Abstract:
There is provided a fiber laser processing machine, a fiber connection method and a fiber laser oscillator that are capable of improving the beam quality. A fiber laser processing machine comprises: a processing machine body provided with a laser processing head for emitting laser beams; a fiber laser oscillator including a fiber laser module for generating the laser beams and a feeding fiber cable for collectively taking out the laser beams generated by the fiber laser module; and a process fiber cable for transmitting the laser beams taken out by the feeding fiber cable of the fiber laser oscillator to the laser processing head of the processing machine body. The feeding fiber cable and the process fiber cable are joined by fusion, and the feeding fiber cable and the process fiber cable have an equal core diameter.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a fiber laser processing machine as well as a fiber connection method and a fiber laser oscillator used in the fiber laser processing machine. 
       BACKGROUND ART 
       [0002]    A fiber laser processing machine is an apparatus for performing processing such as cutting of a workpiece by emitting laser beams onto the workpiece. In a conventional fiber laser processing machine, a fiber laser oscillator includes a plurality of fiber laser modules for generating laser beams and a feeding fiber cable for collectively taking out the laser beams generated by the plurality of fiber laser modules, and the feeding fiber cable is connected, by a coupling unit, to a process fiber cable for transmitting the laser beams to a processing head. 
         [0003]    PTD 1 describes the following four points as disadvantages in the case of using this coupling unit. 
         [0004]    (a) in the coupling unit, a collimator lens and a focusing lens are used to transmit the laser beams from the feeding fiber cable to the process fiber cable. Therefore, there is an aberration in laser beams caused by the lenses, which results in a reduction in output. 
         [0005]    (b) A core diameter of the process fiber cable is larger than a core diameter of the feeding fiber cable, and thus, the luminance of the laser beams is reduced when the laser beams are transmitted. 
         [0006]    (c) The coupling unit has an influence on the size of the fiber laser oscillator and it is difficult to reduce the size of the fiber laser oscillator. 
         [0007]    (d) The laser beams are transmitted through the collimator lens and the focusing lens, and thus, adjustment thereof is difficult. 
         [0008]    In order to solve the foregoing, PTD 1 proposes fixing the feeding fiber cable and the process fiber cable within a cylindrical body made of glass, with a laser beam emission end of the feeding fiber cable facing a laser beam incidence end of the process fiber cable with a prescribed gap therebetween. 
         [0009]    As another solution, fusing the feeding fiber cable and the process fiber cable is also under study. PTD 1 describes that in either method, the core diameter of the feeding fiber cable is approximately  50  and the core diameter of the process fiber cable is approximately 100 to 200 μm, which is larger than the core diameter of the feeding fiber cable. 
       CITATION LIST 
     Patent Document 
       [0010]    PTD 1: Japanese Patent Laying-Open No. 2012-27241 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0011]    However, PTD 1 describes that when the feeding fiber cable and the process fiber cable are fused, distortion of the shape of the cores in these cables occurs at a portion where heat is applied during fusion, which causes deterioration of the beam quality, and thus, the configuration described in PTD 1 cannot withstand the use in practice. 
         [0012]    The present invention has been made in light of the aforementioned problems and an object of the present invention is to provide a fiber laser processing machine, a fiber connection method and a fiber laser oscillator that are capable of improving the beam quality. 
       Solution to Problem 
       [0013]    In order to increase the cutting speed of the fiber laser processing machine, the inventors of the present invention first considered increasing a power density PD (line density) expressed by the following equation (a), which has a proportional relationship with the cutting speed. 
         [0000]        PD=P /( d×ρ )   (a)
 
         [0014]    where P represents a power, d represents a spot diameter (focal point diameter), and power density PD represents power per unit area. 
         [0015]    In order to increase power density PD, increasing power P is conceivable. However, when the power is increased, the consumed electric power increases and the running cost increases. Therefore, the inventors of the present invention considered decreasing spot diameter d. Spot diameter d is expressed by the following equation (b).  FIG. 13  is a schematic view schematically showing an external optical system. 
