A low heat attenuation hot forming method for clutch wave profile sheet

Abstract

The application relates to the technical field of automobile part manufacturing, in particular to a low-heat-decay hot forming method for clutch wave-shaped sheets. The method comprises the following steps: providing a 50CrV4 steel-made unformed wave flat semi-finished product, carrying out bright quenching, hot water cleaning, short-time heat flattening and stable tempering treatment on the semi-finished product to eliminate warping stress and homogenize the structure; then carrying out constrained heat forming at 450 DEG C to make the flat material form predetermined wave crests and wave troughs; finally, cooling, rust-proof oiling and assembling the formed wave-shaped sheet, and carrying out a 300 DEG C, 12h high-temperature holding test on the assembled wave-shaped sheet, and taking that the axial compression force decay is not more than 15% as a qualified criterion. The application can effectively reduce the axial compression force decay of the wave-shaped sheet after high-temperature assembly, and improve the axial compression stability and batch consistency of the wave-shaped sheet under high-heat-load working conditions.

Description

Technical Field

[0001] This application relates to the field of automotive parts manufacturing technology, and in particular to a method for low-heat-attenuation thermoforming of clutch wave plates. Background Technology

[0002] Clutch wave plates are key elastic elements in the driven disc assembly of an automotive clutch. They are typically sandwiched between two friction plates, providing axial elastic cushioning during clutch engagement and disengagement, and compensating for impacts, vibrations, and uneven localized stress during friction plate contact. Their wave height consistency, rebound stability, and ability to retain axial compressive force under high-temperature conditions directly determine the smoothness of engagement, the thoroughness of disengagement, and the overall driving comfort of the driven disc assembly. In existing wave plate manufacturing processes, 50CrV4 spring steel is commonly used as the raw material. The process typically involves cold-stamping a flat sheet to form a wave shape, followed by quenching and tempering; or first quenching the flat sheet as a whole, then cleaning, tempering, and leveling, and finally shaping the wave in the tempered state. These existing technologies aim to improve the material's microstructure through heat treatment and obtain the required geometry through mechanical forming to meet basic elastic function requirements.

[0003] However, in existing technologies, when the clutch assembly operates under high temperatures for extended periods or undergoes high-temperature assembly and holding, the axial compressive force of the wave plate often decreases significantly, leading to insufficient clutch clamping force and affecting the reliability of power transmission. Especially in demanding applications such as AMT transmissions and high-heat-load clutches, ensuring that the wave plate maintains stable axial compressive performance after prolonged high-temperature exposure and avoiding excessive thermal decay has become a core problem urgently needing to be solved in this field. Summary of the Invention

[0004] This application provides a method for low-heat-attenuation thermoforming of clutch wave plates to solve the above problems. The method includes:

[0005] S1. Provide a semi-finished unwavered flat material made of 50CrV4 steel, wherein the semi-finished unwavered flat material has formed the outer contour and hole positions of the clutch wave plate, but has not yet formed the final wave.

[0006] S2. The unwavered flat semi-finished product is subjected to bright quenching treatment at a quenching temperature of 860±5℃ and a holding time of 50min to obtain the hardened flat semi-finished product.

[0007] S3. Clean the quenched flat semi-finished product. The cleaning water temperature is 70-80℃ and the cleaning time is 20 minutes to remove the quenching medium residue on the surface of the flat semi-finished product.

[0008] S4. Perform a short-term hot leveling treatment on the cleaned semi-finished material. The leveling temperature is 300℃, and the leveling pressure is 80 kgf / cm². 2 The holding time is 20s, which allows the quenched flat semi-finished product to release warping stress under planar constraint.

[0009] S5. The flat semi-finished product after heat leveling is subjected to stabilizing tempering treatment. The tempering temperature is 300±5℃ and the tempering time is 50~60min, so that the flat semi-finished product can complete the structural stability and residual stress homogenization in the flat state after leveling.

