WO1998019806A1 - Tubular metal joint assembly and manufacturing tool therefor - Google Patents

Abstract

An expansion tool (10) for forming at least one toroidal deformation (21) in a tubular metal element (20), including: a shank (12) mountable in a driving machine for rotary movement; a toolbar or workhead (11) on the shank and co-axial therewith; a pair of diametrically spaced, circumferentially extending, grooves or slots in the toolbar or workhead, each groove having an inclined floor or ramp; and a respective expansion ball (14) in each groove, each ball being movable from a respective retracted position to a respective extended position, so arranged that: on insertion of the toolbar or workhead in the tubular element (20), and on rotation of the shank in one direction by the driving machine, the expansion balls move from their retracted positions to their extended positions to progressively form at least one toroidal deformation in the tubular element.

Description

TITLE: "TUBULAR METAL JOINT ASSEMBLY AND

MANUFACTURING TOOL THEREFOR" BACKGROUND OF THE INVENTION

1. Field of the Invention This invention relates to a method of, eg., and apparatus, for fixing together tubular metal construction elements. The invention further relates to an expansion tool, which when positioned inside a tubular element, is operable to generate a toroidal deformation in the tubular element against an intersecting element at a joint to lock the two elements together.

2. Prior Art

The principal existing fabrication industry work practice applied in joining different size metal tube, bar or flat is welding, whereby the smaller tube members are butt welded to rail members; or the smaller tubes are welded in place upon insertion in or at the point of passing through the larger rail member. Alternatively, fixing is effected by mechanical application of screws, bolts, rivets or the like. Both the foregoing methods possess a number of inherent disadvantages.

The foregoing practices of welding, bolting or riveting are labour intensive, slow and costly. Some industry applications employ high capital cost robotic plant to increase welding productivity. Robotic welding technology requires large floor areas, substantial jigging and significant maintenance of account of sophistication. Post-welding processing, such as de-splattering and grinding, is required to remove any hazardous material, and to smooth all weld zones for aesthetic purposes, prior to re- application of protective metal coating agents to the weld heat affected zone. This additional processing adversely impacts upon process flow efficiency, productivity and costs.

In some industry applications, steel tube is preferred to aluminium for strength and security. However, welding adversely affects the coating integrity of all pre-galvanised tube coatings, by destroying the galvanised coating in the weld heat zone. To properly rectify coating damage, steel tube should be re-coated by hot dip galvanising, which is an additional costly process. If effective re-coating of steel is not completed, degradation to the joint area ultimately occurs, followed by scale and rust. Welding nullifies the advantages of pre-galvanised steel products and maintains the status quo advantage of aluminium over steel where possible corrosion is a factor, although effective welding of aluminium tube is more sensitive than steel welding and is therefore more likely to fail or fracture upon impact or from physical abuse. Further disadvantages associated with welding and post- welding processes are serious exposures to health and injury risk. "Palmer Tube Mills Material Safety Data Sheet 1.1.9 Rev 1 Feb 96 WORKPLACE HAZARDS AND HEALTH EFFECTS: - Potential Exposure" quotes as follows: "(a) Eye Cutting, grinding, sanding, etc., are potentially injurious to eye tissue.

(b) Skin During operations using or producing heat (welding, grinding, etc.) Burns may result from contact with hot surfaces.

(c) Inhaled During welding operations, fume emissions can cause metal fume fever. Fumes may also irritate the eye and mucous membranes. Dust produced by some operations may deposit in the eye and nose and may irritate the respiratory tract. Long-term exposure to iron oxide fumes may produce a benign lung condition (siderosis). High concentration of iron oxide fumes may increase the risk of lung cancer in operations exposed to pulmonary carcinogens.

(d) Workplace - Atmospheric Contaminants The National Occupational Health and Safety Commission (Australia) have set exposure limits for particulate welding fume. Engineering controls for operations producing fumes or particulates must ensure that ventilation is adequate to maintain air concentrations well below exposure limits.

