Punching press

Punching press having a top cutter which is vertically movable by an axially guided ram. The top cutter extends beyond the cross-sectional surface area of the ram and cooperates with a bottom cutter mounted on the machine table. The ram is constructed as an angle section, particularly as an equal-limbed L-section, at least on the place of mounting for the top cutter and at least over an axial length corresponding to the length of stroke of the top cutter. The axial guiding system for the ram comprising a pin-and-bush guide which is disposed on the cutting clearance and comprising at least two pins and associated guide bushes situated at a distance from each other on the ram and on the machine frame in an axially parallel configuration.

The invention relates to a punching press, more particularly a coping 
press, with a top cutter moved vertically by an axially guide ram and 
extending beyond the cross-sectional surface area of said ram, and with a 
bottom cutter which is attached to the machine table. 
The top cutter of punching presses of the kind described hereinbefore and 
disclosed in the U.S. Pat. No. 3,850,067 is mounted on a cantilevered arm 
of the ram which is arranged laterally of the shearing clearance between 
the two cutters. The length of the cantilevered arm therefore defines the 
shortest distance between the cutting clearance and the closed external 
surface of the ram and thus also defines the maximum attainable punching 
depth. Greater punching depths of these known machines therefore call for 
a correspondingly increased cantilevered length of the arm which retains 
the top cutter so that at least the ram but as a rule the entire machine 
must be constructed in heavier form if an equally clean cut is to be 
obtained in view of the correspondingly increased lever transmission ratio 
between the ram axis and the place at which the cutting forces act. A 
punching press of this kind, which must be constructed to a 
correspondingly large size, must be regarded as overdimensioned if it can 
achieve greater punching depths but is required to process lighter sheet 
metal gauges which call for correspondingly lower cutting forces. In these 
cases it is therefore common practice at the present time to use smaller 
machines but in which the workpiece is repeatedly processed. For example, 
in the production of sheet metal containers produced from rectangular 
blanks, the four corners of which must be correspondingly notched, the 
finished diagonal dimension must be initially cut at each corner in a 
first operation as indicated in the left-hand part of FIG. 5 by the 
diagonal cut edges a. In a further operation the diagonal cut edges a are 
then notched to the finished depth dimension to provide the corresponding 
cut edges b and c. Compared with a single operation this results in twice 
the operating costs and duplicated processing also calls for greater skill 
to ensure that both cuts performed on each corner of the sheet metal blank 
actually provide the desired finished dimension. 
According to an earlier proposal the ram of a comparable punching press is 
constructed as a tubular member, preferably of circular cross-section, and 
the cutting clearance of the two cutters is then disposed within the 
internal diameter of such ram. Furthermore, to provide axial guiding for 
the ram the bottom end thereof is provided with a pin-and-bush guide 
system comprising at least two diametrically arranged pins and associated 
guide bushes on the ram or on the machine frame respectively as well as a 
top support bearing which supports the top ram end near the bottom cutter 
on the machine frame in a concentric configuration. 
The object of the invention is to provide a punching press, more 
particularly a punching press which can be used as a coping press capable 
more particularly of performing corner notching in one operation and 
generally permitting a greater punching or notching depth for workpieces 
with a curved or polygonal edge and having a construction of lighter 
weight. 
In a punching press of the initially mentioned kind this problem is solved 
in that the ram is constructed as an angle section, more particularly as 
an equal-limbed L-section, at least at the place of attachment for the top 
cutter and at least over an axial length corresponding to the length of 
stroke of said cutter. 
With this construction of the ram according to the invention the distance 
between the cutting clearance and the external surface region of the ram 
required as a stop abutment for the sheet metal to be machined defines the 
punching depth and is increased but avoiding a like increase in the 
distance between the cutting clearance and the ram axis as was necessary 
in known punching presses if an increase of the punching depth was to be 
obtained. Since such a greater punching depth can be achieved without a 
corresponding increase of the distance between the cutting clearance and 
the ram axis it is possible for the ram to retain its less massiive 
construction so that no special problems regarding axial ram guiding and 
supporting of the ram on the machine casing occur even with such greater 
punching depth. 
