Abstract:
A method for quantitatively assessing a quality of a weld joint includes positioning an electromagnetic radiation source adjacent the weld joint. The electromagnetic radiation source may be aligned to direct a beam of electromagnetic radiation onto the weld joint. A detector for capturing the electromagnetic radiation emitted from the electromagnetic radiation source may be positioned adjacent the weld joint along a side opposite the electromagnetic radiation source, such that the weld joint is positioned between the electromagnetic radiation source and the detector. A radiographic image of the weld joint may be obtained by directing the beam of electromagnetic radiation toward the weld joint and onto the detector. A weld joint quality rating may be determined for the weld joint based at least in part on the radiographic image.

Description:
BACKGROUND 
       [0001]    Various destructive and non-destructive inspection methods and techniques have been developed for examining weld joints in welded assemblies. The methods include various non-destructive inspection techniques utilizing, for example, eddy-current, ultrasonic and radiographic technologies. These non-destructive inspection methods allow the welded assemblies to be used after the inspection process is completed. Other weld inspection techniques tend to be destructive in nature and may render the welded assembly unsuitable for use after the inspection process is completed. For example, inspection techniques involving sectioning and subsequent microscopic examination of the weld are destructive in nature and typically do not permit use of the welded assembly after inspection. Further, destructive weld inspection techniques are capable of only providing a reasonable indication of a probable rather than actual quality of the welds being produced. Thus, non-destructive inspection techniques tend to be more useful for determining a quality of the welds that will actually be placed in service. 
       SUMMARY 
       [0002]    Disclosed is an apparatus and method for inspecting a weld joint using non-destructive radiographic imaging. The disclosed inspection process is particularly applicable to spot welds. The process involves obtaining a digital radiographic image of a weld joint. The radiographic image may alternatively be captured on film and converted to a digital image for analysis. A spot weld may appear on the radiographic image as a dark spot surrounded by a brighter corona. The dark spot indicates a location of a weld nugget and the brighter corona corresponds to a heat affected zone caused by the welding process. A light intensity level of the dark spot corresponding to the weld nugget indicates the quality of the weld joint. Generally speaking, a lower the light intensity level (i.e., darker the spot) the better the weld quality. A quantitative weld joint quality rating may be determined based on data obtained from the radiographic image. The weld joint quality rating represents the quality of the weld joint and may be used to evaluate whether the quality of the weld joint is sufficient or further inspection of the weld joint may be warranted. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]    The various features, advantages and other uses of the present apparatus will become more apparent by referring to the following detailed description and drawings, in which: 
           [0004]      FIG. 1  is a schematic illustration of an exemplary radiographic inspection system for performing non-destructive testing of a weld joint; 
           [0005]      FIG. 2  is a schematic illustration of a radiographic image of an exemplary spot weld; 
           [0006]      FIG. 3  is a schematic illustration of a radiographic image of sample test panel including multiple spot welds of varying weld quality; and 
           [0007]      FIG. 4  is a close-up view of the radiographic image illustrated in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0008]    Disclosed is an apparatus and method for inspecting a weld joint using non-destructive radiographic imaging. The disclosed inspection process may be particularly applicable to spot welds. The process involves obtaining a digital radiographic image of a weld joint. The radiographic image may alternatively be captured on film and converted to a digital image for analysis. A spot weld may appear on the radiographic image as a dark spot surrounded by a brighter corona. The dark spot indicates a location of a weld nugget and the brighter corona corresponds to a heat affected zone caused by the welding process. A light intensity level of the dark spot corresponding to the weld nugget indicates the quality of the weld joint. Generally speaking, a lower the light intensity level (i.e., darker the spot) the better the weld quality. A quantitative weld joint quality rating may be determined based on data obtained from the radiographic image. The weld joint quality rating represents the quality of the weld joint and may be used to evaluate whether the quality of the weld joint is sufficient or further inspection of the weld joint may be warranted. 
