Method for improving precision of automobile body-in-white welding fixture

Abstract

This invention discloses a method for improving the accuracy of automotive body-in-white welding fixtures, comprising: setting an elastic compensation component between the positioning component and the base of the fixture; forming a heat insulation layer on the surface of the fixture facing the welding heat source; acquiring the real-time temperature at the positioning component; and changing the deformation state of the elastic compensation component through a compensation adjustment mechanism when the real-time temperature exceeds a preset threshold. This method for improving the accuracy of automotive body-in-white welding fixtures, by setting an elastic compensation component with adjustable compression and setting a heat insulation layer on the fixture surface, forms a thermal deformation adaptive compensation mechanism, thereby enabling real-time compensation of thermal deformation during welding, maintaining the long-term stability of the positioning reference, and improving positioning accuracy.

Description

Technical Field

[0001] This invention belongs to the field of automotive manufacturing equipment technology. Specifically, this invention relates to a method for improving the precision of automotive body-in-white welding fixtures. Background Technology

[0002] Body-in-white welding fixtures are crucial process equipment for ensuring the dimensional accuracy of body welding. During welding operations, the instantaneous concentrated heat load continuously acts on positioning elements such as locating pins and support blocks, which can easily cause uneven thermal expansion and thermal creep deformation, resulting in a rapid decrease in the accuracy of the positioning elements after heating.

[0003] In existing technologies, offline static calibration is often used to control fixture accuracy. This method cannot detect thermal displacement deviations under welding conditions in real time and lacks an effective adaptive compensation mechanism for thermal deformation. It is difficult to detect errors that occur in actual production in a timely manner, resulting in a decrease in positioning accuracy and failing to meet the high-precision and high-stability mass production requirements of body-in-white.

[0004] This paper provides a method for improving the accuracy of automotive body-in-white welding fixtures, particularly regarding how to improve positioning accuracy. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a method for improving the accuracy of automotive body-in-white welding fixtures, with the purpose of improving positioning accuracy.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for improving the accuracy of automotive body-in-white welding fixtures, comprising: An elastic compensation component is installed between the positioning component of the fixture and the base; A heat insulation layer is formed on the surface of the fixture facing the welding heat source; Obtain the real-time temperature at the positioning component; When the real-time temperature exceeds a preset threshold, the deformation state of the elastic compensation component is changed by the compensation adjustment mechanism.

[0007] The elastic compensation component includes a disc spring assembly. When setting the elastic compensation component, the disc spring assembly is given a pre-compression amount and a stiffness. The pre-compression amount is any value greater than or equal to 1.2 mm and less than or equal to 1.8 mm, and the spring stiffness is any value greater than or equal to 500 N / mm and less than or equal to 600 N / mm.

[0008] The heat insulation layer is disposed on the surface of the fixture facing the welding electrode, and the heat insulation layer is made of silicon nitride ceramic material.

[0009] The method for improving the accuracy of automotive body-in-white welding fixtures further includes introducing a cooling medium into the cooling channels formed inside the base.

[0010] The introduction of the cooling medium includes supplying a coolant with a temperature ≤32°C to the cooling channel, wherein the flow rate of the coolant is set to any value greater than or equal to 8L / min and less than or equal to 12L / min.

[0011] The real-time temperature of the positioning component is obtained by a temperature sensor installed at the positioning component. The temperature sensor has a measurement range of -20℃ to 300℃ and a resolution of ≤0.1℃.

[0012] The preset threshold is set to any value greater than or equal to 55°C and less than or equal to 62°C; when the real-time temperature at the positioning component exceeds the preset threshold, the compensation adjustment mechanism increases the compression of the elastic compensation component, and the adjustment amplitude ranges from greater than or equal to 0.3mm to less than or equal to 0.5mm.

[0013] The method for improving the precision of automotive body-in-white welding fixtures also includes: Based on the overall vehicle design benchmark of the body-in-white, reference holes and reference surfaces are set on the base, and the position of the positioning component is calibrated.

[0014] The method for improving the precision of automotive body-in-white welding fixtures also includes: A global coordinate system for the body-in-white was established using a laser tracker, and the fixture was statically calibrated offline. Multiple feature points were measured to assess the positioning accuracy. A displacement detector is installed on the positioning member and / or clamping member to continuously monitor the displacement deviation under simulated welding conditions; A visual inspection unit is set up at the end of the production line to capture key dimensions of the welded body-in-white in real time and compare them with a standard digital model. When the deviation exceeds the limit, a calibration prompt is triggered.

[0015] The laser tracker establishes the global coordinate system by measuring at least three non-collinear reference points.

[0016] The displacement detector has a resolution of ≤0.05mm and continuously monitors the displacement deviation for 150 to 250 welding cycles.

