Effect of Tool Material and Process Parameters on Surface Conditions in Single Point Incremental Forming (SPIF) of Polymeric Materials

Abstract

Abstract Single point incremental forming (SPIF) is a relatively new process for forming sheet products. Typically, the sheet is clamped into a fixture and is incrementally formed by moving a hemispherical end-mill tool using a multi-axis CNC milling machine. The tool deforms the material in each pass until the desired geometry is achieved. Friction between the tool and the formed sheet can have detrimental effects on the final geometry. The increase in friction coefficient can result in a significant decrease in sheet formability due to excessive thinning and subsequent fracture. Additionally, tool rotational speed may also contribute to the surface roughness of the formed part. The interaction between the tool and workpiece materials over relatively small areas of surface asperity is typically where friction and subsequent damage take place. The purpose of this research is to study the effect tool rotational speed as well as tool-workpiece material interaction on the surface condition and formability of formed components. Three polymeric materials have been considered herein, namely polypropylene (PP), polycarbonate (PC), and polyvinyl chloride (PVC). Spindle speeds varied from 600 to 1800 rpm. Four tool materials were also investigated, namely stainless steel, copper 110, beryllium-copper, and thermoplastic syntactic foam. Full factorial design of experiments took place. The parts were allowed to form until fracture takes place. Subsequently, the height of the cone was measured and used as representation of formability. Additionally, surface roughness and asperity height distribution were analyzed using both profilometry and microscopy. The aim is to explore possible correlations between process parameters and surface condition and their effect on single point incrementally formed shapes.