Laser beam machining head

Abstract: In a laser beam machining head, when a filler wire and an optical axis of a laser beam are arranged coaxially, a convex roof mirror and a concave roof mirror are combined to divide the laser beam into two separate laser beams so that no laser beam is projected onto a filler wire feed pipe. Furthermore, the filler wire is fed from outside the laser beams to a condensing position via a filler wire guide in the spacing between the separate laser beams, or an electrode supported by a water flow pipe or an electrode holding pipe is brought close to the condensing position. Alternatively, a laser beam machining head comprises a dividing optical system for dividing laser light into two separate laser beams, and providing spacing therebetween; a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting it onto a cutting site of an object to be cut; and an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width. Or the tip opening of the inner assist gas nozzle is slender; or its tip side is inclined, and the angle of inclination is variable; or the relative positions of the inner assist gas nozzle and a workpiece, or the relative positions of the focal position of the condensing optical system and the workpiece are variable independently; or an outer assist gas nozzle surrounding the separate laser beams is provided.

Description: Field of the Invention The present invention is useful when applied to a laser beam machining head of a laser beam machine for cutting or piercing a workpiece of a metal or the like. 2. Description of the Related Art Fig. 13 is a vertical sectional view showing the constitution of a tip portion of a conventional, typical laser beam machining head. A laser beam machining head 301 shown in the drawing is provided in a laser beam machine (its machine body is not shown) which cuts an object 302 to be cut, such as carbon steel. As shown in Fig. 13, a lens-barrel 305 houses a condensing optical system (an imaging lens system) 304 composed of a plurality of lenses 310, and a protective glass 307 for protecting the condensing optical system 304. The condensing optical system 304 condenses laser light 303, and projects it onto a cutting site 302a of the object 302 to be cut. On this occasion, a focal position, f, of the laser light 303 condensed by the condensing optical system 304 is usually adjusted to lie within the object 302 to be cut, as illustrated in the drawing. The laser light 303 is generated by a laser oscillator such as a YAG laser oscillator (not shown), and then transmitted to the condensing optical system 304 by an optical transmission means such as an optical fiber or mirrors (not shown). On a laser light ejection side of the condensing optical system 304 (i.e., a lower end portion of the lens-barrel 305), an assist gas nozzle 306 is attached in such a manner as to surround the laser light 303 that has been ejected from the condensing optical system 304. The assist gas nozzle 306 is shaped like a truncated cone with a tip side (lower end side) becoming thin, and has an opening 306a at the tip side. To a side surface of the assist gas nozzle 306, an assist gas supply pipe 308 is connected. The assist gas supply pipe 308 is tied to an assist gas supply device (not shown). That is, an assist gas Q T transported from the assist gas supply device is introduced into the assist gas nozzle 306 via the assist gas supply pipe 308, and is jetted through the tip opening 306a of the assist gas nozzle 306 toward the cutting site 302a of the object 302 to be cut. A cutting operation for the object 302 to be cut, by means of the laser beam machine equipped with the laser beam machining head 301 of the above-described constitution, is performed in the following manner: First, the laser beam machining head 301 is brought close to the object 302 to be cut, by the use of a laser beam machining head moving device (not shown) . Also, the distance between the tip of the assist gas nozzle 306 and the surface of the object 302 to be cut (i.e., work distance), h, is kept so that there will be no contact between the assist gas nozzle 306 and the object 302 to be cut. In this condition, either the laser beam machining head 301 is moved by the laser beam machining head moving device in a direction perpendicular to the sheet face of Fig. 13, or the object 302 to be cut is moved by a work moving device (not shown) in a direction opposite to the moving direction of the laser beam machining head. In accordance with this movement, the laser beam machining head 301 condenses the laser light 303 by the condensing optical system 304, and projects it onto the cutting site 302a of the object 302 to be cut, thereby fusing the cutting site 302a. Simultaneously, an assist gas is' jetted toward the cutting site 302a from the tip opening 306a of the assist gas nozzle 306, and introduced into the cutting site 302a, to blow away and remove fused metal within the cutting site 302a. Thus, the object 302 to be cut is laser cut. US-A-4 167 662 which is regarded as closest prior art discloses a method and an apparatus for cutting and welding using a laser beam directed towards a workpiece. SUMMARY OF THE INVENTION The laser beam machining head of the present invention that attains the above object is characterized by the following: 1. A laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut or pierce the workpiece, comprising: a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams; a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site or a piercing site of the workpiece; and an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, or a hole diameter of the piercing site. 2. A laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut the workpiece, comprising: a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams; a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site of the workpiece; and an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, and a length of the opening of the tip portion being larger than the width of the opening. 3. A laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut the workpiece, comprising: a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams; a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site of the workpiece; and an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, and a tip side of the inner assist gas nozzle being inclined in a direction of cutting. 4. The laser beam machining head of 3 above, wherein an angle of inclination of the inner assist gas nozzle can be varied independently of a direction of projection of the laser light. 