FR2630363A1 - LASER BEAM CUTTING APPARATUS OF SHEET OR PLATE MATERIAL AND CUTTING HEAD FOR SUCH APPARATUS - Google Patents

Abstract

Said cutting device, in particular for cutting leather or other soft materials and/or materials having localized flaws, includes: a fixed table with a cutting tray (110) to receive the spread-out material in sheet form (120); a support carriage arranged over the fixed table and mobile relative thereto along a first translation direction; an apparatus, also arranged over the fixed table and mobile relative thereto along a second translation direction, perpendicular to the first one; means for producing a powerful laser beam; a cutting head, cooperating with the carriage and the apparatus and including optical means for focusing and vertically projecting the laser beam onto a target point of the material spread out on the cutting tray; and control means activating the respective motors of the carriage and of the apparatus so that the target point follows a predetermined cutting path. The lower part (530, 540) of the cutting head is designed as an enclosed volume, closed in its lower end by a nozzle (550) pressing against the material in sheet form (120), touching it or coming very close to it, said nozzle having, vertically from the target point, an axial opening through which the laser beam exits towards the target point, said enclosed volume being linked to a pressure source so that, while the material in sheet form is being cut at the target point, a pressurised fluid is ejected through the nozzle on this very point.

Description

LASER BEAM CUTTING APPARATUS
SHEET OR PLATE MATERIAL,
AND CUTTING HEAD FOR SUCH A DEVICE
The present invention relates to an apparatus for cutting by laser beam a sheet or plate material.

 As will be seen below, the invention is particularly advantageous for cutting thin and flexible materials (very light skins, for example) or slightly thick but whose surface is warped (for example crumpled leathers ), or of materials with localized defects (typically, leathers) nevertheless, the invention is in no way limited to the cutting of materials of this type, and it has proved to be particularly effective for such varied materials than cardboard, fiber cement, plastics, etc.

 Until now, laser beam cutting devices have had a structure of the type illustrated in FIG. 1.

 In these known devices, a fixed table 10 has in the central part a cutting plate 11 receiving one or more pieces 12 of the material to be cut, spread out on this cutting plate. For flexible materials, the cutting plate must be a perforated plate connected to a suction pump making it possible to press the piece of material against the cutting plate by suction, unraveling this part so as to make it perfectly flat.

 The apparatus also comprises a first mobile element 20, which can sweep the table over its entire width, in a direction X, and a second mobile element 30 which can sweep the table over its entire length, in a direction Y perpendicular to the direction X. These elements slide on respective rails 14, 14 and 15, 15 rigidly mounted on the table at the periphery of the cutting plate.

 The assembly also includes a power laser 40, for example a CO2 laser, mounted at a fixed station on the table 10 and receiving its energy from a power supply 41, also mounted at a fixed station on the table or in the vicinity thereof. this.

 This laser shoots towards a first mirror 13; fixed, which returns the laser beam to a second mirror 21, carried by the mobile element 20 and therefore mobile relative to the first mirror 13.

 The beam thus reflected twice finally strikes a third mirror 31, carried by the movable element 30 and inclined at 45O so as to return the laser beam vertically downwards, which until now has propagated in a horizontal plane.

 The laser beam thus reflected three times strikes, a few centimeters below the mirror 31, the sheet material 12 at a target point which will depend on the position of the two mobile elements 20 and 30.

 The localized heating will immediately volatilize the material, thus performing its cutting.

 The drive motors X and Y of the mobile elements 20 and 30 are controlled by a computer 50, which also controls the supply 41 so as to interrupt or restore the firing of the laser beam according to the desired cut.

 This computer 50 is itself controlled by a cutting program previously stored, for example on a tape 51, after a programmer has determined, by means of an appropriate CAD / CAM system, the contours of the parts to be cut and their positioning on the sheet of material to be cut, all of this information being of course fully digitized to allow cutting.

 This device structure has a number of drawbacks.