[0017] The method for improving the precision of automotive body-in-white welding fixtures also includes: Establish an electronic file for the fixture, recording the operation history and wear data of the positioning and clamping components; The positioning and clamping components are maintained in a graded manner according to preset life indicators. The graded maintenance includes daily maintenance, periodic maintenance and preventive maintenance.

[0018] The method for improving the accuracy of automotive body-in-white welding fixtures of the present invention forms a thermal deformation adaptive compensation mechanism by setting an elastic compensation component with adjustable compression and setting a heat insulation layer on the surface of the fixture. This allows for real-time compensation of thermal deformation during the welding process, maintaining the long-term stability of the positioning reference and improving positioning accuracy. Attached Figure Description

[0019] Figure 1 This is a flowchart of the method for improving the precision of automotive body-in-white welding fixtures according to the present invention; Figure 2 This is a schematic diagram of the adaptive thermal deformation compensation system; Figure 3 This is a schematic diagram of the disc spring assembly; Figure 4 This is a schematic diagram of the working status of the laser tracker; Figure 5 This is a schematic diagram of the adjustable positioning block; The markings in the above figures are as follows: 1-base, 2-positioning component, 3-mounting seat, 4-elastic compensation component, 5-heat insulation layer, 6-quick-change module body, 7-temperature sensor, 8-compensation adjustment mechanism, 9-disc spring assembly, 10-laser tracker, 11-adjustable positioning block, 12-second drive motor, 13-linear guide rail. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more comprehensive description of the present invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the present invention. However, the present invention can be implemented in different forms and is not limited to the embodiments described in the text. Rather, these embodiments are provided to make the disclosure of the present invention more thorough and complete.

[0021] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," and similar expressions used in this document are for illustrative purposes only.

[0022] It should be noted that in the following embodiments, the terms "first" and "second" do not represent an absolute distinction in structure and / or function, nor do they represent the order of execution, but are merely for the convenience of description.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly associated with those skilled in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments and is not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] The technical concept of this invention includes: The body-in-white is the load-bearing base of the entire vehicle, and its geometric dimensional accuracy directly determines the assembly matching quality, structural strength, and driving performance of the entire vehicle. The body-in-white is usually formed by assembling hundreds of stamped sheet metal parts through multiple welding processes such as spot welding and arc welding. In the body-in-white welding process, the welding fixture undertakes the functions of precise positioning, reliable clamping, and deformation constraint of the stamped parts. It is a key process equipment to ensure the dimensional consistency of each sub-assembly and the body assembly and to control the amount of welding deformation. Its accuracy level and adaptability directly determine the final manufacturing quality of the body-in-white. Existing body-in-white welding production lines mostly adopt a regional independent fixture architecture. The fixtures for each sub-assembly, such as the front compartment, side panels, floor, and rear panel, establish independent positioning reference systems. When the sub-assemblies are assembled into the body assembly, cumulative deviations and reference misalignments are easily generated between multiple sets of references, directly leading to out-of-tolerance key feature dimensions of the body assembly. This not only increases the matching difficulty of subsequent final assembly processes but also easily causes quality problems such as vehicle sealing and ride comfort. Meanwhile, during welding operations, spot welding and arc welding stations release a large amount of concentrated heat instantaneously. Positioning elements such as locating pins and support blocks, which directly act on the surface of thin sheet metal, are subjected to alternating heat loads for extended periods, easily leading to uneven thermal expansion and thermal creep deformation. This is especially true for thin sheet metal parts such as side panels and door frames, where the dimensional accuracy of the positioning elements rapidly decreases after heating, further exacerbating the welding thermal deformation of sheet metal parts and causing the body contour to deviate from design requirements. Regarding accuracy control, the current industry standard for testing and calibrating welding fixtures generally uses offline static measurement methods. This only allows obtaining static accuracy data of the fixtures at room temperature when the production line is stopped, failing to recreate the thermal stress and dynamic load states under actual welding conditions. Dynamic errors such as positioning offsets and clamping loosening generated in real time during production are difficult to capture in a timely manner. Offline calibration results deviate significantly from actual production accuracy, failing to effectively support closed-loop control of process accuracy and making it difficult to detect errors in actual production. The technical solution of this invention is as follows: like Figures 1 to 5 As shown, this embodiment of the invention provides a method for improving the accuracy of automotive body-in-white welding fixtures, including: An elastic compensation component 4 is provided between the positioning component 2 of the fixture and the base 1. The positioning component 2 includes a positioning unit. A heat insulation layer 5 is formed on the surface of the fixture facing the welding heat source; Obtain the real-time temperature at positioning component 2; When the real-time temperature exceeds the preset threshold, the deformation state of the elastic compensation component 4 is changed by the compensation adjustment mechanism 8.

[0025] Specifically, such as Figure 1 As shown, this embodiment of the invention provides a method for improving the accuracy of automotive body-in-white welding fixtures. Through benchmark unification, adaptive compensation for thermal deformation, dynamic calibration, intelligent maintenance, and flexible quick-change technology, the accuracy of body-in-white welding fixtures can be significantly improved and stabilized over a long period of time.