5. A laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut or pierce the workpiece, comprising: a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams; a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site or a piercing site of the workpiece; and an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, or a hole diameter of the piercing site, and wherein: relative positions of the inner assist gas nozzle and the workpiece can be varied independently of relative positions of a focal position of the condensing optical system and the workpiece; or the relative positions of the focal position of the condensing optical system and the workpiece can be varied independently of the relative positions of the inner assist gas nozzle and the workpiece. 6. In the laser beam machining head described above, an outer assist gas nozzle may be provided at an exit side of the condensing optical system so as to surround the separate laser beams launched from the condensing optical system, and the assist gas may also be jetted through a tip opening of the outer assist gas nozzle. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: Fig. 1 is a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to a first embodiment of the present invention; Fig. 2(a) is a cross sectional view showing the constitution of the tip portion of the laser beam machining head (a sectional view taken along line D-D in Fig. 2(b), and Fig. 2(b) is a vertical sectional view taken in a direction of an arrow C in Fig. 1; Fig. 3 is a constitution drawing of an optical system provided in the laser beam machining head; Fig. 4 is a perspective view showing a constitution of a dividing optical system in the above optical system; Fig. 5 is an explanation drawing showing a flow of an assist gas; Fig. 6 is a graph showing a comparison of cutting speeds; Fig. 7 is a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to a second embodiment of the present invention; Fig. 8(a) is an enlarged view taken on line E-E Fig. 8(a) is an enlarged view taken on line E-E in Fig. 7, and Fig. 8(b) is a view taken on line H-H in Fig. 7 on which a section of an assist gas flow jetted through an inner assist gas nozzle has been superimposed; Fig. 9 is a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to a third embodiment of the present invention; Fig. 10 is a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to an fourth embodiment of the present invention; Fig. 11 is a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to a fifth embodiment of the present invention; Fig. 12 is another vertical sectional view showing the constitution of. the tip portion of the laser beam machining head according to the fifth embodiment of the present invention; Fig. 13 is a vertical sectional view showing a constitution of a tip portion of a conventional, typical laser beam machining head; Fig. 14 is an explanation drawing showing a flow of an assist gas; Fig. 15 is an explanation drawing of a thinned assist gas nozzle; and Fig. 16 is an explanation drawing showing a state of a cut surface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the accompanying drawings. [First Embodiment] Fig. 1 is a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to a fifth embodiment of the present invention. Fig. 2(a) is a cross sectional view showing the constitution of the tip portion of the laser beam machining head (a sectional view taken along line D-D in Fig. 2(b)). Fig. 2(b) is a vertical sectional view taken in a direction of an arrow C in Fig. 1. Fig. 3 is a constitution drawing of an optical system provided in the laser beam machining head. Fig. 4 is a perspective view showing a constitution of a dividing optical system in the above optical system. A laser beam machining head 121 shown in Figs. 1 and 2(a) and 2(b) is provided in a laser beam machine (its machine body is not shown) for cutting an object 122 to be cut, such as carbon steel. As shown in Fig. 1, a condensing optical system (an imaging lens system) 124, and a protective glass 125 for protecting the condensing optical system 124 are provided in a lens-barrel 123. The condensing optical system 124 condenses two separate laser beams 126a, 126b (to be described later on in detail) created by division, and projects the resulting condensed light onto a cutting site 122a of the object 122 to be cut. A focal position, f, of the laser beams 126a, 126b condensed by the condensing optical system 124 is usually adjusted to lie within the object 122 to be cut, as illustrated. As shown in Fig. 3, the optical system of the laser beam machining head 121 is composed of the condensing. optical system 124 and a dividing optical system 127. The condensing optical system 124 is composed of a plurality of lenses 128 disposed vertically with suitable spacing from each other. The dividing optical system 127 is composed of a concave roof mirror 129 and a convex roof mirror 130 as a pair. The concave roof mirror 129 is disposed obliquely above-the condensing optical system 124, while the convex roof mirror 130 is disposed obliquely to be opposed to the concave roof mirror 129. Above the convex roof mirror 130, a tip portion of an optical fiber 131 is located. Thus, laser light 126 is emitted by a YAG laser oscillator (not shown), then transmitted through the optical fiber 131, and ejected from the tip of the optical fiber 131 toward mirrors 130a, 130b of the convex roof mirror 130. As shown in Fig. 4, the concave roof mirror 129 is depressed at the center in the shape of a valley, and comprises two mirrors 129a, 129b. Whereas the convex roof mirror 130 projects at the center in the shape of a mountain, and comprises the two mirrors 130a, 130b. Thus, the laser light 126 launched from the optical fiber 131 is reflected by the convex roof mirror 130 as two semicircular laser beams 126a, 126b divided from the laser light 126 at the center. That is, the laser light 126 from the optical fiber 131 is circular in cross section. Whereas the laser light 126, reflected and divided by the mirrors 130a, 130b of the convex roof mirror 130, becomes the two semicircular separate laser beams 126a, 126b, which are transmitted to the concave roof mirror 129, with these beams being spaced from each other. Then, the separate laser beams 126a, 126b are reflected by the mirrors 129a, 129b of the concave roof mirror 129, respectively, and transmitted to the condensing optical system 124. In the condensing optical system 124, the laser beams 126a, 126b are condensed and projected onto the cutting site 122a of the object 122 to be cut, as stated earlier (see Figs. 1, 2(a) and 2(b)). The spacing between the separate laser beams 126a and 126b can be adjusted by changing