Patent Publication Number: US-2016243651-A1

Title: Material processing system

Description:
TECHNICAL FIELD 
     The present invention relates to welding equipment and processes, and more particularly to laser cladding, also known as laser welding or additive manufacturing of a material that is deposited on a base material. 
     BACKGROUND 
     Overlay welding or overlay hard-facing, otherwise known as cladding, involves the deposition of corrosion, erosion or wear resistant materials over a surface of a component to impart the beneficial properties of the cladding materials onto the surface of a metal component or part. The clad material is typically formed as a continuous clad coating of lateral overlapping beads, forming a pore-free, continuous surface of material that increases the thickness of the region. For remanufacturing of a worn part, a thin layer of worn-away material is replaced or a thin layer of the beneficial clad material is added to the workpiece. The industry is looking for methods of replacing worn-away metal or adding beneficial clad material without changing the part either dimensionally or materially by too much heat. 
     Laser cladding specifically address a need in all these areas by providing a low heat input, thin weld overlay, low dilution cladding. Laser cladding is a process in which the heat source is replaced by a laser which can be a CO2, Neodymium:YAG, fiber laser or diode laser. A laser focused as a line source is specifically well suited for wide thin laser cladding and the CO2, Nd:YAG, and fiber laser can be optically transformed to create such a line. Specifically, the diode laser has a naturally occurring spot that is a line with an approximate top hat profile that is very well suited for laser cladding that is preferably thin with low surface roughness and low dilution. 
     However, the top hat profile is not the ideal beam to achieve a top hat heating profile. An improved laser beam profile is that which has an intensity power distribution that is more intense at the outer regions. The heating profile also determines the melting profile during cladding. With a perfect top hat beam, the heat will be the greatest in the middle of the beam and taper off isotropically at the edges. This is even more pronounced using a standard Gaussian shaped beam which comes naturally from CO2, fiber coupled Nd:YAG, fiber lasers and diode lasers. Due to surface tension of the melt puddle, material factors, and type of cladding environments, such as cover gas, the resulting clad shape is rounded with a thicker center and tapering toward the ends (a lunular-type shape). This leads to undesirable surface morphology with humping in the middle of the clad track, which subsequently leads to large surface roughness and variable clad thickness during clad overlapping. It is desirable to be able to clad the base material with a uniform cladding material thickness from one clad track to the next. In addition, if the surface is at an edge it is desirable to pull the puddle to the edge without melting the edge. It is also desirable to be able to affect the weld puddle in real time to repair a clad while it is still in a molten or semi-molten state. 
     U.S. Application Publication No. 2013/0105447 relates to a material processing system for a workpiece, The system includes a primary laser source, a. secondary laser source, and a feeder proximate to a surface location of the workpiece. The feeder supplies a deposit material on a surface of the workpiece. The primary laser is directed to the deposit material at the surface of the workpiece, and is directed across the width from a main side to an auxiliary side. A secondary laser is directed to a desired location within the width of the deposit material to achieve a tailored and uniform cladding layer thickness in the workpiece. However, the primary laser and secondary laser may consume excessive power and also increases the equipment cost. 
     Hence, there is a need of an improved methodology to achieve uniform cladding layer thickness with good edge quality in the cladding layer of the workpiece with minimal power and minimal equipment cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a material processing system for a base material in accordance with an embodiment of the present disclosure; 
         FIG. 2  is a side view of a processing head for the material processing system in accordance with an embodiment of the present disclosure; 
         FIG. 3  is a perspective view of a cartridge (multi-faceted prism) attached to the processing head of  FIG. 2 ; 
         FIG. 4  is an exemplary power density distribution profile of an incident laser beam after passing through the cartridge in the processing head; and 
         FIG. 5  is another exemplary power density distribution profile of the incident laser beam after passing through the cartridge in the processing head. 
     
    
    
     SUMMARY 
     In an aspect of the present disclosure, a material processing system for a base material is provided. The material processing system includes a material feeder having a distal end proximate to a surface location of the base material. The feeder supplies a cladding material to the surface location from the distal end. A laser source provides a laser beam. A processing head receives the laser beam from the laser source and directs the laser beam on the cladding material. A cartridge located in the processing head deflects the laser beam. The cartridge changes a power density distribution profile of the laser beam. 
     DETAILED DESCRIPTION 
     Wherever possible, the same reference numbers will be used throughout the drawings to refer to same or like parts,  FIG. 1  illustrates a material processing system  10 . The material processing system  10  is a laser cladding system. Laser cladding is a method of depositing material by which a powdered or wire feedstock material is melted and consolidated by use of a laser in order to coat part of a substrate or fabricate a near-net shape part. 
