Study On Final Forging Of Hollow Valve Based On Cross Wedge Rolling Preformed Blank

As one special form of engine valve, the current manufacturing processes of hollow valve mainly includes two processes:one is electric upsetting or extrusion plus forging plus drilling, that first uses electric upsetting or extrusion process to form solid valve, then deep drilling processing. This method has many processes, the production efficiency is low, the rough quality is unstable, and the drill wear is serious. The other is anti extrusion, according to the shape of the valve cavity, the steel core is fabricated as the upper die, and the die is extruded and forged into the valve product with the inner cavity by using the die. The method of forming the valve cavity is limited by the size of the steel core and extrusion pressure is too large, die wears quickly, and the production input is large, it is difficult to promote in the domestic. The way of using CWR to produce the preformed blank of hollow valve, then forming the parts of the hollow valve by forging process has the advantages of high production efficiency, good product quality, low processing cost and easy to achieve automation production, it can overcome the shortcomings of electric upsetting or extrusion plus forging plus drilling and anti-extrusion. In this paper, the final forging process of hollow valve based on CWR preformed blank was studied, analysis the influence of different preform shape and size on the final forging process and the final forgings and optimize it, the specific content include the following aspects:1)The design of the hollow tube blank in the preforming of CWR and the basic forming rule of the final forging forming process. According to the characteristics of CWR process and the shape and size requirements of the final forging, the hollow valve KT-483Q was putted as the research object, the preformed blank of the hollow valve was designed, and the final forging process was simulated by the finite element software and analyzed the processing which including the metal flow regularity, the effective stress and strain, and the distribution of the flow grid etc., and the forming mechanism of the final forging process of rough blanks was understood.2)The impact factors of the final forging process of the preformed blank and the failure modes in the final forging process. Take the hollow valve KT-483Q as the research object, the factors that affecting the final forging process of the preformed blank and the final forgings were simulated by the DEFORM-2D/3D, which including the volume compensation, the gradient of the end face, the ratio of height to diameter, the relative thickness ratio, the size deviation of the blank, the transition fillet radius, the core shaft length, the friction coefficient, etc. and the failure modes of simulation process were analyzed. And the results of the simulation show that the above factors have disproportionate impacts on the metal regularity, the effective stress and strain, the temperature distribution of the final forging process of the preformed blank and quality of the final forgings:the volume compensation is too small or the size deviation of rough blank is too large to cause mold cavity defects probably; Excessive volume compensation, high diameter ratio may lead the end of the rough blank,the transition fillet to fold in the final forging process; The convex core shaft length is not enough to guarantee the final forging cavity shape etc. Through the analysis of numerical simulation results, the design principle of the preformed blanks and the final forging die is obtained to meet the requirements of CWR forging process.3) Example verification. Choosing other types of hollow valves, according to the obtained design principle, the appropriate preforming blank and the final forging die are designed and the final forging forming process is simulated and the simulation results are analyzed to verify the accuracy and reliability of the design principle.The research for the final forging process of hollow valve based on CWR preformed blank was conducted in this article. The design principle of the hollow valve preformed blanks and the final forging die was determined to meet the requirements of CWR forging process. It lies the foundation for using the cross wedge rolling forging process to produce the preformed blank of hollow valve. It has the vital significance to the popularization and application of the cross wedge rolling forging process of hollow valve.