[0026] During spot welding, the instantaneous temperature of the electrode can reach over 800℃. A large amount of heat is conducted through the workpiece to the positioning component 2 of the fixture, causing uneven thermal expansion and thermal creep of the positioning unit. Under long-term alternating heat load, the positioning accuracy will rapidly decrease, especially in thin-walled curved parts such as side door frames and pillars, where thermal deformation has a more significant impact on dimensional accuracy. In this embodiment of the invention, passive elastic compensation technology is adopted, and thermal insulation barriers are set up to achieve active temperature control through cooling. Through the synergistic effect of the elastic compensation component 4, the thermal insulation layer 5, the cooling channel, the temperature sensor, and the compensation adjustment mechanism 8, adaptive compensation for welding thermal deformation can be achieved.

[0027] In this embodiment of the invention, the elastic compensation component 4 is disposed between the positioning member 2 and the base 1, and is an actuating element used to counteract welding deformation. Figure 2 and Figure 3 As shown, the elastic compensation component 4 includes disc spring assemblies 9 and mounting bases 3. Multiple disc spring assemblies 9 are provided. One end of each disc spring assembly 9 is connected to the positioning member 2, and the other end is connected to the mounting base 3. The mounting base 3 is mounted on the base 1. The base 1 is provided with a guide and limiting structure to restrict the horizontal displacement of the disc spring assemblies 9, allowing them to undergo elastic deformation only in a direction perpendicular to the positioning surface of the positioning unit, thus preventing the elastic compensation from introducing additional horizontal positioning deviations.

[0028] During the fixture assembly stage, an initial pre-compression amount is pre-set for the disc spring assembly 9, ensuring that the positioning component 2 is in a stable elastic pre-tightened state during the static positioning stage. In this embodiment of the invention, when setting the elastic compensation component 4, a pre-compression amount and stiffness are set for the disc spring assembly 9. The pre-compression amount of the disc spring assembly 9 is any value greater than or equal to 1.2 mm and less than or equal to 1.8 mm, and the spring stiffness is any value greater than or equal to 500 N / mm and less than or equal to 600 N / mm. This parameter setting ensures sufficient elastic compensation stroke while maintaining support rigidity.

[0029] In a specific embodiment of the present invention, for positioning elements used in easily deformable areas such as side door frames and pillars, the pre-compression of the disc spring assembly 9 is set to 1.5 mm, and the spring stiffness of the disc spring assembly 9 is set to 550 N / mm.

[0030] During the welding of the body-in-white using the welding fixture, the passive compensation function of the elastic compensation component 4 is manifested in two stages: The first stage is the welding shrinkage stage. When the weld point cools and solidifies, the steel sheet of the body-in-white tends to shrink inward, applying a pulling force towards the inside of the steel sheet to the positioning component 2. At this time, the pre-compression of the disc spring assembly 9 is further compressed, generating a reverse elastic restoring force to counteract the welding shrinkage tension and prevent the positioning component 2 from shifting inward with the workpiece. The second stage is the thermal expansion stage. The high temperature of welding is conducted to the positioning unit through the workpiece, causing the positioning unit to have an outward thermal expansion displacement tendency. At this time, the disc spring assembly 9 releases part of the pre-compression to absorb the thermal expansion displacement of the positioning unit, preventing the positioning unit from being rigidly pushed and shifting. Through the above-mentioned bidirectional elastic compensation, welding stress and small thermal deformation can be passively offset without external power input, controlling the flatness error of the positioning surface within 0.04mm / m and maintaining the positional stability of the positioning reference.

[0031] In this embodiment of the invention, reducing the conduction of welding heat to the fixture body from the source is a key step in controlling thermal deformation. A heat insulation layer 5 is disposed on the surface of the fixture facing the welding electrode, and the heat insulation layer 5 is made of silicon nitride ceramic material. By forming the heat insulation layer 5 on the surface of the fixture facing the welding heat source, the heat transfer path is blocked by the low thermal conductivity material, thereby reducing the temperature rise rate and total temperature rise of the positioning unit.

[0032] Specifically, the heat insulation layer 5 is mainly set on the surface of the fixture facing the welding electrode, which is the area where the welding heat input is most concentrated, covering all heated surfaces of the fixture within a 50mm radius around the spot welding electrode. The heat insulation layer 5 is made of silicon nitride ceramic material, which has low thermal conductivity and can effectively block the high temperature of spot welding from being conducted into the fixture. If the heat insulation layer 5 is set on the surface of the positioning unit, it can significantly reduce the temperature rise rate of the positioning unit. At the same time, the disc spring assembly 9 at the bottom of the positioning component 2 is in a pre-compressed state, which can passively offset the welding shrinkage stress and minor thermal deformation of the thin plate during welding, achieving basic elastic compensation.

