In the production process of all automobile stamping parts, the frequency of quality problems in the door inner panel is generally higher than that of other products, and the matching of the related door assembly and the white body is also prone to problems. In order to reduce the frequency of such problems in the production process, this article systematically summarizes the relatively common quality problems of the door inner panel stamping parts, and conducts in-depth analysis and research on the causes of the problems, formulates fundamental solutions and decomposes them to The key steps corresponding to the mold development process, so that engineers can systematically manage these issues during the mold development process.
With the rapid development of the automobile industry, competition among major brands has become increasingly fierce, and new models are launched faster and faster. At the same time, the past fixed mold development cycle is difficult to meet the actual needs of mold development. In particular, the door inner panel mold is extremely unstable during the development process, and it is difficult to debug and produce later, which affects the entire vehicle development cycle. The development and management specifications of the door inner panel mold can provide help for the subsequent model development of the door inner panel, shorten the mold development cycle, and manufacture new models more quickly and efficiently.
Main management direction of door inner panel mold development
Product design direction
The product design stage mainly verifies whether the product has defects, whether the formability is sufficient, and whether the product can meet the production stability. At this stage, it focuses on the problems that occur in the design stage of each vehicle model. The key classifications and concerns are as follows: ⑴Noodle defect management (figure 1). The focus is to standardize the product design errors, where the stamping die cannot be completed or where it is difficult to manufacture. ⑵Formability management. Carry out CAE analysis on the data in the product design stage (Figure 2), and combine with previous model cases to focus on the difficult positions of formability. ⑶ Product stability management. When designing the shape of the door inner panel, designers often neglect the production stability, resulting in on-site debugging that cannot meet the production requirements. This problem should be focused on management and control. The product design does not consider the robot’s grasping position as shown in Figure 3.
Figure 1 Flour defect caused product cracking
Figure 2 CAE analysis and comparison
Figure 3 Product design does not consider the robot’s grasping position
Mold design direction
The mold design of the door inner panel is mainly based on process design and structural design. In the process development stage, focus on issues and process arrangements are determined. In the structural design stage, the mold structure is simplified and standardized to reduce the weight of the mold and reduce the cost of mold development. At the same time, the mold surface is refined to make the research and debugging of the door inner panel easier, and the production efficiency is improved.
Mould manufacturing and debugging direction
The mold debugging method (draw bead, research and distribution, etc.) and verification method (first piece verification, process verification) are controlled. The mold debugging report (A) is shown in Figure 4.
Mold pre-acceptance direction
The key steps and processes of mold acceptance are controlled and confirmed (stability verification, profile scanning confirmation, napping trend evaluation, etc.). The key process of mold pre-acceptance is shown in Figure 5.
Door inner panel mould design technology management
⑴ The window frame is drawn deeply, causing frequent dark cracks.
⑵The rear part adopts a positive trimming and shaping structure, which causes the uneven trimming line of the lower part to be twisted.
⑶ There is no extra meat on both sides of the lower corner, causing serious corner wrinkles.
⑷The parting line design at the corner of the window frame is too tortuous, causing serious local wrinkles.
⑸There is no scrap knife in the middle scrap area, resulting in low drawing margin, frequent cracking during production, and process problems.
Process control points
⑴ The drawing direction is the vertical direction of the top surface as the punching direction.
⑵The drawing should be drawn to the end once, and the secondary drawing structure will be temporarily cancelled.
⑶ The corners are easy to wrinkle position to design more than meat.
⑷The lower part of the door adopts a repaired structure.
⑸The rupture knife is designed with a large punching hole in the middle of the drawing to enhance the forming margin.
⑹The position of tailor-welded welds shall be processed according to CAE analysis results.
Key points of mold structure
Figure 4 Mold debugging report (A)
Figure 5 Key process of mold pre-acceptance
OP10: Add guide keys for drawing die and blank holder to improve stability; Tailor-welded blanks do not use inserts for drawing, and are directly chrome-plated after entering the factory. ⑴Add a guide key between the blank holder and the die to improve the drawing stability; ⑵The working parts are all GGG70L, which increases the wear resistance; ⑶The frame-oriented form is adopted to improve the guiding accuracy and stability.
OP30: The shaping block is in the form of forgings, and a 5mm thick debugging pad is added to the bottom. The post-process pressing core adopts the design full-conformity form; the later stage adopts the processing avoidance form according to the die surface design; the shaping insert adopts the air-cooled steel structure to ensure the convenience of later mold debugging and prepare for the addition of standard backing plates for later molds.
Mold manufacturing debugging control
Manage and control mold processing, debugging methods (drawing bead, research and distribution, etc.), and verification methods (first piece verification, process verification). The castings of key parts must have inspection reports, and third-party inspections should be conducted if necessary to ensure that the quenching hardness of the mold and the quality of the overall castings are qualified. Detect the appearance of castings to confirm whether they meet the quality requirements, such as casting sand holes, casting pores, casting deformation, etc. The traditional number milling process can better reflect the design effect of the die surface of the door inner panel. The drawing die cannot be processed by the traditional rough machining → semi-finishing → finishing → rough grinding → quenching → fine grinding. Because the quenching process in the traditional processing technology will cause excessive mold deformation, which greatly reduces the effect of mold surface treatment. The improved processing technology should adopt the processing technology of rough machining→semi-finishing→quenching→finishing→grinding, and laser quenching can be used if conditions permit.
The difficulty in debugging the drawing die of the door inner panel is to balance the cracks and wrinkles. The debugging sequence is: (1) firstly adjust the size and position of the sheet; (2) adjust the pressure parameters such as forming pressure, blank holder force, ejection height, etc.; (3) confirm whether to adjust the process residual meat according to the cracking and wrinkling of the parts; (4) according to the blanking Adjust the height and position of the drawing bead according to the situation, and finally complete the debugging of the drawing die by optimizing the product fillet or changing the shape.
First round of commissioning
⑴The drawing die material of the inner panel of the door has a large flow rate, so the bonding surface of the material must be controlled by emphasis. Insufficient grinding rate of the material pressing surface and uneven feeding will cause the material flow to be difficult to control, as shown in Figure 6. The setting of drawbeads should follow the principle of internal tightness and external looseness. On the basis of the middle part of XY, 100% of the bonding rate of the inner side of the tendons is guaranteed.
⑵Before the mold is installed on the machine tool, the height of the ejector pin must be confirmed. The height of the ejector pin shall be positioned with the same ejector pin hole for height measurement, and the accuracy shall be controlled within ±0.1mm.
⑶Before debugging, confirm the material grade, material thickness, size, manufacturer’s information, and comply with CAE analysis data.
⑷ Debug with the ejection height and pressure ±10% provided by CAE. In order to ensure that the mold is not damaged, confirm whether the pressing surface is consistent after the die and the blank holder are in contact. If there is a problem, the ejection force must be increased in time to prevent wrinkles. The pleats crush the pressing surface.
⑸Wrinkle focuses on the corners and the door frame of the door with door frame, as shown in Figure 7.
In addition to cracks and wrinkles, the following points should be paid attention to in the first round of debugging:
⑴The side wall shrinks. The forming depth of most door inner panels is more than 140mm, which belongs to deep drawing forming. After forming, stamping parts have different degrees of shrinkage, which affects the sealing gap between the door and the side wall. It is important to confirm the shrinkage of the door, hinge and door lock.