Abstract:
A laser cladding device for applying a coating to a part comprising a laser which can generate laser light, which is adapted to heat the coating and the part, a main body defining a laser light channel adapted to transmit the laser light to the part, a coating channel adapted to transmit the coating to the part, and a vacuum channel and a nozzle having an exit. The nozzle comprises a delivery port at one end of the laser light channel, a coating port at one end of the coating channel, and a vacuum port at one end of the vacuum channel, wherein the vacuum port is positioned generally adjacent the delivery port In operation the vacuum port draws a vacuum, pulling the coating towards the part.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. Pat. application No. 12/249,009 entitled “Laser Cladding Device With An Improved Nozzle” and filed on 10 Oct. 2008, now issued as U.S. Pat. No. 8,117,985, which claims priority benefit of U.S. Provisional Patent application No. 60/998,188 filed on Oct. 10, 2007. The entire disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present invention relates to the field of laser cladding, and more particularly to a laser cladding device having an improved nozzle. 
     BACKGROUND 
     Laser cladding by powder metal injection is used in manufacturing, component repair, rapid prototyping and coating. A laser beam travels down a passage to exit out a port in focused alignment with a flow of powdered metal, typically a conical flow around the laser. The laser melts both a thin layer of a surface of a part and the metal powder introduced to the surface, allowing the molten powdered metal to fuse with the surface of the part. This technique is well known for producing parts with enhanced metallurgical qualities such as a superior coating with reduced distortion and enhanced surface quality. Layers of various thicknesses can be formed on the part using laser cladding with the general range being 0.1 to 2.0 mm in a single pass. 
     Known nozzles for laser cladding have various levels of complexity. A common type is based on a concentric design with the laser beam passing through the center of the nozzle. Surrounding the central laser beam are concentric ports that may be formed as an annulus or continuous ring, segments of rings, or holes which deliver an inert shield inert gas, the powdered metal carried by an inert gas, and in some cases an outer shaping gas. However, such known nozzles for laser cladding assemblies are limited in that the majority of the gas flow is deflected away from the laser weld zone. Therefore a significant amount of the powdered metal directed at the weld zone actually escapes the process altogether. It would be desirable to provide a laser cladding device where the amount of powdered metal delivered to the laser welding zone and therefore to the part is increased. 
     SUMMARY 
     In accordance with a first aspect, a laser cladding device for applying a coating to a part comprises a laser which can generate laser light, which is adapted to heat the coating and the part, a main body defining a laser light channel adapted to transmit the laser light to the part, a coating channel adapted to transmit the coating to the part, and a vacuum channel and a nozzle having an exit. The nozzle comprises a delivery port at one end of the laser light channel, a coating port at one end of the coating channel, and a vacuum port at one end of the vacuum channel, wherein the vacuum port is positioned generally adjacent the delivery port. In operation the vacuum port draws a vacuum, pulling the coating towards the part. 
     From the foregoing disclosure and the following more detailed description of various preferred embodiments it will be apparent to those skilled in the art that the present invention provides a significant advance in the technology of laser cladding devices. Particularly significant in this regard is the potential the invention affords for providing a high quality, low cost laser cladding device with greatly increased powder catchment. Additional features and advantages of various preferred embodiments will be better understood in view of the detailed description provided below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a laser cladding device in accordance with a preferred embodiment, showing a manipulator arm, a main body and a nozzle. 
         FIG. 2  is a cross section view of the nozzle of  FIG. 1 . 
         FIG. 3  is a cross section view of the nozzle of  FIG. 1  shown with the flow of gases and powdered metal coating shown pulled toward the vacuum port. 
         FIG. 4  is a schematic block diagram of a preferred embodiment of a control system for the laser cladding device. 
         FIG. 5  is an alternate preferred embodiment of a nozzle of a laser cladding device, showing a vacuum port provided with side ports. 
         FIG. 6  is a cross section view of the nozzle of  FIG. 5  shown with the flow of inert gas and powdered metal shown pulled toward the vacuum port. 
