WO2019082114A1

WO2019082114A1 - Laser cutting head for machine tools

Info

Publication number: WO2019082114A1
Application number: PCT/IB2018/058326
Authority: WO
Inventors: Nicola MENEGHETTI; Enzo Gesuita
Original assignee: Salvagnini Italia S.P.A.
Priority date: 2017-10-26
Filing date: 2018-10-25
Publication date: 2019-05-02
Also published as: IT201700121730A1

Abstract

A laser cutting head powerable by a laser emitting apparatus through optical transmission means (41) and as sociable with a machine cutting tool, comprising a collimating group (2) for collimating a laser beam (L) coming from the laser emitting apparatus and comprising at least a collimating lens (3) and a supporting element (4) adapted to support the collimating lens (3) and movable along an adjusting direction (X); a focusing group (5) for focusing the laser beam (L) coming out collimated from the collimating group (2); actuator means (7; 17, 27) for moving the supporting element (4) with the collimating lens (3) along the adjustment direction (X) to vary a focal point of the laser beam (L) coming out focused from the focusing group (5); casing means (15, 16; 55) which form an internal space (20) closed and hermetically isolated from an external environment and adapted to entirely contain the collimating group (2), focusing group (5) and actuator means (7; 17, 27); the actuator means (7; 17, 27) comprise electromagnetic actuator means that include fixed armatures (8; 18; 28), which bear coils (8a; 18a; 28a) powered by electric current and are integrated in an internal wall of said casing means (15, 16; 55), and movable armatures (9; 19; 29) which bear permanent magnets or bodies in ferromagnetic material (9a; 19a; 29a) and are integrated in the supporting element (4).

Description

Laser cutting head for machine tools

The invention concerns laser cutting devices for cutting machine tools, and in particular relates to a laser cutting head for use in an optical fibre laser cutting system in a cutting and/or punching machine tool for metal sheets.

In the field of machine tools for processing sheet metal and metal plates, the use of laser systems to cut, engrave and weld the pieces is well known and widespread.

As is known, the laser is a device capable of emitting, by means of a process of stimulated emission, a monochromatic light beam which is coherent in space namely concentrated in a rectilinear beam and having very high brightness (luminance). The possibility of concentrating a large amount of energy in a very small area allows the laser device to cut, engrave and weld metals. Metal materials are typically cut by vaporisation, and especially by fusion. In the latter case, the laser beam leads to the fusion of a small point of the metal and the fused metal (scum) is removed by a blow or jet of gas.

Different types of laser sources can be used to generate a beam of light which is suitable for cutting metals. Typically gas lasers are used (carbon dioxide C0₂, monoxide) and solid state lasers (laser diodes with doped glass and fibre lasers).

In machine tools, the high energy levels required for cutting metal sheets, also of great thickness, the dimensions and weight of the laser emitter apparatuses are such to prevent their placement on the machine. The laser beam is therefore focused on work pieces by a laser cutting head or focusing head which is connected to the emitting apparatus through an optical chain (C0₂ laser) or a transmission fibre (optical fibres, for example in YAG laser diodes). In virtue of its reduced dimensions and contained weight, the laser cutting head can in fact be moved by the machine tool with precision and speed to perform the cutting of the product.

In the so-called fibre laser cutting systems, in which an optical fibre cable is used to bring the laser beam to the cutting head, the latter typically comprises an optical collimating group that transmits the light beam coming out from the optical fibres to an optical focusing group capable of focusing the collimated laser beam on the piece to be cut.

The focused laser beam or ray comes out from the cutting head through a nozzle which concentrates the blow or jet of gas used to remove the scums generated by the fusion of the metal and limit the likelihood that the same can reach the focusing group. For this purpose, a transparent element or glass is provided at the nozzle, that separates the inside of the cutting head from the outside and allows the passage of the laser beam output by the optical focusing group. The latter makes it possible to focus the laser beam, that is, position its focal point or focus on a given point on the surface of the piece to be cut, or just below the surface.

The exact positioning of the focal point in which all the power of the laser beam is concentrated is required to perform the correct cutting of the material.

The optical focusing group typically comprises a focusing lens mounted on a drawer or lens-slide, movable along an adjusting direction which is parallel to the direction of the laser beam so as to allow it to focus. More precisely, the lens drawer is moved by a respective actuator that is controlled as a function of the distance between the laser cutting head and the surface of the piece, this distance being detected by a suitable sensor mounted on the same cutting head. The surface of the piece (for example a very large sheet) is in fact generally irregular, non-planar, curved.

Further laser cutting heads for machine tools are known in which the correct focusing of the laser beam, that is, the positioning of the focal point on the piece, is carried out by suitably moving the lens, or one of the lenses, of the optical collimating group, which is mounted on a respective drawer or lens-slide that is linearly movable. In this case, the focusing lens can be kept stationary.

In both configurations of the laser cutting head, the focusing lens or collimating lens and its relative lens-drawer are housed inside the laser cutting head, in a chamber that is suitably closed and separated from the external environment so as to prevent the entry of contaminants and foreign objects (in particular the scums generated by the cutting) which might dirty the lenses and therefore alter their optical characteristics.

The actuator which moves the lens-drawer is generally positioned on the outside of the chamber and connected to said drawer by means of mechanical connection elements that pass through one or more openings of the laser cutting head.

Suitable seals are provided at said openings to prevent the entry of contaminants and foreign objects in the internal chamber. However, the seals do not ensure the hermetic closure of the internal chamber, especially in cases of prolonged and intensive use of the laser cutting head, both because of their configuration and shape that must allow the linear sliding of the supporting elements and because of the degradation of the material subjected to heavy operating conditions. Periodically it is therefore necessary to clean the internal chamber and the focusing lens to remove any particles and scum which have penetrated therein.

Similar problems afflict the known laser cutting heads provided with an actuator for moving the collimating lens or focusing lens, positioned inside the internal chamber of the cutting head. In this case, the lenses are dirtied over time by particles and contaminants generated during the operation of the actuator itself and by the motion transmission means which connect the actuator to the lens slide.

The insertion of the actuator and the motion transmission means within the laser cutting head then involves the disadvantage of increasing the size of the head itself.

Cooling systems are provided to cool the laser cutting head and in particular the focusing lens.

A small fraction of the energy of the laser beam that passes through the lenses (collimating and focusing lenses) is indeed absorbed and converted into heat for several reasons, mainly due to the non-absolute transparency of the optics (coating and substrate). The heat generated by prolonged use causes a rise in the temperature of the entire head and in particular of the focusing lens, which is also very close to the piece to be processed, that is, the melting area of the same.

