FR2723018A1 - Cutting materials using laser - Google Patents

Abstract

The method for cutting materials, utilising the energy emitted by a power laser, involves depositing a thin film (P) of water on the material (M) to be cut or machined, simultaneously with radiation (R) produced by a laser (L), at the point or zone of radiation impact.

Description

Method of cutting various materials, using energy

emitted by a power laser.

  The present invention relates to a cutting process using the energy emitted by a power laser, this process being applicable to cutting various materials such as metals (steel, copper, bronze, aluminum, etc.), plastics, wood, semiconductors, ceramics, copper, fabrics, etc. It is known to use the energy emitted by a power laser to cut hard (such as, for example, steel and aluminum) or soft (such as

rubber).

  Power lasers are already widely used in

  metallurgy for industrial cutting of various metals.

  For example, it is known to cut steel using C02 lasers, operating in continuous emission or in pulsed mode. In this case, the powers used are relatively very high, that is to say of

The order of 500 watts to 106 watts.

  It is also known to cut aluminum using Nd-YAG lasers operating in pulsed mode at very high powers, also of the order of 500 watts at

106 watts.

  Are also used to cut various materials, Argon lasers also operating at powers

  very high, of the order of 103 to 106 watts.

  The complex process of the interaction between laser radiation and matter resulting in fusion and

cut, is well known.

  We know that the energy emitted by a power laser is poorly absorbed by metals which reflect a large part of this energy. For example, the emissivity of aluminum is around 0.5 for an Nd-YAG laser,

  while it is significantly lower for copper.

  As a result, the amount of energy absorbed by certain materials, such as metals, is relatively low at the start of the interaction process, and it is only by using significant energies that the parts

  metal can be cut or welded.

  For example, if we consider the use of an Nd-YAG laser for cutting an aluminum part, the laser energy applied to this part will cause: - initially, a microstructural modification (microfissuring, microfusion, instability of interatomic bonds), due to thermal elevation; - secondly, the rise in temperature at the point of impact, up to the melting temperature of the metal; this level is used for welding; - thirdly, an additional rise in temperature to the vaporization temperature of the

  metaL which, once reached, allows the cutting of metal.

  The disadvantages of laser cutting include: - the importance of the necessary powers, which requires the use of expensive and bulky devices; - by the fact that part of the deposited energy is reflected; - by the fact that part of the applied energy is diffused around the cutting zone, which creates a greater or lesser heat loss, depending on the thermal conduction of the metal; - by the fact that to create a constant and uniform cut, it is necessary to maintain, at the point of impact and along the cutting line, as a function of the speed of movement, a temperature higher than the melting temperature; in this way, the edges of the cut tend to melt and to solidify along the cut line, which creates an irregular cut; - by the vaporization of the metal in the interaction zone, in an ambient medium, which generates an ionization cloud which creates a barrier to the photonic emission, therefore reducing the efficiency of the laser emission; This is the reason for which we recommend laser cutting under a gaseous emission (helium) which prevents the formation of an ionization cloud; - by the creation, due to thermal expansion, around the point of impact or in the areas located along the cutting line, of a structural modification or change of the crystal structure of the metal which can, because of this , undergo micro-fractures and therefore present points of weakness, away from the cutting line; - by the difficulty of obtaining a good cut of the semiconductors; in addition to a cristaLLine modification of semiconductors, it is difficult to intervene on small thicknesses; - by the fact that La coupe is accompanied by significant carbonization on the banks of La coupe, on organomineral materials. An object of the present invention is to remedy the drawbacks of the methods and installations for cutting known materials, using the energy supplied by Le

laser radiation.

  According to a first characteristic arrangement of the invention, this object is achieved by a process according to which a thin film or film of water is deposited on the material to be machined or cut, at the same time as the radiation or emission produced by a laser, at the point of impact of said radiation or in the area of this point

impact.

  According to another characteristic arrangement of the invention, the thin film or film of water is deposited on the material to be machined or cut, in the form of a jet.

an air / water mixture.

  According to another characteristic arrangement of the invention, the thin film or film of water has a thickness of the order of one to a few tens of microns and, for example, a thickness of the order of 10 to

microns.

  Several cases can arise, in

depending on the type of laser used.

  1.) - The laser energy is absorbed by the metal, but The laser emission is not absorbed by the water (example: -4- Nd-YAG laser having a wavelength of 1.06 pm, or from

0.532 Gm).

  In this case, even at low energy, the metal (or certain other materials) undergoes a structural modification and a thermal rise. Water enters the microcracks created by the thermal effect, between the pulses of the laser emission, and undergoes a transformation into vapor inside the microcracks, as a result of

Thermal elevation of the metal.