     The material processing system  10  includes a workpiece  12  made of a base material. The base material may be any metal based material in accordance with the scope of the present disclosure. The workpiece  12  may he of any shape, size, dimensions as per the scope of the present disclosure. The workpiece  12  may have a single or multiple surfaces on which laser cladding has to be performed. A fixture (not shown) may hold the workpiece  12  in proper orientation for the laser cladding to be performed. The fixture may include means to locate and fix the workpiece  12  in multiple orientations. The fixture may also include means to rotate, translate or elevate the workpiece  12  in three dimensions. 
     The material processing system  10  further includes a material feeder  14 . The material feeder  14  may be any conventional feeder capable of delivering a supply of a cladding material on a surface  15  of the workpiece  12 . In the illustrated example, the material feeder  14  may deliver the cladding material in a powder form. However, it is contemplated that the material feeder  14  may also deliver the cladding material in other forms as well, such as in a wire form etc. In some applications, the material feeder  14  may additionally warm and/or engulf the cladding material in a shield gas as the cladding material is delivered. The material feeder  14  has a distal end  16  proximate to the surface  15  of the workpiece  12 . The material feeder  14  supplies cladding material to the surface  15  of the workpiece  12  through the distal end  16 . 
     The material processing system  10  further includes a controller  18 . The controller  18  regulates a feed rate and/or angle of the cladding material supplied by the material feeder  14 . As shown, the controller  18  is coupled to a sensor  20 . The sensor  20  may be any type of sensor able to provide information about characteristics of a melt pool formed on the surface  15  of the workpiece  12 . The sensor  20  may provide the controller  18  with information about the melt pool such as a thickness of the melt pool, surface finish of the melt pool etc. The controller  18  is also communicably coupled with the material feeder  14  and may provide instructions regarding controlling feed rate and/or angle of the cladding material being delivered at the surface  15  of the workpiece  12 . 
     The material processing system  10  may further include a laser source  22 . The laser source  22  may be, for example, a high-energy CO2 laser, ND:YAG laser, or any other type of solid-state, fiber-delivered laser capable of melting the cladding material as it is delivered at the surface  15  of the workpiece  12 . In the illustrated embodiment, the laser source  22  is configured to produce a laser beam  24  having a generally circular or square shape. A dimension (For e.g., diameter) of the laser beam  24  may be provided so as to suit the need of the current application. The laser beam  24  may have a characteristic power density distribution across the diameter. The power density distribution may have a top-hat distribution profile, a Gaussian distribution profile etc. These power density distribution profiles are a characteristic property of the laser source  22 . Such power density distribution profiles correspond to formation of a melt pool which has a higher concentration of thermal energy being supplied in center as compared to edges of the melt pool. 
     The power density distribution profile of the laser beam  24  determines shape, size and other characteristics of the melt pool. The top-hat profile or the Gaussian profile may lead to formation of a melt pool having thick material deposition in center and relatively thin material deposition at edges which may be undesirable. Therefore, the power density distribution profile of the laser beam  24  is altered by passing through a processing head  26 . 
       FIG. 2  illustrates the processing head  26 . The processing head  26  receives the laser beam  24  and directs the laser beam  26  towards the surface  15  of the workpiece  12 . The processing head  26  may include appropriate means of insulation to handle the laser beam  24 . The processing head  26  may have multiple additional systems to handle the laser beam  24  such as cooling system etc. (not shown). The processing head  26  has a first end  28  and a second end  30 . The first end  28  of the processing head  26  receives the laser beam  24 . The second end  30  of the processing head  26  delivers the laser beam  24  at the surface  15  of the workpiece  12 . It may also be contemplated that the processing head  26  may have the laser source  22  integrated with the processing head  26 . A pair of axes is defined with respect to the first end  28  and the second end  30 . X-axis is illustrated as passing through the first end  28  and parallel to the direction of incident laser beam  24 . Y-axis is defined as passing through the second end and perpendicular to the X-axis. 
     The first end  28  and the second end  30  may be oriented at an angle ‘α’ to each other. The angle ‘α’ is defined as the angle between X-axis and the Y-axis. Although, the angle ‘α’ is illustrated as ninety degrees, the angle ‘α’ may have any value in the range of zero to ninety degrees. The processing head  26  may include means to vary the angle ‘α’ as per the need of the application. The processing head  26  may be communicably coupled with the controller  18  to control the angle ‘α’. The processing head  26  may further include means to move the processing head  26  relative to the workpiece  12 . The fixture and the processing head  26  may move together so as to cover all the surfaces of the workpiece  12  as required. The processing head  26  further includes a cartridge  32  (shown in  FIG. 3 ) to deflect the laser beam  24  coming from the first end  28  towards the workpiece  12  through the second end  30 . 
       FIG. 3  illustrates the cartridge  32  installed in the processing head  26 . The cartridge  32  deflects the laser beam  24  towards the surface  15  of the workpiece  12 . The cartridge  32  also modifies the power density distribution profile of the laser beam  24 . The cartridge  32  may be a multi-faceted prism. A design of the prism defines the power density distribution profile of the laser beam  24 . In various embodiments, the design of the prism may be varied so as to get a desired power density distribution profile of the laser beam  24  at the surface  15  of the workpiece  12 . 