This increase in temperature causes a variation in the refractive index of the lens itself and therefore a shift of the focus. This phenomenon, commonly known with the term "thermal focus shift", then makes it impossible for the cutting system to focus the laser beam in the desired and optimal point on the surface of the piece, with a consequent decay of cutting characteristics up to the impossibility to perform the cutting itself.

The increase in temperature can also cause damages to the surface layer generally provided on the surfaces of the lenses, causing a further variation in the optical characteristics of the latter.

To resolve this problem, cooling systems are known which provide for the introduction of gas (typically nitrogen) at controlled temperatures inside the focusing head so as to lap and thus cool the focusing lens.

The external cooling of the casing of the head that encloses the focusing group is not in fact sufficient to ensure adequate cooling of the focusing lens.

However, the cooling systems with gas flow have the disadvantage of requiring the use of expensive technical gases (for example nitrogen) that are free of contaminants. Particles or foreign objects or contaminants contained in the gas can in fact settle on the focusing lens causing, in addition to a variation of the optic refractive index, absorption of the energy of the laser beam and therefore a reduction in the power available for cutting. Furthermore, due to the intense energy absorption at the areas where particles and contaminants have deposited, with a consequent increase in the local temperature, over time and with use the lens is damaged up to its destruction.

Moreover, said systems are rather complex and expensive to manufacture and require periodic maintenance.

An object of the present invention is to improve the known laser cutting heads for cutting machine tools, and in particular the cutting heads for optical fibre laser cutting systems. Another object is to provide a laser cutting head capable of ensuring effective and optimal isolation of an internal chamber containing the optical collimating and focusing groups of the laser beam with an external environment, so as to prevent the entrance therein of contaminating elements and particles, in particular solid and gaseous scums generated by laser cutting.

A further object is to achieve a laser cutting head having compact shape and particularly limited dimensions.

Another further object is to obtain a laser cutting head which makes it possible to simply and effectively cool the optical collimating and focusing groups in the internal chamber, also with intense and prolonged use.

In a first aspect of the invention, a laser cutting head is provided according to claim 1. In a second aspect of the invention, a laser cutting head is provided according to claim 15. The invention can be better understood and implemented with reference to the accompanying drawings that illustrate a non-limiting exemplary embodiment, in which: figure 1 is a sectional view of the laser cutting head of the invention;

figure 2 is an enlarged and partial view of the cutting head of figure 1 which shows in particular a collimating group of the laser beam and relative actuator means;

figure 3 is an enlarged and partial view of a variant of the laser cutting head;

figure 4 is an enlarged and partial view of another variant of the laser cutting head of the invention;

figure 5 is an enlarged and partial view of another variant of the laser cutting head; figure 6 is an enlarged and partial view of a further variant of the laser cutting head of the invention;

figure 7 is an enlarged and partial view of a further variant of the laser cutting head of the invention;

figure 8 is an enlarged and partial view of another embodiment of the laser cutting head of the invention;

figure 9 is a sectional view of another embodiment of the laser cutting head of the invention; figure 10 is an enlarged and partial view of a variant of the cutting head of figure 9. With reference to figures 1 and 2, a laser cutting head 1 is shown according to the invention, which can be powered by a laser emitting apparatus, of known type and not shown in the figures, through optical transmission means 41 and associable with a machine tool to perform cutting, engraving and welding on a piece 50. In particular, the emitting apparatus is a stimulated emission apparatus of a solid-state laser type and the optical transmission means 41 comprise an optical fibre cable capable of transporting the laser beam generated by the emitting apparatus to the laser cutting head 1.

The laser cutting head 1 comprises a collimating group 2 to collimate the laser beam L coming from the laser emitting apparatus, a focusing group 5 to focus the laser beam coming out collimated from the collimating group 2. The latter comprises at least a collimating lens 3 and a supporting element 4 suitable for supporting the collimating lens 3 and movable along an adjusting direction X, the latter being substantially parallel to the direction of the laser beam coming out from the optical transmission means 41.

In the illustrated embodiment, the laser cutting head 1 further includes a reflective surface or mirror 10, interposed between the collimating group 2 and the focusing group 5 and arranged to reflect, in particular at about 90°, toward the focusing group 5 the laser beam L coming from the collimating group 2.

The laser cutting head 1 further comprises casing means 15, 16 which form an internal space 20 suitable for containing the collimating group 2, the focusing group 5, the mirror 10 and actuator means 7 connected to, and adapted to move the supporting element 4 with the collimating lens 3 along the adjusting direction X, to vary a focal point of said laser beam L coming out focused from the focusing group 5.

The internal space 20, formed by the casing means 15, 16, is closed and hermetically isolated, that is, air-tight closed from an external environment where the laser cutting head 1 is. The casing means 15, 16 prevent the entrance inside the laser cutting head 1, inside the internal space 20, of contaminants and foreign objects, in particular solid and gaseous scums and residues generated by laser cutting, which could dirty the lenses of the collimating group 2 and focusing group 3 and/or the mirror 10. For this purpose, the casing means 15, 16 are provided with a first input opening 39 coupled to the optical transmission means 41, which allows entrance into the internal space 20 of the laser beam L generated by the emitting apparatus, and with a second output opening 31 placed at a cutting nozzle 30 and sealingly closed by a separating glass 32, as better explained in the following description, which allows the transmission of the laser beam collimated and focused from the laser cutting head 1. The casing means 15, 16 do not have additional openings or holes for the passage of electrical or mechanical connection elements.

The actuator means 7 are entirely contained in the internal space 20.

In the embodiment illustrated in figures 1 and 2, the casing means comprise in particular a first casing 15 adapted to contain at least the collimating group 2 and the actuator means 7 and a second casing 16 adapted to contain the mirror 10 and the focusing group 5. The first casing 15 and the second casing 16 have respective cavities that form the internal space 20. The first casing 15 has a substantially cylindrical shape, while the second casing 16 has the shape of a parallelepiped.

The actuator means 7, 17, 27 comprise electromagnetic actuator means that include fixed armatures 8; 18; 28, which bear coils 8a; 18a; 28a powered by electric current and are integrated in, that is, in a single body with, an internal wall of the casing means 15, 16; 55, and movable armatures 9; 19; 29 which bear permanent magnets or bodies in ferromagnetic material 9a; 19a; 29a and are integrated in, that is, in a single body with, said supporting element 4.

