An investigation on the effects of tool rotational speed and material temper on post-ISF tensile properties of Al2219 alloy

Incremental Sheet Forming (ISF) is a novel cold sheet forming process. This study aims at investigating the influence of tool rotational speed on post-ISF tensile properties of two tempers of Al2219 alloy namely Al2219-O and AA2219-T6. The rotational speeds are changed from 50 to 2000 rpm while keeping the other parameters fixed. The sheets are formed into the frustum pyramid of fixed wall angle of 45°. It is found that post-ISF tensile strength of both tempers experiences a drop with increasing tool speed. The ultimate strength (UTS) of O-temper decreases from 236 to 153 MPa and its yield strength (YS) decreases from 171 to 81 MPa. Similarly, the ultimate strength of T6 temper reduces from 306 to 170 MPa and its yield strength reduces from 239 to 110 MPa. Moreover, upon forming, the O-temper generally endures a gain while the T6 temper endures a loss in strength. These properties show strong correlation with the forming induced temperature, particles density/size and grain size. It is noticed that friction heating rate at the tool sheet interface increases with the spindle speed thereby reducing the density of second phase particles and increasing the size of particles and grains. These microstructural variations in turn cause corresponding reductions in the yield and tensile strengths of material. These results identify the role of spindle rotation in ISF and thus will serve as a guideline in process design to achieve desired post-ISF properties of the chosen alloys.