Using the Finite Element Method to Determine the Temperature Distributions in Hot-wire Polystyrene Cutting

Hot-wire cutting is a common material removal process used to shape and sculpt plastic foam materials, such as expanded polystyrene (EPS). Due to the low cost and sculpt-ability of plastic foams they are popular materials for large sized (> 1 m3) prototypes and bespoke visual artefacts. Recent developments in robotic foam sculpting machines have greatly increased the ability of hot-tools to sculpt complex geometrical surfaces bringing the subject into the realm of subtractive rapid prototyping/manufacturing. Nevertheless foam cut objects are not being exploited to their full potential due to the common perception that hot-wires are a low accuracy cutting tool. If greater accuracy for hot-wires can be obtained, it could provide a low cost method of producing high value functional engineering parts. Polystyrene patterns for lost foam casting are one such possibility. A nonlinear transient thermal finite element model was developed with the purpose of predicting the kerf width of hot-wire cut foams. Accurate predictions of the kerfwidth during cutting will allow the tool paths to be corrected off-line at the tool definition stage of the CAM process. Finite element analysis software (ANSYS) was used to simulate the hot-wire plastic foam cutting. The material property models were compiled from experimental data and commonly accepted values found in literature. The simulations showed good agreement with the experimental data and thus the model is thought to be reliable. The simulations provide an effective method of predicting kerf widths, under steady state cutting conditions. Limitations and further developments to the model are described.