Research On Screw Digital Modeling And CNC Milling

The screw pump belongs to the high precision mechanical product.In recent years,its application range is expanding,the demand is increasing,and the surface is becoming mere and more complex.The requirement of its machining precision is also improved,which brings some difficulty to the design and processing of the screw.And at present,the domestic high-end screw pump products are basically dependent on import.Therefore,the research on the design and processing of core components of the screw pump has a very important theoretical and practical significance.The research object of this paper is.the screw pair of the core components of a double screw dry vacuum pump.Contact theory,space envelope 'theory and tool design theory are used as tools.Based on the principle of screw configuration,Contact theory,space envelope theory and tool design theory are used as tools to set up a mathematical model of screw tooth profile.And on the basis of these,the performance characteristics analysis and processing of the screw are carried out.The main contents of this dissertation are shown as follows:(1)On the basis of studying the forming principle of cylindrical spiral surface,a mathematical model of single head pitch inner concave screw rotor is established.Determine the form of the curve of each section of the cross section of the screw and the equation of the screw surface.It lays the foundation for the research of the performance characteristics of the screw,the design of the screw machining tool and the studying of the milling process.(2)Based on the intermeshing theory of screw rotor,the expression of relative velocity in the coordinate system of the female rotor and the male rotor is derived.The equation of the contact line of the rotor tooth surface is established.The projection condition of the line of contact between the teeth and the rotation angle of the screw rotor in different coordinate systems is analyzed,and a formula for calculating the length of the line of contact between the teeth is deduced.According to the linear equation,the specific formula of area utilization coefficient and the formula of theoretical pumping speed are derived,and the factors affecting the area utilization coefficient and the theoretical pumping speed are analyzed.The optimum range of the ratio of the radius of the Involute generating circle with the root circle and the ratio of the root circle with the tip radius is obtained:0.5???0.3?1???0.6.And the practical plan to improve the speed of theoretical pumping is to improve the area utilization coefficient and screw speed.(3)According to the most general case of screw design,the tooth profile at cross section of screw is made up of discrete points.Based on the meshing principle,combined with the spatial location relationship between screw and cutter,the three spline interpolation method is applied to solve the tooth form of screw forming cutter.Analysis of the shape and space position of the line of contact between the two processes.The form-position geometric method is used to design the forming cutter.By comparing the design method with the meshing principle,it is concluded that the form-position geometric method can overcome the calculation error caused by the sharp point of the helical gear profile when designing the tool.By the way,the calculation process is more convenient,and the accuracy of the tooth profile obtained by the form-position geometric method is verified.(4)Combined with the theory of tool design,the optimal design of the tool structure is completed.Analyzes the movement and interpolation of each axis in the process of machining the screw of a forming cutter,and obtains the interpolation error and completes its path planning.At the same time,the possibility of using standard milling cutter for screw processing is put forward.The different interpolation ways of each part of the tooth profile at cross section of screw are arranged.The specific interpolation errors are analyzed,and the comparison between them is made,and their advantages and disadvantages are obtained.