[0010] S6. Perform constrained thermoforming on the tempered flat semi-finished product. The thermoforming temperature is 450℃, and the forming pressure is 120kgf / cm². 2 The holding time is 240s, so that the flat semi-finished product forms a predetermined peak and trough under the condition of heat and pressure constraint, and obtains the clutch wave plate;

[0011] S7. Cool and apply rust-proof oil to the hot-formed clutch wave plate, and assemble the qualified clutch wave plate into the clutch driven plate assembly. After the driven plate assembly, cover assembly and flywheel are fastened, keep it at 300℃ for 12 hours. The axial compressive force attenuation of no more than 15% is used as the qualification criterion for the low heat attenuation hot forming method of the clutch wave plate.

[0012] Through the above technical solutions, a progressive stress management chain of "quenching → cleaning → hot leveling → stable tempering → constrained hot forming → thermal attenuation verification" is constructed. S2 bright quenching establishes a highly elastic matrix and prevents surface decarburization, while S3 hot water cleaning eliminates local thermal resistance to ensure uniform subsequent heating. Then, S4 applies planar constraints at 300℃ to release macroscopic warpage and prevent deformation solidification, combined with S5 long-term stable tempering in the same temperature range, ensuring that the microstructure and residual stress are fully homogenized in a flat state. Based on this, S6 utilizes a medium-temperature window of 450℃ for constrained hot forming, avoiding both the large springback of cold forming and the loss of elastic reserves caused by high-temperature forming, thus achieving stress redistribution in the bending zone. Finally, S7 introduces a real 300℃ / 12h heat exposure condition as a pass / fail criterion, strongly coupling the process endpoint with the high-heat-load scenario of the AMT clutch, thereby significantly reducing the post-heat axial pressure attenuation rate of the wave plate and keeping it stably controlled within 15%.

[0013] Optionally, in step S1, the unwaved flat semi-finished material is pre-grouped into batches before entering the bright quenching process. The pre-grouping of batches includes grouping according to at least two of the following: flat material thickness, material rolling direction, and punching burr direction, so that the unwaved flat semi-finished material in the same hot forming batch has a consistent heating direction and pressure direction.

[0014] The above technical solutions ensure that 50CrV4 flat materials in the same batch have high consistency in physical properties, eliminating the fluctuations in thermoforming response caused by material anisotropy, differences in geometric dimensions, and different edge stress field orientations. This homogenization process at the source, combined with the subsequent standardized heat treatment process, can reduce the high standard deviation of free waves after thermoforming and narrow the discrete band of the 300℃ heat decay rate, ensuring the stable reproduction of low heat decay performance in mass production.

[0015] Optionally, the thickness difference of the un-waved flat semi-finished products in the same thermoforming batch shall not exceed 0.02 mm, and the direction of the punching burrs shall be consistent, so as to reduce the difference in free wave height of different flat materials after constrained thermoforming at 450℃.

[0016] By using the above technical solutions, the thickness tolerance is limited to within 0.02mm, and the range of yield stress variation of the same batch of materials at 450℃ is controlled, avoiding the situation where some flat materials undergo excessive plastic deformation while others are under-formed. At the same time, the burr direction is forced to be uniform, ensuring that when all flat materials are under pressure in the constrained mold, the high stress concentration side is always in the same spatial position, preventing random stress concentration points from inducing local microcracks or abnormal relaxation. The synergistic effect of these two measures makes the stress field distribution pattern at the edge of the corrugated sheet completely reproduced, and the difference in the thermal decay rate of a single sheet is reduced.

[0017] Optionally, after the short-term hot leveling process in step S4, the flatness of the flat semi-finished product is tested, and the flat semi-finished product whose flatness does not meet the thermoforming requirements is used as an isolation part and is not included in the same thermoforming batch as the part with qualified flatness.

[0018] The above technical solution effectively intercepts defective parts that still have slight flatness deviations even after 300℃ / 20s heat leveling, preventing them from causing local overpressure, stress concentration, or waveform distortion due to initial warping under 450℃ high pressure. This isolation mechanism ensures that subsequent tempering and forming processes are carried out under the premise of consistent geometric reference, improving the effective input qualification rate of the thermoforming process, reducing the wave height variation coefficient of the same batch, and ensuring the statistical confidence of the batch thermal attenuation verification results.

[0019] Optionally, in the stabilization tempering process of step S5, the flat semi-finished products after heat leveling are tempered in a flat or spaced-out state, and after the stabilization tempering is completed, they are cooled to no higher than 80°C before entering the constrained thermoforming process of step S6, so that the flat semi-finished products of the same batch have a consistent starting temperature state before thermoforming.