 First of all, it is easy to see that the path of the laser beam from the exit of the laser tube 40 to the target point can vary in significant proportions depending on the position of the mirrors 21 and 31, the length of this path possibly ranging from a few decimeters for a target point located at the top left in the figure, up to several meters for a target point located at the bottom right (the dimensions of a cutting board are typically 1.5 m wide by 2 , 5 to 3 m long).

 This will result in an impossibility of optimally focusing the laser beam for all the cutting positions, because if the focusing is ensured for example in the center of the table, we will observe a progressive defocusing of the beam at the target point as and when that one will deviate from this center, because of the corresponding increase or decrease in the length of the path of the laser beam.

 In addition, the mirrors 21 and 31 are mobile mirrors, therefore subject to various mechanical games and system vibrations, which cause an additional defocusing of the laser beam and, in any event, limit the maximum cutting speed permitted by a such device.

 A second series of drawbacks of this type of device relates to the rigorous safety measures that must be taken due to the use of a power laser: indeed, for obvious safety reasons, it must be strictly impossible for a user to inadvertently pass his hand through the path of the laser beam, or even for an object (cloth, etc.) to come into it. even if it is possible to install protective boxes for the path going from the laser tube to the mirror 31, the region between this mirror 31 and the cutting plate, that is to say the region (which may have a free height of several centimeters) where the laser beam propagates vertically towards the cutting plate before striking the material, remains an excessively dangerous area, so that one generally encloses the whole system in a protective casing 60 preventing any access to the cutting plate during the laser operating phases.

 A third drawback is due to the fumes produced during the cutting of the material: the fact that> as we saw above, the path of the laser beam is a free path over a significant length, it is absolutely necessary to avoid that the fumes obscure the beam. This drawback is all the more accentuated as the path of the beam is long and as a containment enclosure for the cutting plate has been provided for safety reasons. It is then necessary to provide powerful means for extracting the fumes 61 in order to ensure vigorous ventilation of the interior volume of the casing 60 and also to ensure satisfactory cooling of this volume (due to the problems of rapid heating in this closed volume).

 Yet another drawback, which was mentioned above, is the need to provide a suction table producing a suction effect that is sufficiently vigorous to be able to press the material against the cutting table; the suction will have to be all the stronger as the material is little inclined to spread easily (for example, thick leather such as that used for the production of shoe soles, this material also being often more or less wrinkled after tanning).

 It can thus be seen that this results in a relatively complex system, therefore costly to produce and susceptible to various failures.

 In addition, the prior digitization of the shapes to be cut is a long and complex operation, which is hardly possible except for large series of cutting of identical parts on sheets of material having substantially always the same dimensions; moreover, this digitization operation requires an operator with a sufficiently high level of qualification so that he can program and correctly handle the computer and its CAD / CAM software ensuring this digitization.

 One of the aims of the present invention is to propose a structure for a laser beam cutting device which eliminates all of the aforementioned drawbacks.

More specifically, the invention aims to achieve an apparatus structure:
- providing a very short and constant length path between the tube
laser and the target point, thus avoiding all the problems of
beam defocus and path-related problems
propagation of the laser beam in free space (security,
darkening by fumes),
~ avoiding the need for an external casing while preventing seeing the
laser beam along its entire path to the target point, which
provides total security,
~ ensuring, without the need for ventilation
powerful, excellent smoke evacuation and very good
cooling of the target point area,
~ allowing to cut difficult materials because little or not
prone to spread and flatten under their own weight, without it being
need to use a vacuum table to suck this
material against the cutting table, and
~ which is very simple to handle, in particular by removing any
digitization of the shapes to be cut, which allows
operate this device under the control of a lesser operator
qualification.

 In addition, the simplification of the structure of the device (absence of casing, suction table, scanning means, etc.) makes it possible to ensure increased robustness and above all to reduce the manufacturing cost in very significant proportions.

