Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/36—Removing material
  • B23K26/38—Removing material by boring or cutting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/14—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor
  • B23K26/146—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor the fluid stream containing a liquid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/02—Iron or ferrous alloys
  • B23K2103/04—Steel or steel alloys
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/02—Iron or ferrous alloys
  • B23K2103/06—Cast-iron alloys

Definitions

• the present invention relates to the technique of laser beam cutting of parts in sheets or the like, of relatively large thickness, of iron-carbon alloy (steel or cast iron), or of other materials such as ceramics.
• thermal energy cutting processes are already known using an oxygen supply to carry out an exothermic reaction for iron oxidation, in particular the long-known processes of oxy-acetylene cutting or similar, of cutting with electric arc and, more recently, cutting by laser beam, plasma, summer, making it possible to obtain significant energy densities at the cutting point.
• the performance of these processes depends on the nature and density of the energy source, and on the oxygen supply conditions (type and diameter of the gas supply nozzle, pressure and flow rate of the gas).
• suction means placed on the side of the sheet opposite to the cutting head is already known, in particular in laser sheet cutting methods. These means are intended to evacuate the gases resulting from the cutting and the slag formed during it.
• the invention relates to a laser cutting method using a cutting head comprising a laser beam source and an oxygen supply nozzle, characterized in that, in order to perform cuts in thick iron-carbon alloy or ceramic products, a coolant is added to the surface of the product to be cut located on the side of the cutting head and a vacuum is generated on the other side of the product existing pressure on the side of the cutting head, greater than or equal to 0.25 bars.
• a coolant is added to the surface of the product to be cut located on the side of the cutting head and a vacuum is generated on the other side of the product existing pressure on the side of the cutting head, greater than or equal to 0.25 bars.
• the depression is greater than or equal to 0.01 xe + 0.15 where e is the thickness of the product in mm.
• the coolant can generally be any fluid, at low temperature.
• a liquid will be used, having better heat exchange capacities than a gas, such as water, or an aqueous solution or emulsion, such as for example an oil-water emulsion of the type conventionally used in metal machining by cutting tool.
• the suction carried out on the side opposite to the cutting head in certain known laser cutting processes has the purpose of removing the slag formed during cutting as well as the gases brought in or generated by the cutting, but , even if this suction implicitly causes a certain circulation of gas in the cutting line, the depressions used are not sufficient to cause sufficient cooling of the material, on the two sides of the cutting line, typical of the present invention.
• the laser used is a gas laser, continuous or pulsed, of the conventional type such as a CO 2 or CO laser.
• a gas laser continuous or pulsed, of the conventional type such as a CO 2 or CO laser.
• Such a laser makes it possible to obtain a power density of the order of 1000 KW / cm 2 at the focal point of the laser beam and, in cutting applications, this is assisted, in known manner, by an oxygen supply, under a relatively low pressure (of the order of 1 bar), brought by a nozzle into the orifice from which the laser beam passes. This supply of oxygen is necessary to cause oxygen cutting.
• the laser focusing device Given the large thicknesses to be cut, the laser focusing device will be adjusted to obtain a long focal distance, of the order of 250 to 350 mm.
• the flaring effect of the cutting line mentioned above is not so much due to the proper geometry of the laser beam as to the excessive heating of the material caused by the supply of oxygen.
• FIG. 1 in section, the region of the cutting line in a sheet 1, obtained by a conventional laser cutting process from a thick steel sheet. 10 mm, the groove having a width of about 0.3 mm.
• the shaded areas 11, which would delimit the parallel flanks of the ideal cutting line, have in fact disappeared by fusion under the effect of the energy supply of the oxygen flow (arrow 12) provided by the nozzle 13 of the cutting head. .
• these zones are all the more important when the material is less thermally conductive, or when it is already strongly heated by a cut made previously in the vicinity, since the dissipation by conductivity of the thermal energy supplied is then hampered.