         [0009]    Referring now to the discussion that follows and also to the drawings, illustrative approaches to the disclosed systems and methods are described in detail. Although the drawings represent some possible approaches, the drawings are not necessarily to scale and certain features may be exaggerated, removed, or partially sectioned to better illustrate and explain the present invention. Further, the descriptions set forth herein are not intended to be exhaustive or otherwise limit or restrict the claims to the precise forms and configurations shown in the drawings and disclosed in the following detailed description. 
         [0010]      FIG. 1  illustrates an exemplary radiographic inspection system  20  for performing non-destructive examination of a weld joint  21 , and in particular, as spot weld, formed in a workpiece  23  to determine its quality. The radiographic inspection system  20  may employ a radiographic imaging system  24  for obtaining radiographic images of the weld joint  21 . Various imaging technologies may be employed to obtain the radiographic images of the weld joint  21 , including but not limited to, digital radiography (also known as radioscopy) and film radiography. The radiographic imaging system  24  may include an electromagnetic radiation source  26  operable to generate an electromagnetic radiation beam  28  and a detector  30  for capturing the electromagnetic radiation energy emitted from the radiation source  26 . The electromagnetic radiation source  26  and the detector  30  are generally arranged on opposite sides of the weld joint  21  that is being inspected. The electromagnetic radiation source  26  may be positioned such that the electromagnetic radiation beam  28  is directed onto the weld joint  21 . Electromagnetic radiation passing through the workpiece  23  and weld joint  21  may be captured by detector  30 . 
         [0011]    The electromagnetic radiation beam  28  emitted from radiation source  26  may operate at a range of frequencies, such X-rays and gamma-rays. Thick materials may require use of higher energy electromagnetic radiation than thin materials to obtain a satisfactory radiographic image. X-rays typically have lower energy than gamma-rays and may be better suited for examining thin materials, whereas higher energy gamma-rays may be better suited for examining thicker materials. In practice, the operating parameters of the electromagnetic radiation used to generate a radiographic image may be tailored to accommodate the physical and material characteristics of particular weld joint being inspected. 
         [0012]    With continued reference to  FIG. 1 , the detector  30  may have any of various configurations. For example, the detector  30  may be configured as a digital detector or a film based detector. Configurations employing a film based detector may require additional image processing equipment for converting a film based radiographic image to a digital image suitable for further electronic processing. A digital detector may be configured to include a fluorescent screen or an array of solid state sensors. The digital detector may also employ re-usable flexible phosphor plates to capture images. After being exposed to electromagnet radiation emitted from electromagnetic radiation source  26 , the exposed plates may be processed through a laser scanner to produce an image that may be delivered to a monitor  32  for viewing. The resulting digital image, whether originating from a film based detector or a digital detector, may be electronically stored for future retrieval and analysis. These are only of few examples of the types of detector technologies that may be employed with detector  30 . Other methods and/or technologies capable of producing high quality digital radiographic images may also be employed. 
         [0013]    Continuing to refer  FIG. 1 , the radiographic imaging system  24  may include an image processor  34 , which may be operably connected to the electromagnetic radiation source  26  and the detector  30 . The image processor  34  may be any type of handheld, desktop, or other form of single computing device, or may be composed of multiple computing devices. The processing unit in the image processor  34  may be a conventional central processing unit (CPU)  36  or any other type of device, or multiple devices, capable of manipulating or processing data and information. A memory  38  of the image processor  34  may be a random access memory device (RAM) or any other suitable type of storage device. Memory  38  may include data  40  that may be accessed by CPU  36  using a bus  42 . 
         [0014]    Memory  38  may also include an operating system  44  and installed applications  46 , including programs that enable the CPU  36  to control operation of the radiographic imaging system  24 , as well as analyze and process the data and information collected by the detector  30 . The image processor  34  may also include secondary, additional, or external storage  48 , for example, a memory card, flash drive, or any other form of computer readable medium. The installed applications  46  may be stored in whole or in part in the external storage  48  and loaded into the memory  38  as needed for processing. 
