TECHNICAL FIELD

The present invention relates to a hole stamping tool assembly, and then particularly but not exclusively to a stamping tool assembly of the kind which comprises a u- shaped main body or C-frame, the outer portion of one arm of which is provided with a recess for supporting a die and the outer part of the other arm of which is provided with a hole or cylindrical bore which is opera¬ tive in guiding a punch holder and associated punch, wherein an upper plate is arranged to hold the punch holder spaced from the die, with the aid of spring devices (cup springs), so as to enable a workpiece to be stamped to be introduced between the punch and die.

The force delivered by the stamping machine on the punch holder during a stamping operation will exceed the force required to compress the spring devices and the required stamping force, wherein the force transmitted to the spring device during its compression is adapted to lift the punch subsequent to stamping a hole in said work- piece.

BACKGROUND PRIOR ART

Stamping machines of this kind are previously known in many different forms.

One example of such stamping tools is the stamping tool referenced 25JL and sold by "Raskin sa, Lausanne-Ver- nand, Cheseaux", Switzerland.

This and other known stamping tools use spring devices

in the form of a pack of so-called cup springs or Bel¬ leville spring washers, comprising a plurality of convex or concave spring washers where, in constructing the pack, a concave surface of a first spring washer is turned to face a concave surface of an adjacent spring washer, whereas the convex surface of the first cup washer shall face a convex surface of another, adjacent spring washer, and so on, such as to obtain thereby a spring device which can only be compressed when sub- jected to very large compression forces, these forces being subsequently utilized withdraw the punch out of engagement with the workpiece, upon completion of a stamping operation.

GB-A-2 050 910 teaches a stamping tool in which a spring pack is housed in an outer sleeve.

This sleeve, however, is fully open at both of its ends and has an inwardly extending lip or flange provided midway along its long axis.

A spring pack (consisting of cup springs or Belleville spring washers) compressed by a given axially acting force is enclosed in the sleeve, said spring pack sup- porting against the lip and being urged towards an upper lip or plate placed in a groove in the sleeve.

There is obtained in this way a cassette unit which, comprises a pre-compacted spring pack housed in a sleeve and which can be readily replaced _y another cassette.

When considering the circumstances surrounding the construction, it will be seen that if the sleeve is to be able to fulfill the purpose now intended, it will be necessary to produce the sleeve from "steel material", it

since very strong forces are required to hold together a spring pack, even when the pack is only pre-tensioned to a small extent.

Those forces acting on the sleeve will be greater when the cassette unit is used in a hole stamping tool.

Moreover, it will be seen that in the case of this known embodiment the sleeve is not displaced towards the plate so as to engage said plate, and that the spring proper¬ ties of the "sleeve" can be added to the spring proper¬ ties of the spring pack, during a stamping operation.

US-A-2,876,276 teaches ways and means in stamping tools for generating a counter-force in two series-connected stages, with the aid of two series-connected resilient or elastic sleeves.

SUMMARY OF THE INVENTION TECHNICAL PROBLEMS

When considering the state of the prior art as described in the aforegoing and in the mentioned publications, it will be seen that a technical problem resides in the provision of providing simple protective or shielding device which will shield the spring device in the event of a fracture of one of the spring washers forming said device.

It will also be seen that a technical problem resides in the provision of a simple devoce for protecting a spring pack of the aforesaid kind which is successful in elimi¬ nating the hazard risk associated with cup spring packs when one of the cup springs fractures. When a cup spring forming part of such a spring pack fractures it is quite usual that parts of the broken spring will be thrown

powerfully from the stamping tool,therewith presenting the risk of injury to the machine operator and to per¬ sons in the vicinity of the tool.

It will also be seen that a technical problem resides in providing auxiliary spring means which act as a comple¬ ment to the cup springs or Belleville spring washers and which will not generate disturbing noise, as do the cup springs, during the compression and expansion to which the spring means is subjected in use, and also to reduce the noise level of the cup springs.

It will also be seen that a technical problem is one of realizing the advantage gained when using a plastic cup spring protective device which will also reduce the level of disturbing sound generated by compression and expansion of the cup springs, and which can be advanta¬ geously used to take-up a part of the impact forces generated in the stamping tool.

A further technical problem is one of realizing that this complementary spring means can be given a larger length of stroke in the stamping tool used, and there¬ with enable harder and thicker workpieces to be stamped than is possible in practice when using solely cup springs as the spring force generator.

