The Effect Of Interpolation Methods On The CNC Milling Quality

With the rapid development of manufacturing industry, kinds of curved surface have been used in aviation, automobile, ship and electronic industries, and the mainstream way of manufacturing complex surfaces is Numerical Control Machining. At present, most of the numerical control system use linear interpolation and circular interpolation. The processing paths are divided into segments of small lines and arcs, and feedback system controls the trajectory of cutting tool in order to approach the design shapes and sizes. Segments of small lines and arcs are continually refined to meet the requirements of machining precision, which results the lower productivity.In this thesis, the free surface was formed by the NURBS curve fitting, the influences on manufacturing precision are researched when the surface was manufactured using linear interpolation, circular interpolation and NURBS interpolation. The experiments were carried out to verify the theoretical results.Firstly, there different methods including the uniform parameterization method, the accumulated chord length parameterization method and the centripetal parameterization method were used to fit the NURBS curve according to a group of known cutter location data points. Based on the amplificatory local area images and the fitting error analysis charts, the fitting curve by the accumulated chord length parameterization method is closest to the original curve.Secondly, the node vector and the control points were calculated based on the NURBS curve construction method, and then the FANUC NC program was compiled. The aluminum block was manufactured by the CNC with FUNUC18i-MB system using linear interpolation, linear-circular interpolation and NURBS interpolation, and the surface contour was measured by the three-coordinate measuring machine.Through the comparative analysis, the results of academic and experiment are fitting well. The tool path of the NURBS could improve the accuracy of dimension and shape; better the quality of manufacturing and smooth of surface; reduce the workload of subsequent polishing and meet the requirement of good performance manufacture of the CNC; improve the processing efficiency. The code amount of NURBS interpolation reduced to 50%-80% than the line interpolation. The work in this thesis gives a novel idea for cured surface molding, the experimental verification of the academic result give the basis for the following development of manufacturing accuracy by path planning in the future.