GB1594815A - Welding of end fixtures to tubes - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO THE WELDING OF END FIXTURES TO TUBES (71) We, MARTIN-THOMAS LIMITED, a British Company, of South Way, Walworth Industrial Estate, Andover, Hants., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the welding of end fixtures to tubes.

An example of such tubes and fixtures is as used in the construction of frames, braces and other components for prefabricated aluminium scaffolds. Such examples are shown and described in the specification of British Patent No. 1396602.

The fixtures may be in the form of hooks, eyes, cones or spigots and are made as castings, forgings or other suitable fabrication process which fit into the ends of an extruded or similar tube.

One present method of securing the fixture to the tube is by means of a manually applied seam weld using an inert gas tungsten arc non-consumable electrode process TIG (Tungsten Inert Gas) extending part way around the tube.

This type of seam weld may be also carried out semi-automatically or mechanised using an inert gas metal arc MIG (Metal Inert Gas) consumable electrode process. However weld quality and appearance has to date proved inferior to the tungsten arc (TIG) process for this application, and automation is difficult because of the necessity to rotate the tube at a controlled speed. The voltage required is different for starting welding and stopping and difficulty of precise control leads to welds of varying appearance.

Moreover it is generally accepted engineering practice when using this type ofweld subjected to critical tension loads to provide an additional mechanical fixing.

It is the object of the present invention to apply a weld of good appearance and technical quality which will minimize the need for additional mechanical fixing and will facilitate automatic welding, According to the invention we provide a process for attaching an end fixture member to a tube member one located within the other, comprising forming an aperture in the outer member and welding the outer member to the inner member by a welding process in which a consumable electrode is melted at the same speed as it is being fed progressively to a weld that extends transversely of the length of the tube through an aperture in the outer member and penetrates to the inner member, the welding being effected by a pulsed arc metal-inert-gas-process, the consumable electrode being fed into the aperture and the pulsed arc being continued both for a predetermined period.

A power source incorporating electrode spool, powered wire drive rolls, wire feed timer and control unit using an air cooled welding torch used for the normal MIG welding process may be used for the technique involved by the invention.

The consumable electrode and gas nozzle head may be held stationery and positioned above the aperture in either the tube or fixture. An arc is struck during which the consumable electrode is fed into the aperture for a predetermined timed sequence dependent on the required weld size or type.

For some tupes of plug weld it may be preferable to rotate or move the electrode head.

The timer automatically stops the wire feed, shielding gas flow and current. Multiple electrode and gas nozzle heads may be operated from a single control.

A weld may be effected by applying the pulsed arc directed through the tube or fixture aperture (which may be drilled or punched) but useful results have been obtained by drilling part way into the shank of the fixture to form a recess in line with said aperture. The hole in the tube and fixture may be effected concurrently.

The weld metal will be supplied in usual manner by feeding a consumable electrode of weld metal to the welding position.

The possibility of using a weld metal system to fill a small hole did not at first seem likely to succeed especially because of lack of tight contact between the tube and fixture and thickness of tube material, and because of so many variables e.g. hole depth, distance of hole from tube end, arc voltage and current, period of application, gas flow. weld rod type and size and torch design. However, we have found that it is quite possible to achieve success although normally a few adjustments of these variables will be required. For example, we have been successful with a hole 5 mm deep and 22 mm from the tube end, arc voltage 20 at 230--250 amps, consumable electrode speed 565 mm per minute, electrode (at plus 5% silicon) 1.2 mm diameter. The tube is stationary and the circuit just switched on for 0.6-1.8 seconds to fill the hole with weld metal.

One problem was to make the plug weld more or less flush with the exterior surface of the tube but this can be accomplished with suitable adjustment of the welding variables such as consumable electrode rate or current setting.

In an alternative arrangement for welding tubes and fixtures to form a frame the tube and fixtures may be arranged in required disposition with welding heads at all required disposition with welding heads at all required positions to weld simultaneously by operation of a common control. Drill heads may also be incorporated and operated automatically from this control.