To this end, the present invention provides a laser beam cutting device comprising
~ a fixed table with a cutting plate receiving the material in
spread sheet,
- a support trolley, placed above the fixed and mobile table by
relation to the latter in a first direction of translation,
- a crew, also placed above the fixed and mobile table
relative to the latter in a second direction of translation,
perpendicular to the first,
~ means for producing a power laser beam,
~ a cutting head, cooperating with the carriage and the crew, and
comprising optical means for focusing and projecting
vertically the laser beam at a target point of the spread material
on the cutting deck
~ control means, actuating the respective motors of
movement of the carriage and the crew so as to describe
at the target point a predetermined cutting path,
Characteristically of the invention, the lower part of the cutting head is produced in the form of a closed volume closed at its lower end by a nozzle coming to bear against the sheet material, in contact with the latter where in its immediate vicinity, this nozzle having, to the right of the target point, an axial orifice traversed by the laser beam in the direction of this target point, said enclosed volume being connected to a pressure source so as to produce, simultaneously with the cutting of the sheet material at the target point, ejection by the nozzle of a pressurized fluid at this same location.

According to a certain number of other advantageous characteristics of the present invention:
- the outer surface, facing the sheet material, of the nozzle
is a convex surface; the nozzle preferably having a shape of
revolution, the convex surface is then substantially spherical, its
radius of curvature being advantageously between one and three
times the radius of the nozzle;
- the nozzle, at least in the region of its turned external surface
to the sheet material, is made in the form of a part
solid material of high thermal conductivity;
- the diameter of the axial orifice is between 1 and 4 mm ;;
- the internal wall of the orifice, upstream of the outlet thereof, forms
a convergent, and the outer surface, facing the material in
sheet, the nozzle has a plurality of radial ridges
regularly distributed whose profile, in a radial plane, is a
divergent profile;
- the nozzle is movable in vertical translation relative to the part
bottom of the cutting head, the connection between these two elements
comprising a spring for compensating the mass of the nozzle
- the surface of the cutting plate on which the material rests
sheet has a plate whose material and / or structure
on the one hand have a high coefficient of friction compared
to the sheet material and on the other hand a plate whose material
and / or the structure has a low heat capacity.
plate of the cutting plate can in particular present for this purpose
honeycomb structure
- Means for extracting the fumes are also provided, creating a
depression under the cutting plate, this being formed of a
material and / or structure allowing it to be crossed by
gas.

Other characteristics and advantages of the invention will appear on reading the detailed description below, made with reference to the appended drawings in which
- Figure 1, above, is a plan view of an apparatus structure
cutting prior art,
- Figure 2 is a plan view, taken along line II-II of the
Figure 3, of a cutting apparatus structure according to the present
invention,
- Figure 3 is a longitudinal section along line III-III of the
FIG. 2, of this same device,
- Figure 4 shows the detail, marked W in Figure 3, of the part
lower of the cutting head,
FIG. 5 is a sectional view, along the line VV in FIG. 6,
the nozzle of the lower part of the cutting head illustrated
figure 4,
- Figure 6 is a bottom view of the same nozzle, taken along the
line VI-VI of Figure 5, and
~ Figures 7 to 10 are schematic views, homologous to the
Figure 3, illustrating the operating mode of the apparatus of this
invention.

 Figures 2 and 3 are general views of the cutting apparatus of the present invention, installed on a fixed table 100 having a cutting plate 110 receiving the sheet material to be cut. This table 100 receives a support carriage 200 sliding on longitudinal rails 130 and driven along these rails by motors 210.

 This support trolley 200 itself receives a mobile assembly 300 which can be moved on rails 220 of the support trolley in a direction Y perpendicular to the direction X of movement of the support trolley relative to the fixed table 100; the moving element 300 is driven along the rails 220 by motors 310.

 In this way, by the combined movement of the crew relative to the support carriage and the support carriage relative to the table, the crew 300 will be able to sweep the entire surface of the cutting table 110.

