Abstract:
An external focused ultrasonic beam, non-destructive, open-air, inspection method of sheet metal spot and seam weldments using a probe in combination with motion measurement of the probe over the weldments during inspection without immersion of the material. Reflected ultrasonic waves are received and signals produced and processed or displayed as A-scan, B-scan and C-scan images that are easily recognized. An A-Scan is based on the time-of-flight difference between the outer surface, the weldment and inner and opposite surfaces of the component. B-scan and C-scan indicate the degree of weld fusion and provide data relative to fused thickness and defects sheet metal or welds. A special purpose scanner that enables ultrasonic examination welds. Scanner is pencil like ultrasonic probe with bearing face and position sensing device disposed adjacent a weld position. Scanner collects data for method to determine various characteristics of welded items.

Description:
This application claims priority from U.S. Provisional Application Ser. No. 60/354,688 filed Feb. 6, 2002, and is a continuation of utility patent application having Ser. No. 10/361,714 and filed on Feb. 6, 2003, now abandoned. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a specialized scanner and method of inspecting the integrity of spot and seam welds and more particularly it relates to an ultrasonic, nondestructive method of inspecting spot and seam welds. 
   2. Description of the Prior Art 
   Heretofore, the inspection of spot and seam welds has been performed using visual, radiographic and ultrasonic methods; as described in the Nondestructive Testing Handbook (Metals Handbook, 9th Edition, Volume 17, “Nondestructive Evaluation and Quality Control”, ASM International, Metals Park, Ohio, September, 1989, pg. 335) and the Metals Handbook (Nondestructive Testing Handbook, 2nd Edition, Volume 7. “Ultrasonic Testing”, American Society for Nondestructive Testing, Columbus, Ohio, 1991, pgs. 10–12 and pgs. 557–566). The visual and radiographic methods reveal little or nothing concerning the fusion of these welds. The prior art ultrasonic method referred to in the literature as a pulse-echo method however is generally referred to as a ring down technique throughout the industry (Nondestructive Inspection of Spot Welds, Overview of Symposium held at Center for Nondestructive Evaluation Nov. 6, 1997). It makes use of the reflected amplitude and the envelope formed in time by many multiple reflections. Basically an envelope of these reflections are used to indicate if the weld is fused or not. Destructive sampling techniques of welds have also been in use. This has been done by either separating the sheets with a chisel or with a tensile pull technique. Another destructive technique in common use cuts through the weldment, polishes and enhances the weldment so that the dimensions of the fused part of the weld can be measured optically. In this prior art, (Recommended Practices for Test Methods for Evaluating the Resistance Spot Welding Behavior of Automotive Sheet Steel Materials, SAE publication ANSI/AWS/SAE/ D8.9-97; Specification for Resistance Welding of Carbon and Low-Alloy Steels, American Welding Society, AWS C1.4M/C1, 4:1999), the part is destroyed and the dimensions of the weld are used to infer the weld quality. 
   Although there are many ultrasonic transducers and scanners in the prior art none has adapted to the features needed to measure the unique parameters and topology encountered in spot welds. The prior art has used immersion scanners for making B-scan and C-scan images that are convenient for making the measurements required. This process requires the part be placed in a tank of water having sufficient volume to immerse the spot weld being inspected, orienting the part to the transducer and scanner axis and drying the part afterwards. The immersion tank must fit the largest part and, as a result is usually too large to be made portable. The water in the tank requires conditioning and adds to the size of the system. A skilled operator is required to use such equipment to make proper images. 
   It would be advantageous to have a technique and system that includes the capability to accurately measure dimensions of fusion in the weldment and to determine the presence of weld defects. Using the dimensions of the fused sections as a quality indicator would make the ultrasonic process highly reliable and accurate and save on industrial injury which sometimes occurs during the expensive destructive quality tests of welds. Additionally, a compact, lightweight scanner that is better adapted to the scanning needs of spot weld inspection in a factory environment is needed, one that can make all the measurements, in the manufacturing environment, and require lessor skills and training. The present invention provides such a technique and system, as well as a compact, lightweight scanner design. 
