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 and multi axis numerical control laser cutting machines, The level and ability of domestic enterprises to produce automobile panel molds have been greatly improved, and even some enterprises have reached the world advanced level.


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


Since our manufacturing of large-scale precision molds started late, although we can rapidly improve our ability in processing hardware through procurement, there is still a big gap between us and foreign advanced mold manufacturing companies in terms of design and manufacturing experience accumulation, manufacturing process level, mold materials, etc. In recent years, our automobile mold market has gradually changed from Class A and class B to high-end precision and complex class C car molds along with the products required in the automobile main engine market. 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 technology research and development and innovation.


1. Establishment of design and commissioning experience data accumulation mechanism


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, whole process CAE analysis, rebound prediction and compensation, fine die surface design, etc. its purpose is to do everything possible to move the traditional late debugging of the mold to the design stage. During the mold manufacturing process, the machining accuracy is strictly guaranteed by means of white light scanning and other detection means. During the first round of mold commissioning, the process designer and mold surface designer are required to be on the site to analyze the causes of defects in the first mold test and determine the optimization scheme, and save the optimization process one by one, and finally record the final state of the mold, including the drawing bead, drawing fillet, surface gap change, surface over tension, etc., and finally save the entire mold surface to the database after photographic scanning. The strain thinning information of the actual parts is extracted by the grid strain measuring equipment as shown in Fig. 4, and compared with the CAE analysis results. These materials are continuously 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. Mold rough machining based on casting blank scanning point cloud

Limited by the domestic casting level, large-scale casting blanks often have the problems of deformation and uneven allowance, which leads to the phenomenon of poor safety and processing efficiency in NC rough machining. With the popularization and application of white light scanning technology, such problems have been effectively controlled. At present, the white light scanning equipment is mainly used to quickly collect the surface data of the casting and generate the processing blanks that can be directly used for NC programming. The processing efficiency is greatly improved by adopting the methods of large-diameter disk cutting, layered small cutting and fast feeding. 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 have found a problem: under the premise of very good precision detection, the mold clamping clearance, that is, the mold clamping rate, is not ideal when the mold is working on the press. The fitter still needs a lot of manual clamping work to ensure the dynamic clamping rate of the mold. Through analysis and summary, we have found several main factors that affect the mold clamping rate: quenching deformation after finishing, non-uniformity of punching plate thinning, and elastic deformation of the mold with the press table. In view of these factors, we take corresponding strategies, such as adopting the process route of finishing after quenching; In the design of die surface, the reverse deformation compensation is carried out according to the sheet thinning results of CAE analysis and the elastic deformation law of the press, and a good application effect is obtained in the production.


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


The process route of finishing after quenching can effectively control the quenching deformation of the mold, but it also brings some other problems, such as thinning of the hardened layer, low processing efficiency, and large tool consumption. Laser surface hardening (strengthening) technology is the development direction to solve related problems thoroughly. When the laser irradiates the metal surface, the material surface layer can be heated to a very high temperature in a very short time to make it undergo phase transformation. Due to the extremely short heating time, the cooling speed 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 the general heat treatment. The surface hardness after treatment is 20% - 40% higher than that of the general hardening process, and the wear resistance is increased by 1-3 times. The mold surface hardening treatment with temperature not exceeding 300 ℃, material of steel or gray cast iron, gm241, and the depth of hardened layer can reach o More than 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 surface wear-resistant life 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 hardening (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, the manufacture of such molds is bound to adopt a large number of advanced processing and measuring equipment. The introduction of these equipment must also promote the change and upgrading of the series of manufacturing processes and manufacturing processes. By optimizing the processing process route, we have conducted in-depth research on many problems affecting the mold processing efficiency and processing quality, and constantly improved our mold manufacturing level.