Punching die with a damping member

A punching die includes a punch body and a punch head provided for an upper portion of the punch body. The punch head is struck by a striker. The punching die further includes a punch guide disposed at a lower portion of the punch body, a retainer collar disposed over the punch guide and fitted to the punch body, a stripping spring interposed between the punch head and the retainer collar, and an elastically deformable damping member being interposed between an upper surface of the punch guide and a lower surface of the retainer collar.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a punching die, and more specifically to a 
punching die which can prevent punching noise generated during punching 
processing of work. 
2. Background Art 
Generally, the punching processing is effected by moving up and down an 
upper die against work placed on a lower die. Therefore, whenever the work 
is punched out, punching noise is inevitably generated. In order to 
prevent the generation of the punching noise, generally a damping material 
such as urethane has been provided at the bottom portion of a punch guide 
for constituting a part of the upper die. 
In the general way of providing a damping material such as urethane at the 
bottom portion of the punch guide, however, there exists a problem in that 
needle-shaped dust or refuse is inevitably produced during punching 
processing and further adheres onto the damping material or scratches the 
surface of the work to be punched out. In addition, there exist other 
problems in that the damping material is short in life time and difficult 
to be mounted at the bottom of the punching die. 
SUMMARY OF THE INVENTION 
With these problems in mind, therefore, it is the primary object of the 
present invention to provide a punching die provided with a damping member 
excellent in punching noise prevention performance, long in life time, and 
easy to be mounted on the punching die. 
To achieve the above-mentioned object, the present invention provides a 
punching die which includes a punch body and a punch head provided for an 
upper portion of the punch body. The punch head is struck by a striker. 
The punching die further includes a punch guide disposed at a lower 
portion of the punch body, a retainer collar disposed over the punch guide 
and fitted to the punch body, a stripping spring interposed between the 
punch head and the retainer collar, and an elastically deformable damping 
member being interposed between an upper surface of the punch guide and a 
lower surface of the retainer collar. 
Further, it is preferable that the damping member is interposed in a first 
part of a space between the upper surface of the punch guide and the lower 
surface of the retainer collar, and is not interposed in other second part 
of the space. 
In the punching die according to the present-invention, when the striker 
strikes the punch head, the punch guide first collides against the work. 
The shock generated when the punch guide collides against the work can be 
absorbed by the elastically deformable damping member interposed between 
the lower surface of the retainer collar and the upper surface of the 
punch guide, so that punching noise can be reduced. Further, the damping 
member is long in the life time and easy to be attached on the punching 
die.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will be described hereinbelow with 
reference to the attached drawings. 
In FIG. 1, a turret punch press 1, for instance is provided with a 
rotatable upper turret 3 and a rotatable.lower turret 5 as upper and lower 
die holders, respectively. In the respective upper and lower turrets 3 and 
5, a plurality of turret holes 7 and 9 are formed at appropriate angular 
intervals along the circumferences of the turrets 3 and 5, respectively. A 
plurality of upper and lower dies 11 and 13 are fitted into the respective 
upper and lower turret holes 7 and 9, respectively. 
FIG. 1 shows the state in which only one upper die 11 and only one lower 
die 13 are mounted on the upper turret 3 and the lower turret 5, 
respectively. In more detail with reference to FIG. 1, a punch guide 15 
movable up and down and constituting a part of the upper die 11 is fitted 
to the turret hole 7. A stripper plate 17 is formed integral with the 
lower portion of the punch guide 15. 
Further, a punch body 19 is fitted to the punch guide 15 so as to be 
movable up and down. Further, the punch guide 15 is formed with a key 
groove 21 so as to be engageable with a key 23 of the punch body 19 and 
another key 25 of the upper turret 3, respectively. 
A punch head 27 is fixed to the upper portion of the punch body 19 with 
screws 29. A retainer collar 31 is fitted to the punch body 19. On the 
upper portion of the punch guide 15, a stripping spring 33 is interposed 
between the retainer collar 31 and the punch head 27 so as to always urge 
the punch body 19 in the upward direction. In addition, a lift spring 35 
is interposed between a flange portion 15F of the punch guide 15 and the 
bottom of a hole 3H formed in the upper turret 3 so as to always urge the 
punch guide 15 also in the upward direction. 
