Elevated-temperature single-point incremental forming for biomedical implants: Microstructural evolution and dimensional precision

Incremental forming offers a flexible approach for manufacturing patient specific implants with complex asymmetric geometries. Titanium is ideal for biomedical implants due to biocompatibility and corrosion resistance but exhibits limited room temperature formability. Elevated temperatures can improve formability during single point incremental forming of titanium sheets, but the material response under such forming conditions is still not fully understood. In this study, a heat assisted single point incremental forming setup with cartridge heaters was developed to fabricate a patient-specific cranial implant geometry from commercially pure titanium grade 2 sheets at 204 °C. Geometric accuracy was evaluated using material thickness distribution, springback and geometric deviation analysis. The deformation behaviour during elevated temperature single point incremental forming was investigated through microstructural and texture evolution using electron backscatter diffraction analysis at progressive forming depths. The formed implant exhibited relatively uniform thickness distribution and limited springback, with a maximum bend angle of 5.991°. Microstructural analysis revealed significant grain refinement, with the average grain size decreasing from 16 to 1 μm and the fraction of low-angle grain boundaries increasing from 18.6% to 32.2%. Texture evolution was characterized by progressive weakening of the initial rolling texture and increasing orientation dispersion, with only a weak tendency towards alignment along the { 1 ¯ 2 1 ¯ 8 } fibre at higher forming depths. The electron backscatter diffraction observations indicate progressive grain subdivision, substructural evolution and continuous redistribution of crystallographic orientations during elevated-temperature single point incremental forming. The observed microstructural features are also suggestive of localized recovery processes at higher forming depths.