[0033] The method for improving the accuracy of automotive body-in-white welding fixtures according to embodiments of the present invention further includes introducing a cooling medium into a cooling channel formed inside the base 1. The base 1 has a cooling channel inside. The introduced cooling medium includes supplying a coolant with a temperature ≤32°C to the cooling channel, and the flow rate of the coolant is set to any value greater than or equal to 8L / min and less than or equal to 12L / min.

[0034] Based on passive heat insulation, the heat conducted to the fixture body is actively removed by introducing a cooling medium, which can reduce the heat transferred to the positioning unit and help to stabilize the working temperature of the positioning unit within the set range, thus suppressing the generation of long-term thermal creep deformation.

[0035] Preferably, the cooling medium flow rate is set to 10L / min, and the cooling medium temperature is set to ≤30℃. This parameter setting ensures cooling efficiency while avoiding vibration and noise caused by excessive cooling water flow rate. The cooling system's start / stop is linked to the robot welding program: when the welding program starts, the cooling system starts simultaneously, enabling the cooling medium to circulate within the fixture's cooling channels and continuously remove heat conducted during welding; after the welding program ends, the cooling system runs for a set delay until the fixture temperature drops to room temperature before stopping, preventing heat accumulation.

[0036] In this embodiment of the invention, the real-time temperature of the positioning unit is obtained by a temperature sensor installed at the positioning unit. The temperature sensor has a measurement range of -20℃ to 300℃ and a temperature resolution of ≤0.1℃.

[0037] Although passive compensation and active temperature control can significantly reduce the magnitude of thermal deformation, fluctuations in welding heat input and changes in ambient temperature can still lead to residual thermal deviation. Therefore, in this embodiment of the invention, a temperature sensor is set to collect the temperature data of the positioning unit in real time, and in conjunction with the compensation and adjustment mechanism 8, a closed-loop active adjustment of thermal deformation is achieved, further improving the positioning accuracy.

[0038] Specifically, the temperature sensor is installed at the heated location of the positioning unit, specifically inside the positioning unit near the workpiece contact surface, to ensure that the collected temperature data accurately reflects the actual heating state of the positioning element. In this embodiment of the invention, the temperature sensor has a measurement range of -20℃ to 300℃ and a temperature resolution ≤0.1℃.

[0039] Preferably, the temperature sensor has a temperature resolution of 0.1℃. Using a platinum resistance temperature sensor with a resolution of 0.1℃ provides high temperature measurement accuracy and fast response, enabling the capture of instantaneous temperature changes during the welding process. The temperature signal collected by the temperature sensor is transmitted in real-time to the fixture's control system via cable, providing real-time temperature data for compensation and adjustment.

[0040] In this embodiment of the invention, the compensation adjustment mechanism 8 is drivenly connected to the elastic compensation component 4, and is used to dynamically adjust the compression amount of the elastic compensation component 4 according to the temperature signal. The preset threshold is set to any value greater than or equal to 55°C and less than or equal to 62°C. When the real-time temperature at the positioning unit exceeds the preset threshold, the compensation adjustment mechanism 8 increases the compression amount of the elastic compensation component 4, and the adjustment amplitude ranges from greater than or equal to 0.3 mm to less than or equal to 0.5 mm.

[0041] In this embodiment of the invention, the compensation adjustment mechanism 8 includes a first drive motor and a first transmission mechanism connected to the first drive motor. The first drive motor is connected to the mounting base 3 through the first transmission mechanism. The first transmission mechanism converts the rotational motion of the first drive motor into the linear motion of the mounting base 3. The mounting base 3 is movably mounted on the base 1, thereby pushing the disc spring assembly 9 to change the pre-compression amount. The first transmission mechanism is a lead screw transmission mechanism, which can convert rotational motion into linear displacement. The first drive motor is fixedly mounted on the base 1 of the fixture, and the first drive motor is electrically connected to the control system of the fixture and is controlled by the control system. The first drive motor is a servo motor with a built-in high-precision encoder, and the displacement control accuracy can reach 0.01mm, which can effectively ensure the accuracy of compensation adjustment.

[0042] The adjustment process of the compensation adjustment mechanism 8 is as follows: The control system presets a temperature threshold, which ranges from 55℃ to 62℃. When the real-time temperature of the positioning unit collected by the temperature sensor does not exceed the preset threshold, the compensation adjustment mechanism 8 maintains its current position, and the elastic compensation component 4 performs passive compensation. When the real-time temperature of the positioning unit collected by the temperature sensor exceeds the preset threshold, the control system outputs an adjustment command to the compensation adjustment mechanism 8, driving the elastic compensation component 4 to increase the compression. The first drive motor rotates in the forward direction, driving the mounting base 3 to move linearly through the first transmission mechanism, pushing the disc spring group 9 to increase the compression. The adjustment amplitude of the compression ranges from 0.3mm to 0.5mm, which matches the thermal expansion of the positioning unit in this temperature range, accurately offsetting the positioning displacement caused by thermal expansion. When welding is completed and the fixture temperature gradually drops, the compensation adjustment mechanism 8 adjusts in the reverse direction according to the temperature drop. The first drive motor rotates in the reverse direction, driving the mounting base 3 to move linearly through the first transmission mechanism, releasing the disc spring group 9, thereby gradually reducing the compression of the elastic compensation component 4, ensuring that the positioning reference remains stable throughout the temperature change process.

