Abstract:
A method for detecting the integrity of a bond of a multi-piece work piece includes capturing a first image of the work piece, stressing the work piece, capturing a stressed image of the work piece, and comparing the first image of the work piece with the stressed image of the work piece to determine the integrity of the bond.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure is related to non-destructively testing weld coalescence. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0003]    Bonding is a method of joining two materials together to form a single contiguous material into a work piece. The bonding process can include adhering, welding, and crimping. The two materials can be like materials, i.e., metals combined together or plastics combined together, or dissimilar materials, i.e., a combination of dissimilar metals or combination of metals and plastics. In the case of welding, the two materials are typically of similar chemical composition, e.g., each composed of a ferrous or nonferrous metals, or can be differing chemical composition, e.g., combining ferrous and nonferrous metals. The welding processes can include many forms, including arc welding, oxyfuel welding, resistance welding, electroslag welding, laser beam welding, ultrasonic welding, and electron beam welding. 
         [0004]    Welding can be localized or run the length of the interaction of the work piece. Examples of localized welding are spot welding and projection welding. Spot welding is typically a form of resistance welding wherein two electrodes hold the work pieces together and current is run through the electrodes to form a weld nugget. Projection welding utilizes raised sections on one or both of the materials to be joined. Heat can be applied to the raised sections creating a weld nugget at the projections. 
         [0005]    The welding process has many variables to consider including the duration and the amount of energy used. Once these have been determined, the welding process may be consistently repeated. Variation in either the duration or the amount of energy supplied can cause weak weld integrity or no weld integrity when an incomplete or no weld is formed in the work piece. The incomplete or no weld having weak integrity or no integrity results in less than desired joint properties, e.g., strength and electrical transfer, and can cause unexpected performance of the work piece. 
       SUMMARY 
       [0006]    A method for detecting the integrity of a bond of a multi-piece work piece includes capturing a first image of the work piece, stressing the work piece, capturing a stressed image of the work piece, and comparing the first image of the work piece with the stressed image of the work piece to determine the integrity of the bond. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0008]      FIG. 1  schematically illustrates an exemplary intercell connector that includes a plurality of welds for use in a battery, in accordance with the disclosure; 
           [0009]      FIG. 2  is a schematic illustration of a shearography testing apparatus in use on a work piece, in accordance with the present disclosure; 
           [0010]      FIG. 3  is a schematic illustration of an exemplary work piece having a bonded area and a free area with a representative shear diagram during loading, in accordance with the disclosure; 
           [0011]      FIGS. 4-1 ,  4 - 2 , and  4 - 3  are schematic illustrations of shearography results during vibrational loading of a work piece with three good spot welds at different vibrational frequencies, 4.5 KHz, 9.3 KHz, and 11.5 KHz, respectively, in accordance with the present disclosure; and 
           [0012]      FIGS. 5-1 ,  5 - 2 , and  5 - 3  are schematic illustrations of shearography results during vibrational loading of a work piece with single good spot weld at different vibrational frequencies, 5.0 KHz, 8.7 KHz, and 11.9 KHz, respectively, in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same,  FIG. 1  schematically illustrates an exemplary intercell connector  10  that includes a plurality of bonds, i.e., spot welds  12 , for use in a battery. The intercell connector  10  includes a connector bus  14  for interconnecting a plurality of plates  16 . The connector bus  14  has a generally U-shaped cross section that extends from a first end  18  to a distal second end  20 . The U-shaped cross section includes a base  22  and first and second attachment members  24  and  26 , respectively. The second end  20  includes an interconnection tab  28  for interconnecting the battery to other batteries and devices as is required for a specific application. 
         [0014]    The first and second attachment members  24 ,  26  are welded to a respective first and second sets of plurality of plates  30 ,  32 . The first and second sets of plurality of plates  30 ,  32  includes an inner plate  34 , a middle plate  36 , and an outer plate  38 . Since the first and second sets of plurality of plates  30 ,  32  iares identical, only the first set of plurality of plates  30  will be described in detail. The inner plate  34 , middle plate  36 , and outer plate  38  include a vertical section  40  that generally overlap the vertical attachment member  24  for bonding thereto. In the exemplary embodiment the bonding is achieved by three spot welds  12  securing the first set of plurality of plates  30  to the connector bus  14 . The inner plate  34  extends below the base  22 , steps inwardly toward a center of the base  22 , then downwardly in a generally vertical direction away from the base  22  to a bottom edge  42 . The middle plate  36  extends generally vertically downward to a bottom edge  44  in line with the bottom edge  42 . The outer plate  38  is symmetrically opposite of the inner plate  34  about the middle plate  36 , i.e., the step is outwardly away from the center of the base  22  and has a bottom edge  46  in line with bottom edge  42 . The inner plate  34 , middle plate  36 , and outer plate  38  can then be inserted into an electrolyte reservoir thereby creating a chemical reaction to produce electricity. It will be apparent that the first and second set of plurality of plates  30 ,  32  can be a plurality of pasted plates, Planté plates, flat plates, tubular plates, or any other electrode capable of transferring electricity when introduced into an electrolyte. 
