Patent Publication Number: US-2022226930-A1

Title: Laser processing head and laser processing machine

Description:
TECHNICAL FIELD 
     The present invention relates to a laser processing head and a laser processing machine. 
     BACKGROUND ART 
     Patent Literature 1 describes a laser processing machine that performs laser processing by use of an assist gas. The laser processing machine described in Patent Literature 1 includes a supply hole for the assist gas in a side surface of a laser processing head, and the assist gas supplied from external assist gas supply means is introduced from the supply hole into the laser processing head and blown from a nozzle tip. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: Japanese Patent Application Laid-Open Publication No. S63-187589 
       
    
     SUMMARY 
     Usually, a laser processing head is formed in a tubular shape, and a supply hole for an assist gas is provided in a portion of a side surface of the laser processing head. For example, when this laser processing head is moved in an X-axis direction and Y-axis direction that are horizontally orthogonal to cut a plate material, a height of dross generated during cutting in one axial direction might be different from a height of dross generated during cutting in the other axial direction. That is, cutting directionality might be generated in the height of the dross generated in laser cutting, and further improvement in product quality is desired. 
     Therefore, a problem to be solved by the present invention is to provide a laser processing head and a laser processing machine in which cutting directionality is hard to occur in height of dross and product quality improves in laser processing by use of an assist gas. 
     To solve the above problem, a laser processing head according to an aspect of the present invention includes a tubular main body, and a gas supply part disposed in the main body and allowing an assist gas supplied from outside to flow into an internal space of the main body. The gas supply part includes a first gas supply hole extending along a first axis on a plane orthogonal to an axis of a tube of the main body and opening at an inner circumferential surface of the main body, a second gas supply hole forming a predetermined angle relative to the first axis around the axis, extending along a second axis on the plane orthogonal to the axis and opening at the inner circumferential surface, and a flow path forming ring facing the inner circumferential surface with a predetermined interval, and forming a cylindrical space extending along the axis between the flow path forming ring and the inner circumferential surface. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing a laser processing machine  61  that is an implementation example of a laser processing machine according to an embodiment of the present invention. 
         FIG. 2  is a partially sectional view of a laser processing head  1  included in the laser processing machine  61 . 
         FIG. 3  is a partially enlarged view in  FIG. 2 . 
         FIG. 4  is a cross-sectional view at a S 4 -S 4  position in  FIG. 2 . 
         FIG. 5  is a schematic view showing flow of an assist gas AG supplied to the laser processing head  1 . 
         FIG. 6  is a cross-sectional view corresponding to  FIG. 4 , and a view showing a laser processing head  1 A that is a comparative example of the laser processing head  1 . 
         FIG. 7  is a schematic view showing flow of an assist gas AG supplied to the laser processing head  1 A. 
         FIG. 8A  is a schematic plan view showing a moving direction of the laser processing head  1  in pressure distribution measurement of the assist gas AG. 
         FIG. 8B  is a side view of a partial cross section for explaining a pressure distribution measuring method. 
         FIG. 9  is a schematic plan view showing a cutting path for evaluating cutting directionality of a dross height. 
         FIG. 10  is a graph showing a pressure distribution measurement result of the assist gas AG in the laser processing head  1 . 
         FIG. 11  is table showing a dross highest value Dd when cutting is performed with the laser processing head  1 . 
         FIG. 12  is a graph showing a pressure distribution measurement result of the assist gas AG in the laser processing head  1 A of the comparative example. 
         FIG. 13  is a table showing a dross highest value Dd when cutting is performed with the laser processing head  1 A. 
         FIG. 14  is a schematic view showing flow of an assist gas AG in a first modification of the laser processing head  1 . 
