High-flux extrusion needle valve start-stop control method

Abstract

The invention relates to a needle valve start-stop control method for high-flux extrusion, and relates to the technical field of additive manufacturing processes. According to the method, opening and closing of the needle valve are accurately controlled, the characteristics of extrusion materials, the size of a nozzle channel, the target extrusion flow and path motion parameters are combined, the start and stop time and the motion state of the needle valve are optimized, and continuous and stable discharging in the printing process is ensured. The method specifically comprises the steps that material dripping is restrained through pressure management and micro-rollback operation in a non-printing section, stable flow building is ensured through prepressing, valve opening and synchronous acceleration operation in an initial section, a needle valve is maintained to be opened in a steady-state section, flow fluctuation is avoided, and the wire drawing phenomenon is avoided through short rollback operation. The end forming consistency is further improved by closing the needle valve and executing short rollback at the printing end section. According to the method, accurate needle valve start and stop control can be achieved, the printing quality is optimized, and the post-processing cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, specifically to a needle valve start / stop control method for high-throughput extrusion. Background Technology

[0002] In high-throughput melt extrusion additive manufacturing, large nozzle diameters (e.g., 1 mm and above) or granular screw extrusion are commonly used to improve printing efficiency. However, under high-throughput conditions, the residual pressure in the melt channel and the viscoelasticity and inertial effects of the fluid are significantly enhanced, leading to several problems, especially in non-printing sections (such as path drift, transitions, and layer changes). Specifically, residual molten material at the nozzle exit, if not completely removed, can cause dripping contamination, affecting material control and part appearance throughout the printing process. Simultaneously, at the beginning of the printing path, the inability to precisely control the initial flow rate of the molten material often results in under-extrusion or sudden surges, further impacting print quality. At the end, failure to quickly return or cut off the molten material leads to stringing or material buildup, affecting the surface quality and dimensional consistency of the printed object.

[0003] In the prior art, a liquid material printhead for a 3D printer, disclosed in publication number CN110524868A, is a printhead solution that controls the material flow through valve needle action. The focus is on the structure of the printhead and the flow control, but it does not address how to effectively manage start-up and stop pressure, control valve needle timing and motion acceleration and deceleration synchronization under high-throughput melt extrusion conditions, nor does it provide a comprehensive control method to suppress dripping in the non-printing section, stabilize flow in the starting section, and suppress filament pulling and material accumulation in the ending section.

[0004] Another needle valve type anti-drooling nozzle, disclosed in CN208529591U, is a nozzle structure that closes the outlet with a needle valve to prevent drooling. Although this solution focuses on preventing material overflow through structural interception, it fails to provide a process method for synchronous control of pressure unloading, retraction, initial pre-pressure, valve opening and closing, and kinematics of the needle valve and extrusion drive, which are specific to the path transition characteristics in additive manufacturing. It cannot effectively solve the problems of "empty path contamination" and "end morphology inconsistency" in high-throughput extrusion.

[0005] Therefore, while existing technologies have touched upon this issue, they have not yet provided an integrated solution that can effectively manage nozzle control, achieve precise coordination between needle valve start / stop and extrusion drive, and solve a series of problems in the high-throughput extrusion process, including drip contamination in the non-printing section, under-extrusion surge in the initial section, and wire pulling and material accumulation in the final section. Summary of the Invention

[0006] To address the aforementioned problems, this invention discloses a needle valve start-stop control method for high-throughput extrusion. Before executing the extrusion path, based on the characteristics of the extruded material, nozzle channel size, target extrusion flow rate, and path motion parameters, the method determines the needle valve closed position, needle valve open position, pre-pressure parameters, micro-retraction parameters, short-retraction parameters, pressure unloading strategy, synchronous acceleration curve, and needle valve start-stop trigger conditions. During the non-printing segment, the starting segment, the steady-state segment, and the ending segment, the method coordinates the opening and closing of the needle valve and the extrusion drive output according to the control parameters, thereby achieving continuous and stable nozzle discharge, drip suppression in the non-printing segment, and smooth flow transition in the starting and ending segments, thus improving the consistency of part boundary forming and surface quality stability.

