GB2040202A - Welding a hollow member at one end thereof to a surface of another member - Google Patents

Abstract

In welding a hollow member 44 (e.g. of circular cross-section) to the surface of another member 46, a welding tool having an outwardly directed tip 14 is located within the hollow member with the tip pointing towards the internal edge of the hollow member where it lies on the surface of the other member, and the welding tool is activated whilst the hollow member and the other member are both moved relatively to the tool so that a weld is formed between the two members completely on the inside of the hollow member. The specification refers particularly to gas (e.g. CO2, helium or argon) or vacuum-shielded consumable electrode arc welding. It also refers to automatically or profile-follower controlled welding of a hollow member of non-circular cross-section, and to additional welding of the hollow member to a further member, e.g. to a surrounding member by way of internally effected welding through the wall of the hollow member. <IMAGE>

Description

SPrC-: -iCATION Isnpscscmenas in or relating to welding The inventon relates to welding and is particularly directed to the solution of the problem of securing one end of a hollow member to a surface of another member. One circumstance in which this problem arises is in the manufacture of tubular steel frames where a first tubular frame member projects at right angles from a second tubular frame member and a joint has to be formed between the end of the first frame member and a flank of the second frame member. it is possible to weld around the outside of the end of the first frame member but whilst this is effective it produces an unsightly appearance at the joint.In the case of furniture frames for example, the appearance of this weld is usually unacceptable, and it has to be trimmed by grinding, and even then the appearance is often not satisfactory.

According to this invention a method of welding one end of a hollow member to a surface of another member comprises the steps of placing the end of the hollow member against the surface of the other member, positioning a welding tool with an outwardly directed tip within the hollow member with The tip pointing towards the internal edge of the hollow melriberwherethat edge lies on the surface of the other member, activating the welding tool and causing relative movement between the tool and both the hollow member and the other member, so that a weld is formed between the two members in the region of the said internal edge of the hollow member, the weld so formed being completely on the inside of the hollow member. Preferably the two members are given a rotational movement relatively to the tool.

The advantage of this method will be immediately apparent, in that the appearance of the weld is of no aesthetic significance since it is not visible on the outside of the joint formed between the hollow member and the other member. Also, the method is of particular advantage where the hollow member is elongate so that conventional methods of welding could not be used to form a weld within the hollow member at the one end thereof. It is a further advantage of the invention that the method is generally more efficient in terms of time and materials used than conventional methods (whether by welding, or using threaded securing means, or the like methods) of securing a hollow member to a surface.

According to a preferred feature of the invention the weld is formed in an inert atmosphere for example, by providing an inert gas such as carbon dioxide (C02), or a vacuum in the hollow member adjacent to the region where the weld is formed.

Thus in the preferred method, the welding tool has a tip through which a welding electrode (or welding wire) is projected towards the internal edge of the hollow member where the weld is formed, and there is at least one gas inlet or outlet in the lower end of the tool. So that the inert atmosphere can be provided adjacent to where the weld is to be formed.

According to another preferred feature of the invention, the tip of the welding tool is smoothly curved so that the welding electrode can be easily fed to the site of the weld through the tip during the welding operation. It is further preferred that the tip of the welding tool curves smoothly in one direction and then has a region of inflexion before smoothly curving in the opposite direction towards the outer end of the tip. Alternatively, or in addition, the tip may be offset from the longitudinal axis of the welding tool to enable the electrode to be fed through the tip. The tip may be replaceable by a tip of a different size, shape or material.

It has been found that by providing two smooth curves in the tip of the welding tool so that a region of inflexion occurs between the two curves (one curve being convex and the other concave when viewed from one side), the welding electrode is still able to be fed through the tip during the welding operation even where the hollow member has an internal diameter only slightly greater than the external diameter of the welding tool, i.e. the smallest bore within which the welding tool may be accomodated and/or located.

The method may further comprise the step of forming one or more other weld(s) within the hollow member, or through the wall(s) of the hollow member. The other weld(s) could, for example be formed by the welding tool to secure the hollow member to a short tubular section forming part of the other member and surrounding the hollow member, in which case the welding tool is required to melt part of the wall of the hollow member inside the tubular section and part of the wall of the tubular section itself to form the weld. Alternatively, a completely separate elemant may be attached to the outside of the hollow member by welding through the wall of the hollow member.In order that such another weld may be formed through a wall of the hollow member more electrical energy would be required than that needed to form the weld between the hollow member and the other member but preferably, the supply of electrical energy of the welding tool is variable. It will be appreciated that the or each other weld need not be circular and could comprise a spot weld, long run weld, or the like.

