speed;

[0034] A relationship confirmation module configured to establish the relationship between the heat transfer parameter α and the fan speed A linear function with a linear relationship as follows: Using the constant temperature experimental data of each group and the calculated heat transfer parameter α i , k and b are calculated by the least squares method to determine the relationship between the heat transfer parameter α and the fan speed ;

[0035] A simulation heat transfer curve calculation module configured to combine the relationship between the obtained heat transfer parameter α and the fan speed with the Fourier heat conduction formula of the continuous heating process in the simulation model establishment module to calculate the simulation heat transfer curve.

[0036] Preferably, the system further includes: a verification module configured to perform tests in a reflow soldering furnace using the same experimental parameters as the simulation heat transfer curve to verify the accuracy of k and b.

[0037] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0038] 1) The present invention aims to determine the heat transfer parameters in the continuous heating process of the reflow soldering furnace, reduce the error between the output curve and the simulation curve of the reflow soldering furnace, improve the calculation accuracy, and provide guidance for the temperature control in the continuous heating process.

[0039] 2) The present invention calculates the relationship between the heat transfer parameters and the fan speed by the least squares method, realizes the dynamic tuning of the heat transfer parameters, is conducive to quickly determining the changing heat transfer parameters in the continuous heating process, and improves the efficiency of simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof of this application are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0041] Figure 1 is a schematic flow chart of the method of the present invention.

[0042] Figure 2 (a)-(c) are the constant temperature experimental data curves of the embodiments of the present invention.

[0043] Figure 3 is an example of a comparison diagram between the actual operation curve and the simulation curve of the final optimized parameters of the embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] To make the purpose, technical solution and effects of the present invention clearer and more definite, the following further describes the present invention in detail with reference to the accompanying drawings and by way of examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0045] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily limit to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0046] Embodiment

[0047] Figure 1 It is a schematic flow diagram of a method for determining the heat transfer coefficient of a continuous heating process.

[0048] As Figure 1 shown, a method for determining the heat transfer coefficient of a continuous heating process specifically includes the following steps:

[0049] Step 1: Conduct temperature simulation modeling on the reflow soldering furnace according to Fourier's law of heat conduction. The heat transfer formula for its continuous heating process is:

[0050]

[0051] where α is the heat transfer parameter, T(t) is the temperature of the workpiece in the reflow soldering furnace at time t, is the temperature inside the reflow furnace at time t, and Δt is generally taken as 0.25 s.

[0052] Step 2: Conduct a constant temperature experiment to determine the heat transfer parameter. In this embodiment, a certain thirteen-zone reflow soldering furnace is used for the experiment. The workpiece is placed in the reflow soldering furnace, the chain speed v = 1035 mm / min is set, the temperature of each zone is taken as 150 °C, and the constant fan frequency is experimented, the workpiece temperature is recorded, and three groups of constant temperature experiment data are obtained as Figure 2 (a) - (c) shown. Calculate their α i values according to the three groups of temperature data. The calculation formula is as follows:

[0053]

[0054] α1 = 0.0225, α2 = 0.0277, α3 = 0.0324 are obtained.

[0055] Step 3: Establish a linear function between the heat transfer parameter and the fan speed. The linear relationship is shown as follows:

[0056]

[0057] Calculate the parameters in the linear function formula, using the known conditions α1 = 0.0225, α2 = 0.0277, α3 = 0.0324, and Calculate k and b by the least squares method. The calculation formula is as follows:

[0058]

[0059]

[0060] where, represents the average value of multiple groups of fan speeds, represents the average value of multiple groups of heat transfer parameters.

[0061] After calculation, k = 0.00254437 and b = 0.00470299 are obtained.

[0062] Step 4: Combine the relationship between the obtained heat transfer parameters and the fan speed with the Fourier heat conduction formula in the continuous heating process in Step 1 to calculate the simulation curve. According to the same parameters as the simulation curve, that is, the chain speed v = 1470 mm / min and the wind speed The temperature parameters of the thirteen temperature zones are 70 °C, 85 °C, 100 °C, 115 °C, 130 °C, 145 °C, 230 °C, 250 °C, 235 °C, 235 °C, 200 °C, 180 °C, and 150 °C respectively. Conduct experiments in the reflow soldering furnace system to verify the accuracy of the parameters.

