I. Introduction
Automotive body panels refer to irregularly shaped surface and internal parts made of thin metal sheets that form the body or cab of a car, covering the engine and chassis. They serve both as decorative exterior parts and as load-bearing, shell-like components. The manufacturing of body panels is a crucial step in automotive body production. Exterior body panels include: four doors, two hoods, left and right fenders, left and right side panels, and a roof. Surface quality requirements stipulate that there should be no ripples, wrinkles, dents, scratches, edge scratches, or other defects that detract from the aesthetic appearance. Decorative lines and ribs on body panels must be clear, smooth, symmetrical, and have uniform transitions; the connections between lines between body panels must be seamless. This standard dictates that automotive body panel molds must also meet relevant standards, imposing higher requirements on dimensional accuracy and surface quality. An automotive body panel typically requires processes such as drawing, trimming, punching, and shaping/flanging to complete the stamping process. Therefore, automotive body panel molds are broadly classified into drawing dies, trimming and punching dies, and shaping/flanging dies, each set consisting of different parts. Specifically, the following are examples: drawing dies: punches, dies, blank holders, etc.; trimming and punching dies: punches, blank holders, trimming cutters, punches, etc.; flanging and shaping dies: punches, blank holders, flanging cutters (shaping cutters), etc.
II. Manufacturing Process
(1) Determination of processing technology. Processing technology is actually a broad category, ranging from how to clamp the parts to how to manufacture them, all of which are composed of individual process steps. Clamping requirements: The pressure plate must be pressed on the pad block. No more than two jacks are allowed to be stacked. Even if a shim cannot be placed under the pressure plate, a jack must be added for auxiliary support. When using a jack for auxiliary support, a dial indicator must be used to check the zero position on the mold, and then the jack is rotated to check if the dial indicator needle has moved. A complete and advanced process should include the following aspects: detailed name of the object to be processed; detailed tolerance and accuracy requirements; detailed processing steps; and strict verification procedures.
(2) Selection of Equipment Parameters. Advanced processing technology and equipment are the important foundation for improving productivity and ensuring product quality. CNC machining has evolved from simple surface machining to comprehensive machining of both surface and structural surfaces. Based on the experience of automotive mold manufacturing companies such as Toyota and COMAU, a processing mold production line consisting of 6 CNC machine tools can basically meet the development and manufacturing needs of the entire mold system. In terms of the actual situation in China, most of the machines currently used are Japanese Okuma Machine Tools, SNK, and domestic Shenyang Machine Tools. Roughing, semi-finishing, and finishing of molds should be completed on different machine tools because, considering their cost, different machine tools play different roles.
(3) Programming Strategy Selection. When data, equipment, and processing technology are relatively complete, the most important factor in determining the surface quality of the mold is the programming strategy. The tool path on the mold surface best reflects the quality. Here are some points: how to achieve a reasonable roughing method to improve efficiency and save costs; how to select processing methods for products of different shapes to improve quality. These two points are common problems faced by domestic panel manufacturers. Due to the increasing demands on product requirements and mold quality, most manufacturers have to face these issues. Taking the door outer panel drawing punch as an example, a comparison is made between roughing with a D50R25 ball end mill and a D63R8 bullnose end mill. The parameters are shown in Table 1:
Table 1 Comparison of various parameters such as cutting tools
The results in Table 1 show that, under the same conditions, the bullnose cutter is the most suitable choice for roughing compared to traditional ball end mills, improving overall roughing efficiency by approximately 32%, while also enhancing the machine tool's stress stability and safety. Here, we propose another concept for programming and machining cover parts: combining different machining methods based on shape characteristics and regional importance. Taking the front door outer panel drawing punch as an example, the drawback of using only parallel machining and three-dimensional offset machining is the creation of corner creases at toolpath corners, leaving obvious tool marks on the product surface, which is unacceptable for outer panel molds. While parallel machining generally yields good results, it can cause uneven toolpath step distances on steep walls, leading to incomplete machining of local surfaces and affecting mold surface quality. Based on the latest concept, different machining methods are combined for different locations. The front door outer panel drawing punch surface is achieved by combining 90° parallel machining of the product area with three-dimensional offset machining of the process supplementary surface. The results are excellent. Actual processing results show that selecting appropriate processing methods based on different parts and characteristics has the following advantages: uniform toolpaths in key areas, high surface quality, no creases, reduced tool wear, no obvious tool joint marks at multi-tool joints, and reduced machine tool load.
III. Conclusion
In conclusion, through the accumulation and research of new technologies and knowledge in automotive body panel molds, I have come to realize the importance of innovation and breakthroughs. For our country's automotive body panel mold industry to take a significant leap forward, we need a thirst for innovation, a spirit of innovation, and diligent exploratory efforts. Only in this way can our mold industry break free from outdated processes and conservative thinking. And only in this way can our country's machinery manufacturing industry reach a higher level.
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