Research On CNC Grinding And Milling Performance Of Ball End Mill

Ball end mills are extensively used in machining of various kinds of surfaces for mold,automobile and aviation manufacturing.The spherical cutting edge on the ball part of mill directly affects the cutting performance and the tool life.Recently,the efficient and accurate method of CNC grinding for the ball end mill has attracted considerable critical attention in industry.The ball end mill with planar rake face in fairly use can hardly adapt to today's diverse processing requirements.More complicated structures of ball end mill products are explored.But,they may inevitably rely on numeric approximation and controversial accuracy.This paper presents an adaptive and intuitive method for end mill rake/clearance face modelling.The rake face is a developed ruled surface to fulfill the desired normal rake angle.A simple and strict procedure for rake angle calculation is detailed,in the terms of surface curve frame,a basic conception in the differential geometry.Each straight generator on the rake face is the instantaneous contact line on the profile of 1A1 grinding wheel in the relative motion sequence.Just as the normal vectors of the wheel profile coincides with that of the mill surface on the contact point,the rake face of end mill can be determined.Revolution surface of the bottom curve on the rake face avoids the interference between the wheel with the designed rake face while machining.There are two types of clearance faces in both concave and flat-shapes to be designed.One clearance face is ground by the outer circle and the other is ground by the side-face of 11V9 cup wheel.The former method is similar to the rake face grinding to generate a ruled clearance surface with a constant clearance angle;the latter has a character of approximate straight generator.Moreover,the equidistance curves of the cutting edge on the sphere are deduced from the geodesic curve to adjust position of the cutting edge.Using the proposed modelling method as a platform is the very helpmate of model modification and performance amendment.A practical example of ball end mill grinding is detailed,using 5-axis CNC grinder model PTG-6 produced by Star cutter Company.A software package,including three function blocks,the structure deign,process planning and grinding process,is developed by MicrosoftVisual C# for machining ball end mill.The 3D grinding simulation is carried out by commercial software VERICUT.As an example,two computation procedures of the discrete data,that is equidistance parameter increment method and equidistance chord method,are compared.The simulation results show that the latter method is more effective and robust than the former one under the same computational accuracy.The measurement results show that the average value of profile tolerance for the spherical cutting edge is 0.01 mm inspected by the tool measuring instrument Zoller Genuis3.That is less than the requirement tolerance of GB Standards for the ball end mill.Its validity is verified by good agreement between the results computed and the data measured.The on-line machining tests show that the newly designed mills have the same grade of milling forces and wear,compared with the standard mill.