[0063] The comparison between the operation curve of the reflow soldering furnace and the simulation curve is as Figure 3 shown. It can be concluded that in the 1st - 13th temperature zones, that is, 0 - 160 s, the experimental curve and the simulation curve have a high degree of fitting, indicating that the parameter calculation is accurate. If the workpiece type is changed, or the internal temperature field of the reflow soldering furnace is changed, it is necessary to return to Step 2 to re - conduct the constant temperature experiment and calculate the heat transfer parameters α, k, and b.

[0064] On the other hand, the present application also discloses a heat transfer coefficient determination system for a continuous heating process, specifically including:

[0065] A simulation model establishment module, configured to perform temperature simulation modeling on the reflow soldering furnace according to the Fourier heat conduction law. The heat transfer formula for its continuous heating process is:

[0066]

[0067] where, α is the heat transfer parameter, T(t) is the temperature of the workpiece in the reflow soldering furnace at time t, is the temperature inside the reflow soldering furnace at time t, and Δt is a preset time interval;

[0068] A heat transfer parameter determination module, configured to set experimental parameters, conduct a constant temperature experiment in a reflow soldering furnace, obtain multiple sets of constant temperature experiment data, and calculate the corresponding heat transfer parameter α according to the multiple sets of constant temperature experiment data i , wherein the experimental parameters include chain speed, zone temperature, and fan speed;

[0069] A relationship confirmation module, configured to establish a linear function between the heat transfer parameter α and the fan speed , and its linear relationship formula is: Using each set of constant temperature experiment data and the calculated heat transfer parameter α i , calculate k and b by the least squares method, so as to determine the relationship between the heat transfer parameter α and the fan speed ;

[0070] A simulated heat transfer curve calculation module, configured to combine the obtained relationship between the heat transfer parameter α and the fan speed with the Fourier heat conduction formula of the continuous heating process in the simulation model establishment module to calculate the simulated heat transfer curve. In a preferred embodiment, the system further includes: a verification module, configured to conduct an experiment in a reflow soldering furnace using the same experimental parameters as the simulated heat transfer curve to verify the accuracy of k and b.

[0071] In summary, in view of the problem that the heat transfer parameters in the temperature model of the continuous heating process of the reflow soldering furnace have a great influence on the calculation results and are difficult to directly measure, the present application provides a method and system for determining the heat transfer coefficient of the continuous heating process. According to the principle of the continuous heating process of the reflow soldering furnace, a continuous heating temperature model of the reflow soldering furnace is established through the Fourier heat transfer theorem, constant temperature experiments are conducted to obtain data, the heat transfer parameters are determined according to the experimental data, and finally a linear function relationship between the heat transfer parameters and the fan speed is established by the least squares method, realizing the dynamic tuning of the heat transfer parameters, which is beneficial to quickly determining the changing heat transfer parameters in the continuous heating process and improving the simulation efficiency. At the same time, the present application reduces the error between the output curve and the simulation curve of the reflow soldering furnace and improves the calculation accuracy, providing guidance for the temperature control of the continuous heating process.

[0072] The specific embodiments of the present invention have been described in detail above, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions made to the present invention are also within the scope of the present invention. Therefore, equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention.

[0073] The above has described the specific embodiments of the present invention in detail, but they are only examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions made to the present invention are also within the scope of the present invention. Therefore, equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention.