With particular reference to the embodiment illustrated in figures 1 and 2, the electromagnetic actuator means comprise a linear electromagnetic actuator 7 of the movable plunger type, equipped with a fixed or static armature 8 which houses two coils or solenoids 8a powered by electric current and is integrated in an internal wall of the casing means 15, 16 and a movable armature 9, so-called core or plunger, comprising at least a body 9a in ferromagnetic material and also integrated in the supporting element 4. In particular the fixed armature 8 is formed by a portion of the internal wall of the casing means 15, 16 and the coils 8a are fixed directly to the latter. The movable armature 9 is formed by a portion of the supporting element 4, the magnetic body 9a being fixed to an external wall of the latter.

The movable armature 9 is linearly moved along the adjusting direction X when it is subject to the magnetic fields generated by the two antagonist coils 8a, powered by electric current. By modulating and controlling the parameters of the electric current (intensity, voltage and frequency), it is possible to change the magnetic fields of the two antagonist coils 8a so as to adjust the direction and magnitude of the displacements of the movable armature 9, and therefore of the supporting element 4 and the collimating lens 3, along the adjusting direction X. In this way it is possible to vary the focal point of the laser beam L on the piece 50 to be processed, as better explained in the following description.

Linear guiding means 11 are fixed to an internal wall of the casing means 15, 16, in particular an internal wall of the first casing 15, to slidably support and guide the supporting element 4 along the adjusting direction X, preventing movements and/or oscillations transverse to this adjusting direction X, which would cause a shift of the focal point of the laser beam L and/or a modification of the size and/or shape of this focal point on the piece 50.

The linear guiding means comprise, for example, a guiding bushing 11 provided with balls 12, in particular balls made of ceramic material with low friction, slidable on an external wall 4b of the supporting element 4. The latter has an internal through cavity 40 for the passage of the laser beam L output from the optical transmission means 41. The supporting element 4 has in particular a hollow tubular shape, for example cylindrical, and has a first end 4a, in particular furthest from the optical transmission means 41, adapted to support the collimating lens 3 inside the internal through cavity 40, and a second end 4c, in particular closest to the optical transmission means 41 and facing a connector 42 that connects the aforesaid optical transmission means 41 to the casing means 15, 16.

It is worth noting that the guiding bushing 11 with the balls 12 made of ceramic material with low friction does not require for its operation, that is, for the linear sliding of the supporting element 4, the use of lubricants which could contaminate and dirty the lenses 3, 6 and the mirror 10. In addition, when the ceramic balls 12 roll on the external wall of the supporting element 4, they substantially do not generate particles that could also contaminate the internal space 20 of the laser cutting head 1.

The laser cutting head 1 also comprises anti-rotation means, of a known type and not shown in detail in the figures, housed inside the casing means 15, 16 and arranged to prevent the supporting element 4 from rotating about an axis parallel to the adjusting direction X when moved by the actuator means 7. The rotation of the collimating lens 3 can in fact cause a shift of the focal point of the laser beam L and a variation in the size and/or shape of this focal point on the piece 50.

The laser cutting head 1 of the invention further comprises a position sensor 23 housed inside the casing means 15, 16, in particular the first casing 15, and provided to measure linear displacements of the supporting element 4 along the adjusting direction X. In this way, thanks to the position sensor 23, a control unit of the machine tool is able to perform a feedback control of the actuator means 7 which makes it possible to correctly position the collimating lens 3, that is, the focal point of the laser beam on the piece 50.

In the embodiment illustrated in figures 1 and 2, the position sensor 23 is, for example, an inductive sensor capable of detecting the position of a measuring element of an elongated shape along the adjusting direction X and fixed to an external wall of the supporting element 4. The position sensor 23 can however comprise an optical sensor.

The laser cutting head 1 also comprises a further supporting element 24 fixed to an internal wall of the casing means 15, 16 and arranged to support at least the focusing lens 6 of the focusing group 5. More precisely, the further supporting element 24 comprises a flange fixed to the internal walls of the second casing 16 and able to house and support the focusing lens 6.

The laser cutting head 1 also comprises the cutting nozzle 30 fixed to the casing means 15, 16 and through which the focused laser beam comes out. The cutting nozzle 30 concentrates a blow or jet of gas intended to distance the scums generated by the fusion of the work piece and at the same time limits the probability that the aforesaid scums can reach the focusing group 5, the reflective mirror 10 and the collimating group 2 inside the laser cutting head 1.

The cutting nozzle 30 is fixed to a lower portion of the casing means 15, 16 that comprise the output opening 31 for the emission of the laser beam L focused by the focusing group 5 and the separating glass 32 to sealingly close said output opening 31 while allowing the passage of the laser beam L which passes through the cutting nozzle 30 and strikes the work piece 50. The output opening 31 is formed on a bottom wall 34 of the second casing 16. The sealed closure of the output opening 31 through the separating glass 32 is guaranteed by a suitable sealing element 33.

The separating glass 32 together with the additional supporting element 24 and the focusing lens 6 forms in the internal space 20 of the casing means 15, 16, in particular inside the second casing 16, an intermediate chamber 20c arranged to hermetically separate the mirror 10 and the collimating group 2 from the output opening 31. For this purpose the focusing lens 6 is sealedly mounted on the further supporting element 24.

The intermediate chamber 20c constitutes a barrier that is interposed between the external environment (through the output opening 31) and the portion of the internal space 20 wherein the collimating group 2 and the mirror 10 are contained. In addition to the separating glass 32, the focusing lens 6 with the relative supporting element 24 also form a physical barrier that prevents entry into the laser cutting head 1 of any particles and foreign objects and, in particular, of scums generated by the fusion of the work piece that could penetrate if the seal between the separating glass 32 and the bottom wall 34 were comprised, for example due to damage or degradation of the sealing element 33.

The laser cutting head 1 of the invention also includes a cooling unit 25 fixed externally to a respective wall of the casing means 15, 16 and thermo-conductive means 26 that connect the supporting element 4 to the aforesaid wall of the casing means so as to extract by thermal conduction from the supporting element 4 and the collimating lens 3 the heat generated in the latter when crossed by the laser beam L. For this purpose, the supporting element 4 and at least the respective wall of the casing means 15, 16 are made of a high thermal conductivity material.