         [0000]        d= (α× M×λ×fL )/ D  
 
         [0000]      =(β× M×λ×fL )/ fC    (b)
 
         [0016]    where α and β represent coefficients, M represents a laser spread angle (beam mode), λ represents a wavelength of a laser beam, fL represents a focal length of a condenser lens, and fC represents a focal length of a collimator lens. 
         [0017]    In order to decrease spot diameter d, decreasing focal length fL of the condenser lens or increasing focal length fC of the collimator lens is conceivable. However, due to a restriction of mechanical dimension, it is difficult to decrease focal length fL of the condenser lens, and due to a restriction of lens diameter of the collimator lens, it is difficult to increase focal length fC of the collimator lens. Thus, in order to decrease spot diameter d, the inventors of the present invention considered decreasing laser spread angle M which is also referred to as “beam mode”. As is also described in PTD 1, according to the conventional idea, the limit of the core diameter of the feeding fiber cable is approximately 50 μm and the limit of the core diameter of the process fiber cable is approximately 100 to 200 μm, which is larger than the core diameter of the feeding fiber cable, from the perspective of connecting the cables, and decreasing the core diameter of the process fiber cable to be smaller than 100 μm has not been conceived. Furthermore, fusion of the feeding fiber cable and the process fiber cable has not been recognized as a realistic connection method, either. 
         [0018]    The present invention has achieved improvement in beam quality by fusion of the feeding fiber cable and the process fiber cable, which has been conventionally regarded as unrealistic. The present invention provides the following aspects. 
         [0019]    (1) A fiber laser processing machine comprising: 
         [0020]    a processing machine body provided with a laser processing head for emitting laser beams; 
         [0021]    a fiber laser oscillator including a fiber laser module for generating the laser beams and a feeding fiber cable for collectively taking out the laser beams generated by the fiber laser module; and 
         [0022]    a process fiber cable for transmitting the laser beams taken out by the feeding fiber cable of the fiber laser oscillator to the laser processing head of the processing machine body, wherein 
         [0023]    the feeding fiber cable and the process fiber cable are joined by fusion, and 
         [0024]    the feeding fiber cable and the process fiber cable have an equal core diameter. 
         [0025]    (2) The fiber laser processing machine according to (1), wherein each of the feeding fiber cable and the process fiber cable has a uniform core diameter. 
         [0026]    (3) The fiber laser processing machine according to (1) or (2), wherein the fiber laser oscillator includes a casing that houses the fiber laser module and the feeding fiber cable, and 
         [0027]    a fused portion of the feeding fiber cable and the process fiber cable is arranged on a drawable fusion table housed in the casing. 
         [0028]    (4) The fiber laser processing machine according to (3), wherein the processing machine body includes a cabin that houses the laser processing head and forms an external shape of the processing machine body, and 
         [0029]    the cabin includes, at a side surface, an oscillator housing portion that houses the fiber laser oscillator, and the fiber laser oscillator is housed in the oscillator housing portion in a state of the casing. 
         [0030]    (5) A fiber connection method used in a fiber laser processing machine comprising: a fiber laser oscillator including a fiber laser module for generating laser beams and a feeding fiber cable for collectively taking out the laser beams generated by the fiber laser module; and a process fiber cable for transmitting the laser beams taken out by the feeding fiber cable to a laser processing head, the fiber connection method being for connecting the feeding fiber cable and the process fiber cable, wherein 
         [0031]    fusion is performed on a drawable fusion table provided in a casing of the fiber laser oscillator. 
         [0032]    (6) A fiber laser oscillator comprising: 
         [0033]    a fiber laser module for generating laser beams; 
         [0034]    a feeding fiber cable for collectively taking out the laser beams generated by the fiber laser module; and 
         [0035]    a casing that houses the fiber laser module and the feeding fiber cable, 
         [0036]    the fiber laser oscillator being connected to a process fiber cable for transmitting the laser beams to a laser processing head, wherein 
         [0037]    the feeding fiber cable and the process fiber cable are joined by fusion, and 
         [0038]    a fused portion of the feeding fiber cable and the process fiber cable is arranged on a fusion table housed in the casing in a drawable manner. 