As regards axial ram guiding and the support of the ram on the machine 
frame the invention permits the adoption of a simpler embodiment because 
smaller forces are transmitted to the ram axis under comparable 
conditions. In terms of achieving optimum cutting quality the invention 
also provides that the ram is axially guided by pin-and-bush guiding 
means, preferably situated directly adjacent to the cutting clearance or 
in the transverse plane which accommodates the cutting clearance and 
comprising at least two pins disposed on the ram and on the machine frame 
and associated guide bushes. Doubling of the pins and guide bushes is 
advantageous since in addition to providing precise axial guiding for the 
ram it also at least substantially prevents the creation of a torque with 
respect to the ram axis, particularly if the pin guide is situated on the 
ram axis side which is distal from the cutting clearance. As regards the 
attainable cutting quality this can be improved still further by means of 
such a pin-and-bush guide in accordance with a particularly advantageous 
embodiment of the invention in which each pin is coupled to the associated 
guide bush through a ball socket joint comprising a joint ball disposed on 
the pin end and a ball socket which is axially slidable in the guide bush 
and is arranged concentrically therewith. Such ball sockets ensure that 
even large lateral forces which act on the pin-and-bush guide have no 
detrimental effect on the guiding accuracy, an effect which could occur by 
directly guiding the pins on the associated guide bush due to the pin axis 
being aligned at an angle to the axis of the guide bush so as to lead to 
greater edge pressure and therefore to an increase of the clearance 
between the pin and the guide bush so that axial guiding of the ram 
becomes progressively less accurate when allowing for wear in the course 
of time. Inaccurate ram guiding however finally enables the top cutter to 
deflect at the moment of the cutting operation so that a corresponding 
reduction of the cutting quality must be expected. However, in the 
presence of such ball socket joints any angular position of the pins 
mounted on the ram will have no detrimental effect on the entire axial 
guiding of the ram because it results merely in a specific displacement of 
the press force which acts on the associated ball socket without resulting 
in a change in the manner in which this is guided on the surrounding guide 
bush of the pin-and-bush guiding system.

The illustrated punching press is constructed as a coping press due to the 
top cutter 2, attached to the top end of a vertically movable ram 1, 
comprising two individual cutters 3 and 4 arranged at right angles to each 
other to provide a corresponding rectangularly constructed cutting 
clearance in conjunction with a bottom cutter 7 attached to the machine 
table 5 of the machine frame, the entirety of which is designated with the 
numeral 6. The bottom cutter 7 also comprises two individual cutters 8 and 
9 which are individually screw-mounted to the machine table 5 so that they 
can be simply exchanged. 
The ram 1 is constructed over its entire axial length as an equal-limbed 
L-section the top end of which is provided with a mounting plate 10 for 
the top cutter 2. Said mounting plate 10 can be integral with the angle 
section or it can be a separate component which is welded to the angle 
section or is otherwise rigidly connected thereto so that the top cutter 2 
is firmly held on the ram 1. As can be seen more particularly by reference 
to the cross-section according to FIG. 2, the top cutter 2, which is 
attached to the ram 1, projects beyond the cross-sectional surface area of 
the angle section in a configuration which is such that the internal 
cross-sectional edges of the two equally long limbs 11 and 12 and the 
cutter edges, which produce the cutting clearance and are associated with 
the two individual cutters 3 and 4 of the top cutter provide a square 
contour. The transverse plane, in which the top cutter 2 is situated and 
which is associated with the ram 1, therefore forms a block-shaped cavity 
13 which is defined on the one hand by the vertical internal surfaces of 
the two limbs 11 and 12 and on the other hand by the vertical internal 
surfaces of the two individual cutters 3 and 4 of the top cutter and whose 
axis 14' practically coincides with the axis of the centre of gravity of 
the two cutters 2 and 7 with which the accuracy of axial guiding of the 
ram 1 is to be aligned. The axial length of the cavity 13 must be at least 
equal to the length of stroke of the top cutter 2 so that the full 
notching depth can be utilized when notching sheet metal in one operation, 
the said full notching depth being defined in FIG. 2 by the distance 
between the corner points 14 and 15. To retain the said longer notching 
depth the points 14 and 15 the ram 1 need only be constructed as an angle 
section at the place of attachment for the top cutter 2 and only at least 
over the axial length corresponding to the length of stroke of said cutter 
and the remaining length of the ram can be constructed in any desired 
manner, for example in solid form if this should result in particular 
advantages for guidance or advantages for a specific kind of drive for the 
ram. 