         FIG. 7  is another alternate preferred embodiment of a laser cladding device, shown with an adjustably mounted lens. 
         FIG. 8  is a schematic diagram of a preferred embodiment of a controller for the laser cladding device of  FIG. 7 . 
         FIG. 9  is an end view of the laser cladding device showing the ports. 
         FIG. 10  is a schematic diagram of a zoom lens assembly according to some embodiments of the present disclosure. 
     
    
    
     It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the laser cladding device, as disclosed here, including, for example, the specific dimensions of the vacuum port, will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to improve visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity of illustration. All references to direction and position, unless otherwise indicated, refer to the orientation illustrated in the drawings. 
     DETAILED DESCRIPTION 
     It will be apparent to those skilled in the art, that is, to those who have knowledge or experience in this area of technology, that many uses and design variations are possible for the laser cladding device disclosed here. The following detailed discussion of various alternative and preferred features and embodiments will illustrate the general principles of the invention with reference to a laser cladding device suitable for use in the manufacture of metal parts with enhanced metallurgical properties. Other embodiments suitable for other applications will be apparent to those skilled in the art given the benefit of this disclosure. 
     Turning now to the drawings,  FIG. 1  shows a portion of a laser cladding device  10  in accordance with a preferred embodiment. The device is adjustably mounted via manipulator arm  22  connected to main body  30 . A nozzle  20  is attached to the main body. The nozzle  20  and main body  30  are preferably formed as separate components, but could be formed of a one piece or unitary construction. Laser light, such as laser beam light from a fiber laser, along with a coating such as a powdered metal are introduced to a part at a work zone adjacent the nozzle.  FIG. 2  shows a cross section view of a preferred embodiment of the nozzle  20 . The body  30  of the laser cladding device  10  provides mounting for the nozzle  20  and all of the other nozzle components. The laser beam, not shown, passes along a central axis of the laser cladding device  10  through a laser light channel  118 , entering a delivery chamber  115  formed in the nozzle  20 . As seen in  FIG. 2 , laser light travels from above and can be focused by lens  26  at a point below and outside an end or exit  99  of the nozzle  20 , i.e., at a part in a work zone. 
     After the laser beam passes through the lens  26  the light can pass through an optional window  28  in the channel  118 . The window may be mounted and located by a spacer ring  112  on the main body as shown in  FIG. 2 . The laser beam then passes into the delivery chamber  115 , formed in the nozzle. The delivery chamber  115  may have, for example, a generally circular cross section. Further, an inert gas, not shown may pressurize the delivery chamber  115 . This shield gas aids in preventing the accumulation of smoke, powdered metal, and work zone splatter on the window  28 , or when the window is not present, on the lens  26 . The spacer ring  112  may be adjustable. The lens  26  and window  28  may be optionally adjustable as well. 
     At the end or exit  99  of the nozzle a series of materials are introduced. From the center delivery chamber  115 , the laser light and a shield gas exits a delivery port  15  at the end  99 . In accordance with a highly advantageous feature, a vacuum port  14  is provided generally adjacent the delivery port  15 . In operation a vacuum or reduced pressure is drawn at the vacuum port  14 . In effect, other materials are pulled toward the vacuum port  14 . The use of a negative pressure or vacuum zone near the central area of the laser cladding nozzle, i.e., near the delivery port  15 , serves to remove some of the inert gas being used to deliver the powdered metal coating and some of the gas which provides the shaping gas flow. The net effect of this negative pressure or vacuum zone is to pull the gas flows towards the central axis of the laser cladding nozzle so that more material arrives at the work zone. This advantageously results in the deposition of more powdered metal in the work zone and less of the powdered metal escaping the work zone. 
