Method of and apparatus for the fine cutting (punching) of articles

Fine die stamping of workpieces from sheet metal is effected by clamping the workpiece between a die plate and guide plate, supporting the portion of the material to form the article by an ejector which is displaced along with the punch, and driving the supported portion of the material into a hole in the die plate having flanks tapered away from the guide plate and punch so that swaging occurs on the separated portion with or upon its separation from the balance of the workpiece material.

FIELD OF THE INVENTION 
Our present invention relates to a method of and to a tool for the fine 
cutting of workpieces and particularly for the fine stamping or punching 
of workpieces from a piece of material utilizing a punch or stamp plunger 
and a cutting plate or die plate formed with a recess having generally the 
shape of the article to be formed by the punching and stamping operation. 
BACKGROUND OF THE INVENTION 
As used herein, the term "fine cutting" is intended to describe a 
high-precision stamping or punching of articles from sheet material, 
especially metal objects from metal strip, utilizing a punch having the 
profile of the article to be produced, and a cutting plate or die plate 
having an opening of complementary profile. 
While generally punching and stamping are coarse processes capable only of 
producing blanks or articles which may be further shaped and which may 
deviate significantly in size or shape from the desired article, owing to 
deformation of the material to be punched, the inability to effectively 
control distortion during the punching or stamping operation, and other 
factors in the operation, a high quality punching and stamping process and 
tool has been developed for what can be described as fine stamping or fine 
punching. 
In the latter system articles can be shaped to narrow tolerances because 
the workpiece is firmly held all around the hole and the punch during the 
step of driving the material into the hole which constitutes the punching 
operation. 
In such a system a guide plate is juxtaposed with the die plate or cutting 
plate, the material, e.g. steel strip of a thickness of 0.3 millimeters to 
about 15 millimeters is fed between this guide plate and the die plate, 
the two parts clamp the material between them. A punch shiftable in the 
guide plate is displaced in registry with a hole of predetermined size and 
shape complementary to the size and shape of the punch, to drive the 
material through the hole and shear it from the strip. To support the 
material against distortion while it is being pressed through the hole, 
the article is supported during the stamping operation by an ejector which 
can have generally the same shape as the punch and between which the 
article is clamped during the displacement with the article from the 
strip. In other words around the perimeter of the hole, the material is 
supported by clamping it between the two plates while within the outline 
or perimeter of the hole, the material is supported by clamping it between 
the punch and the ejector. 
The guide plate and/or the die cutting plate can be provided with an 
annular tooth or barb which can penetrate into the strip close to the 
periphery of the hole to prevent lateral displacement of the material 
during the stamping operation. 
The resistance exerted by the ejector to the displacement of the stamping 
ram can amount to 10 to 20% of the cutting force which must be developed 
by the punch. This ensures that from the initial displacement of the 
material, the portion of the material which is adapted to form the article 
remains firmly clamped between the punch and the ejector. 
The principles of fine cutting, the state of the art relevant thereto and 
the guide lines involved will be apparent from the publication VDI 3345 
"FEINSCHNEIDEN" May 1980 (VDI Guidelines). 
Because of the close tolerances required between the punch and hole in the 
die plate, generally the punch does not enter this hole and on the edges 
of the workpiece turned toward the punch thin burrs may remain. The bore 
in the guide plate in which the punch is displaced generally also has the 
same shape and size as the hole into which the article is forced in the 
punching operation. 
OBJECTS OF THE INVENTION 
It is the principal object of the present invention to provide a fine 
punching or fine stamping method capable of producing by a fine cutting 
operation of the type described, articles of especially high fabrication 
tolerances and in a manner which improves upon earlier methods. 
Another object of this invention is to provide an improved tool for the 
stamping of articles from sheet metal and especially sheet or strip steel 
of the thicknesses set forth previously. 
SUMMARY OF THE INVENTION 
These objects and others which will become apparent hereinafter are 
obtained, in accordance with the present invention in a method of 
fabricating articles by a fine stamping operation in which a sheet 
workpiece, e.g. steel band or strip, is clamped between a guide plate and 
a die plate in the manner described, a punch is displaceable in the guide 
plate in alignment with a cavity of complementary configuration and 
dimensions and the workpiece is engaged between this punch and an ejector 
so that the article as it is formed is also clamped, and the article 
pressed out of the strip or sheet material is pressed into a cavity which 
has at least some conical or wedge-shaped tapered flanks at least over a 
portion of the periphery so that such inclined flanks are complementarily 
imparted to the workpiece. 
