FRICTION AND EXTERNAL SURFACE ROUGHNESS IN SINGLE POINT INCREMENTAL FORMING: A study of surface friction, contact area and the ‘orange peel’ effect

Abstract

This work studied the effects of step size, angle, spindle speed, and feed rate on the external surface roughening, orange peel effect, observed in single point incremental forming (SPIF). Experimental results were used to estimate models to categorize the extent of orange peel roughening based on visual inspection and on surface roughness measurements. Tests were performed at very high rotational speeds and feed rates and showed various influences on surface roughness, thickness distribution, and grain size. Friction at the tool-sheet interface was also studied with a completely instrumented tool that measured and recorded torsion and forming forces through deformation strains. Coefficients of friction for each part were determined and through statistical analysis, the influence of each of the following forming parameters was established: material thickness, formed shape, tool size, step size, forming speeds (feed rate and rotational speed), and forming angle. Multidimensional response surfaces were generated to show when and under what condition friction was minimized. A new contact zone representation for SPIF was also established. This formulation used common forming parameters and geometric considerations to determine the contacting zone between the sheet and the tool. Area models were proposed for both the tangential and torsional component of friction in SPIF.