GB2161112A

GB2161112A - Laser beam undercutting of commutator bars

Info

Publication number: GB2161112A
Application number: GB08515759A
Authority: GB
Inventors: R Ashcroft
Original assignee: CONTROL LASER Ltd
Current assignee: CONTROL LASER Ltd
Priority date: 1984-06-22
Filing date: 1985-06-21
Publication date: 1986-01-08
Also published as: GB8415986D0; GB8515759D0

Abstract

A method of undercutting commutator bars wherein to effect removal of insulating material along the sides of the insulating segments (5) the laser beam is directed parallel to a radius (R) but offset therefrom by a distance (X). By this means the laser beam is caused to impinge on the side wall of the insulator during the undercutting process. To effect undercutting of the other side of the insulator the commutator body (1) is moved not only forward and back along the rotational axis (2) but it is also moved transversely at the end of each stroke whereby the laser beam is caused to impinge on the commutator offset by a distance (Y) to the other side of the radius (R), the offset (Y) being equal to that of the offset (X). <IMAGE>

Description

SPECIFICATION Undercutting commutator bars using a laser beam This invention relates to cutting surfaces formed of materials with portions of different absorptive properties in relation to laser beam energy. In a preferred aspect this invention relates to the undercutting of cummutator bars by means of a laser beam wherein use is made of the differences in absorptive indices of laser energy between the different materials which, in this application, comprise the metal bars of a commutator and the insulant therebetween.

The conducting bars in commutators are separated from each other by an insulating material which may be mica or a synthetic plastics. As the insulating material wears less rapidly than the metal commutator bars it is a common practice to undercut the insulating material so that a slot is formed between each bar and this is usually done by a mechanical means such as a circular saw. With such a method a difficulty is that the saw cannot get into the corner formed by the riser on the commutator bar, it is slow and there is tool wear.

It has been proposed to undercut the insulator by means of a laser beam focused on or near the surface of the commutator and impinging thereon in a radial direction. With this method the commutator is rotated at such a speed, in relation to the laser beam energy, that the metal bars are substantially unaffected by the laser beam but the insulating material is removed which thereafter leaves a V or U-shaped slot between adjacent commutator bars.

The slot so formed has a V or U-shaped base and the length of the insulating material is undercut by means of moving the commutator along its longitudinal axis relative to the laser beam. A V or U-shaped base to the slot is less desirable than having a square base and, furthermore, it is preferable if the sides of the slot are free of insulating material, which is not the case when a saw cutting method is used.

It is one object of this invention to provide a method of removing one of two adjacent materials so as to provide a sharp boundary where the one material is removed over its full depth to expose the full depth of the side of the other material.

It is a further object of this invention in a preferred aspect to provide a method of undercutting the insulator using a laser beam in which the sides of the slot can be left clear of insulating material.

According to this invention, there is provided a method for undercutting one of two adjacent materials having differing energy absorption characteristics in relation to a laser beam, in which method the direction of impengment of the laser beam is offset from a line normal to the surface at the point of impingement, one material being preferentially ablated to provide a sharp or undercut boundary.

According to a preferred aspect of this invention there is provided a method for undercutting the insulating material between adjacent commutator bars using a laser beam wherein the direction of impingement of the laser beam onto the commutator is offset from a radial line to a line forming the projection of a chord through the commutator, the offset from the radius being sufficient such that the laser beam impinges on a side of the slot.

To provide for the other side of any slot to be cut in a similar manner the commutator is so mounted relative to the laser beam that it may be moved whereby the beam is displaced to the other side of the radial by a distance equal to the aforesaid offset.

Advantageously two laser beams may be used each being offset from the radial so as to undercut both sides of any one of the slots during rotation of the commutator. In a further preferred arrangement a number of pairs of laser beams may be directed towards the commutator each offset from a radial by an appropriate amount and spaced at intervals around the circumference of the commutator.

It has been found that a jet of gas which is caused to impinge at the point of action of the laser beam on the commutator assists scavenging during the undercutting process.