         FIG. 15  is a schematic view showing flow of an assist gas AG in a second modification of the laser processing head  1 . 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     A laser processing head according to an embodiment includes a tubular main body, and a gas supply part disposed in the main body and allowing an assist gas supplied from outside to flow into an internal space of the main body. The gas supply part includes a first gas supply hole extending along a first axis on a plane orthogonal to an axis of a tube of the main body and opening at an inner circumferential surface of the main body, a second gas supply hole forming a predetermined angle relative to the first axis around the axis, extending along a second axis on the plane orthogonal to the axis and opening at the inner circumferential surface, and a flow path forming ring facing the inner circumferential surface with a predetermined interval, and forming a cylindrical space extending along the axis between the flow path forming ring and the inner circumferential surface. In the laser processing head according to the embodiment, the predetermined angle may be an angle other than 180°. In the laser processing head according to the embodiment, the gas supply part may include n (n is an integer equal to or more than 3) gas supply holes shifting from each other around the axis, extending along an axis orthogonal to the axis and opening to the cylindrical space, and at least one of the n gas supply holes may have different angle pitches with two adjacent gas supply holes around the axis. 
     A laser processing machine according to an embodiment includes the laser processing head according to the embodiment, a laser oscillation device configured to supply a laser beam to the laser processing head, an assist gas supply device configured to supply an assist gas to the first gas supply hole and the second gas supply hole, and a moving device configured to move the laser processing head  1  relative to a workpiece. In the laser processing machine according to the embodiment, an assist gas with the same pressure may be supplied to the first gas supply hole and the second gas supply hole. 
     According to the laser processing head and laser processing machine of the embodiment, cutting directionality is hard to occur and product quality improves in a dross height in laser processing by use of the assist gas. 
     The laser processing head and laser processing machine according to the embodiment of the present invention will be described in accordance with a laser processing head  1  and a laser processing machine  61  as implementation examples.  FIG. 1  is a perspective view showing an entire configuration of the laser processing machine  61 . Respective directions of up, down, left, right, front and rear in the following description are prescribed by arrow directions shown in  FIG. 1 . 
     The laser processing machine  61  irradiates a workpiece W that is a material to be processed with a laser beam Ls, and subjects the workpiece W to processing such cutting or hole making. The laser processing machine  61  includes a laser oscillation device  62 , a processing main body  63 , an NC device  64 , and an assist gas supply device  65 . 
     The laser oscillation device  62  is, for example, a fiber laser oscillation device, and generates the laser beam Ls. The processing main body  63  includes a table  63   a  supporting the workpiece W, and an X-axis carriage  63   b  disposed on the table  63   a  to be movable in an X-axis direction (right-left direction). 
     The X-axis carriage  63   b  is provided with a Y-axis carriage  63   c  movable in a Y-axis direction (front-rear direction) orthogonal to an X-axis on a horizontal plane. The Y-axis carriage  63   c  is provided with a Z-axis holder  63   d . The Z-axis holder  63   d  supports the laser processing head  1  movably in a Z-axis direction (up-down direction). The X-axis carriage  63   b  and the Y-axis carriage  63   c  function as moving devices that relatively move the workpiece W and the laser processing head  1  in the X-axis direction and Y-axis direction, respectively. 
     A fiber cable  4  is connected between the laser oscillation device  62  and the laser processing head  1 . The laser beam Ls generated in the laser oscillation device  62  is supplied via the fiber cable  4  to the laser processing head  1 . The assist gas supply device  65  outputs a high purity gas or rich gas such as nitrogen via a hose  8 . The hose  8  is branched to a hose  8   a  of a first gas path and a hose  8   b  of a second gas path by a branch part  9 . The hose  8   a  is connected to a gas supply port P 1  of the laser processing head  1 , and the hose  8   b  is connected to a gas supply port P 2  of the laser processing head  1 . That is, the assist gas AG is supplied to the laser processing head  1  separately from the respective gas supply port P 1  and gas supply port P 2 . 
     The processing main body  63  is not limited to the above configuration, if the workpiece W and the laser processing head  1  are relatively movable in the X-axis and Y-axis directions. For example, the X-axis carriage  63   b  may be fixed so that the laser processing head  1  is movable in the Y-axis and Z-axis directions, and the workpiece W may be moved by an unshown clamper in the X-axis direction. 