[0007] To achieve the above objectives, the present invention provides a needle valve start / stop control method for high-throughput extrusion, comprising the following steps: Before executing the extrusion path, the control parameters required for needle valve start-stop control are determined based on the characteristics of the extruded material, nozzle channel size, target extrusion flow rate and path motion parameters. The control parameters include needle valve closed position, needle valve open position, pre-pressure parameters, micro-retraction parameters, short-retraction parameters, pressure unloading strategy, synchronous acceleration curve and needle valve start-stop trigger conditions. When the path enters the non-printing section, the control needle valve closes and releases the residual molten material in the nozzle channel until no more molten material flows out of the nozzle outlet and the residual molten material reaches the target state. The printhead moves along the non-printing section path and always keeps the needle valve closed. When the path enters the printing start section from the non-printing section, a pre-pressure parameter is applied under the condition that the needle valve is closed, so that the extrusion state in the channel enters the stable output range. When the pre-pressure reaches the threshold and the nozzle temperature is within the allowable extrusion temperature range, the needle valve is placed in the open state, and a continuous and stable relationship between the extrusion output state and the path movement state is established according to the synchronous acceleration curve. During the steady-state printing phase, the needle valve is kept open. While maintaining the correspondence between the extrusion drive output state and the path motion state, the extrusion output is continuously adjusted according to the changes in the extrusion drive output state to compensate for flow deviations caused by changes in material viscosity, speed fluctuations, or thermal disturbances. When the path enters the printing end section or is about to enter the non-printing section, the needle valve is closed and a short retraction operation is performed to cut off the material before the end of the path. After the residual extrusion state reaches the preset condition, it continues to move along the non-printing section path. During the needle valve start / stop control process, if the needle valve start / stop triggering conditions are not met, an abnormal handling operation is performed to avoid abnormal start / stop affecting the forming quality.

[0008] The technical solution provided in this invention has the following technical effects: The needle valve start-stop control method for high-throughput extrusion of this invention can precisely control the start-stop behavior of the needle valve throughout the extrusion process, effectively improving the stability and material quality during extrusion. Specifically, in the non-printing stage, needle valve closure, pressure unloading, and micro-retraction operations can effectively suppress dripping and avoid contamination during transfer. In the initial printing stage, combined with pre-pressure parameters and synchronous acceleration curves, stable needle valve opening can be achieved, ensuring stable material output in the initial stage and avoiding under-extrusion or sudden surges. In the steady-state stage, precise control of the synchronization between extrusion flow rate and nozzle movement state ensures continuous stability of output and compensates for flow deviations caused by changes in material viscosity or temperature fluctuations. In the final printing stage, needle valve closure and short retraction operations can promptly cut off the molten material, preventing stringing and end-piece accumulation, thereby improving forming quality. Throughout the process, key parameters such as nozzle temperature, pressure, and nozzle speed are monitored in real time, and intelligent protection is provided for abnormal situations, effectively avoiding the impact of potential faults on printing quality. Through these measures, the present invention significantly improves the forming consistency and surface quality stability in high-throughput extrusion processes, and reduces post-processing costs and material waste. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic flowchart of a needle valve start / stop control method for high-throughput extrusion provided in an embodiment of this application. Detailed Implementation

[0011] This invention precisely controls the start and stop timing and movement state of the needle valve by combining the characteristics of the extruded material, the nozzle channel size, the target extrusion flow rate, and the path motion parameters. This ensures a stable material output state at the beginning of the path and effectively eliminates dripping in non-printing sections through pressure management and retraction operations. Furthermore, a synchronous acceleration strategy is employed to coordinate the nozzle speed and extrusion drive output, ensuring continuous and consistent material output and nozzle movement during printing, effectively improving boundary forming consistency and surface quality stability.

[0012] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0013] It should be noted that the terms "first," "second," etc., used in the specification and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, platform, product, or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or modules not explicitly listed or inherent to these processes, methods, products, or devices.

