A flexible repair method for automobile leaf spring based on reversible thermoplastic mold

Abstract

The present application belongs to the field of automobile remanufacturing and advanced maintenance process, and particularly relates to a flexible repairing method for automobile leaf plate based on reversible thermoplastic mold, which comprises the following steps: step S100, digitizing reference surface: obtaining original surface data of automobile leaf plate through 3D scanning to generate a digital reference model; step S200, rapid generation and circulation of customized mold: material selection and pretreatment, flexible heat treatment, surface negative pressure / pressure covering plastic forming, rigidification cooling and shaping, mold resetting; step S300, clamping and in-mold precise shaping repair: using a pneumatic hammer to perform impact repair under the precise constraint of the mold; step S400, post-processing and quality verification: disassembling the mold and performing quality inspection on the repaired leaf plate; the present application realizes rapid customization and unlimited resetting of the mold by using the reversible thermoplasticity of PCL, and realizes efficient, high-precision and low-cost repair of automobile leaf plate sheet metal damage.

Description

Technical Field

[0001] This invention belongs to the field of automotive remanufacturing and advanced repair technology, specifically a flexible repair method for automotive fenders based on reversible thermoplastic molds. Background Technology

[0002] Currently, there are two main technical approaches to automotive fender sheet metal repair: purely manual repair and repair assisted by specialized rigid molds. Among them, I. Purely manual restoration relies entirely on the technician's experience and feel, using tools such as hammers, shims, and contour restoration machines to restore curved surfaces through observation, touch, and tapping. Its main drawbacks are as follows: (1) High uncertainty in quality: The quality of repair is strongly correlated with the skill of the technician. Different technicians may have different results for the same damage, and defects such as "orange peel texture", "hard spots" and "secondary stretching" are likely to occur.

[0003] (2) Inefficient: The repair time for a single part is as long as 30-60 minutes or even longer, which cannot meet the production rhythm of large-scale remanufacturing.

[0004] (3) High labor and training costs: Senior sheet metal technicians are scarce and the training period can take several years.

[0005] II. Specialized rigid mold-assisted repair involves creating specialized metal (such as steel or aluminum alloy) molds for specific parts of specific car models, providing a precise support reference for the repair. Its main drawbacks are as follows: (1) Poor economic efficiency: The cost of a single mold can be as high as tens of thousands to hundreds of thousands of RMB.

[0006] (2) Extremely poor flexibility: One mold corresponds to only one part of a single car model and cannot be modified. To cope with multiple car models, a huge mold library needs to be established, which occupies a huge amount of capital and storage space.

[0007] (3) Slow response speed: The mold design, processing and debugging cycle takes several weeks, making it impossible to respond to urgent or small-batch repair orders.

[0008] (4) Inconvenience caused by physical properties: The mold is heavy and the operation is labor-intensive. Summary of the Invention

[0009] The purpose of this invention is to address the aforementioned shortcomings by providing a flexible repair method for automotive fenders based on reversible thermoplastic molds. By utilizing the reversible thermoplasticity of PCL, the method enables rapid customization and unlimited resetting of the mold, thereby reducing mold costs, improving repair efficiency, and achieving efficient, high-precision, and low-cost repair of automotive fender sheet metal damage.

[0010] To achieve the above objectives, a flexible repair method for automotive fenders based on reversible thermoplastic molds is designed, including the following steps: Step S100, Digitization of the reference surface: Obtain the original surface data of the car fender through 3D scanning and generate a digital reference model; Step S200: Rapid generation and recycling of customized molds; Step S300, clamping and in-mold precision shaping and repair: use a pneumatic hammer to perform impact repair under the precise constraint of the mold; Step S400, Post-processing and quality verification: Disassemble the mold and conduct a quality inspection on the repaired fender.

[0011] Furthermore, in step S100, a non-contact 3D scanner is used to perform a high-precision scan on the intact target leaf plate reference component to obtain 3D point cloud data of its inner and outer surfaces, and to reconstruct a high-fidelity digital model.

