Patent Publication Number: US-2022226931-A1

Title: Processing machine

Description:
TECHNICAL FIELD 
     The present invention relates to a processing machine. 
     BACKGROUND ART 
     For example, JP 2002-59286A (PTL 1) discloses a laser processing device that performs laser welding by irradiating a portion to be welded with laser light while a wire is supplied to the portion to be welded. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Laying-Open No. 2002-59286 
     SUMMARY OF INVENTION 
     Technical Problem 
     Laser direct metal deposition (L-DMD) is a process of additive manufacturing (AM) in which a powdered or wire-like metal is directed by a nozzle into a molten pool generated on a metal surface by a laser beam. The L-DMD process may be used in various AM applications including 3D printing, coating, and 3D part repair. 
     Choice of a material form depends on application, and introduces several specific advantages and disadvantages. The main advantage of the use of the powder is high process stability and robustness, and is selection of a wide range of materials and ability to mix several material powders in order to create alloy and a graded material part. On the other hand, the use of the wire as compared to the powders offers the advantages including low price of a wire material, high material use efficiency and a deposition rate, and no problem like handling safety and environmental pollution. The use of the powder may be harmful to both a human and a machine. In addition, due to an oxidation issue, the wire material is easy to store and is applied to the deposition of a reactive material such as Al and a Ti alloy. 
     In order to perform laser direct wire deposition (L-DWD), in the simplest case, a deposition head is used by means in which the wire is laterally fed into the molten pool generated by the laser beam directed orthogonally to a workpiece surface. In this case, the efficiency and stability of the process is influenced by an angle of lateral feed and can be either from a front, a back, or a side of the generated molten pool. One of major drawbacks of the lateral feeds is asymmetry of the process and dependency of an involved direction, which can be partially solved by an L-DWD head with different feed directions. 
     Another approach to achieve symmetry of the L-DWD process, the direction independence, and the high process stability is to axially feed the wire relative to the laser beam. This may be achieved by a number of laser beams located around the axially fed wire, or an annular laser beam. Despite several advantages and improvements achieved by the wire feeding in the axial direction, the stability of the L-DWD process indicates high sensitivity to a parameter of the process, particularly in an initial transition phase. 
     An object of the present invention is to solve the above problems, and to provide a processing machine that achieves the high process stability in annular laser beam direct wire deposition (ALB-DWD). 
     Solution to Problem 
     A processing machine according to the present invention is a processing machine that performs additive manufacturing. The processing machine includes: a laser irradiation device configured to irradiate a workpiece with an annular laser beam; a wire feeding device configured to feed a wire from an inside of the annular laser beam emitted from the laser irradiation device toward the workpiece; and a control device configured to control the processing machine. A workpiece irradiation proportion parameter (WIP) represented by the following equation is defined. 
       WIP= P   wp   /P    
     (P wp : laser beam power introduced onto the workpiece surface when the wire exists in an irradiation region of the laser beam) 
     (P: laser beam power introduced onto the workpiece surface when the wire does not exist in the irradiation region of the laser beam) 
     In this case, at a beginning of the additive manufacturing, the control device controls the wire feeding device so that a wire end abuts on the workpiece surface. At a beginning of the additive manufacturing, the control device determines initial power P 0  of the laser beam based on the WIP, and controls the laser irradiation device so that the workpiece is irradiated with the laser beam at the initial power P 0 . 
     According to the processing machine configured as described above, when the wire end abuts on the workpiece surface at the beginning of the additive manufacturing, the workpiece is irradiated with the laser beam at the initial power P 0  determined based on the WIP, whereby a molten bond in an appropriate form can be formed between the workpiece surface and the wire end. At the beginning of the additive manufacturing, the workpiece and the wire are simultaneously heated by the laser beam by abutting the wire end on the workpiece surface. For this reason, the melt pool on the workpiece surface and the molten bond between the workpiece surface and the wire end can be generated in a short time. Accordingly, according to the present invention, the process stability can be enhanced in the initial phase at the beginning of the additive manufacturing. 
     Preferably, the control device includes: a storage configured to store data related to a relationship between the WIP and the initial power P 0  of the laser beam to be set; a controller configured to determine the initial power P 0  of the laser beam by comparing the WIP at the beginning of the additive manufacturing to the data stored in the storage; and a communicator configured to communicate the initial power P 0  of the laser beam determined by the controller to the laser irradiation device. 
     According to the processing machine configured as described above, the initial power P 0  of the laser beam can be appropriately determined according to the value of the WIP at the beginning of the additive manufacturing. 
     Preferably, the processing machine further includes an infrared camera configured to observe the workpiece surface. The controller specifies the WIP by estimating the laser beam power introduced onto the workpiece surface from a pixel value of an infrared image obtained by the infrared camera. 
     According to the processing machine configured as described above, the WIP at the beginning of the additive manufacturing can be easily specified using the pixel value of the infrared image obtained by the infrared camera. 
     Preferably, the control device controls the laser irradiation device so that the power of the laser beam increases to power P S  larger than the initial power P 0  after the irradiation of the laser beam is continued for a certain period of time with the initial power P 0 . 