[0014] Example 1, as Figure 1 As shown, a needle valve start / stop control method for high-throughput extrusion includes the following steps: S1. Before executing the extrusion path, determine the control parameters required for needle valve start / stop control based on the characteristics of the extruded material, nozzle channel size, target extrusion flow rate, and path motion parameters. These control parameters include needle valve closed position, needle valve open position, pre-pressure parameters, micro-retraction parameters, short-retraction parameters, pressure unloading strategy, synchronous acceleration curve, and needle valve start / stop trigger conditions. Furthermore, the pre-compression parameters include pre-compression amount and pre-compression time. The pre-compression amount is determined by driving the extrusion mechanism to advance molten material along the nozzle channel when the needle valve is closed, and recording the cumulative advance stroke of the extrusion mechanism when the target channel filling degree is reached based on the flow characteristics of the extruded material and the nozzle channel size. The pre-compression time is determined by recording the time taken for the extrusion mechanism to reach the cumulative advance stroke. The pre-compression amount and pre-compression time are used to introduce molten material into the nozzle channel before the needle valve is opened, so as to form an extrusion preparation state that can be used for subsequent stable material output.

[0015] Furthermore, the pressure unloading strategy includes: Micro-retraction release: During the movement of the non-printing section, the extrusion mechanism pushes back a small amount of material in the opposite direction, causing some of the residual molten material in the nozzle channel to flow back, reducing the nozzle outlet pressure and preventing material from dripping. Short retraction release: Before the end of the non-printing segment or before the start of the printing end segment, the extrusion mechanism uses a large reverse propulsion amount to return the residual material at the nozzle exit to the inside of the nozzle channel, thereby achieving a clean cut-off at the nozzle tip and suppressing stringing and material build-up at the tip. Continuous micro-flow ensures that during the movement of the non-printing section, the extrusion mechanism maintains a small amount of propulsion or idles, so that the residual pressure in the nozzle channel decays evenly, ensuring that the nozzle moves safely along the non-printing section and that the nozzle does not drip. The combined strategy, based on the non-printing section length, nozzle channel length, material flow characteristics, and target extrusion flow rate, selects a single strategy or combines micro-retraction release, short-retraction release, and continuous micro-reflow to achieve effective control of nozzle residual pressure.

[0016] Furthermore, the synchronous acceleration curve is determined based on the path speed acceleration process of the initial printing segment. This ensures that during the needle valve opening process, as the nozzle speed increases from the initial nozzle speed of the initial printing segment to the target printing speed, the extrusion drive output state simultaneously increases from the extrusion drive output state at the completion of pre-pressure to the extrusion drive output state corresponding to the target extrusion flow rate. Here, the nozzle speed... Extrusion drive output status ; The moment when the synchronous acceleration interval begins. The moment when the synchronous acceleration interval ends. The initial nozzle speed for printing the first segment. For target printing speed, This refers to the extrusion drive output state when pre-compression is complete. The extrusion drive output state corresponding to the target extrusion flow rate.

[0017] Furthermore, the needle valve start / stop triggering condition is determined based on at least two of the following state variables: nozzle temperature, extrusion drive output state, nozzle movement speed and acceleration, and valve needle position or opening degree. When the threshold relationship or combination relationship of the state variables is satisfied, the needle valve is controlled to perform an opening or closing action. The threshold relationship or combination relationship of the state variables is as follows: The nozzle temperature meets the set allowable extrusion temperature range; The extrusion drive output state is within the target flow rate variation range, satisfying the extrusion load state. The nozzle's movement speed or acceleration meets the preset deceleration or acceleration conditions; The valve needle position or opening degree is within the set opening or closing threshold range.

[0018] Specifically, before executing the extrusion path, for needle valve start / stop control, the movement position of the needle valve in the nozzle channel is first calibrated. By driving the needle valve to move along its movement direction, the position where the tip of the valve needle is completely in contact with the nozzle flow channel and the molten material cannot pass through the nozzle outlet is determined, and this position is set as the needle valve closed position. The needle valve is then driven to move in the opening direction until the tip of the valve needle completely exits the effective flow channel of the nozzle and the nozzle cross section is no longer blocked by the valve needle, and this position is set as the needle valve open position.

[0019] Before executing the extrusion path, with the needle valve closed, the extrusion mechanism is driven to advance molten material into the nozzle channel to determine the pre-compression parameters, which include the pre-compression amount and the pre-compression time. First, the effective filling length of the nozzle channel with the needle valve closed is determined based on the structural dimensions of the nozzle channel, and the channel volume corresponding to the nozzle channel is calculated based on the cross-sectional area of ​​the nozzle channel. Based on this, and considering the flow characteristics of the extruded material at the target extrusion temperature, the extrusion mechanism is controlled to advance the molten material into the nozzle channel at a speed corresponding to the target extrusion flow rate until the material volume corresponding to the cumulative advance stroke of the extrusion mechanism reaches the channel volume corresponding to the nozzle channel. The cumulative advance stroke of the extrusion mechanism at this point is recorded, and this cumulative advance stroke is determined as the pre-compression amount. After determining the pre-compression amount, the extrusion mechanism is continuously advanced with the molten material at a speed corresponding to the target extrusion flow rate. The time taken from the start of advancement to reaching the pre-compression amount is recorded, and this time is determined as the pre-compression time.