       Advantageous Effects of Invention 
       [0039]    According to the aspect described in (1) above, the feeding fiber cable and the process fiber cable are connected by fusion. Therefore, the process fiber cable having the core diameter equal to the core diameter of the feeding fiber cable can be used, and a reduction in luminance caused by a difference in core diameter can be suppressed, and the beam quality can be improved. In addition, due to fusion, the core diameter of the process fiber cable can be made smaller than that of a conventional process fiber cable, and the laser spread angle (BPP: Beam Parameter Product) which is also referred to as “beam mode” can be decreased, and the cutting speed can be increased. 
         [0040]    According to the aspect described in (2) above, a reduction in luminance caused by a difference in core diameter can be suppressed and the beam quality can be improved, without providing any special processing to the feeding fiber cable and the process fiber cable. 
         [0041]    According to the aspect described in (3) above, the fusion treatment for the feeding fiber cable and the process fiber cable becomes easy. The fusion treatment, which is normally performed in a clean room of a factory and the like, can be performed at a site where the fiber laser processing machine is assembled, at a site where the fiber laser processing machine is placed, or the like. As a result, at the time of replacement and the like of the process fiber cable, the fusion table is drawn out from the casing of the fiber laser oscillator, and thereby, the fusion treatment can be easily performed. 
         [0042]    According to the aspect described in (4) above, as compared with the case of placing the fiber laser oscillator at a distance from the fiber laser processing machine body, the fiber laser processing machine is well integrated, and the entire size of the fiber laser processing machine can be reduced because the fiber laser oscillator can be housed in the cabin of the processing machine body. In addition, the fiber laser oscillator and the fiber laser processing machine body can be conveyed together, with the feeding fiber cable and the process fiber cable fused. 
         [0043]    According to the aspects described in (5) and (6) above, the fusion treatment for the feeding fiber cable and the process fiber cable becomes easy. The fusion treatment, which is normally performed in a clean room of a factory and the like, can be performed at a site where the fiber laser processing machine is assembled, at a site where the fiber laser processing machine is placed, or the like. As a result, at the time of replacement and the like of the process fiber cable, the fusion table is drawn out from the casing of the fiber laser oscillator, and thereby, the fusion treatment can be easily performed. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0044]      FIG. 1  is a cross-sectional view showing a fiber connection structure according to one embodiment of the present invention. 
           [0045]      FIG. 2  is a schematic plan view of a laser processing machine according to one embodiment of the present invention. 
           [0046]      FIG. 3  is a schematic side view of the laser processing machine shown in  FIG. 2 . 
           [0047]      FIG. 4  is a perspective view of a processing head drive mechanism. 
           [0048]      FIG. 5  is a perspective view of a processing head. 
           [0049]      FIG. 6  is a back view of the laser processing machine shown in  FIG. 2 . 
           [0050]      FIG. 7  is a perspective view of the right side surface side of the laser processing machine shown in  FIG. 2 . 
           [0051]      FIG. 8  is a perspective view of the left side surface side of the laser processing machine shown in  FIG. 2 . 
           [0052]      FIG. 9  is a perspective view showing a state in which a door of a laser oscillator is open. 
           [0053]      FIG. 10  is a view showing the inside of a fusion box. 
           [0054]      FIG. 11  is a graph showing the upper limit cutting speed with respect to a plate thickness in each fiber laser processing machine. 
           [0055]      FIG. 12  is a graph showing the upper limit cutting speed in each fiber laser processing machine, and  FIG. 12(   a ) is a graph when the plate thickness is 1 mm and  FIG. 12(   b ) is a graph when the plate thickness is 2 mm. 
           [0056]      FIG. 13  is a schematic view schematically showing an external optical system. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0057]    One embodiment of a fiber connection structure according to the present invention will be described first. 
