Apparatus and method of hot bulge forming, and product formed by hot bulge forming

Abstract

In a hot bulge forming apparatus 1 , a preheated tubular material 10 b is disposed in a cavity 33 A defined by dies 21 A, 31 A, air is supplied into an interior of the tubular material 10 b so that the tubular material 10 b is pressed against cavity surfaces 211 A, 311 A by the pressure of the air to thereby form the tubular material 10 b into a shape defined by the cavity 33 A. Thereafter, the resulting tubular material 10 c is disposed in a cavity 33 B defined by dies 21 B, 31 B, and air is supplied into an interior of the tubular material 10 c so that the tubular material 10 c is pressed against cavity surfaces 211 B, 311 B by the pressure of the air to thereby form the tubular material 10 c into a shape defined by the cavity 33 B while the tubular material 10 c is cooled by the cavity surfaces 211 B, 311 B. Projecting portions 331 each having an arc-shaped section are formed at portions of the cavity surfaces 211 A, 311 A against which lengthwise end sides of the tubular material 10 b are pressed.

1 . A hot bulge forming apparatus comprising:
 a first die; and   a second die,   wherein a preheated tubular workpiece is formed by disposing the preheated tubular workpiece in a cavity of the first die, supplying a fluid into an interior of the workpiece so as to press the workpiece against a cavity surface of the first die by virtue of a pressure of the fluid to form the workpiece into a shape defined by the cavity surface, and thereafter, disposing the workpiece in a cavity of the second die, and supplying a fluid into the interior of the workpiece so as to press the workpiece against cavity surface of the second die by virtue of a pressure of the fluid so that the workpiece is cooled by the cavity surface while being formed into a shape defined by the cavity surface, and   wherein the hot bulge forming apparatus further comprises a projecting portion having an arc-shaped section and formed at a portion of the cavity surface of the first die against which a lengthwise end side of the workpiece is pressed.   
     
     
         2 . A hot bulge forming method comprising:
 providing a recess portion having an arc-shaped section at a lengthwise end side of a tubular workpiece; and   forming the tubular workpiece by disposing the tubular workpiece which is preheated and provided with the recessed portion in a cavity of a die and supplying a fluid into an interior of the workpiece so as to press the workpiece against a cavity surface of the die by virtue of a pressure of the fluid.   
     
     
         3 . A product which is formed through hot bulge forming and comprises a recess portion having an arc-shaped section at a lengthwise end side of the product.