   SUMMARY OF THE INVENTION 
   Spot and seam weldments in sheet metal components are non-destructively inspected by a method in which a focused ultrasonic beam is directed into the weldment from the outside surface together with a means for measuring the motion of the ultrasonic beam over the weldment without the welded material being immersed in water or some other liquid. Reflected ultrasonic waves are received and signals indicative thereof are produced and processed or displayed as image forms that are easily recognized by an operator. This data is displayed as an A-Scan where a predetermined time window is established on the display, based on the time-of-flight difference between the outer surface, the weld interface or interfaces and the inner or opposite surface of the component. Certain ultrasonic signals are indicative of the degree of complete fusion in the weld zone and provide data relative to the total fused thickness and to defects either in the sheet metal or in the weld. 
   A manual or mechanized scanner is used to move the ultrasonic transducer in a predetermined scanning motion on the surface of the part at a constant height stand-off distance. This ultrasonic transducer both generates the transmitted waves and receives the reflected waves from the weldment. Coupling of the ultrasonic transducer to the component is achieved via a continuous liquid couplant column (usually water filled). Encoder readings are received from the scanner, which provides dimensional data, relating the position of the ultrasonic transducer on the surface of the part. By combining the ultrasonic and the encoder data, B and C-Scan images (cross sectional and plan views) of the component are generated and displayed. These images are easily used to determine the quality of the weldment in question. These displays are then used to measure the diameter of spot welds, the distance between spot welds, the length and widths of seam welds plus the size, shape and location of defects, such as porosity or lack of fusion, within the weldments, plus laminar type defects, either in the base material or the weld zones. 
   A “pencil like” probe having an interchangeable tip is used to perform inspections of spot weldments in sheet metal components. This probe can be hand manipulated for scanning purposes, or can be attached to some mechanical scanners. The hand manipulation permits the examination of spot welds that are in locations with minimal or tight clearances, in locations on complex surfaces and orientations, and in locations where access is limited and complex. The probe is elongated to allow the user some flexibility in gripping the probe. 
   In order to make a useful inspection of the spot weld, some bearing means is required for moving the probe against and across the spot weld area of sufficiently uniform rate and to position an ultrasonic transducer at a sufficiently uniform space above the spot weld area. The hub tip bearing surface material is selected to facilitate easy scanning. The tip of the probe uses an interchangeable “hub” having a diameter large enough to traverse the surface marks made by the welding electrodes during the welding process. 
   The encoder is attached to a clamp to a top plate by a rod connecting it to the probe housing. The clamp serves as a position reference to the top plate using a magnetic clamp, a vacuum clamp or, if used on a reasonably level surface, clamping can be accomplished by a sufficiently weighty block. 
   These features when combined in this fashion, result in a feasible and portable scanner that is capable of making a broad range of nondestructive spot weld measurements without the need for an immersion tank. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of four metal plates that overlap various degrees of each other to illustrate typical spot and seam welds; 
       FIG. 2  is a simplified side plan view of the ultrasonic transducer and liquid column of the present invention showing ultrasonic propagation to and from the metal plates and the weld; 
       FIG. 3  is similar to  FIG. 2  with details of a transducer scanner added; 
       FIG. 4  illustrates a combination x and y axis scan pattern on the surface of a first plate at the location of a seam weld with a second plate; 
       FIGS. 5 ,  6  and  7  illustrate the use of ultrasonic techniques using A-scans, B-scans and C-scan to evaluate spot and seam weldments; 
       FIG. 8  is a system block diagram of the present invention; 
       FIG. 9  illustrates a spot weld cross section showing representative dimensions that are practical to be measured using the probe of the present invention; 
       FIG. 10  illustrates the nominal size and shape of a typical weld electrode; and 
     FIG.  11 provides sample dimensions for a weld electrode as shown in  FIG. 10 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The spot and seam type welds used to attach two or more sheets, or plates, of metal together are addressed, as shown, in  FIGS. 1 ,  2 ,  3 ,  4 ,  6  and  7  where the measurement of fused weldment dimensions is one of the objectives of the present invention. Since ultrasonic waves penetrate a fused weld zone, the method of the present invention is capable of non-destructively, in open-air, determining the length of a continuous fused section(s) which easily relate to weld strength without immersing the material being tested in water or another liquid. Additionally, ultrasound is sensitive to common weld defects which will be seen below. 
