| 摘要 |
PROBLEM TO BE SOLVED: To provide a cavity forming method capable of suppressing the collapse of a cavity and surface defects at a time of forming the cavity in a metal member by friction stir processing.SOLUTION: A helical groove 3a is formed in an outer circumferential surface of a stir pin 3 of a cavity formation rotary tool 1A, the helical groove 3a is formed clockwise from upward to downward, an outside diameter of a shoulder portion 2 and an outside diameter of a tip end of the stir pin 3 are set so that a value obtained by dividing the outside diameter of the shoulder portion 2 by the outside diameter of the tip end of the stir pin 3 is from 1.4 to 2.2, an angle of the helical groove 3a with respect to a reference plane whose normal corresponds to an axial direction of the stir pin 3 is set from 20 degrees to 40 degrees, a helical groove portion 12 in which the helical groove 3a is formed and a flat portion 11 in which the helical groove 3a is not formed are formed in the stir pin 3, the helical groove portion 12 is formed from the tip end of the stir pin 3, and the cavity formation rotary tool 1A is made to rotate clockwise in a view from above at a time of moving the gap formation rotary tool 1A relative to a metal member. |