 This equipment 300 carries at one of its ends a read head 400 and at the opposite end a cutting head 500.

 Furthermore, the cutting plate 110 is divided into two zones of substantially identical sizes, namely a cutting zone 110a which occupies the right half of the table in FIG. 3, and a reference zone 110b which occupies the left half of Table.

 These two zones 110a and 110b, which do not overlap, are spaced by a distance D2 equal to the distance D1 (FIG. 2) separating, on the movable assembly, the read head 400 from the cutting head 500, so that the cutting head 500 can be made to traverse a trajectory identical to that of the read head 400, the read head 400 scanning the area 110b following the same trajectory as the cutting head 500 scanning the area 110a .

 The apparatus also includes a transfer glass 700 of transparent material (mineral or synthetic glass) which slides in the direction X on rails 140 fixed to the table 100; this transfer glass has a size slightly greater than each of the two zones 110a or 110b, so that it is possible to entirely cover either one or the other of these zones according to the position to which it has been made to slide (for example, in FIG. 2, the transfer glass covers the reference area 110b).

 We will explain later, with reference to FIGS. 7 to 10, the use of this transfer glass and the manner in which it allows the copying onto the sheet material 120 of a template 710 placed on the glass so as to cut from it. material a part 150 of identical shape to the template.

 As far as the crew 300 is concerned, the latter carries - as a characteristic of the present invention - all of the elements for producing, deflecting and focusing the laser beam.

 More precisely, as illustrated in FIG. 3, the crew carries the laser tube 600. For this, the laser tube chosen must be of a model that is sufficiently light and resistant to be able to be carried on the mobile assembly 300 and resist vibrations generated by the movements thereof.

 One can in particular use for this purpose a CO2 laser having the structure described in FR-A-2 577 076, which meets these various constraints. The power of the laser can for example be of the order of 100 W, which typically allows an average cutting speed of the order of 3 to 4 m / min for standard leathers of thickness 2 to 3 mm.

 The laser beam produced by the tube 600 is then reflected downwards in a vertical direction by a mirror 510, then focused by a lens 520 before striking the material to be cut 120.

 As we can see, thanks to this structure the path of the laser beam is both very short and of constant length - which avoids any defocusing problem as in the structure of Figure 1-, and remains confined inside of the housing of the cutting head 500 - which avoids obscuring by the fumes and provides safety which is incommensurate with that of the cutting apparatus in FIG. 1.

 The crew 300 also carries, on the side of the read head 400, a sensor 410, which forms the read head itself and which is a conventional type contrast reader which can follow the edge of the template 710 or any other part. or plan, in particular a plan traced on a tracing layer posed on the ice 700.

 The signals delivered by this sensor 410 are transmitted to a decoder circuit 420 which will determine the deviation of the read head from the edge or the line to be followed and deliver control signals to a control unit 430 ensuring the appropriate control. motors X and Y (motors 310 and 210) so as to maintain the read head on the edge or the line and to advance it along this edge or this line with a given curvilinear speed, determined according to the material and the contour to be cut, as is well known in the art.

 The driving circuit 430 also controls the laser 600 so as to interrupt the production of the laser beam at the appropriate times, for example when moving from cutting a closed contour to that of another closed contour.

The circuit 420 and / or the circuit 430 can be circuits on board the crew 300 or else circuits installed at a fixed station near the table, in particular in the case where the functions of these circuits are executed by a microcomputer ,
In FIG. 4, the lower part 530 of the cutting head 500 is shown in more detail, which carries a telescopic element 540 terminated at its lower end by a nozzle 550.

 The element 540 is mounted on the lower part 530 of the cutting head by means of a compensation spring 542 which reduces the apparent weight of the assembly formed by the element 540 and its nozzle to a very low value. 550, so as not to overstress the sheet material 120.