The thermo-conductive means comprise at least a flexible thermo-conductive element 26 made of high thermal conductivity material, for example a ribbon of braided copper and/or a ribbon coated with graphite sheets or a ribbon of copper coated with a polyimide film (Kapton®). One end of the flexible thermo-conductive element 26 is fixed to a wall of the supporting element 4, while the remaining end is fixed to an internal surface of the wall of the casing means 15, 16, in particular a wall of the first casing 15. The cooling unit 25 is instead fixed to an external surface of the aforesaid wall of the casing means 15, 16 at the end of the flexible thermo-conductive element 26 so as to extract the heat transmitted from the latter to the wall of the casing means 15, 16. The flexibility of the thermo-conductive element 26 does not in any way hinder the movement of the supporting element 4 along the adjusting direction X in the operation of the laser cutting head 1.

The cooling unit 25 comprises one or more Peltier cells 37 and a heat sink element 38. The cold side of the Peltier cell 37 is externally fixed to the wall of the casing means 15, 16, while the hot side of the Peltier cell 37 is connected to the heat sink element 38.

The laser cutting head 1 of the invention includes a further cooling unit 35 fixed externally to a respective wall of the casing means 15, 16, in particular to an external surface of a wall of the second casing 16, in order to extract from the latter the heat which radiates by thermal conduction from the focusing lens 6, warmed by the heat that is generated when crossed by the laser beam L. For this purpose, the further supporting element 24 and at least the respective wall of the casing means 15, 16 are made of a high thermal conductivity material.

The further cooling unit 35 comprises one or more Peltier cells 37 and a heat sink element 38. The cold side of the Peltier cell 37 is externally fixed to the wall of the casing means 15, 16, while the hot side of the Peltier cell 37 is connected to the heat sink element 38.

The further cooling unit 35 is also positioned on said wall of the casing means 15, 16, also at said bottom wall 34, so as to extract by thermal conduction the heat that is generated in the separating glass 32 when crossed by the laser beam L. In fact, the heat radiates by conduction from the separating glass 32, through the bottom wall 34, to the wall of the casing means 55 to whose exterior the further cooling unit 35 is fixed. In this way, the separating glass 32 can also be cooled and its duration increases considerably.

In a version of the laser cutting head 1 of the invention not shown in the figures, the lenses 3, 6 of the collimating group 2 and focusing group 5 are cooled by a cooling system of a known type which envisages the introduction of gas (typically nitrogen) at controlled temperatures inside the laser cutting head 1 so as to lap and then cool the lenses.

In the operation of the laser cutting head 1 of the invention, the laser beam coming from the laser emitting apparatus through the optical transmission means 41 is collimated by the collimating group 2 and reflected by the mirror 10 toward the focusing group 3 from which said laser beam comes out collimated and, through the cutting nozzle 30, it strikes the piece 50 to be processed. The correct positioning of the focal point or focus of the laser beam L on the piece 50 to be cut (at a given point of the surface of the piece to be cut or just below said surface) is carried out by appropriately moving the collimating lens 3 along the adjusting direction X, the focusing lens 6 being fixed. This movement can be carried out in a precise and accurate manner by the actuator means 7 inserted and internally housed inside the casing means 15, 16. Similarly, the guiding means 11 which support and guide the supporting element 4 of the collimating lens 3 along the adjusting direction X, the anti- rotation means and the position sensor 23 are also completely housed inside the casing means 15, 16. In this way the internal space 20 can be advantageously hermetically isolated, that is, air-tight closed, from an external environment wherein the laser cutting head 1 is. In fact, it should be noted that the only openings envisaged on the casing means are the input opening 39 and the output opening 31, respectively for the input and output of the laser beam, closed by the optical transmission means 41 and the separating glass 32. The laser cutting head 1 of the invention is therefore able to ensure an effective and optimal isolation of the internal space 20 containing the collimating group 2 and focusing group 5 of the laser beam L with an external environment, so as to prevent the entrance of either gaseous or solid contaminants and foreign objects, in particular of the scums generated by the cutting, in the laser cutting head itself.

It should also be noted that the electromagnetic actuator means 7, which comprise a linear electromagnetic actuator with movable plunger, and the guiding means 11, which comprise a guiding bushing with ceramic balls, substantially do not generate particles or debris in operation that can contaminate the internal space 20 of the laser cutting head 1 and thus dirty the lenses 3, 6 and the mirror 10.

Moreover, since the fixed armature 8 and the movable armature 9 of the linear electromagnetic actuator 7 are integrated respectively in an internal wall of the casing means 15, 16 and in the supporting element 4, the laser cutting head 1 of the invention is particularly compact and with limited overall dimensions.

Thanks to the cooling units 25, 35 provided with Peltier cells 37, placed on the exterior of the casing means 15, 16 and connected to the supporting elements 4, 24 of the collimating lens 3 and focusing lens 6, it is also possible to effectively extract by thermal conduction the heat generated in the lenses by the crossing of the laser beam L. Since the cooling units 25, 35 are fixed externally to the casing means 15, 16 and extract the heat from the walls of the latter which spread by thermal conduction from the lenses 3, 6 through the supporting elements 4, 24 and the thermo-conductive means 26, connection openings on the casing means are not necessary and the internal space 20 of the laser cutting head 1 is isolated from the external environment.

The particular configuration of the laser cutting head 1 of the invention makes it additionally possible to achieve numerous other advantages as described below.

The focusing lens 6 which is fixed and must not be moved to vary and adjust the focal point of the laser beam on the piece 50, can be positioned at a greater distance from the cutting nozzle 30, that is, from the same piece 50 being processed (substantially at the maximum amount of adjustment travel necessary in the case of laser cutting heads with a movable focusing lens). In this way the focusing lens 6 is subjected to a lower thermal gradient due to the heat generated by the fusion of the piece being processed and its integrity and durability are better preserved.

Consequently the separating glass 32 can also be positioned at a greater distance from the piece 50, where it is more difficultly reached by splashes of melted material of the piece being processed. The duration of the separating glass 32 thus considerably increases and the time intervals between one maintenance service and the next also increases.

The separating glass 32 can also be positioned near the focusing lens 6, which is fixed at a minimum distance from the latter and such to make it possible to minimize the power density of the laser beam L on said separating glass 32. The laser beam L, which comes out convergent from the focusing lens 6 to make the focal point on the piece 50, crosses an area of the separating glass 32 which progressively decreases with the increase of the distance of the latter from the focusing lens 6. At a minimum distance from the focusing lens 6 this area is at its maximum and the power of the laser beam L is distributed on said wider area, causing a lower power density and therefore lower energy. The separating glass 32 is therefore less stressed from a thermal perspective and its duration increases. As already indicated above, using a fixed focusing lens 6 (mounted on the further supporting element 24), it is also possible to form in the internal space 20 of the casing means 15, 16 an intermediate chamber 20c that hermetically separates the mirror 10 and the collimating group 2 from the output opening 31 and is able to block the entry of particles and foreign objects in the laser cutting head 1 if the seal between the separating glass 32 and the relative supporting flange 34 is compromised, for example due to damage or degradation of the sealing element 33. It should also be noted that the two barriers formed, one by the separating glass 32 and the bottom wall 34 of the second casing 16 and the other by the focusing lens 6 and the further supporting element 24, are cooled by the further cooling unit 35.