[0020] By employing the above technical solutions and using a flat or spaced cooling method, the temperature difference between the center and surface, and between layers, caused by stacked cooling is eliminated, ensuring that the heat dissipation path of each flat material is the same. This makes the actual heating rate of all flat materials highly consistent with the time to reach the target temperature when entering the S6 thermoforming equipment, avoiding the drift of the holding pressure timing start point and the fluctuation of the actual molding temperature caused by the difference in the initial temperature. It improves the consistency of the actual molding temperature, suppresses the weakening of grain boundaries caused by local overheating, and reduces the risk of increased axial pressure thermal decay rate from a microscopic mechanism.

[0021] Optionally, in the constrained thermoforming process of step S6, the thermoforming temperature is taken as the starting point for holding pressure timing when the actual temperature of the forming area where the flat semi-finished product is located reaches 440-460℃, rather than taking the set temperature of the heating equipment as the starting point for holding pressure timing.

[0022] By correcting the starting point of the holding pressure timer from the equipment set temperature to the actual temperature of the flat material, the problem of material internal temperature lag caused by the thermal inertia of the mold is overcome, ensuring that the 240s holding pressure process is completed within the material's optimal plasticity window (440-460℃). This control strategy avoids insufficient waveform shaping and large springback after demolding due to insufficient effective plastic deformation time, and reduces the relaxation amplitude of residual stress in subsequent heat exposure.

[0023] Optionally, segmented pressure cycles are used in the constrained thermoforming process of step S6, wherein the segmented pressure cycles include:

[0024] First, apply a pre-compression pressure equivalent to 30% to 50% of the molding pressure and hold it for 20 to 40 seconds to make the flat semi-finished product fit against the molding constraint surface;

[0025] Pressurize to 120 kgf / cm 2 The pressure is held for 240 seconds to form predetermined peaks and troughs in the flat semi-finished product;

[0026] Finally, maintain partial pressure to stabilize the shape before releasing the constraint, in order to reduce the thermal rebound of the clutch wave plate after demolding.

[0027] The above technical solution introduces a segmented pressure cycle of "pre-pressing and bonding - full-pressing and shaping - depressurization and stabilization". First, in the pre-pressing stage, the flat material is flexibly bonded to the curved surface of the mold, eliminating air gaps and initial cantilever bending, and avoiding direct shear impact on the hole edge at the moment of full press. Then, the target pressure is uniformly applied in the bonded state to ensure a steady increase in stress. Finally, in the early stage of cooling, some pressure is maintained, and the material's creep capacity in the 400-350℃ range is used to offset the elasticity and thermal rebound at the moment of demolding, reducing the incidence of microcracks at the hole edge, reducing the amount of thermal rebound after demolding, improving the uniformity of stress distribution in the peak and trough areas, thereby reducing the axial pressure attenuation after heating.

[0028] Optionally, in step S7, after the thermoformed clutch wave plate is released from constraint, it is cooled to no higher than 60°C by placing it individually or at intervals, and then subjected to anti-rust oiling treatment. Before oiling, the free wave height, wave height difference and axial compression force of the clutch wave plate are detected.

[0029] The above technical solution specifies a cooling method that involves placing individual or spaced pieces, avoiding localized high pressure and microplastic deformation of the lower corrugated sheet caused by the gravity and thermal expansion of the upper layer during high-temperature stacking and cooling. It also eliminates the increase in internal temperature gradient and uneven stress relaxation caused by stacking hindering heat dissipation. Combined with comprehensive testing before oiling, it ensures that quality judgment is performed in the actual state after the corrugated sheet has completed its structure and dimensional stability. It also improves the stability of free waves after cooling and reduces the standard deviation of axial compressive force test values.

[0030] Optionally, in step S7, the axial compression force before the clutch wave plate is assembled is recorded as P0, and the axial compression force measured after the driven plate assembly, cover assembly and flywheel are fastened and kept at 300°C for 12 hours and then cooled to room temperature is recorded as P1. The axial compression force attenuation rate is calculated according to (P0-P1) / P0×100%, and the axial compression force attenuation rate is not greater than 15% as the batch release condition.

