| Practical applications of contour turning are found in the automotive (e.g., wheels, camshafts), biomedical (artificial bones), aerospace, and other manufacturing industries. Several challenges such as large cutting forces, excessive part deflections, localized vibrations, and difficulties in chip-management, are encountered while machining contoured parts. These challenges are caused due to the effects of the workpiece geometric variations on the metal removal mechanics. The geometric variations in contoured workpieces cause variations in the uncut chip-geometry and effective tool-angles, and consequently produce variations in the cutting forces and process stability along the toolpath. Therefore, the simple turning process-planning (cutting condition and tooling selection) strategies prove to be inadequate for contouring applications. In this research the effects of the workpiece geometry variations on the cutting forces and stability variations in contour turning are examined.; The workpiece geometric variations are classified into axial, radial, and combined axial-radial variations, and a mechanistic model is developed to study the effects of these variations on the cutting forces. The model is experimentally validated for both axial and radial contouring processes. The phenomenon responsible for the force variations are studied, and the combined effects of tool geometry, part geometry, and cutting conditions on the force variations in combined contouring are analyzed via a design of simulation experiments scheme. Strategies for attaining lower cutting forces and lower force variations in contour turning are identified.; The stability variations in axial contour turning are investigated via a frequency domain analysis. Three-dimensional stability-limit diagrams, third dimension being the toolpath, are generated for machining a workpiece with concave-convex contours. The reasons for the stability variations along the toolpath are analyzed in terms of the overlap factor (amount of regeneration) and the cutting stiffness variations. A mechanistic model based force-feedback scheme for disturbance rejection and tracking control in radial contour turning is proposed. The stability issues for the force-feedback design are addressed and the relative tracking performance of acceleration and force feedback controllers at various levels of process parameters (depth of cut, feedrate, etc.) are analyzed. |