[0012] Further, step S200 includes the following sub-steps: S210, Material Selection and Pretreatment: Based on the area and curvature complexity of the leaf to be repaired, select PCL sheets of appropriate thickness and size, and clean the surface of the PCL sheets. S220, Flexible Heat Treatment: The PCL sheet is completely immersed in a hot water bath with constant temperature control at 70℃-80℃ and heated continuously for 3-10 minutes to melt the crystalline areas inside the PCL. S230, curved surface negative pressure / compression molding, completes the production of upper and lower molds; S240, rigid cooling and shaping: The mold that has been shaped is forced to cool, so that the movement of the molecular chain segments of the PCL material is frozen, recrystallized, and quickly restored to a hard solid. At this time, the mold surface is the precise negative shape of the reference part surface. S250, Mold Reset: After repairing all the leaves of the current model, put the upper and lower molds back into the hot water bath to perform step S220, so that the material softens again and can be easily flattened or kneaded into the initial shape, preparing for the next production of a new mold.

[0013] Furthermore, S230 includes the following steps: Upper mold making: The softened PCL sheet is quickly covered on the outer surface of the reference part. Uniform pressure is applied manually or using a flexible pressure bladder to ensure that the material fits tightly with every curved feature of the reference part without leaving any gaps. Lower mold making: Using the same method as the upper mold making, the lower mold is made on the inner surface of the reference part.

[0014] Furthermore, in S240, when the mold that has been shaped is forcibly cooled, air convection cooling at a constant room temperature of 20-25°C is used for 5-10 minutes or auxiliary air cooling for 3-8 minutes; and after recrystallization, the hardness of the solid reaches Shore D50-60.

[0015] Further, step S300 includes the following sub-steps: S310, Magnetic Assisted Positioning and Clamping: Place the damaged blade to be repaired on the worktable; first place the lower mold on the inside, then cover the outside with the upper mold. Relying on the magnetic attraction force generated by the neodymium iron boron strong magnets embedded in the edges or non-working areas of the upper and lower molds, the upper and lower molds are automatically and accurately aligned, and the blade is firmly clamped in the cavity to prevent relative displacement during the impact process. S320, In-Mold High-Frequency Micro-Impact Forming: The operator uses a pneumatic ball-head hammer or flat-head hammer to perform high-frequency, low-amplitude impacts on the damaged area on the outer surface of the upper mold; at the same time, the inner surface of the lower mold provides full-area, conformal, and rigid support for the deformed area; through this in-mold impact method, it is ensured that the extension and springback of the metal sheet are strictly limited within the original design surface range, thereby achieving precise restoration of damage and avoiding over-repair or the generation of new defects.

[0016] Furthermore, in S320, the outer surface of the upper mold is a concave surface with the same curvature as the outer surface of the fender, and the inner surface of the lower mold is a convex surface with the same curvature as the inner surface of the fender.

[0017] Furthermore, in step S400, after disassembling the mold, the repaired fender is inspected using a 3D scanning device or an optical comparator and compared with the digital reference model obtained in S100 to verify the repair accuracy.

[0018] Compared with the prior art, the present invention has the following advantages: (1) Revolutionary reduction in mold cost: Through steps S200 and S250, this invention transforms the mold from a "fixed asset" into a "low-value, easily consumable temporary tooling". The cost of a set of PCL materials is only one-thousandth or even one-ten-thousandth of that of traditional metal molds. Moreover, through unlimited resetting, it achieves "one set of materials, applicable to all models", and the mold inventory cost is theoretically reduced by 100%.

[0019] (2) Step-by-step improvement in repair efficiency: The entire mold making cycle (S200) of this invention can be controlled within 20 minutes, and the repair operation (S300) becomes simple and fast due to the mold guidance. The total repair time of a single part can be shortened by more than 50% compared with pure manual repair.

[0020] (3) Standardization and leapfrog improvement of repair quality: The present invention uses the digital benchmark of S100 and the precise replication of S230, so the mold itself is the "standard"; the "in-mold impact" process of S320 eliminates quality fluctuations, enabling junior technicians to achieve the repair effect of senior technicians, and significantly improving the product qualification rate.

[0021] (4) Technological integration and creativity: The creativity of this invention is also reflected in the application of the known properties of PCL material to solve specific industrial problems in automotive sheet metal repair through a carefully designed and interconnected process system (S100-S400). This is not a simple material replacement, but a system-level process innovation that produces a synergistic effect of "1+1>>2", solving the long-standing bottleneck of flexible production in the industry and is worth promoting and applying. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the upper mold used to create the air hammer impact zone (convex surface) of the present invention; Figure 2 This is a schematic diagram of the structure of the leaf support area (concave surface) made by the lower mold of the present invention; Figure 3 This is a schematic diagram of the structure of the pneumatic palm hammer that can be used in this invention; Figure 4 This is a schematic diagram of the process flow for steps S100 and S200 of the present invention. Figure 5 This is a schematic diagram of the process flow for steps S300 and S400 of the present invention; Figure 6 This is a schematic diagram of the decision-making process after step S400 of the present invention regarding whether all fenders in this batch have been repaired and whether to switch to a new model. Detailed Implementation