         [0058]    A fiber connection structure  1  according to the present embodiment is applied to, for example, a fiber laser processing machine  10  described below, and as shown in  FIG. 1 , a feeding fiber cable  2  and a process fiber cable  3  having the same core diameter are connected by fusion. In  FIG. 1 ,  2   a  represents a core of feeding fiber cable  2 ,  2   b  represents a clad of feeding fiber cable  2 ,  3   a  represents a core of process fiber cable  3 ,  3   b  represents a clad of process fiber cable  3 , and  4  represents a fused portion. In the present specification, when a difference in core diameter between the two fiber cables is equal to or less than ±10%, these two fiber cables are regarded as having the same core diameter. For example, when the core diameter of feeding fiber cable  2  is 50 μm, feeding fiber cable  2  and process fiber cable  3  are regarded as having the same core diameter and the respective core diameters are regarded as being equal if the core diameter of process fiber cable  3  is within the range of 50±5 μm. 
         [0059]    Feeding fiber cable  2  and process fiber cable  3  having the equal core diameter are fused as described above, and thus, a reduction in luminance caused by a difference in core diameter between both cables  2  and  3  is suppressed and the beam quality is improved. In addition, the coupling unit is eliminated, and thus, there is no aberration in laser beams caused by the collimator lens and the focusing lens, which makes it possible to avoid a reduction in output, an increase in size of the apparatus caused by the coupling unit, and complication of lens adjustment. 
         [0060]    Feeding fiber cable  2  and process fiber cable  3  may have the same core diameter only at a fused portion  4 . It is, however, preferable that each of feeding fiber cable  2  and process fiber cable  3  has a uniform core diameter. Thus, a reduction in luminance caused by a difference in core diameter can be suppressed and the beam quality can be improved, without providing any special processing to feeding fiber cable  2  and the process fiber cable. In the present specification, when a distribution of the core diameter of the fiber cable is within the range of ±10% or less, this fiber cable is regarded as having a uniform core diameter. For example, when feeding fiber cable  2  (or process fiber cable  3 ) has a core diameter of 50±5 μm over the entire length thereof, feeding fiber cable  2  (or process fiber cable  3 ) is regarded as having a uniform core diameter. 
         [0061]    The fusion treatment is performed by arranging feeding fiber cable  2  and process fiber cable  3  such that end faces thereof face each other, and heating feeding fiber cable  2  and process fiber cable  3  with both end faces abutting each other. This fusion treatment can be performed by using an optical fiber fusion splicer. It is, however, preferable to perform the fusion treatment by using a core-direct-view-type optical fiber fusion splicer which is excellent in centering capability. By using the optical fiber fusion splicer to perform the fusion treatment, process fiber cable  3  having the core diameter smaller than that of a conventional process fiber cable can be used. Since cables  2  and  3  having the small core diameters are connected, laser spread angle M can be decreased and the cutting speed can be increased. 
         [0062]    The core diameter of each of feeding fiber cable  2  and process fiber cable  3  is preferably about 100 μm or smaller, and more preferably about 50 μm or smaller. A clad diameter is not particularly limited, and feeding fiber cable  2  and process fiber cable  3  may have different clad diameters or the same clad diameter. 
         [0063]    Next, a fiber laser processing machine to which fiber connection structure  1  according to the present invention is applied as well as a fiber laser oscillator will be described with reference to  FIGS. 2 to 10 . 
         [0064]    As shown in  FIGS. 2 and 3 , a fiber laser processing machine  10  (hereinafter referred to as “laser processing machine”) mainly includes a processing machine body  20 , a fiber laser oscillator  21  (hereinafter referred to as “laser oscillator”) and a control device  22  connected to processing machine body  20 , a pallet changer  23  disposed to be connected to processing machine body  20 , an assist gas supply portion  27  including a booster compressor  24  and an air compressor  25  used to separate a nitrogen gas in the air, or an oxygen gas cylinder  26  and the like, a chiller unit  28  for supplying cooling water that cools laser oscillator  21  and a laser processing head  40  (hereinafter referred to as “processing head”), and a dust collector  29  for removing dust and the like that occur during processing. 
