AU648646B2

AU648646B2 - Process for machining a work piece using a laser

Info

Publication number: AU648646B2
Application number: AU12172/92A
Authority: AU
Inventors: Johann Herrmann
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 1991-03-15
Filing date: 1992-03-11
Publication date: 1994-04-28
Anticipated expiration: 2012-03-11
Also published as: DE4108541A1; AU1217292A; EP0503539A1; DE59200673D1; EP0503539B1

Description

640 46

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION NAME OF APPLICANT(S): Linde Aktlengesellschaft ADDRESS FOR SERVICE: oo oo o 0 eoeo *eo DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

INVENTION TITLE: Process for machining a work .iece using a laser The following statement is a full description of this invention, including the best method of performing it known to me/us:la- The present invention relates to a process for machining a work piece, in particular surface machfining, using a laser beam focussed on the work piece and using an additional gas beam directed at the focal point of the laser beam.

Many optical processes using lasers replace purely mechanical machining processes for machining work pieces. With surface machining of work pieces, instead of using mechanical chamfering or milling, the effort is made to employ processes which remove material from the work piece by means of a laser beam focussed on the work piece surface with the assistance of a gas beam directed at the focal point of the laser beam. Due to the focussed laser beam, the material vaporizes on the work piece surface. The vaporized material is removed by means of the gas beam. This type of machining displays a high degree of precision and repeatability. The problem arises with the process described, however, that the evaporated material condenses again and accumulates on the surface of the work piece. This means that the desired quality of machining is not ensured. Furthermore, the material freshly accumulated on the work piece turns out to be a disadvantage during ensuing machining of the work piece, since the surface of the work piece to be machined displays irregularities which need to be removed by a separate procedure.

The object of the present invention is therefore to demonstrate a process of the type initially mentioned which avoids the aforementioned disadvantages in a simple 25 manner.

.According to the present invention, there is provided process for machining a work piece, in particular surface machining, using a laser beam focussed on the work piece and using an additional gas beam directed at the focal point of the laser beam, whereby material of the work piece is removed from the work piece by means of the focussed laser beam with assistance from the gas beam, and wherein the work piece is electrostatically charged during said machining.

940216,p:\opr\ph,12172-92.046,1 -2- The electrostatic charging of the work piece to be machined according to the present invention also imparts a unipolar electrostatic charge to the evaporated material.

As a result of this charge, an electrostatic repelling force with respect to the work piece acts on the evaporated material, effectively preventing renewed accumulation and fastening of the machined material on the machined work piece. This brings about an essential increase in quality in the machining of materials with lasers, with a simultaneous increase of the material evaporation rate. This is valid especially for machining of surfaces when there is only partial machining of the surface, as is the case with engraving or inscription.

The gas beam can be composed of inert gas such as He, Ar, N2 or mixtures thereof, or of reactive gas such as 02, C0 2 mixtures thereof or gas mixtures containing CO 2 and/or 02. In the process according to the present invention a gas composition of inert gas and reactive gas turns out to be an advantage. The reactive gas supports removal of the material from the work piece.

As a further development of the inventive concept in the process according to the present invention, an electrostatic field is advantageously produced for the electrostatic charging of the work piece in the space between the work piece surface and a nozzle through which the laser beam and gas beam are guided against the work piece. To achieve this a body can be electrostatically charged antipolar to the work piece. Additionally to the already described i -pelling force, an attracting force now acts on the vaporized material by means of the oppositely charged body. The evaporated material subsequently does not accumulate on the work piece surface, 25 rather on the antipolar charged body. The nozzle tip itself can be used as the charged body, as can with particular advantage an electrode which is located between work piece surface and nozzle. An additional electrode creates the decisive advantage whereby accumulations of the evaporated material on it are unproblematical and whereby the electrode can easily be changed. Machining of the work piece occurs with removal of the material in the desired direction, that is, towards the electrode and away from the machined work piece surface.

r o I 940216,p:\oper\phh,12172-2.046,2 -3- An annular electrode is used to advantage for the aforementioned charged body, which is arranged axially symmetrical to the laser beam axis or to the direction of flow of the gas beam, such that the laser beam and gas beam are guided through the annular aperture of the electrode. The annular electrode may thereby be designed as a torus or as a disc anode.

The process according to the present invention is suited to machining of any material which can be charged electrostatically. Examples are metals, semi-conductors, synthetics and rubber. The work piece to be machined is preferably positively charged.

