Vice Chairman of China Mould Industry Association
Honorary Director, State Key Laboratory of Material Forming and Mould Technology, Huazhong University of Science and Technology
Li Zhigang
Mold is the basic process equipment of the automotive industry. More than 90% of the parts in the automobile production need to be shaped by the mold. It takes about 1,500 sets of molds to make a regular car, of which about 1,000 sets of stamping dies. In the development of new models, 90% of the workload is carried out around the change of the body profile. About 60% of the development cost of new models is used for the development of body and stamping processes and equipment. About 40% of the total manufacturing cost of the vehicle is the cost of the body stamping and its assembly.
In the development of the automotive mold industry at home and abroad, the mold technology presents the following development trends.
Mold three-dimensional design
     The three-dimensional design of the mold is an important part of the digital mold technology, and is the basis for the integration of mold design, manufacturing and inspection.
Japan's Toyota, the United States and other companies have achieved the three-dimensional design of the mold, and achieved good application results.
Some of the practices adopted by foreign countries in the three-dimensional design of molds are worth learning. The first is to separate the die face design from the structural design. The former adopts the surface design, the latter adopts the solid design; the second is to cancel the traditional 2D drawing, and give the 3D sketch and the plan sketch of the necessary size according to the needs of each process. The third is modular design, which greatly shortens the mold design time by standardizing the mold structure and establishing a three-dimensional standard parts library and a typical structure library. Some automotive mold manufacturers have also developed special 3D design modules for some typical and standardized molds such as drawing die, which further improves the design efficiency.
In addition to facilitating integrated manufacturing, the three-dimensional design of the mold is convenient for interference inspection, and can perform motion interference analysis to solve a problem in the two-dimensional design. The three-dimensional design of the mold can make the solid shape of the casting foam completely CNC machining, which improves the precision of the casting and creates conditions for subsequent fine processing. Since the result of the three-dimensional design is a three-dimensional model of the mold, the construction surface of the mold, such as the guide surface, the mounting surface of the insert, the screw hole, etc., can realize the programming of the numerical control machining, which is beneficial to improve the automation degree of the processing.
Simulation of the stamping process (CAE)
     In recent years, with the rapid development of computer software and hardware, the simulation technology (CAE) of the stamping process has played an increasingly important role. In the United States, Japan, Germany and other developed countries, CAE technology has become a necessary part of the mold design and manufacturing process, widely used to predict forming defects, optimize the stamping process and mold structure, improve the reliability of mold design, and reduce the test time. Many domestic auto mold companies have also made significant progress in the application of CAE and achieved good results. The application of CAE technology can greatly save the cost of trial mold and shorten the development cycle of stamping die, which has become an important means to ensure the quality of the mold. CAE technology is gradually transforming mold design from empirical design to scientific design.
Due to the application of CAE technology, GM Company of the United States predicts possible problems before the actual manufacturing of the mold, and improves it, greatly reducing the possibility of problems, so the test work can be completed in one week. The development cycle of the mold has been shortened by 80%, the mold development cost has been reduced by 50%, and the quality of the stamping parts has been greatly improved. Due to the breakthrough in this bottleneck, GM's new car product development capabilities have also improved, and now has the ability to develop 14 new models each year.
At present, commercial software for sheet metal forming analysis has a high success rate in predicting cracking and wrinkling problems, generally up to 80% to 90%, mainly because these softwares have higher accuracy in calculating strain. At present, there is still a need to further study the rebound problem. Because the stress calculation accuracy of these software is not high, the deviation during the rebound is predicted to be large, and sometimes the rebound calculation result in the opposite direction may occur. In addition, the forming analysis of all processes, the analysis of continuous forming, the formability analysis of difficult-to-shape materials, and the simulation of press line are all issues that need further research and development in the future.
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