Metal deforming – By application of fluent medium – or energy field – With cutting
Reexamination Certificate
2001-04-09
2001-10-23
Jones, David (Department: 3725)
Metal deforming
By application of fluent medium, or energy field
With cutting
C072S058000, C083S053000, C083S054000
Reexamination Certificate
active
06305201
ABSTRACT:
This invention relates to method and apparatus for forming unobstructed holes in hollow hydroformed metal parts and more particularly to forming an unobstructed hole in hollow hydroformed metal parts with a punch while leaving multiple slugs produced by cutting action of the punch integral with and internal of the part.
BACKGROUND OF THE INVENTION
It is well known in the art of hydroforming hollow metal parts to use the hydroforming pressure to assist a punch in piercing one or more holes in the hydroformed part while the part remains in the hydroforming die. The hydroformed part can take various shapes as for example a chassis frame and engine cradle for a motor vehicle wherein one or more holes are required in these hydroformed parts for the attachment of one or more other frame or cradle forming parts respectively. This piercing operation with a punch can produce a detached slug left in the hydroformed part that may or may not be undesirable. In the latter case and depending on whether a single hole is punched or aligned holes in opposite sides of a hydroformed part are punched, the detached slugs in either situation can be removed as disclosed in U.S. Pat. No. 5,398,533 issued Mar. 21, 1995 and U.S. Pat. No. 5,666,840 issued Sep. 16, 1997 which are both assigned to the assignee of this invention.
Is also well known in the case of where a loose slug left in the hydroformed part is undesirable, that the piercing can be accomplished with a punch that produces a slug that remains integral with the hydroformed part. This is shown and labeled as “Prior Art” in
FIG. 1
of the accompanying drawings. In this case, as in other hydroforming operations, a hollow metal part
10
has initially been forced by hydraulic fluid
11
at high pressure to conform to the surface of a die cavity
12
in a hydroforming die
14
comprising mating die halves
16
and
18
. A punch
20
mounted for reciprocal movement in a cylindrical bore
22
in the upper die half
16
has, as distinguished from the above cited U.S. Patents, a chamfered or beveled portion
24
of limited peripheral extent that interrupts the sharp peripherally extending cutting edge
26
at the end face
28
of the punch. The chamfered portion
24
extends through a small arc about the periphery of the punch face, for example 45 degrees, and as a result, when the punch is advanced into the part while the internal hydraulic pressure is maintained and cutting of the part takes place with the remaining cutting edge
26
, a small portion
30
of the slug
32
that is produced remains intact or integral with the hydroformed part and is forced with the slug by the punch face into the interior of the hydroformed part.
In the above cited U.S. Patents and
FIG. 1
, the punches illustrated produce circular holes in the hydroformed part. However, it is also well known by those skilled in this art that these punches as well as punches in general can be made to produce various hole shapes such as square, rectangular, triangular or other common geometrical shapes or an irregular shape as required for a particular hydroformed part. In either event and as particularly concerns the piercing of hydroformed parts, there are limitations on the size of the hole that can be punched and particularly where the slug is left attached to the side of the hole as in the case of the Prior Art in FIG.
1
. For example and again referring to
FIG. 1
, where any internal cross sectional dimension A of the hydroformed part
10
is less than dimension B of the slug
32
that lies in the same plane with the former dimension and in this case is the diameter of the punch, the slug can hit the opposite interior side of the part as the slug is punched as shown in FIG.
1
. This can produce several undesirable results such as is the case with the slug
32
obstructing the hole as shown and thereby shortening the depth of the hole which could be unacceptable for the reception of a mating part (not shown). The worst condition has been found to be a miss-shaped hole with a very distorted side and results from the slug hitting the interior of the part and then being further bent by the punch as shown by the deformed portion
30
A of the slug illustrated with phantom lines.
SUMMARY OF THE INVENTION
The present invention in method and apparatus for forming unobstructed holes with constant cross sectional dimensions in hollow hydroformed metal parts without leaving a loose slug in the part solves such problems by forming multiple slugs of significantly less size than that where a single slug would be punched to form the same size hole and leaving them attached to (integral with) the side of the hole in a manner internal of the part so as to not obstruct the hole from within the part or with their formation and bending cause distortion of the shape of the hole. Moreover, this is accomplished while the hydroforming pressure is maintained in the part while still in the hydroforming die and utilized without incurring any significant leakage of the hydraulic fluid in the multiple slug forming and bending operations of the present invention.
In the present invention, this is accomplished with a single punch that can be readily adapted within the teachings of this invention to produce holes of various sizes and shape by forming the configuration of the punch end face and the cutting edge configuration on the punch end face according to the number, size and shape of the multiple slugs desired for the particular size and shape of hole desired while still maintaining all the slugs integral with the part and not allowing them to obstruct or cause distortion of the hole. Moreover, the multiple slugs are bent into the interior of the part in a certain manner by the punch so as to not only not obstruct the hole, but also to add considerable surrounding side area to the hole resulting in a substantially improved mating joint for the part to be attached in the hole.
In the method and apparatus of the present invention, the punch employed has a cylindrical peripheral side conforming to the desired hole shape and an end face having an outwardly projecting, centrally located, angled cutting edge with ends terminating at the peripheral side of the punch. This central cutting edge has a high point that prior to hydroforming the part contacts with an unsupported section of the part opposite the punch end face to initiate a stress riser in this section on closing the die about the part. Then during hydroforming of the part in the die, the internal hydraulic pressure forming the part also stretches and bends the unsupported wall section outward about the above high point significantly increasing the magnitude of the stress riser.
Following hydroforming of the part, the punch is advanced while maintaining the hydraulic pressure in the part causing the high point on the central cutting edge to fracture the stretched wall section at the stress riser and this cutting edge to then split and cut or shear the stretched wall section in directions toward the peripheral side of the punch to form oppositely facing sheared edges in the stretched wall section. Simultaneously, oppositely angled cutting edges at opposite ends of the central cutting edge which terminate at the peripheral side of the punch then shear or cut the stretched and bent wall section in directions away from the oppositely facing cut edges with the aid of the hydraulic pressure to form oppositely extending slugs that remain integral with the part. As the punch continues to be advanced, smoothly contoured portions of the punch end face with further aid of the hydraulic pressure bend the slugs as they are being cut into the interior of the part and eventually the peripheral side of the punch with further punch movement engages the slugs with an interference fit and forces them into positions in the part while maintaining the integrity of the internal hydraulic pressure so as to form an unobstructed hole in the part. There are at least two such slugs that are formed in this manner to form a hole and more such slugs can be formed in a similar ma
Ghiran Mircea
Oberski Paul C
General Motors Corporation
Jones David
Leahy Charles E.
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