   The present invention uses a focused ultrasonic beam with a means for encoding transducer movement to measure the length and penetration of a fused weldment. The present invention uses an ultrasonic transducer selected to provide a signal with a frequency that will be transmitted by properly fused weldments and blocked, or refelcted by weldment defects. The focused ultrasonic beam is also used to measure critical lengths of fusion in both spot and seam welds as shown in  FIG. 1 . The dimensions labeled  1 ,  1 ′,  1 ″ represent the length of the spot welds depicted,  2  represents the length of the fusion zones of the seam weld depicted and  3  represents the distance between fusion zones, the welds being made in the welded plates (or sheets)  7 ,  7 ′,  7 ″,  7 ′″ as depicted in  FIG. 1 . Defect dimensions and location are also measured by the present invention; such as those illustrated as weld lack of fusion  4 , porosity  5  or laminar defects  6  as illustrated in  FIG. 1 . 
   Spot and seam weld(s) of the types illustrated in  FIG. 1  are normally used to fuse two or more sections of sheet metal together. As such they can be considered as a lap type joint. They are produced by placing electrodes in contact with opposing surfaces of the sheets to be fused and directly in line with each other. A predetermined amount of pressure is applied to assure good contact of the electrodes with the metallic surfaces and good contact between the surfaces to be joined. An electrical current is then passed from one electrode to the other flowing through the metal sheets generating heat in the metal. The proper combination of heat and applied pressure results in a portion of the surfaces of the two sheets being welded, or fused, together. Normally the position of such welds can only be seen visually due to a slight surface depression caused by the pressure of the electrodes and possibly by some discoloration due to the heat. Naturally the size of the actual fusion zone is critical to the integrity of the component as is the detection of defects which could jeopardize the integrity of the weld itself. Such defects include lack of fusion within the weld zone ( 4 ), porosity ( 5 ) and laminar type defects ( 6 ), either in the weld, or in the base material of the sheets adjacent to the fused areas. In the case of a series of spot welds the distance between the fused zones of the welds can have a direct effect on the overall strength of the welded component. 
   All of these quality related features can be detected, measured and evaluated using the present invention.  FIG. 1  is a diagram showing the different types of resistant weld configurations and include illustrations of defects such as the lack of fusion in a weld and plate laminations adjacent to a weld edge. The dimensions of interest in determining weld strength can be measured; such as the length of the fusion zones of spot welds, the distance between spot welds plus the length and width of seam welds. To accomplish this, a beam of ultrasound (typically 5–25 MHz) is directed into the metal sheets just above the area of fusion. 
   Since the velocity of sound in metals has been predetermined and is known, the time of flight of the ultrasonic beam in the material is directly related to the distance the beam travels to reach and return from a reflector. In the case of two or more metal sheets that have been fused together, that distance will be the total combined thicknesses of the two sheets; if there is no fusion zone or if the fusion is incomplete the distance traveled will be much less. All of this data is processed by a data acquisition system (see  FIG. 8 ) into commonly used displays (Nondestructive Testing Handbook, Volume II. Edited by the Society for Nondestructive Testing, Ronald Press, N.Y. 1963, pgs 43–34 through 43–36). It can be displayed as amplitude (intensity) vs. time on an oscilloscope type display both in real time or at some convenient later time using data storage techniques. 
