Vehicle door frame multi-material composite forming process

Abstract

The invention discloses a car door frame multi-material composite forming process, which adopts a multi-material partition matching design, completes forming through a closed-loop continuous processing line, and comprises the following steps: S1, raw material pretreatment: carrying out feeding, uncoiling and leveling, tension elimination and thickness detection on coiled materials of different materials; s2, parameterized rolling forming is conducted, specifically, a multi-axis servo rolling line is adopted for conducting progressive rolling and real-time precision straightening on the pretreated raw materials; s3, on-line laser cutting is carried out, and fixed-length cutting and cutting face treatment are carried out on the formed workpiece; s4, precise punching is conducted, specifically, punching and hole site detection of workpiece mounting holes are completed through a numerical control punching machine; s5, flanging and shaping are conducted, specifically, a numerical control oil pressure punching machine is adopted for conducting flanging machining and shaping detection on the end of the workpiece; and S6, detecting and warehousing: completing full inspection and accurate measurement through a special inspection tool and precise measurement equipment, and warehousing after rust-proof treatment. The multi-material composite design requirement is completely met, and the forming consistency is guaranteed from the source.

Description

Technical Field

[0001] This invention relates to the field of automotive door frames, and more specifically to a multi-material composite molding process for automotive door frames. Background Technology

[0002] As a key load-bearing and decorative component of the vehicle body, the car door frame directly affects the assembly precision, structural strength, sealing performance, and overall vehicle safety. Its processing quality and production efficiency have a significant impact on the automotive manufacturing industry's large-scale production, cost control, and product competitiveness. To meet the dual requirements of strength and lightweight design in different parts of the door frame, existing door frames generally employ a multi-material combination design. Specifically, DC01 low-carbon steel is used in non-load-bearing areas, B340LA low-alloy high-strength steel in secondary load-bearing areas, and HC420LA high-strength steel in core load-bearing areas. Through this differentiated material combination, an optimal balance between structural performance and lightweight design is achieved.

[0003] However, current processing techniques for this type of multi-material composite door frame still have significant shortcomings, making it difficult to adapt to design requirements and production needs. Specific shortcomings are as follows: First, the material switching adaptability is poor. Due to the large difference in strength between the three types of steel, DC01, B340LA and HC420LA, the existing rolling forming parameters (pressure and speed) cannot be universally applied. When switching to process steels of different strengths, cross-sectional dimension deviations are likely to occur, affecting the forming quality of the door frame. Second, the processes are fragmented. Core processes such as roll forming, laser cutting, precision punching, and flanging are carried out independently. The workpiece needs to be transferred multiple times, which can easily cause deformation during the transfer process, thus affecting the straightness and torsion accuracy of the door frame (design requirement ≤0.5mm / M), making it difficult to meet the requirements of high-precision processing. Third, the investment in specialized tooling is large. The four types of door frames—front left, front right, rear left, and rear right—require individually designed forming rollers and tooling fixtures, lacking standardized components. This results in excessively long changeover cycles (typically ≥2 hours), reducing production efficiency and significantly increasing tooling investment and production costs. Therefore, those skilled in the art have provided a multi-material composite molding process for car door frames to address the problems mentioned in the background. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a multi-material composite molding process for car door frames, employing a multi-material zone matching design and completing the molding process through a closed-loop continuous processing line, comprising the following steps: S1: Raw material pretreatment, including feeding, unwinding and leveling, tension relief and thickness detection of roll materials of different materials; S2: Parametric roll forming, using a multi-axis servo roll forming line to progressively roll and straighten the pre-treated raw material in real time with precision; S3: Online laser cutting, which performs fixed-length cutting and surface treatment on the shaped workpiece; S4: Precision punching, which uses a CNC punching machine to complete the punching of mounting holes and hole position detection on the workpiece; S5: Flanging and shaping, using a CNC hydraulic punch press to perform flanging and shaping inspection on the ends of the workpiece; S6: Inspection and warehousing. Full inspection and precise measurement are completed using special inspection tools and precision measuring equipment. After rust prevention treatment, the product is stored in the warehouse. The closed-loop continuous processing line consists of core processing equipment connected by a servo synchronous conveying mechanism, and the conveying process is equipped with workpiece anti-deformation lifting fixtures.