       FIG. 2  shows the vacuum port  14  connected to a vacuum channel  109 . There may be one or more vacuum channels  109 , depending in part upon the anticipated flow of gas and material. Also shown is coating port  12  connected to a coating channel  110 , and an optional shaping gas port  16  connected to a shaping gas channel  111 . As shown in  FIG. 2 , each port has a generally conical shape. The ports are preferably manufactured from materials that can accommodate high temperatures, such as ceramics, tungsten, titanium, chromalloy, etc. There is no need for them all to be manufactured from the same materials; however, it is expected that the innermost conical shapes are going to be exposed to the highest temperatures as a result of the flow of material and gases. It will be readily apparent to those skilled in the art, given the benefit of this disclosure, that the relative lengths of the ports are for illustrative purposes only and may be adjusted depending upon a given application. As another example, a length of the shaping gas port  16  can exceed a length of the coating port  12 . Also, a length of the coating port  12  can exceed a length of the vacuum port  14 , and a length of the vacuum port  14  can exceed a length of the delivery port  15  for the laser light. Each port can advantageously form at least part of a ring or annulus around an adjacent port. In the preferred embodiment shown in  FIG. 2 , the delivery port  15  is in the center, and the vacuum port  14  is immediately adjacent the delivery port, that is, they share a common wall over at least a portion of their length near the end  99 . Most preferably the vacuum port circumferentially surrounds the delivery port  15 . The coating port  12  is positioned adjacent the vacuum port  14 , and the optional gas shaping port  16  is the outermost annulus.  FIG. 9  is an end view showing concentric ports  16 ,  12 ,  14  positioned around a delivery port  15  for the laser light. 
     The laser cladding device  10  comprises several components arranged in such a way as to provide flow paths to draw a vacuum, a flow path for an inert gas plus powdered metal or other suitable coating, and a flow path for an optional shaping gas flow. Most preferably the geometry of the laser cladding nozzle&#39;s construction is such that the convergence point of all of the gas flows is approximately coincident with a laser focal point. The coating port  12  delivers a coating material to the part to be subjected to the laser cladding process. Typically the coating port delivers a coating material in the form of a powdered metal in combination with an inert gas which urges the powdered metal towards the part. The inert gases used in the laser cladding process can be helium, argon, etc., each of which provides various advantages based on their physical properties, such as, specific heat, density, etc. 
     An optional chamber  106  in the vacuum port  14  may provide an accumulation volume between the vacuum port and the vacuum channel  109 . There may be one or more vacuum channel to vacuum port connections depending upon the anticipated flow of inert gas and powdered metal. Optional chamber  107  in the coating port can provide an accumulation volume between the inert gas and powdered metal connection channel  110  and coating port  12 . There may be one or more inert gas and powdered metal piping connections depending upon the anticipated flow of inert gas and powdered metal. Optional chamber  108  in the shaping gas port  16  aligns with the shaping gas channel  111  providing an accumulation volume between the shaping gas channel  111  and the shaping gas port  16 . There may be one or more shaping gas piping connections depending upon the anticipated flow of shaping gas. 
       FIG. 3  shows an approximate flow of gases and coating materials in response to the vacuum pulled by the vacuum port  14 . Arrow  404  corresponds to the direction of laser light, heading parallel to central axis  402 , to part  401  in the work zone. The inert gas flows out of and into the laser cladding nozzle  20  are shown with moderate levels of vacuum applied. Only the gas flows to one side of the laser cladding nozzle centerline,  402 , are shown for clarity. The influence of the surface of the part  401  that is being laser clad is to ultimately force all of the exiting inert gas flows,  404 ,  406 , and  407  outward in a radial direction away from the nozzle centerline,  402  after they impinge onto the surface of part  401 . The influence of a moderate vacuum induces a flow  403  of inert gases and solids (from the coating port  12 ) into the laser cladding nozzle vacuum port  14 . In the cases where there is an inert gas flow into the interior zone of the laser cladding nozzle vacuum port then some of that inert gas will flow (in the direction of arrow  404 ) out of the interior zone and towards the surface of the part  401  being clad while another portion of that gas will flow (in the direction of arrow  405 ) into the vacuum port  14  to form part of the vacuum channel flow  403 . The majority of the inert gas and powdered metal flow  406  exiting from the coating port  12  travels towards the surface of part  401 . However some of the flow  408  is pulled towards the nozzle centerline  402  and enters the vacuum port  14  to make up part of the flow  403 . The net effect of the diversion of flow of the inert gas and powdered metal  406  by the flow  408  created by the vacuum channel flow  403  is to keep more of the powdered metal near the centerline  402  of the laser cladding nozzle, and thereby improve metal cladding efficiency. The inert shaping gas flow  407  out of the shaping gas port  16  is also influenced by the flow of gases  403  into the vacuum port  14 . While some of the shaping gas flow is still diverted (in the direction of arrow  409 ) away from the nozzle centerline  402 , some flows in the direction of arrow  410  and provides additional radial pressure on the inert gas and powdered metal flow  406 , thereby providing additional impetus for the powdered metal to stay in the proximity of the nozzle centerline,  402 . 
