Machining of elliptical curve profile for application in manufacturing industries

Abstract

Manufacture of products with freeform curves is the need of the day in manufacturing industries like turbine blades, automobile bodies, aerofoils etc. Such profiles are usually manufactured on high precision machines. High precision (CNC) machines are required to enhance product quality at a reasonable cost. CNC programs with preparatory codes (G01, G02, or G03) provide automation, but the machines are restricted to the ability of linear and circular interpolators. Hence, due to the unavailability of appropriate preparatory function, machining of these curved shaped components causes difficulty on CNC machines. The CAD / CAM software divides the profile into the numbers of small linear segments. The transmission of the linear segments from software to CNC machine is subjected to errors. It results in noise and lost data. The discontinuity of the freeform toolpath deteriorates the surface quality and shape accuracy due to linear segments. To enhance the shape accuracy and surface quality, the numbers of linear segments are to be increased. Each linear segment to be machined is adding a single block in the part program. It will increase the size of the part program and program memory size at the cost of the surface quality. To achieve better surface quality and shape accuracy, MACRO programming is required. In the present work, the freeform regular axis-symmetrical profile (i.e. ellipse) is machined on mild steel (MS) and aluminum material using NURBS as well as Hermite interpolators. 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®). Radial and chordal errors are the least in the case of NURBS interpolation compared to Hermite interpolation. A better surface finish is observed while the elliptical profile is machined on mild steel and aluminium with MACRO programming