Abstract:
An apparatus ( 10 ) and method for evaluating an effect of a surface presentation angle (A). The apparatus supports a plurality of samples ( 12 ) separated by support plates ( 18 ) between end plates ( 22 ) in a shish kebab arrangement. A groove ( 34 ) is formed on each side of each support plate for receiving an edge of each respective sample at a different angle relative to an axis of impingement ( 32 ). A clamping mechanism ( 20 ) holds the end plates, support plates and samples together in the fixed orientation exposing each sample surface at a different presentation angle, yet at the same distance from a process end effector ( 30 ). The sample impingement surfaces are exposed to the process, and the effect of the different surface presentation angles is determined from the samples. Process variables to counter the effects of surface presentation angle may be identified and controlled.

Description:
This application claims benefit of the 11 May 2012 filing date of U.S. provisional patent application No. 61/645,824 which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of metrology. 
     BACKGROUND OF THE INVENTION 
     Energy beams such as laser or electron beams are known to be used as a heat source for certain manufacturing and repair processes such as welding, hard-facing and overlay coating, such as may be used during the repair of gas turbine engine components. The angle of incidence of the energy beam is an important variable that affects the quality of the process. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section IX identifies a change of more than ±10 degrees in the relative angle between the axis of the beam and the impinged work piece surface (angle of incidence) as an essential variable for such processes. Angled surfaces cause an otherwise focused and maximum power density beam to be spread over a broader surface having an elliptical rather than round shape. Moreover, the effect of gravity varies as a surface undergoing a process is inclined from horizontal, and such changes may adversely affect processes utilizing a molten weld pool or powders. Relatively little work has been published to quantify these effects for material and/or heat additive processes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in the following description in view of the drawings that show: 
         FIG. 1  is a plan view of an embodiment of an apparatus for evaluating an effect of surface presentation angle. 
         FIG. 2  is a side view of the support plate of the apparatus of  FIG. 1  and an energy source as they may be relatively positioned during a process. 
         FIG. 3  is a side view of the apparatus of  FIG. 1  with a schematic illustration of a temperature control system for the samples. 
         FIG. 4  is a plan view of another embodiment of an apparatus for evaluating an effect of surface presentation angle. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The term “surface presentation angle” is used generally herein to describe the orientation of a surface undergoing a process relative to a reference direction, such as relative to an angle of incidence of an energy beam or relative to horizontal. 
     The present invention is useful for evaluating the effect of surface presentation angle for material and/or heat additive processes such as laser or electron beam welding, laser hard-facing overlay, laser corrosion-resistant overlay, etc. The present invention provides a device that fixtures an array of samples at a variety of different, known, and controlled surface presentation angles such that a single pass of a processing device produces a full complement of processed test samples. By holding process variables constant as the process progresses over the differently angled surfaces, the effect of surface presentation angle can be demonstrated. Alternatively, by varying process variables for each differently angled surface, a process can be qualified to produce consistent results across a range of surface presentation angles. 
       FIG. 1  illustrates one embodiment of an apparatus  10  for evaluating an effect of surface presentation angle.  FIG. 1  is a simplified embodiment of the invention utilizing only two samples. While this simplified embodiment is useful for illustration and discussion purposes, one skilled in the art will recognize that more than two samples may be preferred for evaluating the effect of surface presentation angle over a wider range of angles. The apparatus  10  illustrates two samples  12 ,  12 ′ and a fixture  14  supporting the samples  12 ,  12 ′ in fixed relative orientations presenting their respective impingement surfaces  16 ,  16 ′ at respective different angles. The fixture  14  includes a support plate  18  disposed between the samples  12 ,  12 ′. The fixture also includes a clamping mechanism  20  compressing two end plates  22 ,  22 ′ together to hold the support plate  18  and samples  12 ,  12 ′ together in fixed relative positions. In this embodiment, the clamping mechanism  20  includes two threaded rods  24  held in tension by nuts  26  threaded onto ends of the rods  24  for urging the end plates  22 ,  22 ′ toward each other. The rods  24  pass through holes  28  in the end plates  22 ,  22 ′. In other embodiments, the samples may be larger and may also include holes for accommodating passage of the rods  24 . 
