Toward Better Formability of Polymeric Materials in Single Point Incremental Forming: Effect of Process Parameters

Single-Point Incremental Forming (SPIF) is a process for low quantity production or prototyping of sheet products. It involves a sheet secured in a fixture, formed by the downward forces of a hemispherical endmill tool in a CNC mill. Multiple passes of the endmill tool deform the material until the desired geometry is attained. This study examines several combinations of SPIF process parameters, namely initial wall angle, feed rate, and step-down size, and their effect on the formability of the formability. Three materials were examined, polycarbonate (PC), polypropylene (PP) and polyvinylchloride (PVC). The following are the ranges in which the forming parameters were varied: feed rate from 1000 to 2000 rpm, wall angle from 10° to 30°, and step-down from 0.1 to 1.0 mm. The parameters that are held constant are the sheet material, tool material and diameter, and spindle speed. Sheets are formed by a 12.5 mm diameter copper 110 tool that is fixed in the spindle with no applied rotational speed, i.e., the spindle can rotate freely. It was found that the increase in wall angle results in local decrease of the thickness along the sides of the formed shape. Also, the results showed that feed rate has no significant effect on formability; however, an anomaly was observed that suggests there could be a threshold value after which thinning would be more pronounced. In all cases, the results showed heavy dependance on materials thermoplastic properties, particularly each material’s glass transition temperature.