Finally, it is worth noting that the fixed focusing lens 6, in addition to being positioned furthest from the piece 50 being processed, can be positioned closer to the collimating lens 3, that is, closer to the mirror 10. The smaller optical path that separates the two lenses makes it possible to obtain greater energy efficiency because the laser beam L power dispersed around the optical axis of the focusing lens is lesser.

Figure 3 illustrates a variant of the laser cutting head 1 which differs from the embodiment described above and illustrated in figures 1 and 2 for the electromagnetic actuator means which comprise a linear motor with permanent magnets 17 provided with a fixed armature, or stator, 18, provided with coils 18a and fixed to an internal wall of the casing means 15, 16 and a movable armature 19, provided with permanent magnets 19a and fixed to an external wall of the supporting element 4. Also in this variant, linear guiding means 11 are provided which are fixed to an internal wall of the casing means 15, 16 and intended to slidably support the supporting element 4 along the adjusting direction X, thereby preventing movements and/or oscillations transverse to this adjusting direction X. The linear guiding means comprise a guiding bushing 11 provided with balls 12, in particular made of ceramic material with low friction, slidable on an external wall 4b of the supporting element 4.

A position sensor 23 is housed inside the casing means 15, 16, in particular the first casing 15, to measure the linear displacement of the supporting element 4 along the adjusting direction X in such a way as to allow a control unit of the machine tool to perform feedback control of the actuator means 17 for correctly positioning the collimating lens 3, that is, the focal point of the laser beam on the piece 50.

Figure 4 illustrates another variant of the laser cutting head 1 of the invention which differs from the embodiment described above and illustrated in figures 1 and 2, for the electromagnetic actuator means which comprise a linear motor with permanent magnets 17 provided with a fixed armature or stator 18, provided with coils 18a and integrated in, or formed by, a wall of the casing means 15, 16 and a movable armature 19, provided with permanent magnets 19a and integrated in the supporting element 4. More precisely, the fixed armature 18 is formed by an annular portion of the wall of the first casing 15 from which the polar expansions for the coils 18a radially extend toward the inside.

Similarly, the movable armature 19 is integrated in, or formed by, the supporting element 4 of the collimating lens 3 and the permanent magnets 19a are fixed to an external wall of the supporting element 4.

Also in this embodiment, linear guiding means 11 are provided which are fixed to an internal wall of the casing means 15, 16 and intended to slidably support the supporting element 4 along the adjusting direction X, thereby preventing movements and/or oscillations transverse to this adjusting direction X. The linear guiding means comprise a guiding bushing 11 provided with balls 12, in particular made of ceramic material with low friction, slidable on an external wall 4b of the supporting element 4.

A position sensor 23 is housed inside the casing means 15, 16, in particular inside the first casing 15, to measure the linear displacement of the supporting element 4 along the adjusting direction X in such a way as to allow a control unit of the machine tool to perform a feedback control of the actuator means 17 for correctly positioning the collimating lens 3, that is, the focal point of the laser beam on the piece 50.

This embodiment of the laser cutting head 1 of the invention is particularly compact and easier to build.

Figure 5 shows another variant of the laser cutting head 1, wherein the actuator means comprise a rotary electric motor 27 fixed to an internal wall of the casing means 15, 16 and acting through screw-nut screw means 43 on the supporting element 4. More precisely, the electric motor 27 includes a fixed armature or stator 28 provided with coils 28a powered by electric current, fixed to an internal wall of the casing means 15, 16, and a rotary movable armature or rotor 29 provided with permanent magnets 29a and connected through the screw-nut screw means 43 to the supporting element 4. More precisely, the movable armature 29 is connected to a nut screw 44 of the screw-nut screw means 43, in order to rotate the latter about a rotation axis parallel to the adjusting direction X.

The screw-nut screw means 43 comprise a ball screw wherein the nut screw 44 is provided with an internal helical groove for the sliding of balls 46, in particular made of ceramic material, while the supporting element 4 acts as a screw and has a helical groove on a respective external wall, in which the aforesaid balls 46 slide. The latter are preferably preloaded to reduce possible plays and ensure a high level of precision in the transformation of the motion from rotary to linear.

Rolling bearings 45 are interposed between an internal wall of the casing means 15, 16 and the nut screw 44 for rotatably supporting the latter in its rotation.

Anti-rotation means, of known type and not shown in detail in the figures, are provided and housed inside the casing means 15, 16 to prevent the supporting element 4 from rotating with the nut screw 44 about the rotation axis during operation.

Figure 6 shows another variant of the laser cutting head 1 of the invention provided with actuator means comprising a rotary electric motor 27 associated with an internal wall of the casing means 15, 16 and acting through screw-nut screw means 43 on the same supporting element 4. More precisely, the electric motor 27 includes a fixed armature or stator 28 provided with coils 28a powered by electric current, integrated in, or formed by, an internal wall of the casing means 15, 16, and a rotary movable armature or rotor 29 provided with permanent magnets 29a and connected through the screw-nut screw means 43 to the supporting element 4. More precisely, the movable armature 29 is integrated with a nut screw 44 of the screw-nut screw means 43 in order to rotate the latter about a rotation axis parallel to the adjusting direction X. More precisely, the fixed armature 28 is formed by an annular portion of the wall of the first casing 15 from which the polar expansions for the coils 28a radially extend toward the inside. The movable armature 29 is formed by a portion of the nut screw 44 and the permanent magnets 29a are fixed directly to an external wall of an end of said nut screw 44.

The operation of the variants of the laser cutting head 1 described above and illustrated in figures 3 to 6 is substantially similar to that of the embodiment of figures 1 and 2.

With particular reference to the variants of the laser cutting head 1 of the invention described above and illustrated for example in figures 4 and 6, it is noted that the actuator means 7, 17, 27 of the supporting element 4 which supports the collimating lens 3 comprise linear or rotary electromagnetic actuators wherein at least the respective fixed armatures 8, 18, 28 which bear the coils 8a, 18a, 28a powered by electric current can be advantageously integrated or directly created in an internal wall of the casing means 15, 16, in particular of the first casing 15. More precisely, one or more annular portions of said internal wall act as fixed armatures to which the coils can be fixed.