     Next, description will be made as to the laser processing head  1  in detail with reference to  FIG. 1  to  FIG. 4 .  FIG. 2  is a vertical sectional view of a lower part in the laser processing head  1 , and  FIG. 3  is a partially enlarged view of  FIG. 2 .  FIG. 4  is a cross-sectional view at a S 4 -S 4  position in  FIG. 2 . 
     The laser processing head  1  includes a tubular main body  1   a  including a hole  1   a   1  extending along an axis CL 1  and a nozzle  1   b  detachably attached to a tip of the main body  1   a . In the main body  1   a , an unshown collimation lens and a focusing lens  1   e  and protective glass  1   g  shown in  FIG. 2  are arranged from a side to which the fiber cable  4  is connected on the axis CL 1  of the main body  1   a  that is an optical axis of the laser beam Ls. The main body  1   a  may be formed in an L-shape with a configuration where a mirror is disposed between the collimation lens and the focusing lens  1   e , to reflect the laser beam Ls by 90° with the mirror. 
     The laser beam Ls that is supplied from the laser oscillation device  62  and incident as a divergent beam from an outlet end face (not shown) of the fiber cable  4  into an internal space of the main body  1   a  is collimated to a parallel beam by the collimation lens. The laser beam Ls collimated to the parallel beam is focused, for example, as a convergent beam on a focal point of a processed part of the workpiece W by the focusing lens  1   e , and emitted out from an opening  1   b   1  in a tip of the nozzle  1   b.    
     As shown in  FIG. 2 , the main body  1   a  includes a flange part  1   f  protruding outward in a portion between the focusing lens  1   e  and the nozzle  1   b  in an axial direction. As shown in  FIG. 4 , the flange part  1   f  possesses an outer shape of a cross section that is substantially rectangular, and has four corners formed in a circular-arc shape and the other portions as linear edges  1   f   3  to  1   f   6 . In a pair of opposite corners  1   f   1  and  1   f   2 , gas supply holes  11  and  12  are formed opening at an inner circumferential surface  1   a   2  of the hole  1   a   1  to communicate with an internal space Vc of the hole  1   a   1 , respectively. The gas supply holes  11  and  12  correspond to the first gas supply hole and the second gas supply hole, respectively, and function as supply paths to introduce the assist gas AG supplied from the outside into the main body  1   a.    
     As shown in  FIG. 4 , the gas supply hole  11  is a straight circular hole having a predetermined inner diameter D 11 . An axis C 11  corresponding to the first axis forms a predetermined angle θa as an acute angle in a counterclockwise direction in  FIG. 4  relative to a center line C 3  orthogonal to the axis CL 1  and orthogonal to the edges  1   f   3  and  1   f   5 . Hereinafter, “orthogonal” means “crossing at right angles” unless otherwise noted. The gas supply hole  12  is a straight circular hole having a predetermined inner diameter D 12 . An axis C 12  corresponding to the second axis forms a predetermined angle θb as an acute angle in a counterclockwise direction in  FIG. 4  relative to the center line C 3  orthogonal to the axis CL 1 . The angle θa and the angle θb may be the same angle, but are more preferably set to different angles. That is, as shown in  FIG. 4 , when an obtuse angle formed by the axis C 11  and the axis C 12  is a predetermined angle θc, the angle θc is more preferably an angle other than 180°. In this case, an example of the angle θa is 50°, and an example of the angle θb is 43°. The gas supply hole  11  and the gas supply hole  12  are formed at the same position in the axial direction in which the axis CL 1  extends. That is, the axis C 11  and axis C 12  are included on the same plane orthogonal to the axis CL 1 . 