The welding tool may be mounted within the hollow member on an insulation blockwhich locates in the hollow member but electrically insulates the welding tool from the hollow member. The insulation block may also ensure that the welding tool when mounted on the insulation block is located within the hollow member aligned along the longitudinal axis thereof. This alignment of the welding tool aids the positioning of the welding tip relatively to the welding site and ensures that when relative rotation between the hollow member and the welding tool occurs, a substantially circular weld is formed. Thus the method of welding is of particular advantage where the hollow member is of circular cross-section.However, it is possible to provide simultaneous coordinated movement of the welding tool and the insulation block in conjunction with the relative rotation or other relative movement of the hollow member and the other member to obtain different types of weld suitable for hollow members of cross-sections other than circular.

It will be appreciated that the method of welding according to the invention lends itself to automated welding since when the correct insulation block and tip have been chosen for the weld in question and have been positioned within the hollow member, the sequence of steps of the method of welding are substantially the same for many different crosssection of article being welded (corresponding to the particular cross-section of the hollow memberto be welded). The position of the welding tool could also be aligned relatively to the hollow member to provide a weld between the other member and the hollow member for a whole range of sizes of hollow member.

In order to ensure that the weld is formed at the internal edge of the hollow member, the tip of the welding tool must be located at the correct axial distance from the end of the hollow member which lies on the other member (the radius of the weld being a function of the said axial distance and the exit angle of the welding tool at its tip).

The invention also includes an article formed by the method of welding according to the invention.

A method of welding in accordance with the invention will now be described by way of example only, with reference to the accompanying drawings of which: Figure 1 is a cross-sectional side elevation of a welding tool mounted within a hollow member, the hollow member being located on the upper surface of another member; Figure 2 is a detailed view of the tip of the welding tool shown in Figure 1, and Figure 3 is a diagrammatic side view of an alternative means of mounting a welding tool in a hollow member to that shown in Figure 1.

An inert-gas metal arc welding tool is indicated generally at 10 and comprises a tubular body portion 12 having a hollow copper tip 14 at its lower end 16, and cylindrical connecting head 18 at its upper end 20. An intermediate connector 22 which is hollow connects the head 18 to an elongate hollow copper barrel 24, which forms the greatest proportion of the length of the body portion 12.

The copper tip 14 is located within a brass ferrule 25 at the lower end of the barrel 24 and projects downwardly therefrom. The brass ferrule 25 is soldered to the lower end of the barrel 24 and is coaxial therewith. The copper tip 14 is tubular and the lower end of a metal electrode 26 is threaded through the tool 10 from the top end and out through the tip 14.

A motor (not shown) is arranged to feed the electrode 26 slowly through the tool 10 during welding, because during welding the electrode 26 melts away at the lower end thereof to form the metal flux for the weld. A nylon liner 27 surrounds the electrode 26 within the tool 10, and this liner 27 is housed within a mild steel tubular sheath 29. The sheath 29 is itself located within the copper barrel 24 and is coaxial therewith but there is an annular chamber 32 between the barrel 24 and the sheath 29.

An electrical cable 28 passes into the head 18 and is connected to the electrode 26 to supply the electrode with electrical energy. when the tool 10 is operated an electrical arc is struck between the electrode and a workpiece causing the electrode 26 to melt and Flow on to the workpiece and also causing part of the parent metal of the workpiece to melt to form the weld.

Afeed tube 30 is connected to the intermediate connector 22 and is arranged to supply carbon dioxide gas (cm2) through the connector 22 into the annular chamber 32. The feed tube 30 is sealed around its entry to the connector 22, as is the electrode 26 around its entry to the head 18. A series of outlet ports 36 which are formed axially through the ferrule 25 allow the carbon dioxide to pass from the chamber 32 to the area around the tip 14 and the projecting lower end of the electrode 26. Thus the weld formed by the tool 10 is created in an inert atmosphere of carbon dioxide gas.The weld so produced is generally stronger and more durable than a similar weld formed in air since the oxygen and nitrogen from the air tend to diffuse into the melting metal from the electrode as the weld is formed and cause weakening of the weld. The weld formed in carbon dioxide gas is relatively uncontaminated.

The welding tool 10 so far described is relatively conventional, except for the tip 14. The upper end 38 of the tip 14 is threaded into the brass ferrule 25 and is firmly held in position by a locking grub screw 40 which is threaded through the side of the ferrule 25 and is tightened against the tip 14. This arrangement allowsthetipto be replaced.