the arrangement of the convex roof mirror 130 and the concave roof mirror 129, and the angles of the vertices of the mountain and the valley of the convex roof mirror 130 and the concave roof mirror 129. At an exit side of the condensing optical system 124 (at a lower end portion of the lens-barrel 123), an outer assist gas nozzle 132 is attached so as to surround the separate laser beams 126a, 126b launched from the condensing optical system 124, as shown in Figs. 1, 2(a) and 2(b). The outer assist gas nozzle 132 is shaped like a truncated cone with a tip side (lower end side) becoming thin, and has an opening 132a at the tip side. To a side surface of the outer assist gas nozzle 132, an assist gas supply pipe 133 is connected. The assist gas supply pipe 133 is tied to an assist gas supply device (not shown). Thus, an assist gas Q 2T transported from the assist gas supply device is introduced into the outer assist gas nozzle 132 via the assist gas supply pipe 108, and is jetted through the tip opening 132a of the outer assist gas nozzle 132 toward the cutting site 122a of the object 122 to be cut. The outer assist gas nozzle 132 is provided to protect the condensing optical system 124. In detail, the outer assist gas nozzle 132 itself protects the condensing optical system 124 from a metallic vapor, heat, etc. generated during cutting. Furthermore, jets of an assist gas from the tip opening 132a of the outer assist gas nozzle 132 prevent metallic vapor, etc. from penetrating through the tip opening 132a into the outer assist gas nozzle 132. To the side surface of the outer assist gas nozzle 132, an inner assist gas nozzle 134 is fixed in such a manner as to pass through this side surface. This inner assist gas nozzle 134 is in the shape of a thin tube, and is placed between the separate laser beams 126a and 126b. Moreover, the inner assist gas nozzle 134 gradually thins toward its tip side (lower end side), and an opening diameter (opening width) d i of its tip opening 134a is nearly equal to a cutting width (kerf width) w (e.g., 2 to 3 mm) of the cutting site 122a of the object 122 to be cut. Concretely, there are a case in which the opening diameter d i is equal to the cutting width w, and a case in which the opening diameter d i is slightly smaller than the cutting width w (the illustrated case). Even if the opening diameter d i is somewhat larger than the cutting width w, this is more effective than the earlier technologies. That is, since the laser light 126 is divided by the dividing optical system 127 into the two separate laser beams 126a and 126b, the inner assist gas nozzle 134 can be placed between the separate laser beams 126a and 126b. The so placed inner assist gas nozzle 134 can be formed into a desired thinness without interference with the separate laser beams 126a and 126b. The inner assist gas nozzle 134 is tied to the assist gas supply device (not shown) via the assist gas supply pipe (not shown). That is, an assist gas Q 1T transported from the assist gas supply device is introduced into the inner assist gas nozzle 134 via the assist gas supply pipe, and is jetted through the tip opening 134a of the inner assist gas nozzle 134 toward the cutting site 122a of the object 122 to be cut. Most of the assist gas Q 1T is fed into the cutting site 122a. A zone with a length L (>4d i ) in the tip portion of the inner assist gas nozzle 134 is set at a constant internal diameter d i . This stabilizes the flow of the assist gas jetted from the inner assist gas nozzle 134, thereby increasing its directivity. A cutting operation for the object 122 to be cut, by means of the laser beam machine equipped with the laser beam machining head 121 of the present first embodiment, is performed in the following manner: First, the laser beam machining head 121 is brought close to the object 122 to be cut, by the use of a laser beam machining head moving device (not shown). Also, the distance between the tips of the inner assist gas nozzle 134 and the outer assist gas nozzle 132 and the surface of the object 122 to be cut (i.e., work distance), h, is kept at, say, 3 to 4 mm so that there will be no contact of the inner assist gas nozzle 134 and the outer assist gas nozzle 132 with the object 122 to be cut. In this condition, either the laser beam machining head 121 is moved by the laser beam machining head moving device in a direction perpendicular to the sheet face of Fig. 1, or the object 122 to be cut is moved by a work moving device (not shown) in a direction opposite to the moving direction of the laser beam machining head. In accordance with this movement, the laser beam machining head 121 divides the laser light 126 into two beams by the dividing optical system 127, condenses these separate laser beams 126a, 126b by the condensing optical system 124, and projects the condensed light onto the cutting site 122a of the object 122 to be cut, thereby fusing the cutting site 122a. Simultaneously, an assist gas is jetted from the tip opening 132a of the outer assist gas nozzle 132 to prevent penetration of metallic vapor, etc. into the outer assist gas nozzle 132 and protect the condensing optical system 124. Furthermore, an assist gas is jetted from the tip opening 134a of the inner assist gas nozzle 134, and introduced into the cutting site 122a, to blow away fused metal within the cutting site 122a and remove it therefrom. Thus, the object 122 to be cut is laser cut. During this laser cutting, as shown in Fig. 5, the assist gas jetted from the outer assist gas nozzle 132 flows out to both sides of the cutting site 122a from the gap between the outer assist gas nozzle 132 and the object 122 to be cut (assist gases Q 3 , Q 4 ). Whereas the assist gas jetted from the inner assist gas nozzle 134 is mostly fed into the cutting site 122a, because the opening diameter d i of the inner assist gas nozzle 134 is nearly equal to the cutting width w. That is, the assist gas can be fed with high efficiency into the cutting site 122a. Thus, even if the amount of assist gas fed from the assist gas supply device is not increased, the amount of the assist gas fed into the cutting site 122a can be increased markedly in comparison with the earlier technologies. Moreover, the opening diameter d i of the inner assist gas nozzle 134 is so small that the jet velocity of the assist gas jetted from the inner assist gas nozzle 134 becomes much higher than in the earlier technologies. The gas pressure can also be raised, without restrictions imposed by the pressure resistant strength of the optical parts. Because of these advantages, the kinetic energy of the assist gas fed into the cutting