Punch for cold backward extrusion forging

Abstract

A punch 1 includes a forming land portion 2 formed in parallel with a punch axis 7 , a forming R-portion 3 having an arc-shaped cross-section and formed continuously with the forming land portion 2 on a tip end side with respect to the forming land portion 2 , and a recess portion 5 formed on a base end side with respect to the forming land portion 2 and having a diameter smaller than a diameter of the forming land portion 2 . A Rockwell hardness HRF of the blank 20 is within a range of 65 to 105. The curvature radius R of the forming R-portion 3 of the punch 1 is set to be larger than the thickness L of a cylindrical peripheral wall portion 21 of the forged product 25 . The length B of the forming land portion 2 of the punch 1 is set within a range of 0.05 to 0.15 mm. The recess width C of the recess portion 5 with respect to the forming land portion 2 of the punch 1 is set within a range of 0.15 to 1.0 mm.

1 . A punch for cold backward extrusion forging for use in producing a closed-end cylindrical forged product by subjecting a metal blank to cold backward extrusion forging, comprising:
 a forming land portion formed in parallel with a punch axis;   a forming R-portion having an arc-shaped cross-section and formed continuously with the forming land portion on a tip end side with respect to the forming land portion; and   a recess portion formed on a base end side with respect to the forming land portion and having a diameter smaller than a diameter of the forming land portion,   wherein a Rockwell hardness HRF of the blank is within a range of 65 to 105,   wherein a curvature radius of the forming R-portion is set to be larger than a thickness of a cylindrical peripheral wall portion of the forged product,   wherein a length of the forming land portion is set within a range of 0.05 to 0.15 mm, and   wherein a recess width of the recess portion with respect to the forming land portion is set within a range of 0.15 to 1.0 mm.   
     
     
         2 . A cold backward extrusion forging device equipped with the punch as recited  claim 1 . 
     
     
         3 . A production method of a shaped member for a brake piston in which a metal blank is subjected to cold backward extrusion forging to form a shaped member for a closed-end cylindrical brake piston using a punch for cold backward extrusion forging, the punch including a forming land portion formed in parallel with a punch axis, a forming R-portion having an arc-shaped cross-section and formed continuously with the forming land portion on a tip end side with respect to the forming land portion, and a recess portion formed on a base end side with respect to the forming land portion and having a diameter smaller than a diameter of the forming land portion, wherein a Rockwell hardness HRF of the blank is set within a range of 65 to 105,
 wherein a curvature radius of the forming R-portion of the punch is set to be larger than a thickness of a cylindrical peripheral wall portion of the shaped member,   wherein a length of the forming land portion of the punch is set within a range of 0.05 to 0.15 mm, and   wherein a recess width of the recess portion of the punch with respect to the forming land portion is set within a range of 0.15 to 1.0 mm.   
     
     
         4 . The production method of a shaped member for a brake piston as recited in  claim 3 ,
 wherein the blank is subjected to cold backward extrusion forging in a forming cavity of a forming die corresponding to the punch,   wherein an outer peripheral edge portion of a bottom surface of the forming cavity of the forming die is provided with a concave portion formed continuously from a peripheral surface of the forming cavity, and   wherein the concave portion is configured to control stagnation of a material of the blank at a corner and vicinity thereof in the forming cavity between the bottom surface of the forming cavity and the peripheral surface of the forming cavity by allowing inflow of the material of the blank into the concave portion at the time of forging the blank.   
     
     
         5 . The production method of a shaped member for a brake piston as recited in  claim 4 ,
 wherein an opening width of the concave portion is set to be equal to or larger than a thickness of the peripheral wall portion of the shaped member.   
     
     
         6 . The production method of a shaped member for a brake piston as recited in  claim 4 ,
 wherein a side surface of the concave portion arranged on a center side of the forming cavity is inclined so that an opening width of the concave portion becomes wider.   
     
     
         7 . The production method of a shaped member for a brake piston as recited in  claim 3 ,
 wherein at least one of a value obtained by dividing a surface roughness Ra of an upper surface of the blank by a surface roughness Ra of an outer peripheral surface of the blank, a value obtained by dividing a surface roughness Rz of an upper surface of the blank by a surface roughness Rz of an outer peripheral surface of the blank, a value obtained by dividing a waviness Wa of an upper surface of the blank by a waviness Wa of an outer peripheral surface of the blank, and a value obtained by dividing a waviness Wz of an upper surface of the blank by a waviness Wz of an outer peripheral surface of the blank is set within a range of 0.5 to 1.5.   
     
     
         8 . The production method of a shaped member for a brake piston as recited in  claim 3 , wherein a constituent material of the blank is an aluminum alloy subjected to a solution treatment without being subjected to an O-treatment. 
     
     
         9 . A production method of a brake piston, comprising:
 subjecting the shaped member for a brake piston obtained by the production method of a shaped member for a brake piston as recited in  claim 3  to an artificial aging treatment.   
     
     
         10 . A production method of a closed-end cylindrical forged product in which a metal blank is subjected to cold backward extrusion forging to form the closed-end forged product using a punch for cold backward extrusion forging, the punch including a forming land portion formed in parallel with a punch axis, a forming R-portion having an arc-shaped cross-section and formed continuously with the forming land portion on a tip end side with respect to the forming land portion, and a recess portion formed on a base end side with respect to the forming land portion and having a diameter smaller than a diameter of the forming land portion,
 wherein a Rockwell hardness HRF of the blank is set within a range of 65 to 105,   wherein a curvature radius of the forming R-portion of the punch is set to be larger than a thickness of a cylindrical peripheral wall portion of the forged product,   wherein a length of the forming land portion of the punch is set within a range of 0.05 to 0.15 mm, and   wherein a recess width of the recess portion with respect to the forming land portion of the punch is set within a range of 0.15 to 1.0 mm.