[0043] Preferably, the preset temperature threshold is set to 58℃, and the compression adjustment amplitude is set to 0.4mm. When the temperature of the positioning element exceeds 58℃, the servo motor automatically drives the disc spring to increase the compression by 0.4mm, dynamically compensating for thermal deformation and ensuring that the thermal deformation error is ≤0.2mm.

[0044] In this embodiment of the invention, through the combined action of temperature control of the heat insulation layer 5, passive elastic compensation, and active adjustment of the compensation adjustment mechanism 8, the thermal deformation error of the fixture can be controlled within 0.2mm, which is far superior to the thermal deformation level of traditional fixtures without elastic compensation function. This can effectively reduce the decay rate of positioning accuracy and ensure positioning accuracy.

[0045] The method for improving the accuracy of automotive body-in-white welding fixtures according to embodiments of the present invention further includes: Based on the overall vehicle design benchmark of the body-in-white, benchmark holes and benchmark surfaces are set on the base 1, and the position of the positioning component 2 is calibrated so that the fixture positioning benchmarks of the front compartment, side panels, floor and roof sub-assemblies are interconnected.

[0046] The key to controlling the welding precision of the body-in-white lies in the consistency of the positioning reference. If the fixtures of each sub-assembly use an independent reference system, reference misalignment and cumulative errors will inevitably occur during the splicing process, ultimately leading to out-of-tolerance dimensions of the body assembly. In this embodiment of the invention, a unified reference system is constructed based on the overall vehicle design reference of the body-in-white, which can eliminate the causes of reference deviation from the design stage.

[0047] Specifically, based on the overall vehicle GD&T dimension chain design requirements, two main reference holes and one main reference surface on the side outer panel are selected as unified positioning references. The positioning component 2 is arranged in strict accordance with the 3-2-1 positioning principle. For the splicing parts of the side panel and front panel, and the side panel and floor, two sets of elastic over-positioning compensation structures are added to absorb the assembly gap and welding stress concentration of the thick plate without destroying the main reference constraint relationship.

[0048] To ensure the accuracy of the reference, this embodiment of the invention specifies clear manufacturing and assembly accuracy requirements for the positioning component 2, the clamping component, and the base 1. The positioning unit of the positioning component 2 specifically includes two types of components: positioning pins and positioning blocks. The positioning pins are made of 20CrMnTi alloy structural steel, which is carburized, quenched, and cryogenically treated to achieve an accuracy grade of IT5. The clearance between the positioning pins and the workpiece reference hole is controlled within 0.01mm to ensure positioning accuracy and wear resistance. The positioning blocks are made of Cr12MoV mold steel, which, after quenching and cryogenic treatment, achieves a surface hardness of HRC62~65. The machining shape and position accuracy is controlled within ±0.01mm, and the surface roughness Ra≤0.8μm. The positioning working surface is coated with a 10~15μm thick hard alloy coating to further improve wear resistance and impact resistance.

[0049] The clamping components on the fixture are cylinder-driven clamping arms. The clamping force is calculated and determined according to the formula F=K•S•σ, where F is the single-point clamping force, K is the safety factor, S is the clamping contact area, and σ is the ultimate tensile stress of the workpiece material. In this embodiment of the invention, the safety factor K ranges from 2.5 to 3.0. For low-alloy high-strength steel workpieces, the single-point clamping force is set to 30~50kN, which can effectively resist the thermal deformation stress during welding and prevent workpiece movement. The clamping air circuit is equipped with a self-locking valve to ensure that the clamping force fluctuation is controlled within ±3%, avoiding clamping failure caused by air source pressure fluctuations. A wear-resistant polyurethane buffer pad is added to the pressure head part where the clamping arm contacts the workpiece, which ensures clamping friction and avoids damaging the workpiece surface coating. The response time of the clamping mechanism is controlled within 0.8s to match the production cycle requirements of robotic welding.

[0050] Base 1, serving as the installation reference for the entire fixture set, is integrally cast from cast steel and undergoes two annealing and aging treatments to eliminate casting and machining stresses, preventing reference drift during long-term use. The flatness of the reference mounting surface of base 1 is controlled within 0.05mm / m. 2 Within this range, the overall installation levelness is ≤0.035mm / m; the positional accuracy of the reference holes at the four corners of base 1 is controlled within ±0.01mm, and the surface hardness of the reference surface after heat treatment is ≥HRC58, possessing sufficient load-bearing rigidity and wear resistance. The fixtures of each sub-assembly, including the front cabin, side panels, floor, and roof, are all installed based on this unified reference system, ensuring that the positioning references of the fixtures of each sub-assembly are interconnected, thus eliminating the cumulative errors caused by reference conversion at the source.