     One skilled in the art will appreciate that other forms of clamping mechanisms may be used to urge the apparatus together, for example C-clamps, bolts with a fixed heads, partially or intermittently threaded rods, spring-loaded devices, rods with a nut welded in place on one end, etc. 
       FIG. 2  is a side view of the support plate  18  illustrating how the samples are held at the appropriate angles.  FIG. 2  illustrates an energy source  30  and an axis of impingement  32  of an energy beam from the energy source  30  as may be present when the apparatus  10  is used during a material and/or heat additive process. Support plate  18  includes a respective groove  34 ,  34 ′ formed on each of two opposed sides  36 ,  36 ′ for receiving the respective sample  12 ,  12 ′. In the embodiment of  FIG. 2 , groove  34  (illustrated in phantom because it is on the hidden side  36 ) is formed to have a longitudinal orientation that is generally horizontal and perpendicular to the impingement axis  32 . Groove  34 ′ is formed to have a longitudinal orientation that is angled from the horizontal such that impingement surface  16 ′ will have an angle of incidence A° relative to the impingement axis  32 . Edges of the respective samples  12 ,  12 ′ are engaged within the grooves  34 ,  34 ′ to position the samples  12 ,  12 ′ to have the desired surface presentation angles (i.e. 90° for sample  12  and A° for sample  12 ′ in the illustrated embodiment). Note that the end plates  22 ,  22 ′ are illustrated in  FIG. 1  as also having corresponding grooves for receiving the opposed edges of the samples  12 ,  12 ′. In various embodiments, such grooves may be provided only in the end plates, only in the support plate, or in both, as required to provide a desired degree of positional accuracy and support for the samples  12 ,  12 ′. Other embodiments may have more than two samples, with grooves formed to present the sample impingement surfaces at angles such as 15°, 30°, 45°, 60°, 75°, and 90° for example. 
     In  FIG. 2  there is illustrated a point  38  which establishes a fixed distance along the axis of impingement  32  from the energy source  30 . The grooves  34 ,  34 ′ are both formed such that the respective impingement surfaces  16 ,  16 ′ of samples  12 ,  12 ′ are held at this fixed distance from the energy source  30  along the axis of impingement  32  by the apparatus  10  as the energy source  30  moves relative to the apparatus  10  during a process. As the energy source  30  is moved relative to the apparatus  10 , there is established a line of intersection  40  between the energy beam and the samples  12 ,  12 ′ as illustrated in  FIG. 1 , and that line  40  appears as a point  38  in the side view of  FIG. 2  seen perpendicular to the axis of impingement  32 . By maintaining a fixed distance between the energy source  30  and the line of intersection  40  along the samples  12 ,  12 ′, the change in energy flux at the impingement surfaces  16 ,  16 ′ is isolated to the effect of the surface presentation angle A° verses surface presentation angle 90° only. The grooves  34 ,  34 ′ are formed such that line of intersection  40  can be considered as an axis of rotation when moving from one sample  12  to the next sample  12 ′ so that the surfaces  16 ,  16 ′ are each presented at an equal distance from the energy source  30 . 
     One skilled in the art will appreciate that the relative motion between the apparatus  10  and the energy source  30  (or other process device) may be accomplished by moving the apparatus  10  or the energy source  30  or both. Apparatus  10  not only fixes the samples in their relative orientations, but the presence of the support plate  18  between the samples  12 ,  12 ′ also provides a degree of physical isolation of the samples  12 ,  12 ′ as they individually and consecutively undergo the process as the energy source  30  is traversed relative to the apparatus  10 . The apparatus  10  may be formed of steel, aluminum or other suitable metal, and in one embodiment, the support plate  18  may include a ceramic material to provide additional thermal isolation between samples  12 ,  12 ′. This may be useful when it is desired to maintain the two samples  12 ,  12 ′ at different temperatures during the process and when it is important to ensure that processing of one of the samples does not unintentionally affect (e.g. preheat) a second subsequent sample&#39;s processing.  FIG. 3  illustrates a side view of the apparatus  10  and a temperature control system  42  which includes a fan  44  for directing unheated air across sample  12  and for directing air through a heater  46  and then across sample  12 ′. Such an arrangement facilitates the collection of data correlating the effect of sample temperature on the process in conjunction with the effect of surface presentation angle. Other temperature control systems may be envisioned, such as electrical resistance heaters applied to at least one sample, the use of a chiller to cool air passing over a sample, induction coils, water cooled chill blocks, etc. 