[0005] Preferably, the multi-material zoning design is as follows: the non-load-bearing area uses 1.0mm thick DC01 low-carbon steel, the secondary load-bearing area uses 1.2mm thick B340LA low-alloy high-strength steel, and the core load-bearing area uses 1.5mm thick HC420LA high-strength steel.

[0006] Preferably, the core processing equipment includes a 50-axis servo roller pressing line, a 1500W fiber laser cutting machine, a five-axis CNC punch press, a 15T CNC hydraulic punch press, a coordinate measuring machine, and a door frame four-in-one special inspection tool. The 50-axis servo roller pressing line is equipped with an adjustable pressure module and 12 universal forming rollers. The accuracy of the coordinate measuring machine is 0.001mm, and the conveying speed of the servo synchronous conveying mechanism is adjustable from 0-6m / min.

[0007] Preferably, in the raw material pretreatment, the raw material is fed using a three-station hydraulic uncoiler, which is equipped with a tensioning chuck with a tensioning force adjustable range of 60-80kN. The uncoiling and leveling process uses a 24-roll precision leveler, with the upper roller gap adjusted according to the raw material thickness, and the adjustment tolerance being ±0.02-±0.03mm. The lower roller speed is 3-5m / min, and the flatness of the raw material after leveling is ≤0.15mm / M.

[0008] Preferably, in the raw material pretreatment, tension elimination adopts a closed-loop or adjustable tension control system, the applied tension is 12-15kN, the tension fluctuation is ≤±0.5-±0.8kN, the raw material detection adopts an online laser thickness gauge or a handheld thickness gauge, and the raw material is directly rejected when the thickness deviation exceeds ±0.02mm.

[0009] Preferably, in the parametric roll forming process, the hydraulic system of the 50-axis servo roll forming line is preheated to 20MPa, and the roller temperature is controlled at 25-35℃ by a water cooling system. Differentiated roll forming parameters are set for three different materials: DC01 has a roll forming pressure of 85-90MPa and a roll forming speed of 5m / min; B340LA has a roll forming pressure of 105-110MPa and a roll forming speed of 4m / min; and HC420LA has a roll forming pressure of 135-140MPa and a roll forming speed of 3m / min.

[0010] Preferably, in the parametric roll forming process, the 12 general forming rollers are divided into "the first 3 sections for leveling, the middle 6 sections for cross-sectional forming, and the last 3 sections for finishing and straightening". The finishing and straightening process is equipped with dual laser displacement sensors to detect the straightness and torsion of the door frame in real time. The detection frequency is 10 times / second. After forming, the straightness and torsion of the door frame are ≤0.5mm / M, and the cross-sectional dimensional tolerance is ≤±0.2mm.

[0011] Preferably, in the online laser cutting, a pneumatic linkage positioning fixture or a quick-change positioning fixture is used to position the workpiece, with a positioning repeatability of ≤0.05-0.06mm, a clamping force of 6-8kN, and laser cutting parameters of: cutting power of 1000-1200W, cutting speed of 2.5-3m / min, auxiliary gas of nitrogen with a pressure of 0.7-0.8MPa, focal position of 0.5mm below the upper surface of the workpiece, workpiece length tolerance controlled within ±0.3mm after cutting, and end burr height ≤0.05mm.

[0012] Preferably, the precision punching uses φ8mm or φ10mm precision punching dies, the die gap is adjusted to 0.04-0.055mm, the punching speed is 10-15 times / minute, the punching force is 75-100kN, and the punching sequence is "small holes first, then large holes, end holes first, then middle holes". Hole position detection uses a vision inspection system or a handheld hole position inspection gauge, with hole position tolerance ≤0.1mm and hole diameter tolerance ±0.02mm.

[0013] Preferred: Suitable for large-scale continuous production of a single door frame or small-batch, multi-batch alternating production of four types of door frames. When producing in small batches, the fixtures and molds adopt a tool-less quick-change structure with a changeover time of ≤28 minutes. After the changeover, the first piece passes full inspection by a special inspection tool and a coordinate measuring machine before mass production. When inspecting and warehousing, precise testing is performed by batch sampling, with a sampling ratio of 5 pieces out of every 200 pieces or 3 pieces out of every 50 pieces. All test data are automatically stored to form a batch quality report.