With springs that have a long length of stroke when stamping hard and/or thick material, more powerful force-absorbing spring means are required than when _'» stamping softer materials. 1

A technical problem thus resides in realizing that with suitable dimensioning of simple hollow cylindrical bodies it is possible to adapt force take-up to prevail-

ing circumstances with respect to stroke length, work- piece hardness and thickness, the configuration and size of the punch and the dimensioning of the cup springs.

It will also be seen that a technical problem resides in realizing that a complementary spring means intended for solving one or more of the aforesaid technical problems shall be made from a plastics material and given a hollow-cylindrical form.

It will also be seen that a highly qualified technical problem resides in selecting from those plastic mate¬ rials at present available a plastic material having properties which will fulfill the aforesaid requirements and solve the aforesaid technical problems, solely by shaping the plastic material into a hollow cylinder. This hollow cylinder shall be given internal dimensions which coincide, or substantially coincide with the outer dimensions of the spring device, such that the hollow- cylindrical element will enclose the spring device with a small clearance therebetween.

It will also be seen that a technical problem is one of realizing that a hollow-cylindrical plastic element placed around the cup washers not only protects the cup washers effectively but also that said hollow-cylindri¬ cal element can be used as a complementary spring means capable of use in existing stamping machines.

Another technical problem is one of realizing the advantage afforded by the fact that such a complementary spring means will enable one and the same stamping machine equipped with given cup springs to be used effectively for stamping thicker and/or harder metal sheet workpieces than those for which the machine was

intended.

A further technical problem is one of realizing that simple dimensioning of the complementary spring means will not only produce changes in the available punch restoring force, but can also be used to decide when and during which part of a stamping operation such changes shall be effected, such as for instance, solely at the end of the downward travel of the punch.

Finally, another technical problem is one of realizing that the use of two such complementary spring means will enable the hammer of the machine to be given a longer length of stroke, without having any deleterious effect on the machine, while enabling the punch restoring force to be increased to a level above that afforded by the cup springs.

SOLUTION For the purpose of solving one or more of the aforesaid technical problems, the present invention departs from a prior art hole stamping tool assembly having a U-shaped main body part or C-frame, the outer part of one arm of which has provided therein a recess for supporting a die and the outer part of the other arm of which is provided with a hole or bore operative in guiding a punch holder and associated punch, wherein a plate which coacts with the upper punch holder is effective in holding the punch holder spaced from the die, by means of one or more spring devices (cup springs, Belleville spring washers etc.) , such as to enable a workpiece to be introduced between the punch and the die.

During operation of a stamping or pressing machine, the force acting on the punch holder will exceed the force

required to compress the spring device and the forces required to carry out the stamping operation, wherein the force transmitted to the spring device during the compression thereof is adapted to lift the punch out of engagement with the workpiece upon completion of a stamping operation.

The cup washers of the spring device of such a stamping machine are enclosed in a hollow-cylindrical, plastic element, the inner dimensions of which coincide with, or at least substantially coincide with (are slightly larger than) the outer dimensions of the spring device, such as to provide a protective sleeve which surrounds the cup springs.

According to the present invention, the hollow-cylindri¬ cal element is made from a material which has properties similar to or equal to the properties of the material designated "Adiprene", and that the tubular element and the cup springs are arranged for parallel compression.

According to one embodiment of the invention, said material will have a hardness corresponding to or sub¬ stantially corresponding to the hardness of the material "Adiprene 99 A".

It is also proposed that the wall of the protective hollow-cylindrical element is thin, in relation to its outer diameter, and that said element is provided with an upper, inwardly extending collar, such as to form a cavity adjacent an upper plate of the punch holder.

The hollow-cylindrical element will preferably have a length such that the spring device can be compressed along a first section before the hollow-cylindrical

δ element is compressed, thereby enabling the hollow- cylindrical element, to take-up part of the force genera¬ ted by the stamping machine.

Finally, it is proposed that the uppermost cup spring of the stock of cup springs shall be replaced with a larger cup springwasher positioned in the upper part of the punch holder, wherein the hollow-cylindrical element and the spring device are arranged for co-action with said larger cup spring when the punch holder is urged down¬ wards by the stamping machine, and therewith take-up part of the force generated by the stamping machine, at the same time, increasing the force with which the punch is withdrawn from the workpiece.

ADVANTAGES

Those advantages primarily associated with the present invention resides in the possibility of protectively enclosing previously known spring devices in the form of cup springs, etc. in a plastic, hollow-cylindrical element and therewith afford a solution to the problem associated with fractured cup springs and also to the problem of noise generated by said cup springs during a working process.

Moreover, the hollow-cylindrical element is able to take-up the forces generated by stamping tools or machi¬ nes during anhe actual stamping stroke.