     FIG. 2  is a simplified diagram of an ultrasonic probe  8  including an ultrasonic transducer  11  and a liquid column  25 . The ultrasonic transducer  11  produces an ultrasonic beam  10 , that passes through liquid column  25  (typically water filled), directed to the top of upper plate  12 . Beam  10  passes through the top of the entry plate  12  to a weld  14 . If fusion has occurred (i.e., weld  14  is a good weld) beam  10  will pass through weld  14  and through the near side of bottom plate  13 . In that situation ultrasonic beam  10  is be reflected back to transducer  11  from bottom surface  15  (the far surface of plate  13 ) (where two or more plates are joined together typically referred to as lap welded). If fusion has not occurred, or a lack of fusion exists, or some other discontinuity is present (i.e., a poor or incomplete weld), beam  10  will not pass through fusion zone  14  and instead is reflected back to transducer  11  from the far side of plate  12  instead of surface  15  as discussed above for a good weld. As probe  8  is moved relative to the surface of plate  12  at a constant height stand-off distance to a location above a point where there is no fusion zone between plates  12  and  13 , or if weld  14  is poor, ultrasonic beam  10  will be reflected back from the far-side of plate  12 , instead of from surface  15 . 
     FIG. 3  adds more details to that which is shown in  FIG. 2 . Here scanner  70  includes ultrasonic probe  8 , position encoder  20 , replaceable nose piece  28 , rod  30  and traction clamp  26 . Within probe housing  24  of probe  8  is ultrasonic transducer  11  and liquid column  25  (introduced in  FIG. 2 ), and a data connector  9  at the distal end to connect ultrasonic transducer  11  to a data acquisition system  23  (see  FIG. 8 ). The proximate end of probe housing  24  includes a cone section  27  that tapers down to a cylindrical tip  18 . At the juncture of cone  27  and tip  18 , there is a membrane  29  to retain the liquid within liquid column  25 . Tip  18  makes contact with the surface to be scanned with nose piece  28  surrounding the lower portion thereof and having a couplant inlet  22  shown extending laterally into the upper region of tip  18 . To allow measurement of different size welds of interest, the diameter of nose piece  28  can be varied by selecting one with a, diameter that complements the weld size. The couplant between the top surface of sheet  12 , and tip  18  and nose  28  is typically water that is supplied via couplant inlet  22  from a source not shown. 
   Position encoder  20  is connected to the exterior of probe housing  24  close to the surface being scanned. Coupled to encoder  20  (shown extending to the left) is rod  30  that is connected to traction clamp  26  that is in contact with the top surface of the workpiece being scanned (top of bottom sheet  13  in this view). Encoder  20  also provides an output signal to data acquisition system  23  (see  FIG. 8 ). Tip  18  of probe  8  is shown in contact with the top surface of sheet  12  of the workpiece, as in  FIG. 2 , to examine weld  14  between plates  12  and  13  using focused ultrasonic beam  10  delivered through cone section  27 . Encoder  20  measures the lateral movement of probe  8  relative to the surface of the workpiece. The output signals from encoder  20  and transducer  11  are routed to an ultrasonic data acquisition system  23  (see  FIG. 8 ). 
   Transducer  11 , for the inspection of welds, normally has a frequency range of 5 to 25 MHz, depending on the material and thickness to be examined (e.g., sheets  12 ,  13 ). Additionally, the material of membrane  29  is selected to be thin and essentially transparent to ultrasonic beam  10  at the frequencies of interest. As mentioned above, the proximate section of housing  24  consists of a cone  27  angled so that the focused ultrasonic beam  10  only exits through a small hole in tip  18 , where probe  8  contacts plate  12  to perform the desired examination. Cone  27  is shown filled with a couplant (usually water or another liquid) that is sealed therein by membrane  29 . If desired, a couplant inlet (not shown) could also be provided to the interior of probe assembly  24  to replenish any couplant which may slowly escape, as desired or as the result of a leak from one of the components. Alternatively, couplant entering tip  18  from couplant inlet  22  could also provide the coupling medium for the focused ultrasonic beam  10  to travel through cone  27  and to wet the workpiece surface to couple ultrasonic beam  10  to plate  12 . The focused ultrasonic beam  10  allows the size of cone  27  to be minimized and to yet provide high spacial resolution to weld  14 . 
