Quality assurance measures for stamping parts
The stamping process is the first manufacturing link of the whole vehicle, and its product quality directly affects the quality level of the subsequent process. Many OEMs have listed the quality of stamping parts as a key improvement and guarantee item. How to design high-quality stamping parts in the product development stage?
Early stage of SE analysis
The focus of SE analysis includes part formability, manufacturability, positioning and tolerance accuracy, etc.
1. Formability analysis
Formability analysis is to analyze problems such as product cracking, wrinkling, slip line, impact line and springback deformation, and provide solutions.
The formability analysis mainly includes: whether the part has negative angles, avoiding sharp corner forming (for example: in order to ensure the formability of the part, no sharp corner transitions should appear in the transition area between the back door and the rear taillight), and the choice of symmetrical shape for the outer cover part ( Avoid slip lines during the forming process), the height of the inner/outer curvature of the workpiece (to avoid the occurrence of cracking/wrinkling of the flange), the angle of the flange (usually 90°~105°), the edge of the flange For the change of the hemming shape of the workpiece (the change area is greater than 30mm) and the sharp corners, pay attention to the hemming width (usually the height is not higher than 3-5mm), etc.
The review of the difficulty of forming mainly includes: appropriate splitting of large parts and changing the shape of the part (such as: try to ensure that the part is formed in a straight line, and then choose a large arc transition; try to choose one ridge line for the four doors to cooperate with each other; Eliminate the springback of the part and increase the springback rib; reduce the design forming depth and avoid sharp changes in shape, etc.).
2. Process determination
The stamping process needs to check the part process arrangement and trimming angle; analyze the problems of poor trimming, excessive burr and too long in the later stage, and give solutions; review the applicability of the line body arrangement, etc.
(1) Requirements for forming conditions: principal strain of drawing: outer plate > 0.03, inner plate > 0.02; thinning rate < 0.2; wrinkling: outer plate A-level surface 0%, inner plate < 3% of material thickness;
(2) Requirements for trimming conditions: See Table 1 for the minimum angle requirements for vertical cutting. See Table 2 for the angle requirements of bevel trimming. The requirements for punching conditions are shown in Table 3.
3. positioning analysis
The selection of RPS datum should meet the 3-2-1 (or N-2-1) principle and the principle of coordinate parallelism and unity. The RPS point should select a part with sufficient rigidity and no deformation; it should be parallel to the coordinate line of the vehicle as much as possible, and should be selected at a position with the same cross-sectional shape (changes in the cross-section will easily cause deformation of the part, and it is difficult to locate accurately); The positioning direction of the surface is different, and the positioning datum hole should not coincide with the positioning datum plane as much as possible (90° in theory); in order to reduce the positioning error, the datum should be kept consistent during the subsequent production and use; in order to improve the quality of the product, the positioning The datum should also be selected as far as possible where the parts to be welded have fit requirements or functional requirements.
For the same parts, the positioning reference position should be unified as far as possible; the parts must be positioned independently without relying on the fit and positioning of adjacent parts; for parts with poor rigidity, additional positioning points can also be added to meet the positioning of the parts Stability requirements.
4. Tolerance accuracy determination
The quality requirements of different parts of the parts are different, and the tolerance accuracy requirements are also different (for example, the flange contour tolerance of the outer panel that affects the body clearance is generally ±0.5mm or ±0.7mm, while the flange contour tolerance of other parts is ± 1.0mm or greater; the height tolerance of flanges with matching requirements is generally about 0.5mm, while the height tolerance of other flanges is above 1.0mm). Since the outer cover affects the appearance quality of the vehicle, the size and appearance requirements are stricter than other structural parts. The car body is divided into A, B, C and D areas according to different areas. From A to D, the quality requirements are lowered in turn. The quality requirements for different positions of the same part are also different. For example, the accuracy requirements for reference holes and reference surfaces are higher, followed by assembly holes and mating surfaces, and other parts without matching requirements are lower (generally above ±1.0mm) . Tolerance design should be maximized under the premise of ensuring quality.