         [0065]    In the present embodiment, “frontward” refers to a direction closer to processing machine body  20  in a direction of arrangement of processing machine body  20  and pallet changer  23  (in the X direction in  FIG. 2 ), and “rearward” refers to a direction closer to pallet changer  23  in this direction of arrangement. In addition, “leftward” and “rightward” are expressed by directions when viewing the frontward from the rearward in a direction orthogonal to the direction of arrangement (in the Y direction in  FIG. 2 ). 
         [0066]    Housed in a cabin  30  that forms a part of processing machine body  20  and forms an external shape of processing machine body  20  are a pallet drive mechanism  32  for driving a pallet  31  in a prescribed direction, i.e., in a longitudinal direction (X direction) of cabin  30 , processing head  40  for emitting laser beams for processing a workpiece W mounted on pallet  31 , a processing head drive mechanism  49  for driving processing head  40 , and a collection conveyor  60  for collecting scraps and the like cut during processing. 
         [0067]    As shown in  FIG. 4 , processing head  40  is provided in processing machine body  20  and is movable in the X direction, in a width direction (Y direction) of cabin  30 , and in a vertical direction (Z direction) of cabin  30  by processing head drive mechanism  49 . Specifically, a beam-like X-direction movable platform  42  is arranged to span a pair of support platforms  41  provided right and left, and this X-direction movable platform  42  is driven in the X direction by an X-axis motor  43 . A Y-direction movable platform  45  that is driven by a Y-axis motor  44  and is movable in the Y direction is also disposed at X-direction movable platform  42 . Y-direction movable platform  45  is driven in the Y direction by a rack and pinion mechanism for meshing a not-shown pinion fixed to a rotation shaft of Y-axis motor  44  with a not-shown rack arranged in X-direction movable platform  42 . In addition, by using a rack and pinion mechanism driven by a Z-axis motor  46 , processing head  40  is disposed at Y-direction movable platform  45  so as to be movable in the Z direction. 
         [0068]    Processing head  40  shown by a solid line in  FIG. 2  and a dotted line in  FIG. 3  indicates a state of being located at the most frontward part in the X direction (a position where pallet  31  is placed during processing), and processing head  40  shown by an alternate long and short dash line in  FIGS. 2 and 3  indicates a state of being located at the most rearward part in the X direction. 
         [0069]    A process fiber cable (only a tip thereof is shown)  3  extending from laser oscillator  21  is routed through an X-direction cableveyor (registered trademark)  48   x  and a Y-direction cableveyor (registered trademark)  48   y,  and is connected to processing head  40 . Also arranged in processing head  40  are a collimator lens  51  for parallelizing the laser beams emitted from an emission end of process fiber cable  3 , and a condenser lens  52  for condensing the parallelized laser beams. Condenser lens  52  is provided such that a position thereof can be freely adjusted in the Z direction with respect to processing head  40 . 
         [0070]    As shown in  FIG. 5 , a cooling pipe  56  provided from chiller unit  28  is connected around processing head  40  to cool the emission end of process fiber cable  3  and the surroundings of condenser lens  52 . Furthermore, provided around processing head  40  are a gas supply pipe  57  for supplying an assist gas such as a nitrogen gas or an oxygen gas from assist gas supply portion  27  into processing head  40 , and a gas supply pipe  58  connected to a side nozzle  54  for spraying the assist gas such as the nitrogen gas or the oxygen gas toward the neighborhood of a laser nozzle  53  of processing head  40 . 
         [0071]    These cooling pipe  56  and gas supply pipes  57  and  58  pass through a Z-direction cableveyor (registered trademark)  48   z,  and then, are routed to X-direction cableveyor (registered trademark)  48   x  and Y-direction cableveyor (registered trademark)  48   y,  together with process fiber cable  3 , and are connected to chiller unit  28  and assist gas supply portion  27 . 
         [0072]    When laser oscillator  21  is actuated, the laser beams pass through process fiber cable  3  and are parallelized by collimator lens  51 . Further, the parallelized laser beams enter condenser lens  52  to be condensed, and are emitted from laser nozzle  53  to a portion of workpiece W to be processed, and processing head  40  processes workpiece W. During processing, the assist gas supplied from assist gas supply portion  27  is injected from laser nozzle  53  and side nozzle  54  toward the portion of workpiece W to be processed, such that the molten metal generated during processing is blown away. 