The invention has been found to be especially applicable to the fabrication 
of gear wheels, star wheels, spur wheels and cog wheels (hereinafter 
collectively referred to as toothed wheels) and whose teeth have flanks 
which are not parallel in an axial sense, but rather are inclined toward 
one another in a given direction and at a given angle. 
Thus an aspect of the invention resides in the formation of toothed wheels 
whose flanks are inclined in this way to the axis of rotation. 
It should be noted that the invention also includes a system in which apart 
from defining the outer periphery of the article via the outer 
configuration of the stamp and the complementary hole, either the stamp 
(punch) or the ejector can be provided with inner punch elements while the 
other is provided with a complementary hole to define an inner periphery 
of an annular article or various holes or like formations in the article 
within the extenernal outline. 
According to one embodiment of the invention the hole initially juxtaposed 
with the punch is provided with flanks conically converging away from the 
punch so that the size of the hole at its side confronting the punch is 
larger than the size of the hole turned away from the punch while the 
punch has a size and configuration corresponding to that of the hole at 
its side turned toward the punch. In this case, the punching operation, 
i.e. the physical separation of the article from the workpiece coincides 
with the step of driving the workpiece into the inclined flank hole. The 
workpiece is thereby internally compressed during the punching operation 
while being clamped between the punch and the ejector and is in effect 
coined so as to expand slowly along the punch axis and uniformly over the 
entire area between the punch and the ejector. 
According to a feature of the invention the inner surface of the workpiece 
contour defined by the die plate forms coining, swaging or embossing 
surfaces over at least part of the periphery to a depth so that it is 
preferably equal to the thickness of the articles which are inclined in 
the stamping direction to the ejector axis. 
By contrast with the usual fine punching and stamping tools, the generatrix 
of the inner surface of the article defining contour of the die plate does 
not remain parallel to the ejector axis but rather is inclined away from 
the surface on which the workpiece rests initially with a convergence 
toward the ejector axis of predetermined conicity or inclination equal to 
the inclination which is desired to remain at the workpiece periphery. 
At least the portion of the hole of the die plate turned toward the 
workpiece or material is thus formed as a swaging die which comprises the 
punched article inwardly. Advantageously, this portion of the hole has a 
height (axial dimension) slightly greater than the thickness of the 
workpiece material to allow this material to flow in the direction of the 
axis during the swaging step. 
Naturally, one of the important advantages of the present invention is that 
it allows the fabrication of articles with completely or partially 
inclined flanks during the punching operation and without separate or 
special machining operations. The method utilizes a relatively simple 
apparatus and indeed can utilize a converging die plate which can be 
machined to provide the taper. 
Sometimes problems are encountered with very thin materials or in the 
punching of rings having relatively small area without the intrinsic 
stability required for a combined stamping or swaging operation. In these 
cases we may utilize a two step process whereby, in a first step, the 
article is partially stamped from the workpiece by conventional fine 
stamping processes utilizing a die plate whose hole is not provided with 
one tapered flank. This die plate is then replaced by a die plate whose 
hole has tapered flanks and the punching operation is continued or 
completed to effect the swaging and the separation of the article from the 
workpiece material. 
Both steps can of course be carried out in a single machine in succession. 
In practice the first step does not differ significantly from the fine 
cutting process for the production of a partial stamping (see 
VDI-Richtlinien page 7, 3.6 Umformvorgange Example 6 ff). 
The only difference is that the partially expressed material corresponds to 
the finished workpiece in this standard process. With the present 
invention the partially expressed article is then swaged in the swaging 
die hole.

SPECIFIC DESCRIPTION 
The tool shown in FIG. 1 comprises, as is usually the case, a cutting or 
die plate 10 which is juxtaposed with a guide plate 14 and is provided 
with a hole 11 which has a contour 22 corresponding to the shape of an 
article 25 to be produced by stamping therein. The hole 11 receives an 
ejector 12 of complementary profile which is displaceable along the punch 
axis 13. 
Similarly, the guide plate 14 is provided with a hole 15 of the same 
contour and dimensions as the end of the hole 14 turned toward the punch 
16 of complementary configuration which is displaceable in this hole. The 
punch 16 is, of course, coaxial with the ejector 12. Naturally, an inner 
die can be formed within the punch 16 which can receive a receptive 
ejector while an inner punch is disposed within the ejector 12 to punch 
out the center, for example, of a gear wheel which can be fabricated by 
the punch and can have the configuration shown in FIGS. 7 and 8. In this 
case the tool can operate in accordance with the 2.1 working principle of 
page 2 of the VDI guidelines 3345 previously mentioned. 