     Preferably, the control device controls the wire feeding device so that wire feeding is started toward the workpiece at an identical time when the power of the laser beam starts the increase from the initial power P 0 . 
     Preferably, the machining apparatus further includes a moving mechanism configured to move the laser irradiation device and the workpiece relative to each other. The control device controls the moving mechanism unit so that the laser irradiation device and the workpiece start to move relative to each other while the power of the laser beam increases from the initial power P 0  to the power P S . 
     According to the processing machine configured as described above, the process can be stably transitioned from the initial phase at the beginning of the additive manufacturing to the steady phase in which the additive manufacturing is continuously performed on the workpiece. 
     Advantageous Effects of Invention 
     As described above, according to the present invention, the processing machine that achieves the high process stability in the ALB-DWD can be provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating a setup of an annular laser beam direct wire deposition (ALB-DWD). 
         FIG. 2  is a diagram illustrating a profile of an annular laser beam (ALB). 
         FIG. 3  is a diagram illustrating an initial wire end position (without wire) for a workpiece irradiation proportion parameter (WIP) measurement and an initial process phase policy. 
         FIG. 4  is a diagram illustrating the initial wire end position (with wires) for the WIP measurement and the initial process phase policy. 
         FIG. 5  is a diagram illustrating a laser pulse thermal footprint I and related I a  at h wp =4.5 mm. 
         FIG. 6  is a diagram illustrating the laser pulse thermal footprint I and related I a  at h wp =4.5 mm. 
         FIG. 7  is a diagram illustrating a laser pulse thermal footprint I wp  and related I a,wp  at h wp =4.5 mm and WIP 79%. 
         FIG. 8  is a diagram illustrating the laser pulse thermal footprint I wp  and related I a,wp  at h wp =4.5 mm and WIP 79%. 
         FIG. 9  is a diagram illustrating a molten bond formed between a workpiece surface and a wire. 
         FIG. 10  is a diagram illustrating wire collision. 
         FIG. 11  is a diagram illustrating a pendant droplet. 
         FIG. 12  is a graph illustrating a policy A of an initial phase of the ALB-DWD. 
         FIG. 13  is a graph illustrating a policy B of the initial phase of the ALB-DWD. 
         FIG. 14  is a graph illustrating a policy C of the initial phase of the ALB-DWD. 
         FIG. 15  is a table illustrating a process parameter and characteristic time in the policy A, the policy B, and the policy C. 
         FIG. 16  is a graph illustrating dependence of initial laser beam power P 0  on the WIP. 
         FIG. 17  is a graph illustrating treatment time t s  and a related melt pool temperature T mp,s . 
         FIG. 18  is a diagram illustrating stability of a process at a wire feeding speed v w =10 mm/s. 
         FIG. 19  is a diagram illustrating the stability of the process at the wire feeding speed v w =20 mm/s. 
         FIG. 20  is a diagram illustrating an influence of the WIP on a sectional shape of a deposition layer at P s =1.1 kW. 
         FIG. 21  is a diagram illustrating the influence of the WIP on the sectional shape of the deposition layer at P s =1.8 kW. 
         FIG. 22  is a block diagram illustrating a configuration of a processing machine according to an embodiment. 
         FIG. 23  is a flowchart illustrating a step for specifying the initial power Po of laser beam. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention will be described with reference to the drawings. In the drawings referred to below, the same or corresponding member is denoted by the same reference numeral. 
     Investigation of Initial Transition Phase and Stability of Annular Laser Beam Direct Wire Deposition (ALB-DWD) 
     Setup and Workpiece Irradiation Proportion Parameter (WIP) of Annular Laser Beam Wire Deposition 
       FIG. 1  is a diagram illustrating a setup of the ALB-DWD. The setup for the ALB-DWD is schematically illustrated in  FIG. 1 . The setup includes an ALB-DWD head  20 , a wire feeding device  31 , a workpiece moving stage  51 , a process monitoring system  41  and a continuous 2.5-kW, 1080-nm-wavelength fiber laser source (not illustrated). 
     In ALB-DWD head  20 , collimated laser beam is transformed into an annular laser beam (ALB) by a beam forming unit  22 . The ALB is guided coaxially with an axis of a wire guide tube  27  by two reflection mirrors  23 ,  24  and focused on a workpiece surface by a focusing optical component  25 . A metal wire is axially fed to a center of the annular laser beam using wire feeding device  31  including a wire straightener  33 , a wire feeder  34 , and a wire guide tube  27 . 
     A co-axial gas nozzle  26  is used to convey Ar shielding gas in a melt pool and around a wire deposition zone on the surface of the workpiece clamped the workpiece moving stage (horizontal moving stage)  51 . 
     A workpiece standoff position (WSP) with respect to an ALB focal position is determined using a laser distance sensor  44 , the WSP being represented by h wp . A high-speed CMOS vision camera  43  and a two-color in-axis pyrometer  28  are used to perform visualization of a DWD process and monitoring of a melt pool temperature. An infrared camera (IR)  42  is used for an ALB profile and WIP characterization. 
       FIG. 2  is a diagram illustrating an ALB profile (caustic).  FIG. 3  is a diagram illustrating an initial wire end position (without wire) for WIP measurement and an initial process phase policy.  FIG. 4  is a diagram illustrating the initial wire end position (with wires) for the WIP measurement and the initial process phase policy. 