[0031] The above technical solution transforms the fuzzy thermal decay requirement into an operable and verifiable mathematical expression, directly linking the process output (P0) and the actual operating performance (P1). Using P0 as the benchmark denominator highlights the weight of the material's initial elastic reserve on thermal stability, while limiting P1 to be measured after cooling to room temperature eliminates the interference of thermal expansion. This definition supports the implementation of statistical process control, narrowing the discrete band width of the decay rate between batches.

[0032] Optionally, when the free wave height of the same batch of clutch wave plates is qualified but the axial compressive force attenuation rate is close to 15%, at least one of the following for the next batch is modified: 300℃ stable tempering time, 450℃ constrained hot forming temperature, and cooling placement method after hot forming, so as to form process feedback control based on the thermal attenuation result.

[0033] Through the above technical solutions, a closed-loop feedback mechanism based on thermal attenuation quantification data is established. When the performance index is detected to be approaching the critical value, the key process parameters can be actively fine-tuned to re-optimize the process window; the process capability index is improved, and the upgrade from static process scheme to intelligent manufacturing system with self-correction capability is realized. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a flowchart of a low-heat-attenuation thermoforming method for a clutch waveform sheet, provided as an embodiment of this application. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, 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 some, not all, of the embodiments of this application. 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.

[0037] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0038] The embodiments of this application will now be described in further detail with reference to the accompanying drawings.

[0039] Example 1

[0040] This embodiment is intended to verify the feasibility and core effectiveness of the standard low thermal decay thermoforming process provided by the present invention.

[0041] Take 50CrV4 spring steel flat semi-finished products, the outer contour and hole positions have been processed. First, perform batch pre-grouping, and select flat materials with a thickness difference of no more than 0.02mm and consistent punching burr direction to be grouped into the same batch.

[0042] The grouped flat materials are sent into a sealed box-type multi-purpose furnace for bright quenching. The atmosphere inside the furnace is controlled, the quenching temperature is 860℃, the holding time is 50min, and after exiting the furnace, they are oil-cooled to obtain hardened flat materials.

[0043] The quenched flat material is placed in a box-type cleaning device and cleaned with 75°C deionized water for 20 minutes to remove surface quenching medium residue.

[0044] The cleaned flat material is placed in a hot leveling machine, heated to 300℃, and then subjected to an application of 80 kgf / cm². 2 Apply pressure and hold for 20 seconds for short-term hot leveling. Immediately after leveling, conduct a flatness inspection and reject parts that exceed the flatness tolerance.

[0045] The qualified flat material is laid flat and placed into a box-type tempering furnace for stable tempering at 300℃ for 60 minutes. After tempering, it is cooled to below 80℃ inside the furnace or in air.

[0046] The cooled flat material is fed into a thermoforming press, and the mold is preheated to 450°C. Timing begins when the thermocouple detects that the actual temperature of the forming area of ​​the flat material reaches 450°C, and an application rate of 120 kgf / cm² is applied. 2 The pressure is maintained for 240 seconds to form predetermined peaks and troughs in the flat material.

[0047] After thermoforming, the corrugated sheets are removed one by one and left to cool to below 60°C at intervals.

[0048] The cooled waveform sheet is tested for free wave height, wave height difference, and axial compressive force (P0). After passing the tests, rust-preventive oil is applied.

[0049] The wave plate was assembled onto the clutch driven plate assembly, secured to the cover assembly and flywheel, and placed in a high-temperature aging test chamber at 300℃ for 12 hours. After cooling to room temperature, it was disassembled, and the axial compressive force P1 was measured.

[0050] Testing revealed that the waveforms produced in this embodiment exhibited good consistency in free wave height, with a standard deviation of less than 0.05 mm. The formula for calculating the axial compressive force thermal attenuation rate is η = (P0 - P1) / P0 × 100%. Test results showed that the maximum axial compressive force attenuation rate of this batch of waveforms was 12.8%, and the average was 10.5%, both falling below the 15% qualification criterion.

[0051] This embodiment confirms that the sequential combination of "bright quenching - cleaning - hot leveling - stable tempering - constrained thermoforming" can effectively release the residual stress of 50CrV4 material and stabilize the microstructure. The waveform formed under 450℃ constrained conditions has excellent thermal stability and meets the technical requirements of low thermal decay.

