| Automobile industry is main in our country's economy. With drastic market competition, reducing cost and raising quality have become very important. The precise forging technology is one of effective methods which can reduce cost and raise quality. Cold extrusion belongs to precise forging, and is among the best process of the Net Shaping in material forming. It has high manufacture precision, stable quality and is suitable for production in bulk. Another advantage of cold extrusion lies in products themselves, especially surface and a subsurface of the parts can keep the cold-harden appearance. Its residual pressure stress of surface not only can raise the hardness and the strengths of the materials, but also can raise fatigue life of parts.With the development of computer technology and the maturity of FE theory, the application of computer simulation technique permeates everywhere. Volume forming numerical simulation's application on precision forging technique is a surmount progress in precision forging process. With the FEM simulation technique, the whole deformation process can be displayed on the computer, and the data got from simulation can be applied directly on practice experiments. It can not only save much material prepare , but greatly shorten manufacturing cycle .Spline is usually employed for circumferential orientation of part, such as gear and pulley, and torsion transmission, as well as axial orientation and axial motion. The cold extrusion of spline has less time ,more hardness and strength than other manufacture methods. There are many key parameters in the cold extrusion processof spline. These parameters have important influence on the products quality. The finite element software DEFORM can optimize these parameters.The dimensional accuracy of the cold forged products is strongly dependent on the elastic characteristics of the die. Therefore, a design method that makes the the pre-stressed die with interferences has been proposed for precise cold forging. For the design, Lame's equation is used and the diameter ratios and interferences are determined by using the maximum inner pressure without yielding of rings after shrink fitting and during cold forging. The cold extrusion combined dies program has been developed, the program uses the VBA technique based on AutoCAD ActiveX. With the aid of the software MSC.MARC, the finite element method is adopted to analyze the combined dies in regard to contact linearly under two different conditions respectively. One is under the fitting pressure merely, and the other is under inner pressure. The corresponding regularity of deformation and stress distribution are derived, which are coincident with the program results. This study provides the technological support for the structure optimization of multi-layer combined dies.Summing up all above content,the author builds the model with UG, simulates the forming process with DEFORM, develops the"Cold Extrusion Combined dies Compute Aid Design"program, and has done some experiment. The research model comes from Nan Jing YUEJIN Car Corporation. The research content includes:1. The author analyzes the cold extrusion process of spline shaft and researches on influence of work piece diameter, lubricate, work piece hardness, half angle of entrance, ligament on spline shaft extrusion forming. The author also analyzes phenomenon of axial destabilization and upsetting problem in the process of cold extrusion, especially long shaft.2. The author optimizes the key parameters of spline cold extrusion with DEFORM software. The author discusses the following situations in the process of cold extrusion: friction coefficient 0.12 and 0.20, ligamentlength 4mm,6mm,8mm,10mm, work piece diameterФ59.4mm andФ59.0mm, half angle of entrance 20°, 30°,40°. The author analyzes loads, velocity field , stress and strain. Finally, the author confirms these parameters which make the least extrusion force and the best quality.3. The author analyzes the calculations of the combined dies, and develops a program with VBA based on AutoCAD ActiveX. The author calculates the combined dies dimensions with the program by the simulation results of DEFROM and optimizes each layer dimensions and interferences between layers with MSC.MARC.4. The author designs and draws the part and assembly drawings, and manufactures the dies. Lastly, the author successfully makes the products on the YB32-200T press machine.Parameter optimization and numerical simulation based on experience knowledge of practical production are proved to be correct by the results and can be used to direct the practical production. |