[0020] With the needle valve closed, the nozzle outlet is changed from continuous discharge to a state where no molten material overflows by reverse driving the extrusion mechanism. The corresponding reverse extrusion stroke is recorded and set as the micro retraction parameter to suppress dripping in the non-printing section. In the printing end section, the reverse extrusion stroke is increased until the molten material at the nozzle outlet completely flows back into the channel and does not remain at the nozzle end. This stroke is set as the short retraction parameter.

[0021] To address the release of residual extrusion within the nozzle channel, a pressure unloading strategy is selected based on the nozzle channel length and the material's flow characteristics under heating conditions. This strategy considers the non-printing section length, nozzle channel length, target extrusion flow rate, and material flow characteristics. After the needle valve closes, the strategy controls the residual pressure within the channel to decrease until no more material flows out of the nozzle outlet. Specifically, for cases with low residual pressure or short non-printing section movement distances, a micro-retraction release is employed. A small amount of reverse propulsion by the extrusion mechanism allows some residual material to flow back, reducing nozzle outlet pressure and preventing dripping. Before the end of the non-printing section or the beginning of the printing section, a short-retraction release is used. A larger reverse propulsion by the extrusion mechanism returns residual material from the nozzle outlet to the channel interior, achieving clean end-cutting and suppressing stringing and material buildup. For long non-printing section movement distances or high-viscosity materials, continuous micro-retraction or idling is employed. The extrusion mechanism maintains a small propulsion amount or idling to uniformly decrease residual pressure, ensuring safe movement of the nozzle along the non-printing section without dripping. In complex operating conditions, the above strategies can be executed sequentially or in combination to effectively release nozzle residual pressure and control material output.

[0022] During the movement of the needle valve from the closed position to the open position, based on the changes in printing speed and extrusion flow rate at the beginning of the path, an acceleration relationship is set between the needle valve opening time and the extrusion drive output state and the nozzle movement state. This ensures that the extrusion output changes synchronously with the nozzle movement according to a preset curve, thereby establishing a continuous and stable initial output segment after the needle valve opens. The acceleration relationship between the needle valve opening time and the extrusion drive output state and the nozzle movement state is set as a synchronous acceleration curve. During the needle valve opening process, the nozzle movement speed and extrusion drive output state gradually increase according to the set synchronous acceleration curve, ensuring that the nozzle movement and extrusion output remain synchronized in the initial stage. The synchronous acceleration curve is determined based on the path speed acceleration process in the initial printing stage. In the preparation stage of the initial printing stage, the needle valve is kept closed and the pre-pressure operation is completed, and the extrusion drive output state at this time is recorded. and time point After the needle valve starts to open, a synchronous acceleration interval is set, starting from time... arrive Inside, the nozzle speed changes from the initial nozzle speed. Linear ramp-up to target printing speed nozzle movement speed Simultaneously, the extrusion drive output state changes from the extrusion drive output state corresponding to the completion of pre-compression. The extrusion drive output state increases linearly to the target extrusion flow rate. Extrusion drive output status Within the synchronous acceleration interval, the current time is obtained at each time sampling point. And calculate the corresponding nozzle movement speed. and extrusion drive output status This drives the nozzle to move and advances the extrusion mechanism, ensuring that the nozzle movement is synchronized with the extrusion output. When the time is up... Or the printhead speed and extrusion output state achieve the target printing speed. Extrusion drive output state corresponding to the target extrusion flow rate Then, the printing process enters the steady-state phase.

[0023] Before executing the extrusion path, for needle valve start / stop control, needle valve opening and closing trigger conditions are set based on state variables during the extrusion process. These state variables include nozzle temperature, extrusion drive output status, nozzle movement speed and acceleration, and valve needle position or opening. During extrusion path execution, nozzle temperature, extrusion drive output status, nozzle movement speed and acceleration are acquired in real time and combined with the current valve needle position or opening as state variables for needle valve start / stop determination. Based on the extruded material characteristics, nozzle channel size, and path movement characteristics, trigger threshold ranges for needle valve opening or closing are preset.