Guidance on ventilation systems is provided in Health and Safety in Welding, Tech Note 7 1989 - Welding Technology Institution of Australia. Contamination concentrations should be determined in accordance with AS2853.1 - 1991. Operations in confined places should meet AS2865 -

1986 " It is clearly evident that existing industry practices involving welding pose serious occupational health risks.

Examination of prior art in relation to proposed mechanical fixing fabrication methods has identified the intended use of complex and laborious methods of attempted assembly such as "swaging" and "wedging" of smaller members at the point they pass through or intersect the horizontal member or rail. These methods involve use of complex and specialised swaging tools applying various apparatus to apply mechanical leverage or force to effect geometric profile distortion. Given that most common nominal bore sizes of cylindrical picket tube is 13mm to 16mm, the internal bore working area is so restrictive that it is a technical impossibility to apply many of the proposed swaging methods to effectively join members of multi-joint tubular panels. Although several of the prior art methods are the subject of the grant of Patents, interestingly, as a result of technical difficulty, complexity, practicality and cost, such methods have not been commercially adopted.

Prior art investigation further informs of process and assembly methods necessitating the manufacture of specialised metal tube extrusions having specific internal profile structure of female geometry designed to accommodate male tube geometry by engagement, then distorting means effected by swaging pressure internally. To apply such prior art methods, it is necessary to first arrange for the extrusion of specific production run female/male cross-sectional tubular profiles. The cost of special run extrusion profile tube is prohibitive. The process is selective and restrictive, and therefore, is not commercially viable. The methods require specialised costly tooling and the benefits of such proposed methods remain obscure. SUMMARY OF THE PRESENT INVENTION

It is an object of the present invention to provide a method of joining a tubular metal element to an intersecting element by eliminating the need to weld the elements or use conventional fastening systems. It is a preferred object to provide a method where deformation of the tubular element against the intersecting element locks the elements permanently together.

It is a further preferred object that the intersecting element may be of tubular or flat configuration, and the tubular element may be of square, rectangular or circular section.

It is a still further preferred object to provide such a method where the wall of the tubular element undergoes a toroidal deformation to effect the locking of the elements.

It is a still further preferred object that two or more spaced deformations are provided in the tubular element to lock the intersecting elements therebetween.

It is a still further preferred object to provide an expansion tool operable to form the deformation(s) in the tubular element.

It is a still further preferred object to provide such a tool which is relatively simple and inexpensive to manufacture; has a long life, requires minimal maintenance; and is highly suitable for repetitive use, at high production rates, in computerised (eg., CNC) equipment.

Other preferred objects will become apparent from the following description. In one aspect, the present invention resides in an expansion tool for forming at least one toroidal deformation in a tubular metal element, including: a shank mountable in a driving machine for rotary movement; a toolbar or workhead on the shank and co-axial therewith; a pair of diametrically spaced, circumferentially extending, grooves or slots in the toolbar or workhead, each groove having an inclined floor or ramp; and a respective expansion ball in each groove, each ball being movable from a respective retracted position to a respective extended position, so arranged that: on insertion of the toolbar or workhead in the tubular element, and on rotation of the shank in one direction by the driving machine, the expansion balls move from their retracted positions to their extended positions to progressively form at least one toroidal deformation in the tubular element.

Preferably, the shank and toolbar are formed integrally.

In one embodiment, the grooves or slots are axially aligned, so arranged that the expansion balls form a single toroidal deformation.

In a second embodiment, the grooves or slots have an axial spacing along the toolbar or workhead, so arranged that the expansion balls simultaneously form two axially spaced, toroidal formations in the tubular element.

In a third embodiment, two pairs of expansion balls are provided, so arranged to simultaneously form four toroidal deformations in the tubular element. Preferably, in their retracted positions, the expansion balls extend a small radial distance from the toolbar or workhead to engage an inner wall of the tubular element. The inclined floor or ramp in each groove or slot may be planar or curved.