     An annular flow path forming ring  1   d  with the axis CL 1  being a center axis is attached to a lower part of the main body  1   a  in the laser processing head  1 . The flow path forming ring  1   d  has a peripheral wall portion  1   d   1 . The peripheral wall portion  1   d   1  with a bottom as a tip extends in an annular shape, and faces the inner circumferential surface  1   a   2  of the hole  1   a   1  with a gap of a predetermined distance da that is a predetermined interval in a radial direction shown in  FIG. 2  and  FIG. 4 . The distance da is constant over an entire circumference, and the gap of the distance da is acquired to form a cylindrical space Va between the inner circumferential surface  1   a   2  and an outer circumferential surface  1   d   1   a  of the peripheral wall portion  1   d   1 . 
     An annular flow path adapter  1   c  with the axis CL 1  being a center axis is attached to the lower part of the main body  1   a . An upper part of the flow path adapter  1   c  enters inside the flow path forming ring  1   d . The flow path adapter  1   c  has a peripheral wall portion  1   c   1 . The peripheral wall portion  1   c   1  with a top as a tip extends in an annular shape, and faces an inner circumferential surface  1   d   1   b  of the flow path forming ring  1   d  with a gap of a predetermined distance db in the radial direction shown in  FIG. 2  and  FIG. 4 . The distance db is constant over the entire circumference, and the gap of the distance db is acquired to form a cylindrical space Vb between the inner circumferential surface  1   d   1   b  of the flow path forming ring  1   d  and an outer circumferential surface  1   c   1   a  of the peripheral wall portion  1   c   1 . 
     As shown in  FIG. 2 , the laser processing head  1  includes the gas supply hole  11  and the gas supply hole  12 , and the flow path forming ring  1   d  and the flow path adapter  1   c , as a gas supply part GK that supplies the assist gas AG from the outside into the internal space Vc of the main body  1   a . Consequently, as shown with arrows DR in  FIG. 3 , the assist gas AG is supplied from the outside through the gas supply hole  11  and the gas supply hole  12  with the same pressure and flow rate, and flows into the space Va with a width in the radial direction that is the distance da as shown with arrows DRa. The space Va communicates with the space Vb on a side of a lower end portion of the peripheral wall portion  1   d   1  of the flow path forming ring  1   d , and the assist gas AG flowing into the space Va passes through the lower end portion of the peripheral wall portion  1   d   1  to flow into the space Vb with a width in the radial direction that is the distance db as shown with arrows DRb. The space Vb has an upper end side that opens into the hole  1   a   1 , and hence the assist gas AG flowing into the space Vb from a lower part side flows upward as shown with arrows DRc to flow from an upper end portion of the space Vb into the internal space Vc of the hole  1   a   1  as shown with arrows DRd. 
       FIG. 5  is a schematic plan view showing flow of the assist gas AG with arrows, which is supplied to the space Va through the gas supply holes  11  and  12  in the laser processing head  1 , and showing the space Va with a circle. 
     As shown in  FIG. 5 , when the assist gas AG supplied from the gas supply hole  11  flows into the space Va, the flow branches to gas flow AG 11 R that is clockwise flow and gas flow AG 11 L that is counterclockwise flow. On the other hand, when the assist gas AG supplied from the gas supply hole  12  flows into the space Va, the flow branches to gas flow AG 12 R that is clockwise flow and gas flow AG 12 L that is counterclockwise flow. 
     The space Va is modelled as a closed circular shape on a cross section orthogonal to the axis CL 1 , and hence the gas flow AG 11 R and gas flow AG 12 L collide at a collision point Pt 1  that is a midpoint on an upper circular arc of  FIG. 5  where flow distances from inflow points  11   a  and  12   a  into the space Va in a circumferential direction are about the same. On the other hand, the gas flow AG 11 L and gas flow AG 12 R collide at a collision point Pt 2  that is a midpoint on a lower circular arc of  FIG. 5  where flow distances from the inflow points  11   a  and  12   a  in the circumferential direction are about the same. 
       FIG. 6  is a view to be compared to  FIG. 4 , and a view showing a cross-sectional shape in a flange part  1   f A of a laser processing head  1 A that is a comparative example to the laser processing head  1 . As shown in  FIG. 6 , the laser processing head  1 A of the comparative example includes a gas supply hole  11 A corresponding to the gas supply hole  11  in the laser processing head  1  of the implementation example, and does not include a gas supply hole corresponding to the gas supply hole  12  in the laser processing head  1 . That is, an assist gas AG supplied from outside flows through the gas supply hole  12 A that is one supply path into the laser processing head  1 A. 