       FIGS. 5 and 6  are diagrams illustrating a laser pulse thermal footprint I and related I a  at h wp =4.5 mm.  FIGS. 7 and 8  are diagrams illustrating a laser pulse thermal footprint I wp  and related I a,wp  at h wp =4.5 mm and WIP=79%. 
       FIG. 2  illustrates an example of an experimentally obtained ALB profile above a focal position, the experimentally obtained ALB profile with convergence θ=15° and a wedge angle γ=1.7° is applied to a direct wire deposition (DWD) process. A dotted line and a two-dot chain line represent the boundaries of laser beam intensity I Ib  at an inside 1/e 2  and an outside D4σ. 
     The boundaries are estimated from laser pulse thermal footprint intensity on a thin graphite layer, and measured by an IR camera at different WSPs where the wire does not exist at a focal point of the ALB as illustrated in  FIG. 3 .  FIGS. 5 and 6  illustrate footprint intensity I measured at WSP hwp =4.5 mm and a related laser beam intensity profile 1 a (r) averaged along 360°. 
     As illustrated schematically in  FIG. 4 , when the wire exists, simultaneous irradiation and heating of the wire and the workpiece surface may be achieved in line symmetry. In general, a rate of irradiation of the workpiece and the wire depends on the ALB profile, the WSP, and the initial wire-end position indicated by h we  in  FIG. 2 . 
       FIGS. 7 and 8  illustrate an example of a distribution of the laser beam thermal footprint intensity I wp  and related laser beam intensity profile I a,wp  (r) averaged along 360°, which are measured at the WSP where a graphite-coated wire end exists at h wp =4.5 mm and h we =0.0 mm. By the simultaneous laser beam irradiation of the workpiece and wire end, lower intensity I wp  and lower energy input to the workpiece surface are achieved. 
     In order to characterize the power of the laser beam irradiation of the workpiece and the ratio of the related energy input, the WIP (Workpiece irradiation proportion parameter) is defined by the following equation (1). 
     
       
         
           
             
               
                 
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     At this point, P wp  and P represent the ratio of the laser beam power introduced onto the workpiece surface when the wire exists at the ALB focal point and when the wire does not exist at the ALB focal point. P wp  and P may be calculated by integration of T a,wp (r) and I a (r) as defined in the second term of equation (1). In this case, P wp  and P are estimated by summing pixel values of a related IR image of the laser pulse thermal footprint intensities I wp  and I. In this case, this gives WIP=79%. Based on the specified WIP, the ratio of the laser power P used for heating the wire end is defined as 1−WIP. 
     Initial Transition Phase and Process Stability 
       FIG. 9  is a diagram illustrating a molten bond formed between the workpiece surface and the wire.  FIG. 10  is a diagram illustrating wire collision.  FIG. 11  is a diagram illustrating a pendant droplet. 
     A laser DWD process is considered stable as long as a bond initially established between a melt pool and the fed wire end ( FIG. 9 ) persists along an entire deposition path. This is achieved by proper energy input in space and time, and requires precise time synchronization of time depending on laser beam power, wire feed and workpiece scan speed. 
     In general, process instability due to improper energy input causes either a non-molten wire end and a workpiece surface collision ( FIG. 10 ) or a pendent droplet ( FIG. 11 ), and both results in unsuccessful formation or destruction of the previously established molten bond. The latter is particularly important during the initial transition phase of the DWD process and is essential for further stability and steadiness of the process. 
       FIG. 12  is a graph illustrating a policy A of an initial phase of the ALB-DWD.  FIG. 13  is a graph illustrating a policy B of the initial phase of the ALB-DWD.  FIG. 14  is a graph illustrating a policy C of the initial phase of the ALB-DWD.  FIG. 15  is a table illustrating process parameters and characteristic time in policy A, policy B, and policy C. 
     The following three different initial phase policies take into account two possible initial wire end positions. Specifically, above the workpiece surface, h we &gt;0.0 mm, and on the workpiece surface, h we =0.0 mm are considered and compared. In the experiment, an SS316 wire having a diameter of 0.6 mm and an SS304 workpiece having a dimension of [w×1 ×h]=[25×60×10] mm are used. 
       FIGS. 12 to 14  illustrate preset laser beam power P (t), wire feeding speed v w (t), workpiece feeding speed v wp (t), and measured melt pool temperature T mp (t) for three proposed initial phase policies performed at WIP=92%. 
     The first two examples belong to two considered initial policies A and B with h we &gt;0.0 mm. The advantage of these two policies is that the melt pool can be generated without blocking the laser beam by the wire and reducing the power. 
     However, the laser beam reflected from the workpiece surface can then lead to uncontrollability of the irradiation of the wire end by the direct laser beam. An initial laser beam power P 0  that is too high or too low may result in either uncontrolled formation of the pendant droplet from the wire end or collision of the wire end and the workpiece surface. 