[0051] In this embodiment of the invention, dynamic monitoring is conducted under simulated actual welding conditions. The spot welding current is set to 9.5 kA, welding time to 360 ms, and the arc welding current to 90 A, welding speed to 250 mm / min, completely replicating the heat input and load conditions in production. Displacement deviation is continuously monitored for 150 to 250 welding cycles, and the maximum deviation and fluctuation range are statistically analyzed. Preferably, continuous monitoring for 200 welding cycles can be set to fully verify the accuracy and stability of the fixture under continuous heat load. This embodiment of the invention requires that the displacement deviation value after 200 consecutive cycles be ≤0.2 mm. If this threshold is exceeded, an early warning is triggered, prompting the operator to perform calibration and maintenance.

[0052] In this embodiment of the invention, a vision inspection unit, specifically a binocular vision inspection system, is configured at the end of the production line. Facing the side panel assembly station after welding, it captures key dimensional features of the workpiece in real time, including doorway dimensions, hole coordinates, and contour. The inspection system automatically compares the collected point cloud data with a standard digital model, calculates the actual deviation of each feature, and automatically triggers a calibration prompt when the deviation exceeds the allowable range of ±0.2mm, pushing the notification to the production line control system. Furthermore, a pressure sensor is installed at the locating pin. By detecting the pressure threshold when the locating pin is inserted into the reference hole, it determines whether the workpiece is properly assembled, preventing dimensional deviations caused by incorrect or missing parts.

[0053] The method for improving the accuracy of automotive body-in-white welding fixtures according to embodiments of the present invention further includes: A global coordinate system for the body-in-white was established using a laser tracker 10, and the fixture was statically calibrated offline. Multiple feature points were measured to evaluate the positioning accuracy. Displacement detectors are installed on positioning component 2 and / or clamping component to continuously monitor displacement deviation under simulated welding conditions; A visual inspection unit is set up at the end of the production line to capture key dimensions of the welded body-in-white in real time and compare them with a standard digital model. When the deviation exceeds the limit, a calibration prompt is triggered.

[0054] Traditional fixture accuracy control relies solely on offline static measurements, which cannot reflect the thermal stress and dynamic deformation states under actual welding conditions. Calibration results deviate significantly from actual production, making it difficult to support closed-loop accuracy control. This invention constructs a dual-dimensional detection and calibration system combining static offline calibration and dynamic online monitoring. This system ensures both the static accuracy of the reference and covers dynamic deviations during production, achieving full-state control of fixture accuracy. Static offline calibration is the fundamental guarantee of fixture accuracy, used to establish a reference coordinate system and calibrate the initial accuracy of positioning elements. In this embodiment, a laser tracker 10 is used as the metrology device for static calibration, establishing a global coordinate system for the body-in-white and performing offline calibration of the fixture.

[0055] In embodiments of the present invention, such as Figure 4 As shown, before calibration, the laser tracker 10 is fixed on the measurement platform, and the device's attitude is adjusted to ensure no obstruction between it and all measurement feature points. The body-in-white is mounted on a fixture, which positions and clamps the body-in-white, ensuring it is in a free and stress-free state. During calibration, at least three non-collinear reference points are first selected on the body-in-white. The laser tracker 10 is used to measure the three-dimensional coordinates of each reference point sequentially. The origin, coordinate axis directions, and reference plane of the coordinate system are determined through coordinate fitting calculations, establishing a unified three-dimensional coordinate system aligned with the theoretical coordinate system of the body design model.

[0056] After establishing the coordinate system, 30 key feature points on the fixture are selected for precision measurement. These 30 key feature points cover the diagonal endpoints of the doorway, the column reference point, the beam reference point, the center point of the positioning pin, and the working surface of the positioning block, thus covering the main positioning area of ​​the fixture. Each feature point is measured eight times repeatedly. After removing outliers, the mean of the valid data is selected as the measured coordinate value of that point according to the 6σ statistical principle. The measured coordinates are compared with the theoretical coordinates of the digital model to calculate the deviation. When the deviation exceeds the allowable range, the position of the positioning element is corrected by adjusting the mounting shims of the positioning element until the deviation of all feature points meets the accuracy requirements. After calibration, the flatness of the positioning reference surface must be ensured to be ≤0.03mm / m. 2 The positioning accuracy of the locating pin is ≤ ±0.02mm.

[0057] In this embodiment of the invention, static calibration can only reflect the fixture accuracy under normal temperature and no load conditions. To understand the dynamic accuracy under actual welding conditions, displacement detectors and visual inspection units are deployed to achieve real-time dynamic monitoring during the welding process. The displacement detectors are installed at key positioning points of the positioning component 2 and the clamping component to collect real-time displacement deviations of the positioning elements during the welding process.