   Additionally, traction clamp  26  provides a position reference from the workpiece using either a magnetic clamp, a vacuum clamp or, if used on a reasonably level surface, traction clamp  21  could be a sufficiently weighty block. Alternately, encoder  20  could be mounted to a portion of probe  8  other than that shown in  FIG. 3 . Normally probe  8  is hand held and scanning is performed manually; however, a motor driven scanning mechanism could also transport probe  8 . 
   Replaceable nose piece  28  sliding on the high point of the plate  12  provides improved accuracy in first plate height measurements (distortion  93  and indentation depth  90  in  FIG. 9 ) as probe  8  is moved along plate  12 . Nose piece  28  acts as a bearing and provides a steady reference against plate  12 , allowing accurate measurements of the surface, thickness and electrode impression of plate  12 . 
   As a result of the combination of probe  8 , encoder  20 , clamp  26  and selectable nose piece  28 , measurements in addition to those of the quality of an internal weld are practical by using the present invention. Examples of height related dimensions include: the measurement of high points in the weld area, the depth of defects, the welded thickness and the depth of indentation of the surfaces at the point of the weld. Also, the shape, the orientation and/or the diameter of the weld electrode indentation can be measured relative to the surface of the top plate using this probe. The shape of the welding electrode can also be measured. In addition, the thickness of the finished weldment can be measured. Further, any combination of the above parameters can be measured. 
   If traction clamp  26  is a traction wheel with encoder  20  connected to the center axis thereof, as probe  8  is moved, the traction wheel rolls along the top surface of plate  12  with that rotation converted to distance traveled by encoder  20 , which provides position information when the starting point of the scan is known and thus the location of transducer  11  with respect to weld  14  can be determined. Use of a typical position encoder  20  to measure the relative location of the ultrasonic transducer  11  accomplishes the acquisition of the essential ultrasonic data related to weldment dimensions in front of, and behind, the plane depicted in  FIG. 3  (top and bottom surfaces of sheets  13  and  12 , respectively). 
   In  FIG. 3  transducer  11  is focused so the focal zone includes the working depth of the welds of interest. In some cases, particularly when using larger diameter beamwidths for focused ultrasonic beam  10  on uneven or distorted surfaces, a flexible membrane may be added above the contact surface of probe  8  (see U.S. Pat. No. 6,298,727), so that the bottom of liquid column  25  takes the shape of the distorted surface and good coupling is maintained. 
   The steadiness gained by sliding nose piece  28  of probe  8  over or across the high point of the weld is also compatible with a commonly used ultrasonic technique known as “surface following” or “automated surface following” and is utilized in the ultrasonic signal processing current practice. 
   The present invention includes the elements of a system that are used to accurately measure the aforementioned dimensions in the weldment and to determine the presence, the location, the shape and to classify weld defects. Obtaining the ultrasonic measurements of weldment dimensions is non-destructive and provides a highly reliable, timesaving, unique and accurate means of determining the quality of spot welds. 
     FIG. 4  is a sketch illustrating two plates  32  and  33  attached one to the other by weldment  31 . To obtain a C-scan of weldment  31 , a scanning pattern  30  as shown in  FIG. 4  is used. The prior art contains several means for evaluating the weld dimensions from the ultrasonic data such as commonly referred to as A-scans, B-scans and C-scans (Metals Handbook, 9th Edition, Volume 17, “Nondestructive Evaluation and Quality Control”, ASM International, Metals Park, Ohio, September, 1989, pg. 335; Nondestructive Testing Handbook, 2nd Edition, Volume 7. “Ultrasonic Testing”, American Society for Nondestructive Testing, Columbus, Ohio, 1991, pgs. 10–12 and pgs. 557–566). In order to collect a proper B-scan the operator must use the same judgment for positioning the ultrasonic beam as used in positioning the weldment cuts for the destructive evaluations. A raster scan eliminates the need for accurate positioning of the B-scan by employing the C-scan ultrasonic techniques. This is especially useful when evaluating a seam weld as shown in  FIG. 4 . 