[0024] When the printhead enters the non-printing or printing end segment, the current values ​​of the printhead's speed and acceleration are continuously acquired, and it is determined whether they meet the preset deceleration or stop threshold conditions. While meeting the preset deceleration or stop threshold conditions, it is further determined whether the extrusion drive output state is in the output range corresponding to reduced or maintained material output, and whether the valve needle position or opening has not yet reached the preset closed position. If the combination of state variables meets the set threshold conditions, the trigger condition for needle valve closure is determined to be met, and the needle valve is controlled to move from the open position to the closed position. When the printhead enters the printing start segment, the changes in the printhead's speed and acceleration are acquired in real time, and it is determined whether they meet the preset start or acceleration threshold conditions. While meeting the preset start or acceleration threshold conditions, it is determined whether the extrusion drive output state has returned to the target flow rate change range, and whether the nozzle temperature is within the allowable extrusion temperature range. If the combination of state variables meets the set threshold conditions, the trigger condition for needle valve opening is determined to be met, and the needle valve is controlled to move from the closed position to the open position.

[0025] S2. When the path enters the non-printing section, the control needle valve closes and releases the residual molten material in the nozzle channel until no more molten material flows out of the nozzle outlet and the residual molten material reaches the target state. Then, the printhead moves along the non-printing section path while keeping the needle valve closed throughout. Furthermore, controlling the needle valve to close and release the residual molten material in the nozzle channel includes setting the material outflow start point at the nozzle outlet as the initial position of the reverse extrusion stroke, while adjusting the reverse extrusion speed of the drive mechanism until the material at the nozzle outlet completely flows back into the nozzle channel, and monitoring the flow rate change at the nozzle outlet. When the flow rate gradually decreases below the set target value, the reverse extrusion operation is stopped.

[0026] Specifically, when executing the extrusion path and entering the non-printing section, the needle valve is first driven to switch from the open state to the closed state to ensure that the nozzle flow channel is completely closed and to prevent molten material from overflowing due to the nozzle not being completely closed. After the needle valve closes, the residual molten material in the nozzle channel is released through reverse extrusion or micro-retraction. First, the starting point of material outflow at the nozzle outlet is set as the initial position of the reverse extrusion stroke. Then, the reverse extrusion speed of the drive mechanism is adjusted to gradually reduce the intensity of molten material outflow at the nozzle outlet until the material at the nozzle outlet completely flows back into the nozzle channel. The flow rate change at the nozzle outlet is monitored. When the flow rate gradually decreases below the set target value, it indicates that the residual molten material at the nozzle outlet has basically flowed back into the nozzle, and reverse extrusion stops. The preset target value is determined by the gradual decrease in actual nozzle output during the non-printing segment. Specifically, when the nozzle is closed and the extrusion mechanism is idling or running with a very small advance, the dripping of molten material at the nozzle outlet or the flow rate signal is continuously measured. The minimum retraction stroke corresponding to when the nozzle outlet flow rate just begins to decrease to a stable level without overflow is recorded, and the flow rate value corresponding to this stroke is set as the preset target value to determine the timing of reverse extrusion completion. After completing the reverse extrusion or micro-retraction operation, the needle valve is ensured to remain closed until the printhead enters the next printing segment. When the nozzle moves along the non-printing section path, the needle valve is always kept closed to prevent molten material from overflowing and to ensure that no dripping occurs in the non-printing section.

[0027] S3. When the path enters the printing start section from the non-printing section, a pre-pressure parameter is applied with the needle valve closed to bring the extrusion state in the channel into a stable output range. When the pre-pressure reaches the threshold and the nozzle temperature is within the stable window, the needle valve is opened, and a continuous and stable relationship between the extrusion drive output state and the path motion state is established according to the synchronous acceleration curve. Specifically, before the path transitions from the non-printing section to the printing initiation section, the needle valve remains closed. Confirm that any residual molten material in the nozzle channel has flowed back into the channel via a micro-retraction or short-retraction operation, and that no more dripping occurs at the nozzle exit. Based on the pre-compression parameters, including pre-compression amount and pre-compression time, drive the extrusion mechanism to advance molten material into the nozzle channel until the nozzle channel pressure reaches the pre-compression threshold. Simultaneously, monitor the nozzle temperature to ensure it remains within the allowable extrusion temperature range. With the needle valve closed, record the moment the nozzle channel pressure reaches the threshold and the corresponding extrusion stroke; this stroke serves as the completion marker for the pre-compression of the initiation section. Based on this marker, drive the needle valve to move in the opening direction until the valve needle tip completely exits the nozzle channel, and the nozzle flow path is no longer obstructed.