In a second aspect, the present invention resides in an apparatus for forming at least one toroidal deformation in a tubular metal element including: a driving machine having a base frame; at least one clamping head or jaw on the base frame to support the tubular element; and an expansion tool as hereinbefore described.

In a third aspect, the present invention resides in a method for forming at least one toroidal deformation in a tubular metal element including the steps of: inserting an expansion tool in the tubular element; and rotating the expansion tool, by a driving machine, the expansion tool having a pair of expansion balls in respective grooves or slots in a toolbar or workhead, the grooves or slots each having an inclined floor or ramp to move the expansion balls from a respective retracted position to a respective extended position to progressively form the toroidal deformations. In a fourth aspect, the present invention resides in a method of joining a tubular metal element to an intersecting element, including the steps of: inserting the tubular element through at least one hole in the intersecting element; and forming at least one toroidal deformation in the tubular element, by the method hereinbefore described, adjacent the intersecting element to lock the elements together.

Preferably, where the intersecting element is a second tubular element, and aligned holes are formed in opposed walls portions of the second tubular element, respective toroidal deformations, or respective pairs of toroidal deformations, may be formed in the tubular element adjacent the aligned holes to lock the element together.

In a modified embodiment, the expansion tool may undergo both rotary and axial movement to form the, or each, toroidal deformation with a complex shape. Preferably, the complex shape conforms to the configuration of an adjacent wall portion of the intersecting element. BRIEF DESCRIPTION OF THE DRAWINGS

To enable the invention to be fully understood, a number of preferred embodiments will now be described with reference to the accompanying drawings, in which: FIG. 1 is a perspective, part-sectional view showing the expansion tool forming a single toroidal deformation in a tubular element;

FIG. 2 is a sectional end view taken on line 2-2 on FIG. 1 ;

FIG. 3 is a side elevational view of the tool;

FIG. 4 is a sectional end view taken on line A-A on FIG. 3; FIG. 5 is a side view of an expansion tool for forming double toroidal deformations in a tubular element;

FIG. 6 is a sectional end view taken on lines XX and YY on FIG. 5;

FIG. 7 is a perspective view showing the tool of FIGS. 1 to 4, being operated to form a complex toroidal deformation in the tubular element;

FIG. 8 is a side view of an expansion tool for forming quad toroidal deformations in the tubular element;

FIG. 9 is a sectional end view taken on lines XX and YY on FIG. 8;

FIGS. 10 (a) to (g) are schematic end or side views showing alternative joints between a circular-section tubular element and a rectangular-section (tubular) intersecting element;

FIG. 11 is a sectional end view of the joint of FIG. 10(d) on a larger scale;

FIGS. 12(a) to (h) are schematic end and side views showing alternative joints between a circular-section tubular element and a circular-section intersecting element;

FIGS. 13(a) and (b) are schematic side views showing alternative joints between a circular-section tubular element and a solid intersection element; FIG. 14 is a sectional end view of a square-section tubular element after the formation of the toroidal deformation;

FIG. 15 is a schematic perspective view of a computer controlled robotic machine for the expansion tool; FIG. 16 is a schematic perspective view of an alternative robotic machine, suitable for manufacture of a fence; and

FIG. 17 is an end elevational view of a clamp assembly for holding the tubular elements during the toroidal deformation(s) by the expansion tool. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 to 4, the expansion tool 10 is shown in FIGS. 1 and 2 inserted into a circular-sector metal tube or pipe 20 (eg., the post of a fence panel).

The tool 10 has a toolbar (or workhead) 11 , which is coaxially mounted on (and preferably formed integrally with) a shank 12 engageable in the drive head of a CNC machine (not shown). To aid alignment of the expansion tool 10 when inserted into the tube 20, the nose 13 of the toolbar 11 is bevelled (see FIGS. 1 and 3). Two expansion balls 14, 15 are provided at substantially diametrically opposed locations, axially aligned, on the toolbar 11. Respective grooves 16, 17 with the same radius as the balls 14, 15 are cut into the toolbar 11.