         [0073]    As shown in  FIGS. 2 and 3 , pallet drive mechanism  32  is disposed at a position facing a right side surface of pallet  31  along the X direction, and has an endless chain  34  rotationally driven by a drive motor  33 , and a rail  35  on which a plurality of rollers  36  provided on the lower surface side of pallet  31  are guided in a rolling manner and which supports pallet  31 . When endless chain  34  is rotationally driven by drive motor  33 , a pin (not shown) provided at endless chain  34  engages with an engagement portion (not shown) of pallet  31  and pallet  31  on rail  35  is moved in the X direction. 
         [0074]    As shown in  FIGS. 6 to 8 , a gull wing  38  which is an open/close door is provided on a front surface  30 F of cabin  30 , and on a rear surface  30 B which is the opposite side of front surface  30 F, a loading/unloading port  37  formed in the shape of a horizontally long slit is provided to correspond to pallet changer  23 . Thus, at the time of processing of large-lot products, pallet  31  having workpiece W placed thereon is loaded/unloaded through loading/unloading port  37 , and at the time of processing of small-lot products, workpiece W is loaded/unloaded from gull wing  38 . As a result, the loading/unloading operation corresponding to the lot size can be performed. 
         [0075]    On front surface  30 F of cabin  30 , a first control panel  75  is also arranged at a lateral part of gull wing  38 . On a left side surface  30 L, a second control panel  70  is arranged closer to rear surface  30 B. Furthermore, a foot switch  76  that can be foot-operated by the operator is arranged at front surface  30 F of cabin  30  and below gull wing  38 . 
         [0076]    A concave oscillator housing portion  30   a  that houses laser oscillator  21  is arranged at a substantially central portion of a right side surface  30 R of cabin  30 . As shown in  FIG. 9 , laser oscillator  21  arranged in this oscillator housing portion  30   a  is configured such that, in a box-type casing  80 , a plurality of (four in the present embodiment) fiber laser modules  81  for generating laser beams are vertically stacked and housed, and a combiner  83  having an output cable  82  from each fiber laser module  81  connected thereto is housed above fiber laser modules  81 . Furthermore, a fusion box  84  connected to combiner  83  by feeding fiber cable  2  is housed above combiner  83 . 
         [0077]    As shown in  FIG. 10 , process fiber cable  3  connecting to processing head  40  is inserted into fusion box  84  on the opposite side of the side into which feeding fiber cable  2  is inserted, and fused portion  4  of feeding fiber cable  2  and process fiber cable  3  is arranged in fusion box  84 . Combiner  83  and fusion box  84  are arranged on a combiner table  85  and a fusion table  86  that can be drawn out from casing  80 , respectively. 
         [0078]    Referring again to  FIGS. 2 ,  3  and  6 , pallet changer  23  is arranged to face rear surface  30 B of cabin  30  having loading/unloading port  37 . Pallet changer  23  has a movable frame  62  driven upwardly and downwardly by a drive mechanism  61  shown in  FIG. 2 , and two pallets  31  can be arranged vertically in two stages on an angular substantially C-shaped rail  63  provided at right and left lateral parts of movable frame  62 . 
         [0079]    Upper pallet  31  is placed on an upper rail surface  63   a  of angular substantially C-shaped rail  63 , and lower pallet  31  is placed on a lower rail surface  63   b  of angular substantially C-shaped rail  63 . A height of pallets  31  arranged in two stages on angular substantially C-shaped rail  63  is adjustable such that when movable frame  62  is driven upwardly and downwardly by drive mechanism  61 , pallets  31  on angular substantially C-shaped rail  63  can move upwardly and downwardly to come level with rail  35  disposed in cabin  30 . Therefore, pallet  31  located at the same height as that of rail  35  can be loaded/unloaded between pallet changer  23  and the inside of cabin  30  through loading/unloading port  37 . 