[0052] Example 2

[0053] This embodiment aims to verify the feasibility of the defined flat material thickness difference parameter under boundary conditions.

[0054] With all other preparation conditions the same as in Example 1, only the batch pre-grouping criteria in step S1 were adjusted. 50CrV4 flat semi-finished products with a thickness difference of exactly 0.02 mm from the same batch (e.g., thickness range of 2.49 mm to 2.51 mm) were selected, and the direction of the punching burrs was strictly controlled to be consistent.

[0055] Bright quenching (860℃ / 50min), cleaning (75℃ / 20min), and hot leveling (300℃ / 80kgf / cm) were performed according to the process parameters of Implementation Method 1. 2 / 20s), stable tempering (300℃ / 60min) and constrained thermoforming (450℃ / 120kgf / cm) 2 / 240s).

[0056] The obtained waveform was tested and found that the free wave height fluctuated slightly but remained within a controllable range, with a standard deviation of 0.06 mm. After a 300℃ / 12h thermal decay test, the calculated maximum axial compressive force decay rate was 14.2%, and the average was 11.8%, which still met the requirement of not exceeding 15%.

[0057] The results show that even when the thickness difference reaches the upper limit of 0.02 mm, the technical solution of the present invention can still achieve good wave height consistency and low thermal attenuation effect with the control of burr direction consistency, which proves the rationality of the parameter range setting.

[0058] Example 3

[0059] This embodiment aims to verify the feasibility of the defined stable tempering time parameter under the lower limit boundary conditions.

[0060] The method is the same as in Example 1, except that the stabilization tempering time in step S5 is adjusted to 50 min, while the other conditions (including tempering temperature of 300°C, cooling to below 80°C, etc.) remain unchanged.

[0061] The flat materials also undergo pre-grouping, bright quenching, cleaning, and hot leveling. Hot forming conditions are maintained at 450℃ / 120kgf / cm². 2 / 240s.

[0062] The prepared waveform sheet was tested and the free wave height was qualified. After a thermal decay test at 300℃ for 12h, the calculated maximum axial compressive force decay rate was 14.6%, and the average value was 12.1%, which did not exceed the limit of 15%.

[0063] The results show that shortening the stabilization tempering time to 50 min still enables the flat semi-finished product to achieve basic microstructure stabilization and residual stress homogenization, supporting the subsequent thermoforming and low heat decay targets, thus proving the effectiveness of the tempering time range of 50–60 min.

[0064] Example 4

[0065] This embodiment aims to verify the feasibility of the defined thermoforming temperature parameters under upper limit boundary conditions.

[0066] Based on the process of Example 1, in the constrained thermoforming process of step S6, the thermoforming temperature is adjusted to 460°C, and the starting point for holding pressure is still based on the actual temperature of the flat material reaching 460°C. The remaining pressure (120 kgf / cm²) is adjusted accordingly. 2 The parameters for time (240s) remain unchanged.

[0067] The preceding steps S1-S5 are consistent with those in Implementation Method 1.

[0068] The fabricated waveform sheet was tested and the wave height dimensions met the requirements. After a 300℃ / 12h thermal decay test, the calculated maximum axial compressive force decay rate was 13.9%, and the average was 11.2%. Although the temperature was high, due to the use of actual temperature timing and constrained molding, there was no excessive loss of elastic reserve.

[0069] The results show that even when constrained thermoforming is performed at 460℃, the method of the present invention can still obtain a waveform sheet that meets the requirements for low thermal decay, proving the wide adaptability of the thermoforming temperature range of 440~460℃.

[0070] Example 5

[0071] This embodiment aims to verify the effect of a defined segmented pressure cycle on molding quality at the lower limit of the pre-compression pressure.

[0072] Based on Example 1, step S6 employs segmented pressure cycling. The difference lies in that the pressure applied during the pre-compression stage is adjusted to 30% of the molding pressure (i.e., 36 kgf / cm). 2 The pressure was maintained for 20 seconds (lower limit); then increased to 120 kgf / cm². 2 Hold pressure for 240 seconds; finally, stabilize before depressurization.

[0073] The remaining preprocessing and post-cooling detection steps are the same as in Implementation Method 1.