Similarly the movable armatures (plunger or rotor) can be integrated with the supporting element 4, that is, formed by an end portion of said supporting element 4, the permanent magnets being fixed to an external wall of the latter.

These embodiments of the actuator means 7, 17, 27 substantially integrated into the casing means 15, 16 and into the supporting element 4 of the collimating lens 3 make it possible to simplify the structure of the laser cutting head 1 of the invention and contain its sizes and dimensions. At the same time, the casing means 15, 16 close the internal space 20 in a hermetic manner.

With reference to figure 7, a further variant of the laser cutting head 1 of the invention is illustrated which differs from the embodiment described above and illustrated in figures 1 and 2 in that it comprises sealing means 21, 22 which connect the ends 4a, 4c of the supporting element 4 to internal walls of the casing means 15, 16 and are configured to allow the supporting element 4 to be movable along the adjusting direction X. The sealing means 21, 22, in cooperation with the supporting element 4 and the internal walls of the casing means 15, 16 form in the internal space 20 a first chamber 20a containing the collimating lens 3, the mirror 10 and the focusing group 5 and a second chamber 20b hermetically separated from the first chamber 20a and containing the actuator means 7. More specifically, inside the first casing 15, the sealing means 21, 22 form and delimit with the supporting element 4 the second chamber 20b of annular shape that houses, in addition to the actuator means 7, the guiding means 11, the position sensor 23, the anti- rotation means and the thermo-conductive means 26 which connect an external wall of the supporting element 4 to an internal wall of the first casing 15.

The first chamber 20a, which includes the through cavity 40, formed by the supporting element 4 and containing the collimating lens 3, and the volume inside the second casing 16 in which the mirror 10 and the focusing group 5 are housed, is hermetically separated, that is, isolated from the second chamber 20b. In this way any particles and foreign objects and contaminants, for example already present in the actuator means 7, guiding means 11, position sensor 23, anti-rotation means and thermo-conductive means 15, cannot reach and contaminate the coUimating lens 3, the focusing lens 6 and the mirror 10 in a step of mounting and assembling the laser cutting head 1.

The sealing means 21, 22 comprise, for example, a first bellow gasket 21 and a second bellow gasket 22, formed by respective cylindrical sleeves made of extendible material, for example rubber or silicone. The first bellow gasket 21 connects the first end 4a of the supporting element 4 to an internal wall of the first casing 15, while the second bellow gasket 22 connects the second end 4c of the supporting element 4 to an internal wall of the first casing 15 at the connector 42 of the optical transmission means 41.

Alternatively, the sealing means 21, 22 can comprise respective labyrinth seals formed by the ends 4a, 4c of the sealing element 4 with the internal walls of the first casing 15.

In this variant of the laser cutting head 1 of the invention, the electromagnetic actuator means comprise, for example, a linear electromagnetic actuator 7 of the movable armature type having a fixed armature 8, which houses the two coils 8a powered by electric current, integrated in, or formed by, an internal wall of the casing means 15, 16 and the movable armature 9, integrated in or formed by the same supporting element 4, with the magnetic body 9a fixed to an external wall of the latter.

It is also envisaged that the supporting element 4 is formed by a first part comprising the first end 4a and the external wall 4b that interacts with the linear guiding means 11 and by a second part that includes the movable armature 9 of the linear electromagnetic actuator 7, the first part and the second part of the supporting element 4 being mutually connected by fixing means of a known type.

Thanks to this variant of the laser cutting head of the invention, it is possible to ensure the complete isolation of the coUimating and focusing groups from the external environment, minimizing the risks that particles and residues can contaminate and dirty the coUimating and focusing lenses, thereby making it possible to increase the duration and have optimal performance over time, thus avoiding alterations of optical characteristics.

Figure 8 shows a further embodiment of the laser cutting head 1 of the invention which differs from the embodiment described above and illustrated in figures 1 and 2 for the casing means 15, 16 and the cutting nozzle 30. The casing means 15, 16, and in particular the second casing 16 of the latter, in fact, comprise a bottom wall 54 provided with a tubular cavity 55, which extends inside the internal space 20 in the direction of the focusing group 5, in particular of the focusing lens 6, and has, adjacent to and facing the latter, the output opening 31 for the output of the collimated and focused laser beam L. The tubular cavity 55 is arranged for housing a terminal element 56, also of a tubular shape, having a first internal end 56a that supports the separating glass 32 and capable of sealing, in cooperation with the latter, the output opening 31. More precisely, the first internal end 56a of the terminal element 56 is coupled through a suitable first seal 53 to the output opening 31, when the terminal element 56 is inserted in the tubular cavity 55 in an assembly configuration.

The terminal element 56 also comprises a second external end 56b that supports the cutting nozzle 30. The latter can also be integrated and in a single piece with the terminal element 56. The terminal element 56 and the cutting nozzle 30 form a through cavity 58 for the passage of the laser beam L coming out of the focusing lens 6.

The second external end 56b of the terminal element 56 is sealingly coupled, for example by means of a suitable flange and a second seal 57, with an external surface of the bottom wall 54 of the second casing 16. In this way, the terminal element 56 forms with the tubular cavity 55 of the bottom wall 54 a further intermediate chamber 20d which hermetically separates and is interposed between the external environment and said internal space 20, more precisely between the external environment and the intermediate chamber 20c formed inside the second casing 16 by the bottom wall 54 with the tubular cavity 55, by the separating glass 32 and by the further supporting element 24 on which the focusing lens 6 is sealingly mounted.

In this variant of the laser cutting head 1 of the invention, there are therefore two intermediate chambers 20c, 20d that separate the part of the internal space 20 wherein the collimating group 2, the mirror 10 and the focusing group 5 are contained from the external environment. The two intermediate chambers 20c, 20d form a triple barrier constituted by the further supporting element 24 that sealingly mounts the focusing lens 6, by the first internal end 56a of the terminal element 56 which is coupled by means of the first seal 53 to the output opening 31 and supports the closure lens 32 and by the second external end 56b of the terminal element 56 that sealingly couples with the external surface of the bottom wall 54 through the second seal 57. The aforesaid triple barrier prevents the entrance inside the laser cutting head 1 of any particles and foreign bodies and, in particular, of the scums generated by the fusion of the piece 50 being processed. It should be noted that the hermetic separation with the external environment is implemented in the further intermediate chamber 20d by two distinct and separate seals 53, 57 which guarantee the greater effectiveness and reliability of the seal.