       FIG. 4  illustrates an apparatus  50  wherein six samples  52  are fixtured at six different surface presentation angles, as compared to the two samples of  FIG. 1 . The support plates  54  and end plates  56  of  FIG. 4  have like dimensions so that the threaded rods  58  pass through each of the plates  54 ,  56 , forming a structure that can be described as a “shish kebab” of alternating samples and plates disposed along the rods. In this embodiment, nuts  60  are provided on each side of each plate  54 ,  56 , with each nut  60  urged against a respective plate to hold the plate in a fixed position relative to the rod and relative to adjacent plates. The provision of nuts  60  on both sides of each plate provides an added degree of fixturing precision for constraining dimensional variations that might otherwise be introduced by normal machining tolerances. 
     Other embodiments of the invention may incline the samples to either or both sides of the plane of processing (the plane established by the axis of impingement and travel motion). Furthermore, angles may be inclined to a side toward or away from the axis of impingement within the plane of processing. 
     In use, the apparatus  10 ,  50  is assembled to support the samples, and it is then positioned on a work table in proximity to a process end effector, such as a laser beam and powder disbursement nozzle. The process is then activated and the end effector is moved across the apparatus such that the process, for example laser cladding, is performed on each of the samples consecutively. The process may be temporarily interrupted as the end effector passes over the end plates and support plates. One or multiple passes of the process may be made over the samples. The apparatus is then disassembled and the samples are inspected to determine the results of the process. If the process variables were held constant, the effects of surface presentation angle will be demonstrated in the samples. The process may be evaluated to determine process variables that can be changed to counteract the effect of surface presentation angle. A set of samples may be exposed to the process with such variables being appropriately controlled as the end effector functions over each respective sample across the apparatus. If such samples demonstrate process results within a desired degree of similarity among the samples, the process can be qualified for use within the demonstrated range of surface presentation angles. In this manner, fundamental investigations may be made to quantify the effects of surface presentation angle alone or in conjunction with other sample and process attributes, for example but not limited to the following: 
     
       
         
               
               
             
           
               
                   
               
               
                 PROCESS 
                 ATTRIBUTE 
               
               
                   
               
             
             
               
                 laser 
                 surface roughness 
               
               
                 transformation 
                 coatings to absorb the laser beam 
               
               
                 hardening 
               
               
                 laser welding 
                 reflectivity effect on penetration 
               
               
                   
                 reflectivity effect on plasma suppression gas 
               
               
                   
                 gravitational effect on molten pool 
               
               
                 electron beam 
                 charging effects deflecting the electron beam 
               
               
                 welding 
                 power density changes affecting penetration 
               
               
                 laser cladding 
                 gravitational effects 
               
               
                   
                 reflectivity effect on powder capture efficiency 
               
               
                   
                 reflectivity effect on dilution from the substrate 
               
               
                 water jet 
                 deflection of water stream affecting cut quality 
               
               
                 cutting 
               
               
                   
               
             
          
         
       
     
     While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.