 The element 540 is provided with an axial duct 541 communicating with a lateral tube 543 itself connected, by means of a flexible tube 544, to a pressure source, for example a compressor providing an overpressure of the order of 5 to 10 bars relative to atmospheric pressure.

 The outlet 545 in the lower part of the conduit 541 communicates with the interior volume of the nozzle proper 550, fixed to the element 540 by screws 546 so that the entire volume communicating with the pipe 543 is a closed volume, with the exception of central orifice 552 of the nozzle; the pressurized air supplied by the tubing 543 will therefore essentially be used for blowing through the nozzle 550 (incidentally, the pressurized air may also be used for cooling the focusing lens 520, by providing an appropriate air circulation around that -this).

 The nozzle 550, shown in isolation in FIGS. 5 and 6, is for example a massive piece of revolution in pure copper (because of the excellent thermal properties of this material), in which a cavity 551 communicating with the outside has been machined. an axial orifice 552 whose diameter is between 1 and 4 mm, values ensuring ejection of the pressurized air at a sufficiently high speed, while letting the laser beam pass (whose diameter is of the order of 0, 1 mm) with sufficient margin to absorb possible mechanical and / or optical misalignments of the laser beam relative to the axis of the nozzle.

The channel 553 downstream of the orifice 552 places the latter in communication with the cavity 551, and it is preferably produced in the form of a convergent, so as to produce an acceleration of the pressurized air to be ejected while maintaining a laminar flow regime for it.

Furthermore, there is provided at the outer periphery of the orifice 552 a counterbore 554 of shallow depth (so as not to disturb the dynamics of ejection of air through the orifice 552), so as to avoid the presence of a sharp edge in contact with the sheet material which will come into contact with the nozzle at this point
Finally, the external surface 555 of the nozzle is a convex surface, preferably substantially spherical and with a radius of curvature preferably between one and three times the radius of the nozzle 550. This spherical surface 555 is provided with a plurality of ridges radial 556, for example four in number as illustrated, these grooves having, in a radial plane, a divergent profile as illustrated in FIG. 5.

 Thanks to this nozzle structure, a convergent / divergent system is formed, constituted respectively by the convergent passage 553 upstream of the opening 552 and the radial ridges 556 downstream of this same opening.

 This convergent / divergent structure will produce by Venturi effect suction at the level of the radial slots and therefore, as illustrated in FIG. 4, a very slight lifting of the sheet material which will come into intimate contact with the surface 555 of the head. nozzle, whereas, in the absence of air blowing, it would be at a distance of 0.1 to 0.2 mm from the latter.

This intimate contact of the head with the material to be cut will have several advantageous consequences
~ first of all, the cutting precision is maximum, since the
sheet material is sucked up and relaxed at the cutting point, which
located very precisely at the outlet of orifice 552 itself
in the case of a sheet material which does not spread under the effect of
its own weight,
~ the lateral ejection of air around the nozzle will allow the
sheet material, thereby facilitating its subsequent application to the
cutting head when moving it,
- the user never sees the beam, so safety is
total,
~ the extremely localized ejection at the cutting point ensures
excellent cooling of the cut material; we could see
experimentally that even on certain reputable materials
difficult, for example thick leathers, cutting does not leave
practically no burn marks along the contour of the part
which, in addition to the aesthetic aspect, is particularly important for
example in the case of shoe soles, where the stitching is
made near the edge of the cut piece, so where it is
cutting must preserve the integrity of the material
immediate vicinity of the cutting plot,
~ the sheet material is in contact with the convex surface 555 on
a relatively large extent around the cutting point, this
which avoids any significant heating of the material in
this region thanks to the heat drain effect provided by the part
massive copper which constitutes the nozzle 550,
- finally, the ejection of air around the cutting point ensures
dispersion of fumes, especially preventing them from rising
by the housing of the cutting head 500 while obscuring the beam
laser.