Claims

1. A method for determining the heat transfer coefficient of a continuous heating process, characterized in that Including: S1. Conduct temperature simulation modeling on the reflow soldering furnace according to Fourier's law of heat conduction. The heat transfer formula for its continuous heating process is: where α is the heat transfer parameter, T(t) is the temperature of the workpiece in the reflow soldering furnace at time t, is the temperature inside the reflow soldering furnace at time t, and Δt is the preset time interval; S2. Set the experimental parameters, including the chain speed, the temperature of each zone, and the fan speed, conduct a constant-temperature experiment in the reflow soldering furnace, obtain multiple sets of constant-temperature experimental data, and calculate the corresponding heat transfer parameter α according to each set of constant-temperature experimental data i ; S3. Establish a linear function of the heat transfer parameter α and the fan speed The linear relationship is as follows: Using the constant temperature experiment data of each group and the calculated heat transfer parameter α i , calculate k and b by the least squares method, so as to determine the linear relationship between the heat transfer parameter α and the fan speed ; S4. Combine the obtained linear relationship between the heat transfer parameter α and the fan speed with the Fourier heat conduction formula of the continuous heating process in step S1 to calculate the simulated heat transfer curve.

2. The method for determining the heat transfer coefficient in a continuous heating process according to claim 1, characterized in that, In step S1, the preset time interval Δt is 0.25 s.

3. The method for determining the heat transfer coefficient in a continuous heating process according to claim 1, characterized in that, Step S2 specifically includes the following steps: Place the workpiece in the reflow soldering furnace, select at least three combinations from the temperature of each temperature zone: 150°C, 200°C, 250°C, and a constant fan speed for experiments, record the workpiece temperature, and calculate the heat transfer parameter α according to the three groups of temperature data i The calculation formula is as follows:

4. The method for determining the heat transfer coefficient in a continuous heating process according to claim 1, characterized in that Step S3 specifically includes the following steps: Using multiple sets of fan speeds set in the constant temperature experiment and multiple sets of heat transfer parameters α calculated in step S2 i , calculate k and b by the least squares method, and the calculation formula is: Among them, represents the speed of the i-th group of fans, α i represents the heat transfer parameter of the i-th group, i = 1, 2, 3; represents the average value of the speeds of multiple groups of fans, represents the average value of the heat transfer parameters of multiple groups.

5. The method for determining the heat transfer coefficient in a continuous heating process according to claim 1, wherein After step S4, the method further includes the following steps: S5. Conduct experiments in the reflow soldering furnace with the same experimental parameters as the simulated heat transfer curve to verify the accuracy of k and b.

6. The method for determining the heat transfer coefficient in a continuous heating process according to claim 1, characterized in that, After step S4, the method further includes the following steps: If the workpiece type is changed or the internal temperature field of the reflow soldering furnace is changed, return to step S2 to conduct the constant temperature experiment again, and calculate the heat transfer parameters α, k, and b.

7. A heat transfer coefficient determination system for a continuous heating process, characterized in that, Including: A simulation model establishment module, configured to conduct temperature simulation modeling on the reflow soldering furnace according to Fourier's law of heat conduction. The heat transfer formula for its continuous heating process is: where α is the heat transfer parameter, T(t) is the temperature of the workpiece in the reflow soldering furnace at time t, is the temperature inside the reflow soldering furnace at time t, and Δt is the preset time interval; A heat transfer parameter determination module, configured to set experimental parameters, conduct a constant temperature experiment in a reflow soldering furnace, obtain multiple groups of constant temperature experiment data, and calculate the corresponding heat transfer parameter α according to the multiple groups of constant temperature experiment data i , wherein the experimental parameters include chain speed, zone temperature, and fan speed; A relationship confirmation module is configured to establish a linear function between a heat transfer parameter α and a fan speed The linear relationship is as follows: Using each set of constant temperature experiment data and the calculated heat transfer parameter α i , calculate k and b by the least squares method, so as to determine the relationship between the heat transfer parameter α and the fan speed ; The simulation heat transfer curve calculation module is configured to combine the relationship between the obtained heat transfer parameter α and the fan speed with the Fourier heat conduction formula of the continuous heating process in the simulation model establishment module to calculate the simulation heat transfer curve.

8. A heat transfer coefficient determination system for a continuous heating process according to claim 7, characterized in that, The system further includes: a verification module, configured to conduct experiments in the reflow soldering furnace with the same experimental parameters as the simulated heat transfer curve to verify the accuracy of k and b.

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