[0058] In this embodiment of the invention, the displacement detector uses a high-precision displacement sensor with a resolution of ≤0.05mm. The displacement detector continuously monitors the displacement deviation for 150 to 250 welding cycles.

[0059] Preferably, the displacement detector can be an eddy current displacement sensor with a resolution of 0.05 mm, which can continuously monitor the displacement deviation of 200 welding cycles to achieve non-contact measurement, which is wear-free and has a fast response.

[0060] The method for improving the accuracy of automotive body-in-white welding fixtures according to embodiments of the present invention further includes: Establish an electronic file for the fixture, recording the operation history and wear data of positioning component 2 and clamping component; The positioning component 2 and the clamping component are maintained in a graded manner according to the preset life index. The graded maintenance includes daily maintenance, periodic maintenance and preventive maintenance.

[0061] Therefore, in this embodiment of the invention, by establishing a data-driven, full-lifecycle intelligent maintenance mechanism, and through electronic records and hierarchical maintenance strategies, long-term stable monitoring of fixture accuracy can be achieved.

[0062] Specifically, a dedicated electronic file is created for each fixture, comprehensively recording data throughout its entire lifecycle, from design and manufacturing to use and maintenance. The electronic file includes: design parameters, manufacturing precision, calibration data, maintenance records, number of insertions and removals of positioning components, and wear data, enabling full lifecycle traceability. It also includes maintenance records such as calibration records, component replacement records, and fault repair records.

[0063] In this embodiment of the invention, a three-level hierarchical maintenance mechanism is implemented, covering daily maintenance, periodic maintenance and preventive maintenance. Different levels correspond to different execution cycles and maintenance contents, taking into account both efficiency and accuracy.

[0064] Routine maintenance is performed every shift by the production line operator. Specific tasks include: cleaning welding slag, dust, and other debris from the surface of positioning component 2 to ensure the positioning surface is clean and free of foreign objects; checking the working pressure of the cylinder of the clamping component. The normal working pressure is 0.8MPa, and the allowable pressure fluctuation range is ±0.2MPa. If the pressure exceeds the range, troubleshoot the air circuit fault in time; and confirming the status of the positioning pin and the buffer pad.

[0065] Regular maintenance is performed weekly by a technician. The specific tasks include: the technician uses a portable coordinate measuring machine to randomly check the positioning accuracy of the fixture, and when the deviation exceeds the allowable range, compensation adjustment is made by using 0.2mm thick shims.

[0066] Preventative maintenance is performed monthly by equipment engineers based on data from electronic records. This involves the mandatory replacement of positioning components that have reached their lifespan threshold to prevent accuracy failure due to excessive wear. The mandatory replacement thresholds are set as follows: 15,000 to 25,000 insertion / removal cycles for the positioning pin, or 0.15mm to 0.25mm of wear on the positioning block. Preferably, mandatory replacement is required when the positioning pin has reached 20,000 insertion / removal cycles or the positioning block has a wear ≥0.2mm. After replacement, accuracy recalibration is performed, and the replacement and calibration data are entered into the electronic record. Simultaneously, spare parts for critical and easily damaged components such as positioning pins, positioning blocks, and disc springs are stocked to ensure efficient replacement.

[0067] In embodiments of the present invention, such as Figure 5 As shown, the positioning unit is an adjustable positioning block 11. The positioning component 2 also includes a quick-change module body 6 and a position adjustment mechanism disposed on the quick-change module body 6. The position adjustment mechanism is connected to the adjustable positioning block 11 and is used to adjust the position of the adjustable positioning block 11.

[0068] A linear guide rail 13 is installed on the quick-change module body 6. The linear guide rail 13 guides the adjustable positioning block 11, and the linear guide rail 13 and the adjustable positioning block 11 are slidably connected. The position adjustment mechanism mainly includes a second drive motor 12 and a second transmission mechanism connected to the second drive motor 12. The second drive motor 12 is connected to the adjustable positioning block 11 through the second transmission mechanism. The second transmission mechanism converts the rotational motion of the second drive motor 12 into the linear motion of the adjustable positioning block 11. The adjustable positioning block 11 is movably mounted on the linear guide rail 13, thereby pushing the adjustable positioning block 11 to move linearly and adjust its position. The second transmission mechanism is a lead screw transmission mechanism, which can convert rotational motion into linear displacement. The second drive motor 12 is fixedly mounted on the quick-change module body 6. The second drive motor 12 is electrically connected to the control system of the fixture and is controlled by the control system. The second drive motor 12 is a servo motor with a built-in encoder to ensure the accuracy of the positioning block position adjustment.