• the flaring of the cutting line is all the more important the thicker the sheet, which has in practice limited until now the use of laser cutting to steel sheets of lower thickness. about 10 mm. From 10 to 20 mm, the geometry of the cutting line is of poor quality, limiting the production of the cut pieces to simple shapes. Beyond 20 mm, cutting is impossible due to an enlargement of the heat affected area, widening such that the molten metal can no longer be removed to make an effective cut.
• the zones 16 affected thermally whose importance, at the level of the middle zone in the thickness of the sheet, results from the concentration in this area cutting energy.
• this concentration of heat can cause significant heating of the sheet in the vicinity of the cutting line, which is troublesome for making other cuts nearby.
• the metal of these zones can be melted and entrained by the flow of the oxygen supplied, causing a digging of the sides of the groove, or even risking closing the latter on the side of the underside in s' resolidifying there.
• the mechanical characteristics of the heat affected areas are deteriorated (weakening of the edge of the cut parts, reduction in their resistance to wear, summer).
• the method according to the invention makes it possible, thanks to the supply of cooling fluid to the upper face of the sheet, on the side of the cutting head, and to the forced circulation of this fluid in the cutting line, under the effect of the depression created on the other side of the sheet, effectively cooling the sides of the groove over the entire thickness of the sheet, and therefore limiting the extent of the heat affected zone.
• the strong depression created between the two faces of the sheet allows better evacuation of the slag from the groove than in the methods according to the prior art.
• This slag entrainment effect is favorably influenced by the kinetic energy of the fluid molecules passing through the bleeding, energy which is all the higher as the depression, and therefore the speed of the fluid, is high, the kinetic energy also being increased when the coolant is a liquid.
• the process according to the invention makes it possible, by the cooling effect of the fluid circulating in the bleeding, to keep the cut product at low temperature (for example around 70 to 80 °) and, in combination with an efficient removal of slag, stabilizes the cutting front, even in the case of a narrow width, less than 1 mm and typically of the order of 0.3 mm, when cutting from a sheet of very thick material, for example around 20 mm. It makes it possible to keep the width of the groove practically constant over the entire thickness of the sheet, and consequently allows the production of holes of small section, of dimension significantly less than the thickness of the sheet, for example the production in a sheet metal 20 mm thick, oblong holes in length
• the method according to the invention allows the successive production without delay of cut lines very close to each other, the production of holes or recesses close to the edge of the sheet metal, and the production of parts with sharp angles, all these cuts being impracticable in thick products by the cutting methods according to the prior art.
• the method according to the invention reduces the risk of embrittlement of steel by hydrogen by preventing the formation of an austenization zone capable of absorbing hydrogen. .
• the reduction in the heat affected zone allows cutting into alloys which have already undergone a heat treatment (for example steels of high hardness, hardened and tempered) without altering the mechanical characteristics, in particular the hardness, of the parts thus cut.
• a heat treatment for example steels of high hardness, hardened and tempered
• the method according to the invention is for example particularly suitable for the manufacture of sheets perforated and very thick screening grids
• the invention also relates to a laser cutting device which is particularly suitable for implementing the method mentioned previously.
• This device is characterized in that it comprises: - a cutting head comprising a laser beam source and an oxygen supply nozzle, - a conduit for supplying a cooling fluid to the surface of the product to cut, opening next to the cutting head, - a suction box connected to a suction group and having an opening located in front of the cutting head and provided at its periphery with a seal intended for be placed against the surface of the product to be cut opposite the cutting head, - means for regulating the vacuum generated in the said box by the said suction group to maintain the said vacuum at a value greater than or equal to 0.25 bars .
• the means for regulating the vacuum comprise a relief valve connected to the box, to put the inside of the box in communication with the ambient atmosphere and means for regulating the opening of said relief valve in function of the open section of the orifices or cutting lines produced by the cutting in the product.