In a further development of the invention the nozzle is advantageously charged electrostatically with the same polarity as the work piece to be machined. This effectively prevents accumulation of the evaporated material on the nozzle. The unipolar electrostatic charging of the nozzle proves particularly advantageous if an antipolar electrostatically charged electrode is used between the nozzle and work piece. This ensures that no material accumulates in the nozzle duct or can reach the b. focus lens.

20 The invention will be explained in greater detail hereinafter, by way of example only, with reference to two embodiments.

Figure 1 shows machining of a work piece with electrostatic charging of the work piece, and 25 Figure 2 shows machining of a work piece with electrostatic charging of the .oo: work piece and an antipolar electrostatically charged annular electrode.

Figure 1 illustrates machining of a work piece by use of a laser. The parallel incident laser beam 1 is focussed in a nozzle tip by means of a focussing lens 2. The focussed laser beam is directed through nozzle 3 to work piece 4, whereby the focal point of the focussed laser beam lies on the work piece surface of the work piece to be machined. Inert and/or reactive gas is pumped into the injector cup by way of o i Y 940216,p:\oper\phh12172-92.046,3 -4a lateral gas supply 5. A sharp gas beam is formed in nozzle 3 and is guided against the point of machining on the work piece. According to the present invention, this was charged electrostatically, and positively in the embodiment. The removed, likewise positively charged material is repelled from the work piece, making possible work piece machining of a high quality.

Figure 2 also illustrates machining of a work piece using a laser and essentially matches that in Figure 1. Reference numbers 1 to 5 are therefore identical in both figures. In contrast to the process illustrated in Figure 1, however, an annular electrode 6 in the form of a disc anode is used in addition. Whereas the work piece has positive potential as in Figure 1, annular electrode 6 in Figure 2 is electrostatically negatively charged. Evaporated positively charged material is subsequently attracted by the annular electrode and thus accumulates on the annular electrode.

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Claims

1. Process for machining a work piece, in particular surface machining, using a laser beam focussed on the work piece and using an additional gas beam directed at the focal point of the laser beam, whereby material of the work piece is removed from the work piece by means of the focussed laser beam with assistance from the gas beam, and wherein the work piece is electrostatically charged during said machining.

2. Process as claimed in Claim 1, wherein the gas beam comprises inert gas.

3. Process as claimed in Claim 2, wherein the inert gas is selected from He, Ar, N 2 and mixtures of any two or more thereof.

4. Process as claimed in Claim 1, wherein the gas beam comprises reactive gas.

Process as claimed in Claim 4, wherein the reactive gas comprises 02, C0 2 mixtures thereof or a gas mixture containing CO 2 and/or 02. 20

6. Process as claimed in Claim 2 or 3 and in Claim 4 or 5, wherein the gas beam is composed of a mixture of inert and reactive gas.

7. Process as claimed in any one of the preceding claims wherein an electrostatic 0 field is produced in the space between the work piece surface and a nozzle through which the laser beam and gas beam are guided against the work piece, at least in the area adjacent the work piece surface.

8. Process as claimed in Claim 7, wherein the electrostatic field is produced by a body charged antipolar to the work piece to be machined, which is located between the work piece surface and nozzle. ~a

9. Process as claimed in Claim 8, wherein to produce the electrostatic field, an 940216,p:\opcr\phh,12172-92.046,5 1 -6- annular electrode is introduced between the nozzle and work piece, through which the laser beam and gas beam are supplied.

Process as claimed in any one of the preceding claims, wherein the work piece is electrostatically positively charged.

11. Process as claimed in any one of the preceding claims, wherein a nozzle through which the laser beam and the gas beam are supplied is charged electrostatically with the same polarity as the work piece.

12. A process for machining a work piece substantially as hereinbefore described with reference to the drawings. DATED this 16th day of February, 1994. LINDE AKTIENGESELLSCHAFT I" By its Patent Attorneys DAVIES COLLISON CAVE too *4g4 4 940216,p:\oper\phh, 12172-92.046,6 ABSTRACT The present invention relates to a process for machining of a work piece, in particular surface machining, using a laser beam focussed on the work piece and an additional gas beam directed at the focal point of the laser beam, whereby the work piece according to the present invention is electrostatically charged. This prevents renewed accumulation of the evaporated material on the work piece surface. The gas beam comprises inert and/or reactive gas. By use of an annular electrode charged antipolar electrostatically to the work piece, the electrostatic forces acting on the removed material are increased. An attracting force based on opposite charging of evaporated material and annular electrode is added for ".15 attracting force based on identical charging of evaporated material and work S" piece. S S S *S S. G325 G 91/20 (0014k) Ob/ed-15.03.91-