A CUTTING HEAD FOR PROCESSING BY MEANS OF A LASER BEAM

Abstract: A cutting head for cutting a material by means of a laser beam (1) focused in a pressure chamber (4) endling in a nozzle (6). Through a pipe (7) connected to the chamber, said chamber is capable of receiving pressure gas for blowing out the gas through the nozzle. According to the invention pressure gas is fed both to the front and the back of the beam-focusing unit or units in the chamber (4). In this manner the beam-focusing units do not limit the pressure within the chamber.

Description: Title: A Cutting Head for Processing by Means of a Laser Beam Technical Field The invention relates to a cutting head for processing such as cutting a material by means of a laser beam di¬ rected to a pressure chamber ending in a nozzle and which through a pipe connected thereto is capable of receiving pressure gas for blowing out the gas through the nozzle, said pressure gas furthermore being directed to the back of the beam-focussing unit or units. Background Art A cutting head of this type is known for instance from British patent application No. 2,064,399, whereby pressure gas is fed to a chamber bounded by a focussing lense and a nozzle. As a result a blowing out of gas at the cutting spot is produced which improves the quality of the cut¬ ting. However, this known lense limits the pressure with¬ ing the chamber. Disclosure of Invention The object of the present invention is to provide a cut¬ ting head permitting an increasing of the pressure in the laser cutting head, and the cutting head according to the invention is characterised in that a feeding of pressure gas of a relatively high pressure both to the front and the back of the beam-focussing unit or units in the cham¬ ber is permitted by the laser beam directed to the pres¬ sure chamber being focussed in a small opening to the pressure chamber. As a result the beam-focussing unit no longer limits the pressure within the chamber. The beam-focussing unit is advantageously formed by a OMH lense system focussing in a focal point immediately out¬ side the nozzle. As an alternative the focussing unit may be formed by one or more concave reflectors, at least one of said refleσ- tors being situated within the pressure chamber. In order to prevent reflections, if any, from reacting on the laser beam source, the part of the chamber situated behind the focussing unit may advantageously comprise a light transmission opening which is narrow compared to the opening of the nozzle. In this manner the laser beam source does not "see" the object. Brief Description of Drawings The invention will be described below with reference to the accompanying drawing, in which Fig. 1 illustrates a cutting head according to the inven¬ tion which includes a lense nozzle system, and Fig. 2 illustrates a cutting head comprising a nozzle system with reflecting focussing units. Best Mode for Carrying Out the Invention The cutting head illustrated in Fig. 1 for cutting a mate¬ rial comprises a lense 2 focussing the laser beam 1, which is thereby concentrated in a focal point 3. Through this focal point, the laser beam enters a pressure chamber 4. Subsequently, the laser beam 1 is re-spread until it meets a lense system 5 including one or more lenses. This opti¬ cal system focusses the laser beam 1 in another focal point immediately outside the pressure chamber, said laser beam leaving said chamber through a nozzle 6. At the same time a pressure gas in the form of for instance oxygen, OMPf argon or usual atmospheric air is fed to the pressure chamber 4 through a gas pipe 7. The focussed laser beam is suitable for processing immediately below the nozzle 6, e.g. for cutting a metal plate whereby the plate is displaced relative to the nozzle 6 perpendicular to the spreading direction of the laser beam and the gas beam. The feeding of gas both to the front and to the back of the focussing lense system 5 is for instance carried out through a branching, an adjustment device optionally be- ing provided in at least one of the branch pipes. The pressure in the chamber 4, is for instance 25 atm. A particular advantage of such avery high pressure is that a better cutting quality than previously is thereby achieved, at the same time as the cutting can be carried out at a higher velocity since the blowing out of " gas re-. moves melting drops and metal vapours, if any. A certain regulation of pressure may optionally exist so as to reduce the differential pressure between the front and the back of the lense 5. Two different gases may op- tionally be used. For high effects concave reflectors 8, 9 may be used as focussing units, whereby the loss in effect of the lenses is avoided. Fig. 2 illustrates a cutting head comprising two concave reflectors of suitable focal lengths. The laser beam 1 is here' focussed by the concave reflector 8 through an open¬ ing 10 of the pressure chamber and enters said pressure chamber 4. In this chamber the concave reflector 9 focus- ses the diverging laser beam which subsequently leaves the pressure chamber 4 through the nozzle 6. Here pressure gas is also fed through a gas inlet 7, and the focussed laser beam and the gas beam coaxial therewith are appli- cable for processing such as cutting an article. The opening of the nozzle 6 is preferably significantly greater than the distance to the article, since a laminar gas flow is thereby prod ι ced in the cutting area whereby refracting effects of shock waves and turbulent flows, if any, are avoided. In addition, it turned out that the po¬ larisation is of great importance since the refraction de¬ pends on the polarisation. In order to obtain the highest possible cutting capacity, the E-vector of the laser beam must be parallel to the cutting direction. In order to ob¬ tain a uniform cutting circularly polarised light can ad¬ vantageously be used. The laser used is typically a CO-, laser radiating infra¬ red light. The effect of the laser is typically about 200 - 5000 w. • . The present cutting velocities in a 2 mm thick steel plate are about 5 m/min, which apparently corresponds to only about 15% of the theoretical maximum. The notch width may apparently be reduced to about 0.1 mm. The cutting head according to the invention renders it possible to cut at a far higher velocity than previously. In order to prevent reflections, if any, of the article from reacting on the laser beam source, the light trans¬ mission opening of the chamber may optionally be made narrower than the opening of the nozzle. Other measures may, however, also be employed. - j E OMM

Claims: Claims : 1. A cutting head for processing such as cutting a material by means of a laser beam (1) directed to a pres¬ sure chamber (4) ending in a nozzle (6) and which through a pipe (7) connected thereto is capable of receiving pressure gas for blowing out the gas through the nozzle (6) , said pressure gas furthermore being directed to the back of the beam-focussing unit or units, c h a r a c ¬ t e r i s e d in that a feeding of pressure gas of a re- latively high pressure both to the front and the back of the beam-focussing unit or units in the chamber (4) is permitted by the laser beam (1) directed to the pressure chamber (4) being focussed in a small opening {3) to the pressure chamber (4) . 2. A cutting head as claimed in claim 1, c h a r ¬ a c t e r i s e d by the light transmission opening (3) being narrow compared to the opening of the nozzle (6) . 3. A cutting head as claimed in claim 1 or 2, c h a r a c t e r i s e d by feeding various gases to the various sections, e.g. oxygen to the cutting side and air to the inlet side. UMΠ

Inventors: OLSEN FLEMMING, OLSEN, FLEMMING
Applicants: INST PRODUKTUDVIKLING
Application year: 1984
Main classification: B23K26
IPC codes: B23K26