The invention also enables the tensile force of the cup springs to be complemented with an additional spring means, solely by replacing the uppermost cup spring with a cup spring of larger diamete,r or by a larger plate, and by placing a hollow-cylindrical plastic element over the cup springs lying beneath said uppermost cup spring

or plate.

The main characteristic features of an inventive stamp¬ ing machine are set forth in the characterizing clause of the following Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail with reference to the accompanying drawings; in which

Figure 1 is a perspective view of a known stamping tool; Figure 2 illustrates in larger scale the spring device enclosed by a hollow-cylindrical element, partially shown in section; Figure 3 is a side view of the hollow-cylindrical ele¬ ment, partially in section;

Figure 4 is a side view, partially in section, of an embodiment in which two hollow-cylindrical elements are used; and Figure 5 is a side view, partially in section, of an embodiment in which the upper part or plate of the punch holder is configured to co-act with a hollow-cylindrical element.

DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED

Figure 1 is a perspective view of a known stamping tool assembly having a U-shaped main part or C-frame, the outer part la' of one arm la of which is provided with a recess 2 for supporting a die 3, and the outer part lb' of the other arm lb of which is provided with a hole 4 or cylindrical bore operative in guiding an upwardly and downwardly movable punch holder 5 with associated punch, said punch being indicated by the reference numeral 6.

A stamping machine (not shown) is intended to urge the punch holder 5 and the punch 6 downwards, against the action of the spring force generated by cup springs 8, The term cup spring as used here and in the following includes all manner of dished or saucered spring washers, Belleville spring washers, etc.

An upper plate 7 on the punch holder 5 is intended to hold the punch holder 5 spaced from the die 3, with the aid of a spring device in the form of cup springs, such as to enable a workpiece (not shown) to be introduced between the punch 6 and the die 3. The upper edge of the punch holder 5 may extendinwardly, such as to form an equivalent to the aforesaid plate 7.

The cup springs 8 hold the punch holder 5 and the punch 6 urged towards an upper position, said holder and punch being latched in said position by latching means.(not shown) , therewith enabling the workpiece (not shown) to be inserted between the punch 6 and the die 3. The workpiece is introduced into the space referenced 10 in Figure 1.

The force acting downwardly on the punch holder 5 and generated by the stamping or pressing machine during a stamping operation is selected so as to exceed the force intended for compression of the spring device 8 and also the force required to effect a stamping operation, wherein the force transmitted to the spring device 8 during compression of the springs in the direction of arrow "PI" is adapted to lift the punch 6 out of engage¬ ment with the workpiece, when the springs are released subsequent to completion of a stamping operation. The thicker and harder the workpiece, the larger the force required.

The spring device 8 comprises a plurality of mutually superimposed, convex and concave cup springs, or Bel¬ leville spring washers, with one concave side of a first cup spring facing towards a concave side of an adjacent cup spring, and the convex surface of said first cup spring facing towards the convex surface of an adjacent cup spring, thereby enabling the cup springs to be compressed in relation to one another, the compression force being absorbed by the cup springs as they flatten out.

In accordance with the present invention the spring device 8 is enclosed in a hollow-cylindrical, plastic element 11, one embodiment of which is shown in side view in Figure 3.

The internal dimensions "d" of the hollow-cylindrical element coincide with, or at least substantially coin- cide with the corresponding outer diameters of the spring device 8 used, which means that the inner dia¬ meter "d" will coincide with or be slightly greater than the outer diameter of the cup springs 8. The vertical axial extension "H" of the element 11 coincides with, or is somewhat greater than or smaller than the vertical extension of the spring device 8 when said cup springs thereof are in their relaxed state, i.e. not compressed with the aid of the plate 7.

The material from which the hollow-cylindrical element 11 is made has inherent spring properties.

It is proposed in accordance with the present invention that the hollow-cylindrical element is made from a material having properties equal to or similar to those

of the material "Adiprene", and. it is particularly proposed that said material shall have a hardness cor¬ responding to or substantially corresponding to the hardness of the material known as "Adiprene 99 A".

The element 11 shall be capable of acting as a shield in the event of fracture of the cup springs 8. (It will be understood that the shielding effect provided by the tubular element 11 is not limited solely to shielding those in the vicinity of the tool from flying debris, but that the element will also effectively dampen the sound generated by the springs, and also will protect the springs from breakage in a secondary fashion, because the element relieves the spring device of some of its load.)

In this case, the distance "D-d" will be small and the element will be provided with an upper shoulder or collar 12- intended to surround the plate 7 on the punch holder 5.