The workpiece 17 can be a sheet steel strip which is fed between the plates 
10 and 14 and can be engaged by an annular tooth or barb 18 which bites 
into the workpiece directly around the contour 22 and prevents extrusion 
outwardly of the workpiece material. 
The article contour 11 formed in the die plate 110 is tapered away from the 
punch 16 over an axial length 20 that is slightly less than the thickness 
21 of the workpiece material. It has its largest cross section in the 
plane 19 of contact between the die plate 10 and the material 17. The 
conical flanks have been illustrated at 22. 
The term "conical" has been used herein to describe the taper because the 
articles which are fabricated are generally round. However, when a 
polygonal article is made, the taper may have a wedge configuration, i.e. 
can include linear flanks with planar convergence. 
The smaller cross section of the contour 11 has been represented at q while 
the larger cross section or diameter is represented at Q. The punch 16 has 
the larger cross section whereas the ejector 12 has the smaller cross 
section or diameter. The inclination or angle of taper 24, shown with 
respect to a generatrix 23 of the conical taper can be 3.degree. to 
4.degree.. 
As can be seen from FIG. 5 a circular article 25 can have the frustoconical 
flank 26. 
The piece 27 adapted to form the article is pressed between the ejector 12 
and the punch 16 as it is driven out of the workpiece 17 and into the 
swaging die 22 within the die plate. FIG. 1 illustrates the end position 
from whence the tool is opened and the ejector 12 drives the article in 
the opposite direction. 
The tool shown in FIG. 1 can be utilized in a conventional fine punching 
machine and with the customary operating sequence. 
An unpunched workpiece 17 is inserted between the die plate 10 and the 
guide plate 14 and these plates are moved toward one another to clamp the 
workpiece tightly between them, driving the tooth 18 into the workpiece. 
The punch 16 and the ejector 12 are then displaced toward one another and 
against the workpiece to clamp the portion of the workpiece 17 which will 
ultimately form the article 25 between them. While the counter pressure of 
the ejector 12 is applied, the punch 16 is advanced forward the die plate 
to cut the article 25 free from the workpiece 17 and swage it with the 
desired taper in the swaging zone 22. After the single step punching and 
swaging, the die plate and guide plate can be separated from one another, 
the punch 16 retracted and the ejector 12 raised to eject the finished 
article. 
FIG. 3 shows the first stage of a two-stage method. In this system, the die 
plate 110 is provided with the ejector 112 while the guide plate 114 has 
the tool 118 and the punch 116. The punch 116 is here of the same cross 
section Q as the ejector 112 and the bore 111 is of the same cross section 
as the bore 115, i.e. the die plate hole does not have a taper. 
The partially pressed portion 127 of the workpiece 117 results after the 
punch 116 has been advanced, partially through the workpiece 117 by a 
punching process otherwise similar to that described in connection with 
FIG. 1. The ejector 112 supports the portion 127 to enable its withdrawal 
from the die plate 110 and the die plate 110 is replaced by a swaging 
plate 210. 
With the section 127 connected at the ligature 128 to the remainder of the 
workpiece 117 the die plate is replaced by the swaging plate 210 which has 
the tapered hole 222 over length 220 slightly greater than the width of 
the portion 127. 
The swaging plate 210 and the guide plate 214 are again clamped against the 
workpiece 217. This thickness 221 is slightly less than the dimension 220 
previously described. 
Once the ejector 212 and the punch 216 have clamped the portion 127 of the 
workpiece between them, the punch is advanced to cut loose the article 225 
which is simultaneously swaged to receive the tapered flank 226 in the 
formation of the article 225 (FIG. 6). 
The tool can then be opened and the workpiece ejected by the ejector 212. 
The common axis 213 of the punch and the ejector, the generatrix 223, the 
angle 224 and the plane 219 all correspond to the elements described in 
connection with FIG. 1, and identified by corresponding reference numerals 
without the hundreds digit. 
In FIGS. 7 and 8 we have shown diagrammatically a typical article which can 
be fabricated by the fine punching operation of the invention and which 
can comprise an external toothed ring-shaped wheel 30 whose teeth 31 have 
flanks 32 and 33 (FIG. 8) which are inclined at angles 35 to one another 
and have a certain conicity with respect to the rotation axis 34. The 
roots 36 between the teeth and the heads 37 of the teeth can have 
generatrices which lie parallel to the axis 34. Naturally, only part of 
the periphery of a workpiece need be tapered, in accordance with the 
invention, and with the appropriate construction of the swaging and 
punching portions it is possible to apply tapers to internal surfaces as 
well.