[0014] The technical effects and advantages of this invention are as follows: 1. This invention has strong adaptability to multiple materials: For the three different steel materials DC01, B340LA and HC420LA required for non-load-bearing, secondary load-bearing and core load-bearing areas, it accurately sets differentiated rolling parameters to match the mechanical properties and thickness requirements of each material, effectively avoiding the forming defects caused by a single parameter, achieving precise forming of the three materials, ensuring that the cross-sectional dimensional tolerance of the formed door frame is ≤±0.2mm, fully adapting to the multi-material composite design requirements, and ensuring the consistency of forming from the source.

[0015] 2. The invention features highly efficient process integration: It breaks away from the traditional model of independent operation of each process and integrates core processes such as raw material uncoiling, parametric roll forming, online laser cutting, precision punching, and flanging into a closed-loop continuous processing flow. It eliminates the need for manual transfer of workpieces and reduces workpiece transfer by more than 3 times compared to existing processes, significantly reducing the risk of secondary deformation during transfer. At the same time, it increases production efficiency by 40% and significantly improves the capacity benefits of large-scale production.

[0016] 3. Low changeover cost of this invention: It adopts a universal 12-segment forming roller, eliminating the need to equip different models of door frames with special forming rollers. Combined with quick-change tooling fixtures, it greatly simplifies the changeover process and shortens the changeover time to less than 30 minutes, completely solving the problem of cumbersome and time-consuming changeover in traditional processes. At the same time, the universal design reduces the investment in special tooling, reducing tooling investment costs by 50%, and significantly reducing the overall cost of multi-model, small-batch production.

[0017] 4. The invention has stable precision: The entire process, including forming, cutting, and punching, is equipped with a real-time positioning compensation mechanism. Combined with the real-time detection and closed-loop adjustment of dual laser displacement sensors, and the full inspection of the door frame with a special inspection fixture, the invention effectively controls key indicators such as the straightness and torque of the door frame and the accuracy of the holes, ensuring that all precisions meet the design requirements. At the same time, the assembly qualification rate is increased to 99.2%, which greatly reduces the rework rate and waste of defective products. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to specific embodiments. The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and design various embodiments with various modifications suitable for a particular purpose.

[0019] A multi-material composite molding process for car door frames is applied to four types of car door frames: front left, front right, rear left, and rear right. The door frame materials and thicknesses are strictly matched to the design requirements: the non-load-bearing area uses 1.0mm thick DC01 low-carbon steel, the secondary load-bearing area uses 1.2mm thick B340LA low-alloy high-strength steel, and the core load-bearing area uses 1.5mm thick HC420LA high-strength steel. The core processing equipment includes a 50-axis servo roller pressing line (equipped with an adjustable pressure module + 12 universal forming rollers), a 1500W fiber laser cutting machine, a five-axis CNC punch press, a 15T CNC hydraulic punch press, a coordinate measuring machine (accuracy 0.001mm), and a door frame four-in-one special inspection fixture. Each process is connected by a servo synchronous conveying mechanism (conveyor speed adjustable from 0-6m / min) to form a closed-loop continuous processing line. During the conveying process, workpiece anti-deformation lifting fixtures are provided to avoid workpiece deflection deformation caused by suspension. Example 1 This embodiment is applicable to the large-scale continuous production of a single automotive door frame (such as the front left door frame). Its core focus is on the long-term stability of machining accuracy, the continuity of the production process, and maximizing production efficiency. There are no changeover operations throughout the process, and all process parameters are controlled automatically in a closed loop. Specific machining parameters and detailed process requirements are as follows: S1: Raw material pretreatment Raw material feeding: The whole rolls of DC01 (inner diameter 508mm, outer diameter 1200mm), B340LA (inner diameter 508mm, outer diameter 1100mm), and HC420LA (inner diameter 508mm, outer diameter 1000mm) are respectively hoisted to the three-position hydraulic uncoiler. The uncoiler is equipped with tensioning chucks, and the tensioning force of the chucks is adjusted to 80kN to prevent the roll from slipping or swaying. Uncoiling and leveling: The uncoiled material is fed into a 24-roll precision leveler. The gap between the upper rollers of the leveler is adjusted to DC01: 1.0±0.02mm, B340LA: 1.2±0.02mm, and HC420LA: 1.5±0.02mm. The lower roller is the active roller with a rotation speed of 5m / min. The warping and wavy deformation of the material are eliminated by the squeezing and rolling of the upper and lower rollers. The flatness of the material after leveling is ≤0.15mm / M. Tension relief: The leveled raw material is fed into a dual tension roller group. A closed-loop tension control system is used to apply a constant tension of 15kN with tension fluctuation ≤ ±0.5kN. The tension stretching eliminates the internal stress generated in the roll material during rolling and storage, while ensuring that the raw material enters the subsequent process at a uniform speed without deviation. Raw material inspection: After pretreatment, the thickness of the raw materials is detected by an online laser thickness gauge. Raw materials with a thickness deviation exceeding ±0.02mm are directly rejected to ensure the accuracy of raw material entry.

