Abstract:
A method of brazing an assembly ( 202 ) having at least two aluminum workpieces coupled at a joint includes applying a flame to the joint of the aluminum workpieces; monitoring the flame color; and upon detecting a change in the flame color, maintaining a temperature at the joint.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to brazing of workpieces, and more particularly, to a method and system for brazing aluminum workpieces. 
         [0002]    Brazing is used to join metal workpieces by heating a joint of the workpieces (e.g., via a torch) and applying a filler to the joint once the workpieces have reached a suitable temperature. The filler melts into the joint, and when cooled creates a mechanical attachment between the workpieces. 
         [0003]    Controlling heat during brazing can be challenging when working with certain materials. In aluminum brazing, it is hard to know when the workpiece is hot enough to apply the filler, as the aluminum workpiece does not undergo a color change when heated. Often, operators will melt and ruin the workpieces because they overheat and melt the joint. The brazing temperatures may be only 100-200 degrees away from the melting temperature of the workpiece, leaving operators with little margin for error in brazing aluminum. As such, improvements in brazing aluminum would be well received in the art. 
       BRIEF DESCRIPTION 
       [0004]    According to one aspect of the invention, a method of brazing an assembly having at least two aluminum workpieces coupled at a joint includes applying a flame to the joint of the aluminum workpieces; monitoring the flame color; and upon detecting a change in the flame color, maintaining a temperature at the joint. 
         [0005]    According to another aspect of the invention, a system for brazing an assembly having at least two aluminum workpieces coupled at a joint includes a flame unit for applying a flame to the joint coupling the aluminum workpieces; an optical detection unit for monitoring the flame; a machine for controlling a relative position between the flame and the assembly; and a controller coupled to the flame unit and the machine, the controller controlling at least one of flame intensity and relative position of the flame and the assembly in response to the optical detection unit. 
         [0006]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0008]      FIG. 1  illustrates brazing of workpieces in an exemplary embodiment; 
           [0009]      FIG. 2  is a flowchart of a process of brazing workpieces in an exemplary embodiment; 
           [0010]      FIG. 3  illustrates an automated brazing system in an exemplary embodiment; and 
           [0011]      FIG. 4  illustrates an automated brazing system in another, exemplary embodiment. 
       
    
    
       [0012]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  illustrates brazing of workpieces in an exemplary embodiment. As shown in  FIG. 1 , an assembly includes workpieces  10  and  12  being joined by brazing. Workpiece  10  may be an aluminum heat exchanger body and workpiece  12  may be an aluminum u-shaped fitting. A flame  20  is applied to the joint of workpieces  10  and  12  until the joint reaches a heat sufficient to melt a filler material. The source of flame  20  may be torch using known fuel types (e.g., propane, oxy-acetylene, propylene, natural gas, MAPP, hydrogen, LP, acetylene). The fuel type may be any fuel-air/oxygen combination, which produces a blue type flame, in order to create a color change when used on aluminum as described herein. Once a suitable temperature is reached, filler material  22  is applied to the joint. Alternatively, filler mater can be pre-assembled into the joint as a ring, wire, foil or paste. The filler material melts into the joint between workpieces  10  and  12 , and once cooled, secures the workpieces  10  and  12 . Flux may be applied to the joint prior to applying heat, or the filler material  22  may include a flux coating or core. 
         [0014]      FIG. 2  is a flowchart of a process for brazing aluminum workpieces to prevent overheating, and destruction, of the workpieces. The process begins at  100  where the workpieces are assembled at a joint, such as the joint between workpieces  10  and  12  of  FIG. 1 . At  102 , heat is applied to the joint by applying a flame to the joint. At  104 , the color of the flame is monitored to detect a color change. Initially, the flame is blue-green in color. As the aluminum is heated, the absorption spectrum of the flame surrounding the aluminum workpieces shifts to absorb more of the green-blue color of the flame. This is perceived by the user as a shift in flame color to a red-orange color. 
         [0015]    If at  104  no change in flame color is perceived, the process loops back to  102  and continues until a change in flame color is detected at  104 . Once a change in flame color is detected, flow proceeds to  106  where the temperature at the joint is maintained, but not increased. This may be performed by physically moving the torch farther from the joint or reducing the intensity of the flame (e.g., by adjusting a knob on the torch). The color change indicates that the aluminum workpieces are at sufficient temperature to melt the filler. Reducing the heat at  106  prevents overheating of the joint and damaging the workpieces, while still maintaining the joint at a temperature sufficient to melt the filler material. At this stage, the filler may be applied to the joint at  108 . 