To form the grooves 16, 17, a ball nose cutter is plunged into the toolbar 11 until the centre of the cutter tip is at centre point A in FIG. 4. The cutting tool is then moved in a substantially circular path, with a centre radius R, about point C, until the centre of the cutter tip is at centre point B, thus forming the respective groove with an inclined (or ramp) floor 18, 19. The balls 14, 15 are placed in the grooves 16, 17 and the toolbar 11 is deformed at 16a, 17a to permanently restrain the balls 14, 15 in the grooves 16, 17. Referring to the sectional end views in FIGS. 2 and 4, the expansion balls 14, 15, when in their "retracted" positions, protrude slightly above the radial surface of the toolbar 11 when the centres of the expansion balls 14, 15 are co-incident with the centre points A. When the tool 10 is rotated clockwise, the expansion balls 14, 15 contact the inner walls of the pipe 20 to be expanded and they roll along the grooves 16, 17 until the centres of the balls 14, 16 are at centre points B (ie., the balls are in the "fully extended" positions). At these points, the radial contact points of the two expansion balls 14, 15 have moved outwardly, thus deforming the pipe 20 at the two points where the balls 14, 15 contact the inner tube wall. As the tool 10 is further rotated clockwise the expansion balls 14, 15 rotate around the centre points B in the sockets formed by the end of the grooves 16, 17. This allows the balls 14, 15 to roll against the inside of the pipe 20 as the toroidal expansion 21 around the full pipe circumference is completed. This rolling action reduces friction and galling, reducing the driving torque required, and thereby minimising the effects of galling or scoring of internal wall coatings.

When the tool 10 is rotated anti-clockwise, the expansion balls 14, 15 roll along the grooves 16, 17 until their centres are co-incident with centre points A (ie., the balls are returned to their "retracted" positions). Thus, the balls 14, 15 disengage from the pipe 20 and remain disengaged whilst the tool 10 is rotated anti-clockwise.

Thus, to effect a toroidal deformation joint by fixing cross- constructional members as shown in FIGS. 1 and 10, the method would be: a) rotate toolbar 11 anti-clockwise and insert into pipe 20, 320 in the required position; b) rotate toolbar 11 clockwise to actuate expansion balls 14, 16 to effect deformation 21 , 321 of the pipe 20, 320; c) rotate toolbar 11 anti-clockwise and move axially in pipe 20, 320 to the next locking position on the other tube wall; d) rotate toolbar 11 clockwise to effect the second toroidal deformation 32, 324 of the pipe 20, 320; and e) rotate toolbar 11 anti-clockwise and withdraw from pipe 20, 320 (optionally other locking points can be effected along the pipe 20).

The expansion tool 110 in FIGS. 5 and 6 has two balls 114, 115 linearly offset along the toolbar 111 and therefore produces two toroidal deformations simultaneously. This facilitates locking, eg., a picket 420 by simultaneously deforming the picket 420 on both sides of the wall of the intersecting tubular member as in FIGS. 10 (c) and (d). For this tool, the cutting tool is moved substantially transversely from centre point AA to centre point BB to form the grooves 116, 117.

The expansion tool 10 of FIGS. 1 to 4 does have one advantage over the tool 110 of FIGS. 5 and 6. Note that the ball grooves 14, 15 are circular in tool 10. This reduces the ball diameters and improves the pressure contact angle between the balls 14, 15 and the inside of the deformed tubular member of the pipe 20. Improved contact angle ensures a more positive grip between the balls 14, 15 and the inner wall of the pipe 20, thus eliminating any possibility of slippage resulting in partially formed or incomplete circumferential deformations 21.

Other elliptical cutting paths may be used to obtain slight modifications and adjustments to pressure contact angles, but require more complex machining procedures.

As shown in FIG. 7, if the shank 12 is simultaneously rotated and moved axially, as indicated by the arrows, a complex toroidal deformation 21a can be formed in the tube 20 (eg., to be used in the joints shown in FIGS. 12 (e) to (h)).