[0020] S2: Parametric roll forming Equipment debugging: Start the 50-axis servo roller pressing line, preheat the hydraulic system to the working pressure of 20MPa, adjust the adjustable pressure module to the batch production setting, and control the roller temperature at 25-35℃ through the water cooling system to prevent dimensional deviations caused by roller overheating; Parameter settings: Based on the mechanical properties of the three materials, differentiated rolling parameters are set through the CNC system. The parameters are stored in segments and automatically recalled. DC01: Rolling pressure 90MPa (roller reduction 0.15mm / segment), rolling speed 5m / min, servo motor speed 1200r / min; B340LA: Rolling pressure 110MPa (roller reduction 0.12mm / segment), rolling speed 4m / min, servo motor speed 960r / min; HC420LA: Rolling pressure 135MPa (roller reduction 0.10mm / segment), rolling speed 3m / min, servo motor speed 720r / min; Progressive rolling: The 12 general-purpose forming rollers are divided into "the first 3 sections for leveling, the middle 6 sections for cross-section forming, and the last 3 sections for finishing and straightening". The first 3 sections of rollers eliminate the residual deflection of the raw material, the middle 6 sections of rollers gradually roll the raw material into the door frame design cross-section (U-shaped main cross-section + reinforcing rib secondary cross-section), and the last 3 sections of rollers are used in conjunction with the built-in laser straightening fixture for finishing. Real-time precision control: The straightening fixture is equipped with dual laser displacement sensors to detect the straightness and torsion of the door frame in the up-down and left-right directions in real time. The detection frequency is 10 times / second. If the detected value exceeds 0.4mm / M, the system automatically adjusts the spacing and angle of the last three rollers to achieve closed-loop automatic straightening, ensuring that the straightness and torsion of the door frame after forming are ≤0.5mm / M and the cross-sectional dimensional tolerance is ≤±0.2mm. Molding inspection: For every 50 pieces produced continuously, one piece is randomly selected for cross-sectional contour scanning. The cross-section gauge is used to compare it with the design model to confirm that there are no defects such as missing parts, bulges, or folded edges.

[0021] S3: Online laser cutting Positioning and clamping: The formed door frame workpiece is sent to the laser cutting machine by the servo conveyor mechanism. The workpiece is positioned at both ends and lifted in the middle by the pneumatic linkage shared positioning fixture. The positioning reference is the lower surface of the reinforcing rib of the door frame section. The clamping force of the fixture is 8kN and the positioning repeatability is ≤0.05mm to prevent the workpiece from moving during the cutting process. Cutting parameter settings: 1500W fiber laser cutting machine settings: cutting power 1200W, cutting speed 3m / min, auxiliary gas is nitrogen (pressure 0.8MPa) to prevent oxidation of the cutting surface, focal position is 0.5mm below the upper surface of the workpiece; Fixed-length cutting: The system is automatically programmed according to the design length of 1850mm for the front door frame. The laser head cuts at a constant speed along the length of the workpiece. After cutting, the length of the workpiece is automatically detected by the online length measuring sensor. The length tolerance is controlled within ±0.3mm. Defective products are automatically rejected by the sorting mechanism. Cutting surface treatment: After cutting, the end of the workpiece is free of burrs (burr height ≤ 0.05mm), and no secondary grinding is required.

