| Screw parts are widely used in many industrial fields,such as machinery,chemical industry,petroleum and others,and play a crucial role in related equipment.With the exploration of the materials characteristics and processing technology,more and more special requirements were proposed to develop a variety of special-shaped screw.The variable diameter,lead and groove-depth shaped screw is a kind of complex shaped screw with three variable parameters.This kind of screw parts are difficult to machine because the surface is complex and the quality is influence by the combined effects of the geometrical parameters of screw,cutter parameters and machining parameters.The current research mainly focused on the screws with two variable parameters which were fabricated through the 4-axis or 5-axis CNC milling machine.Although the multi-axis machine tool can realize the high efficiency and high precision processing,the cost of the machine tool and the complicated working procedure limit its promotion in the domestic small and medium-sized enterprises.Whirling is a kind of milling method with several standard machine tools mounted on a high-speed rotary cutter,which can be classified as inner whirling and external whirling.In terms of the inner whirling,because the large diameter of the cutter head,the cutting speed is high,and the contact line of the tool rotating surface and the workpiece surface is relatively long.Therefore,the cutting process is stable with high surface finish,so it commonly used in screw manufacture.In addition,as the whirling machine can be reformed from ordinary CNC lathe at a low cost,it has a better prospect of application in the small and medium-sized enterprises.Based on the above two points,this paper proposes to study the processing of variable diameter,lead and groove-depth screws with 3-axis whirling machine.Based on the study of the configurational characteristics of the screw parts,this research is expected to discuss its whirling method,form a theoretical error model,and provide a new method for NC milling of the variable diameter,lead and groove-depth shaped screw parts which is a new idea for the high efficiency and low cost processing.To be specific,firstly,the geometric models of the variable diameter,lead and groove-depth shaped screw surface and tool rotating surface are established based on the principle of screw forming.Then,on the basis of spatial engagement theory,the spatial envelope condition formula of 3-axis whirling has been derived to analyze the limitation of space envelope method used on 3-axis whirling machine.According to these,the theoretical error model of section envelope method is established and thecalculation method of cutter location is optimized.After these,the method of cutter path planning is further discussed.Finally,based on the above theoretical research,a machining simulation system based on the UG and MATLAB calculating modules which are related to entire calculation process have been developed.In order to verify the whole process,the experiment of a extrusion screw model is carried out which proves the above theory and proves that the 3-axis whirling can be used to machine variable diameter,lead and groove-depth screws. |
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