The invention is further described by way of example and with reference to the accompanying drawings, wherein: Figure 1 illustrates diagrammaticallly the known method of undercutting commutator bars using a laser beam, Figure 2 shows diagrammatically the method according to this invention using a laser beam offset from a radial, Figure 3 illustrates the method using two laser beams each being offset from the radial, Figure 4 shows the use of two pairs of beams being aligned in the same plane, and Figure 5 shows a number of pairs of beams aligned in a multiplicity of planes.

Referring to the drawings, Fig. 1 shows a known method of undercutting commutator bars using a laser beam wherein the commutator body 1 is rotated about its longitudinal axis 2 whilst a laser beam 3 is directed at the commutator surface along a radial. Due to the selective absorptive indices of the commutator bars 4 and the insulating segments 5 the laser beam causes the insulation to be preferentially removed without any significant affect on the metal of the commutator bars 4. To effect undercutting of all the insulator strips 5 the commutator body 1 is rotated about the axis 2 and at the same time oscillated along the direction of the axis 2 to produce undercutting over the whole length.

Referring to Fig. 2 and according to this invention, in order to effect removal of insulating material along the sides of the insulating segments 5 the laser beam 3 is directed parallel to a radius R but offset therefrom by a distance X. By this means the laser beam on the side wall of the insulator during the undercutting process. To effect undercutting of the other side of the insulator the commutator body 1 is moved not only forward and back along the rotational axis 2 but it is also moved transversely at the end of each stroke whereby the laser beam is caused to impinge on the commutator offset by a distance Y to the other side of the radius R, the offset Y being equal to that of the offset X.

Fig. 3 shows an alternative method wherein two separate beams 3 and 3a are used to effect the undercutting, each beam being displaced from the radius R by a distance X, thus being caused to impinge on opposed sides of the undercut insulator segment 5.

Referring to Fig. 4 of the drawings, this shows the commutator body 1 wherein the insulator segments are undercut by means of laser beams 3 and 3a directed from one side of the body by an offset distance from the radius and also by further beams 3b and 3c which are directed from an opposite side of the body. Fig. 5 shows further development of the embodiment of Fig. 4 wherein additional pairs of beams 30 to 33 are directed at the body from different planes, each beam being offset by a suitable distance from a radial.

The advantages of using one or more pairs of beams as shown in the embodiments of Figs. 3 to 5 is that the commutator body need only be oscillated along its rotational axis without requiring a rectilinear motion to undercut an opposed side of the insulator segment.

Claims

1. A method for undercutting one of two adjacent materials having differing energy absorption characteristics in relation to a laser beam, in which method the direction of impingement of the laser beam is offset from a line normal to the surface at the point of impingement, one material being preferentially ablated to provide a sharp or undercut boundary.

2. A method in accordance with claim 1, for undercutting the insulating material between adjacent commutator bars using a laser beam wherein the direction of impingement of the laser beam onto the commutator is offset from a radial line to a line forming the projection of a chord through the commutator, the offset from the radius being sufficient such that the laser beam impinges on a side of the slot.

3. A method in accordance with claim 2, wherein to provide for the other side of any slot to be cut in a similar manner the commutator is so mounted relative to the laser beam that it may be moved whereby the beam is displaced to the other side of the radial by a distance equal to the aforesaid offset.

4. A method in accordance with claims 2 or 3, wherein two laser beams may be used each being offset from the radial so as to undercut both sides of any one of the slots during rotation of the commutator.

5. A method in accordance with claim 4, wherein a number of pairs of laser beams may be directed towards the commutator each offset from a radial by an appropriate amount and spaced at intervals around the circumference of the commutator.

6. A method in accordance with any preceding claim, wherein a jet of gas which is caused to impinge at the point of action of the laser beam on the commutator assists scavenging during the undercutting process.

7. A method for undercutting one of two adjacent materials substantially as herein described and exemplified by the drawings.

8. A method for undercutting commutator bars substantially as described herein and exemplified by the drawings.