An elastically deformable damping member 37 such as urethane is interposed 
between the upper surface 51 of the flange 15F of the punch guide 15 and 
the lower surface 52 of the retainer collar 31. The damping member 37 is 
interposed in an outer circumferential part 53.of a space 54 between the 
upper surface 51 and the lower surface 52, and is not interposed in a 
inner circumferential part 55 of the space 54. The distance C between the 
upper surface 51 and the lower surface 52 in the outer circumferential 
part 53 is longer than the distance D between the upper surface 51 and the 
lower surface 52 in the inner circumferential part 55. In the inner 
circumferential part 55, the upper surface 51 is spaced from the lower 
surface 52 when the punch head 27 is not struck by the striker 45, so as 
to provide the stroke in which the damping member is deformed. 
Further, an O-ring 39 is interposed between the inner circumference of the 
flange 15F and the outer circumference of the retainer collar 31. On the 
upper side of the punch head 27, a striker 45 movable up and down is 
attached on an upper frame (not shown) for constituting a part of the 
turret punch press 1. 
On the other hand, a die 41 constituting the lower die 13 is fitted to the 
turret hole 9 of the lower turret 5. The lower die 41 is formed with a die 
hole 43 at a position directly under the punch body 19. 
On the basis of the above-mentioned construction, when the striker 45 is 
lowered to press the punch head 27 in the downward direction, the punch 
guide 15 is lowered by the downward motion of the punch body 19 against 
the elastic force of the lift spring 35, and collides against the work W 
placed on the lower die 41. Here, the reason why the lift spring 35 is 
compressed is that the spring constant of the lift spring 35 is determined 
to be smaller than that of the stripping spring 83. Once the punch guide 
15 collides with the work W, the punch guide 15 cannot further move 
downward. Accordingly, the stripping spring 38 is then compressed. That 
is, the punch body 19 is lowered against the elastic force of the 
stripping spring 33, so that the work W is punched out by a punching edge 
formed at a lower end of the punch body 19 in cooperation with the die 
hole 43 of the lower die 41. 
The shock generated when the punch guide 15 collides against the work W can 
be absorbed by an elastic deformation of the damping member 37 interposed 
between the upper surface of the flange 15F of the punch guide 15 and the 
lower surface of the retainer collar 31. In addition, an excessive 
deformation of the damping member 37 can be prevented by the presence of 
the dimension that the distance C in the outer circumferential part 53 is 
longer than the distance D in the inner circumferential part 55. In other 
words, since the urging force of the stripping spring 33 can be 
transmitted from the lower surface of the retainer collar 31 to the upper 
surface of the punch guide 15 through the damping member 37 within a 
predetermined deformation limit, it is possible to improve the life time 
of the damping member 37. 
When the punch guide 15 collides with the work W, since two metallic 
members collide with each other under a very strong urging force of the 
stripping spring 33, the load applied by the stripping spring 33, the 
damping member 37, and the lift spring 35 increases abruptly as shown by a 
curve A in FIG. 2, so that a shock is generated. In the punching die of 
the present invention, since the damping member 37 is interposed between 
the upper surface 15F of the punch guide 15 and the lower surface of the 
retainer collar 31, it is possible to reduce the load applied by the 
stripping spring 33 as shown by a curve B in FIG. 2, so that a shock can 
be reduced effectively. Therefore, it is possible to prevent the 
generation of punching noise, as compared with the conventional punching 
die. Further, since the damping member 37 is interposed between the punch 
guide 15 and the retainer collar 31, the damping member 37 can be mounted 
easily. 
The above-mentioned embodiment has been described only by way of example. 
Without being limited thereto, however, various modifications may be made. 
For instance, in the embodiment shown in FIG. 1, the damping member 37 
does not exist between the upper surface 51 and the lower surface 52 in 
the inner circumferential part 55. But even if the damping member 37 is 
disposed extending into the space between the upper surface 51 and the 
lower surface 52 in the inner circumferential part 55, it is possible to 
obtain the same damping effect as with the case of the above-mentioned 
embodiment. 
As described above, in the punching die according to the present invention, 
since the elastically deformable damping member is interposed between the 
upper surface of the punch guide and the lower surface of the retainer 
collar, it is possible to prevent the generation of the punching noise 
effectively, while improving the life time of the damping member and 
facilitating the mounting process of the damping member on the punching 
die.