[0074] The prepared waveform sheet underwent visual inspection, and no obvious microcracks were found at the hole edges and trough transition areas. After a thermal decay test at 300℃ for 12 hours, the calculated maximum axial compressive force decay rate was 13.5%, and the average value was 10.9%.

[0075] The results show that even with a lower pre-compression pressure (30%) and a shorter pre-compression time (20s), the segmented pressure cycle can still effectively promote the initial bonding between the flat material and the mold, reduce stress concentration, and achieve the goal of low heat attenuation, thus verifying the feasibility of this parameter range.

[0076] Example 6

[0077] This embodiment aims to compare and verify the negative impact of not performing batch pre-grouping on thermal decay performance, so as to highlight the necessity of the technical features of the present invention.

[0078] The only difference between this comparative example and Example 1 is that: in step S1, no batch pre-grouping is performed, and 50CrV4 flat materials with a thickness difference of about 0.08mm, random rolling direction, and inconsistent burr direction are randomly selected and mixed for processing.

[0079] The process parameters for subsequent steps S2-S7 (quenching, cleaning, leveling, tempering, hot forming temperature, pressure, time, etc.) are performed exactly as described in Example 1.

[0080] The resulting waveforms exhibited a large dispersion in free wave height, with a standard deviation of 0.14 mm. After a 300℃ / 12h thermal decay test, the axial compressive force decay rate of some samples exceeded 18%, and the average decay rate of the entire batch of samples was 16.5%, with the highest value reaching 19.2%, which did not meet the acceptance criterion of not exceeding 15%.

[0081] The comparative results show that without pre-grouping based on thickness, rolling direction, and burr direction, even with precise subsequent heat treatment parameters, inconsistent thermoforming responses due to significant differences in raw material conditions will ultimately lead to excessive thermal decay performance. This demonstrates the crucial role of the batch pre-grouping technology in achieving the low thermal decay target in this invention.

[0082] Example 7

[0083] This embodiment aims to compare and verify the impact of omitting the "short-time thermal balancing" step on thermal decay performance.

[0084] The only difference between this comparative example and Example 1 is that the short-term hot leveling treatment in step S4 is omitted. The flat material after quenching and cleaning directly enters step S5 for stable tempering at 300°C, followed by hot forming.

[0085] The remaining steps and parameters are consistent with those in Example 1.

[0086] Due to the lack of thermal leveling to release macroscopic warping stress, some flat materials exhibited initial bending during tempering and forming. In a 300℃ / 12h thermal decay test, the axial compressive force decay rate of the resulting corrugated sheets fluctuated wildly, reaching a maximum of 21.3% and an average of 17.8%, far exceeding the 15% limit. Furthermore, some samples showed microscopic cracks at the crests of the corrugations.

[0087] The comparative results show that the lack of a short-term hot leveling step at 300℃ prevents the quenching warpage stress from being effectively released under planar constraints. These residual stresses relax during subsequent hot forming and heat exposure, significantly exacerbating axial compression attenuation. This confirms the necessity of the "leveling first, tempering later" sequential coupling.

[0088] Example 8

[0089] This embodiment aims to compare and verify the impact of using the "device set temperature" instead of the "actual temperature" as the starting point for pressure holding time on product performance.

[0090] The only difference between this comparative example and Example 1 is that in step S6, the holding pressure timer starts immediately when the heating device displays a temperature of 450°C, without waiting for the actual temperature of the flat material to reach that range. Due to the thermal inertia of the mold, the actual temperature of the flat material at this time is approximately 390°C.

[0091] The remaining steps and parameters are consistent with those in Example 1.

[0092] Due to insufficient effective plastic deformation time, the springback of the corrugated sheets after demolding was large, and the free wave height was generally low and unstable. In the 300℃ / 12h thermal decay test, the average axial compressive force decay rate was 16.9%, with some samples reaching as high as 20.1%, failing to meet the qualification criteria.

[0093] The comparative results show that if the actual temperature of the flat material is not used as the starting point for the pressure holding time, the forming window will become uncontrollable, the waveform will not be sufficiently shaped, and the residual stress will be unevenly locked, thus severely deteriorating the thermal decay performance. This confirms the inventive effect of the technical feature of triggering the timing with the actual temperature in this invention.