       FIG. 7  is a view to be compared to  FIG. 5 , and a schematic view showing flow of the assist gas AG in the laser processing head  1 A of the comparative example. As shown in  FIG. 7 , in the laser processing head  1 A, the assist gas AG passes through one gas supply hole  11 A and is supplied from an inflow point  11   a A to a space Va. On flowing into the space Va, the assist gas AG branches to gas flow AGR that is clockwise flow and gas flow AGL that is counterclockwise flow. 
     The gas flow AGR and gas flow AGL collide only at one point of a collision point PtA where flow distances from the inflow point  11   a A in the space Va are the same and which is opposite to the inflow point. That is, the assist gas AG collides at two collision points Pt 1  and Pt 2  in the space Va in the laser processing head  1  of the implementation example, and collides at one collision point PtA in the space Va of the laser processing head  1 A in the comparative example. 
     When the flow of the assist gas AG in the space Va of the laser processing head  1  is compared to that of the laser processing head  1 A, two collision points Pt 1  and Pt 2  are generated in the laser processing head  1 , and at the respective collision points Pt 1  and Pt 2 , a pressure rises and the flow is disturbed. In this case, however, the pressure rise and flow disturbance are suppressed more than in a case where the gas flow collides at one collision point PtA as in the laser processing head  1 A. Also, the flow disturbance of the assist gas AG at the collision points Pt 1  and Pt 2  generated in the space Va of the laser processing head  1  propagates as the flow disturbance in the circumferential direction also to the flow of the assist gas AG flowing through the space Vb into the hole  1   a   1 . However, this disturbance in the circumferential direction is suppressed to be smaller than disturbance of the flow of the assist gas AG in the circumferential direction in the hole  1   a   1  of the laser processing head  1 A. 
     Also, in the laser processing head  1 , respective axes C 11  and C 12  of two gas supply holes  11  and  12  are not on a straight line in top view from an axis CL 1  direction and, for example, the angle θa is set to 50° and the angle θb is set to 43°. That is, the gas supply holes  11  and  12  are arranged shifted from a position to divide the space Va into two equal parts in the circumferential direction. Consequently, positions in the circumferential direction and gas flow disturbance degrees at two collision points Pt 1  and Pt 2  are not steady, and the gas flow disturbance is averaged and suppressed more while shifting from the circumferential position, in a process of entering from the space Va through the space Vb into the hole  1   a   1 . 
     That is, the laser processing head  1  includes two gas supply holes  11  and  12  as part of the gas supply part GK of the assist gas AG, and the two gas supply holes  11  and  12  are arranged at the positions where the cross-sectional shape is not evenly divided in the circumferential direction. The assist gas AG flowing from the two gas supply holes  11  and  12  into the space Va functioning as air reservoir collides at two collision points Pt 1  and Pt 2  to cause the flow disturbance. However, since the collision points Pt 1  and Pt 2  are arranged at the positions that are not evenly divided in the circumferential direction, the assist gas AG flows into the space Vb in a state where the flow disturbance does not become steady. Consequently, the flow disturbance of the assist gas AG is gradually suppressed in a process of passing through the space Va and the space Vb, and the assist gas AG flows into the hole  1   a   1  in a state where the flow is averaged in the circumferential direction. 
     As described above, distribution of circumferential flow of the assist gas AG injected from the laser processing head  1  including two gas supply holes  11  and  12  is disturbed less and uniformized more than that of circumferential flow of the assist gas AG injected from the laser processing head  1 A only including one gas supply hole  11 A. 
     Next, description will be made as to a difference between the flow of the assist gas AG blown from the laser processing head  1  of the implementation example and the flow of the assist gas AG blown from the laser processing head  1 A of the comparative example, because the difference was confirmed by experiment A and experiment B. 
