Forming limit for incremental stretching of aluminum and aluminum alloy blanks by single-tool-path process

摘要

An incremental stretching process with a single tool-path for sheet metals is useful for reduction of the tool-path schedule. However, the forming limit has not been revealed sufficiently for the single-tool-path process. In order to clarify the forming limit in the incremental stretching with a single tool-path, aluminum and aluminum alloy blanks are stretched to truncated conical shells with several values of half-apex angle, and the deformation behavior is examined. Experimental results show that forming limit is determined by the onset of cracking which propagates to circumferential direction in the early stage of the process. It is found that velocity of tool, V, and thickness of blank have major influences on the forming limit. The forming limit increases with decreasing V, and attains a maximum value at V_m; for V below V_m, a decrease in forming limit is caused by the low-cycle fatigue effect. Although the chemical composition of blank materials has a significant influence on the forming limit, the temper condition of blank materials has no influence on the forming limit. From considering of Sine law, experimental results show that the value of limiting strain is 2 to 30 times as high as that of work-hardening exponent of the blank. It is concluded that the forming limit of the incremental stretching is higher than that of press forming.