[0023] This invention belongs to the field of automotive remanufacturing and advanced repair processes. Specifically, it relates to a process method that utilizes the physical properties of reversible thermoplastic polymer materials (especially polycaprolactone, PCL) to achieve efficient, high-precision, and low-cost repair of automotive fender sheet metal damage through rapidly customizable and infinitely reconfigurable molds.

[0024] Polycaprolactone (PCL) is a biodegradable synthetic polyester with an extremely low glass transition temperature (approximately -60°C) and a melting point of only around 60°C. This characteristic allows it to soften in hot water at 60-70°C and harden rapidly at room temperature. This material is commonly used in handicrafts, medical models, and low-melting-point 3D printing filaments.

[0025] Existing technologies treat the material properties of PCL and the demanding industrial sheet metal repair scenarios as two isolated technical fields. The technical problem this invention aims to solve is: how to creatively apply the low-cost, reversible shaping characteristics of PCL to the specific industrial scenario of automotive fender repair, and to design a complete, closed-loop process to systematically resolve the fundamental contradictions in cost, efficiency, flexibility, and quality consistency inherent in traditional repair methods.

[0026] The primary objective of this invention is to provide a method for repairing automotive fenders, which enables "zero inventory cost" and "instant response" of molds. Another objective is to transform sheet metal repair from a "craft" into a standardized and replicable "industrial process" through this method, significantly reducing reliance on operator skills and greatly improving repair efficiency and quality consistency.

[0027] The core of this invention lies in constructing a closed-loop process flow that includes "data acquisition -> instant mold generation -> in-mold repair -> mold reset".

[0028] As attached Figure 1 To be continued Figure 6 As shown, this invention provides a flexible repair method for automotive fenders based on reversible thermoplastic molds, comprising the following steps: Step S100: Digitize the reference surface.

[0029] A non-contact 3D scanner is used to perform high-precision scanning of the intact target fender reference component, acquiring 3D point cloud data of its inner and outer surfaces, and reconstructing a high-fidelity digital model. This step ensures the accuracy of the repair target and is the source of subsequent mold precision.

[0030] Step S200: Rapid generation and recycling of customized molds.

[0031] This step is the core of achieving "flexibility" and "low cost," and its sub-steps are as follows: S210, Material Selection and Pretreatment: Based on the area and curvature complexity of the leaf to be repaired, select a PCL sheet of appropriate thickness (5-15mm recommended) and size. The sheet surface can be cleaned beforehand to ensure no impurities affect bonding accuracy.

[0032] S220, Flexible Heat Treatment (Phase Change Activation): The PCL sheet is completely immersed in a hot water bath at a constant temperature of 70℃-80℃ and heated continuously for 3-10 minutes. At this temperature, the crystalline regions inside the PCL melt, and the material undergoes a glass transition, macroscopically transforming from a hard solid to a soft, transparent "playdough" state with extremely high plasticity and adhesion.

[0033] S230, curved surface negative pressure / compression molding: Upper mold making: The softened PCL sheet is quickly covered onto the outer surface of the reference part. Uniform pressure is applied manually or using a flexible pressure bladder to ensure that the material fits tightly against every curved feature of the reference part (such as wheel arches, edges, and waistlines) without gaps. In this state, the joints of multiple small PCL sheets can be easily pinched together to form a single unit.

[0034] Lower mold making: Using the same method as the upper mold making, the lower mold is made on the inner surface of the reference part.

[0035] S240: Rigid Cooling and Shaping (Phase Change Completed): Forced cooling of the molded part. This can be achieved using constant room temperature (20-25℃) air convection cooling (5-10 minutes) or auxiliary air cooling (3-8 minutes). The molecular chain movement of the PCL material is frozen, recrystallized, and rapidly restored to a hard solid state with a Shore D50-60 hardness (close to hard rubber or nylon), sufficient to withstand subsequent impact forces. At this point, the mold surface is the precise negative shape of the reference part's curved surface.

