Study of Forming Limit for Rotational Incremental Sheet Forming of Magnesium Alloy Sheet

Abstract

As a lightweight material, magnesium is being increasingly used for automotive parts. However, due to a hexagonal-closed-packed (hcp) crystal structure, in which only the basal plane can move, magnesium alloy sheets exhibit a low ductility and formability at room temperature. Press forming of magnesium alloy sheets is conventionally performed at elevated temperatures of 200°C to 250°C and thus is known as energy consumed forming. Therefore, in view of an energy saving forming technology, we study magnesium alloy sheet forming by a rotational incremental sheet forming (RISF) at room temperature, where the rotational tool generates local heat of specimen enough to accelerate plastic deformation. The flow curves of the magnesium alloy sheet are obtained and calculated at elevated temperatures, while the yield loci of the magnesium alloy sheet are measured at room temperature. Using RISF, a square cup of 80-mm width, 80-mm length, and 25-mm height is then formed from a magnesium alloy sheet at room temperature. In addition, the strain distribution is obtained and compared with the forming limit curve (FLC) by considering the effect of the tool radius and is found to effectively predict the forming limit of a magnesium alloy sheet in RISF.

Ductile Fracture Prediction in Rotational Incremental Forming for Magnesium Alloy Sheets Using Combined Kinematic/Isotropic Hardening Model

“…[15][16][17] Kim and Yang [18] proposed a double-forming technique to improve formability, assuming that only shear deformation occurs in the material. Plus, Park et al [19] studied and showed the possibility of cup incremental forming of a magnesium sheet at RT with a rotational tool, where the tool rotates itself.…”

“…Therefore, Park et al [19] proposed rotational incremental sheet forming, which improves the formability of sheet materials, when compared with ISF, due to the large amount of heat generated in the contact area as a result of the friction energy at the tool-specimen interface and plastic deformation energy from the shear deformation.…”

“…If quasi-static experiments, at the same strain rate, are carried out at two different temperatures, denoted by the superscripts in Eqs. [18] and [19], the ratio r between the stresses at a specific plastic strain can be expressed as…”

“…The tool radius was 6 mm and the feed rate was 400 mm/ min. As used in a previous study, [19] in the experiment, the spindle speed of the tool was 4000 rpm counterclockwise in the -z direction until the temperature of the tool reached 373 K (100°C) in the case of a 45 deg wall angle, and then set to 3000 rpm. When the temperature of the tool exceeded 373 K (100°C), chips of magnesium were generated in the contact area between the specimen and the tool.…”

Process Investigation of Incremental Sheet Forming: The Evolution Towards Multi-Pass Deformation Design

“…In particular, Park et al (2010) used the rotational tool to accelerate plastic deformation of magnesium forming using SPIF. During the rotational incremental forming process, a large amount of heat is naturally generated in the contact area due to friction energy at the tool-specimen interface and plastic deformation energy by shear deformation.…”