   Turning now to  FIGS. 5A ,  5 B and  5 C with each illustrating an oscilloscope displays of a typical A-Scan of reflected ultrasonic signals from different reflectors associated with the welds, as shown in  FIGS. 1 and 2 . In each of  FIGS. 5A ,  5 B and  5 C, the horizontal axis of each A-scan is calibrated in time lapse after the initial pulse, IP, or distance  43  into the material and the vertical axis is calibrated in amplitude  44  of the signals.  FIG. 5A  shows an A-scan  40  of reflections  46 ,  46 ′ and  46 ″, at intervals of one thickness of a plate  7  in  FIG. 1 , that correspond to a situation where there is no fusion between two plates, which is the same as the reflections of a single plate, i.e., the reflections for an interval of one thickness of a plate taken on the left side of plate  7  in  FIG. 1 . Note, the time lapse (or material distance  43 ) starting with the IP and continuing with  46 ,  46 ′ and  46 ″ represent the same values in each of  FIGS. 5A ,  5 B and  5 C.  FIG. 5B  shows an A-scan  41  of reflections  46 ′ that correspond to a point where there is full fusion between two plates such as weld  14  between plates  12  and  13  in  FIG. 2 . A-scan  41  of  FIG. 5B  also represents reflections that correspond to a point on a stack of three plates where there is full fusion between the top and middle plates and a lack of fusion between the middle and bottom plates, thus the reflections are from the bottom surface of the middle plate  7 ′ which is substantially the same as the reflections from two plates with full fusion between them.  FIG. 5C  shows an A-scan  42  of reflections  46 ″ that correspond to a point on a stack of three plates where there is full fusion between the top and middle plates  7  and  7 ′ and full fusion between the middle and bottom plates  7 ′ and  7 ″ with the two fusion points being substantially aligned with each other. 
     FIG. 6A  is a cross-section view that shows a number of different weldments between plates  51 ,  52  and  53  from top to bottom, one on top of the other. Starting from the left there is a point  58  that lacks fusion between plates  51  and  52  where an attempted weld has failed and there is no weld between plates  52  and  53 . Approximately in the center of  FIG. 6A , proceeding horizontally left to right there is a point  57  where there is good fusion between plates  51  and  52  and the lack of fusion at point  58 ′ between plates  52  and  53 , immediately below point  57 . Proceeding further to the right in  FIG. 6A , there is a point  60  where there is full fusion between plates  51  and  52  and full fusion at point  60 ′ between plates  52  and  53 , immediately below point  60 . 
     FIG. 6B , in lateral alignment with  FIG. 6A , shows a B-scan  50  (see Metals Handbook, 9th Edition, Volume 17, “Nondestructive Evaluation and Quality Control”, ASM International, Metals Park, Ohio, September, 1989, pg. 335) cross-sectional image of the three plates and weldments of  FIG. 6A . The use of a B-scan is useful for making a recordable image of the quality of the weldment with the B-scan image being a plot created from a combination of the continuous digitization and storage of ultrasonic A-scan data ( FIG. 5 ) and the positional data from encoder  20  ( FIG. 3 ). The B-scan  50  horizontal axis is the length traveled along the surface of the component being inspected by probe assembly  8  containing ultrasonic transducer  11  that produces focused ultrasonic beam  10  (in this case along the top of plate  51  in  FIG. 6A ). The vertical axis is the time of flight  54  (time of flight  54  is equated to distance below the top surface of the top plate  51 ) of the ultrasonic signals from the reflectors encountered. The amplitude of the ultrasonic signals vary as the sound propagates through the material and can also be displayed using a color code or a grey scale  55  at any combination of scan length  54 ′ and distance  54  into the material. The location of the transition amplitude peaks  46 ,  46 ′ and  46 ″ from the A-scans of  FIGS. 5A ,  5 B and  5 C correspond to the gray scale transitions  56 ,  56 ′ and  56 ″ in the B-scans of  FIGS. 6A and 6B . 