[0028] After the needle valve opens, a correspondence is established between the nozzle's movement distance along the path and the extrusion mechanism's advance amount, based on the synchronous acceleration curve. That is, for every incremental movement of the nozzle along the path, the extrusion mechanism advances a corresponding extrusion amount according to the synchronous acceleration curve. The extrusion mechanism executes a step-by-step advance action according to the pre-set synchronous acceleration curve, with each step corresponding to the nozzle's incremental movement along the path, ensuring that the extrusion output continuously increases with the nozzle's movement. During the advance process, the extrusion mechanism synchronously advances the molten material while the nozzle moves along the path, keeping the extrusion drive output state synchronized with the nozzle movement state. After all advance actions are completed, the needle valve remains open, the extrusion mechanism remains in the final advance position, and the nozzle outlet produces a continuous and stable output, thus establishing a continuous and stable relationship between the extrusion drive output state and the path movement state.

[0029] S4. During the steady-state printing phase, keep the needle valve open. While maintaining the correspondence between the extrusion drive output state and the path motion state, continuously adjust the extrusion output according to the changes in the extrusion drive output state to compensate for flow deviations caused by changes in material viscosity, speed fluctuations, or thermal disturbances. Specifically, during the steady-state printing phase, the needle valve remains open to ensure the nozzle flow channel remains continuously open, resulting in continuous material output. With the needle valve open, the extrusion mechanism outputs molten material according to the target extrusion flow rate, while the nozzle moves along the printing path. During extrusion, the extrusion drive output status is monitored in real time via a pressure sensor or extrusion drive feedback signal. Based on the path movement status, the advance amount of the extrusion mechanism is controlled according to a pre-set synchronous acceleration curve to maintain a correspondence between the extrusion drive output status and the path movement status. When the extrusion drive output status deviates from the target flow rate, an adjustment operation is performed: if the extrusion drive output status is lower than the target flow rate, the advance amount of the extrusion mechanism is increased to restore the nozzle output to the target flow rate; if the extrusion drive output status is higher than the target flow rate, the advance amount of the extrusion mechanism is reduced or the advance is paused briefly to return the nozzle output to the target flow rate. This monitoring and adjustment continues until the nozzle completes the steady-state path movement, ensuring that the correspondence between the extrusion drive output status and the path movement status remains stable.

[0030] Throughout the steady-state printing process, the needle valve is kept open to ensure continuous and stable material output from the nozzle. At the same time, the flow deviation caused by changes in material viscosity, speed fluctuations, or thermal disturbances is compensated by real-time monitoring and adjustment of the extrusion drive output state, ensuring the consistency of the printed boundary and internal structure.

[0031] S5. When the path enters the printing end segment or is about to enter the non-printing segment, the needle valve is placed in the closed state, and a short retraction operation is performed to cut off the material before the end of the path. After the residual extrusion state reaches the preset condition, it continues to move along the non-printing segment path. Specifically, when the path enters the printing end segment or is about to transition to the non-printing segment, the needle valve remains open and extrusion continues. When the nozzle reaches the beginning position of the end segment, the needle valve is driven to move in the closing direction until the tip of the valve needle completely enters the nozzle flow channel, blocking the nozzle outlet and closing the needle valve. After the needle valve closes, the extrusion mechanism is immediately driven to perform a short retraction operation, causing the residual molten material at the nozzle outlet to flow back into the nozzle channel, thus completing the material cut-off before the path ends. During the short retraction operation, the nozzle outlet flow rate and the feedback status of the extrusion mechanism are monitored in real time to determine whether there is still molten material overflowing from the nozzle tip. When there is no more dripping or continuous material stringing at the nozzle outlet, and the extrusion mechanism feedback shows that the residual pressure or thrust in the channel remains stable, the residual extrusion state is considered to have reached the preset condition. After the residual extrusion state reaches the preset condition, the needle valve remains closed, and the nozzle continues to move along the non-printing segment path while the extrusion mechanism advances, ensuring that there is no more molten material output from the nozzle during the movement of the non-printing segment, achieving safe movement of the non-printing segment.