FIGS. 7 and 8 show an expansion tool 210 with four balls 214, 215, 214a, 215a, all linearly offset. This tool 210 is capable of effecting four toroidal deformations simultaneously, eg., for the joint which is shown in FIG. 10(d). The alternative expansion tool head configurations demonstrates the capability to effect a variable number of toroidal deformations singularly or plurally.

Referring to FIG. 11 , it can be seen how the cross- constructional members are mechanically deformed and the mechanical lock is achieved. The rail member 330 has a hole drilled or punched through it, and the cylindrical member or pipe 320 is passed through the hole in the upper and lower walls 331 , 332 of the rail member 330. Toroidal deformations 321 to 324 are produced in the tube 320 above and below the walls 331 , 332 of the rail member 330.

FIGS. 10(a) to (g) show various deformation options for intersecting a round tubular section 320 into a rectangular tubular section 330. FIG. 10(e) shows an option whereby the rectangular tubular section has only one wall drilled, with the round tubular section abutting the internal wall of the intersecting rectangle. FIGS. 10(f) and (g) illustrate the toroidal deformation applied to intersecting tubular members at various angles off right angles which facilitates raked and gradient and assembly panels typical of staircase railings and balustrades.

FIGS. 12(d) to (h) show various deformation options for fixing intersecting cylindrical tubular sections 420, 430. FIGS. 12(a) to 12(d) illustrates locking options with toroidal deformation expansions 421- 424 applied in plan section square to the picket axis. In FIGS. 12(e) and

(f), the toroidal deformation expansion(s) 421 , 422 are curved to match the radius of the larger intersecting tube 430. This method can be applied to any of the options in FIGS. 12(a) to 12(d) providing a mechanically stronger joint. FIG. 12(h) illustrates the tubular members 420, 430 intersecting at an angle off 90°.

As shown in FIGS. 13(a) and 13(b), a tubular pipe 520 can be locked to a flat metal bar or plate 530 by the deformation 521 , 522. This arrangement is particularly suitable for fence construction where the bars 530 act as fence rails connecting the posts or pickets 520. The toroidal deformation expansion method can be applied to square hollow tubular section 620 as shown in FIG. 14. Note the protruding radial arc sectors 421 (a) to (d) of the toroidal deformation 421 from the flat walls of the square section. The member into which the square section 620 is to be deformed would require square holds to facilitate cross-constructional joining. Referring to FIG. 15, the expansion tool 510 has its elongate shank 512 engaged in a driver head 651 of a CNC-controlled machine 650, which has a drive motor 652 for one drive head 651. As shown, linear guides 653, 654 and drive units 655, 656 enable the expansion tool 610 to be moved in three axes. In this embodiment, a fence post 620 is being joined to a flat metal rail 630.

Referring now to FIG. 16, the mechanical expansion tool 710 is rotated by tool motor 752. Support 757 guides the expansion tool 710. Linear guide 754 and drive unit 756 position expansion tool 710 in the correct longitudinal position along the assembly panel, whilst guide 753 and drive unit 755 allow the height of the expansion tool 710 to be selected. When expansion tool 710 is in the correct longitudinal position and height relative to the cross constructional member 720 to be locked, tool motor 752 propels tool motor 752 along guide 759, thus inserting expansion tool 710 to the correct position inside the cross constructional member 720. Tool motor 752 is then reversed, and rotated clockwise for two revolutions, thus effecting the toroidal deformation. Positional CNC programming of these functions facilitates the deformations of all joints in the assembled panel. Guide 753 and drive unit 755 enable adjustment of the expansion tool 710 height, which allows the unit to effect deformations along curved longitudinal members held in the assembly jig. The longitudinal rail members 730. 730 are the upper side of the finished panel assembly. Part of the assembled panel is not shown so as to avoid obscuring the robotic superstructure.

