Brief analysis on die manufacturing technology of automobile panel

At present, the gap between the main processing hardware of domestic mainstream automobile mold enterprises and the international level is rapidly narrowing, which is mainly reflected in the fact that in recent years, domestic automobile mold enterprises have purchased a large number of advanced numerical control equipment, including three-axis to five axis high-speed machining machines, large-scale Longmen numerical control machining centers, advanced large-scale measurement and debugging equipment, multi axis numerical control laser cutting machines, etc, The level and ability of domestic enterprises to produce auto panel dies have been greatly improved. Some enterprises have even reached the world's advanced and synchronous level.

The improvement of processing capacity also promotes the improvement of processing technology. At present, the numerical control machining of automobile mold has developed from simple profile machining to comprehensive numerical control machining including structural surface; The foam solid mold used for casting has developed from manual manufacturing to integral layered NC machining; A large number of high-speed NC machining for high efficiency, high precision and high surface quality are adopted; From the traditional manual processing according to the map, the current processing mode of no map, few people or even unmanned has gradually formed.

Since we started manufacturing large-scale precision molds late, although we can rapidly improve our ability in processing hardware through procurement, there is still a large gap compared with foreign advanced mold manufacturing companies in terms of accumulated design and manufacturing experience, manufacturing process level, mold materials, etc. In recent years, our automobile mold market has gradually changed from A-level and B-level products to high-end precision and complex C-level car molds, and we also pay more and more attention to the technical improvement in these aspects. However, these aspects are technical secrets for any advanced mold enterprise, and we have to rely mainly on independent technological research and innovation.

1. Establishment of data accumulation mechanism for design and commissioning experience

Continue to explore the fine design mode in the early stage of mold development. The so-called fine design mainly includes: robust and reasonable stamping process design, full process CAE analysis, springback prediction and compensation, fine die surface design, etc. its purpose is to do everything possible to move the traditional mold late commissioning work to the design stage, and strictly ensure the machining accuracy through white light scanning and other detection means in the mold manufacturing process. During the first round of mold commissioning, process designers and mold surface designers are required to be on site to analyze the causes of the defects of the first mold trial and determine the optimization scheme, and save the optimization process one by one. Finally, the final state of the mold is recorded, including drawing ribs, drawing fillets, surface gap changes, surface over tension and so on. Finally, the entire mold surface is saved to the database after photographic scanning. The strain thinning information of the actual parts is extracted by the grid strain measurement equipment as shown in Figure 4, and compared with the CAE analysis results.

These materials are constantly accumulated, sorted, analyzed, archived and modified, and finally summarized into the design experience database of the enterprise, which will be applied in the design of similar workpieces in the future.



2. Rough machining of mold based on scanning point cloud of casting blank

Limited by the domestic casting level, large-scale casting blanks often have problems of deformation and uneven allowance, which leads to the phenomenon of poor safety and low processing efficiency in NC rough machining. With the popularization and application of white light scanning technology, such problems have been effectively controlled. At present, white light scanning equipment is mainly used to quickly collect the surface data of castings and generate processing blanks that can be directly used for NC programming. The processing efficiency is greatly improved by using large-diameter disc cutter, layered small cutting, and fast feed. The empty tool walking is reduced by 100%, and the NC rough machining efficiency is increased by about 30%.



3. Die surface compensation based on sheet thinning and press elastic deformation

Through long-term mold development practice, we found a problem: when the mold is processed by high-precision numerical control, on the premise of very good accuracy detection, the mold clamping clearance, that is, the mold clamping rate we often say, is not ideal when the mold is working on the press. Fitters still need a lot of manual clamping work to ensure the dynamic mold clamping rate of the mold. Through analysis and summary, we found several main factors that affect the clamping rate: quenching deformation after finishing, the non-uniformity of stamping plate thinning, and the elastic deformation of the die with the press workbench. In view of these factors, we adopt corresponding strategies, such as adopting the process route of finish machining after quenching; When designing the die surface, the reverse deformation compensation is carried out according to the thinning result of the sheet metal analyzed by CAE and the elastic deformation law of the press, and a good application effect is achieved in production.



4. Apply laser surface quenching (strengthening) and laser cladding technology to reduce quenching deformation of dies

Adopting the process route of finish machining after quenching can effectively control the quenching deformation of the die, but it also brings some other problems, such as the thinning of the hardened layer, low machining efficiency, large tool consumption and so on. Using laser surface quenching (strengthening) technology is the development direction to completely solve the related problems. When laser irradiates the metal surface, the surface layer of the material can be heated to a very high temperature in a very short moment to make it phase change. Due to the extremely short heating time, the cooling rate of the material surface is very high, about 103 times that of the general quenching cooling. Due to the above characteristics, the laser surface strengthening layer has different properties from general heat treatment. The surface hardness after treatment is 20-40% higher than that of general hardening process, and the wear resistance is increased by 1-3 times. When the temperature is not more than 300 ℃, and the material is steel or gray cast iron, gm241, the surface of the mold is hardened, and the depth of the hardened layer can reach more than 0.5mm, and the hardness can reach more than HV800. The microstructure of quenched hardened layer is ultra-fine martensite and carbide. According to the specific working conditions and materials, the wear-resistant life of the surface after laser quenching can reach 5 ~ 10 times, and the most important thing is that the deformation after quenching is much smaller than that after flame or induction quenching. The application of laser surface quenching (strengthening) technology is affected by the use cost, quenching efficiency and other factors. At present, it is only a small-scale application attempt.

5. Conclusion

Based on the characteristics of precision, complexity and single piece production of large-scale automobile molds, advanced processing and measuring equipment are bound to be widely used in manufacturing such molds. At the same time of introducing these equipment, we must also promote the change and upgrading of series manufacturing processes and manufacturing processes. By optimizing the processing route, we conduct in-depth research on many problems that affect the efficiency and quality of mold processing, and constantly improve our mold manufacturing level.