         [0015]    To facilitate positioning of the electromagnetic radiation source  26 , particularly in manufacturing environments employing automated production systems, the radiation source may be attached to a robot  50 . The robot  50  may have any of a variety of configurations depending on the requirements of a particular application. The robot  50  may include multiple servo mechanisms for controlling movement of the robot  50 . The servo mechanisms are capable of generating forces that cause the robot  50  to perform a desired movement. For example, the servos mechanisms may cause rotation of the robot  50  about its base  52 , as well as rotation of a wrist  54  of the robot  50  relative to an arm  56  of the robot  50 . The CPU  36  of the image processor  34  may be in communication with the robot servos mechanisms to control movement of the robot  50 . 
         [0016]    With continued reference to  FIG. 1 , the radiographic inspection system  20  may include a fixture  58  for supporting the workpiece  23  relative to the electromagnetic radiation source  26  and the detector  30 . The fixture  58  may include various features for securely supporting the workpiece  23 . For example, the fixture may include various pins  60  engageable with the workpiece  23  and clamping devices  62  for securing the workpiece  23  to the fixture  58 . The fixture  58  may be stationary or moveable. For example, the fixture may include rollers  64  to facilitate positioning the fixture  58  and the workpiece  23  relative to the radiographic imaging system  24 . Configuring the fixture  58  to be moveable allows the fixtures  58  to be preloaded with a workpiece  23  prior to being moved into position relative to the radiographic imaging system  24 . 
         [0017]    The radiographic imaging inspection system  20  may be employed in connection with an automated production system, such as an assembly line. The assembly line may consist of multiple workstations that include various tooling and equipment used to produce the workpiece  23 , and may include forming, cutting, welding and assembly equipment. The radiographic inspection system  20  may be one of multiple work stations arranged along the assembly line. The fixture  58  may be used to transport the workpiece  23  between workstations of the assembly line. The radiographic inspection system  20  may be an integral part of the assembly line and configured to automatically inspect the weld joint  21 . 
         [0018]    Employing the robot  50  to position the electromagnetic radiation source  26  relative to the weld joint  21  and the fixture  58  for transporting the workpiece  23  to and from the radiographic inspection system  20  facilitates automatic operation of the radiographic inspection system  20 . For example, the fixture  58  may be used to transport and position the workpiece  23  within the radiographic inspection system  20 . With the workpiece  23  positioned within the radiographic inspection system  20 , the image processor  34  may operate robot  50  to position the electromagnetic radiation source  26  relative to the weld joint  21 . The radiographic imaging system  24  may then be activated to obtain a radiographic image of the weld joint  21 . When the inspection process is completed, the fixture  58  may be moved to transport the workpiece  23  out of the radiographic inspection system  20 . 
         [0019]      FIG. 2  schematically illustrates an example of a radiographic image  65  of the weld joint  21  formed in workpiece  23  that may be captured using the radiographic imaging system  24 . The weld joint  21  may be formed by joining a first sheet metal panel  66  to a second sheet metal panel  68 . In this particular example, a spot weld  70  is used to join the sheet metal panels, but other welding techniques may also be employed. 
         [0020]    With continued reference to  FIG. 2 , the spot weld  70  may appear in the radiographic image  65  as a generally circular-shaped spot having a dark center region  72  surrounded by a corona  74 . The corona  74  may appear brighter in the radiographic image  65  than the center region  68 . The center region  68  generally coincides with a location of the weld nugget  22  of the spot weld  70  (see  FIG. 1 ). An outer boundary  76  of the center region generally corresponds to an outer boundary  77  of the weld nugget  22 . The weld nugget  22  is formed during the welding process and results from local melting of the first and second sheet metal panels  66  and  68 . The melted material solidifies to form the weld nugget  22 . The size of the weld nugget  22  generally corresponds to the size of the center region  72  in the radiographic image  65 . Generally speaking, the larger the center region  72  the larger the weld nugget  22 . 
         [0021]    Although the center region  72  is illustrated as having a substantially circular shape, in practice the center region  72  may also have any other geometric shape. The actual size and shape of the center region  72 , and correspondingly, the size of the weld nugget  22 , may be dependent on various factors, including but not limited to, the shape of electrodes used to produce the spot weld  70 , the material composition of the sheet metal panels  66  and  68 , the presence of debris on a surface of the sheet metal panels  66  and  68 , and a thickness of the sheet metal panels  66  and  68 , as well as other factors. The center region  72  may have an average diameter “D”. 