The tip 14 emerges from the brass ferrule 25 in a position offset from the longitudinal axis of the tool 10. The tip 14 curves outwardly and downwardly from the ferrule and crosses a plane containing the longitudinal axis of the tool 10 so that the tip is bowed as shown clearly in Figure 2. A bore 41 for the passage, of the electrode is formed in the ferrule 25 in upward extension of the bowed tip 14 and this bore is inclined to the longitudinal axis of the tool 10 so that it leads smoothly into the bowed tip, and the outward sweep of the electrode 26 through the brass ferrule 25 ensures that no kinks occur in the electrode as it is fed into and through the copper tip. An alternative arrangement has also been envisaged in which the electrode 26 is fed substantially along the longitudinal axis of the tool 10 and the tip itself has two curves in it.In this alternative arrangement the tip curves smoothly in one direction has a region of inflexion, and then curves smoothly in the opposite direction in much the same manner as the lower end of the tip 14. The two smooth curves in the tip of the alternative arrangement ensure that no kinks occur in the electrode as it is fed through the tip.

In this example, the workpiece 42 comprises a cylindrical metal tube 44 standing upright, with its lower end resting on a square cross-section support tube 46. (The workpiece may be part of a frame of an article of furniture for example). The two members forming the workpiece are clamped together and they are also clamped to a turntable (not shown), with the longitudinal axis of the tube coincident with the axis of rotation of the turntable. An annular insulating block 48 is provided and the lower end of the tool 10 extends through and is located in the block 48 which in turn is located within the tube 44 so that the tool is substantially coaxial with the tube 44. The Insulating block 48 is made of electrically insulating material so that it insulates the.workpiece 42 electrically from the tool 10.The tip 14 is positioned immediately adjacent to the side wall 49 of the tube 44 owing to the outward curvature of the tip and eventually the tip is located adjacent to the bottom of the tube 44 in the correct position for welding to commence. With the tool 10 thus arranged in the tube 44, the tip 14 and the portion of the electrode 26 therein, are positioned so that the lower end of the electrode 26 is just contacting the region of the lower inner rim 50 of tube 44 where it contacts the flat upper surface of the support tube 46. By virtue of its location the tool is adapted to form a weld 52 at the junction between the internal edge at the lower end of the tube 44 and the top face of the tube 46.However, during the welding operation, the turntable is rotated and therefore both the tubes rotate relatively to the tip of the welding tool, and a continuous weld 52 is formed all round the internal edge at the lower end of the tube 44. It will be appreciated that since the weld 52 is formed within the tube 44, the weld 52 is not visible when the workpiece is viewed externally. Therefore, the weld 52 is of no aesthetic significance as far as the finished workpiece 42 is concerned. This method of welding from within a hollow member such as the tube 44 is thus of great advantage over exterior welding methods, for example, in the field of tubular furniture manufacture where exterior welds on metal tubes are difficult to disguise and generally detract from the appeal of the furniture.

It is essential that the tip 14 does not come into contact with the side of the tube 44 when the welding operation is commenced or the electrical energy supplied to the tool 10 would be short circuited through the tip 14 to the workpiece 42 and the tool 10 would not operate correctly.

It will be appreciated that instead of holding the tool stationary and rotating the workpiece, it would be possible to hold the workpiece stationary and rotate the tool, but this would complicate the tool construction, since it would be necessary to provide a notary seal between the gas inlet and the tool.

It will be understood that by merely allowing the tool 10 to remain on the longitudinal axis of the tube 44 whilst relative rotation between the workpiece 42 and the tool 10 occurs, the lower end of the electrode which forms the weld 52, will describe a circular path on the two tubes 44 and 46 resulting in a circular weld. This is desired where the tube 44 is of circular cross-section but the method of welding according to the invention can nevertheless be adapted to produce other types of weld which conform to cross-sections of other tubes such as tubes of oval or elliptical cross-sections and the like. In order to produce these other types of weld it is necessary for a fine control to be exercised either on the tool 10 as it is moved relatively to the workpiece 42, or on the workpiece as it is moved relatively to the tool.This could be achieved for example by clamping the tool 10 at the head 18 thereof, and then manipulating the tool 10 by means of an automatic controlier, the sequence of movement of the tool 10 being programmed into the controller prior to any desired welding operation. The whole welding process according to the invention could then be automated for example, the axial location of the tool 10 within the workpiece 42, the operation of the tool 10 and carbon dioxide supply coupled with the feeding of the electrode and the relative movements of the tool 10 and workpiece 42 could all be controlled by an automatic controller rather than being subjected to manual control. For the more complex welds, the insulating block 48 could be modified so as to allow a greater degree of movement of the tool 10 within the tube 44 or other workpiece.Thus for example the insulating block 48 could be fitted into the workpiece surrounding the lower end of the barrel 24 without contacting it initially, and be shaped so as to limit the extent of movement of the barrel 24, rather than locate the tool 10 in a fixed position as previously described, the function of the insulating block 48 being to prevent contact of the tool 10 with the tube 44. Also, as illustrated in the alternative arrangement in Figure 3, for welds which are smooth curves, the insulating block could comprise a spring-loaded cam-follower arrangement adapted to maintain the lower end of the electrode at a fixed distance from the lower rim 50 of the tube 44 or other hollow workpiece member. Thus, the cam-follower arrangement could cope with many different hyperbolic curves.Such a cam-follower arrangement 54 which is illustrated in Figure 3 comprises a fixed stop 56 fastened to one side of the tool 10 so that it engages with an inside face 58 of the hollow workpiece member 44 in which the tool 10 is located and thus maintains the tool 10 at a fixed distance from the inside wall of the workpiece member 44 (so that the electrode is always jus in contact with the lower inner rim 50 of the member 44). A cam-follower 60 at the other side of the tool 10 has a spring 62 connected thereto, the spring extending between the follower 60 and the tool 10. The follower 60 is loaded by the spring 62 in a direction perpendicular to the longitudinal axis of the tool 10 and the member 44, to push the tool against the fixed stop 56.