   Note that in B-scan  50 , other than in alignment with, and below welds  57  and  60  in  FIG. 6A  there is no variation, i.e., all three gray scale color bands are shown indicating that there is no, or poor, fusion between any of plates  51 ,  52  and  53  in those regions. In the center of B-scan  50 , corresponding to where there is good fusion between plates  51  and  52  at weld  57 , and poor fusion at attempted weld  58 ′ between plates  52  and  53  in  FIG. 6A , there is an absence of a color transition at interface  56 ′ thus indicating that weld  57  is a good quality weld between plates  51  and  52 . The width of the weld image  57 ″ is directly related to the width of the fusion in weld  57  in  FIG. 6A . The lack of fusion of attempted weld  58 ′ between plates  52  and  53  results in a transition line in the B-scan image  50  in the area  58 ″ that corresponds to the return  46 ′ in A-scan  41  of  FIG. 5B . Full fusion of the plates in welds  60  and  60 ′ in  FIG. 6A  produces no transition in the B-scan image at levels corresponding to  56  and  56 ′, however the reflection from the bottom of plate  53  produces a transition at level  56 ″ below the weld fusions  60  and  60 ′. The length  57 ″ of the B-scan made with a focused ultrasonic beam  10  represents a measure of the length of weld  57  along the scan length  54 ′. This important relationship affords a new and different means for evaluating spot welds. The A-scan  42  of  FIG. 5C  produced when the ultrasonic transducer is over welds  60  and  60 ′ shows a response  46 ″ corresponding to the transition at  56 ″ in  FIG. 6B . The width of the B-scan image in this region corresponds to the width common to welds  60  and  60 ′ and the corresponding full fusion quality of those welds. 
   The concepts of the A- and B-scans extend to include the use of C-scans for evaluating the area dimensions for spot welds.  FIG. 7A  is the same cross-sectional view of the workpiece as in  FIG. 6A .  FIG. 7B , in lateral alignment with  FIG. 7A , illustrates a typical plan view C-scan image  50 ′ of the weldments of  FIG. 7A  that are being inspected. The vertical and horizontal axes of the C-scan image show the width and the length of the area scanned, respectively, (obtained from encoder  20 ) and include images showing the quality and the location of the ultrasonic reflectors. With this type of image either the amplitude or the time of flight of the signals from the ultrasonic reflectors can be displayed using a color code or a gray scale. The C-scan is especially useful for determining the quality of seam welds by measuring the width and area, and the continuous length of the fusion area. 
   In  FIG. 7B  there is no change in the gray scale of the C-scan in the region corresponding to the lack of fusion at attempted weld  58  in  FIG. 7A . In the regions of the C-scan that correspond to the good fusion at weld  57  and full fusion at welds  60  and  60 ′ in  FIG. 7A  both produce substantially the same gray scale color change and are shown circular assuming that the weldments at points  57 ,  60  and  60 ′ are each circular and extend into the plane of  FIG. 7A . 