         [0022]    The corona  74  encircling the weld nugget  22  (i.e., center region  72 ) generally corresponds to a heat affected zone caused by the welding process. The corona  74  typically extends outward from the center region  72 , and may have a radial thickness “T”. The corona  74  may appear to be brighter than the center region  72  in the radiographic image  65 . The size and shape of the of the corona  74  may vary depending on various factors, including but not limited to, the shape of the electrodes used to produce the spot weld  70 , the material composition of the sheet metal panels  66  and  68 , the presence of debris on the surface of the sheet metal panels  66  and  68 , and a thickness of the sheet metal panels  66  and  68 , as well as other factors. It is possible that a spot weld may not produce a corona  74  that is detectable in the radiographic image  65 . 
         [0023]    With continued reference to  FIG. 2 , a quality of the weld joint  21  may be assessed and quantified based on information collected from the radiographic image  65 . The radiographic image  65  may reveal several detectable weld quality indicators that individually and/or collectively may be used to qualitatively assess the quality of the weld joint  21 . The weld quality indicators may include, for example, the average diameter D of the center region  72 , the radial thickness T of the corona  74 , and an average light intensity level of the center region  72 . In particular, it has been determined that an average light intensity level of the center region  72  is a reasonably accurate indicator of the quality of the spot weld  70 . For example, a low light intensity level (i.e., dark center region  72 ) generally corresponds to a better quality weld joint. Conversely, a high light intensity level (i.e., bright center region  72 ) may indicate a poorer quality weld joint. 
         [0024]    A weld joint quality rating may be determined for the spot weld  70  based at least in part on the average light intensity level of the center region  72 . The weld quality rating may be determined directly from information obtained from the radiographic image  65  when formatted as a digital image. Additional processing may be required to determine the average light intensity level of the center region  72  when the radiographic image is formatted as a film based image. 
         [0025]    When formatted as a digital black-and-white image, the radiographic image  65  may be composed of shades of gray, varying from black at the weakest light intensity level to white at the strongest light intensity level. A magnified view of an exemplary digital image  78  of spot weld  70  is schematically illustrated in  FIG. 4 . The digital image  78  may be made up of a plurality of adjoining generally square-shaped pixels  79 . A light intensity level of each individual pixel  79  may vary to produce the radiographic image of the spot weld  70 . In the exemplary digital image  78 , the darker shaded pixels  81  correspond to the center region  72  of the spot weld  65 , and the lighter shaded pixels  83  correspond to the corona  74 . In the example image illustrated in  FIG. 4 , the pixels  82  corresponding to the center region  72  are all shown to have substantially the same light intensity level. Similarly, the pixels  83  corresponding to the corona  74  are all shown to have substantially the same light intensity level. In practice, however, the individual pixel corresponding to the center region  72  and the corona  74  will likely have differing light intensity levels. 
         [0026]    The weld joint quality rating may be computed for the spot weld  70  by separately determining a light intensity level for each of the individual pixels  81  that together form the center region  72 . The light intensities of the pixels  81  forming the center region  72  may then be numerically averaged to determine the weld quality rating of the spot weld  70 . 
         [0027]    To assess whether a particular weld joint has sufficient quality based on its determined weld joint quality rating, the weld joint quality rating may be compared against a database of verified weld joint quality ratings for similarly configured weld joints for which the quality of the weld joint has been previously confirmed. The database of verified weld quality ratings may be stored in memory  38  of image processor  34 , or external storage  48 . Verifying a quality of a weld joint may include destructively testing the weld joint to confirm its actual quality. 