As regards the top position of the ram 1 a collector plate 16 for punching 
waste is inserted between the two limbs 11 and 12 of the angle section 
beneath the transverse plane in which the cutting clearance is 
accommodated so that the punching waste can be deflected to a guide plate 
17, arranged at an angle, and from there to a container (not shown) which 
is situated adjacent to the machine. The drive for the ram 1 is designated 
in its entirety with the numeral 18 and is situated in the axis of the 
centre of gravity 14' of the two punching cutters 2 and 7, said drive 
comprising a hydraulic cylinder 19 mounted on the ram and a piston 20 
which is mounted on the machine frame. The piston 20 is provided with an 
axial port, aligned with the axis of the centre of gravity 14', for the 
delivery of hydraulic fluid against the floor of the cylinder 19 to enable 
the working stroke of the ram to be performed. Restoring springs, not 
shown, are provided for the return stroke of the ram. A triple 
pin-and-bush guide system is provided for axial guiding of the ram 1 and 
forms a kind of three-point support for the ram on the two top positions 
21 and 22 near the cutting clearance and on the place 23 which acts on the 
bottom ram end. Since the pin-and-bush guiding system is identically 
constructed at these three places, the description hereinbelow can be 
confined to the pin-and-bush guidance system situated at the place 22 and 
illustrated in FIG. 4. 
The pin-and-bush guidance system 22 comprises a pin 24, which is flanged on 
the ram 1 or on its mounting plate 10 for the top cutter 2 and is pulled 
tight against the ram by a screw-fastener 26 which is disposed in the pin 
axis 25. A guide bush 27 is bolted on the machine frame 6 coaxially with 
the pin 24 and a further bush 28 is axially slidable in said guide bush 
27. The ball socket 29 of a ball socket joint is attached to the bush 28 
which is therefore also coaxial with the pin axis 25 and the joint ball 
30, which is associated with the ball socket joint, is slid on the free 
end of the guide pin 24 and is retained on said pin by means of a mounting 
plate 31. The ball socket 29 on the other hand is retained on an internal 
stop abutment of the bush 28 by means of a sleeve 32 which is inserted 
into the mounting bush 28. 
As can be seen more particularly by reference to the sectional view 
according to FIG. 2, all three pin guides 21, 22 and 23 are situated on 
the side of the centre of gravity axis 14' which is distal from the 
cutting clearance. The two top pin guides 21 and 22 are arranged on 
different sides of the vertical plane which accommodates the said centre 
of gravity axis 14' and the measured distance defining the punching depth 
between points 14 and 15, the bottom pin-and-bush guiding system 23 being 
disposed in the said vertical plane on the other hand to achieve a 
corresponding large stability for the previously mentioned three-point 
bearing system. Since the two top pin-and-bush guides 21 and 22 act 
directly adjacent to the cutting clearance this ensures that the size 
thereof is maintained constant even for larger cutting forces and a 
constant cutting quality is thus ensured. 
Finally, it should be mentioned that the ram can be either an integral 
casting or can be a component which is welded together from several 
individual components. Sectional shapes other than an equal-limbed 
L-section can be considered, including a ram which is at least partially 
constructed as a half-shell, depending in first place on a particular 
application for such a machine.