The tubes are usually round but the technique may be used also for other geometric shapes.

In the accompanying drawings: FIGURE I shows a "Tee" casting joint comprising a tube 15 surrounded by a collar 16 to which is connected a tube 17. Welds 18, 19 are made in accordance with the invention. The collar has a spigot 20 (Figure 3) within the end of the tube 17.

FIGURE 2 is a sectional view on the plane B--B on Figure l; FIGURE 3 is a sectional view on the plane A-A on Figure l; FIGURES 2 and 3 show a drilled hole in the collar at 21 and complete weld 18 and 19.

FIGURES 4 and 5 show a tube 25 welded to a spigot 26 by two welds 28, 29 which are close together so as to run into each other.

FIGURE 5 is a sectional view on the plane C--C on Figure 4.

FIGURES 6, 7 and 8 are views similar to Figure 4 showing different shapes of welds.

FIGURE 9 is a perspective view of a hook 30 attached to a tube 31 by a spigot on the hook engaged in the tube and welded to it by welds 32, 33. Figure 10 is a view showing a modified form of weld.

FIGURE 11 shows an arangement for drilling by drills 36, 37 on fixed axes and welding by welding heads 38, 39 also on fixed axes, the work being rotated between drilling and welding.

FIGURE 12 is a perspective view showing a layout for welding hooks on both ends of each of a series of tubes 40 moved successively step by step towards a welding station by a convenor 41 At the welding station there are two welding heads 43, 44 operating on opposite ends of the tubes. Two pairs of drills are also provided similar to 36, 37. The tube is drilled, then rotated a predetermined angle to bring the drilled hole to the welding position. The tube is then held stationary during welding. The tube is rotated e.g. 180 by known torque devices, and held during drilling and welding by clamps.

WHAT WE CLAIM IS:- 1. A process for attaching an end fixture member to a tube member one located within the other comprising forming an aperture in the outer member and welding the outer member to the inner member by a welding process in which a consumable electrode is melted at the same speed as it is being fed progressively to a weld that extends transversely of the length of the tube through an aperture in the outer member and penetrates to the inner member, the welding being effected by a pulsed arc metal-inert-gasprocess, the consumable electrode being fed into the aperture and the pulsed arc being continued both for a predetermined period.

2. A process as claimed in claim 1 wherein the tube member is the outer member.

3. A process as claimed in claim 2 wherein a recess is provided in the inner member in line with said aperture.

4. A process as claimed in claim 1 wherein a series of tubes are fed by a conveyor successively to a welding position, each tube is drilled, then rotated automatically by a predetermined angle to bring the drilled hole to the welding position and clamped during drilling and welding.

5. A process as claimed in claim 1, wherein the aperture and recess are formed in a single drilling operation.

6. A process as claimed in any of claims 1 to 5 wherein two apertures are provided running into each other and filled with weld metal.

7. A process as claimed in claim I wherein two such welds closely adjacent to each other are made slmultaneously by welding heads located at an angle to each other.