     As noted above, some of inert gas flow being delivered by the nozzle will be drawn into the reduced pressure or vacuum zone or opening near the center of the laser cladding nozzle. The amount of inert gas drawn in will depend on three factors, the size of the opening, the shape and location of the opening, and the magnitude of the negative pressure being applied. Based on the values of the above three factors, it is possible to foresee the case where the majority of the inert gas being delivered by the nozzle can be drawn into the negative pressure or vacuum opening in the nozzle. In fact if all of the values are arranged properly it would also be possible to recapture the majority of the powdered metal being delivered by the nozzle. This ability to either recapture or control the amount of powdered metal would allow for a quick and easily controllable means to reduce or cut off the flow of powdered metal as required during the laser cladding process. Such a reduction or complete cut off of powdered metal flow could be advantageous during a laser cladding process that is under automatic computer control, allowing reduction in metal deposition during directional changes or reversal of the path that the laser cladding nozzle is traversing. 
       FIG. 4  shows a schematic block diagram of the overall device controller and related components required for using the laser cladding device  10 . Overall system control is provided by the master control computer  327  which provides coordination information to and receives data from the control elements in the system; namely, the robot controller,  328 , the laser power controller,  329 , the shaping gas flow control valve,  303 , the powdered metal mixing system,  308 , the inert gas control valve for the powdered mixing unit,  313 , the vacuum flow control valve,  316 , the weld zone vision control system,  330 , and the optional interior of the nozzle inert gas control valve,  325 . There may of course be many other secondary control sensors that supply information on various aspects of the laser cladding system&#39;s operation to the master control computer,  327 ; their omission from  FIG. 4  is done for the sake of simplicity only. 
     During operation, the laser cladding nozzle  20  is moved over the surface of the part being clad  401  through the use of a robot manipulator  305  under the control of the robot controller  328  as directed by the master control computer  327 . Simultaneous with the movement of the laser cladding nozzle  20  over the surface of the part  401  being clad, the laser, not shown, is focused by the laser cladding nozzle optics onto the surface of part  401 . At the same time the laser controller  329  controls the power output of the laser as directed by the master control computer  327 . Also at the same time, all under the control of the master control computer  327 : 1) the flow of the inert shaping gas from supply tank # 1 ,  302  is controlled by flow control valve  303 ; 2) the flow of inert gas from supply tank # 2 ,  311  is metered into the powdered metal mixing system  308  by the gas flow control valve  313 , while powdered metal is drawn from the powdered metal supply tank  310  before the combined inert gas and powdered metal is delivered to the laser cladding nozzle port  14 ; 3) the vacuum control valve  316  is used to control the level of vacuum present at the laser cladding nozzle port  14 , the inert gases and solids collected by the nozzle are passed through the solids precipitation unit  318  and the solids are sent to the powdered metal recovery unit  322  while the inert gases are sent to the inert gas recovery unit  320  which also supplies the vacuum; and 4) optionally, the delivery of inert gas from inert gas tank # 3 ,  326  to the delivery chamber  115  of the laser cladding nozzle channel is controlled by flow control valve  325 . A weld or work zone vision control system  330  observes the weld zone and provides control information to the master control computer  327  based on the quality of the cladding being applied. The weld zone vision control system  330  can be fixed in place, mounted on the robot manipulator  305  or mounted on a separate robot manipulator, dependent upon the size and complexity of the surface  401  being laser clad. 