[0022] S4: Precision punching Workpiece positioning: The cut workpiece is sent to a five-axis CNC punch press and is positioned by contouring of the cross section. The inner side of the U-shaped main cross section after the door frame is formed is used as the reference. The workpiece is completely positioned by four pneumatic positioning pins and two pressure blocks. The positioning accuracy is ≤0.03mm. Mold installation: Equipped with a universal mold frame, it can install φ8mm and φ10mm precision punching dies. The die clearance can be adjusted to φ8mm:0.04mm and φ10mm:0.05mm. The punch is made of cemented carbide to ensure the wear resistance of punching. Punching process: Set the punching parameters: punching speed 15 times / minute, punching force φ8mm: 80kN, φ10mm: 100kN. The five-axis punch press automatically identifies the workpiece positioning reference through the CNC system and completes the punching of all mounting holes according to the design drawings. The punching sequence is "small holes first, then large holes, end first, then middle" to prevent the workpiece from cumulative deformation due to continuous punching. Hole position inspection: After punching, the vision inspection system automatically detects the hole position coordinates, hole diameter and burrs on the hole edge. The hole position tolerance is ≤0.1mm, the hole diameter tolerance is ±0.02mm and the burr height is ≤0.05mm. Defective products are automatically traced and reworked.

[0023] S5: Edge Shaping Mold debugging: Set the 15T CNC hydraulic punch press to continuous working mode, install the special flanging die for the end of the door frame. The flanging die consists of a punch, a die, and a pressure ring. Adjust the pressure ring pressure force to 3kN to prevent the workpiece from wrinkling during the flanging process. Flanging process: The punched workpiece is fed into the flanging die and quickly clamped with the door frame cross-section as the positioning reference. The pressure of the main cylinder of the hydraulic press is adjusted to 12T, the slide descending speed is 50mm / s, and the pressure holding time is 2s to complete the 90° flanging of the overlapping area at the end of the door frame. The flanging height is precisely controlled to 5mm (height tolerance ±0.1mm). Shaping inspection: After the flange is completed, the overlap gap is checked by the gap inspection gauge to ensure that the gap is ≤0.6mm. At the same time, check that there are no cracks, wrinkles or springback at the flange. If springback occurs, the system will automatically adjust the holding time and the pressing force.

[0024] S6: Detect and store data Rapid full inspection: The door frame after flanging and shaping is sent to the inspection station and 100% full inspection is carried out using a door frame four-in-one special inspection tool. The inspection items include: straightness, torsion, cross-sectional dimensions, overlap gap, mounting hole position accuracy, and appearance quality. The inspection time is ≤30s / piece. Qualified parts proceed to the next step, and unqualified parts are labeled and sent to the rework area. Sampling and precision testing: 5 pieces are randomly selected from each batch of 200 pieces and precision testing is carried out using a coordinate measuring machine. The testing adopts automatic comparison of CAD digital model. The testing items include: cross-sectional profile, hole position coordinate tolerance, flange height and angle. All test data are automatically stored to generate a production batch quality report. Rust prevention treatment: Qualified parts pass through a spray-type rust prevention treatment line, where water-soluble rust inhibitors are sprayed on them, and the rust prevention film thickness is 5-8μm to prevent rusting during storage; Warehousing and receiving: Rust-proofed workpieces are stored on special racks equipped with anti-deformation slots. Each layer stores ≤10 pieces to avoid workpieces being stacked and deformed by pressure. After warehousing, the workpieces are scanned and entered into the production system to achieve batch traceability.

[0025] In this embodiment, the precision indicators of the front left door frame after processing consistently meet the design requirements, the assembly qualification rate is stable at 99.35%, the single-shift output is increased by 42% compared with the existing process, and there are no problems such as workpiece deformation during transportation or cross-sectional dimension deviation, which fully adapts to the needs of large-scale production.

