GB2168638A

GB2168638A - Thermal cutting

Info

Publication number: GB2168638A
Application number: GB08429224A
Authority: GB
Inventors: John Thomas Pauley; Michael Craig Langley
Original assignee: CONTROL LASER Ltd
Current assignee: CONTROL LASER Ltd
Priority date: 1984-11-19
Filing date: 1984-11-19
Publication date: 1986-06-25
Also published as: GB8429224D0

Abstract

When a sheet (10), e.g. of steel, is cut by a relatively moving, localised energy source such as the laser (3) beads of dross tend to accumulate on opposite sides of the cut on the side of the sheet (10) remote from the energy source (3). This dross subsequently has to be removed in a separate operation, e.g. by milling or grinding. To prevent the accumulation of dross the present invention provides a source (12) of gas under pressure which flows from a nozzle (13) across the underside of the sheet (10). The nozzle (13) remains stationary relative to the cutter (3) whether the sheet (10) moves in the direction of the arrow or whether, in a modification, the sheet (10) is clamped to remain stationary and the cutter (3) and nozzle (13) move in synchronism. <IMAGE>

Description

SPECIFICATION Thermal cutting This invention relates to thermal cutting, and more particularly to a method and apparatus for removing dross from the region of a cut made by an energy source such as a laser beam.

When a sheet material such as a metal sheet or plate is given a line cut by the application to one side of it of a source of localised heat, such as a laser beam, material in the region of the cut tends to accumulate on the opposite side of the sheet or plate. The line or bead of material, known as "dross", usually has to be removed from the cut material in a separate operation such as milling or grinding.

An object of the present invention is to obviate, or substantially to reduce the need for, such subsequent dross removal or separate finishing operation.

In accordance with one aspect of the present invention there is provided a method of cutting sheet material by means of a relatively moving, localised energy source impinging on one side of the sheet, wherein gas is caused to flow along the opposite side of the sheet to remove dross during the cutting operation.

In accordance with another aspect of the present invention there is provided apparatus for carrying out the method of the immediately preceding paragraph, comprising means for directing a flow of a gas under pressure across a region of the side of the sheet remote from that impinged upon by said energy source, said means remaining stationary relative to the energy source when the latter and the sheet are relatively moved.

The said flow directing means may comprise a nozz#le positioned to direct a jet of said gas approximately parallel to said other side of the sheet or toward the sheet at an angle typically in the range 50 to 100.

A deflector, e.g. of metal, may be fixed to the nozzle to extend from the side thereof nearer the sheet almost into contact with the sheet.

Platens may be disposed adjacent said remote side of the sheet on opposite sides of said flow directing means to define between said platens a channel for the gas flow. In the region of said nozzle said channel may have a tapered inlet end.

Preferred embodiments of the present invention will now be described with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a side sectional elevation of apparatus for carrying out the method of the present invention, taken on the line I-I of Figure 2, Figure 2 is a sectional elevation on the line Il-Il of Figure 1, Figure 3 is a detail on a larger scale of the apparatus of Figures 1 and 2, Figures 4 and 6 illustrate respectively in plan view and in side elevation and on an enlarged scale a sheet of metal cut by a laser beam without using the method and apparatus of the present invention, and Figures 5 and 7 are views similar to Figures 4 and 6, respectively, of a similar sheet cut by similar equipment but where the method and apparatus of the present invention have been employed.

The drawings illustrate a sheet or plate 10 of metal undergoing a line cut by a laser beam cutting nozzle 3 as the sheet 10 and nozzle 3 undergo relative movement in the plane of the sheet 10 as indicated by the arrow in Figure 1. Suitable equipment for this purpose is well known per se and will not be described in more detail. If solely the equipment so far referred to is used dross will accumulate on the underside of the sheet 10 in the region of the cut as indicated at 11 in Figures 4 and 6.

These lines or beads 11 of adherent dross will have to be removed from the cut sheet 10 in a subsequent, separate milling or grinding operation.