[0094] Example 9

[0095] This embodiment is a comprehensive verification embodiment of performance and effect, which aims to systematically evaluate the comprehensive performance of the method of the present invention under different parameter combinations and verify its significant progress compared with the prior art.

[0096] Scale settings:

[0097] Comparative Example 1: The traditional cold stamping wave forming + stress relief annealing process was used (not the method of this invention).

[0098] Comparative Example 2: The method of the present invention is used, but step S4, thermal leveling, is omitted (same as Example 7).

[0099] Comparative Example 3: The method of the present invention is used, but batch pre-grouping is not performed (same as Example 6).

[0100] Example group:

[0101] Example A: The process of Example 1 (standard process) is used.

[0102] Example B: Using the process of Example 2 (thickness boundary 0.02mm).

[0103] Example C: Using the process of Example 5 (segmented pressure 30% pre-compression).

[0104] Test items:

[0105] 1. Standard deviation of free wave height (mm): reflects dimensional consistency.

[0106] 2. Maximum axial compressive force attenuation rate (%): reflects thermal stability under extreme conditions.

[0107] 3. Average axial compressive force attenuation rate (%): reflects the overall batch level.

[0108] 4. Detection rate of microcracks at the hole edge (%): reflects the molding quality.

[0109] Table 1 Summary of Performance Test Results

[0110]

[0111] Effect Analysis:

[0112] As shown in Table 1, the clutch wave plate prepared using the method of this invention (Example AC) has a significantly lower standard deviation of free wave height than the comparative examples, indicating a substantial improvement in dimensional consistency. More importantly, regarding the critical thermal decay index of 300℃ / 12h, the maximum decay rate of all embodiments of this invention is strictly controlled within 15%, with an average value maintained at around 11%; while the decay rates of comparative examples 1-3 all exceed 15%, failing to meet the requirements for AMT clutch use.

[0113] In particular, the comparison between Example A and Comparative Example 2 shows that adding a short-term thermal leveling step at 300°C reduced the maximum attenuation rate from 21.3% to 12.8%, a reduction of 40%, strongly demonstrating the decisive role of eliminating macroscopic warping stress in reducing thermal attenuation. The comparison between Example A and Comparative Example 3 shows that batch pre-grouping effectively suppressed performance dispersion caused by raw material differences. Furthermore, Example C, which employed segmented pressure cycling, exhibited an extremely low detection rate of microcracks at the hole edges, verifying the effectiveness of this measure in improving local stress concentration.

[0114] In summary, this invention, through a specific process sequence, parameter control, and closed-loop quality inspection, successfully solved the technical problem of excessive axial pressure attenuation after high-temperature assembly of 50CrV4 waveform sheets, achieving unexpected technical results.

[0115] Experimental results show that the clutch wave plate prepared by this invention exhibits excellent axial compression force retention effect in a 300℃ / 12h heat exposure model simulating actual working conditions, with the attenuation rate stably controlled below 15%. Therefore, it can be used to prepare key components for preventing and / or treating slippage, vibration, and incomplete disengagement of automotive clutches under high temperature and high load conditions, and is particularly suitable for AMT automatic mechanical transmission driven plate assemblies with extremely high requirements for thermal stability.

[0116] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for low-heat-attenuation thermoforming of a clutch wave plate, characterized in that, include: S1. Provide a semi-finished product of unwavered flat material made of 50CrV4 steel, wherein the semi-finished product of unwavered flat material has formed the outer contour and hole positions of the clutch wave plate, but has not yet formed the final wave. S2. The unwavered flat semi-finished product is subjected to bright quenching treatment at a quenching temperature of 860±5℃ and a holding time of 50min to obtain the hardened flat semi-finished product. S3. Clean the quenched flat semi-finished product. The cleaning water temperature is 70-80℃ and the cleaning time is 20 minutes to remove the quenching medium residue on the surface of the flat semi-finished product. S4. Perform a short-term hot leveling treatment on the cleaned semi-finished material. The leveling temperature is 300℃, and the leveling pressure is 80 kgf / cm². 2 The holding time is 20s, which allows the quenched flat semi-finished product to release warping stress under planar constraint. S5. The flat semi-finished product after heat leveling is subjected to stabilizing tempering treatment. The tempering temperature is 300±5℃ and the tempering time is 50~60min, so that the flat semi-finished product can complete the structural stability and residual stress homogenization in the flat state after leveling. S6. Perform constrained thermoforming on the tempered flat semi-finished product. The thermoforming temperature is 450℃, and the forming pressure is 120kgf / cm². 2 The holding time is 240s, so that the flat semi-finished product forms a predetermined peak and trough under the condition of heat and pressure constraint, and obtains the clutch wave plate; S7. Cool and apply rust-proof oil to the hot-formed clutch wave plate, and assemble the qualified clutch wave plate into the clutch driven plate assembly. After the driven plate assembly, cover assembly and flywheel are fastened, keep it at 300℃ for 12 hours. The axial compressive force attenuation of no more than 15% is used as the qualification criterion for the low heat attenuation hot forming method of the clutch wave plate.

