Abstract: In the aspect of the stretching technology theory, it is demonstrated that mere a technological parameter-tool width ratio is inadeguate, that only when another technological parameter-blank width ratio is replendished, can the stress state in the center zone of stretching blank be correctly described and can the quality of forging be effectively controlled. The expound has been testified by experiments. The stretching technology which requires two technological parameters——blank width ratio and tool width ratio are simultaneously used to control the internal quality of forging is called L Z technology.

Key words: Blank width ratio, Stretching, Tool width ratio