Effect of tool diameter and step size on deformation and microstructural response in robot-assisted incremental sheet forming of AA3003-O

Robot-assisted incremental sheet forming (RAISF) of AA3003-O aluminium sheets (0.56 mm) was investigated to quantify the combined influence of tool diameter and step size on geometric, mechanical and microstructural responses. Variable wall angle conical frusta (VWACF) were fabricated using three tool diameters (5, 10, 15 mm) and three step depths (0.1, 0.3, 0.5 mm). A software-based toolpath was generated in CATIA and executed via ROBOTDK on a six-axis industrial robot. Formability was assessed through limiting wall angle and forming limit curves obtained from circle-grid analysis; spring back was evaluated from the deviation between theoretical and measured cone depths; forming forces were recorded in situ using a dynamometer; surface roughness (Ra, Rq) was characterised by scanning probe microscope (SPM); and crystallite size evolution was quantified using X-Ray diffraction (XRD) with a Modified Scherrer Equation and Williamson–Hall analysis. The limiting wall angle increased with tool diameter (from 49–53° for 5 mm to 61–64° for 15 mm) and exhibited an optimum at ΔZ = 0.3 mm. Average vertical force increased with both tool diameter and step depth, reaching ~ 40 kgF for the 15 mm/0.5 mm condition. Surface roughness varied between Ra ≈ 0.23–0.53 μm depending on tool–step combination. XRD results showed crystallite refinement relative to the base material, with step depth and tool diameter jointly controlling the balance between strain hardening and dynamic recrystallisation.