Process development and monitoring
1. Fixture development
It is usually necessary to determine the stamping parts of the inspection tool as:
(1) Important parts (such as outer plates, parts with special characteristics, etc.);
(2) The structure is complex, the precision is high, and the parts that cannot be detected by general measuring tools (such as the left and right front wheel covers, dash panels, floors, side wall inner panels, etc.) pieces);
(3) Parts that are difficult to form and prone to defects such as rebound and deformation (such as B-pillars, door inner panel reinforcement panels, anti-collision beams, etc. are prone to rebound and quality defects, and the material yield strength exceeds 340 MPa );
(4) Parts that have had problems in the debugging process of previous models or have affected the lap joint and body precision (such as parts such as fuel filler, top cover rear beam, door sill beam and rear section of the door sill beam, etc.).
Technical requirements for the inspection tool: The positioning surface, support surface and clamping point of the inspection tool must be set according to the RPS system in the product part drawing; the accuracy requirements are the position of the reference hole ±0.05mm, the diameter of the reference hole, the outer diameter of the positioning pin, and the reference Surface position degree ±0.10mm, reference plane parallelism/perpendicularity 0.05mm/1000mm, marking pin hole position degree ±0.10mm, marking pin outer diameter tolerance, shape or model knife-shaped surface error ±0.10mm, base plate parallelism /Perpendicularity 0.05mm/1000mm.
2. Mold development
(1) Equipment requirements
①The forming force of the part should account for less than 75% of the output capacity of the equipment, and the forming force stroke meets the curve requirements of the output force of the equipment;
②Equipment parameters meet the mold installation (not beyond the work table, less than 50mm below the work table);
③The closed height is within the required range of the equipment (usually the limit size is reserved for 10-20mm);
④ Offset size ≤ 75mm;
⑤ The stroke of the ejector pin, the pressure of the arranged air cushion/the adjustment of the slider, etc. meet the requirements of the mold;
⑥Repeat positioning accuracy of mobile workbench <0.05mm;
⑦The parallelism between the workbench and the slider is <0.12/1000; the perpendicularity between the stroke of the slider and the workbench is less than 0.3/150.
(2) Supplier selection
During the supplier inspection process, while ensuring that the hardware meets the development requirements, more emphasis should be placed on software confirmation (development capabilities, system operation, and quality assurance capabilities, etc.), and attention should be paid to collecting other customers' evaluations of suppliers. In the process of supplier selection, suppliers should be selected according to the difficulty of molds or parts, and the subcontracting of molds or parts should be carried out by considering the specialties of each supplier.
For the outer panel parts, select internationally renowned or domestic first-class suppliers for development, such as Germany's Barz, Japan's Miyazu, Dongfeng Mold and Tianqi Mold, etc. For high-strength plate parts, suppliers with rich development experience and successful cases can be selected. During the development process, the suppliers of Volkswagen, Toyota, Honda, and Hyundai are mainly considered, and the resource collection of suppliers is paid attention to.
(3) Process monitoring
After signing the contract, the supplier is required to pass on the development plan signed by the project manager, and the supplier is required to make regular progress reports before putting into production.
After the real model is put in, the supplier is required to add photos in the regular progress report process to ensure the authenticity of the progress.
Conduct inspections on suppliers from time to time, evaluate suppliers based on the inspection results, and copy the evaluation results and improvement suggestions to the senior leaders in charge, and inform that the evaluation results will be used as the assessment basis for subsequent cooperation.
When the project is abnormal, on-site supervision is required, and the on-site engineer (SQE) must report the work progress every day, and inform the supplier's senior management of the project progress and abnormal situation, so as to get better support.
(4) Die technical requirements
The rounded corners of the drawing die concave die R>(6~10) times the thickness of the material; the CH hole should be set on the plane as much as possible (the maximum angle on the slope should not exceed 5°); when the thickness of the high-strength sheet is >1.2mm, the blank holder needs Made into an insert structure; the insert is generally divided into blocks according to the 5° angle between the joint surface and the center of the mold; the seam is over a circular arc (10-15mm); the drawing die adopts a conforming guide form; the grinding rate of the outer plate is > 95% , The surface roughness is Ra0.8; the inserts in parts with severe material flow need special treatment (TD, PVD and laser).
Punching die: The pressing force is selected according to the upper limit of the design requirements (all the pressing force of the outer plate parts adopts the nitrogen cylinder); the guide device must be used when the edge is trimmed; when the thickness of the material is > 1mm, the side trimming must have a reverse side device; The structure of the matching part of the part must be compacted; the trimming edge of the part must fit within 15mm.