         [0080]    A workpiece lifter  66  including, at a top portion thereof, a free bearing  64  for moving workpiece W on pallet  31  to cause workpiece W to align with a datum of pallet  31  is also provided below movable frame  62  such that workpiece lifter  66  can be moved up and down (see  FIG. 6 ). In  FIGS. 2 and 3 , a reference character  65  represents a foot switch for actuating a drive mechanism  67  that drives workpiece lifter  66  upwardly and downwardly. 
         [0081]    As shown in  FIG. 2 , a sensor including a photo transmitter  71 , reflectors  72  and a photo receiver  73  is arranged at each corner of a working area WA enclosing pallet changer  23 , and the light emitted from photo transmitter  71  is reflected by three reflectors  72  and received by photo receiver  73 , thereby monitoring entrance and exit of the operator and the like into and from working area WA. An area sensor  74  is also disposed on rear surface  30 B of cabin  30  to detect whether the operator and the like are in working area WA or not. When the sensor including photo transmitter  71 , reflectors  72  and photo receiver  73  or area sensor  74  is actuated, it is determined that the operator and the like are in working area WA, and the loading/unloading operation by pallet changer  23  is prohibited, and thus, the safety of the operator and the like is ensured. 
         [0082]    Fiber connection structure  1  according to the present embodiment is applicable to not only laser processing machine  10  described above but also various fiber laser processing machines. However, by applying fiber connection structure  1  to particularly laser processing machine  10  described above, fused portion  4  of feeding fiber cable  2  and process fiber cable  3  can be arranged on fusion table  86  that can be drawn out from casing  80  of laser oscillator  21 . As a result, the fusion treatment for feeding fiber cable  2  and process fiber cable  3  becomes easy, and the fusion treatment, which is normally performed in a clean room of a factory and the like, can be performed at a site where laser processing machine  10  is assembled, at a site where laser processing machine  10  is placed, or the like. In other words, at the time of replacement and the like of process fiber cable  3 , fusion table  86  is drawn out from casing  80  and a drawn-out portion is covered with a simple clean booth to form a simplified clean room, and thereby, the fusion treatment can be easily performed. Fusion table  86  and fusion box  84  may be formed integrally or separately. 
         [0083]    In addition, combiner table  85  does not always need to be drawable from casing  80 . However, by configuring combiner table  85  to be drawable similarly to fusion table  86 , the work such as replacement, addition and the like of fiber laser module  81  can be easily performed. 
         [0084]    In addition, in laser processing machine  10 , laser oscillator  21  can be housed in oscillator housing portion  30   a  formed in right side surface  30 R of cabin  30 . Therefore, as compared with the case of placing the laser oscillator at a distance from processing machine body  20 , laser processing machine  10  is well integrated, and the entire size of laser processing machine  10  can be reduced because laser oscillator  21  can be housed in cabin  30  of processing machine body  20 . In addition, laser oscillator  21  and fiber laser processing machine body  20  can be conveyed together, with feeding fiber cable  2  and process fiber cable  3  fused. 
       EXAMPLE 
       [0085]    Examples of the present invention will be described hereinafter. 
         [0086]    In order to demonstrate the effect of the fiber connection structure according to the present invention, the cutting speed (hereinafter referred to as “upper limit cutting speed”) in a range of not generating dross (so-called dross-free cutting) was measured by using a fiber laser processing machine having a power of 1 kW in which the fiber connection structure according to the present invention was used (Example 1), a fiber laser processing machine according to the present invention having a power of 2 kW (Example 2), a conventional fiber laser processing machine having a power of 2 kW (Comparative Example 1), a conventional fiber laser processing machine having a power of 4 kW (Comparative Example 2), and a carbon dioxide gas laser processing machine having a power of 2 kW (Comparative Example 3). For the measurement, thin plates made of SUS304 and having three types of plate thicknesses (t=1 mm, 2 mm and 3 mm) were used and cutting was performed linearly. 