Gates 760, 761 allow the cross constructional members to be deformed progressively. Gate 760 is closed so that the assembly robot can lock banks of adjoining members. Gate 761 is open, allowing the operator to continue loading cross constructional members into the adjoining bank without risk of machine operation on that bank. Electronic interlocks are provided on the various gates ensuring separation of the robotic assembly functions from the operator. FIG. 17 illustrates the anti-rotation lock 762 in detail. The solid outline shows the closed lock position, and the dashed outline shows the open position. A pneumatic cylinder 763 drives a roller 764 which contacts jaws 765, 766. The jaws rotate about pivots 767, 768 and have rubber grips 769, 770 to ensure positive friction on round members. The CNC robotic plants have, as shown in FIGS. 15, 16 and

17, been, devised particularly, though not solely, to automotive and semi- automotive numerous industry applications involving the mechanical process of joining the cross-constructional metal members. The cold formed toroidal deformation lock method can be applied to all malleable ductile metals such as steel, aluminium, copper and brass, etc.

This mechanical joining method is applicable to the fixing of constructional elements of the same or differing geometric shape, size or diameter, in a range of metal fabrication industry processes for such product applications as, inter alia, construction, trusses, beams, shelving, racking, fencing, gates, balustrades, guard rails, security grilles, gazebos, arbours, metal framework and the like.

As shown, the toroidal deformation joining is achieved without requiring additional fastening hardware, eg., screws, rivets or bolts. Furthermore, the application of CNC robotic engineering capacity provides extensive flexibility to the type, range and options of fixing cross- constructional members. Some options are fixing against one or more internal or external tube walls or against both internal tube walls or against both external tube walls or by one or more of any combination of the four possible fixing points. Fixing may be disguised internally or effected externally subject to aesthetical requirements. In fixing a tubular member which intersects solid or flat section metal profile, deformation(s) are effected against the surface of the flat sectional material. A further CNC robotic function permits the fixing of cross-members at varying angles, which caters for typical applications such as stair rolling and raked architectural panels. The three-axis robotic plant capability caters for the fixture of curved panels.

The assembly method and CNC program also facilitates the fixing of the same tubular geometric shapes such as cylindrical to cylindrical, square to square or various combinations of geometric profile. Apart from the aforementioned panel type assemblies, the toroidal deformation methodology may be applied to numerous engineering applications using interlocking pipe tubing, such as heat exchanges, radiators, boilers, refrigeration and in the manufacture of metal assemblies such as ladders, mufflers and the like.

The application of CNC robotic engineering principles to the toroidal deformation assembly method significantly increases productivity, dramatically reduces costs and provides a safer, cleaner work environment by elimination of welding, grinding and post welding process functions which are a source of high workplace hazard incidence. The toroidal deformation assembly method effectively eliminates such manual workplace hazard exposure.

The incorporation of CNC robotic plant design to facilitate the use of the deformation expansion tool is highly productive and automation under CNC control introduces wide ranging process flexibility. Increased productivity is a function of rapid machine axes velocities, combining accurate positioning capability which results in a significant reduction in production and assembly time. The CNC robotic assembly plant facilitates the rapid, yet simple, change of program parameters to meet varying job specifications without the need to prepare specialised jigging apparatus for individual production runs. The robotic flexibility facilitates the holding of longitudinal rails with adjustable clamps which caters for different rail lengths, numbers of rails and spacings. The cross- constructional members are placed through the apertures in the longitudinal rails and the CNC robotic capacity allows tracking under computer guidance of the position of each cross-member fixing point regardless of whether the joint is 90° or at an angle or whether assembly is effected to curved longitudinal rails or panels.

The CNC robotic assembly process is low noise, highly energy efficient and uses only electricity and compressed air. Automated process efficiency eliminates welding consumables such as gas, wire, rods, grinding products which are consumed in conventional welding operations. Incorporated in the safety design features is a physical separation between operator and robotic mechanism such that the operator works from the top of the assembly while the robot works from the bottom of the assembly. Additionally, an electronic interlock prevents the robot assembling any bank of cross-constructional members being attended to by the operator.