     In order to solve this problem, the initial wire end position should be above the position of the reflected laser beam focal point as illustrated in  FIG. 3 . In addition, in order to form the melt pool and the molten bond, policy A should use the lower laser beam power P 0  at a beginning of a longer period t mb  as illustrated in  FIG. 12 , or policy B should reduce the laser beam at the higher initial power P m  to P 0  at a time t mp  corresponding to a moment of the melt pool formation as illustrated in  FIG. 13 . 
     At time t mp , the wire feeding at the preset feeding speed v w  and the pre-heating of the wire end are taken place until t mb  when the molten bond is established between the wire end and the workpiece surface. At the time t mb  of the molten bond formation, the workpiece feeding starts at preset feeding speed v wp , and the laser beam power P is linearly increased to Ps within a time of Δt at the same time. 
     In this respect, high and sufficient energy input is achieved to maintain the established molten bond and ensure a smooth transition of the process to a steady phase. The latter is clear from a time course of temperature T mp  measured in the melt pool process, and both the cases settle to around T mp,s 1530° C. at time t s . 
     The values and the relationship of the process parameters P 0 , P m , P s , v w , v wp , the characteristic times t mp , t mb , and Δt t  are mutually dependent on each other, and are complex due to the fed wire end and the laser beam interacting with the workpiece surface. 
     In the considered example of  FIGS. 12 and 13 , for preset wire feeding speed v w =20 mm/s and workpiece feeding speed v wp =5 mm/s, the values of P 0 , P m , P s  and t mp , t mb , Δt t  are experimentally obtained by analysis of a record of a process visualization and given in  FIG. 15 . In policy B, the characteristic times t mp , t mb  and related t s  of the transition to the steady phase are shorter due to higher initial laser power P m =1.3 kW. 
     In order to overcome the above drawbacks related to the initial position of the wire end above the workpiece surface, initial phase policy C in which the wire end is placed on the workpiece surface is proposed as illustrated schematically in  FIG. 4 . In this case, both the workpiece surface and the wire end are simultaneously heated by the laser beam at power P 0  at the preset ratio defined by WIP=92% for the time interval (0, t mb ) required for the establishment of the molten bond. With respect to the previous two policies, in this case, the workpiece and the wire are simultaneously heated, whereby the melt pool and the molten bond are simultaneously generated during the time t mb  when the laser power P 0  is applied. 
     As illustrated in  FIG. 14 , after the moment t mb  of the establishment of the initial molten bond, the laser beam power P 0  is linearly increased to P s  and the wire feed is initiated to prevent interference with the molten bond due to the formation of the pendant droplet. Furthermore, in order to ensure the sufficient energy for the formation of the well-formed molten bond, the feeding of the workpiece is initiated with a slight delay during the linear increase of the laser beam power. This ensures the transition of the process to the steady phase. The significantly earlier transition from the time course of melt pool temperature T mp  to the steady process phase may be observed at time t s =0.80 s. 
       FIG. 16  is a graph illustrating dependence of initial laser beam power P 0  on the WIP.  FIG. 17  is a graph illustrating treatment time t s  and a related melt pool temperature T mp,s . 
     For the previous two policies, it is experimentally observed that in this case, the value of laser beam power P 0  depends only on the WIP, and that in the stable stationary phase, the laser beam power depends on feeding speeds v w  and v wp  in addition to WIP. 
     At different P 0  and P s , characteristic time t mb  and Δt t  are kept constant, and indicate high process robustness. The laser beam power P 0  in  FIG. 16  and the relationship between processing time t s  and related temperature T mp,s  and the WIP in  FIG. 17  are illustrated at P s =1.8 kW. It can be seen that the larger beam diameter and lower energy input to the wire end, together with the increasing WIP, increase non-linearly related laser beam power P 0  required to establish the molten bond at time t mb =0.3 s. Similarly, with increasing WIP, process time t s  increases non-linearly from 0.72 s to 1.33 s and related steady melt pool temperature T mp,s  increases linearly at intervals of 1490° C. to 1590° C. 
     Window of Process Stability 
       FIG. 18  is a graph illustrating the process stability at wire feeding speed v w =10 mm/s.  FIG. 19  is a graph illustrating the process stability at wire feeding speed v w =20 mm/s. 
     In the subsequent result of the stability analysis of the ALB-DWD process, the use of policy C, specifically, an initial position where the wire end is placed on the workpiece surface, and an emphasis on the influence of laser beam power Ps on the WIP and the steady process phase is put. For this purpose, a vast set of the experiment of single layer deposition of the SS304 workpiece having the 0.6-mm diameter on the SS316 wire is performed at different wire and workpiece feeding speeds while the WIP value is varied in the range of 40% to 100%. In the experiment in a specific W1P, the initial laser beam power P 0  between t mb =0.3 s is selected according to the graphs in  FIGS. 16 and 17 . 
     In  FIGS. 18 and 19 , a stability diagram of the ALB-DWD process in a P s -WIP plane is illustrated at wire feed v w =10 mm/s and 20 mm/s, and the insides of a dashed line and a two-dot chain line represent the stability region of the process. A black circle and a white square in the stability region represent the stable process at workpiece feeding speed v wp =5 and 10 mm/s. 