         [0087]      FIG. 11  is a graph showing the upper limit cutting speed with respect to the plate thickness in each fiber laser processing machine.  FIG. 12(   a ) is a graph showing the upper limit cutting speed in each fiber laser processing machine when the plate thickness is 1 mm, and  FIG. 12(   b ) is a graph showing the upper limit cutting speed in each fiber laser processing machine when the plate thickness is 2 mm. 
         [0088]    As can be seen from  FIG. 11 , there was not so large difference in upper limit cutting speed when the plate thickness was 3 mm. However, as the plate thickness became smaller, a large difference was caused in upper limit cutting speed. As is clear from  FIG. 12(   b ), when plate thickness t=2 mm, the fiber laser processing machine in Example 1 exhibited the upper limit cutting speed that was substantially the same level as those of the fiber laser processing machine in Comparative Example 1 and the carbon dioxide gas laser processing machine in Comparative Example 3 having twice the power. In addition, the fiber laser processing machine in Example 2 exhibited the upper limit cutting speed that was more than three times higher than those of the fiber laser processing machine in Comparative Example 1 and the carbon dioxide gas laser processing machine in Comparative Example 3 having the same power, and further, exhibited the upper limit cutting speed that was substantially the same level as that of the fiber laser processing machine in Comparative Example 2 having twice the power. 
         [0089]    As is clear from  FIG. 12(   a ), when plate thickness t=1 mm, the fiber laser processing machine in Example 1 exhibited the upper limit cutting speed that was the same level as that of the fiber laser processing machine in Comparative Example 1 having twice the power, and exhibited the upper limit cutting speed that was about three times higher than that of the carbon dioxide gas laser processing machine in Comparative Example 3 having twice the power. In addition, the fiber laser processing machine in Example 2 exhibited the upper limit cutting speed that was more than twice as high as that of the fiber laser processing machine in Comparative Example 1 having the same power, exhibited the upper limit cutting speed that was more than six times higher than that of the carbon dioxide gas laser processing machine in Comparative Example 3 having the same power, and further, exhibited the upper limit cutting speed higher than that of the fiber laser processing machine in Comparative Example 2 having twice the power. 
         [0090]    Thus, particularly when a thin plate material of 2 mm or thinner was cut, the fiber laser processing machine in which the fiber connection structure according to the present embodiment was used exhibited the upper limit cutting speed that was significantly higher than those of the laser processing machine and the carbon dioxide gas laser processing machine having the same power, and exhibited the upper limit cutting speed that was substantially the same level as that of the laser processing machine having twice the power. This means that the fiber laser processing machine according to the present embodiment can perform the same cutting work in a shorter time than the laser processing machine having the same power due to a difference in upper limit cutting speed, and means that the fiber laser processing machine according to the present embodiment can perform the same cutting work with a smaller amount of consumed electric power than the laser processing machine having twice the power. 
         [0091]    As described above, according to the present invention, feeding fiber cable  2  and process fiber cable  3  are connected by fusion. Therefore, process fiber cable  3  having the core diameter equal to the core diameter of feeding fiber cable  2  can be used, and a reduction in luminance caused by a difference in core diameter can be suppressed, and the beam quality can be improved. In addition, due to fusion, the core diameter of process fiber cable  3  can be made smaller than that of a conventional process fiber cable, and the laser spread angle which is also referred to as “beam mode” can be decreased, and the cutting speed can be increased. 
         [0092]    The present invention is not limited to the aforementioned embodiment, and variation, modification or the like is possible as appropriate. 
         [0093]    For example, the configuration of the inside of casing  80  of laser oscillator  21  is not limited to the aforementioned embodiment, and a plurality of fiber laser modules  81  may be arranged side by side. In addition, at least one fiber laser module  81  may only be housed and the number thereof can be changed as appropriate and a space for placing the module(s) may be made for subsequent addition. 
       REFERENCE SIGNS LIST 
       [0094]      1  fiber connection structure;  2  feeding fiber cable;  3  process fiber cable;  4  fused portion;  10  fiber laser processing machine;  20  processing machine body;  21  fiber laser oscillator;  30  cabin;  30   a  oscillator housing portion;  40  laser processing head;  80  casing;  81  fiber laser module;  86  fusion table.