site 122a becomes great. Thus, the ability of the assist gas to remove fused metal increases remarkably, and the cutting ability is enhanced markedly. Fig. 6 shows a comparison between the cutting speed obtained by the use of the conventional laser beam machining head 301 (see Fig. 13) and the cutting speed obtained by the use of the laser beam machining head 121 according to the present fifth embodiment. As shown in this drawing, when carbon steels with various plate thicknesses are cut, the cutting speed for the laser beam machining head 121 of the present first embodiment is much higher than the cutting speed for the conventional laser beam machining head 301. Besides, the outer assist gas nozzle 132 is provided on the laser light exit side of the condensing optical system 124, and the assist gas is also jetted from this outer assist gas nozzle 132. Thus, protection of the condensing optical system 124 can be ensured. [Second Embodiment] Fig. 7 is a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to a sixth embodiment of the present invention. Fig. 8(a) is an enlarged view taken on line E-E in Fig. 7, and Fig. 8(b) is a view taken on line H-H in Fig. 7 on which a section of an assist gas flow jetted through an inner assist gas nozzle has been superimposed. As shown in Fig. 7, a laser beam machining head 121 according to the present sixth embodiment is the same as the laser beam machining head 121 of the fifth embodiment (see Fig. 1), except the constitution concerning an inner assist gas nozzle 134 to be described later on. Thus, a detailed description of this same constitution is omitted here. As Fig. 8(a) shows, in the laser beam machining head 121 of the present sixth embodiment, a tip opening 134a of the inner assist gas nozzle 134 is thin and elongated along a direction of cutting (a direction of an arrow F). Namely, an opening width d i of the tip opening 134a is nearly equal to a cutting width w of an object 122 to be cut, and an opening length d 1 of the tip opening 134a is larger than the opening width d i . This slender tip opening 134a has a head portion situated above a center c of a tip opening 132 of an outer assist gas nozzle 132 and extending from this position in a direction opposite to the direction of cutting. Cutting of the object 122 to be cut, by means of a laser beam machine equipped with the laser beam machining head 121 of the present sixth embodiment also gives the same actions and effects as those in the fifth embodiment, although its detailed description will be omitted. In the present second embodiment, moreover, the tip opening 134a of the inner assist gas nozzle 134 is in such a slender shape that its opening width d i is nearly equal to the cutting width w of the object 122 to be cut, and its opening length d 1 is larger than the opening width d i . Thus, as is clear from a section 135 of an assist gas flow shown in Fig. 8(b), most of an assist gas jetted from the inner assist gas nozzle 134 can be fed into a cutting site 122a. Further, a larger channel area than in the fifth embodiment can be provided, so that the flow rate of the assist gas jetted from the inner assist gas nozzle 134 (fed into the cutting site 122a) can be increased. For example, suppose that the amount of the assist gas fed from the assist'gas supply device is adjusted to make the velocity of the assist gas jetted from the inner assist gas nozzle 134 in the present second embodiment equal to the velocity of the assist gas jetted from the inner assist gas nozzle 134 in the aforementioned fifth embodiment. In this case, since the channel area is different between the sixth embodiment and the fifth embodiment, the flow rate of the assist gas jetted from the inner assist gas nozzle 134 in the former becomes greater than the flow rate of the assist gas jetted from the inner assist gas nozzle 134 in the latter. As noted above, the present second embodiment can feed the assist gas efficiently into the cutting site 122a, raise the jet velocity of the assist gas, and increase the jet flow rate of the assist gas. Thus, the ability of the assist gas to remove fused metal is even higher than in the fifth embodiment. Consequently, the cutting ability for the object 122 to be cut increases further. [Third Embodiment] Fig. 9 is a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to a third embodiment of the present invention. As shown in Fig. 9, a laser beam machining head 121 according to the present seventh embodiment is the same as the laser beam machining head 121 of the aforementioned first embodiment (see Fig. 1), except the constitution concerning an inner assist gas nozzle 134 to be described later on. Thus, a detailed description of this same constitution is omitted here. As Fig. 9 shows, in the laser beam machining head 121 of the present third embodiment, the inner assist gas nozzle 134 is fixed to a side surface of an outer assist gas nozzle 132, with a tip side of the inner assist gas nozzle 134 is inclined at an inclination angle  in a direction of cutting (Fig. 9 shows cutting in a direction of an arrow G). That is, laser light 126 is divided by a dividing optical system 127 (see Fig. 4) into two separate laser beams 126a, 126b, and the inner assist gas nozzle 134 is placed between these separate laser beams 126a and 126b. Because of this constitution, a condensing optical system 124 need not be inclined, but only the inner assist gas nozzle 134 can be set in an inclined state. In the inner assist gas nozzle 134 of the present third embodiment, like the aforementioned first embodiment, an opening diameter (opening width) d i of a tip opening 134a is nearly equal to a cutting width of an object 122 to be cut. Of course, the tip opening 134a of the inner assist gas nozzle 134 may be in such a slender, elongated shape along a cutting direction that, as in the aforementioned second embodiment, the opening width d i is nearly equal to the cutting width of the object 122 to be cut, and its opening length is larger than the opening width d i . Cutting of the object 122 to be cut, by means of a laser beam machine equipped with the laser beam machining head 121 of the present third embodiment also gives the same actions and effects as those in the aforementioned first embodiment, although its detailed description will be omitted. In the present third embodiment, moreover, the constitution of the inner assist gas nozzle 134 is such that the opening diameter (opening width) d i of the tip opening 134a is nearly equal to the cutting width of the object 122 to be cut, and the tip side of the inner assist gas nozzle 134 is inclined in the cutting direction. Thus, most