GB2319490A

GB2319490A - Spot welding electrode trimmer

Info

Publication number: GB2319490A
Application number: GB9624080A
Authority: GB
Inventors: Alexander Richard Nye
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-11-20
Filing date: 1996-11-20
Publication date: 1998-05-27
Also published as: GB9624080D0

Abstract

A trimming tool for re-forming a convergent tip of an electrode (12) of a spot-welding machine comprises a plurality of trimming blades (20) bounding a convergent recess (22) in a metal body (18). A patch (26) of electrically insulating material on an opposite surface (28) of the body is positioned to prevent the passage of current through the tool should the machine be operated with the tool in position.

Description

RE-FORMING WELDING TIPS In a conventional kind of spot welding machine, opposed copper electrodes are brought together to apply pressure to workpieces held between them, and an electric current passed from one electrode to the other through the workpieces (being electrically conductive) to heat the material of the workpieces locally and achieve a weld between the workpieces.

The copper electrodes used in such machines are generally in the form of stout rods, an end portion of each rod (hereinafter referred to as the tip) being shaped to converge, which results in high local pressure being applied to a workpiece clamped between the two electrodes.

The shape of the rod tip is important to efficient operation of the welding machine, and a trimming tool in the form of a cutter (akin to a multi-bladed pencil sharpener) can be used at intervals to re-form the tip.

The cutter is ordinarily held in an air-driven chuck and rotated on the tip to effect trimming of the rod to restore its shape.

Such cutters are ordinarily of metal and, therefore, electrically conductive. Should a welding machine operator accidentally trigger operation of the welding machine whilst in the process of re-forming one of the electrodes, which in many circumstances can be done very easily if the operator is distracted, the electrodes close on to the cutter and welding current is passed through it. The consequence of this is that the heating of the cutter so caused results in some annealing of the cutter material, so destroying the effectiveness of the cutter blades. This means a wastage of good cutters.

To overcome this problem, consideration has been given to linking the operating controls between the welding machine and the cutter drive, or otherwise overriding the cycle of the welding machine, so as to prevent operation of the former whilst the latter is in process of presenting the cutter to an electrode. However, solutions of this kind tend to be unduly complex.

It is the object of the present invention to overcome the problem aforementioned.

In one of its aspects the invention provides a trimming tool suitable for use in re-forming a convergent tip of a spot-welding electrode by effecting a relative rotation between the electrode tip and the trimming tool about an axis of the tool whilst the tool is applied to the tip, the tool comprising a plurality of trimming elements which are arranged about the axis and bound a convergent recess in a front face of the tool to act upon the electrode tip during re-forming, an area of an oppositely-facing back face of the tool which is centred on the axis being electrically insulated from the trimming elements.

In use of such a tool, should the machine be operated with the tool in place on one of the electrodes the other electrode would be brought into engagement with the central area of the back face of the tool but no current (or at least no current sufficient to heat the tool to a damaging extent) would be passed through the tool.

The tool may be of a conventional form comprising trimming elements presenting elongate blade-like cutting edges which are distributed about the tool axis.

Electrical insulation of a metal tool body forming the trimming elements may conveniently be achieved simply by the provision of an insulating layer over a relevant central part, at least, of what would ordinarily be the back face of the tool. Such a layer can be formed, for example, by adhering a patch of sheet insulating material to the metal surface, or by coating the surface with a setting material such as an epoxy resin.

In another of its aspects the invention provides a trimming tool suitable for use in re-forming a tip of a spot-welding electrode of a spotwelding machine by effecting relative movements between the electrode tip and trimming means arranged at a front face of the tool, an area of an oppositely-facing back face of the tool and the trimming means at the front face of the tool being electrically insulated from one another so as to resist the passage of current through the tool should the machine be operated with the tool positioned between opposed electrodes of the machine.

In yet another of its aspects the invention provides a method of reforming a tip of an electrode of spot welding apparatus in which a trimming tool as set out in the last preceding paragraph or the last preceding paragraph but four is applied to the electrode tip and relative movement between the tool and the electrode caused to effect re-forming of the tip.

There now follows a description, to be read with reference to the accompanying drawings, of an electrode trimming tool and its use which illustrate the invention by way of example.

The accompanying drawing shows a trimming tool positioned between electrodes prior to use.

A spot welding machine comprises upper and lower copper electrodes 10,12, the electrodes being moveable relatively to one another to clamp workpieces (not shown) between them in operation of the machine.

A trimming tool 14 mounted in a holder 16 can be introduced between the electrodes for re-forming the tip of either electrode; the tool is shown in the drawing presented for trimming the lower electrode 12, but can be inverted for operating on the upper electrode instead.

The tool comprises a metal body 18 presenting a plurality of trimming elements 20 arranged uniformly about an axis of the tool; in use of the tool, the electrodes are aligned along the axis. The trimming elements present elongate blade-like cutting edges, as known in a conventional type of tool, the elements bounding a convergent recess 22 in a front face 24 of the tool. In use of the tool, the tool is rotated about its axis (by driving means of the holder 16) to re-form the shape of an electrode tip on to which it has been placed.

A disc 26 of an electrically insulating reinforced plastics material is bonded centrally (i.e. with the tool axis passing through it) to a flat back face 28 of the tool body. Should the electrodes 10 and 12 be brought together on to the trimming tool 14, the upper electrode 10 will engage with the insulating disc 26 presenting a central area of the back face of the tool. No current can, therefore, pass between the electrodes through the tool, the tool so being preserved from excessive heating and consequent damage.

Claims

1. A trimming tool suitable for use in re-forming a convergent tip of a spot-welding electrode by effecting a relative rotation between the electrode tip and the trimming tool about an axis of the tool whilst the tool is applied to the tip, the tool comprising a plurality of trimming elements which are arranged about the axis and bound a convergent recess in a front face of the tool to act upon the electrode tip during re-forming, an area of an oppositely-facing back face of the tool which is centred on the axis being electrically insulated from the trimming elements.

2 A tool according to claim 1 comprising trimming elements presenting elongate blade-like cutting edges which are distributed about the tool axis.

3. A tool according to either of claims 1 and 2 in which a layer of electrically insulating material is provided at said area of the back face of the tool.

4. A tool according to claim 3 in which the layer is formed by an adhesively-applied patch of sheet insulating material.

5. A tool according to claim 3 in which the layer is formed by a coating of a setting material.

6. A trimming tool suitable for use in re-forming a tip of a spotwelding electrode of a spot-welding machine by effecting relative movements between the electrode tip and trimming means arranged at a front face of the tool, an area of an oppositely-facing back face of the tool and the trimming means at the front face of the tool being electrically insulated from one another so as to resist the passage of current through the tool should the machine be operated with the tool positioned between opposed electrodes of the machine.

7. A method of re-forming a tip of an electrode of spot welding apparatus in which a trimming tool as set out in either of claims 1 and 6 is applied to the electrode tip and relative movement between the tool and the electrode caused to effect re-forming of the tip.

8. A trimming tool substantially as hereinbefore described with reference to the accompanying drawing.

9. A method of re-forming a tip of a spot welding electrode substantially as hereinbefore described with reference to the accompanying drawing.