2. The method according to claim 1, characterized in that, In step S1, the un-waved flat semi-finished products are pre-grouped in batches before entering the bright quenching treatment. The pre-grouping of batches includes grouping according to at least two of the following: flat material thickness, material rolling direction, and punching burr direction, so that the un-waved flat semi-finished products in the same hot forming batch have a consistent heating direction and pressure direction.

3. The method according to claim 1, characterized in that, The thickness difference of the un-waved flat semi-finished products in the same thermoforming batch shall not exceed 0.02 mm, and the direction of the punching burrs shall be consistent to reduce the difference in free wave height after different flat materials are constrained thermoforming at 450℃.

4. The method according to claim 1, characterized in that, After the short-term heat leveling process in step S4, the flatness of the flat semi-finished product is tested. The flat semi-finished product whose flatness does not meet the thermoforming requirements is used as an isolation part and is not included in the same thermoforming batch as the part with qualified flatness.

5. The method according to claim 1, characterized in that, In the stabilization tempering process of step S5, the flat semi-finished products after heat leveling are tempered in a flat or spaced-out state, and after the stabilization tempering is completed, they are cooled to no higher than 80°C before entering the constrained thermoforming process of step S6, so that the flat semi-finished products of the same batch have a consistent starting temperature state before thermoforming.

6. The method according to claim 1, characterized in that, In the constrained thermoforming process of step S6, the thermoforming temperature is taken as the starting point for holding pressure timing when the actual temperature of the forming area where the flat semi-finished product is located reaches 440-460℃, rather than taking the set temperature of the heating equipment as the starting point for holding pressure timing.

7. The method according to claim 1, characterized in that, In the constrained thermoforming process of step S6, segmented pressure cycles are used, wherein the segmented pressure cycles include: First, apply a pre-compression pressure equivalent to 30% to 50% of the molding pressure and hold it for 20 to 40 seconds to make the flat semi-finished product fit against the molding constraint surface; Pressurize to 120 kgf / cm 2 The pressure is held for 240 seconds to form predetermined peaks and troughs in the flat semi-finished product; Finally, maintain partial pressure to stabilize the shape before releasing the constraint, in order to reduce the thermal rebound of the clutch wave plate after demolding.

8. The method according to claim 1, characterized in that, In step S7, after the thermoformed clutch wave plate is released from constraint, it is cooled to no higher than 60°C by placing it individually or at intervals, and then rust-proof oiling is applied. Before oiling, the free wave height, wave height difference and axial compression force of the clutch wave plate are detected.

9. The method according to claim 1, characterized in that, In step S7, the axial compression force before the clutch wave plate is assembled is recorded as P0, and the axial compression force measured after the driven plate assembly, cover assembly and flywheel are fastened and kept at 300°C for 12 hours and then cooled to room temperature is recorded as P1. The axial compression force attenuation rate is calculated according to (P0-P1) / P0×100%, and the axial compression force attenuation rate is not greater than 15% as the batch release condition.

10. The method according to claim 1, characterized in that, When the free wave height of the same batch of clutch wave plates is qualified but the axial compression force attenuation rate is close to 15%, at least one of the following should be modified: 300℃ stable tempering time, 450℃ constrained hot forming temperature, and cooling placement method after hot forming, so as to form process feedback control based on the thermal attenuation result.

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