of an assist gas jetted from the inner assist gas nozzle 134 can be fed into a cutting site 122a. At this time, the assist gas is blown onto the cutting site 122a (the site of fusion upon irradiation with the separate laser beams 126a, 126b) obliquely relative to the cutting direction. Thus, if the assist gas is jetted just downward (in a direction at right angles to the cutting direction) at the cutting site 122a as shown in Fig. 16, fused metal is relatively prone to flow in a direction opposite to the direction of cutting, so that a substantial thickness of the plate to be cut becomes larger than the actual plate thickness T. Compared with this case, in the present seventh embodiment, the ability of the assist gas to remove fused metal is enhanced to make the fused metal easier to flow downwardly (because of difficulty in flowing of the fused metal in the direction opposite to the cutting direction). As shown in Fig. 9, therefore, the substantial thickness of the plate cut becomes close to the actual plate thickness T, resulting in a further increase in the cutting ability. [Fourth Embodiment] Fig. 10 is a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to an eighth embodiment of the present invention. As shown in Fig. 10, a laser beam machining head 121 according to the present eighth embodiment is the same as the laser beam machining head 121 of the aforementioned fifth embodiment (see Fig. 1), except the constitution concerning an inner assist gas nozzle 134 to be described later on. Thus, a detailed description of this same constitution is omitted here. Illustration of a support system for the inner assist gas nozzle 134 is also omitted. As Fig. 10 shows, in the laser beam machining head 121 of the present fourth embodiment, like the aforementioned third embodiment, a tip side of the inner assist gas nozzle 134 is inclined (inclination angle ) in a direction of cutting (Fig. 10 shows cutting in a direction of an arrow G). In the third embodiment, the inner assist gas nozzle 134 is fixed to the outer assist gas nozzle 132 (the inclination angle  is fixed). In the present eighth embodiment, on the other hand, the inclination angle  of the inner assist gas nozzle 134 can be varied independently of a direction of projection of laser beams 126a, 126b. Concretely, as shown in Fig. 10, a hole 136 having a vertical width w 2 larger than the diameter of the inner assist gas nozzle 134 is formed in a side surface of the outer assist gas nozzle 132. The inner assist gas nozzle 134 is inserted into this hole 136. Thus, the inner assist gas nozzle 134 can be changed in the inclination angle  independently of a condensing optical system 124 and as indicated by a two-dot chain line in Fig. 10, without being restrained by the outer assist gas nozzle 132. That is, laser light 126 is divided by a dividing optical system 127 (see Fig. 4) into two separate laser beams 126a, 126b, and the inner assist gas nozzle 134 is placed between these separate laser beams 126a and 126b. Because of this constitution, only the inner assist gas nozzle 134 can be inclined independently of the condensing optical system 124, and as in the present eighth embodiment, the inclination angle  of the inner assist gas nozzle 134 can be varied. To vary the inclination angle  of the inner assist gas nozzle 134, a drive device 137, such as an electric motor, a hydraulic cylinder, or a pneumatic air cylinder, and the inner assist gas nozzle 134 may be coupled together via a suitable link mechanism using a gear, shaft or the like, and the inner assist gas nozzle 134 may be pivoted by the drive device 137. Alternatively, an operator may change the inclination angle  of the inner assist gas nozzle 134. In the inner assist gas nozzle 134 of the present fourth embodiment, like the aforementioned first embodiment, an opening diameter (opening width) d i of a tip opening 134a is nearly equal to a cutting width of an object 122 to be cut. Of course, the tip opening 134a of the inner assist gas nozzle 134 may be in such a slender, elongated shape along a cutting direction that, as in the aforementioned seventh embodiment, the opening width d i is nearly equal to the cutting width of the object 122 to be cut, and its opening length is larger than the opening width d i . In Fig. 10, the hole 136 formed in the side surface of the outer assist gas nozzle 132 remains open. As such, part of an assist gas introduced from an assist gas supply pipe 133 may leak through the hole 136. For this and other reasons, if protection of the condensing optical system 124 may not be fully ensured, it is desirable to stop up the hole 136, i.e., to close the gap between the inner peripheral surface of the hole 136 and the outer peripheral surface of the inner assist gas nozzle 134, in order to protect the condensing optical system 124 reliably. In this case, the gap may be closed with such a sufficiently flexible member as not to impede the pivoting of the inner assist gas nozzle 134. Cutting of the object 122 to be cut, by means of a laser beam machine equipped with the laser beam machining head 121 of the present fourth embodiment also gives the same actions and effects as those in the aforementioned first and third embodiments, although its detailed description will be omitted. In the fourth embodiment, moreover, the inclination angle  of the inner assist gas nozzle 134 can be changed. By performing trial cutting with this inclination angle  varied, for example, an optimal inclination angle  adapted for the plate thickness, material, etc. of the object 122 to be cut can be selected. Hence, in comparison with the seventh embodiment, the ability of the assist gas to remove fused metal increases further, and the substantial plate cutting thickness becomes close to the actual plate thickness T, resulting in a further increase in the cutting ability. [Fifth Embodiment] Figs. 11 and 12 are each a vertical sectional view showing a constitution of a tip portion of a laser beam machining head according to a fifth embodiment of the present invention. As shown in Fig. 11, a laser beam machining head 121 according to the present fifth embodiment is the same as the laser beam machining head 121 of the aforementioned first embodiment (see Fig. 9), except the constitution concerning an inner assist gas nozzle 134 to be described later on. Thus, a detailed description of this same constitution is omitted here. Illustration of a support system for the inner assist gas nozzle 134 is also omitted. In the aforementioned first embodiment, the inner assist gas nozzle 134 is fixed to an outer assist gas nozzle 132. In the present fifth