2019 Volume 60 Issue 11 Pages 2416-2425
To form sheet metals into concave-convex mixed shapes without using special machines or dies, a novel forming tool, referred to as a penetrating tool, and a new forming method, referred to as penetrating tool friction stir incremental forming were developed herein. The proposed penetrating tool is composed of two dome shape tools, called the top and bottom tools. The top and bottom tools are vertically symmetric and joined by a middle screw. Pure aluminum (JIS: A1050-O) sheets with a thickness of 2 mm were used for workpieces. Forming of concave, convex, and concave-convex mixed shapes were implemented by using penetrating tool friction stir incremental forming under clockwise and counterclockwise tool path direction. Experimental conditions which obtained by a preliminary experiment were tool gap between the top and bottom tool of 1.8 mm, tool rotation rates of 1000–3000 rpm and tool feed rates of 200–3000 mm/min. Formability by the developed method was evaluated by the formable height or depth. Not only the shapes but also the distribution of thickness of the PTFSIFed sheets were measured. Material flow was discussed by thickness in Z direction due to keeping the volume constant before and after forming. From the experimental result, the concave, convex, and concave-convex mixed shapes can be formed using the proposed method. However, the formable depth or height remained relatively shallow. For more dramatic depth or height forming, groove-like defects occurred in advancing side of the formed sheet and the sheet fractured due to penetration of the sheet by the groove-like defect. From the distributions of thickness in Z direction of formed sheet, the material flow from the advancing to retreating side was shown to cause the groove-like defects.