AU609914B2 - Method of and means for forming a hole in metal - Google Patents

Description

PAS: KA LLIPS ORMONDE AND FITZPATRICK Anrr sHE Patent and Trade Mark Attorneys 367 Collins Street MAIL/ Melbourne, Australia P17/2/81

AUSTRALIA

Patents Act 609914 COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: iThis cdocumnnt contains the amendments made under Section 49 and is correct for printin, -r 1c Complete Specification Lodged: Accepted: Published: Priority Related Art: Name(s) of Applicant(s): Address(es) of Applicant(s): APPLICANT'S REF.: C.A.P. of PI 5942 PETER GEORGE HALL and KENNETH RONALD DAFF 3 Batman Street, Essendon, Victoria 3040, Australia and 2 Hillside Avenue, Dandenong, Victoria 3175, Australia (respectively) Peter George Hall and Kenneth Ronald Daff 4 Actual Inventor(s): REPRINT OF RECEIPT Address or S5 1i Address for Service is: 9 %B C-9- PHILLIPS, ORMONDE AND FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne, Australia, 3000 Complete Specification for the invention entitled: "METHOD OF AND MEANS FOR FORMING A HOLE IN METAL" The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 1: i i i i.!

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This invention relates to a method of and means for forming holes in metal plate, tubular sections and like metal workpieces.

Forming holes in metal sections is a task which is frequently undertaken in many engineering applications. Holes are usually punched, or drilled, although when the hole to be formed is not of circular shape, drilling methods are unsatisfactory. Punching of holes generally requires that the metal section be suppo:cted so no collapsing of the section 0io occurs as a result of punch loading. With tubular sections, this generally means that a support of some description be inserted into the interior of the tube to provide support for the tube. However, not only does the positioning of the zt support delay a punching operation, which is undesirable, but Smany tube interiors are inaccessible which means that providing internal support is impracticable.

It is an object of this invention to provide an improved t r V method of and means for forming such holes which is convenient

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to operate and of relatively simple construction and easily operable. It is an object of the invention in a preferred form to provide a method and means for forming holes in tubular metal sections, channel sections and other metal sections which are difficult to support for the purposes of a Shole forming operation.

According to one aspect of the invention, there is provided a method of forming a hole of predetermined shape in a metal workpiece, including the steps of connecting a said workpiece into an electrical circuit which includes an electrode having a transverse cross-sectional shape which is related to said predetermined shape of the hole, causing an end of the electrode to engage a surface of said workpiece and to thereby complete said circuit, causing current to pass through said completed circuit such as to cause heating of the part of the workpiece engaged by said electrode, and applying pressure between said electrode end and said workpiece so as to cause the electrode to penetrate through said heated part and thereby form said hole, or part thereof.

The reference to a relationship between cross-sectional 39 shapes is to be understood as embracing any situation in which t the electrode cross-sectional shape is such that it is capable of forming the predetermined shape of the hole. For example, a circular section electrode would not be suitable for forming a square hole and consequently does not have a related shape.

A square electrode can be used to form a rectangular hole and therefore does have a related shape.

In many cases, it is desirable for both the cross-sectional shape and size of the electrode to be substantially the same as the shape and size of the hole to be formed. Such an arrangement enables the hole to be formed by a single pass of the electrode through the workpiece, or part thereof. There may be situations where it is convenient or S desirable for the hole to be formed by two or more passes of the electrode, for example, where the hole is of complex C shape. Also, it may be necessary in some cases to use t electrodes of different shapes to form a particular hole.

S That is, one electrode may be used to form one part of the C tZ t hole, and another is used to form another part of the hole.

According to a further aspect of the invention, there is provided apparatus for forming a hole of predetermined shape in a metal workpiece including, a base plate of a nature such as to be adapted to form an electrical conductor, an electrode having an end located adjacent said base plate and normally S spaced therefrom, an electrical circuit which includes said ,t electrode and said base plate, power means operable to cause a current to pass through said circuit when that circuit is 1 completed, and pressure means operable to cause a change in the spacing between said electrode and said base plate, the arrangement being such that said circuit is completed by locating a metal workpiece between and engaging said electrode end and said base plate.