[0069] The position adjustment mechanism drives the adjustable positioning block 11 to move along a set direction, adjusting the positioning position to adapt to the size differences of different vehicle models and improving the fixture's vehicle model adaptability. The second drive motor 12 serves as the power source and is connected to the lead screw of the second transmission mechanism via a coupling; the slider on the lead screw is connected to the adjustable positioning block 11; the linear guide rail 13 is set parallel to the lead screw, providing guidance and support for the movement of the adjustable positioning block 11. The linear guide rail 13 restricts the positioning block to move only along a preset direction, eliminating runout errors during adjustment and ensuring the straightness of the positioning reference.

[0070] In this embodiment of the invention, the position adjustment mechanism drives the adjustable positioning block 11 to move 50mm~100mm, which can cover the differences in positioning dimensions of side pillars and door frames of different models on the same platform. The system pre-stores the positioning coordinate parameters of each model. When changing models, the corresponding parameters can be called with one click to automatically adjust the positioning position of the adjustable positioning block 11. There is no need for manual disassembly or replacement of the positioning block, which greatly shortens the model changeover time and improves the flexibility of the production line.

[0071] After the adjustable positioning block 11 reaches the target position, the second drive motor 12 enters the locked state, forming a stable positioning support in conjunction with the rigid structure of the module body. The quick-change module body 6 adopts a composite structure of high-strength aluminum alloy combined with cast steel reinforcing ribs, balancing lightweight and rigidity. The high-rigidity linear guide rail 13 and the quick-change module body 6 can withstand the impact of external forces during workpiece clamping and welding, preventing the adjustable positioning block 11 from shifting; the repeatability of the position adjustment mechanism ensures the positioning consistency of multiple batches and multiple vehicle models.

[0072] The present invention has been described above with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other situations without modification, are all within the protection scope of the present invention.

Claims

1. A method for improving the accuracy of automotive body-in-white welding fixtures, characterized in that, include: An elastic compensation component is installed between the positioning component of the fixture and the base; A heat insulation layer is formed on the surface of the fixture facing the welding heat source; Obtain the real-time temperature at the positioning component; When the real-time temperature exceeds a preset threshold, the deformation state of the elastic compensation component is changed by the compensation adjustment mechanism.

2. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 1, characterized in that, The elastic compensation component includes a disc spring assembly. When setting the elastic compensation component, the disc spring assembly is given a pre-compression amount and a stiffness. The pre-compression amount is any value greater than or equal to 1.2 mm and less than or equal to 1.8 mm, and the spring stiffness is any value greater than or equal to 500 N / mm and less than or equal to 600 N / mm.

3. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 1, characterized in that, The heat insulation layer is disposed on the surface of the fixture facing the welding electrode, and the heat insulation layer is made of silicon nitride ceramic material.

4. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 1, characterized in that, It also includes introducing a cooling medium into the cooling channels formed inside the base.

5. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 4, characterized in that, The introduction of the cooling medium includes supplying a coolant with a temperature ≤32°C to the cooling channel, wherein the flow rate of the coolant is set to any value greater than or equal to 8L / min and less than or equal to 12L / min.

6. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 1, characterized in that, The real-time temperature of the positioning component is obtained by a temperature sensor installed at the positioning component. The temperature sensor has a measurement range of -20℃ to 300℃ and a resolution of ≤0.1℃.

7. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 1, characterized in that, The preset threshold is set to any value greater than or equal to 55°C and less than or equal to 62°C; when the real-time temperature at the positioning component exceeds the preset threshold, the compensation adjustment mechanism increases the compression of the elastic compensation component, and the adjustment amplitude ranges from greater than or equal to 0.3mm to less than or equal to 0.5mm.

8. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 1, characterized in that, Also includes: Based on the overall vehicle design benchmark of the body-in-white, reference holes and reference surfaces are set on the base, and the position of the positioning component is calibrated.

9. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 1, characterized in that, Also includes: A global coordinate system for the body-in-white was established using a laser tracker, and the fixture was statically calibrated offline. Multiple feature points were measured to assess the positioning accuracy. A displacement detector is installed on the positioning member and / or clamping member to continuously monitor the displacement deviation under simulated welding conditions; A visual inspection unit is set up at the end of the production line to capture key dimensions of the welded body-in-white in real time and compare them with a standard digital model. When the deviation exceeds the limit, a calibration prompt is triggered.

10. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 9, characterized in that, The laser tracker establishes the global coordinate system by measuring at least three non-collinear reference points.

11. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 9, characterized in that, The displacement detector has a resolution of ≤0.05mm and continuously monitors the displacement deviation for 150 to 250 welding cycles.

12. The method for improving the accuracy of automotive body-in-white welding fixtures according to claim 1, characterized in that, Also includes: Establish an electronic file for the fixture, recording the operation history and wear data of the positioning and clamping components; The positioning and clamping components are maintained in a graded manner according to preset life indicators. The graded maintenance includes daily maintenance, periodic maintenance and preventive maintenance.

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