     From the stability diagram at wire feeding v w =10 mm/s, it can be seen that the lower-side stability boundary required for the stable process and the related minimum laser beam power P s,min (WIP), and the higher-side stability boundary, the related maximum laser beam power P s,max (WIP) increase non-linearly with increasing WIP. In this context, a laser beam power stability interval (P s,min , P s,max ) increases until WIP=96% after applied P s,max  reaches the laser-source maximum output power of 2.5 kW. 
     In addition to the stable region, non-stable regions of two qualitatively different DWD processes may be observed. At the lower WIP and laser beam power P s &gt;P s,max , the process becomes unstable due to excessively high energy input to the wire end, causing breakdown of the molten bond and the formation of the pendent droplet. 
     At the higher WIP value and lower laser beam power P s &lt;P s,min , the instability occurs due to too low energy input to the wire end, causing the collision of the wire and the workpiece. Furthermore, the stability region indicated by the white square decreases with increasing workpiece feeding speed to v wp =10 mm/s. Related minimum required laser beam power P s,min  increases and the width of maximum laser beam power P s,max  and a related stability interval (P s, min , P s,max ) decreases. 
     As illustrated in  FIG. 19 , the qualitative characteristic of the stability diagram is illustrated at higher wire feeding speed v w =20 mm/s. However, quantitatively, the process stability may be achieved even in the lower WIPs. Furthermore, minimum laser beam power P s,min  and maximum laser beam power P s,max , and the width of stability interval (P s,min , P s,max ) of the laser beam power increase. 
     In all considered and observed cases, the non-linear increase in P s,min  (WIP) may be related to the fact that with increasing WIP, a higher portion of the laser beam energy is introduced into the workpiece, and thus the higher laser beam power is required to achieve the required wire end melting for the establishment of the molten bond. Furthermore, the reduction of the observed stability region and related interval (P s,min , P s,max ) with increasing workpiece feeding speed v wp  can be explained by the fact that with increasing v wp , the higher laser beam power P s,min  is required for the formation of the melt pool. 
     On the other hand, the observed decrease in P s,max  is probably related to the additional heating of the wire by the laser beam reflected from the generated melt pool, resulting in the process instability due to the formation of the pendent droplet at lower P s . 
       FIG. 20  is a diagram illustrating an influence of the WIP on a sectional shape of a deposition layer at P s =1.1 kW.  FIG. 21  is a diagram illustrating the influence of the WIP on the sectional shape of the deposition layer at P s =1.8 kW. 
     In order to indicate the influence of a geometric characteristic of the deposition layer and dilution of WIP, a selected example of a layer section is illustrated in  FIG. 20  using wire feeding speed v w =20 mm/s, workpiece feeding speed v wp =5 mm/s, laser beam power P s =1.1 kW, WIP=66, 74, and 87%.  FIG. 21  illustrates a selected example of the layer cross section with wire feeding speed v w =20 mm/s, workpiece feeding speed v wp =5 mm/s, laser beam power P s =1.8 kW, WIP=74, 92, and 100%. 
     Results and Discussion 
     Focusing on the initial transition phase of the process, the stability of the annular laser beam direct wire deposition (ALB-DWD) process is considered. The three different initial phase policies are investigated with respect to the initial wire end position, namely, above or on the workpiece surface. The experiment related to the single layer deposition of 0.6 mm diameter SS316 wire on SS304 workpiece were characterized by the melt pool temperature and the process visualization. 
     The results generally indicates that regardless of the initial policy used for the ALB-DWD process, the reason for the stability of the process is inadequate energy input into the workpiece and wire, whereby the collision of the wire end and the workpiece, or the destruction of the established molten bond and the formation of the pendent droplet in the wire end are caused. Using the initial policy in which the initial wire end position is set to the workpiece surface, the workpiece surface can be simultaneously heated with a reset ratio defined by the workpiece-wire irradiation ratio (WIP) as well as the workpiece and the wire. In this policy, an earliest and reliable transition to the stable steady phase of the process may be achieved. 
     In addition, the results of the process stability and the sectional analysis of the deposition layers indicate that, in addition to the general process parameters, the WIP significantly affects the process stability and its robustness as well as the geometric characteristic, mainly the dilution of the deposition layer. 
     Description of Configuration and Operation and Effect of Processing Machine in Embodiment 
     Hereinafter, the configuration of the processing machine according to the present embodiment based on the contents of the above examination and the effects thereof will be described. 
       FIG. 22  is a block diagram illustrating the configuration of the processing machine of the embodiment. Referring to  FIGS. 1 and 22 , a processing machine  10  of the embodiment is a processing machine capable of performing additive manufacturing (AM) of the workpiece. The additive manufacturing is a machining method for producing a three-dimensional shape on a workpiece by attaching a material, and a mass of the workpiece increases before and after the additive manufacturing. 
     Processing machine  10  is a numerically control (NC) processing machine in which various operations for workpiece processing are automated by numerical control of a computer. 
     Processing machine  10  may be an AM/SM hybrid processing machine capable of performing additive manufacturing of the workpiece and subtractive manufacturing (SM) of the workpiece, or may be a processing machine capable of performing only the additive manufacturing of the workpiece. 
     Processing machine  10  performs the additive manufacturing of a workpiece WP by the ALB-DWD (Annular laser beam direct wire deposition) process using an ALB-DWD head  20 . 
