Contactless Heat-Assisted Single Point Incremental Forming

Abstract

This thesis introduces a novel technique called Hot Air Contactless Single Point Incremental Forming (HASPIF) as an alternative to conventional single incremental point forming methods. HASPIF utilises hot compressed air to deform polymer sheets without physical contact with a forming tool, thereby eliminating the need for a rigid tool and reducing costs.

A case study was conducted using a polycarbonate sheet to validate the concept, employing specific parameters such as nozzle speed, air temperature, air pressure, stepdown and initial distance. The results demonstrated accurate shaping of the polycarbonate sheet with minimal springback, although slight deviations and material build-up were observed at the starting point of the nozzle.

Finite element modeling (FEM) was used to analyse the influence of the contactless tool on the shaping process, encompassing computational fluid dynamics (CFD) and transient structural models to estimate the resulting shape and deformation of the polymer sheet. The FEM model not only forecasted the final part of geometries and dimensions but also provided insights into the normal strain progression, which aligned well with experimental data.

Furthermore, the thesis optimised the HASPIF process using a design of experiment (DOE) approach, evaluating five control factors and considering profile variation, thickness variation, and surface roughness as evaluation criteria. The study revealed that air temperature and feed rate had a significant influence on the deformation process, while air pressure and feed rate impacted thickness variation and surface roughness. A prediction model was developed to optimise process parameters, aligning well with predicted profile and thickness variations. However, surface roughness did not exhibit the same agreement due to the stepwise nature and inherent waviness of the contactless forming technique.

In conclusion, this study presents a promising approach for developing innovative contactless forming techniques using hot compressed air as a forming tool, offering advantages such as reduced tool wear and lubrication requirements compared to traditional methods.