• This regulation system has the advantage of being able to let the suction unit operate at its optimum efficiency permanently, by compensating for the increase in fluid flow rate passing through the cut lines or orifices already made in the sheet metal by reducing the flow through the relief valve.
• a another advantage is that the discharge valve allows, even at the start of cutting, to let enter into the box a quantity of ambient air suitable for ensuring in the suction circuit an oxygen concentration lower than the rate likely to cause the ignition of the gas mixture sucked in by the pumping unit.
• FIG. 1 and 2 illustrate the problems encountered during laser cutting according to the prior art, already explained previously,
• FIG. 3 is a schematic representation of the laser cutting installation according to the invention
• Figure 4 is a simplified representation of a mask system intended to close the grooves or orifices already made, to limit the section of suction of the coolant
• FIG. 5 is a graph illustrating the field of application of the method, limited by a curve indicating, as a function of the thickness of the sheet to be cut, the value of the absolute pressure to be maintained under the sheet , when the pressure above the sheet on the side of the cutting head is atmospheric pressure.
• the laser cutting installation shown in FIG. 3, for cutting from a steel sheet 1, comprises a laser cutting head 10 of a type known per se.
• This cutting head shown diagrammatically in the drawing comprises an oxygen injection nozzle 13 with a diameter of 2 mm, supplied under a relative pressure of 1 bar, at the center of which passes the laser beam F.
• This beam is generated by a laser continuous gas, for example a C0 2 laser, having a power of 2 to 3 KW, and a focal length set to 250 mm.
• a suction box 20 open upwards and carrying at the periphery of its opening a seal 21.
• the box 20 is applied against the underside of the sheet, the seal 21 ensuring the seal between the latter and the box.
• the sheet 1 and the box can be fixed, and the cutting head is then moved along the outline of the cuts to be made.
• the cutting head and the box can be fixed, and it is then the sheet which is moved while remaining held in contact with the seal.
• a pipe 19 for supplying a cooling fluid such as water opens above the sheet to be cut, next to the cutting head, the water flow being sufficient for the water to cover the surface sheet metal in a sufficiently large area around the laser beam.
• the box 20 is connected by a suction line 22, provided with an isolation valve 23, to an assembly of accumulation tank 24, itself connected to a suction group 25, via a separator filter 26 impurities and liquids.
• This group is equipped with a suction pump having a large flow rate, for example from 500 to 700 m 3 / h, and making it possible to obtain an absolute pressure at suction of 0.5 bars or less.
• This suction group makes it possible to obtain in the accumulation tanks 24 and in the box 20 a absolute pressure adjustable for example from 0.7 to 0.5 bars depending in particular on the thickness of the sheet 1.
• the large volume of the accumulation tanks makes it possible to maintain them there and in the box 20 of a depression substantially constant despite the variations in flow rate that can occur during cutting, and in particular makes it possible to very quickly generate the required vacuum in the box 20 as soon as the isolation valve 23 opens.
• the accumulation tanks are connected via d valves insulation 27 to a condensate recovery tank 28, to which the filter 26 is also connected.
• the box 20 is also connected by a valve 29 to a device, not shown, making it possible to inject into the box a cooling fluid, for example a water mist, which is used for cooling the box 20 and the gases resulting from the cutting operation, which also has a moderate cooling effect on the underside of the sheet.
• a cooling fluid for example a water mist
• this injection of cooling fluid is in no way similar to the cooling, mentioned in the introduction to this memo, of the cutting zone by jets directed towards this zone from below.
• the use of such jets of liquid under a vacuum as strong as that according to the invention would lead to having to suck excessively large quantities of liquid.
• the invention precisely overcomes these problems.
• Another valve 30 puts the box 20 in communication with the ambient atmosphere, and allows the entry of ambient air into the box under the effect of the vacuum which is generated there by the suction group.
• the opening of this valve, and therefore the air flow entering the tank can be regulated to maintain the vacuum in the box substantially constant.
