Experimental Investigations on the Machining of the Circular Profile Using Hermite and NURBS Interpolators by MACRO Programming Method

Abstract

CNC machines are required to enhance the quality of a product at a reasonable cost. Profiles like turbine blades, dies, car bodies, aerofoil models and vanes are usually to be machined on a CNC machine. Preparatory codes on CNC machines provide automation but restricted with a capacity to machine linear and circular interpolators (G01 and G02 or G03). Hence, due to the non-availability of appropriate preparatory function, CNC machining of these curved shape components causes difficulty. The CAD/CAM systems divide the profile into the numbers of small linear segments. The transmission of the linear segments is subjected to errors between CAD/CAM and CNC systems. It results in lost data and noise. The discontinuity of the curved toolpath deteriorates the surface quality and shape accuracy due to linear segments. To reduce the deviation of the toolpath, the numbers of linear segments are to be increased. Each linear segment to be machine is adding a single block in the part program. It will lengthen the part program and add to the program memory size at the cost of the surface quality. To achieve better shape accuracy, parametric interpolation (i.e. MACRO programming) is required. In the present work, NURBS, as well as Hermite interpolators, is attempted to machine regular axis-symmetrical profile (i.e. circle) using explicit functions. The curved profiles machined by MACRO and conventional programming methods are examined to measure surface quality using surface roughness tester (i.e. Mitutoyo SJ-210®), while toolpath deviation is examined with the actual profile plotted with CAD software (i.e. AutoCAD®).KeywordsCNC millingNURBSHermite curveMACRO programmingShape accuracySurface roughness