embodiment, on the other hand, the relative positions of the inner assist gas nozzle 134 and the object 122 to be cut (spacing h between the front end of the inner assist gas nozzle 134 and the surface of the object 122 to be cut) can be varied independently of the relative positions of a focal position f of a condensing optical system 124 and the object 122 to be cut (distance d f from the surface of the object 122 to be cut to the focal position f); or the relative positions of the focal position f of the condensing optical system 124 and the object 122 to be cut can be varied independently of the relative positions of the inner assist gas nozzle 134 and the object 122 to be cut. Concretely, as shown in Fig. 11, a hole 138 having a vertical width w 3 sufficiently larger than the outer diameter of the inner assist gas nozzle 134 is formed in a side surface of the outer assist gas nozzle 132. The inner assist gas nozzle 134 is inserted through this hole 138. Thus, as indicated by a two-dot chain line in Fig. 11, the vertical position of the inner assist gas nozzle 134 can be changed without being restrained by the outer assist gas nozzle 132, i.e., independently of the condensing optical system 124, whereby the relative positions of the inner assist gas nozzle 134 and the object 122 to be cut (spacing h) can be changed. Alternatively, as indicated by a two-dot chain line in Fig. 12, the vertical position of the condensing optical system 124 is changed independently of the inner assist gas nozzle 134, whereby the relative positions of the focal position f of the condensing optical system 124 and the object 122 to be cut (distance d f ) can be changed. Fig. 12 shows a case in which the distance d f has been made small. That is, laser light 126 is divided by a dividing optical system 127 (see Fig. 4) into two separate laser beams 126a, 126b, and the inner assist gas nozzle 134 is placed between these separate laser beams 126a and 126b. Because of this constitution, only the inner assist gas nozzle 134 can be moved up and down independently of the condensing optical system 124, or only the condensing optical system 124 can be moved up and down independently of the inner assist gas nozzle 134. To move the inner assist gas nozzle 134 vertically, a drive device 139, such as an electric motor or a cylinder, and the inner assist gas nozzle 134 may be coupled together via a suitable link mechanism using a gear, shaft or the like, and the inner assist gas nozzle 134 may be moved vertically by the drive device 139. Alternatively, the inner assist gas nozzle 134 may be moved vertically by a manual force. Similarly, to move the condensing optical system 124 vertically, either a drive device 140, such as an electric motor or a cylinder, or a manual force may be employed. In this case, if only the inner assist gas nozzle 134 is moved downward, or only the condensing optical system 124 is moved upward, then the inner assist gas nozzle 134 will approach the separate laser beams 126a, 126b. To avoid interference between the inner assist gas nozzle 134 and the separate laser beams 126a, 126b, it is necessary to set the distance between the separate laser beams 126a and 126b, or the outer diameter of the inner assist gas nozzle 134. In the inner assist gas nozzle 134 of the present fifth embodiment, like the aforementioned first embodiment, an opening diameter (opening width) d i of a tip opening 134a is nearly equal to a cutting width w of the object 122 to be cut. Of course, the tip opening 134a of the inner assist gas nozzle 134 may be in such a slender, elongated shape along a cutting direction (a direction perpendicular to the sheet face of Figs. 11 and 12) that, as in the aforementioned third embodiment, the opening width d i is nearly equal to the cutting width w of the object 122 to be cut, and its opening length is larger than the opening width d i . In Figs. 11 and 12, the hole 138 formed in the side surface of the outer assist gas nozzle 132 remains open. As such, part of an assist gas introduced from an assist gas supplypipe 133 may leak through the hole 138. For this and other reasons, if protection of the condensing optical system 124 may not be fully ensured, it is desirable to stop up the hole 138, i.e., to close the gap between the inner peripheral surface of the hole 138 and the outer peripheral surface of the inner assist gas nozzle 134, in order to protect the condensing optical system 124 reliably. In this case, the gap may be closed with such a sufficiently flexible member as not to impede the vertical movement of the inner assist gas nozzle 134 or the condensing optical system 124. Cutting of the object 122 to be cut, by means of a laser beam machine equipped with the laser beam machining head 121 of the present fifth embodiment also gives the same actions and effects as those in the aforementioned first embodiment, although its detailed description will be omitted. In the fifth embodiment, moreover, the relative positions of the inner assist gas nozzle 134 and the object 122 to be cut (spacing h) can be varied independently of the relative positions of the focal position f of the condensing optical system 124 and the object 122 to be cut (distance d f ); or the relative positions of the focal position f of the condensing optical system 124 and the object 122 to be cut can be varied independently of the relative positions of the inner assist gas nozzle 134 and the object 122 to be cut. Thus, the following effects are obtained: The relative positions of the inner assist gas nozzle 134 and the object 122 to be cut (spacing h) can be adjusted to optimal positions without inducing changes in the relative positions of the focal position f of the condensing optical system 124 and the object 122 to be cut (distance d f ). That is, the inner assist gas nozzle 134 can be brought as close as possible to the object 122 to be cut, such that the interference between the inner assist gas nozzle 134 and the object 122 to be cut can be avoided. This increases the ability of the assist gas to remove fused metal, thereby increasing the cutting ability. Alternatively, the relative positions of the focal position f of the condensing optical system 124 and the object 122 to be cut (distance d f ) can be adjusted to optimal positions adapted to the material, thickness, etc. of the object 122 to be cut, without inducing changes in the relative positions of the inner assist gas nozzle 134 and the object 122 to be cut (spacing h). This also results in an increase in the cutting ability. The laser beam machining head of the present invention is not restricted to a laser beam machine using a