       FIG. 5  shows an alternate preferred embodiment where the vacuum port  214  is curved and provided with a series of side ports  603  connecting to the coating port  212 . Negative pressure or vacuum acts to pull the inert gas jet that is carrying the powdered metal along a curving surface built into the inner wall of the vacuum port. This will impart a velocity towards the central axis of the laser nozzle of the gas jet and the powdered metal that it is carrying. Such a configuration can place more of the powdered metal in the work zone. The side ports may be drilled into a wall connecting between the vacuum port and the coating port. As shown in  FIG. 5 , more than one side port  603  may be provided. Optionally the side ports  603  may be of varying sizes. As shown in  FIG. 5 , the side port  603  closest to the exit  99  is larger than the side port  603  most remote from the exit  99 . The sizes may be sequentially larger as the side ports  603  approach the exit, as shown. The holes or side ports  603  through the outer wall can be drilled using a high powered laser. 
     With reference to  FIG. 6 , the inert gas flows out of and into the laser cladding nozzle of the embodiment of  FIG. 5  are shown with high levels of vacuum applied. Only the gas flows to one side of the laser cladding nozzle centerline  402  are shown for clarity. The influence of the surface of the part  401  that is being laser clad is to ultimately force all of the exiting inert gas flows,  404 ,  406 , and  407  outward in a radial direction away from the nozzle centerline  402  after they impinge onto the surface of the part  401 . The influence of a high vacuum induces a flow  403  of inert gases and solids into the laser cladding nozzle vacuum port  214 . In the cases where there is an inert gas flow into the delivery chamber  115  of the nozzle delivery port  15  then most of the inert gas will flow out of the delivery chamber  115  into the vacuum port  214  to form part of the vacuum channel flow  403 . Most of the inert gas and powdered metal flow  406  exiting from the coating port  212  travels in several reverse flow paths  502  towards the nozzle centerline  402  and enter the vacuum port to make up part of the flow  403 . Therefore essentially none of the powdered metal being carried in the flow  406  exiting the inert coating port  212  will reach the surface of the part  401  being clad. While some of the shaping gas flow  407  is still diverted away from the nozzle centerline  402  as shown by gas flows  504  some of it as shown by gas flows  503  provide additional radial and vertical pressure on the inert gas and powdered metal flow  406  thereby providing additional impetus for the powdered metal to enter the vacuum port  214 , and make up part of the gas and material flow  403 . 
     Based on the availability of additional powdered metal in the region of the laser melt zone it would be beneficial to enlarge the size of the laser spot on the surface being clad, using a variable focus depth of the laser beam and cladding a larger surface area with every pass of the laser cladding nozzle. The laser spot size should be variable, since for detail work, a smaller spot will be required than for the cladding of larger areas of the surface. Variation of the laser spot size at the surface being clad can be effected by using a motor driven gear system similar to that used in camera zoom lenses. It would also be beneficial to use a laser range finder, mounted to the laser cladding nozzle, coaxially with the laser beam path to measure the distance to the surface being laser clad. This information can then be used in a control loop to adjust the height of the laser focal spot relative to the surface being clad. 
       FIG. 7  shows an alternate preferred embodiment wherein the lens  26  is adjustably mounted.  FIG. 8  is a schematic diagram where a controller for adjusting the laser work zone  903  on the surface of the part  401  being clad is shown. The control function is carried out by the master control computer  327  which gathers data from a coaxial laser range finder  1001  and sends movement commands to the focusing lens servo motor control  1002 . The coaxial laser range finder  1001  can be any one of several commercial units available, based on laser triangulation, focal point determination, or modulation phase detection. The focusing lens servo motor control  1002  can also be a commercial unit that moves the laser focusing lens  26  and its mount  906  relative to the guide housing  905  based on advance or retract signals from the master control computer  327 . 