         [0016]      FIG. 3  depicts an automated brazing system in exemplary embodiments. The system includes a machine  200  in the form of a conveyer for transporting assembly  202 . The assembly  202  includes filler material (e.g., ring, wire, foil or paste) positioned at a joint between the two aluminum workpieces. A flame unit  204  applies a flame to the assembly to heat the joint to a temperature to melt the filler material. An optical detection unit  206  monitors the flame and provides output to controller  208 . The optical detection unit  206  may be a camera generating images or a spectrometer generating spectra of the flame. The output of the optical detection unit  206  is provided to controller  208 . 
         [0017]    Controller  208  processes the output from optical detection unit  206  to control the conveyor  200  and/or the flame unit  204 . Controller  208  may be a general-purpose microprocessor based controller, executing the processes described herein in response to instructions stored in a computer-readable storage medium. If the optical detection unit  206  is a camera, the controller  208  detects a color shift from blue-green to red-orange using image processing. For example, the pixel values (e.g., RGB, HSL, HSV, HSI) from the pixels in the image can be compared to known red-orange pixel values to detect the color shift. If the optical detection unit  206  is a spectrometer, the controller can detect a decrease in the intensity of known wavelengths complementary to red-orange wavelengths, either as an absolute measurement of intensity, or relative to spectral bands where absorption effects do not take place. 
         [0018]    Controller  208  provides control signals to the conveyor  200  and/or the flame unit  204  in response to the output of optical detection unit  206 . If the color shift has not occurred within a predetermined amount of time, controller  208  can adjust the relative position between the flame and the assembly  202  by slowing the conveyor  200 . Further, controller  208  may increase the intensity of the flame from flame unit  204 . Once the color change is detected by controller  208 , controller  208  can increase the speed of conveyor  200  to adjust relative position between the flame and the assembly  202  and/or reduce the intensity of the flame from flame unit  204 . This maintains the temperature at the joint. The color change indicates that the assembly  202  has reached the appropriate temperature to melt the filler material. Reducing the heat prevents overheating of the joint and damaging the workpieces, while still maintaining the joint at a temperature sufficient to melt the filler material. In this manner, the controller  208  prevents damage to the aluminum assembly  202 . 
         [0019]      FIG. 4  depicts an automated brazing system in exemplary embodiments. An assembly  250  to be brazed includes two aluminum workpieces connected at a joint as described above. A first machine  252  includes a flame unit  253  generating the flame to be applied to assembly  250 . Flame unit  253  may be electronically controllable to adjust the flame intensity. Machine  252  may be a robotic arm, or other device capable of electronically controlled motion in three dimensions. Machine  254  manipulates the filler material  255  (e.g., a rod of filler material) to place the filler material  255  at the joint. Machine  254  may be a robotic arm, or other device capable of electronically controlled motion in three dimensions. In alternate embodiments, the joint is pre-packed with filler material, and machine  254  is not utilized. An optical detection unit  256  monitors the flame and provides output to controller  258 . The optical detection unit  256  may be a camera generating images or a spectrometer generating spectra of the flame. 
         [0020]    Controller  258  processes the output from optical detection unit  256  to control machines  252  and  254 . If the optical detection unit  256  is a camera, the controller  258  detects a color shift from blue-green to red-orange using image processing. For example, the pixel values (e.g., RGB, HSL, HSV, HSI) from the pixels in the image can be compared to known red-orange pixel values to detect the color shift. If the optical detection unit  256  is a spectrometer, the controller  258  can detect a decrease in the intensity of known wavelengths complementary to red-orange wavelengths, either as an absolute measurement of intensity, or relative to spectral bands where absorption effects do not take place. 
         [0021]    Controller  258  provides control signals to machines  252  and  254  in response to the output from optical detection unit  256 . If the color shift has not occurred within a predetermined amount of time, controller  258  can position machine  252  to alter the relative position between the flame and the assembly  250  by moving the flame closer to the assembly  250 . Controller  258  may also increase the intensity of the flame produced at flame unit  253 . Once the color change is detected by controller  258 , controller  258  maintains the temperature at the join. Controller  258  may alter the relative position between the flame and the assembly  250  by moving the flame farther from the assembly  252 . Controller  258  may also reduce the intensity of the flame from flame unit  253 , as the color change indicates that the assembly  250  has reached the appropriate temperature to melt the filler material. Maintaining the temperature prevents overheating of the joint and damaging the workpieces, while still maintaining the joint at a temperature sufficient to melt the filler material. Once the color shift is detected, controller  258  commands machine  254  to place the filler material in contact with the joint on assembly  250  to perform the brazing. As noted above, if the joint is pre-packed with filler material, and machine  254  is not utilized. 
         [0022]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.