     Processing machine  10  includes a laser irradiation device  21  and wire feeding device  31 . Laser irradiation device  21  irradiates workpiece WP with an annular laser beam L. Wire feeding device  31  feeds a wire W from the inside of annular laser beam L emitted from laser irradiation device  21  toward workpiece WP. 
     Laser irradiation device  21  includes a laser beam source (not illustrated), beam forming unit  22 , reflection mirrors  23 ,  24 , and focusing optical component  25 . 
     The laser beam source is provided separately from ALB-DWD head  20 . The laser beam source oscillates the laser beam used for the additive manufacturing. The laser beam source oscillates the laser beam with predetermined power (kw) based on a command from a control device  61  (described later). The laser beam oscillated by the laser beam source is guided to ALB-DWD head  20  through an optical fiber (not illustrated). 
     The laser beam made of parallel light along a center axis  101  is input to beam forming unit  22 . Beam forming unit  22  forms the input laser beam into an annular shape (ring shape). For example, beam forming unit  22  includes a pair of axicon lenses disposed to face each other in an axial direction of center axis  101  and a convex lens disposed between the pair of axicon lenses. 
     The laser beam output from beam forming unit  22  has the annular shape, namely, a shape that circulates in an annular shape around center axis  101  when the laser beam is cut by a plane orthogonal to a traveling direction of the laser beam. The laser beam output from beam forming unit  22  has a circular ring shape centered on center axis  101 . 
     Reflection mirror  23  and reflection mirror  24  are arranged in this order from an upstream side to a downstream side in the traveling direction of the laser beam in ALB-DWD head  20 . Reflection mirror  23  is provided on the axis of center axis  101 . Reflection mirror  23  is inclined by 45° with respect to center axis  101 . Reflection mirror  24  is provided on an axis of a center axis  102  parallel to center axis  101 . Reflection mirror  24  is inclined by 45° with respect to center axis  102 . 
     Reflection mirror  23  reflects the annular laser beam output from beam forming unit  22 , thereby directing the annular laser beam toward reflection mirror  24 . Reflection mirror  24  reflects the annular laser beam from reflection mirror  23 , thereby directing the annular laser beam toward optical component  25 . The annular laser beam traveling from reflection mirror  23  toward optical component  25  travels in an axial direction of center axis  102  around center axis  102 . 
     Optical component  25  includes at least one condenser lens. Optical component  25  emits the annular laser beam toward workpiece WP while condensing the annular laser beam. An annular laser beam L emitted from optical component  25  travels in the axial direction of center axis  102  around center axis  102 , and the surface of workpiece WP is irradiated with the annular laser beam L. 
     Wire feeding device (wire feeding unit)  31  includes a spool  32 , a wire straightener  33 , a wire feeder  34 , and a wire guide tube  27 . 
     Spool  32  is formed of a cylindrical body. Wire W serving as a material for additive manufacturing is wound around spool  32 . Wire straightener  33  includes a plurality of rotation rollers linearly arranged on both sides of wire W. When wire W drawn out from spool  32  passes through wire straightener  33 , waviness of wire W is eliminated. 
     Wire feeder  34  is provided between wire straightener  33  and wire guide tube  27  in a feeding direction of wire W. Wire feeder  34  includes drive rollers disposed on both sides of wire W. Wire feeder  34  feeds wire W toward workpiece WP when the drive rollers are rotationally driven. Wire feeder  34  feeds wire W at a predetermined feeding speed based on a command from control device  61  (described later). 
     Wire guide tube  27  has a tubular shape. Wire guide tube  27  extends linearly on the axis of center axis  102 . Wire guide tube  27  penetrates reflection mirror  24  and various lenses in optical component  25 , and extends toward the surface of workpiece WP. Wire W is inserted into wire guide tube  27 , thereby being guided from wire feeder  34  toward workpiece WP. 
     A tip of wire guide tube  27  is disposed inside annular laser beam L emitted from optical component  25  to workpiece WP. 
     Wire W from wire guide tube  27  goes to workpiece WP through the inside of annular laser beam L emitted from optical component  25  to workpiece WP. Wire W from wire guide tube  27  passes on the axis of the center axis  102 , and goes to workpiece WP. The feeding of wire W toward workpiece WP and the irradiation of annular laser beam L toward workpiece WP are in a coaxial relationship. 
     Processing machine  10  further includes a gas nozzle  26 . Gas nozzle  26  extends in a tubular shape from optical component  25  toward workpiece WP. Gas nozzle  26  has a tapered cylindrical shape in which a diameter decreases toward workpiece WP. Gas nozzle  26  is provided so as to surround wire W sent toward workpiece WP and annular laser beam L emitted toward workpiece WP around the axis of center axis  102 . An inert gas G such as an Ar gas injected from gas nozzle  26  blocks between a machining point of the additive manufacturing in workpiece WP and an external atmosphere. 
     Processing machine  10  includes a workpiece moving stage  51 . Workpiece moving stage  51  is provided as a moving mechanism unit that moves workpiece WP with respect to laser irradiation device  21 . 