       FIG. 10  illustrates a zoom lens assembly  1100  that can be utilized with the laser cladding device  10 , e.g., to vary the laser spot size as described above. The zoom lens assembly  1100  can receive laser light from a laser light source  1110  (e.g., a laser diode) and transmit laser light to the part  401  to be coated. The laser light heats the coating and the part  401  in the laser work zone to apply the coating to the part  401 . The laser light exiting the zoom lens assembly  1100  can be altered from that entering the zoom lens assembly to change one or more characteristics of the laser light. For example only, the zoom lens assembly  1100  can be adjusted by the controller (e.g., master control computer  327 ) to alter the beam width of the laser light, and/or the focal point of the laser light. 
     In some embodiments, the zoom lens assembly  1100  can include a collimating lens  1120  and a zoom mechanism  1130 . The collimating lens  1120  can receive and collimate the laser light from the laser light source  1110  to direct the laser light towards the part  401 . The zoom mechanism  1130  can alter the laser light, e.g., by changing the beam width of the laser light. Additionally or alternatively, the zoom mechanism  1130  can vary the focal point of the laser light exiting the zoom lens assembly  1100 . In this manner, the spot size of the laser light on the part  401  that is a specific distance from the laser cladding device  10  can be varied. The zoom mechanism  1130  can include, for example, a zoom collimator in conjunction with a focusing lens, zoom optics or a combination thereof. 
     The controller (e.g., master control computer  327 ) can further be configured to control the level of vacuum (“vacuum level”) of the vacuum port  14  based on the laser spot size or laser work zone. For example only, as the size of the laser work zone increases the vacuum level may be decreased such that the coating can be provided across the larger area. Similarly, as the size of the laser work zone decreases the vacuum level may be increased such that the coating can be provided across the smaller area, and in some cases the extra coating can be captured by the vacuum port to reduce waste. In some embodiments, the controller can adjust the vacuum level in order to shape the coating flow to correspond to the size of the laser work zone. In this manner, the flow of the coating can be shaped to provide a relatively uniform distribution (within about 20%) of coating particles within the laser work zone. The adjustment of the vacuum level can be automatically performed by the controller upon adjustment of the laser work zone, for example by the user adjusting the laser spot size. 
     The presence of oxygen in the laser work zone may result in undesirable oxidation of the coating material during the cladding process. In some embodiments the flow of the shaping gas can act as a shielding gas to inhibit oxygen from entering the laser work zone. As the vacuum level is adjusted, e.g., based on the size of the laser work zone, the controller (e.g., master control computer  327 ) can further be configured to control the level of the flow of shaping gas (“shaping gas flow level”) at the shaping gas port  16  to provide proper shielding of the laser work zone. For example only, as the vacuum level increases, the shaping gas flow level may also be increased to provide shielding. Similarly, as the vacuum level decreases the shaping gas flow may also be decreased. The adjustment of the shaping gas flow can be automatically performed by the controller upon adjustment of the laser work zone and/or vacuum level, for example by the user adjusting the laser spot size. 
     In some embodiments, the laser cladding device  10  can utilize the laser range finder described above to maintain a relatively constant size of the laser work zone (+/−10% of the diameter of the laser spot size). This may be performed through adjustment of the lens  26 /zoom lens assembly  1100  based on range information received from the laser range finder during the cladding operation. The range information can include, e.g., information indicative of the distance to the part  401  being clad. In this manner, a part  401  that includes an irregular surface, e.g., a part  401  with low spots (“grooves”) and/or high spots (“projections”), can be clad with a relatively consistently sized bead of coating. Additionally, it should be appreciated that the vacuum level and shield gas level can also be adjusted based on the size of the laser work zone/range information such that the coating flow is appropriately shaped and the laser work zone is appropriately shielded, respectively, as described above. The adjustment of the lens  26 /zoom lens assembly  1100 , the vacuum level, and/or shield gas level can be performed automatically by the controller, e.g., master control computer  327 . 
     From the foregoing disclosure and detailed description of certain preferred embodiments, it will be apparent that various modifications, additions and other alternative embodiments are possible without departing from the true scope and spirit of the invention. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to use the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.