[0026] Example 2 This embodiment is applicable to small-batch, multi-batch alternating production of four types of automotive door frames: front left, front right, rear left, and rear right. Its core focus is on the adaptability of quick-change tooling and changeover efficiency. The changeover process does not require replacing the 12 universal forming rollers; only the quick-change fixture and dedicated mold need to be replaced. Furthermore, the accuracy of the first piece after changeover quickly meets the standards. All process parameters adopt a segmented adjustable mode. Specific processing steps and detailed process requirements are as follows: S1: Raw material pretreatment Raw material feeding: Based on the material usage of the door frame in the current production batch, the DC01, B340LA, and HC420LA coils are hoisted to the three-position hydraulic uncoiler, and the clamp tension is adjusted to 60kN to accommodate the raw material feeding amount of small-batch production; Uncoiling and leveling: The rolls are fed into a 24-roll precision leveler. The gap between the leveling rolls is adjusted to DC01: 1.0±0.03mm, B340LA: 1.2±0.03mm, and HC420LA: 1.5±0.03mm. The speed of the lower roll is adjusted synchronously with the subsequent rolling speed (3-5m / min). Tension relief: An adjustable tension control system is adopted to apply a tension of 12kN with tension fluctuation ≤ ±0.8kN, which is suitable for the intermittent feeding characteristics of raw materials in small-batch production and eliminates the internal stress of the raw materials at the same time. Raw material inspection: After pretreatment, the raw material is inspected at multiple points using a handheld thickness gauge to ensure that the thickness of the raw material meets the requirements and avoids waste of raw materials in small-batch production.

[0027] S2: Parametric roll forming Equipment pre-adjustment: Start the 50-axis servo roller pressing line, preheat the hydraulic system to 20MPa, adjust the adjustable pressure module to the changeover production setting, and turn on the roller water cooling system normally, with the temperature controlled at 25-35℃; Differentiated parameter settings: Based on the current door frame model being produced, the CNC system calls pre-stored differentiated rolling parameters. These parameters are fine-tuned within the limits defined in the claims to adapt to the precision requirements of small-batch production. DC01: Rolling pressure 85MPa, rolling speed 5m / min, servo motor speed 1200r / min; B340LA: Rolling pressure 105MPa, rolling speed 4m / min, servo motor speed 960r / min; HC420LA: Rolling pressure 140MPa, rolling speed 3m / min, servo motor speed 720r / min; Progressive rolling: The 12 universal forming rollers are divided into "the first 3 sections for leveling, the middle 6 sections for cross-section forming, and the last 3 sections for finishing and straightening". In view of the cross-section design characteristics of the rear right door frame, the system automatically fine-tunes the pressing amount of the middle 6 rollers. During the forming process, the straightening fixture detects the straightness and torsion in real time, and the last 3 rollers are manually adjusted to ensure that the straightness and torsion of the door frame after forming are ≤0.5mm / M, and the cross-sectional dimensional tolerance is ≤±0.2mm. First piece forming inspection: After the first piece is rolled, the cross-sectional dimensions are immediately checked with a cross-section gauge. After confirming that it is qualified, it can proceed to the subsequent process to avoid batch defects.

[0028] S3: Online laser cutting Tooling changeover: If the production involves multiple door frame models, first replace the quick-change positioning fixture of the laser cutting machine. The fixture adopts the "quick-change pin + positioning key" connection method, which allows for tool-less replacement and a replacement time of ≤5 minutes. The quick-change fixture is compatible with the positioning reference of four types of door frames, and the clamping force is adjusted to 6kN, balancing positioning accuracy and clamping efficiency. Workpiece positioning: The formed rear door frame workpiece is sent to the laser cutting machine by a servo conveyor mechanism. The positioning is achieved at both ends by quick-change positioning fixtures. The positioning reference is consistent with that of a single production (lower surface of the reinforcing rib), and the positioning repeatability is ≤0.06mm. Cutting parameter settings: 1500W fiber laser cutting machine settings: cutting power 1000W, cutting speed 2.5m / min, auxiliary gas nitrogen pressure 0.7MPa, focal position 0.5mm below the upper surface of the workpiece, suitable for the cutting rhythm of small batch production; Fixed-length cutting: Automatic programming cutting according to the design length of 1620mm for the rear door frame. After cutting, the length of the workpiece is detected by a handheld length measuring instrument. The length tolerance is controlled within ±0.3mm. The first piece is 100% inspected, and 1 piece is randomly inspected every 10 pieces thereafter.

[0029] S4: Precision punching Die replacement: Replace the quick-change punching die of the five-axis CNC punch press with a universal die frame and replaceable punch / die structure. Only replace the φ8mm and φ10mm punches and dies that match the current door frame. No tooling is required for replacement. Replacement time is ≤7min. The die clearance is adjusted to φ8mm:0.045mm and φ10mm:0.055mm. Workpiece positioning: The cut-off rear door frame workpiece is positioned by contouring of the cross section. Three pneumatic positioning pins + one pressure block enable quick clamping with a positioning accuracy of ≤0.04mm and a clamping time of ≤10s / piece. Punching process: Set the punching parameters: punching speed 10 times / minute, punching force φ8mm: 75kN, φ10mm: 95kN, complete the punching in the order of "small hole first, then large hole", and check the hole position accuracy immediately after punching the first piece; Hole position inspection: The hole position of the first piece is inspected using a handheld hole position inspection gauge. The hole position tolerance is ≤0.1mm. Subsequently, 1 piece is randomly inspected every 5 pieces to ensure punching accuracy.