The toroidal deformation expansion method provides an indestructible panel which is tamper proof and which can not be manually or mechanically disassembled. All joints are "post thru rail" which provides additional strength to the now common economically driven welding practice of tacking cross members to external rail surfaces. With toroidal deformation assembly, engagement occurs between the cross- constructional members over the full circumference of the joint. The process of welding introduces stress due to metal contraction on cooling: however, in toroidal deformation assembly, stress is locally introduced into the grain structure by cold deforming which increases the material strength about the deformation. Cold forming deformation occurs at moderate pressure such that galvanic or protective metal coatings are not degraded or adversely affected. The expansion tool design minimises drag and friction between the inner wall of the tube, thereby minimising the effects of galling or scoring any internal protective coating.

Various changes and modifications may be made to the embodiments described and illustrated without departing from the present invention.

Claims

1. An expansion tool for forming at least one toroidal deformation in a tubular metal element, including: a shank mountable in a driving machine for rotary movement; a toolbar or workhead on the shank and co-axial therewith; a pair of diametrically spaced, circumferentially extending, grooves or slots in the toolbar or workhead, each groove having an inclined floor or ramp; and a respective expansion ball in each groove, each ball being movable from a respective retracted position to a respective extended position, so arranged that: on insertion of the toolbar or workhead in the tubular element, and on rotation of the shank in one direction by the driving machine, the expansion balls move from their retracted positions to their extended positions to progressively form at least one toroidal deformation in the tubular element.

2. A tool as claimed in Claim 1 , wherein: the shank and toolbar are formed integrally.

3. A tool as claimed in Claim 1 or Claim 2 wherein: the grooves or slots are axially aligned, so that the expansion balls form a single toroidal deformation.

4. A tool as claimed in Claim 1 or Claim 2 wherein: the grooves or slots have an axial spacing along the toolbar or workhead, so arranged that the expansion simultaneously forms two axially spaced, toroidal deformations in the tubular element.

5. A tool as claimed in Claim 4 wherein: two pairs of the grooves or slots, and two pairs of the expansion balls are provided, so arranged to simultaneously form four toroidal deformations in the tubular element.

6. A tool as claimed in any one of Claims 1 to 5 wherein: in their retracted positions, the expansion balls extend a small radial distance from the toolbar or workhead to engage an inner wall of the tubular element.

7. A toolbar as claimed in any one of Claims 1 to 6 wherein: the inclined floor or ramp in each groove or slot is planar or curved, in side elevation.

8. An apparatus for forming at least one toroidal deformation in a tubular metal element including: a driving machine having a base frame; at least one clamping head or jaw on the base frame to support the tubular element; and an expansion tool as claimed in any one of Claims 1 to 7.

9. A method for forming at least one toroidal deformation in a tubular metal element including the steps of: inserting an expansion tool in the tubular element; and rotating the expansion tool, by a driving machine, the expansion tool having a pair of expansion balls in respective grooves or slots in a toolbar or workhead, the grooves or slots each having an inclined floor or ramp to move the expansion balls from a respective 0 retracted position to a respective extended position to progressively form the toroidal deformations.

10. A method as claimed in Claim 9 wherein: the expansion tool is as claimed in any one of Claims 1 to 7.

11. A method of joining a tubular metal element to an 5 intersecting element, including the steps of: inserting the tubular element through at least one hole in the intersecting element; and forming at least one toroidal deformation in the tubular element, by the method as claimed in Claim 9 or Claim 10, adjacent the o intersecting element to lock the elements together.

12. A method as claimed in Claim 11 wherein: when the intersecting element is a second tubular element, and aligned holes are formed in opposed wall portions of the second tubular element, respective toroidal deformations, or respective pairs of toroidal deformations, are formed in the tubular element adjacent the aligned holes to lock the elements together.

13. A method as claimed in Claim 11 or Claim 12 wherein: the expansion tool undergoes both rotary and axial movement to form the, or each, toroidal deformation with a complex shape, the complex shape conforming to the configuration of an adjacent wall portion of the intersecting element.