An embodiment of the invention is described in detail in the following passages of the specificaton which refer to the accompanying drawings. The drawings, however, are merely illustrative of how the invention might be put into effect, so that the specific form and arrangement of the various features as shown is not to be understood as limiting on the invention.

In the drawings: 39 Figure 1 is a diagrammatic view of one form of apparatus

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Cr incorporating an embodiment of the invention, Figure 2 is a cross-sectional view through the tip end of one form of electrode suitable for carrying out the method of the invention, Figure 3 is a view similar to Figure 2 but showing a different form of electrode and showing the electrode end engaging a workpiece, Figure 4 is a view taken along line IV-IV of Figure 3, Figure 5 is a view similar to Figure 4 but showing the electrode penetrating through the workpiece, Figure 6 shows the workpiece of Figure 5 with the hole formed therein, Figure 7 is a view taken along line VII-VII of Figure 6, cc Figure 8 is a cross-sectional view of one particular

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form of electrode which is cooled in a particular way, t Figure 9 is a view similar to Figure 7 but showing a different shape hole, Figure 10 is a view similar to Figure 7 but showing a larger hole, Figure 11 is a view similar to Figure 10 but showing the results of using a standard electrode to form the hole, Figure 12 is a cross-sectional view through an electrode which would be suitable for forming the hole of Figure I Example apparatus according to the invention is shown in Figure 1. That apparatus includes a base plate 1 of electrically conductive material, usually a metal, and which "t is adapted to form a suitable support for a workpiece 2. An C electrode 3 of appropriate form is positioned above the base plate 1 so that an end 4 of the electrode 3 is spaced from the adjacent surface 5 of the plate i. Pressure means 6 is connected to the electrode 3 and is operable to cause the electrode 3 to move towards and away from the base plate 1 as depicted by the arrows in Figure 1.

Both the plate 1 and the electrode 3 are connected into a circuit 7 which includes a suitable power source 8 which is operable to cause a high current (either AC or DC) to pass through the circuit 7, when that circuit is closed. The circuit 7 is closed by engaging the electrode 3 against a 39 metal workpiece 2 which is in electrically conductive -al; 1 ,i

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I. i engagement with the plate i. Any suitable control means 9 can be used to control energisation and de-energisation of the power source 8. That control means 9 may include a timer, for example, to automatically control the period of energisation, and means for adjusting the timer to enable variation of the energisation time.

The electrode 3 has a transverse cross-sectional shape which is related to the shape of the hole to be formed in the workpiece 2. In the example shown, that cross-sectional shape is square, but other shapes may be used according to circumstances. Also, in the example shown in Figure i, the hole 10 to be formed in the workpiece 2 has substantially the same shape and size as the transverse cross-section of the S electrode 3.

~cc The end 4 of the electrode 3 may be flat as shown in Figure 2. It is preferred, however, to provide a recess or V" depression 11 in the end 4 as shown in Figure 3 so that a r f narrow land surface 12 (Figure 4) is formed around the perimeter of the end 4.

When the electrode end 4 is engaged with a surface of the workpiece 2 as shown in Figure 3, energisation of the power source 8 causes current to pass through the circuit 7.

In that regard, the workpiece 2 forms a conductor between the S electrode 4 and the base plate 1 and thereby completes the circuit 7. The electrode 3 has a high level of conductivity by comparison with that of the workpiece 2 and as a consequence resistance heating occurs in that part of the workpiece 2 which is engaged by the electrode 3. The degree of heating can be regulated in a number of ways including regulating the level of the current applied to the circuit 7 by the power source 8.

As the temperature of the heated part of the workpiece 2 increases, pressure is applied between the electrode end 4 and the workpiece 2 by appropriate operation of the pressure means 6. The level of that pressure can be regulated to suit circumstances. The combination of heat and pressure results Sin the electrode eventually penetrating through the wall 13 of i the workpiece 2 as shown in Figure 5. That penetration S 39 results from separation of a slug 14 of material from the wall AT 13 which has substantially the same shape and size as the hole (Figures 6 and 7) so formed.

It will be appreciated that the use of an electrode configuration as shown in Figures 3 to 5 results in concentration of heating around the boundary of the hole to be formed. That naturally facilitates the hole forming operation.