YAG laser oscillator, but can also be applied to a laser beam machine using other laser oscillator. The inner assist gas nozzle 134 in each of the fifth to ninth embodiments is a straight nozzle having a tip portion L whose inner diameter is constant (d i ). However, the inner diameter of this tip portion need not be constant, but the nozzle may have a slightly widened tip side. Such a nozzle with a widened tip side is known as a divergent nozzle. When the divergent nozzle is used as the inner assist gas nozzle 134, the flow velocity of the assist gas can be made the sound velocity or higher. As a method for providing the inner assist gas nozzle 134 between the separate laser beams 126a and 126b, it is conceivable to pierce the center of the concave roof mirror 129 and the center of each lens 128 of the condensing optical system 124 shown in Fig. 3, and insert the inner assist gas nozzle 134 of a straight shape into the resulting holes. In this case, however, the resulting laser beam machining head is expensive because of man-hours in production, and so forth. Besides, the optical system is liable to be damaged by the inner assist gas nozzle 134. In view of these disadvantages, it is recommendable to pass the inner assist gas nozzle 134 through the outer assist gas nozzle 132, and provide it between the separate laser beams 126a and 126b at the condensing site for the separate laser beams 126a, 126b (the laser light exit side of the condensing optical system 124), as described in the first to fifth embodiments. The fifth to ninth embodiments have been described in connection with cutting of a workpiece. However, the fifth to ninth embodiments, in particular, are effective when applied to piercing of a workpiece. In this case, the opening width (opening diameter) d i of the tip portion of the inner assist gas nozzle 134 is rendered nearly equal to the hole diameter of the piercing site of the workpiece. According to an aspect of the present invention, a laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut or pierce the workpiece, comprises: a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams; a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site or a piercing site of the workpiece; and an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site or a hole diameter of the piercing site. Thus, the following effects are obtained: The assist gas jetted from the inner assist gas nozzle is mostly fed into the cutting site or the piercing site, because the opening diameter of the inner assist gas nozzle is nearly equal to the cutting width or the'hole diameter. In other words, the assist gas can be fed with high efficiency into the cutting site or the piercing site. Thus, the amount of the assist gas fed into the cutting site or the piercing site can be increased markedly in comparison with the earlier technologies. Moreover, the opening diameter of the inner assist gas nozzle is so small that the jet velocity of the assist gas jetted from the inner assist gas nozzle becomes much higher than in the earlier technologies. The gas pressure can also be raised, without restrictions imposed by the pressure resistant strength of the optical parts. Because of these advantages, the kinetic energy of the assist gas fed into the cutting site or the piercing site becomes great. Thus, the ability of the assist gas to remove fused metal increases remarkably, and the cutting ability or piercing ability is enhanced markedly. According to another aspect of the present invention, a laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut the workpiece, comprises: a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams; a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site of the workpiece; and an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a width of the cutting site, and a length of the opening of the tip portion being larger than the width of the opening. Thus, the following effects are obtained: The tip opening of the inner assist gas nozzle is in such a slender shape that its opening width is nearly equal to the cutting width of the object to be cut, and its opening length is larger than the opening width. Thus, most of an assist gas jetted from the inner assist gas nozzle can be fed into the cutting site. Further, the channel area is increased, so that the flow rate of the assist gas jetted from the inner assist gas nozzle (fed into the cutting site) can be increased. In short, this aspect of the invention can feed the assist gas efficiently into the cutting site, raise the jet velocity of the assist gas, and increase the jet flow rate of the assist gas. Thus, the ability of the assist gas to remove fused metal is further increased. Consequently, the cutting ability increases further. According to a further aspect of the present invention, a laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut the workpiece, comprises: a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams; a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site of the workpiece; and an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, and a tip side of the inner assist gas nozzle being inclined in a direction of cutting. Thus, the following effects are obtained: The constitution of the inner assist gas nozzle is such that the opening width of the tip opening is nearly equal to the cutting width of the object to be cut, and the tip side of the inner assist gas nozzle is inclined in the cutting direction. Thus, most of an assist gas jetted from the inner assist gas nozzle can be fed into the cutting site. At this time, the assist gas is blown onto the cutting site (the site of fusion upon irradiation with the separate laser beams) obliquely relative to the cutting direction. Thus, the ability of the assist gas to remove fused metal is enhanced to make the fused metal easier to flow downwardly (because of difficulty in flowing of the fused metal in the direction opposite to the cutting direction). Therefore, the substantial thickness of the plate to be cut becomes close to the actual plate thickness, resulting in a further increase in the cutting ability. According to a further aspect of the present invention, the laser beam machining head of the previous aspect of the invention is such that an angle of inclination of the inner assist gas nozzle can be varied independently of a direction of projection of the laser light. Thus, the following effects are obtained: The inclination angle of the inner assist gas nozzle can be changed. By performing trial cutting with this inclination angle varied, for example, an optimal inclination angle adapted for the plate thickness, material, etc. of