         [0015]    Each spot weld  12  fuses the inner plate  34 , middle plate  36 , and outer plate  38  to the connector bus  14  and permits efficient current flow from each of the inner, middle, and outer plates  34 ,  36 ,  38  to the connector bus  14 . The connector bus  14  transfers the current flow to the other batteries or devices that are connected therewith. An inadequate spot weld  12  that does not properly fuse a single plate to the remainder of the plurality of plates  30 ,  32  and to the connector bus  14  creates sub-optimum current flow and can prevent current flow altogether. The inadequate spot weld  12  can prevent the battery from providing the expected amount of current thereby preventing proper operation of a device that is being supplied current. The inadequate spot weld  12  can be determined by utilizing shearography. 
         [0016]      FIG. 2  is a schematic illustration of a shearography testing apparatus  50  for use on a work piece  100 , e.g., the intercell connector  10 . The shearography testing apparatus  50  includes a laser  52 , wedge  54 , lens  56 , and image capturing device  58 . The laser  52  is a light emitting device that can be precisely aimed to illuminate specific areas of a target or the entire target, e.g., the work piece  100 . The wedge  54  is capable of changing the trajectory of the light source by a predetermined amount. The lens  56  receives divergent light emissions and refocuses the light emissions at a predetermined distance thereby maintaining a scaled image. The image capturing device  58  is a digital image capturing sensor, such as a CCD sensor as is commonly known in the art, capable of recording an image projected upon the sensor. The lens  56  is located between the work piece  100  and the image capturing device  58  at a predetermined distance to refocus the light emissions in accordance with the shearography testing apparatus  50 . The wedge  54  is located between the work piece  100  and the lens  56  and is positioned over one-half of the lens  56  to create an appropriate change in light trajectory for one-half of the light entering the lens  56 . 
         [0017]    The work piece  100  is positioned within the shearography testing apparatus  50  in a way that allows the laser  52  to illuminate the work piece  100 . The light from the laser  52  can be projected on to the work piece  100  through a beam splitter  60 . The beam splitter  60  spreads the light from the laser  52  over a wider area than the original light beam, represented by a first beam  62  and a second beam  64 . It is understood that discussion of the first beam  62  and second beam  64  is only for easily defined reference points and that the portion in between the first beam  62  and second beam  64  behaves similarly to the closest reference beam. 
         [0018]    The first beam  62  illuminates a first point  66  on the work piece  100  that is refracted toward the lens  56  in a first upper beam  68  and first lower beam  70 . The second beam  64  illuminates a second point  72  on the work piece  100  that is refracted toward the lens  56  in a second upper beam  74  and a second lower beam  76 . The first lower beam  70  and second lower beam  76  enter the lens  56  and are projected onto the image capturing device  58  at a first projected point  86  and a second projected point  88 . 
         [0019]    The first upper beam  68  and second upper beam  74  are projected to the wedge  54 . The wedge  54  refracts a majority of the first upper beam  68  and second upper beam  74  thereby creating an offset of a predetermined amount. The portion of light that is not offset is shown by a first focus beam  80  and a second focus beam  82 . A first image is presented to the image capturing device  58  as indicated by the first projected point  86  and the second projected point  88  representing the area of the work piece  100  between the first point  66  and the second point  72 . The first upper beam  68  and the second upper beam  74  has a focal point along line  84  at the same distance between the lens  56  and image capturing device  58  as the first focus beam  80  and the second focus beam  82 . A second image is presented to the image capturing device  58  as indicated by an offset first projection point  90  and an offset second projection point  92 , the latter corresponding to the position of the first projected point  86 . 
         [0020]    The resulting first and second images provide a superimposed first image on the image capturing device  58  that is recorded. The work piece  100  is subjected to stress, e.g., changes in loading, temperature, vacuum, and vibration, then a superimposed stressed image is recorded from the image capturing device  58 . The first image and the stressed image are compared, i.e., added or subtracted, to determine shear lines and impurities in the work piece  100  to create a shear image. The shear image may be compared to a reference image that indicates an expected resultant image. The comparison can be completed either manually or by way of automation. It is evident that when the work piece  100  is subjected to a vibrational load, the images can be recorded at the extremes of excitation of the work piece  100 , i.e., at a position closest to and furthest from the image capturing device  58 . 