  2.) - The laser energy is absorbed by the metal and by the water (example: YAG-ER laser at wavelength from 2.60 pm to 3.00 pm, or Excimer laser at wavelength from 200 nm to

300 nm).

  In this case, if the penetration of the laser beam into water is greater than the thickness of the water film on the metal: - a) the metal undergoes a microstructural transformation; - b) Water penetrates, during the inter-pulsation periods, Inside the microcracks; - c) The water undergoes an instantaneous vaporization during the following pulsations, even without thermal rise of the metal. In the two cases mentioned above, the brutal transformation of water into vapor, causes a significant release of energy which is exerted in the form of pressure on the walls of the microcavities. This sudden release of pressure causes the fracture of metal microparticles

  which are eliminated and ejected from the interaction zone.

  An important advantage of this cutting method is that the energy required to cut the metal is considerably reduced and therefore does not cause a significant thermal rise of the metal to reach

The desired cutting effect.

  Other advantages of the cutting method according to the invention result from a great improvement: - in the sharpness of the cut obtained; - in the reduction of morphological or structural modifications of the cutting edges; = -5- - in the reduction of microfractures in the vicinity of

cutting edges.

  The above purposes, features and benefits, and

  still others will emerge more clearly from the description which

  follows and attached drawings in which Figures 1 and 2 are schematic views illustrating two free of implementation of the cutting method according to the invention. We describe below some interesting examples of cutting, using Laser energy, of a covered metaL

a thin film of water.

  1. - Cut using a Md-TA6 Laser with a power of the order of 40 watts and operating in put mode, The radiation or emission of this Laser characterized by the following parameters: - Wavelength: 1.06 µm; - pulse duration: 1 to 100 microseconds; - pulse repetition rate: at least 50 Hertz, and more. The laser radiation R emitted by the Laser L and which can be transmitted by an optical fiber F equipping a hand tool or an emission head installed on an automatic machine, is applied to the part or material M to be cut or machined . Advantageously, the laser is adjusted so that the radius R has, at the point of impact,

  a diameter of around 400 microns.

  According to the invention, a thin film or film of water and preferably a film or film P of a gas / water mixture and, for example, an air / water mixture, is deposited on the part or material. M, at the point of impact of radiation R, for example in the form of a jet produced by a nozzle B

  supplied with air or other pressurized gas and water.

  Depending on the diameter of the nozzle, the air and water flow are adjusted to obtain a quantity of water with

  a thickness of the order of 50 microns.

  The use of a mixture of gases such as air and water makes it possible to deposit a very thin film of water P - 6 - having, for example, the aforementioned thickness, on the

  surface of the workpiece or material M to be cut or machined.

  As is apparent from the description which follows, this film may have a thickness of between one and a few tens of microns and, for example, a thickness

from 10 to 50 microns.

  To improve the efficiency of the process, the water, which is transparent to the laser emission, is made more absorbent by incorporating a water-soluble dye. Indeed, the dark colorants (for example black color) soluble in water, make it possible to obtain a

  absorbent solution to Nd-YAG radiation.

  The nigrosine, for example, allows, at a concentration of 0.1 Z, to obtain a sufficient coloration and absorption of the laser radiation and produces an increase in cutting efficiency of the order of 20%, in

  The application to cutting aluminum.

  This cutting process using the energy produced by an Nd-YA6 laser, is particularly suitable for cutting the following materials: aluminum, steel, plastics, wood,

semiconductors, ceramics.

  2. - Caoupe a. by means of a CO2 laser with a power of the order of 100 watts and more, and operating in put mode or in super put mode, The radiation or emission of this Laser being characterized by The following parameters - Wavelength : 10.6 µm - pulse duration: 1 to 100 microseconds; - pulse repetition rate: from 1,000 Hertz to

10,000 Hertz.

  The emission of C02 lasers at 10.6 pu is very absorbed

by Water.

  Advantageously, the laser is adjusted so that the radius R has, at the point of impact, a diameter of

The order of 400 microns.

  As indicated above, a film of water P is formed on the part or material M to be cut or machined, from an emission of an air / water mixture, in the area -7-

impact of laser radiation.

