Design Of The Machine Tool For Trapezoidal Internal Thread Formation By Cold Extrusion With Auxiliary Vibration And Experimental Study

With the development of nuclear power industry,as well as the increase of nuclear power units under construction in China,the market demand for nuclear-level mechanical and electrical products is growing rapidly.Nuclear-level valves currently used in nuclear power plants in China mainly rely on imports.In particular,nuclear-level valves with trapezoidal internal threads are all dependent on imports,because the fatigue life of stainless steel trapezoidal internal threads in the cap cannot meet the service life standards of nuclear-level valves.Its processing technology is strictly locked by foreign countries,which leads to a technology subjugation and monopoly.In view of this situation,this paper presents a new method of stainless steel trapezoidal internal thread formation by cold extrusion with auxiliary vibration,successfully achieved the process of nuclear-level stainless steel trapezoidal internal thread formation by cold extrusion with auxiliary vibration.The main work done in this paper and the achievements made are as follows:(1)By analyzing the forming mechanism and forming process of the traditional cold extrusion process of internal thread,combined with the principle of vibration machining,the machining principle of internal thread formation by cold extrusion with auxiliary vibration is elaborated.Based on this theory,four modes of vibration application and three modes of vibration source delivery are analyzed in detail.(2)The mechanical structure of the machine tool for trapezoidal internal thread formation by cold extrusion with auxiliary vibration is designed in detail.According to the design basis,the overall structure plan of the machine tool is drafted,the main movement of the machine tool,feed movement and excitation device are designed and analyzed in detail.(3)The control system of the machine tool for trapezoidal internal thread formation by cold extrusion with auxiliary vibration is designed in detail.According to the actual machining requirements of the machine tool,the overall design scheme is put forward.Next,the hardware design and software design of the machine tool control system are respectively carried out.Finally,the machine control system is debugged.(4)Trapezoidal thread extrusion tap and its fixture are designed.The cross-section,extrusion,thread parameters,material and coating of extrusion tap are designed and analyzed in detail.At the same time a double-locking squeeze tap chuck is designed,to ensure that the extrusion tap can be fixed in the tap chuck stability during the processing.(5)A stainless steel trapezoidal internal thread formation by cold extrusion with auxiliary vibration experiment is carried out on the self-developed machine tool for trapezoidal internal thread formation by cold extrusion with auxiliary vibration by using the trapezoidal thread extrusion tap which was also self-developed.Results show that this method achieves percentage of thread up to 93.2%.Surface micro hardness reaches over 300 HV.Surface roughness of the teeth is Ra0.53μm.Compared to traditional turning method,the internal thread manufactured by cold extrusion with auxiliary vibration has great improvement on tooth-shape and surface quality,which meet the design quality requirements of nuclear-level products as well.