[0036] S250: Mold Reset (Recycling Interface): After repairing all the leaves of the current model, the upper and lower molds are returned to the hot water bath to perform step S220. The material softens again and can be easily flattened or kneaded back into its initial shape, achieving a physical "data erasure" and preparing it for the next mold making. This step enables the unlimited recycling of mold material.

[0037] Step S300: Clamping and in-mold precision shaping and repair.

[0038] S310: Magnetic Assisted Positioning and Clamping: Place the damaged fender to be repaired on the worktable. First, place the lower mold on the inside, then cover it with the upper mold on the outside. Relying on the magnetic attraction generated by the neodymium iron boron strong magnets embedded in the edges or non-working areas of the upper and lower molds, the upper and lower molds are automatically and precisely aligned, and the fender is firmly clamped in the cavity, effectively preventing relative displacement during the impact process.

[0039] S320: In-mold high-frequency micro-impact forming: The operator uses a pneumatic ball-head hammer or flat-head hammer to apply high-frequency, low-amplitude impacts to the damaged area on the outer surface of the upper mold (a concave surface with the curvature of the fender's outer surface). Simultaneously, the inner surface of the lower mold (a convex surface with the curvature of the fender's inner surface) provides full-area, conformal, and rigid support for the deformed area. This "in-mold impact" method ensures that the metal sheet's elongation and springback are strictly limited within the originally designed surface range, thus achieving precise damage restoration and avoiding over-trimming or the creation of new defects.

[0040] Step S400: Post-processing and quality verification.

[0041] The mold is disassembled, and the repaired fender is inspected using a 3D scanning device or optical comparator. The repair accuracy is verified by comparing it with the digital reference model obtained from S100. The mold can be cleaned and directly used for the repair of the next part of the same type.

[0042] The invention will be further illustrated below with reference to an example of a factory producing 50,000 remanufactured fenders per year: (1) Scenario: The production line receives an order for 100 left front fenders of "Model A".

[0043] (2) S100: The technician uses a blue light 3D scanner to scan the intact left front fender of “Model A”, generate a digital reference, and archive it.

[0044] (3) S200: S210, take out the 10mm thick PCL large plate from the inventory, and cut out the blanks of the upper and lower molds according to the maximum projected area.

[0045] For S220, S230, and S240, two operators work together to immerse the blanks in a 75°C hot water bath for 5 minutes. After removing them, they are pressed and shaped on dedicated reference fixtures, and then sent to the cooling station where they are blown by a fan for 7 minutes. The total time for making the first set of molds is approximately 18 minutes.

[0046] This mold will be used to repair these 100 leaf blades.

[0047] (4) S300: In S310 & S320, the repair station staff clamps and fixes the damaged part and the mold, and uses a pneumatic hammer to repair it; because of the mold guidance, the average repair time per part is reduced to 15 minutes, and there is no need for repeated measurement and comparison.

[0048] (5) Looping and Resetting: After completing the repair of 100 pieces of "Model A", the production line received an order for "Model B".

[0049] S250: The mold for "Model A" is softened by immersing it in a hot water bath, flattened, and then stored.

[0050] Repeat step S200 to create a mold for "Model B" using the same batch of PCL material.

[0051] (6) Effect comparison: Compared with the traditional method, the present invention does not require any new mold cost for model B, and the mold switching time is only about 20 minutes, realizing a truly "flexible production line".

[0052] This invention utilizes the reversible thermoplasticity of PCL to achieve rapid mold customization and unlimited resetting, thereby constructing a dynamic, on-demand mold system. The method of this invention is a complete closed loop, starting with a digital reference and ending with the "data erasure" of the physical mold and material recycling; none of these steps can be omitted. The material properties of the PCL in this invention (low-temperature softening, rapid hardening, unlimited repeatability, and sufficient strength) and the process steps such as magnetic positioning and in-mold impact repair mutually support each other, jointly achieving the final technical effect.

[0053] The contents not described in detail in this specification are existing technologies known to those skilled in the art. The standard parts used can be purchased from the market, and the irregular parts can be customized according to the description and drawings. The specific connection methods of each part adopt conventional methods such as bolts, rivets, and welding that are mature in the existing technology. The machinery, parts and equipment adopt conventional models in the existing technology, and the circuit connection adopts conventional connection methods in the existing technology, which will not be described in detail here.

[0054] This invention is not limited to the above-described embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this invention shall be considered equivalent substitutions and shall be included within the scope of protection of this invention.