     In the experiment A, pressure distribution of the assist gas AG blown from each of the laser processing heads  1  and  1 A was measured in horizontally orthogonal biaxial directions, presence of disturbance was checked, and disturbances were compared. In the experiment B, a height of dross generated in each side of the workpiece W substantially cut along a substantially rectangular cutting path Ct was measured, and maximum values were compared. Hereinafter, each maximum value of the height of the dross in the cutting path Ct will be referred to also as a dross highest value Dd. 
     (Regarding Method of Experiment A) 
     A method of the experiment A will be described with reference to  FIGS. 8A and 8B .  FIG. 8A  is a top view of the workpiece W cut in the experiment A, and  FIG. 8B  is a side view of a partial cross section of the workpiece W and the laser processing head  1  during performing of the experiment A. 
     A through hole Wa is formed in the workpiece W of a plate material in advance, and a pressure gauge  71  is disposed directly below the through hole Wa. Relative to the workpiece W, each of the laser processing heads  1  and  1 A is moved along an X-axis and a Y-axis that are two horizontally orthogonal axes passing through the through hole Wa, while blowing the assist gas AG, and the assist gas AG passing through the through hole Wa and blown on a lower surface side has change in pressure over time that is measured with the pressure gauge  71 . Consequently, the pressure distributions of the blown assist gas AG in the X-axis and Y-axis directions are obtainable independently as to the laser processing heads  1  and  1 A. A diameter of the through hole Wa is set to 1.0 mm, and a measurement range is a range of 4 mm in total including 2.0 mm in front and rear in a moving direction from a center position of each of nozzles  1   b  and  1   b A of the laser processing heads  1  and  1 A. 
     (Regarding Method of Experiment B) 
     As shown in  FIG. 9 , a substantially square cutting path Ct with each rounded corner is set to a workpiece W of a plate material. The cutting path Ct is cut in a counterclockwise direction of  FIG. 9 , that is, a first path Ct 1 , a second path Ct 2 , a third path Ct 3  and a fourth path Ct 4  that are four paths as linear portions are cut in this order, and a dross highest value Dd that is a maximum value of a height of dross generated in each path is measured. Orientations of X and Y-cutting directions are set as shown with (+) and (−) in  FIG. 9 . That is, the first path Ct 1  to the fourth path Ct 4  are, in the cutting order, the first path Ct 1 : (Y−) direction, the second path Ct 2 : (X+) direction, the third path Ct 3 : (Y+) direction, and the fourth path Ct 4 : (X−) direction. Also, in the cutting, a focus position of a laser beam Ls was changed in three stages, a moving velocity was changed in four stages, and each dross highest value Dd was measured. 
     (Results in Laser Processing Head  1  of Implementation Example) 
     Experiment A 
       FIG. 10  shows the results of the experiment A in the laser processing head  1  of the implementation example. As shown in  FIG. 10 , blowing pressure distributions of the assist gas AG in the laser processing head  1  have a smooth pressure change degree, and substantially match with each other in an X-axis direction and a Y-axis direction, and any substantial differences depending on a cutting direction are not recognized. That is, it is seen that the pressure distribution of the assist gas AG blown from the laser processing head  1  is uniform in a circumferential direction. 
     Experiment B 
       FIG. 11  is a table showing the results of the experiment B in the laser processing head  1  of the implementation example. In this table, the dross highest value Dd is divided into four stages depending on a size, and cells in the table are classified with hatching or the like. As shown in  FIG. 11 , in the laser processing head  1 , at focus positions of −2.0 mm and −3.0 mm, the dross highest value Dd is suppressed to a minimum stage equal to or less than 30 μm in the four stages regardless of a moving velocity. Also, at a focus position of −0.5 mm, the dross highest value Dd is suppressed to be equal to or less than 50 μm. At any focus position, any noticeable tendencies or differences due to differences among the first path Ct 1  to the fourth path Ct 4  are not recognized. That is, any cutting directionality is not recognized in dross highest value Dd. 