[0030] S5: Edge Shaping Die replacement: Replace the quick-change flanging die of the 15T CNC hydraulic punch press. The toolless replacement method is also adopted, and the replacement time is ≤6min. The quick-change flanging die is compatible with the end overlap area contour of four types of door frames. Flanging: The punched workpiece is fed into the flanging die, quickly clamped, and the hydraulic press parameters are set as follows: main cylinder pressure 13T, slide descending speed 40mm / s, holding time 3s, to complete 90° flanging, with the flanging height controlled at 5mm (tolerance ±0.15mm); the blank holder pressure is adjusted to 3.5kN to prevent wrinkling caused by workpiece clamping deviation in small batch production; Shaping and inspection: Use a gap gauge to check the overlap gap to ensure that the gap is ≤0.6mm. The first piece is 100% inspected, and after confirming that there is no cracking or springback, it can proceed to the next process.

[0031] S6: Detect and store data First piece full inspection: After the first piece of the current batch is processed, a full inspection is carried out using a door frame four-in-one special inspection tool, and a three-coordinate measuring machine is used for precision measurement. After confirming that all accuracy indicators meet the design requirements, mass production begins. Batch sampling inspection: During mass production, 3 out of every 50 pieces are randomly selected for full inspection, with a focus on straightness, torque, hole accuracy, and overlap gap. Any unqualified pieces are immediately removed from production and the cause is investigated. Rust prevention and warehousing: After qualified parts are sprayed with water-soluble rust inhibitor, they are stored in small batches using a special rack, with ≤5 pieces per layer. They are scanned for warehousing and the production batch and changeover parameters are recorded to provide data support for subsequent production of the same batch.

[0032] In this embodiment, the entire changeover operation (including fixture and mold replacement + first piece debugging) can be completed within 28 minutes, which is far less than the 2-hour changeover cycle of the existing process. After the changeover, all the precision indicators of the door frames processed meet the design requirements, the assembly qualification rate is stable at 99.2%, the tooling investment cost is reduced by 50% compared with the existing process, and it perfectly adapts to the flexible production needs of small batches and multiple batches.

[0033] Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art and related fields based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention, unless otherwise specified or limited, shall be implemented according to conventional means in the art.

Claims

1. A multi-material composite molding process for a car door frame, characterized in that, Employing a multi-material zone matching design, the molding process is completed through a closed-loop continuous processing line, including the following steps: S1: Raw material pretreatment, including feeding, unwinding and leveling, tension relief and thickness detection of roll materials of different materials; S2: Parametric roll forming, using a multi-axis servo roll forming line to progressively roll and straighten the pre-treated raw material in real time with precision; S3: Online laser cutting, which performs fixed-length cutting and surface treatment on the shaped workpiece; S4: Precision punching, which uses a CNC punching machine to complete the punching of mounting holes and hole position detection on the workpiece; S5: Flanging and shaping, using a CNC hydraulic punch press to perform flanging and shaping inspection on the ends of the workpiece; S6: Inspection and warehousing. Full inspection and precise measurement are completed using special inspection tools and precision measuring equipment. After rust prevention treatment, the product is stored in the warehouse. The closed-loop continuous processing line consists of core processing equipment connected by a servo synchronous conveying mechanism, and the conveying process is equipped with workpiece anti-deformation lifting fixtures.

2. The multi-material composite molding process for a car door frame according to claim 1, characterized in that, The multi-material zoning design is as follows: the non-load-bearing area uses 1.0mm thick DC01 low-carbon steel, the secondary load-bearing area uses 1.2mm thick B340LA low-alloy high-strength steel, and the core load-bearing area uses 1.5mm thick HC420LA high-strength steel.