Flanging shaping die: Flanging top controller requires synchronization during work; the end exceeds the flange boundary by 5mm; anti-warping measures should be taken for the outer plate (such as turning both ends first); It is divided into two sequences to complete, and the joints of the two sequences must be overlapped by at least 20mm, and the length of the transition zone is 40-50mm.
In order to ensure the stability of the part, the flanging clearance meets the requirements in Table 4.
development process control
(1) Quality control of mold development
The method and structure of the mold in the early stage of mold development need to be reviewed by multiple parties and then put into production after passing the process.
Monitoring of casting quality: The material must not have defects such as pores, shrinkage cavities, shrinkage porosity, trachoma, cracks and sand.
Monitoring of machining quality: It is necessary to ensure the size and shape accuracy and surface roughness requirements of mold parts; distinguish between different processing methods, and reserve an appropriate amount of machining.
Monitoring of assembly quality (including the use of standard parts): each insert is assembled in place, the bottom surface is ground together no less than 80%, the seam gap is less than 0.03mm, the working surface is evenly colored, the positioning is accurate, and the fastening is firm (and there are loosening measures) .
Debugging quality control: ensure that the material of stamping parts is the same as that of mass production; the debugging equipment should try to use mechanical presses, and the number of debugging strokes is the same as that in production; during debugging, it is not allowed to apply lubricating oil; Wrinkles and other surface defects; for outer panels, no defects that affect the appearance quality are allowed to meet the phased quality goals.
(2) Quality control of inspection tool development
The pre-development structure of the inspection tool needs to be reviewed by multiple parties and passed before it can be put into production and processing.
Quality control of the base of the inspection fixture: the material meets the design requirements; the weld seam of the welded parts of the base must be beautiful and full, and defects such as virtual welding, missing welding and undercut should not occur, and welding spatter should be removed; the welded structural parts should be completely stress-relieved and annealed.
BASE board quality control: the flatness meets the design requirements; the roughness is Ra1.6; the coordinate line is required to be engraved on the bottom plate (the coordinate line marking must be complete), and it is extended to the inspection tool shape, and the error of the position of the coordinate line relative to the reference is 0.2 /1000; the depth and width of the scribing line are both 0.1~0.2mm (the scribing machine is required to scribing).
Shape quality control: After the lowest resin shape surface is processed, the thickness must be more than 60mm to meet the stability and reliability requirements of the inspection tool; for parts with lower flanging, the lowest point of the measurement point on the shape surface of the inspection tool is to the bottom The height of the upper surface of the seat platform is greater than 100mm; ensure the normal measurement of the steel ruler, surface difference gauge and gap ruler; the accuracy meets the design requirements.
The clamping seat is stable and firm; it can move freely without interference; the clamp adopts Jiashou and Jiahe standards.
Debug production stage
In the commissioning and production stage, reasonable testing points and testing standards can be formulated according to the stability of the workpiece, the conformity of the tolerance size, the degree of influence on the on-site production and subsequent customers, and the specific work is as follows:
1. Formulation of detection points
According to the actual loading situation and product requirements, formulate reasonable stamping quality inspection points.
The implementation steps are:
(1) According to the function of the stamping part itself, identify its key and important parts as one of the basis for the detection of stamping quality;
(2) Determine the key and important parts of the part according to the quality standard book of the part and the lap joint and positioning relationship in the welding process, as one of the items that must be inspected for quality;
(3) In the PT production process, pay attention to the changes in the parameters of the stamping production process, and summarize and record the quality instability points caused by the products as one of the mandatory quality inspection items; for the stable inspection points that have no impact on loading , which can be used as a production control point after review and verification.
2. Formulation of testing standards
Identify the parts that affect the accuracy of the body-in-white, make key rectifications, analyze the test data of the parts that do not affect the accuracy of the body, and revise the data based on the actual test values of the product.
Implementation steps:
(1) Collect the test data during the development process of the parts (from each batch of data of samples and PT1, and the average value of the test data of not less than 3 parts in each batch);
(2) Analyze the test data according to the same part and the same part, and determine whether the distribution of the data tends to a stable value;
(3) Revise and adjust the actual test value of the product according to the degree of influence of the historical data in the development process of the part on the customer, the welding and loading results of each batch of parts, and the distribution of the part data.
Finally, based on the revised data of the actual test value of the product and the final test point determined, the inspection reference book is revised and sent to the workshop.