Experimental studies on multistage single point incremental forming of thin high carbon steel sheet

The incremental sheet forming process has gained interest from industrial and research institutions due to its intrinsic advantages, such as process flexibility and a low unit processing cost. However, achieving vertical features in the process is not possible in a single pass due to thinning and tearing of the sheet at the transition zone between vertical and horizontal features, e.g., the wall and base of a part. This limitation has been overcome by using multistage single point incremental forming (MSPIF), which introduces several intermediate tool-pass stages during the process. MSPIF has been shown to mitigate sheet thinning even when the maximum wall angle is reached. Prior research has reported promising results for aluminum alloys, low- and medium-carbon steel alloys, and formable stainless steels. There is a paucity of reported research that explores the suitability of MSPIF for less formable metals such as high-carbon steels, alloy steels, and titanium alloys. Work herein reports a series of experimental studies examining the feasibility of MSPIF for forming high-carbon steel sheets to achieve steep wall angles (70°). The effect of varying tool step down, tool path, and MSPIF strategies on process performance is studied. Selected process performance measures include surface roughness and geometrical conformance. Only one of the six strategies explored reached the maximum slope angle required (70°) for both spiral and contoured tool path movement techniques and for both tool vertical step-down values. While increasing vertical step-down from 0.5 mm/rev to 1.5 mm/rev increases surface roughness, it is found that varying tool path movement does not have a measurable effect. For the geometrical conformance, the overall profile of the formed part is the closest to the nominal profile when vertical stepdown is 1.5 mm/rev and contoured tool path movements are used.