It should also be noted that thanks to this embodiment, the separating glass 32 is positioned adjacent to the focusing lens 6 and at a greater distance from the piece 50, more inside the laser cutting head 1 and where it is more difficultly reached by splashes of fused material of the piece 50 being processed.

Moreover, since the separating glass 32 is positioned close to the focusing lens 6, the power density of the laser beam L is reduced on said separating glass 32. The laser beam L, which leaves the focusing lens 6 convergent, in fact passes a wide area of the separating glass 32 (considering the minimum distance from the focusing lens 6) and the power is distributed on said wider area, causing lower power density and therefore lower energy. The separating glass 32 is therefore also less stressed from a thermal perspective and its duration increases considerably.

The duration of the separating glass 32 also increases in virtue of the further cooling unit 35 that is positioned on the internal wall of the casing means 15, 16 at both the further supporting element 24, which supports the focusing lens 6, and at the bottom wall 54, so as to extract by thermal conduction the heat generated in the focusing lens 6 and the separating glass 32 by the crossing laser beam L. In particular, the heat radiates by conduction from the separating glass 32 through the wall of the tubular cavity 55, the bottom wall 54 and the wall of the casing means 15, 16 to which the further cooling unit 35 is externally fixed. The separating glass 32 can therefore be cooled, similar to the focusing lens 6, and its duration increases considerably.

Also in this embodiment of the laser cutting head 1 of the invention the further supporting element 24 is fixed to the internal wall of the second casing 16 at the further cooling unit 35.

The operation of this variant of the laser cutting head 1 of the invention is substantially the same as that of the embodiment described above and illustrated in figures 1 and 2.

With reference to figure 9, a further embodiment of the laser cutting head 1 of the invention is illustrated which differs from the embodiments described above in that it does not comprise a mirror interposed between the collimating group 2 and focusing group 5. In this embodiment, the casing means comprise a single casing 55 and the laser beam L extends axially inside the laser cutting head 1 from a first input opening 39, coupled to the optical transmission means 41, to a second output opening 31 placed at a cutting nozzle 30. The collimating lens 3 and the focusing lens 6 are aligned along an optical axis F of the laser beam L. The actuator means 27 comprising, for example, the rotary electric motor 27 coupled to the screw-nut screw means 43 make it possible to move the supporting element 4 along the adjusting direction X, parallel to the optical axis F so as to adjust the focal point.

The collimating lens 3 and the supporting element 4 are cooled by the cooling unit 25 fixed externally to the casing 55.

The focusing lens 6, the separating glass 32, the supporting element 24 and the bottom wall 34 are cooled by the further cooling unit 35 fixed externally to the casing 55.

Figure 10 shows a variant of the embodiment of figure 8, from which it differs in that it comprises sealing means 21, 22 which connect the ends 4a, 4c of the supporting element 4 to the internal walls of the casing 55. The sealing means 21, 22, in addition to allowing the supporting element 4 to be moved by the actuator means 7 along the adjusting direction X, form in the internal space 20 with the supporting element 4 and the internal walls of the casing 55 the first chamber 20a containing the collimating lens 3 and the focusing lens 6 and the second chamber 20b hermetically separated from the first chamber 20a and containing the actuator means 7 comprising a movable plunger electromagnetic actuator. The sealing means 21, 22 comprise, for example, a first bellow gasket 21 and a second bellow gasket 22, formed by respective cylindrical sleeves made of extendible material, for example rubber or silicone. The first bellow gasket 21 connects the first end 4a of the supporting element 4 to an internal wall of the casing 55, while the second bellow gasket 22 connects the second end 4c of the supporting element 4 to an internal wall of the casing 55 at the connector 42 of the optical transmission means 41.

The electromagnetic actuator means comprise a linear electromagnetic actuator 7 of the movable armature type having a fixed armature 8, which houses the two coils 8a powered by electric current, integrated in, or formed by, an internal wall of the casing means 55 and the movable armature 9, integrated and formed by the same supporting element 4, with the magnetic body 9a fixed to an external wall of the latter.

It is also envisaged that the supporting element 4 can be formed by a first part comprising the first end 4a and the external wall 4b that interacts with the linear guiding means 11 and by a second part that includes the movable armature 9 of the linear electromagnetic actuator 7, the first part and the second part of the supporting element 4 being mutually connected by fixing means of a known type.

Claims

1. Laser cutting head (1) powerable by a laser emitting apparatus through optical transmission means (41) and associable with a machine tool, comprising:

- a collimating group (2) to collimate a laser beam (L) coming from said laser emitting apparatus and comprising at least a collimating lens (3) and a supporting element (4) suitable for supporting said collimating lens (3) and movable along an adjusting direction (X);

- a focusing group (5) to focus said laser beam (L) coming out collimated from said collimating group (2);

- actuator means (7; 17; 27) to move said supporting element (4) with said collimating lens (3) along said adjusting direction (X) in order to vary a focal point of said laser beam (L) coming out focused from said focusing group (5);

- casing means (15, 16; 55) forming an internal space (20) closed and hermetically isolated from an external environment and suitable for entirely containing said collimating group (2), said focusing group (5) and said actuator means (7; 17; 27); characterized in that said actuator means (7; 17; 27) comprise electromagnetic actuator means that include respective fixed armatures (8; 18; 28), bearing coils (8a; 18a; 28a) powered by electric current and integrated in an internal wall of said casing means (15, 16; 55), and respective movable armatures (9; 19; 29), bearing permanent magnets or bodies in ferromagnetic material (9a; 19a; 29a) and integrated in said supporting element (4).

2. Laser cutting head (1) according to claim 1, wherein said electromagnetic actuator means (7; 17; 27) comprise a linear electromagnetic actuator (7) that includes a fixed armature (8), which houses two coils (8a) powered by electric current and is integrated in an internal wall of said casing means (15, 16; 55), and a movable armature (9), which comprises at least a body (9a) made of ferromagnetic material and is integrated in said supporting element (4), said movable armature (9) being linearly moved along said adjusting direction (X) when subject to magnetic fields generated by said coils (8a).

3. Laser cutting head (1) according to claim 1, wherein said electromagnetic actuator means (7; 17; 27) comprise a permanent-magnet linear motor (17) having a fixed armature (18) provided with coils (18a) and integrated in an internal wall of said casing means (15, 16; 55) and a movable armature (19) provided with permanent magnets (19a) and integrated in said supporting element (4).