the object to be cut can be selected. Hence, the ability of the assist gas to remove fused metal increases further, and the substantial plate cutting thickness becomes close to the actual plate thickness, resulting in a further increase in the cutting ability. According to a further aspect of the present invention, a laser beam machining head of a laser beam machine for projecting laser light onto a workpiece, and also blowing an assist gas at the workpiece to cut or pierce the workpiece, comprises: a dividing optical system for dividing the laser light into at least two separate laser beams, and providing spacing between the separate laser beams; a condensing optical system for condensing the separate laser beams into condensed laser light, and projecting the condensed laser light onto a cutting site or a piercing site of the workpiece; and an inner assist gas nozzle placed between the separate laser beams, a width of an opening of a tip portion of the inner assist gas nozzle being nearly equal to a cutting width of the cutting site, or a hole diameter of the piercing site, wherein: relative positions of the inner assist gas nozzle and the workpiece can be varied independently of relative positions of a focal position of the condensing optical system and the workpiece; or the relative positions of the focal position of the condensing optical system and the workpiece can be varied independently of the relative positions of the inner assist gas nozzle and the workpiece. Thus, the following effects are obtained: The relative positions of the inner assist gas nozzle and the workpiece can be adjusted to optimal positions -without inducing changes in the relative positions of the focal position of the condensing optical system and the workpiece. That is, the inner assist gas nozzle can be brought as close to the workpiece as possible such that interference between the inner assist gas nozzle and the workpiece can be avoided. This increases the ability of the assist gas to remove fused metal, thereby increasing the machining ability. Alternatively, the relative positions of the focal position of the condensing optical system and the workpiece can be adjusted to optimal positions adapted to the material, thickness, etc. of the workpiece, without inducing changes in the relative positions of the inner assist gas nozzle and the workpiece. This also results in an increase in the machining ability. According to a further aspect of the present invention, in the laser beam machining head described in the sixth, seventh, eighth, ninth or tenth aspect of the invention, an outer assist gas is provided at an exit side of the condensing optical system so as to surround the separate laser beams launched from the condensing optical system, and the assist gas is also jetted through a tip opening of the outer assist gas nozzle. Thus, the following effects are obtained: Since the outer assist gas nozzle is provided, and the assist gas is jetted from this outer assist gas nozzle as well, protection of the condensing optical system can be ensured. This invention being thus described, it will be obvious that the same may be varied in many ways, without departing from the scope of the invention as defined in the following claims.

Claims: A laser beam machining head (121) of a laser beam machine for projecting laser light onto a workpiece (122), and also blowing an assist gas (Q1T, Q2T) at the workpiece (122) to cut or pierce the workpiece- (122), comprising: a dividing optical system for dividing the laser light into at least two separate laser beams (126a, 126b), and providing spacing between the separate laser beams; a condensing optical system (124) for condensing the separate laser beams (126a, 126b) into condensed laser light, and projecting the condensed laser light onto a cutting site or a piercing site of the workpiece (122); characterized in that an inner assist gas nozzle (134) is placed between the separate laser beams (126a, 126b), wherein in use the width of an opening of a tip portion of the inner assist gas nozzle (134) being nearly equal to a cutting width of the cutting site or the hole diameter of the piercing site. A laser beam machining head of a laser beam machine according to claim 1, wherein: a length of the opening of the tip portion being larger than the width of the opening. A laser beam machining head of a laser beam machine according to one of the preceeding claims wherein: a tip side of the inner assist gas nozzle (134) being inclined in a direction of cutting. The laser beam machining head of claim 3, wherein: an angle of inclination of the inner assist gas nozzle (134) can be varied independently of a direction of projection of the laser light. A laser beam machining head of a laser beam machine according to one of the preeeeding claims, wherein: relative positions of the inner assist gas nozzle (134) and the workpiece (122) can be varied independently of relative positions of a focal position of the condensing optical system (124) and the workpiece (122); or the relative positions of the focal position of the condensing optical system (124) and the workpiece (122) can be varied independently of the relative positions of the inner assist gas nozzle (134) and the workpiece (122). The laser beam machining head of a laser beam machine according to one of the preceeding claims, wherein: an outer assist gas nozzle is provided at an exit side of the condensing optical system (124) so as to surround the separate laser beams (126a, 126b) launched from the condensing optical system (124), and the assist gas is also jetted through a tip opening of the outer assist gas nozzle.

Inventors: AKABA TAKASHI, HASHIMOTO YOSHIO, ISHIDE TAKASHI, MICHISHITA YUKIO, NAGASHIMA TADASHI, NAGURA YASUMI, NAYAMA MICHISUKE, OKIMURA KOJI, SHIMIZU KATSUSUKE, WATANABE MASAO, AKABA, TAKASHI, HASHIMOTO, YOSHIO, ISHIDE, TAKASHI, MICHISHITA, YUKIO, NAGASHIMA, TADASHI, NAGURA, YASUMI, NAYAMA, MICHISUKE, OKIMURA, KOJI, SHIMIZU, KATSUSUKE, WATANABE, MASAO, Akaba, Takashi, Mitsubishi Heavy Industries, Ltd., Hashimoto, Yoshio, Mitsubishi Heavy Ind., Ltd., Ishide, Takashi, Mitsubishi Heavy Industries, Ltd., Michishita, Yukio, Mitsubishi Heavy Ind., Ltd., Nagashima, Tadashi, Mitsubishi Heavy Ind., Ltd., Nagura, Yasumi, Mitsubishi Heavy Industries, Ltd., Nayama, Michisuke, Mitsubishi Heavy Ind., Ltd., Okimura, Koji, Mitsubishi Heavy Industries, Ltd., Shimizu, Katsusuke, Mitsubishi Heavy Ind., Ltd., Watanabe, Masao, Mitsubishi Heavy Industries, Ltd.
Applicants: MITSUBISHI HEAVY IND LTD, MITSUBISHI HEAVY INDUSTRIES, LTD.
Application year: 1999
Main classification: B23K26
IPC codes: B23K26