  More particularly advantageously in the case of the cut made by means of a C02 laser, the jet J of the air / water mixture is sent obliquely to the surface of the part or material M receiving the laser emission, and not in the axis of this emission, which makes it possible to avoid vaporization of the water (therefore a loss of energy) from a distance. The jet J forms, for example, an angle of the order of 40 to 60 degrees with the surface of the part or material M. This method of laser cutting with C02 is perfectly suitable for cutting the following materials: copper,

  bronze, steel, plastics, ceramics, semiconductors.

  3. - Cut to Lasers whose emission is located in Linfrar * average range with a power of the order of 25 watts and more, The radiation or emission of these Lasers being characterized by The following parameters - Wavelength: from 2.69 µm to 3 / m; - pulse duration: 1 to 100 microseconds; - Pulse repetition rate: Around 30 Hertz

and more.

  The laser radiation in the middle infrared is

Widely absorbed by water.

  Advantageously, these lasers are adjusted so that Their radius R has, at the point of impact, a diameter of

The order of 400 microns.

  In this case, the film of water deposited on the part or

  material to be cut, must be thin (10 to 40 microns).

  Laminating or reducing the thickness of the water film is obtained by increasing the percentage of air in the air / water mixture. In other words, in all cases, the desirable thickness of the thin film or film of water P, depending on the type of laser used, is obtained by varying the percentages of air or other gas and water,

in the air / water mixture.

  The process of cutting materials using the energy emitted by lasers in the middle infrared is more particularly suitable for cutting the following materials: semiconductors, wood, plastics, leathers, ceramics. It is observed that, in all cases, the increase in the repetition rate of the pulses makes it possible to increase the efficiency of the cutting effect produced by the

laser radiation.

  The laser radiation R can be conveyed to the part or material M to be cut or machined by means of an optical fiber (FIG. 1) or focused by means of a lens.

converging optics O (Figure 2).

- 9 -

Claims (9)

R E V E N D I C A T I O N S   1. - Process for cutting various materials, using the energy emitted by a power laser, characterized in that a thin film or film of water (P) is deposited on the material (M) to be machined or cut , at the same time as The radiation or emission (R) produced by the Laser (L), at the point of impact of said radiation or in the area of this point of impact. 2. - Cutting method according to claim 1, characterized in that the thin film or film of water (P) is deposited in the form of a jet (J) of a gas / water mixture and,   preferably in the form of a jet of an air / water mixture.   3. - cutting method according to one of claims 1 or   2, characterized in that the film or film of water (P) has a thickness of the order of one to a few tens of microns and, for example, a thickness of the order of 10 to 50 microns. 4. - Cutting method according to any one of   Claims 1 to 3, characterized in that the jet (J) of the   air / water mixture is sent obliquely to the surface of the part or material (M) receiving the laser emission. 5. - Cutting method according to any one of   claims 3 to 4, characterized in that the thickness   desirable water film (P) is obtained, depending on the type of laser (L) used, by varying the   percentages of air and water in the air / water mixture.   6. - Cutting method according to any one of   Claims 1 to 5, characterized in that a colorant of   dark color, soluble in water, is incorporated in water   used for the formation of the thin film of water (P). - 10 -   7. - Cutting process according to any one of   Claims 1 to 6, characterized in that Le   Laser radiation emitted by an Nd-YAG laser having, for example, a power of the order of 40 watts and operating in pulsed mode, this radiation being characterized by the following parameters - Wavelength: 1.06 μm; - pulse duration: 1 to 100 microseconds; - pulse repetition rate: at least 50 Hertz; this radiation having, at the point of impact, a diameter of The order of 400 microns.   8. - Cutting process according to any one of   claims 1 to 6, characterized in that it is used   Laser radiation emitted by a C02 laser having, for example, a power of the order of 100 watts or more, operating in puLsed mode or in super puLsed mode, this radiation being characterized by the following parameters: - Wavelength: 10.6 µm; - pulse duration: 1 to 100 microseconds; - pulse repetition rate: from 1,000 Hertz to 10,000 Hertz.   this radiation having, at the point of impact, a diameter of The order of 400 microns.   9. - Cutting process according to any one of   claims 1 to 6, characterized in that use is made of   laser radiation emitted by a laser in the middle infrared having, for example, a power of at least 30 watts or more and operating in puLsed mode, this radiation being characterized by the following parameters Wavelength: 2.69 Mrm at 3 mm; - pulse duration: 1 to 100 microseconds; - pulse repetition rate: at least 30 Hertz, or more; this radiation having, at the point of impact, a diameter of The order of 400 microns.