4. Laser cutting head (1) according to any preceding claim, comprising linear guiding means (11) housed inside said casing means (15, 16; 55) and fixed to an internal wall of the latter in order to slidably support said supporting element (4) along said adjusting direction (X), in particular said linear guiding means comprising a guiding bushing (11) provided with balls (12), in particular made of ceramic material with low friction, slidable on an external wall (4b) of said supporting element (4).

5. Laser cutting head (1) according to claim 1, wherein said actuator means (7; 17; 27) comprise a rotary electric motor (27) that includes a fixed armature (28) provided with coils (28a) powered by electric current and integrated in an internal wall of said casing means (15, 16; 55), and a movable armature (29), provided with permanent magnets

(29a) and integrated in said supporting element (4) through screw-nut screw means (43).

6. Laser cutting head (1) according to any preceding claim, wherein said supporting element (4) has an internal through cavity (40) for the passage of said laser beam (L), said supporting element (4) including a first end (4a) suitable for supporting said collimating lens (3) inside said internal through cavity (40), and a second end (4c).

7. Laser cutting head (1) according to claim 6, comprising sealing means (21, 22) arranged to connect said first end (4a) and second end (4c) of said supporting element (4) to internal walls of said casing means (15, 16; 55) and configured to enable said supporting element (4) to be moved along said adjusting direction (X), said sealing means (21, 22), said supporting element (4) and said internal walls of said casing means (15, 16; 55) forming inside said internal space (20) a first chamber (20a) containing said collimating lens (3) and said focusing group (5), and a second chamber (20b) containing said actuator means (7; 17; 27), said first chamber (20a) being closed and hermetically isolated from said second chamber (20b) and from the external environment.

8. Laser cutting head (1) according to claim 7, wherein said sealing means comprise a first bellow gasket (21) and a second bellow gasket (22), in particular formed by respective cylindrical sleeves made of extendible material, said first bellow gasket (21) connecting said first end (4a) of the supporting element (4) to a respective internal wall of said casing means (15, 16; 55), said second bellow gasket (22) connecting said second end (4c) of the supporting element (4) to a respective internal wall of said casing means (15, 16; 55).

9. Laser cutting head (1) according to any preceding claim, comprising a cooling unit (25) externally fixed to a wall of said casing means (15, 16; 55) and thermo- conductive means (26) to connect said supporting element (4) to an internal surface of said wall of said casing means (15, 16; 55), said cooling unit (25) extracting by thermal conduction from said supporting element (4) and from said collimating lens (3), through said wall of said casing means (15, 15; 55), the heat generated by said laser beam (L) when it passes through said collimating lens (3), said supporting element (4), said thermo -conductive means (26) and at least said wall of said casing means (15, 16; 55) being made of high thermal-conductivity material.

10. Laser cutting head (1) according to any preceding claim, comprising a further supporting element (24) fixed internally to a wall of said casing means (15, 16; 55) to support at least one focusing lens (6) of said focusing group (5).

11. Laser cutting head (1) according to claim 10, comprising a further cooling unit (35) fixed externally to a wall of said casing means (15, 16; 55) at said further supporting element (24; 52) in order to extract by thermal conduction from said focusing lens (6), through said wall of said casing means (15, 16; 55) and said further supporting element (24), the heat generated by said laser beam (L) when it passes through said focusing lens (6), said further supporting element (24) and said wall of said casing means (15, 16; 55) being made of high thermal-conductivity material.

12. Laser cutting head (1) according to claim 10 or 11, wherein said casing means (15, 16;

55) comprise an output opening (31), carried out on a bottom wall (34) of said casing means (15, 16; 55) for the exit of said laser beam (L) from said focusing group (5) and a separating glass (32) to hermetically close said output opening (31) allowing the passage of said laser beam (L), said separating glass (32) together with said further supporting element (24) and said focusing lens (6) forming in said internal space (20) an intermediate chamber (20c) that hermetically divides said collimating group (2) from said output opening (31).

13. Laser cutting head (1) according to claim 12, as appended to claim 11, wherein said further cooling unit (35) is fixed externally to said wall of said casing means (15, 16; 55) also at said bottom wall (34; 54) in order to extract by thermal conduction, through said wall of said casing means (15, 16; 55) and said bottom wall (34), the heat generated by said laser beam (L) when it passes through said separating glass (32).

14. Laser cutting head (1) according to any preceding claim, wherein said casing means (15, 16, 55) comprise a bottom wall (54) provided with a tubular cavity (55), which extends inside said internal space (20) in the direction of said focusing group (5), and has an output opening (31) adjacent to and facing the latter, for the exit of the collimated and focused laser beam (L), said tubular cavity (55) being arranged to house a terminal element (56), also of a tubular shape, having a first internal end (56a) that supports a separating glass (32) and capable of tightly sealing, in cooperation with the latter, said output opening (31).

15. Laser cutting head (1) powerable by a laser emitting apparatus through optical transmission means (41) and associable with a machine tool, comprising:

- casing means (15, 16; 55) forming an internal space (20) closed and hermetically isolated from an external environment and suitable for entirely containing said collimating group (2), said focusing group (5) and said actuator means (7; 17; 27); characterized in that said casing means (15, 16, 55) comprise a bottom wall (54) provided with a tubular cavity (55), which extends inside said internal space (20) in the direction of said focusing group (5), and has an output opening (31) adjacent to and facing the latter, for the exit of the collimated and focused laser beam (L), said tubular cavity (55) being arranged to house a terminal element (56), also of a tubular shape, having a first internal end (56a) that supports a separating glass (32) and capable of tightly sealing, in cooperation with the latter, said output opening (31).

16. Laser cutting head (1) according to claim 14 or 15, wherein said first internal end (56a) of said terminal element (56) is arranged to couple with said output opening (31) through a suitable first seal (53), when said terminal element (56) is inserted in said tubular cavity (55) in an assembly configuration.

17. Laser cutting head (1) according to one of claims 14 to 16, wherein said terminal element (56) comprises a second external end (56b) provided with a cutting nozzle (30), said terminal element (56) and said cutting nozzle (30) forming a through cavity (58) for the passage of said laser beam (L) coming out from said focusing group (5).

18. Laser cutting head (1) according to claim 17, wherein said second external end (56b) of said terminal element (56) is sealingly coupled with an external surface of said bottom wall (54) of said casing means (15, 16), said terminal element (56) forming with said tubular cavity (55) of said bottom wall (54) a further intermediate chamber (20d) that hermetically separates and is interposed between the external environment and said internal space (20).

19. Machine tool for cutting and/or punching metal sheets comprising at least one laser cutting head (1) according to any preceding claim.