When the element 11 is positioned in the manner illu¬ strated in Figure 2, .the element 11, in addition to serving as a protective shield should one or more of the cup washers fracture, will also serve as a counter- spring means and will take-up a part of the forces transmitted by the stamping machine to the plate 7 on the punch holder 5. This enables the length of stroke of the stamping machine to be increased and harder mate- rials to be stamped.

Thus, the illustrated element 11 can be caused to serve as an additional or complementary load-absorption spring means, and the value of this load-absorption being determined by the dimensions of the element.

In that case when the element 11 is to be complemented in a manner which will also enable the element to add to the force at which the punch 6 is withdrawn from the workpiece or restored to its starting position,it is proposed that the shoulder 12 is omitted and that the top cup spring 8' of the spring device is replaced with a cup spring 14 having an outer diameter which corres¬ ponds to the outer diameter "D" of the element 11. This cup spring 14 should be stronger than the remaining cup springs.

Figure 4 illustrates an embodiment in which the top cup spring has been replaced with a cup spring 8" (14) of larger diameter.

The outer peripheral surface of the larger cup spring 8" is intended to co-act with the upper edge of a resilient further hollo-cylindrical element 11'. having the form of a hollow cylinder.

In addition to serving as a protective or shielding element, the further resilient element 11' will also serve to take-up part of the forces transmitted by the stamping tool during a stamping stroke, thereby enabling the length of stroke of the stamping machine to be increased, in accordance with what was described in the aforegoing and will also be operative to transmit the compression forces to which it is subjected to the spring device 8 as a complementary force when the punch 5 is withdrawn from the workpiece upon completion of a stamping stroke.

The first mentioned element 11 described with reference to Figure 3 has the same technical effect as that previ-

ously described, but is intended to shield the cup spring 8".

Figure 5 illustrates en embodiment in which the plate 7 is configured to provide a support surface 7' for the element 11', the function of which is equivalent to that described with reference to Figure 4.

It is now possible to dimension the thickness and length of the element 11' in dependence on the desired punch restoring force, therewith enabling a stamping machine to stamp material which requires a larger restoring force than that which can be obtained solely by the cup springs 8.

It is now also possible to adapt the length "H" of the element 11', so that the spring device 8 is forced to be compressed along a first section thereof prior to com¬ pression of the hollow-cylindrical body or element.

The element 11' still serves to shield the cup springs.

The following diameter values are proposed in respect of the element 11', when said element is to function as a spring means:

"D" "d" "H"

50 40 65

60 50 67

70. 3 60 .5 65 9 955 8 822 68

It will be understood that the value "D" can be increa¬ sed if space allows, and therewith obtain an increasing force.

When the punch holder 5 is urged downwards, this down¬ ward force will act initially solely against the force of the springs 8, whereafter both the springs 8 and the element 11 and, when provided, the element 11', will be compressed (the path is determined by the value of "H" and the distance from the undersurface 11a of the ele¬ ment 11 and a flat part 15).

Upon completion of a stamping stroke, the force exerted by the springs 8 and the force exerted by the element 11' are operative in separating the punch 6 from the workpiece. Although the length of the element 11 (and also the element 11') can be chosen from within wide limits, the length of the outer element should be suffi- cient to cover the whole of the spring device. A greater force can be obtained by increasing the thickness and the lengths of the elements.

As beforementioned, the hollow- cylindrical plastic element 11 of Figure 3 is provided with a collar 12 and is operative to shield the whole of the spring device 8.

In the absence of collar 12, the element serves to shield the cup-spring pack 8 as a whole, and without the collar serves as a complementary spring means (11') and the hollow-cylindrical element (11') is intended to support against an uppermost, wider cup spring 8" or plate 7.

There is nothing to prevent a complementary spring device 11' of this kind being provided with a shielding sleeve 11 according to Figure 3, although in this case the inner diameter "d" of the hollow-cylindrical shield¬ ing element 11 will slightly exceed the outer diameter of the complementary, hollow-cylindrical spring device 11'.

It will be understood that the aforedescribed spring device comprising cup springs 8 is not necessary to the function of the invention, but that the inventive prin- ciples can be applied equally as well to other kinds of spring devices.

Also included in the scope of the invention is an em¬ bodiment in which the plate 7 has a thickness and width which also includes the thickness and width of the uppermost, enlarged cup spring 8", as illustrated in Figure 5.

It will also be understood that the invention is not restricted to the aforedescribed and illustrated embodi¬ ments and that modifications can be made within the scope of the following claims.