In one example method of operation, the control means 9 includes a time control unit, and the operation of the method is preferably controlled to provide a current, time and pressure combination adjusted for a particular workpiece 2 in which the hole 15 is to be formed. Thus, a thicker workpiece may require a higher current, or longer time of current v operation, and/or higher pressure for a hole to be formed therethrough than will be required for a similar hole to be Sformed through a thinner workpiece. Current may be stepped up Ctrs from the power source 8 using one or more transformers.

r Any suitable electrode may be selected for the method of of beryllium copper, or another hard copper alloy, are satisfactory. As stated above, the electrode 3 is urged Sagainst a surface of the workpiece 2 during performance of the Smethod, and the force with which the electrode 3 bears against that surface may be adjustable. In some applications the S force may be high to achieve the desired penetration of the electrode 3 through the workpiece 2, and in other applications the force may be quite low. A lower force will usually be S" suitable for workpieces 2 formed of thin walled section. In V situations where a significant force is applied to the workpiece 2, the time it will take to form a hole through the workpiece 2 will be affected by both the force and supplied current.

The hole 15 formed by the electrode 3 passing through the wall 13 will usually be slightly larger in size than the electrode 3. It has been found that the inner edge of the hole 15 formd using the method of the invention is spaced away from the sides of the electrode 3 by approximately 1.5 mm.

Selection of an electrode cross-section will then take this factor into consideration.

i 39 It is usually preferred to provide means for cooling the SAT -6electrode during the operation of the method. Such cooling may be effected by circulating water or other coolant through a chamber 16 or passage formed within the electrode 3.

In a preferred arrangement, cooling of the electrode 3 is effected by means of a vortex tube 17 as shown in Figure 8. Pressurised air is fed into the inlet 18 of the tube 17 and the resulting air stream 19 within the tube 17 is induced to f low towards the end 20 of the tube 17 in a swirling fashion. Part of the air stream 19 is returned down the centre of the tube 17 as shown by arrows 21, and another part escapes through one or more orifices 22 to emerge through the outlet 23. The returning stream part 21 emerges through an opposite end outlet 24 to enter the electrode chamber 16. An S" outlet 25 is provided in the electrode 3 to enable continuous circulation of air within the chamber 16.

Vortex tubes of the foregoing kind are well known as is C their manner of operation. The characteristic feature of such C tubes is that the part of the air stream emerging from the outlet 24 is at a low temperature minus 40 0F), whereas the part emerging from the outlet 23 is at a (relatively high temperature.

The method of the invention may be performed manually or C CC may be automated through suitable automation equipment. There may be a single electrode mounted in position on the apparatus, or there may be a plurality of electrodes adapted to form holes simultaneously or in sequence in a workpiece.

As previously stated, a preferred end configuration of Sthe electrode 3 is shown in Figures 3 to 5, although the form of the central depression 11 could be different to that shown. An electrode 3 having such an end configuration will ensure that current is concentrated around the periphery of the electrode 3 at its contact with the surface of a workpiece 2 and, high current passing down the periphery of the electrode 3 will tend to pass into the workpiece 2 at the points or zone of contact between the electrode 3 and the workpiece 2. Depending on the magnitude of the current, the part of the workpiece 2 which is in contact with the electrode 3 will soften and progress towards a molten state. The 39 electrode 3 is able to pass through the workpiece 2 because of AT -7-ij the softening of the workpiece metal and the pressure applied between the electrode 3 and the workpiece 2. Little, if any, deformation of the workpiece 2 will occur in the region surrounding the electrode 3, so that subsequent cleaning or finishing of the edges of the hole 15 is generally not necessary.

In the arrangement shown in the drawings, the base plate 1 forms part of the circuit 7. That is, the plate 1 is earthed, or otherwise arranged to provide a conductor for passage of current through the workpiece 2. Other arrangements are clearly possible, for example, the workpiece may be connected directly to earth or otherwise connected into the circuit to be a conductive part of that circuit.

As previously mentioned, any suitable configuration of hole may be formed using the method described. Thus, for example, a square hole will be formed using an electrode S having a square cross-sectional shape. Similarly, if a c triangular hole is to be formed, an electrode having a t te Striangular cross-sectional shape will be utilised. Clearly, other configurations of electrodes may be selected to suit a r particular use. In the main, an electrode having a shape and size which corresponds substantially to the shape and size of the hole to be formed, will be selected, but such a selection Sis not essential.