• This regulation can be carried out directly from a pressure measurement in the box. It will be noted that this regulation is necessary, taking into account the constant flow rate of the suction group, to maintain constant during cutting the conditions for circulation of the cooling water in the cut groove, despite the variation in open cross section of the line. cutting holes or holes made in the sheet, resulting from cutting progress.
• the opening of the valve 30 will be adjusted as a function of the position of the laser relative to the sheet by virtue of a prior programming linking this position to the linear length of the cutting line made, or more generally, in the open section in the sheet by cutting.
• a typical process for making a cut is divided into two phases.
• a priming phase is carried out prior to the actual cutting.
• a priming hole of small diameter for example from 0.5 to 0.6 mm, is made in the sheet.
• the CO2 laser cutting head is temporarily replaced by a pulse laser, for example a YAG laser capable of providing a very high specific energy (10 3 to 10 4 J / cm 2 ) with a power density of 10 7 to on
• the cutting phase is then carried out, starting from the priming hole, in accordance with the method according to the invention.
• the suction unit 25 being in service and creating a vacuum in the suction box 20
• the valve 30 is opened to obtain the required vacuum in the box, by example 0.5 bars, then, during cutting, the regulating device then gradually closes this valve, depending on the pressure measured in the box or the length of the cutting line produced, as indicated above.
• the cutting speed is of the order of 0.7 m / min in steel sheets 10 mm thick, 0.5 m / min for a thickness of 20 mm, and 0, 3 m / min for 25 mm sheets.
• the device comprises around the cutting head masks for covering the product to seal the orifices or cutting lines already made.
• This embodiment makes it possible to move the cutting head, with respect to the box and to the sheet metal, over great distances, by limiting the open section of the cutting lines or orifices already made in the sheet metal, since all the cutouts distant from the cutting heads are covered by said masks.
• FIG. 5 schematically illustrates such an embodiment, in which the masks consist of mats 40, for example made of rubber, which are wound or unwound on drums 41 linked to the cutting head 10 as a function of the displacements of the latter .
• FIG. 6 illustrates the field of application of the method according to the invention as a function of the thickness of the cut product.
• Curve 60 established experimentally, defines the minimum depression required (the values indicated on the ordinate are the absolute pressure values P under the sheet, considering that the pressure above the sheet is the atmospheric pressure of 1 bar) as a function of the thickness e of prison.
• the hatched area under this curve is the area of validity of the process.
• a vacuum of 0.5 bar gives the best results in the case of a steel cut thicker than 15 mm.
• a vacuum of 0.25 bars i.e. an absolute pressure of 0.75 bars nevertheless makes it possible to make small diameter holes, for example 3 mm, in a steel thickness of 10 mm.
• the method according to the invention also applies to cutting from other non-planar products, such as tubular or complex shaped parts. . It also applies to cutting in other materials, such as low-alloy steels, manganese steels, coated steels (for example 8 mm thick E36 steel sheet with a layer of 5 mm chromium cast iron ), or ceramics.
• the method according to the invention has made it possible to produce, in 10, 15 and 20 mm thick sheets of highly alloyed abrasion-resistant steel and of manganese steel, and in composite sheets ( steel sheets reloaded with a layer of chromium cast iron) of thickness 5 + 3 mm, 8 + 4 mm and 10 + 5 mm, the following cuts:

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Plasma & Fusion (AREA)
• Mechanical Engineering (AREA)
• Laser Beam Processing (AREA)

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• 1996
  • 1996-01-04 FR FR9600177A patent/FR2743318B1/fr not_active Expired - Fee Related
• 1997
  • 1997-01-02 WO PCT/FR1997/000004 patent/WO1997025178A1/fr not_active Application Discontinuation
  • 1997-01-02 AU AU13822/97A patent/AU1382297A/en not_active Abandoned
  • 1997-01-02 EP EP97900222A patent/EP0874712A1/de not_active Ceased

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