3. The multi-material composite molding process for a car door frame according to claim 1, characterized in that, The core processing equipment includes a 50-axis servo roller pressing line, a 1500W fiber laser cutting machine, a five-axis CNC punch press, a 15T CNC hydraulic punch press, a coordinate measuring machine, and a door frame four-in-one special inspection tool. The 50-axis servo roller pressing line is equipped with an adjustable pressure module and 12 universal forming rollers. The coordinate measuring machine has an accuracy of 0.001mm, and the servo synchronous conveying mechanism has an adjustable conveying speed of 0-6m / min.

4. The multi-material composite molding process for a car door frame according to claim 1, characterized in that, In the raw material pretreatment, the raw material is fed using a three-station hydraulic uncoiler. The uncoiler is equipped with a tensioning chuck, and the tensioning force of the chuck can be adjusted within a range of 60-80kN. The uncoiling and leveling process uses a 24-roll precision leveler. The gap between the upper rollers of the leveler is adjusted according to the thickness of the raw material, with an adjustment tolerance of ±0.02-±0.03mm. The speed of the lower roller is 3-5m / min. After leveling, the flatness of the raw material is ≤0.15mm / M.

5. The multi-material composite molding process for a car door frame according to claim 1, characterized in that, In the raw material pretreatment, tension elimination adopts a closed-loop or adjustable tension control system, the applied tension is 12-15kN, and the tension fluctuation is ≤±0.5-±0.8kN. The raw material is detected by an online laser thickness gauge or a handheld thickness gauge. If the thickness deviation of the raw material exceeds ±0.02mm, it is directly rejected.

6. The multi-material composite molding process for a car door frame according to claim 1, characterized in that, In the parametric roll forming process, the hydraulic system of the 50-axis servo roll forming line is preheated to 20MPa, and the roller temperature is controlled at 25-35℃ by the water cooling system. Different roll forming parameters are set for three different materials: DC01 roll forming pressure is 85-90MPa and roll forming speed is 5m / min, B340LA roll forming pressure is 105-110MPa and roll forming speed is 4m / min, and HC420LA roll forming pressure is 135-140MPa and roll forming speed is 3m / min.

7. The multi-material composite molding process for a car door frame according to claim 1, characterized in that, In the parametric roll forming process, the 12 general forming rollers are divided into three sections: the first three sections are leveled, the middle six sections are formed, and the last three sections are finished and straightened. The finishing and straightening process is equipped with dual laser displacement sensors to detect the straightness and torsion of the door frame in real time. The detection frequency is 10 times / second. After forming, the straightness and torsion of the door frame are ≤0.5mm / M, and the cross-sectional dimensional tolerance is ≤±0.2mm.

8. The multi-material composite molding process for a car door frame according to claim 1, characterized in that, In the online laser cutting process, a pneumatic linkage positioning fixture or a quick-change positioning fixture is used to position the workpiece. The positioning repeatability is ≤0.05-0.06mm, the clamping force is 6-8kN, and the laser cutting parameters are: cutting power 1000-1200W, cutting speed 2.5-3m / min, auxiliary gas is nitrogen, pressure is 0.7-0.8MPa, the focal point is 0.5mm below the upper surface of the workpiece, the length tolerance of the cut workpiece is controlled within ±0.3mm, and the end burr height is ≤0.05mm.

9. The multi-material composite molding process for a car door frame according to claim 1, characterized in that, The precision punching uses φ8mm and φ10mm precision punching dies, with the die gap adjusted to 0.04-0.055mm, the punching speed to 10-15 times / minute, and the punching force to 75-100kN. The punching sequence is "small holes first, then large holes; ends first, then the middle". Hole position detection uses a visual inspection system or a handheld hole position gauge, with hole position tolerance ≤0.1mm and hole diameter tolerance ±0.02mm.

10. The multi-material composite molding process for a car door frame according to claim 1, characterized in that, It is suitable for large-scale continuous production of a single door frame or small-batch, multi-batch alternating production of four types of door frames. When producing small-batch, multi-batch, the fixtures and molds adopt a tool-less quick-change structure with a changeover time of ≤28 minutes. After the changeover, the first piece passes the full inspection of a special inspection tool and a coordinate measuring machine before mass production. When the product is inspected and put into storage, it is sampled and tested in batches. The sampling ratio is 5 pieces out of every 200 pieces or 3 pieces out of every 50 pieces. All test data are automatically stored to form a batch quality report.