         [0028]    With reference to  FIG. 3 , verified weld joint quality ratings for populating the verified weld joint quality rating database residing in memory  38  of image processor  34  may be generated, for example, by producing a test panel having multiple spot welds of differing quality. A radiographic image of the test panel may be captured using the radiographic imaging system  24 . An example of a radiographic image  80  of a test panel  82  is illustrated in  FIG. 3 . The exemplary test panel  82  includes multiple test spot welds  84 . Each test spot weld  84  may have a different weld joint quality rating, as evidenced by a change in light intensity level of a center region  86  of the spot welds  84 . A verified spot weld quality rating may be determined for each of the test spot welds  84  of the test panel  82 . The verified spot weld quality rating may be determined in the manner previously described for determining the spot weld quality rating of spot weld  70 . Each test spot weld  84  may be physically inspected to confirm the quality of each test spot weld  84 , thereby correlating the physically determined weld quality rating with the verified weld joint quality rating. 
         [0029]    To confirm that spot weld  70  is of sufficient quality, the computed weld joint quality rating for spot weld  70  may be compared against the verified weld joint quality ratings residing in memory  38  of image processor  34 . If the computed weld joint quality rating for spot weld  70  is less than a predetermined value, the spot weld  70  may be rejected or flagged for further inspection. The additional inspection may include physically inspecting the spot weld  70  or performing a destructive test procedure on the spot weld. The inspection procedure may also include performing a chisel test on the spot weld  70 . 
         [0030]    Digital radiographic images of spot welds, and their associated weld joint quality ratings, may be stored electronically in a historical weld quality database that may reside in memory  38  of image processor  34 . Alternatively, the radiographic images and associated weld joint quality ratings may be stored in a historical weld quality database that may be separate from image processor  34 , such as external storage  48 . The stored information may be monitored to detect changes in weld quality that may occur, for example, in a manufacturing production line. In addition to helping ensure production of quality parts, the ability to efficiently monitor weld quality levels may provide other benefits, such as detecting problems with production equipment that may adversely affect weld quality and require equipment maintenance to correct. For example, a detected decrease in weld quality may indicate that electrodes on a spot welder are worn and need replacing. 
         [0031]    The historical weld quality database residing in memory  38  of image processor  34  may be configured to electronically store historical weld joint quality ratings related to a particular weld joint. The weld joint quality ratings may relate to a particular spot weld on a workpiece, such as spot  70  on workpiece  23 . The stored weld joint quality ratings may be monitored to detect changes in the quality of welds being produced. If a significant change in the weld joint quality rating is detected, a physical inspection of the weld joint and/or welding equipment may be initiated to determine the source of the problem and plan corrective action. 
         [0032]    With reference to  FIG. 1 , image processor  34  may be in communication with one or more secondary computing systems, such as a quality control system  88 . The quality control system  88  may be configured to further process the data and information collected and/or generated by the radiographic inspection system  20 . The quality control system  88  may be configured for long term electronic storage of electronic weld data and information, including weld joint quality ratings, received from image processor  34 . 
         [0033]    The quality control system  88  may be similarly configured as image processor  34 . For example, quality control system  88  may be any type of handheld, desktop, or other form of single computing device, or may be composed of multiple computing devices. The processing unit in the quality control system  88  may be a conventional central processing unit (CPU)  90  or any other type of device, or multiple devices, capable of manipulating or processing data and information. A memory  92  of the quality control system  88  may be a random access memory device (RAM) or any other suitable type of storage device. The memory  92  may include data  94  that may be accessed by the CPU  90  using a bus  96 . 
         [0034]    Memory  94  may also include an operating system  98  and installed applications  100 , including programs that analyze and process the data and information received from image processor  34 . 
         [0035]    The quality control system  88  may be configured to perform any of the processes performed by image processor  34 , including conducting historical analysis of the weld joint quality ratings stored in the historical weld quality database residing in memory  38  of image processor  34 . The historical weld quality database may also be configured to reside in memory  94  of quality control system  88 . 
         [0036]    It is intended that the scope of the present methods and apparatuses be defined by the following claims. However, it must be understood that the disclosed systems and methods may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope. It should be understood by those skilled in the art that various alternatives to the configurations described herein may be employed in practicing the claims without departing from the spirit and scope as defined in the following claims. The scope of the disclosed systems and methods should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such future examples. Furthermore, all terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those skilled in the art unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc., should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary. It is intended that the following claims define the scope of the device and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. In sum, it should be understood that the device is capable of modification and variation and is limited only by the following claims.