[0032] S6. During the needle valve start / stop control process, if the needle valve start / stop triggering condition is not met, perform an abnormal handling operation to avoid abnormal start / stop affecting the forming quality.

[0033] Specifically, during the needle valve start / stop control process, the trigger conditions for needle valve start / stop are continuously monitored. In the corresponding actions of the non-printing segment, printing start segment, steady-state segment, and printing end segment, abnormal handling operations are performed for cases where the trigger conditions are not met to avoid abnormal start / stop affecting the forming quality. The details are as follows: For the non-printing section control phase: the needle valve should remain closed, and residual molten material in the channel should flow back into the channel through a micro-retraction operation or pressure release. The needle valve start / stop trigger conditions should be judged in real time. If an abnormality occurs in the non-printing section, such as the needle valve not being completely closed or residual material not flowing back, the nozzle movement along the path should be stopped immediately, and the micro-retraction operation should be re-executed until the needle valve is completely closed, ensuring that there is no dripping or stringing in the non-printing section.

[0034] For the initial printing control phase: after pre-compression is completed and the needle valve is ready to open, the needle valve start / stop trigger conditions are judged in real time. If the needle valve opening action is not executed correctly when the trigger conditions are met, an abnormal handling operation is performed, including keeping the needle valve closed, reapplying the pre-compression parameters, and repeating the needle valve opening action until the needle valve opening is synchronized with the nozzle movement and extrusion output, ensuring continuous and stable material output in the initial stage.

[0035] Steady-state control phase: The needle valve remains open to maintain the correspondence between extrusion output and path movement. If the triggering condition is not met, causing the flow rate to deviate from the expected value, abnormal handling operations are performed, including briefly stopping the advance, adjusting the extrusion advance amount, or repeating the needle valve opening and closing action, until the extrusion output and path movement return to the preset correspondence.

[0036] During the final stage of printing control: before the needle valve closes and during the short retraction process, the start and stop trigger conditions of the needle valve are continuously judged. If the needle valve completes the closing or short retraction operation, the nozzle movement is immediately stopped, and the needle valve closing and short retraction operations are repeated to ensure that the material is cut off before the end of the path. Only after the residual extrusion state reaches the preset condition can the nozzle continue to move along the non-printing section path.

[0037] Throughout the entire needle valve start-stop control process, the triggering conditions are continuously monitored at each stage. If an abnormality is detected, the corresponding abnormality handling operation is immediately executed until the triggering conditions are restored, thereby ensuring that the needle valve start-stop action always conforms to the preset logic and protects the molding quality.

[0038] The specific embodiments described above do not constitute a limitation on the scope of protection of this application. Those skilled in the art should understand that various modifications, combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A needle valve start / stop control method for high-throughput extrusion, characterized in that, Includes the following steps, Before executing the extrusion path, the control parameters required for needle valve start-stop control are determined based on the characteristics of the extruded material, nozzle channel size, target extrusion flow rate and path motion parameters. The control parameters include needle valve closed position, needle valve open position, pre-pressure parameters, micro-retraction parameters, short-retraction parameters, pressure unloading strategy, synchronous acceleration curve and needle valve start-stop trigger conditions. When the path enters the non-printing section, the control needle valve closes and releases the residual molten material in the nozzle channel until no more molten material flows out of the nozzle outlet and the residual molten material reaches the target state. The printhead moves along the non-printing section path and always keeps the needle valve closed. When the path enters the printing start section from the non-printing section, a pre-pressure parameter is applied under the condition that the needle valve is closed, so that the extrusion state in the channel enters the stable output range. When the pre-pressure reaches the threshold and the nozzle temperature is within the allowable extrusion temperature range, the needle valve is placed in the open state, and a continuous and stable relationship between the extrusion output state and the path movement state is established according to the synchronous acceleration curve. During the steady-state printing phase, the needle valve is kept open. While maintaining the correspondence between the extrusion drive output state and the path motion state, the extrusion output is continuously adjusted according to the changes in the extrusion drive output state to compensate for flow deviations caused by changes in material viscosity, speed fluctuations, or thermal disturbances. When the path enters the printing end section or is about to enter the non-printing section, the needle valve is closed and a short retraction operation is performed to cut off the material before the end of the path. After the residual extrusion state reaches the preset condition, it continues to move along the non-printing section path. During the needle valve start / stop control process, if the needle valve start / stop triggering conditions are not met, an abnormal handling operation is performed to avoid abnormal start / stop affecting the forming quality.

