The Research On Machining Methods Of Screw Rotors In Oil-free Screw Vacuum Pump

The oil-free screw vacuum pump has been widely used in industrial areas of semiconductor,medicine,grain drying,chemical and pharmaceutical,spatial simulation,and many other industries,which was due to its lists of advantages,such as wide pumping speed range,simple and compact structure,no friction between the pumping component(screw rotors of the fixed lead or gradational pitch),and no oil pollution,and so on.So,the dry screw vacuum pump is also an environmental one that suits the development of world economy and energy saving.However,the machining for screw rotor is always a challenge,as the manufacturing technology falls behind in our country,which leads to the industry of oil-free screw vacuum pump developing slowly and depending on imports.Currently,the machining for screw rotor has gained much more focus from research units and companies.So,it is necessary and desirable to research the processing methods of screw rotor.On account of the machining for screw rotor,this paper mainly analyzes and researches the processing methods of screw rotor based on from milling method and five-axis NC machining method.The fixed-pitch screw rotor is mainly research object when the forming milling method is analyzed in this paper.In this step,the machining principle and process of forming milling method have been learned.And the most important issue is to design formed cutter.In order to design the formed cutter,much work has been done in this paper,including analyzing the helical surface of screw rotor and calculating the normal of it,building relationship between the coordinate system based on screw rotor and the coordinate system based formed cutter,inferring the contacting relation between helical surface of screw rotor and rotative surface of formed surface based on vertical relation between the normal of helical surface and the tangent of formed cutter circle in the coordinate system based on screw rotor.Then the parameters(t,?)deciding the profile of formed cutter have been solved out.In the end,the article gets the theoretical equation of calculating the profile of formed cutter in the coordinate system based formed cutter.Five-axis NC machining method is a universal processing method,which can perform the machining of various screw rotors.Aiming at getting qualified screw rotor smoothly,the five-axis machine tool and cutting tool have been confirmed,cutting parameters and other data have been inferred and calculated.Then according to the given fixed-pitch screw rotor(which has been slotted)and the double-thread screw rotor,this paper plans and analyzes the machining stage of screw rotor,divides helical surface to different areas,then establishes manufacturing procedures of every areas based on UG(a CAD/CAM software),at last,gets the cutter paths of every areas.In order to verify the feasibility of five-axis NC machining method,the paper uses VERICUT software to simulate the machining process of screw rotor.In the simulation process,the motion model of machine tool,blank model and cutter tool model have been established,then the cutter path has been added.After these work,this article gets the simulation result of machining screw rotor.Because the process of referring theoretical equation of the profile of formed cutter is not influenced by profile of screw rotor,and five-axis NC machining method has strong universality,so these two machining methods of screw rotor are not confined by profile of screw rotor.