     (Comparative Example: Results of Laser Processing Head  1 A) 
     Experiment A 
       FIG. 12  shows the results of the experiment A in the laser processing head  1 A of the comparative example. As shown in  FIG. 12 , it is seen that in a blowing pressure distribution of an assist gas AG in the laser processing head  1 A, undulated disturbance in an S-shape occurs in a measurement range Ml from −2 mm to −1 mm in movement in an X-direction shown with a solid line. It is also seen that a pressure difference is noticeably made between the X-direction and a Y-direction in a measurement position range from (+0.5) to (+1.6). Consequently, it is seen that the pressure distribution of the assist gas AG blown from the laser processing head  1 A is not uniform in a circumferential direction. 
     Experiment B 
       FIG. 13  is a table showing the results of the experiment B in the laser processing head  1 A of the comparative example, and can be compared to  FIG. 11 . As shown in  FIG. 13 , in the laser processing head  1 A, a dross highest value Dd is often in excess of 30 μm, and sometimes in excess of 50 μm regardless of a focus position and moving velocity, and it is recognized that the dross highest value tends to be higher than in a case where the laser processing head  1  of the implementation example is used. Also, it is recognized that in cutting in an X-axis direction including cutting of a second path Ct 2  in a (X+) direction and a fourth path Ct 4  in a (X−) direction, the dross highest value Dd tends to be higher regardless of the focus position and moving velocity than in cutting in a Y-axis direction including cutting of a first path Ct 1  in a (Y−) direction and a third path Ct 3  in a (Y+) direction. Thus, the cutting by use of the laser processing head  1 A of the comparative example has a large dross highest value Dd and cutting directionality. For this result, it is presumed that there is a factor that a pressure distribution of an assist gas AG is not uniform in a circumferential direction as revealed in the experiment A. 
     It is seen from the above results that according to the laser processing head  1  and the laser processing machine  61  including the laser processing head  1 , the pressure distribution of the assist gas AG blown from the laser processing head  1  is uniform in the circumferential direction, and the cutting directionality is hard to occur in the dross height. 
     The embodiment of the present invention is not limited to the above configuration, and may be modified without departing from the scope of the present invention. 
     As shown in  FIG. 14 , in a first modification of the laser processing head  1 , two gas supply holes  11  and  12  may be formed on a straight line. In this case, flow disturbances of the assist gas AG that are generated at collision points Pt 3  and Pt 4  comparatively stably propagate to the space Vb, but increase in pressure value in a portion disturbed more than in the laser processing head  1 A is suppressed to be small. 
     As shown in  FIG. 15 , the laser processing head  1  is not limited to the one including two gas supply holes  11  and  12 . For example, in a second modification, the laser processing head  1  may include n (integer equal to or more than 3) gas supply holes shifted from each other around the axis CL 1  and formed along an axis orthogonal to the axis CL 1 .  FIG. 15  shows the second modification including four gas supply holes  11  to  14  and four collision points Pt 5  to Pt 8  generated in flow of the assist gas AG. The laser processing head  1  preferably includes more collision points, because increase in pressure value at each collision point is more suppressed and lowered. Further, in this case, at least one of the n gas supply holes preferably has different angle pitches with two adjacent gas supply holes around the axis CL 1 , because circumferential disturbance of flow of a gas flowing through the internal space Vc is more suppressed. 
     When burr or the like in hole making is generated in edges of portions of the gas supply holes  11  and  12  that open at the inner circumferential surface  1   a   2  of the hole  1   a   1 , the flow of the assist gas AG might be disturbed. Therefore, to remove the generated burr, so-called thread chamfering may be performed, or opening processed portions  11   c  and  12   c  subjected to chamfering, counter boring or the like may be formed as shown in  FIG. 3 . In particular, the opening processed portions  11   c  and  12   c  are formed, so that pressure loss and flow disturbance of the assist gas AG in the gas supply holes  11  and  12  can be suppressed. Thus, the forming of the opening processed portions  11   c  and  12   c  substantially corresponds to increasing of inner diameters of the gas supply holes  11  and  12 , and variances in pressure loss and flow disturbance in two supply paths can be suppressed, so that uniformizing of the circumferential pressure distribution of the assist gas AG blown from the laser processing head  1  can be promoted. 