Claims

1. A method for flexible repair of automotive fenders based on reversible thermoplastic molds, characterized in that, Includes the following steps: Step S100, Digitization of the reference surface: Obtain the original surface data of the car fender through 3D scanning and generate a digital reference model; Step S200: Rapid generation and recycling of customized molds; Step S300, clamping and in-mold precision shaping and repair: use a pneumatic hammer to perform impact repair under the precise constraint of the mold; Step S400, Post-processing and quality verification: Disassemble the mold and conduct a quality inspection on the repaired fender.

2. The flexible repair method for automobile fenders based on reversible thermoplastic molds as described in claim 1, characterized in that: In step S100, a non-contact 3D scanner is used to perform a high-precision scan on the intact target leaf plate reference component to obtain 3D point cloud data of its inner and outer surfaces and reconstruct a high-fidelity digital model.

3. The flexible repair method for automobile fenders based on reversible thermoplastic molds as described in claim 1, characterized in that, Step S200 includes the following sub-steps: S210, Material Selection and Pretreatment: Based on the area and curvature complexity of the leaf to be repaired, select PCL sheets of appropriate thickness and size, and clean the surface of the PCL sheets. S220, Flexible Heat Treatment: The PCL sheet is completely immersed in a hot water bath with constant temperature control at 70℃-80℃ and heated continuously for 3-10 minutes to melt the crystalline areas inside the PCL. S230, curved surface negative pressure / compression molding, completes the production of upper and lower molds; S240, rigid cooling and shaping: The mold that has been shaped is forced to cool, so that the movement of the molecular chain segments of the PCL material is frozen, recrystallized, and quickly restored to a hard solid. At this time, the mold surface is the precise negative shape of the reference part surface. S250, Mold Reset: After repairing all the leaves of the current model, put the upper and lower molds back into the hot water bath to perform step S220, so that the material softens again and can be easily flattened or kneaded into the initial shape, preparing for the next production of a new mold.

4. The method for flexible repair of automotive fenders based on reversible thermoplastic molds as described in claim 3, characterized in that, S230 includes the following steps: Upper mold making: The softened PCL sheet is quickly covered on the outer surface of the reference part. Uniform pressure is applied manually or using a flexible pressure bladder to ensure that the material fits tightly with every curved feature of the reference part without leaving any gaps. Lower mold making: Using the same method as the upper mold making, the lower mold is made on the inner surface of the reference part.

5. The method for flexible repair of automotive fenders based on reversible thermoplastic molds as described in claim 3, characterized in that: In S240, when the mold that has been shaped is forcibly cooled, air convection cooling at a constant room temperature of 20-25℃ is used for 5-10 minutes or auxiliary air cooling for 3-8 minutes; and after recrystallization, the hardness of the solid reaches Shore D50-60.

6. The method for flexible repair of automotive fenders based on reversible thermoplastic molds as described in claim 1, characterized in that, Step S300 includes the following sub-steps: S310, Magnetic Assisted Positioning and Clamping: Place the damaged blade to be repaired on the worktable; first place the lower mold on the inside, then cover the outside with the upper mold. Relying on the magnetic attraction force generated by the neodymium iron boron strong magnets embedded in the edges or non-working areas of the upper and lower molds, the upper and lower molds are automatically and accurately aligned, and the blade is firmly clamped in the cavity to prevent relative displacement during the impact process. S320, In-Mold High-Frequency Micro-Impact Forming: The operator uses a pneumatic ball-head hammer or flat-head hammer to perform high-frequency, low-amplitude impacts on the damaged area on the outer surface of the upper mold; at the same time, the inner surface of the lower mold provides full-area, conformal, and rigid support for the deformed area; through this in-mold impact method, it is ensured that the extension and springback of the metal sheet are strictly limited within the original design surface range, thereby achieving precise restoration of damage and avoiding over-repair or the generation of new defects.

7. The flexible repair method for automobile fenders based on reversible thermoplastic molds as described in claim 6, characterized in that: In S320, the outer surface of the upper mold is a concave surface with the same curvature as the outer surface of the fender, and the inner surface of the lower mold is a convex surface with the same curvature as the inner surface of the fender.

8. The method for flexible repair of automotive fenders based on reversible thermoplastic molds as described in claim 1, characterized in that: In step S400, after disassembling the mold, the repaired fender is inspected using a 3D scanning device or an optical comparator and compared with the digital reference model obtained in S100 to verify the repair accuracy.

Images