This latter arrangement is much simpler and cheaper in operation than arranging for automatic control of the welding tool or workpiece movement, but a cam-follower arrangement such as the arrangement 54 could not cope with hollow members which had acute changes of direction internally such as tubes of square of polygonal cross-section.

In such case an automated control over the movement of the tool 10 relatively to the workpiece would be essential to ensure accurate welding around the lower inner rim 50 of the hollow workpiece member 44.

It will be appreciated particularly from Figures 1 and 2 that unless the tip 14 is smoothly curved it wou Id be extremely difficult to feed the electrode 26 through the tip 14 especially since tubes 44 having different diameters could be used and tips 14 of different curvatures could be used. It has been found that the vertical positioning of the tip 14 in the hollow member 44 and the exit angle of the tip 14 is critical to the method of welding according to the invention since the lower end of the electrode 26 must always be in contact with or near to the region to be welded (i.e. the lower inner rim 50 of the tube 44) and yet the electrode must still be easily fed through the tip.

Alternative embodiments according to the invention are also envisaged, for example, the tube 44 could be welded on any other flat surface instead of the support tube 46, and another type of inert gas such as, for example, helium or argon could be used to replace the carbon dioxide supplied to the tool 10.

If desired, to aid the manual control of the tool 10, an insulated hand grip portion could be fitted to the upper end of the tool 10 so that the positioning of the tool 10 in the tube 44, and the operation of the tool 10 could be made easier.

Claims (15)

1. A method of welding one end of a hollow member to a surface of another member comprising the steps of placing the end of the hollow member against the surface of the other member, positioning a welding tool with an outwardly directed tip within the hollow member with the tip pointing towards the internal edge of the hollow member where that edge lies on the surface of the other member, activating the welding tool and causing relative movement between the tool and both the hollow member and the other member so that a weld is formed between the two members in the region of the said internal edge of the hollow member, the weld so formed being completely on the inside of the hollow member.

2. A method as claimed in Claim 1, in which the relative movement between the tool and both the hollow member and the other member comprises a rotational movement.

3. A method as claimed in Claim 1 or Claim 2, in which the weld is formed in an inert atmosphere.

4. A method as claimed in Claim 3, in which the inert atmosphere comprises an inert gas or a vacuum.

5. A method as claimed in Claim 4, in which the inert gas comprises carbon dioxide.

6. A method as claimed in any one of the preceeding claims, in which the tip of the welding tool is smoothly curved.

7. A method as claimed in Claim 6, in which the tip of the welding tool curves smoothly in one direction and then has a region of inflexion before smoothly curving in the opposite direction towards the outer end of the tip.

8. A method as claimed in any one of the preceding claims, in which the tip of the welding tool is offset from the longitudinal axis of the welding tool.

9. A method as claimed in any one of the preceding claims, in which the tip of the welding tool is replaceable.

10. A method as claimed in any one of the preceding claims, further comprising the step of forming one or more other weld(s) within or through the wall(s) of the hollow member.

11. A method as claimed in any one of the preceding claims, in which a supply of electrical energy to the welding tool is variable.

12. A method as claimed in any one of the preceding claims, in which the welding tool is mounted within the hollow member on an insulation block which electrically insulates the welding tool from the hollow member.

13. A method of welding one end of a hollow member to a surface of another member substantially as herein decribed with reference to the accompanying drawings.

14. A method of welding one end of a hollow member to a surface of another member as claimed in Claim 13, and as illustrated in the accompanying drawings.

15. An article produced by the method according to any one of the preceding claims.