 Furthermore, and also in a characteristic manner of the invention, an aluminum plate 110 having a honeycomb structure is preferably chosen for the surface of the cutting table.

 Such a structure, despite its relative fragility, in fact offers a triple advantage here.

 First, it is permeable to the fumes produced, which will be collected in the volume 160 located below the cutting plate (Figure 3) and discharged by a fan 170 and a sheath. It will be noted that, unlike the suction tables of the prior art, the fan 170 has the function only of discharging the fumes produced locally by the head, without any effect of suction of the material (on the contrary, the suction effect is here achieved by the nozzle 550 which sucks the sheet material upwards, while the suction tables of the prior art suck the sheet material down against the table; too strong suction by the fan 170 would even counteract the suction effect of the nozzle and prevent its correct operation).

 Secondly, the thermal effect of a honeycomb, especially when it is made of aluminum, is practically zero, so that the laser beam produces no localized heating of the cutting plate, unlike the tables. suction cutters of the prior art, which essentially comprise a massive plate of perforated aluminum, but whose perforations are of small diameter in order to allow correct suction of the sheet material against the cutting table; on the contrary, with the structure of the present invention, since the cutting table is not a suction table the openings can be as wide as possible without any detrimental effect (on the contrary, the wider the openings, the better the suction and the lower the thermal capacity of the cutting plate).

 Finally, the honeycomb structure offers the important advantage of having a very high coefficient of friction compared to all more or less flexible sheet materials (leather, fabric, etc.), which prevents the piece of material slide on the cutting deck despite the slight ripple effect that could cause the cutting head and its nozzle to move. Here again, the invention is opposed to the cutting tables of the prior art comprising a perforated aluminum plate, for which the smooth surface of the plate makes it necessary to fix the piece of sheet material on the table by an appropriate means. to prevent it from moving during cutting. The honeycomb structure thus provides a self-locking effect.

 Figures 7 to 10 illustrate the operating mode of the cutting apparatus of the present invention.

 First of all (FIG. 7), the assembly 300 and the transfer glass are pushed back to their respective extreme positions illustrated, so as to completely release the cutting area 110a, on which the operator then deposits the sheet material 120 to cut.

Then (figure 8), the operator slides the transfer glass, which is
was initially located above the reference area 110b, towards the
position where it completely covers the cutting area 110a and the material
in sheet 120 previously positioned on the cutting table 110.

The operator can then (FIG. 9) deposit on the transfer glass 700 the
templates 710, seeing the piece of sheet material 120 by transparency
with its external outline and its possible faults; so he can
arrange to place the different templates so that they can be used
better the available surface, while avoiding depositing templates where the sheet material has defects (typical case of leathers).

Alternatively, instead of depositing templates, he can draw
directly on the glass the outline of the pieces to be cut; the reading head contrast reader will then function as a line-following reader and no longer as an edge-tracking reader.

 Finally (FIG. 10), the transfer glass 700 on which all of the templates 710 have been placed is moved from the cutting area 110a to the reference area 110b by a translation of amplitude D2, distance equal to the distance D1 separating the cutting head and the read head on the crew 300 (FIG. 2).

 The reference area 110b is then entirely covered by the transfer glass 700, the cutting area 110a now being cleared.

 The crew 300 is then moved to the right so that the cutting head 500 comes to be positioned just above the piece of sheet material 120, the read head 400 simultaneously being positioned above the templates 710 placed on the transfer glass.

 The cutting can then begin, the read head 400 controlling the movements of the crew 300 so as to follow the outline of each jig 710; it will be readily understood that this controlled movement will produce an identical correlative displacement of the cutting head 500, performing the cutting of the piece of sheet material 120 exactly at the place where the operator, in the step of the previous figure, had positioned the corresponding template 710.

 As we can see, the cutting is done by direct copying of the position of the templates, with great precision and without the need to digitize the shapes to be cut beforehand.

