Heat Assisted Single Point Forming of Polymer Sheets

The objective of this research is twofold; i) study the formability of thermoplastics using heat assisted single point incremental forming and ii) test the effectiveness of hot air for this application. A conventional process used for forming polymer sheets is thermoforming. In thermoforming, a plastic sheet is heated above its glass transition temperature and vacuum is used to draw the sheet into the die. Thermoforming requires dedicated tooling, heating and vacuum systems. An alternative method is single point incremental forming, used for manufacturing parts from sheet materials without the need of dies/molds. In this process, a tool forms the sheet in a series of localized incremental deformations. This process has been studied in sheet metal forming, but recently has been applied to thermoplastics. Locally applied external heat has been shown to improve the ductility of sheet metals and enhance formability using single point incremental forming. This concept has been tested for improving the formability of polymers in this research. Specifically, in this research a testing set-up has been developed and experiments are conducted to study the impact of external heating on the forming limits, forming forces, surface quality, and failure modes. A single point incremental forming device is modified through the development of a specialized tool holder and nozzle which heats the polymer sheet (lower than the glass transition temperature) and applies the forming loads. The results from the experiments indicate that using heat assisted forming there is: i) an increase in the formability from 27 degrees to 46 degrees when comparing room temperature forming to forming at an elevated temperature, ii) a reduction in the forces needed for forming, and iii) no visible difference in surface finish on the formed parts. Future research includes 1) simulating the localized deformation of the material to enable process planning, 2) increasing the forming forces and heat control of the system, and 3) exploring the manufacturing technique to other materials. This method has a potential to be an economical method for low volume manufacturing of thermoplastic polymer sheets