8. A process for attaching an end fixture

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. aperture. The hole in the tube and fixture may be effected concurrently. The weld metal will be supplied in usual manner by feeding a consumable electrode of weld metal to the welding position. The possibility of using a weld metal system to fill a small hole did not at first seem likely to succeed especially because of lack of tight contact between the tube and fixture and thickness of tube material, and because of so many variables e.g. hole depth, distance of hole from tube end, arc voltage and current, period of application, gas flow. weld rod type and size and torch design. However, we have found that it is quite possible to achieve success although normally a few adjustments of these variables will be required. For example, we have been successful with a hole 5 mm deep and 22 mm from the tube end, arc voltage 20 at 230--250 amps, consumable electrode speed 565 mm per minute, electrode (at plus 5% silicon) 1.2 mm diameter. The tube is stationary and the circuit just switched on for 0.6-1.8 seconds to fill the hole with weld metal. One problem was to make the plug weld more or less flush with the exterior surface of the tube but this can be accomplished with suitable adjustment of the welding variables such as consumable electrode rate or current setting. In an alternative arrangement for welding tubes and fixtures to form a frame the tube and fixtures may be arranged in required disposition with welding heads at all required disposition with welding heads at all required positions to weld simultaneously by operation of a common control. Drill heads may also be incorporated and operated automatically from this control. The tubes are usually round but the technique may be used also for other geometric shapes. In the accompanying drawings: FIGURE I shows a "Tee" casting joint comprising a tube 15 surrounded by a collar 16 to which is connected a tube 17. Welds 18, 19 are made in accordance with the invention. The collar has a spigot 20 (Figure 3) within the end of the tube 17. FIGURE 2 is a sectional view on the plane B--B on Figure l; FIGURE 3 is a sectional view on the plane A-A on Figure l; FIGURES 2 and 3 show a drilled hole in the collar at 21 and complete weld 18 and 19. FIGURES 4 and 5 show a tube 25 welded to a spigot 26 by two welds 28, 29 which are close together so as to run into each other. FIGURE 5 is a sectional view on the plane C--C on Figure 4. FIGURES 6, 7 and 8 are views similar to Figure 4 showing different shapes of welds. FIGURE 9 is a perspective view of a hook 30 attached to a tube 31 by a spigot on the hook engaged in the tube and welded to it by welds 32, 33. Figure 10 is a view showing a modified form of weld. FIGURE 11 shows an arangement for drilling by drills 36, 37 on fixed axes and welding by welding heads 38, 39 also on fixed axes, the work being rotated between drilling and welding. FIGURE 12 is a perspective view showing a layout for welding hooks on both ends of each of a series of tubes 40 moved successively step by step towards a welding station by a convenor 41 At the welding station there are two welding heads 43, 44 operating on opposite ends of the tubes. Two pairs of drills are also provided similar to 36, 37. The tube is drilled, then rotated a predetermined angle to bring the drilled hole to the welding position. The tube is then held stationary during welding. The tube is rotated e.g. 180 by known torque devices, and held during drilling and welding by clamps. WHAT WE CLAIM IS:-

1. A process for attaching an end fixture member to a tube member one located within the other comprising forming an aperture in the outer member and welding the outer member to the inner member by a welding process in which a consumable electrode is melted at the same speed as it is being fed progressively to a weld that extends transversely of the length of the tube through an aperture in the outer member and penetrates to the inner member, the welding being effected by a pulsed arc metal-inert-gasprocess, the consumable electrode being fed into the aperture and the pulsed arc being continued both for a predetermined period.

2. A process as claimed in claim 1 wherein the tube member is the outer member.

3. A process as claimed in claim 2 wherein a recess is provided in the inner member in line with said aperture.

4. A process as claimed in claim 1 wherein a series of tubes are fed by a conveyor successively to a welding position, each tube is drilled, then rotated automatically by a predetermined angle to bring the drilled hole to the welding position and clamped during drilling and welding.

5. A process as claimed in claim 1, wherein the aperture and recess are formed in a single drilling operation.

6. A process as claimed in any of claims 1 to 5 wherein two apertures are provided running into each other and filled with weld metal.

7. A process as claimed in claim I wherein two such welds closely adjacent to each other are made slmultaneously by welding heads located at an angle to each other.

8. A process for attaching an end fixture

to a tube substantially as described.

9. Apparatus for welding fixtures to tubes comprising a conveyor for moving a series of tubes step by step successfully to a drilling and welding position, drilling means are provided for drilling one or more holes in the tube, pulsed-arc-metal-inert-gas-process welding means offset from the drilling means for filling the holes with weld metal, means to rotate each tube to bring the hole from the drilling position to the welding position, and clamp means to hold the tube during drilling and welding.

10. Apparatus as claimed in claim 9 substantially as described and substantially as shown in the accompanying drawings.