     Workpiece moving stage  51  includes a clamp  53 . Clamp  53  has a claw portion, and is configured to be able to clamp workpiece WP by the claw portion. Workpiece moving stage  51  slides workpiece WP clamped by clamp  53  in a horizontal plane by various feeding mechanisms, guide mechanisms, servomotors, and the like. Workpiece moving stage  51  slides workpiece WP in a plane orthogonal to center axis  102 . 
     Workpiece moving stage  51  moves workpiece WP at a predetermined feeding speed based on a command from control device  61  (described later). 
     The moving mechanism that moves laser irradiation device  21  and workpiece WP relative to each other is not limited to the above configuration. For example, ALB-DWD head  20  on which laser irradiation device  21  is mounted may be spatially moved with respect to workpiece WP, or a combination of workpiece moving stage  51  and the configuration for moving spatially ALB-DWD head  20  may be used. The direction (in the embodiment, a horizontal direction) in which laser irradiation device  21  and workpiece WP move relative to each other and the irradiation direction (in the embodiment, a vertical direction) of the annular laser beam from laser irradiation device  21  to workpiece WP have an orthogonal relationship. The direction (in the embodiment, the horizontal direction) in which laser irradiation device  21  and workpiece WP move relative to each other and the feeding direction (in the embodiment, the vertical direction) of wire W from wire feeding device  31  to workpiece WP have an orthogonal relationship. 
     Processing machine  10  further includes infrared camera  42 . Infrared camera  42  observes the surface of workpiece WP. Infrared camera  42  visualizes infrared rays radiated from the workpiece WP with irradiation of the annular laser beam toward the workpiece WP as an infrared image. 
     Processing machine  10  further includes control device  61  that controls processing machine  10 . More specifically, control device  61  controls the laser beam source in the laser irradiation device  21 , the wire feeder  34  in the wire feeding device  31 , the infrared camera  42 , and the workpiece moving stage  51 . 
     Referring to  FIGS. 4, 14, and 22 , in the embodiment, control device  61  executes the ALB-DWD process according to policy C. 
     Control device  61  controls the wire feeding device  31  so that the wire end abuts on the surface of workpiece WP at a beginning of the additive manufacturing. At the beginning of the additive manufacturing, control device  61  determines initial power P 0  of the laser beam based on the WIP (Workpiece irradiation proportion parameter) and controls laser irradiation device  21  to irradiate workpiece WP with the laser beam at initial power P 0 . 
     Control device  61  includes a storage  72 , a controller  71 , and a communicator  73 . Storage  72  stores data related to the relationship between the WIP and initial power P 0  of the laser beam to be set. Controller  71  determines initial power P 0  of the laser beam by comparing the WIP at the beginning of the additive manufacturing to the data stored in storage  72 . Communicator  73  communicates initial power P 0  of the laser beam determined by controller  71  to laser irradiation device  21 . 
     As described above, when the wire end is brought into contact with the workpiece surface at the beginning of the additive manufacturing, the value of the laser beam power P 0  depends only on the WIP. Based on such finding,  FIG. 16  illustrates, as an example of data stored in storage  72 , a relationship between the WIP and the range of the initial power P 0  of the laser beam (the range of a hatched region between the dashed line and the two-dot chain line in the vertical axis direction) in which the initial phase of the ALB-DWD process is stably executed. 
     Referring to  FIG. 16 , when the initial power P 0  of the laser beam is in the range above the dashed line, the energy input to the workpiece is too large, so that the pendant droplet is formed as illustrated in  FIG. 11 . When the initial power P 0  of the laser beam is in the range below the two-dot chain line, the energy input to the workpiece is too small, so that the collision between the wire end and the workpiece surface occurs as illustrated in  FIG. 10 . 
     When the initial power Po of the laser beam is set to the range between the dashed line and the two-dot chain line, as illustrated in  FIG. 9 , the molten bond in an appropriate form can be formed between the workpiece surface and the wire end. 
     The case where the value of the WIP is large corresponds to the case where the value of h wp  in  FIG. 2  is large (the case where the workpiece surface is far from the focal position of the laser beam). As the diameter (beam diameter) of the irradiation region of the laser beam on the workpiece surface increases, the ratio of the energy input to the wire decreases, and the ratio of the energy input to the workpiece increases. In this case, the laser beam irradiation with the larger energy is required in forming the molten bond in the appropriate form between the workpiece surface and the wire end at the beginning of the additive manufacturing. 
     On the other hand, the case where the value of the WIP is small corresponds to the case where the value of h wp  in  FIG. 2  is small (the case where the distance from the focal position of the laser beam to the workpiece surface is close). As the diameter (beam diameter) of the irradiation region of the laser beam on the workpiece surface decreases, the ratio of the energy input to the wire increases, and the ratio of the energy input to the workpiece decreases. In this case, the laser beam irradiation with the smaller energy is required in forming the molten bond in the appropriate form between the workpiece surface and the wire end at the beginning of the additive manufacturing. 
       FIG. 23  is a flowchart illustrating a step for specifying initial laser beam power P 0 . 
     Referring to  FIGS. 22 and 23 , control device  61  controls wire feeding device  31  so that the wire end is positioned while retracted from the workpiece surface (S 101 ). The state in which the wire does not exist in the irradiation region of the laser beam is obtained by this step. 
