GB2130947A - Apparatus for resistance welding - Google Patents

Abstract

The invention relates to resistance welding apparatus which reduces the power needed to perform the weld. An electrode 7 which has a footprint corresponding to the desired weld line is held inclined to the workpiece 4 so as to make only point contact with the workpiece. The electrode is wobbled to move the point of contact progressively along the weld line. In this way the weld is formed gradually thus reducing both the welding current and the rate at which heat is generated. <IMAGE>

Description

SPECIFICATION Method and apparatus for resistance welding The present invention relates to a method and apparatus for resistance welding.

In a known method disclosed in the German Auslegeschrift (Published Specification) 2107368, an annular electrode is applied to a workpiece to overlie simultaneously the entire length of a seam to be welded. The electrode supplies a welding current to the workpiece, and this causes a weld to be formed between any surfaces which the current-flow intersects.

However, in many instances the proposed weld is of a considerable length and therefore demands a heavy welding current. This in turn requires an expensive welding power supply. Furthermore, considerable quantities of heat are produced both during the welding process and in the power supply and the cost of removal of this potentially damaging heat adds to the expense of this method.

In a known rolling resistance welding method two disc shaped electrodes rotate in opposite directions and the workpiece is moved along between them. This method cannot be effectively used with large, bulky workpieces, as the workpieces may be difficult to manoeuvre, to give the desired weld.

In accordance with a first aspect of the present invention, there is provided a resistance welding apparatus, wherein an electrode is capable of being moved with a rocking motion relative to a workpiece so as to displace the point of contact of the electrode with the workpiece progressively along a desired weld line, whereby, during a welding operation, only a portion of the electrode contacts the workpiece within the footprint of the electrode at any given time.

The footprint of the electrode, that is to say the locus of the point of contact of the electrode with the workpiece constitutes the desired weld line.

By only bringing a portion of the electrode into contact with the workpiece at any one particular time, it is possible to reduce both the current demand and the rate of heat production during the welding operation, this being achieved in the present invention by rocking the electrode relative to the workpiece.

Preferably, the electrode is disposed at one end of a diabolo shaped holding member which is pivotably secured at its centre to an arm which is in turn pivotably and displaceably mounted on a support and urges the electrode against the workpiece.

In an embodiment, the holding member slidingly engages at its end remote from the electrode with a crank rotated by a motor to cause rocking of the electrode.

Conveniently, the electrode comprises a ring inclined relative to the plane of the surface of the workpiece.

By employing a ring which contacts one point on the surface of the workpiece at any particular instant in time, it is possible to achieve a uniform weld along a continuous seam. Alternatively, the electrode surface may undulate or be corrugated in a direction normal to the surface of the workpiece, giving rise to a discontinuous weld.

If desired, a circular electrode may additionally be arranged beneath the surface of the workpiece to support the latter.

Advantageously, the electrodes are replaceably mounted so as to be interchangeable.

In one embodiment of the invention, at least one of the electrodes is cup-shaped. By employing such an electrode, it is possible to weld, for example, a short pipe flange from the direction of the pipe end of the flange.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section through a resistance welding apparatus according to the present invention, and Figure 2 is a diagrammatic view of an embodiment of the invention.

In Figure 1, a pipe socket 2 has an annular flange 3 is to be rigidly joined to a structural member 4 by resistance welding. An electrode 7 contacts the workpiece at a point 8 and is capable of being moved in a wobbling or rocking motion as indicated in the Figure by the different positions 9, 9' of the central axis by the arrow 10. The workpiece is supported by an annular backing electrode 6 which contacts the flange 3 along its upper edge.

In operation, the wobbling movement of the electrode 7 causes the point of contact 8 to be progressively displaced along the proposed weld line such that a welding current only flows through the workpiece from the point 8 to the backing electrode 6. Hence, a reliable and tight weld may be achieved with a lower welding current, as a result of which, the cost of the welding transformer may be substantially reduced.

Furthermore, the heat produced by the welding process is dissipated over a comparatively long period of time and thus reduces the cost while increasing the effectiveness of the means provided for cooling the weld.

In Figure 2, parts corresponding to the arrangement as shown in Figure 1 have been provided with the same reference numerals but dashed.

A pipe section 1' having a connection piece 2' and a flange 3' is inserted through an opening 5' in a structural member 4'. The electrode 7' is interchangeably secured to one end of a holding member 10 which is in the shape of a diablo and which is pivotably secured (as indicated by arrows 11 ) to an arm 12. The arm is pivotably and displaceably mounted in a mount 15 and may be displaced as indicated by the arrows 14 or rotated as indicated by the arrows 13. The holding member 10 has a guide groove 16 at its end remote from the electrode 7'. The guide groove 16 accommodates a roller or slider 17 mounted on a crank arm which may be rotated by a motor 19.

The welding pressure at the point 8' may be applied by way of the mount 1 5, the latter being displaced in the direction shown by the arrow 20.

By appropriate selection of the annular electrodes, guide groove 16 and crank arm 18 the desired diameter of circular welded joints may be determined in each case.

In order to weld a seam along a more complicated path, for example an ellipse or a polygon, other control devices may be employed to achieve the necessary wobbling motion of the electrode 7'. Furthermore, the edge of the electrode 7' having thereupon the point of contact 8' may be undulated or corrugated to produce discontinuous welding patterns upon the surface of the workpiece.

Claims (7)

1. A resistance welding apparatus, wherein an electrode is capable of being moved with a rocking motion relative to a workpiece so as to displace the point of contact of the electrode with the workpiece progressively along a desired weld line, whereby, during a welding operation, only a portion of the electrode contacts the workpiece within the footprint of the electrode at any given time.

2. A resistance welding apparatus as claimed in claim 1, wherein the electrode is disposed at one end of an elongate holding member pivotably secured along its length to an arm which is rotatably and slidably supported in a mount, the end of the holding member remote from the electrode being provided with a guide groove in which engages the end of a crank arm rotated by a control motor to cause the rocking motion of the electrode.

3. A resistance welding apparatus as claimed in claim 1 or 2, wherein the electrode footprint is in the form of a ring inclined to the plane of a surface of the workpiece to be welded.

4. A resistance welding apparatus as claimed in any one of the preceding claims, wherein a backing electrode supports the workpiece.

5. A resistance welding apparatus as claimed in any of the preceding claims, wherein at least one electrode is readily replaceable.

6. A resistance welding apparatus as claimed in any of the preceding claims, wherein at least one electrode is cup shaped.

7. A resistance welding apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.