2. The needle valve start / stop control method for high-throughput extrusion according to claim 1, characterized in that, The pre-compression parameters include pre-compression amount and pre-compression time. The pre-compression amount is the cumulative advance stroke of the extrusion mechanism when the nozzle channel reaches the target filling level for subsequent stable output, under the premise of considering the flow characteristics of the extruded material and the size of the nozzle channel, by driving the extrusion mechanism to advance molten material into the nozzle channel with the needle valve closed. The pre-compression amount and pre-compression time are used to introduce molten material into the nozzle channel before the needle valve is opened, so as to form an extrusion preparation state for subsequent stable output.

3. The needle valve start / stop control method for high-throughput extrusion according to claim 2, characterized in that, The pressure relief strategy includes: Micro-retraction release: During the movement of the non-printing section, the extrusion mechanism pushes back a small amount of material in the opposite direction, causing some of the residual molten material in the nozzle channel to flow back, reducing the nozzle outlet pressure and preventing material from dripping. Short retraction release: Before the end of the non-printing segment or before the start of the printing end segment, the extrusion mechanism uses a large reverse propulsion amount to return the residual material at the nozzle exit to the inside of the nozzle channel, thereby achieving a clean cut-off at the nozzle tip and suppressing stringing and material build-up at the tip. Continuous micro-flow ensures that during the movement of the non-printing section, the extrusion mechanism maintains a small amount of propulsion or idles, so that the residual pressure in the nozzle channel decays evenly, ensuring that the nozzle moves safely along the non-printing section and that the nozzle does not drip. The combined strategy, based on the non-printing section length, nozzle channel length, material flow characteristics, and target extrusion flow rate, selects a single strategy or combines micro-retraction release, short-retraction release, and continuous micro-reflow to achieve effective control of nozzle residual pressure.

4. The needle valve start / stop control method for high-throughput extrusion according to claim 3, characterized in that, The synchronous acceleration curve is determined based on the path speed acceleration process of the initial printing segment. During the needle valve opening process, as the nozzle speed climbs from the initial nozzle speed of the initial printing segment to the target printing speed, the extrusion drive output state synchronously increases from the extrusion drive output state at the pre-pressure completion stage to the extrusion drive output state corresponding to the target extrusion flow rate. The nozzle speed... Extrusion drive output status ; The moment when the synchronous acceleration interval begins. The moment when the synchronous acceleration interval ends. The initial nozzle speed for printing the first segment. For target printing speed, This refers to the extrusion drive output state when pre-compression is complete. The extrusion drive output state corresponding to the target extrusion flow rate.

5. The needle valve start / stop control method for high-throughput extrusion according to claim 4, characterized in that, The needle valve start / stop triggering condition is determined based on at least two of the following state variables: nozzle temperature, extrusion drive output state, nozzle movement speed and acceleration, and valve needle position or opening degree. When the threshold relationship or combination relationship of these state variables is satisfied, the needle valve is controlled to perform an opening or closing action. The threshold relationship or combination relationship of these state variables is as follows: The nozzle temperature meets the set allowable extrusion temperature range; The extrusion drive output state is within the target flow rate variation range, satisfying the extrusion load state. The nozzle's movement speed or acceleration meets the preset deceleration or acceleration conditions; The valve needle position or opening degree is within the set opening or closing threshold range.

6. The needle valve start / stop control method for high-throughput extrusion according to claim 5, characterized in that, The control needle valve closes and releases residual molten material in the nozzle channel by setting the material outflow start point at the nozzle outlet as the initial position of the reverse extrusion stroke, adjusting the reverse extrusion speed of the drive mechanism until the material at the nozzle outlet completely flows back into the nozzle channel, and monitoring the flow rate change at the nozzle outlet. When the flow rate gradually decreases below the set target value, the reverse extrusion operation is stopped.

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