     It has been described in the embodiment that both the axis C 11  and the axis C 12  of the gas supply hole  11  and the gas supply hole  12  also spatially cross the axis CL 1  of the main body  1   a  at right angles on the plane orthogonal to the axis. The present invention is not limited to this embodiment, one or both of the respective axes C 11  and C 12  of the gas supply holes  11  and  12  may be formed shifted in a horizontal direction not to cross the axis CL 1  on the plane orthogonal to the axis CL 1 . In this case, a range in which the axis of the gas supply hole is permitted to shift is, for example, a range between positions where radius lines tilted at +30° and −30° relative to the axis C 11  shown in  FIG. 4  cross the inner circumferential surface  1   a   2 , in a case where the shifted axis is the CL 11 . When the gas supply hole is opened so that the axis is in this range, a collision point similar to that of the embodiment is generated between openings of a plurality of gas supply holes, and effects of suppressing pressure rise and flow disturbance can be obtained in the same manner as in the embodiment. 
     The respective axes C 11  and C 12  of two gas supply holes  11  and  12  in the laser processing head  1  do not have to be at the same positions in the axial direction in which the axis CL 1  extends, and may be formed at shifted positions. For example, in the second modification, at least one of three or more gas supply holes may be formed to have an axis at a position in the axial direction that is different from a position of the other gas supply hole. In this case, a gas supply path may be formed at the position in the axial direction in which the axis CL 1  extends, to open to the cylindrical space Va between the inner circumferential surface  1   a   2  of the main body  1   a  and the outer circumferential surface  1   d   1   a  of the flow path forming ring  1   d . Consequently, a point at which the flow is disturbed is harder to be steady in a process in which the assist gas AG flows from the space Va to the space Vb, and the circumferential pressure distribution of the assist gas AG blown from the laser processing head  1  is more uniformized. 
     REFERENCE SIGNS LIST 
     
         
           1  laser processing head 
           1   a  main body 
           1   a   1  hole 
           1   a   2  inner circumferential surface 
           1   b  nozzle 
           1   b   1  opening 
           1   c  flow path adapter 
           1   c   1  peripheral wall portion 
           1   c   1   a  outer circumferential surface 
           1   d  flow path forming ring 
           1   d   1  peripheral wall portion 
           1   d   1   a  outer circumferential surface 
           1   d   1   b  inner circumferential surface 
           1   e  focusing lens 
           1   f  flange part 
           1   f   1  and  1   f   2  corner 
           1   f   3  to  1   f   6  edge 
           1   g  protective glass 
           11  gas supply hole 
           11   a  inflow point 
           11   c  opening processed portion 
           12  gas supply hole 
           12   a  inflow point 
           12   c  opening processed portion 
           4  fiber cable 
           71  pressure gauge 
           8 ,  8   a  and  8   b  hose 
           9  branch part 
           61  laser processing machine 
           62  laser oscillation device 
           63  processing main body 
           63   a  table 
           63   b  X-axis carriage 
           63   c  Y-axis carriage 
           63   d  Z-axis holder 
           64  NC device 
           65  assist gas supply device 
         AG assist gas 
         AG 11 L, AG 11 R, AG 12 L and AG 12 R gas flow 
         CL 1  axis 
         Ct cutting path 
         Ct 1  first path 
         Ct 2  second path 
         Ct 3  third path 
         Ct 4  fourth path 
         C 11  and C 12  axis 
         C 3  center line 
         da and db distance 
         Dd dross highest value 
         D 11  and D 12  inner diameter 
         GK gas supply part 
         Pt 1  to Pt 8  collision point 
         P 1  and P 2  gas supply port 
         Ls laser beam 
         Va and Vb space 
         Vc internal space 
         W workpiece 
         Wa through hole 
         θa and θb angle