       FIG. 4  represents a first exemplary power density distribution profile  34  for the laser beam  24 . Power density distribution profile indicates power supplied to the surface  15  of the workpiece  12  by the laser beam  24  across the area of the melt pool. Y-axis represents the amount of power supplied to the surface  15  of the workpiece  12 . X-axis represents the diameter of a melt pool formed over the surface  15  of the workpiece  12  at which laser beam  24  is supplying power. Therefore, a typical top-hat profile would represent higher amount of power being supplied in a middle region of a melt pool compared to the edges of the melt pool. Such a power density distribution profile would cause humping in the middle of the melt pool. The first profile  34  is similar to a top-hat profile. A spike  36  is provided towards the end. The spike  36  represents higher amount of power supplied at edges compared to middle region of the melt pool by the laser beam  24 . A corresponding first melt pool shape  38  is also shown in  FIG. 4 . A first edge  40  of the melt pool corresponding to the spike  36  illustrates better dimensional accuracy compared to a second edge  42 . More cladding material gets melted and thickness of the melt pool at the first edge  40  is almost equal to thickness of the melt pool at the middle. 
       FIG. 5  shows a second improved power density distribution profile  44 . The second profile  44  is also similar to a top-hat profile. As illustrated, the second profile  44  includes spikes  46  towards both the ends. The spikes  46  at the ends indicate higher intensity at edges of the laser beam  24 . A corresponding second melt pool shape  48  is also shown in  FIG. 5 . Both the edges of the melt pool illustrate better dimensional accuracy. Thickness of the edges is almost the same as thickness of the central portion of the melt pool. Improved power density profiles provide for better dimensional accuracy as well as better rates of metal deposition. Further, post-machining required is also kept to a minimum. 
     The improved power density profiles  34 ,  44  illustrated in  FIGS. 4 and 5  respectively correspond to different shapes of the multi-faceted prism being used as the cartridge  32 . Different shape of the melt pool may be achieved by varying the shape of the prism. The prism may be easily replaced in the processing head  26 . The appropriate prism is designed as per the application requirement and installed in the processing head  26 . Although, the embodiments of the present disclosure have been explained by using a prism as the cartridge  32 , any other optical element may also be utilized as the cartridge  32  to provide similar results. 
     INDUSTRIAL APPLICATION 
     Laser cladding is an additive manufacturing process which deposits a powdered or wire cladding material on a metal surface. The cladding material is melted by use of a laser in order to coat a part of a substrate or fabricate a near net-shaped part. Laser cladding is often used to improve mechanical properties or increase corrosion resistance, repair worn out parts, and fabricate metal matrix composites. A major advantage provided by laser cladding is reduction in lead times and post-processing operations as compared to conventional manufacturing processes. However, laser cladding processes tend to lose this advantage on account of increased time in post-processing operations. Generally, the melt pool created by the laser cladding process appears to be thicker in center portion compared to edges. This occurs due to inherent power density distribution profiles of the laser beam. 
     The present disclosure overcomes the above-mentioned problem by providing means to modify the power density distribution profile of the laser beam  24 . The power density distribution profile of the laser beam  24  is modified by passing the laser beam  24  through the processing head  26 . The processing head  26  includes the first end  28  and the second end  30 . The cartridge  32  is located between the first end  28  and the second end  30 . The laser beam  24  enters the processing head  26  through the first end  28 . The laser beam  24  passes through the cartridge  32 . The power density distribution profile of the laser beam  24  is modified while passing through the cartridge  32 . Thereafter, the laser beam  24  passes through the second end  30  of the processing head  26  and is directed towards the surface  15  of the workpiece  12 . 
     The power density distribution profile of the laser beam  24  is modified in accordance with the shape of the cartridge  32 . Different shapes of the cartridge  32  may be used to achieve various profiles at the workpiece  12 . The exemplary profiles  34 ,  44  as shown in  FIGS. 4 &amp; 5  improve the properties of edge of the melt pool. Due to higher intensity of laser beam  24  at the edges, more cladding material is melted at the edges. Better dimensional accuracy is observed with the improved power density distribution profiles. Also, the shape of the melt pool may be varied as per the need of the application. Further, post-processing operations require lesser time. Little or no post-machining is required as the shape of the melt pool may be controlled in a better manner. Lesser number of passes is required to finish an operation. Thus, there is a reduction in total time required to repair or fabricate the workpiece  12 , in turn causing cost savings. 
     While some of the solutions to the above-mentioned problem facilitate use of a secondary laser to improve the quality of laser cladding at edges, the present disclosure provides a solution without using a second laser. Apart from saving the cost of a second laser, the present disclosure also provides for a simple and less complex process apparatus. In absence of a second laser, the laser beam  24  and the workpiece  12  are provided with additional degrees of freedom relative to each other. Also, operational parameters of only a single laser are to be controlled compared to managing two separate lasers at a time. 
     While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.