         [0021]      FIG. 3  is a schematic illustration of an exemplary work piece  100  having a bonded area, such as a weld, and a free area, an area without any bonding, with a representative shear diagram under loading. The work piece  100  includes an upper member  102  and an adjacent lower member  104  that have a single common bonded area, i.e., spot weld  106 . The load is applied equally to the work piece  100  along the upper and lower members  102 ,  104  in a direction away from the spot weld  106 , i.e., in the direction represented by arrows  108 . The spot weld  106  maintains the relationship between the upper and lower members  102 ,  104  whereas deflection increases as the distance increases from the spot weld, as indicated by the dashed lines. The strain diagram  110  indicates an area of no strain  112  corresponding to the size of the spot weld  106 . However, a relatively large strain  114  exists adjacent the spot weld  106  and decreases as the distance from the spot weld  106  increases. 
         [0022]    A vibrational load  116  may be applied to the work piece. The vibrational load  116  can be randomly applied or controlled to a specific frequency or series of frequencies. The vibrational load  116  results in a similar occurrence as discussed above with relation to the load. That is, as the work piece  100  is excited, the point at which the work piece  100  is bonded, i.e., spot welded  106 , and maintains the relationship between the upper and lower members  102 ,  104 . Deflection of the upper and lower members  102 ,  104  increases as the distance increases from the spot weld, as indicated by the dashed lines. The strain diagram  110  remains the same, i.e., the area of no strain  112  corresponds to the size of the spot weld  106  and a relatively large strain  114  adjacent the spot weld  106  that decreases as the distance from the spot weld  106  increases. This relationship holds for a single spot weld  106  or a series of spot welds. The frequency of the vibrational load  116  can be changed to match the spacing of the spot welds in such a way as to provide easily distinguishable shearography results. It will be apparent that the vibrational load  116  can be at the natural frequency of the work piece or one or more pieces that form the work piece. 
         [0023]    The shearography is able to detect the strain  114  adjacent the spot welds  106  by creating a node point at the location of the spot weld  106 , i.e., the spot welds  106  will show a consistently shaded image during the shearography image comparison. Where a spot weld  106  has weak weld integrity or no weld integrity, the shearography image will show part deflection by way of shaded variation through the portion of the spot weld that has weak or no weld integrity. 
         [0024]      FIGS. 4-1 ,  4 - 2 , and  4 - 3  are schematic illustrations of shearography during vibrational loading of a work piece with three good spot welds at different vibrational frequencies, 4.5 KHz, 9.3 KHz, and 11.5 KHz, respectively.  FIG. 4-1  is illustrative of the work piece  100  excited to a vibrational frequency of 4.5 KHz and displaying three node points  130 , a left node point  131 , a middle node point  133 , and a right node point  135 , indicating three spot welds. The node points  130  indicate well formed spot welds, i.e., the respective node points  130  are consistent with the overall shape of the spot weld. A double image of the left, middle, and right node points  131 ,  133 ,  135  occur due to the shearography images taken at the extremes of the vibration cycle, i.e., the furthest point from the camera and the closest point to the image capturing device, being overlaid upon each other, as described above. Shear lines  132  occur at the 4.5 KHz frequency that wrap around the combination of the three node points  130 . The shear lines  132  begin generally under the middle and left node points  133 ,  131 , respectively, at the edge of the work piece and extend upwardly toward the associated node point  130  and to the left. The shear lines  132  extend around and above the left node point  131 . The shear lines  132  continue by extending to the right node point with a generally upwardly trend. Additional shear lines begin at the top of the middle and right node points and follow the same general pattern. 
         [0025]      FIG. 4-2  is illustrative of the work piece  100  excited to a vibrational frequency of 9.3 KHz and displaying three node points  140 , a left node  141 , a middle node  143 , and a right node  145 , indicating three spot welds. Each of the node points  140  show well formed spot welds. The double image of the node points  140  occur due to the shearography images taken at the extremes of the vibration cycle, as discussed above. Due to the higher frequency with respect to  FIG. 4-1 , the lower shear lines  142  occur along the bottom of each of the node points  140  in a generally half elliptical pattern with a closed end in line with the respective node point  140  and an open end extending to the end of the work piece. Since each of the left node  141 , the middle node  143 , and the right node  145  have associated lower shear lines  142 , the lower shear lines  142  help identify when spot weld is well formed. The upper shear lines  144  start above each of the node points  140  extend upwardly and turn to the right in a generally horizontal direction. 