To obviate the need for such subsequent operation the present invention provides, on the side of the sheet 10 remote from the cutting nozzle 3, a source 12 of gas under pressure. A jet of the gas is directed by a flat nozzle 13 at the free end of a pipe 1 across the region of the underside of the sheet 10 on which the laser beam is impinging. It will be understood that it is immaterial for purposes. of the present invention whether the cutting nozzle 3 is stationary and the sheet 10 moves, or whether the sheet 10 is held stationary and the cutting nozzle 3 moves, e.g.

under the influence of a lead screw or a toothed belt (not shown).

Indicated in broken lines in Figure 2 (only) are clamps 20 which are used to hold the sheet 10 stationary on platens 4 while, in an alternative embodiment of the invention, the cutting nozzle 3 and nozzle 13 move in synchronism relative to the sheet 10. In either embodiment of the invention the nozzle 13 remains stationary relative to the cutting nozzle 3 so that throughout the cutting operation a flow of gas is maintained across the underside of the sheet 10 in the region currently being cut. Flow from the nozzle 13 is directed almost parallel to the underside of the sheet 10, or toward it at an angle in the range 50#100.

As shown in Figure 1 a deflector plate 2 of metal is preferably brazed to the side of the nozzle 13 nearer the sheet 10 and extends from it almost into contact with the sheet 10.

To confine and direct the gas flow the platens 4 adjacent the sheet 10 on opposite sides of the pipe 1 define between them a channel which is parallel-sided throughout most of its length but has a tapered lead-in end 5 in the region of the nozzle 13.

Figures 4-7 each show a silicon steel sheet, 3 mm thick, which has been cut using a 1800 Watts laser moving relative to the sheet at 1.8 metres per minute. In Figures 4 and 6 the sheet has been cut in the usual way without using apparatus according to the present invention.

Figures 5 and 7 show the sheet when it has been cut using the method and apparatus of the present invention, and it will be apparent by comparison with Figures 4 and 6 that adherent dross 11 has been substantially eliminated.

It is envisaged that the present invention will be utilised when the sheet to be cut is of a material other than steel, for example a plastics material. suitable gas for removing the dross may, but need not necessarily, be inert.

Claims

1. A method of cutting sheet material by means of a relatively moving, localised energy source impinging on one side of the sheet, wherein a gas is caused to flow along the opposite side of the sheet to remove dross during the cutting operation.

2. Apparatus for use in removing dross from a sheet of material being cut by a relatively moving, localised energy source, comprising means for directing a flow of gas under pressure across a region of the side of the sheet remote from that impinged upon by the energy source, and means for maintaining said flow directing means stationary relative to the energy source when the latter and the sheet are relatively moved.

3. Apparatus as claimed in claim 2, wherein the flow directing means comprises a nozzle positioned to direct a jet of said gas~approximately parallel to said other side of the sheet.

4. Apparatus as claimed in claim 2, wherein the flow directing means comprises a nozzle positioned to direct a jet of said gas toward the sheet at an angle typically in the range 50 to 100.

5. Apparatus as claimed in claim 4, wherein a deflector is fixed to the nozzle to extend from the side thereof nearer the sheet almost into contact with the sheet.

6. Apparatus as claimed in any one of claims 2-5, wherein platens are disposed adjacent said remote side of the sheet on opposite sides of said flow directing means to define between said platens a channel for the gas flow.

7. Apparatus as claimed in claim 6, wherein, in the region# of the nozzle, said channel has a tapered inlet end.

8. A method of cutting sheet material by means of a relatively moving, localised energy source substantially as hereinbefore described.

9. Apparatus for use in removing dross from a sheet of material being cut by a rela tively moving, localised energy source sub -stantially as hereinbefore described, with refer ence to and as shown in Figures 1-3 of the accompanying drawings with the clamps 20 omitted or Figures 1-3 when modified to permit the use of the clamps 20 of Figure 2.