-C The hole 26 shown in Figure 9 could be formed by making several passes four) of an electrode having a square fC cross-sectional shape. That is, for each pass of the t electrode, the location of the electrode relative to the workpiece 2 is changed. Alternatively, the same hole could be formed by two passes of an electrode having a rectangular cross-sectional shape. In that case, the relative disposition and location of the electrode would be altered for the second pass. It is further possible to form the hole 26 by one pass of an electrode having an appropriate T-shape in transverse cross-section.

special cross-sectional shape to suit particular conditions of use. Figure 10 shows a hole 27 which is formed through one 39 wall 13 of a tubular workpiece 2 and extends the full distance AT -8r between two sides walls 28 of that workpiece 2. If a square electrode of full size was used to form the hole 27, the two side walls 28 would be eroded as shown at 29 in Figure 11. A satisfactory electrode may have a cross-sectional shape as shown in Figure 12.

During use of the Figure 12 electrode, it is found that arcing occurs between each workpiece side wall 28 and the base of the adjacent electrode groove 31 such that a straight side is formed at each side boundary of the hole 28, as shown in Figure As previously stated, the electrode 3 may be made of any suitable material, and a copper alloy is one such material.

The electrode material may be selected according to the material from which the corresponding workpiece 2 is made in 14 order that optimum operational conditions are maintained.

S Preferably, the electrode 3 is made from a material which is non-degradal)le.

4It Various alterations, modifications and/or additions may rt be made to the embodiments of the invention described herein without departing from the spirit or ambit of the invention.

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Claims (13)

1. A method of forming a hole of predetermined shape in a metal workpiece, including the steps of connecting a said workpiece into an electrical circuit which includes an electrode having a transverse cross-sectional shape which is related to said predetermined shape of the hole, causing an end of the electrode to engage a surface of said workpiece and to thereby complete said circuit, causing current to pass through said completed circuit such as to cause heating of the part of the workpiece engaged by said electrode, and applying pressure between said electrode end and said workpiece so as to cause the electrode to penetrate through said heated part S and thereby form said hole, or part thereof.

S2. A method according to claim 1 wherein said hole is tC,, enlarged by penetrating said electrode through said workpiece at two or more adjacent positions on said workpiece.

3. A method according to claim 2 wherein said electrode is square and the hole thus formed is of rectangular configuration.

4. A method according to claim i, wherein the transverse cross-sectional shape of said electrode closely approximates said predetermined shape. A method according to claim 4, wherein the transverse C e t cross-sectional size of said electrode is substantially the same as the size of said hole.

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6. A method according to any preceding claim, wherein said electrode is cooled during said penetration.

7. A method according to claim 6, wherein said cooling is effected by passing fluid under pressure through a vortex tube contained within said electrode.

8. A method according to claim 7, wherein said fluid is air.

9. A method according to any preceding claim, wherein passage of said current is atuomatically terminated after a predetermined time. A method according to any preceding claim, wherein said electrode end has a depression formed therein so that a land surface is formed about the perimeter of that end, and said land surface is engaged with said workpiece surface.

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11. Apparatus for forming a hole of predetermined shape in a metal workpiece including, a base plate of a nature such as to be adapted to form an electrical conductor, an electrode I having an end located adjacent said base plate and normally spaced therefrom, an electrical circuit which includes said electrode and said base plate, power means operable to cause a current to pass through said circuit when that circuit is completed, and pressure means operable to cause a change in the spacing between said electrode and said base plate, the arrangement being such that said circuit is completed by locating a metal workpiece between and engaging said electrode end and said base plate. t

12. A method of forming a hole of predetermined shape I through a metal workpiece, substantially as herein Sparticularly described with reference to what is shown in the accompanying drawings.

13. Apparatus for forming a hole of predetermined shape in a o metal workpiece, substantially as herein particularly described with reference to what is shown in the accompanying drawings. t' DATED: 16th December, 1988 j PETER GEORGE HALL and i KENNETH RONALD DAFF By their Patent Attorneys: PHILLIPS, ORMONDE FITZPATRICK "X0 7151C L