         [0026]      FIG. 4-3  is illustrative of the work piece  100  excited to a vibrational frequency of 11.5 KHz and displaying three node points  150 , a left node  151 , a middle node  153 , and a right node  155 , indicating three spot welds. Each of the node points  150  show three well formed spot welds. The double image of the node points  150  occurs due to the shearography images taken at the extremes of the vibration cycle, as discussed above. Due to the higher frequency with respect to  FIGS. 4-1  and  4 - 2 , the lower shear lines  152  along the bottom of the node points  150  behave differently. The lower shear lines  152  have three groupings, each with a generally half-elliptical pattern with a closed end toward the node point  150 , however only the left set of lower shear lines  152  remains directly under the left node point  151 . The middle set of lower shear lines  152  is offset from the middle node point  153  and generally aligned under a left side of the middle node point  153 . The right set of lower shear lines  152  is formed under the right node point  155  but further extends under a right portion of the middle node point  153 . The upper shear lines  154  are generally centered above each of the node points  150  extending upwardly then turning right to a generally horizontal direction. 
         [0027]      FIGS. 5-1 ,  5 - 2 , and  5 - 3  are schematic illustrations of shearography during vibrational loading of a work piece with single good spot weld at different vibrational frequencies, 5.0 KHz, 8.7 KHz, and 11.9 KHz, respectively.  FIG. 5-1  is illustrative of the work piece  100  excited to a vibrational frequency of 5.0 KHz and displaying a single node point  160  indicating one well formed spot weld and a left and middle indentation  162 ,  164  at areas spot welds failed to form. A double image of the node point  160  and the left and middle indentations  162 ,  164  occur due to the shearography images taken at the extremes of the vibration cycle, i.e., the furthest point from the camera and the closest point to the camera, being overlaid upon each other. Shear lines  166  surround the right node point  160  due to the stability of the spot weld. Both the left and middle indentations  162 ,  164  include a series of shear lines  166  that extend through the left and middle indentations  162 ,  164 . The shear lines  166  extending through the left and middle indentations  162 ,  164  is indicative of a failed spot weld in each of the left and middle indentation locations  162 ,  164 . 
         [0028]      FIG. 5-2  is illustrative of the work piece  100  excited to a vibrational frequency of 8.7 KHz and displaying a single node point  170  and a left and middle indentation  172 ,  174 , respectively at areas spot welds failed to form. A double image of the node point  170  and the left and middle indentations  172 ,  174  occur due to the shearography images taken at the extremes of the vibration cycle, as discussed above. The left and middle indentations  172 ,  174  are indicative of failed spot weld locations. Shear lines  176  surround the right node point  170  due to the stability of the spot weld. The shearography image of the node point  170  is smaller than the respective indentation representing a smaller than expected weld joint indicating weak weld integrity. Both the left and the middle indentations  172 ,  174  include a series of shear lines  176  that extend through the left and middle indentations  172 ,  174  and represent failed spot welds at the left and middle indentation locations. 
         [0029]      FIG. 5-3  is illustrative of the work piece  100  excited to a vibrational frequency of 11.9 KHz and displaying a single node point  180  and a left and middle indentation  182 ,  184 , respectively, at areas spot welds failed to form. A double image of the node point  180  and the left and middle indentations  182 ,  184  occur due to the shearography images taken at the extremes of the vibration cycle, as discussed above. Shear lines  186  surround the right node point  180  due to the stability of the spot weld. The right node point  180  is approximately the same shape as the respective indentation indicating a well formed spot weld. Both the left and middle indentations  182 ,  184  have a series of shear lines  186  extending through the left and middle indentations  182 ,  184  representing failed spot welds at each of the left and middle indentation locations. 
         [0030]    The above description provides information upon which a non-destructive bond detection scheme can be assembled when stressing the work piece and capturing of stressed and non-stressed images or stressed images captured during extremes of excitation. One example can be providing a single frequency that is predicted to provide shear lines for shearographic imaging through non-bonded sections to detect proper bonding. Another example can be matching the vibrational frequency with the natural frequency of the bonded or non-bonded work piece for shearographic imaging to detect proper bonding. Still another example can be providing a series of frequencies for shearographic imaging to detect proper bonding. Yet another example is to capture a non-stressed image and stress the work piece via loading. In any case, a series of look-up tables or charts can be used to easily identify acceptable spot weld integrity with analysis occurring manually or through automation. Additionally, an area calculation can be used to determine if an appropriate amount of bonding has occurred for each bonding location of a work piece. 
         [0031]    The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.