 Very advantageously, provision may be made for a prior step of recognizing the templates 710 present on the cutting zone after the transfer glass has been placed above the reference zone.

By this step, we locate and store, for example by a quick scan of the reference area by the read head, the positions and the respective shapes of each of the templates. The information collected and stored during this preliminary stage is then used as control parameters for the trajectory following means throughout the subsequent cutting stage so as to know where to start cutting a first part. , plan the passages where it will be necessary to modify the speed of travel (cusps, complex shapes, ...), ensure the transfer of the read head to the next part after each part cutting, etc.

Claims (15)

RERIENDICATIONS  1. An apparatus for cutting a sheet or sheet material by laser beam, in particular for cutting leather or other flexible materials and / or having localized defects, comprising #:  ~ a fixed table (100) with a cutting plate (110) receiving the  spread sheet material (120),  - a support carriage (200), placed above the fixed and mobile table  relative to the latter in a first direction of translation  tX),  a crew (300), also arranged above the fixed table, and  movable relative thereto in a second direction of  translation (Y), perpendicular to the first,  ~ means (600) for producing a power laser beam,  ~ a cutting head (500), cooperating with the carriage and the crew, and  comprising optical means (510, 520) for focusing and projecting  vertically the laser beam at a target point of the spread material  on the cutting deck,  ~ control means (420, 430), actuating the motors  respective (210, 310) movement of the carriage and the crew of  so as to describe in point. targets a cutting path  predetermined,  characterized in that the lower part (530, 540) of the cutting head is produced in the form of a closed volume closed at its lower end which appears as a nozzle (550) which is applied against the sheet material (120), at contact thereof where in its immediate vicinity, this nozzle having, in line with the target point, an axial orifice (552) traversed by the laser beam in the direction of this target point, said closed volume being connected to a pressure source of so as to produce, simultaneously with the cutting of the sheet material at the target point, the ejection by the nozzle of a pressurized fluid at this same location.  2. The apparatus of claim 1, in which the outer surface (555), facing the sheet material, of the nozzle (550) is a convex surface,  3. The apparatus of claim 2, wherein the nozzle (550), at least in the region of its outer surface (555) facing the sheet material, is formed as a solid piece of material high thermal conductivity.  4. The apparatus of claim 2, wherein the nozzle (550) has a shape of revolution, the convex surface (555) being substantially spherical.  5. The apparatus of claim 4, wherein the radius of curvature of the spherical convex surface (555) is between one and three times the radius of the nozzle (550).  6. The device of one of the preceding claims, in which the diameter of the axial orifice (552) is between 1 and 4 mm.  7. The apparatus of one of the preceding claims, wherein the internal wall of the orifice, upstream of the outlet thereof, forms a convergent (553).  8. The apparatus of one of the preceding claims, wherein the outer surface (555), facing the sheet material, of the nozzle (550) comprises a plurality of radial ridges (556) regularly distributed.  9. The apparatus of claim 8, wherein the profile, in a radial plane, of these ridges (556) is a divergent profile.  10. The apparatus of claim 1, wherein the nozzle (550) is movable in vertical translation relative to the lower part (530) of the cutting head, the connection between these two elements comprising a compensating spring (542 ) of the mass of the nozzle  11. The apparatus of claim 1, wherein the surface of the cutting plate (110) on which the sheet material rests comprises a plate whose material and / or structure have a high coefficient of friction relative to the material in leaf.  12. The apparatus of claim 1, wherein the surface of the cutting plate (110) on which the sheet material rests comprises a plate whose material and / or structure have a low heat capacity.  13. The apparatus of one of claims 11 or 12, wherein the plate of the cutting plate has a honeycomb structure.  14. The apparatus of one of the preceding claims, further comprising means (160, 170) for extracting smoke creating a vacuum under the cutting plate (110), the latter being formed of a material and / or a structure allowing it to be crossed by gases.  15. A cutting head (500), for a cutting device according to one of claims 1 to 14.