GB2175526A - Welding - Google Patents

Abstract

A method of welding together a socketed component (10) e.g. an aluminium alloy end fitting of a scaffolding member and a spigot component (11) eg an aluminium alloy tube includes forming one or more longitudinal slots (16) in the socket wall and forming weld runs along the edges of the slot(s). The slots provide a length of weld run at least equal to the circumference of the tube. <IMAGE>

Description

SPECIFICATION Welding This invention relates to the securing together by welding of workpieces to form an integral component, particularly but not exclusively where one or more of the workpieces is a tubular formation and/ or where abutting or overlapping areas of the assembled workpieces may be of differing thickness.

The invention can be particularly conveniently employed in the assembly of aluminium or aluminium alloy work pieces, for example the mounting of an aluminium alloy casting or forging on an aluminium or aluminium alloy tube as used in the construction of aluminium scaffolding systems.

Aluminium alloy components used in scaffolding systems are commonly manufactured by attaching tubular aluminium elements to various forms of end fittings, typically aluminium alloy castings, forgings or extrusions, by welding. Due to the high thermal conductivity and low thermal mass of aluminium and its alloy it is usual to secure these joints by using two short circumferential weld runs diametrically opposite each other at the abutment between the end of the tube and a formation of the end fitting, the welds extending over portions only of the joint circumference to avoid melting through the relatively thin wall tube in the vicinity of the weld pools. The strength of the welded joints so formed is proportional to the total length of the weld runs and the thickness of the thinner of the two components (i.e. the tube).Such a joint is illustrated in Figure 1 in which a first workpiece in the form of a cast aluminium alloy end fitting 10 (part only shown) is attached to the end of a second workpiece in the form of a length of aluminium tube 11. A tubular spigot formation 12 of fitting 10 is received in the end of tube 11 and the butt joint between the end face of tube 11 and a shoulder on fitting 10 is secured by a pair of weld runs 13 (one only shown) on diametrically opposite sides of the joint, each extending for about one quarter of the total joint circumference. The effective length of each weld is indicated by the broken line x1 - x2 and this type of joint is known as a "partially welded joint".

The object of the invention is to provide a method of welding work pieces simply and economically to give a finished strength and durability equal to or greater than the theoretical strength of a fully welded joint while retaining the advantages of the partially welded joint.

According to the invention there is provided a method of forming a welded joint integrally connecting a first work piece having a socket formation with a second work piece having a spigot portion operatively received in said socket formation including the steps of forming at least one slot through the wall of the socket formation generally longitudinally thereof or extending in a direction having a substantial longitudinal component and forming a weld run along the edges defining said slot fusing them to the underlying spigot portion.

Preferably there are at least two said slots extending longitudinally of and at diametrically opposite sides of the socket formation and the total length of weld run along the edges of the slots is greater than the length of the circumference of the socket formation.

An example of the invention is now particularly desrcribed with reference to the accompanying drawings wherein; Figure 1 is an example of a prior art welded joint as referred to above; Figure 2 is a side elevation of an assembled joint ready for welding uitlising the method of the invention; Figure 3 is a section on line 3-3 of Figure 2; and Figure 4 is a detail of said section after welding.

In this example the assembly of a component for a tubular scaffolding system is shown (parts broken away) comprising a tubular aluminium member 11 having a cast aluminium alloy end fitting 10 mounted on one end thereof, for example a claw like component for hooked engagement with another aluminium tubular member or a generally conical end fitting to be releasably received within a T connector or other socketed fitting. Component 10 includes a tubular socket formation 13 within which a spigot portion of tube 11 constituted by one end part 14 thereof is a close fit. Socket formation 13 includes an interior abutment face 15 against which the end of part 14 abuts.

A pair of slots 16 are formed through diametrically opposite wail portions of socket formation 13 extending longitudinally of the socket and, in this example, being open-ended at the distal end of formation 13 so that the length of the slots 16 is only slightly less than the full depth of the socket.

The edges defining slot 16 are chamfered at 17 (Figure 3) to provide a reduced metal thickness to facilitate welding.

A weld run 18 is formed along the full length of each slot 16 so that the whole of the length of the edge 19 defining each slot is fused to the outer periphery of the spigot part 14 of tube 13 at 20 (Figure 4). The resulting effective length of the weld joint of each slot is indicated by the broken line x3 - x4 in Figure 2 and the total length of the weld run along the edges of the two slots will exceed or equal the length of the circumference of component 11, i.e. the welds will be equal in strength to a fully welded joint extending around the full circumference. However, the heat input and consequent welding duration will be similar to that of the partially welded joint as known and shown in Figure 1 and there is no risk of melting through the rela tivelythin walled tube 11.

Moreover the difference in thickness or bulk between the two components 11 and 13 in the area of the welds along slot 16 is much less than the difference in thickness or bulk if welding were effected at the end of the relatively thin tube int he position shown in Figure 1 in fusing it to the much thicker shoulder part of the end fitting 10.

A further advantage of the invention is that the stresses in the welded joint are re-distributed. In the case of the conventional joint shown in Figure 1 stress caused by bending moments at the joint subject the ends of the weld runs to higher working stress than their central portions which can give rise to weld fractures, it is a characteristic of welding that the end of weld runs are more likely to suffer weld defects than the central portions and this further tends to reduce the effective weld strength and durability.

In the case of the joint formed according to the invention as shown in Figures 2-4, application of similar bending moments willstress the well runs uniformally without applying higher stresses to the ends thereof and the resulting joint is much less likely to suffer weld failure during the working life of the component.

The invention may be applied to the welding together of work pieces of a wide variety of shapes other than those specifically described above and for a wide range of applications. While the invention has been described in its application to components formed from aluminium or aluminium alloy it is to be understood that the invention may also have application to components formed from other metals or alloys or the welding together of components formed from plastics materials.

Various forms and arrangements of slots or slot may be used, for example there may be a single slot or more than two slots for some applications and the slot or slots may be open ended as described above or have closed ends. They may be rectilinear or curved e.g. following a spiral path about a socket formation such as 13 so that their direction includes a substantial component extending longitudinally of the spigot assembly.

Claims (10)

1. A method of forming a welded joint integrally connecting a first work piece having a socket formation with a second work piece having a spigot portion operatively received in said socket formation including the steps of forming at least one slot through the wall of the socket formation generally longitudinally thereof or extending in a direction having a substantial longitudinal component and forming a weld run along the edges defining said slot fusing them to the underlying spigot portion.

2. A method as in Claim 1 wherein there are at least two said slots.

3. A method as in Claim 2 wherein said slots extend longitudinally of and at dismetrically opposite sides of the socket formation.

4. A method as in Claim 2 or 3 wherein the total length of weld run along the edges of the slots is greater than the length of the circumference of the socket formation.

5. A method as in any preceding claim wherein the slot or slots are open ended at the distal end of the socket formation.

6. A method of forming a welded joint substantially as hereinbefore described with reference to Figures 2, 3 and 4 of the accompanying drawings.

7. An assembly of first and second workpieces connected by the method of any preceding claim.

8. An assembly as in Claim 7 wherein the workpieces are components formed of aluminium alloy

9. An assembly asin Claim 7 or 8 wherein the second workpiece is tubular and has a wall thickness substantially less than that of the socket formation.

10. An assembly as in Claim 7, 8 or 9 being part of a scaffolding system.