     Then, control device  61  controls laser irradiation device  21  so that the workpiece is irradiated with the annular laser beam. Control device  61  controls infrared camera  42  so that the workpiece surface irradiated with the annular laser beam is imaged (S 102 ). 
     An infrared image on the workpiece surface in the state where the wire does not exist in the irradiation region of the laser beam is obtained by this step. Data of the obtained infrared image is transmitted to communicator  73  in control device  61 . 
     Then, control device  61  controls wire feeding device  31  so that the wire end abuts on the workpiece surface (S 103 ) The state in which the wire exists in the irradiation region of the laser beam is obtained by this step. 
     Then, control device  61  controls laser irradiation device  21  so that the workpiece is irradiated with the annular laser beam. Control device  61  controls infrared camera  42  so that the workpiece surface irradiated with the annular laser beam is imaged (S 104 ). 
     The infrared image on the workpiece surface in the state where the wire exists in the irradiation region of the laser beam is obtained by this step. Data of the obtained infrared image is transmitted to communicator  73  in control device  61 . 
     Then, control device  61  specifies the WIP (S 105 ) Specifically, control device  61  estimates laser beam power P introduced onto the workpiece surface when the wire does not exist in the irradiation region of the laser beam from the pixel value of the infrared image obtained in step S 102 . Control device  61  estimates laser beam power P wp  introduced onto the workpiece surface when the wire exists in the irradiation region of the laser beam from the pixel value of the infrared image obtained in step S 104 . Control device  61  calculates the WIP (=P wp /P) using the estimated values of laser beam power P and laser beam power Pw p . 
     In the embodiment, the case where the value of the WIP is specified based on the pixel value of the infrared image on the workpiece surface is described, but the present invention is not limited thereto. For example, the value of the WIP may be theoretically calculated using equation (1) in the item of [Investigation of Initial Transition Phase and Stability of ALB-DWD] described above. 
     Then, control device  61  determines initial output P 0  of the laser beam based on the value of the WIP specified in the previous step (S 106 ). In this step, controller  71  in control device  61  determines initial power P 0  of the laser beam by comparing the WIP specified in the previous step to the data stored in storage  72 . 
     Then, control device  61  controls laser irradiation device  21  so as to start the additive manufacturing with initial output P 0  of the laser beam determined in the previous step (S 107 ). Consequently, workpiece WP is irradiated with the annular laser beam at initial power P 0  while the wire end abut on the surface of workpiece WP, and the additive manufacturing is started. 
     In the embodiment, initial power P 0  of the laser beam is determined based on the WIP at the beginning of the additive manufacturing, whereby the molten bond in the appropriate form can be formed between the workpiece surface and the wire end. In addition, the workpiece and the wire are simultaneously heated by the laser beam by bringing the wire end into contact with the workpiece surface at the beginning of the additive manufacturing. Because of this, the melt pool on the workpiece surface and the molten bond between the workpiece surface and the wire end can be generated in a short time. For these reasons, the stability of the ALB-DWD process can be enhanced in the initial phase at the beginning of the additive manufacturing. 
     After S 107 , control device  61  controls laser irradiation device  21 , wire feeding device  31 , and workpiece moving stage  51  so that the ALB-DWD process is performed according to the condition (laser beam power, wire feeding speed, and workpiece feeding speed) of policy C in  FIG. 14 . 
     Specifically, control device  61  controls laser irradiation device  21  so that the power of the laser beam increases to power P S  larger than initial power P 0  after the laser beam irradiation is continued with initial power P 0  for a certain period of time. Control device  61  controls wire feeding device  31  so that starts the feeding of the wire toward the workpiece at the same time when the power of the laser beam starts the increase from initial power P 0 . Control device  61  controls workpiece moving stage  51  so that the workpiece starts to move while the power of the laser beam increases from initial power P 0  to power P S . 
     According to such a configuration, the ALB-DWD process can be stably transitioned from the initial phase at the beginning of the additive manufacturing to the steady phase in which the additive manufacturing is continuously performed to the workpiece. 
     The values of the laser beam power, the wire feeding speed, and the workpiece feeding speed in  FIG. 14  are merely examples, and are not particularly limited in the present invention. 
     It should be considered that the disclosed embodiment is an example in all respects and not restrictive. The scope of the present invention is defined by not the description above, but the claims, and it is intended that all modifications within the meaning and scope of the claims and their equivalents are included in the present invention. 
     INDUSTRIAL APPLICABILITY 
     The present invention is applied to a processing machine capable of performing additive manufacturing. 
     REFERENCE SIGNS LIST 
       10 : processing machine,  20 : ALB-DWD head,  21 : laser irradiation device,  22 : beam forming unit,  23 ,  24 : reflection mirror,  25 : optical component,  26 : gas nozzle,  27 : wire guide tube,  28 : two-color in-axis pyrometer,  31 : wire feeding device,  32 : spool,  33 : wire straightener,  34 : wire feeder,  41 : process monitoring system,  42 : infrared camera,  43 : vision camera,  44 : laser distance sensor,  51 : workpiece moving stage,  53 : clamp,  61 : control device,  71 : controller,  72 : storage,  73 : communicator,  101 ,  102 : center axis