     FIG. 8  is a block diagram of the system of the present invention with which inspections to determine the integrity of weldments and to obtain dimensional measurements of the present invention discussed above can be made. What is shown here is the interconnection of the probe  8  of  FIG. 3  with the full measurement system including couplant supply  80  with tubing connecting same to couplant inlet  22 , data acquisition system  23  with the cables to probe  8  and encoder  20 , welder indentations  34  in plates  12  and  13  opposite weldment  14  between plates  12  and  13 , and an indication of the direction of travel of probe  8  when it is moved during a scan. Data acquisition system  23  includes a pulser/receiver, a digitizer, a data acquisition unit and a data analysis unit. Attached to data acquisition system  23  is monitor/printer  74 . A recording instrument in the form of a printer or magnetic recorder records the A-, B- and C-scan images from the monitor to provide a hard copy of the inspection results. Representative images Of B-scan  75  and A-scan  76  are shown in data acquisition system  23  as they might appear on the monitor. B-scan and C-scan images are difficult to draw and these drawings are an idealized version of actual images. 
     FIG. 9  is a drawing of a representative cross section of a typical resistance spot weld  100  between plates  12  and  13 . The dimensions shown here illustrate the weldment dimensions that can be obtained using the B-scan and C-scan techniques of the present invention. These include the spot weld nugget  96  width and area. Additionally, use of the special probe  8  and scanner  70  arrangement as described in relation to, and shown in,  FIG. 3 , additional measurements can be made that include: indentation depth  90  and width  95 , top plate  12  thickness (t)  94 , plate distortion  93 , and welded thickness (t w )  91 . 
     FIG. 10  has been included to illustrate the nominal size, shape and proportions of a typical weld electrode for use with sheet steel, however, there are other shapes of electrodes in common use. The portions of the electrode that create the surface impression on the material being internally weld is the size and shape of the face together with the bevel angle adjacent the face. Typically the face of an electrode is round with a diameter A and the bevel angle is typically 45°±1°. The dimensions and shape of the nose of the electrode substantially determine the shape of the weld impression. The depth of the weld impression is substantially determined by three other factors: the material type, the pressure applied to the material by the face of the electrode during welding, and the amount of heat generated during the welding process. The other dimensions and shape of the electrode shown in  FIG. 10  are more generally dictated by the welding machine tooling and for heat distribution in the electrode and have little or no effect on the size, shape and depth of the weld impression. Sample dimensions of a weld electrode of  FIG. 10  are given in  FIG. 11 . 
   The list below provides representative calculations that are enabled by the present invention. These calculations are typically made with a computer from the various measures of the spot weld characteristics and have been included here to illustrate that these calculations are practical using the methods and apparatus of the present invention.
         10-1. Plate thickness (tm)=ultrasonic velocity in plate material* (t n −t n−1 )
           Calculated in region near start or end of scan. Where t n  is the time of flight for the ultrasonic signal return from surface “n” following the previous ultrasonic signal in this region. Usage is as input to a table of acceptable weld diameters to be used in production.   
           10-2. Criteria for button diameter=4*SQRT(tm)   10-3. Spot Welding Electrode Impression Dimension
           (requires curve fit of B-scan and C-scan data) (see FIG. A 1 —The Dimension  1  and Angle left  and Angle right  of Specification for Resistance Welding of Carbon and Low-Alloy Steels, American Welding Society, AWS C1.4M/C1,4:1999)   
           10-4. Indentation=ultrasonic velocity of the couplant*(the longest time of flight to the first surface−the time of flight from the first surface (near the edge of the scan)).   10-5. Distortion=ultrasonic velocity of the couplant*(the shortest time of flight to the first surface+the time of flight from the first surface (near the edge of the scan)).   10-6. Yield=number of acceptable welds in weld group=Number of welds acceptable/Number of welds inspected in the group.   10-7. Comparison to Metalagraphic Test.
           The SWEPS probe of the present invention can be used with commercial ultrasonic systems to detect cracks, holes, porosity, non-metallic inclusions, and indentation.
 
The plate thickness can be calculated at the beginning and end of a scan using the equation of 10-1. The plate thickness of 10-1 is then used to calculate, or from a look-up table, to obtain the button dimension(s) with calculation 10-2. The shape of the welding electrode impression  34  ( FIG. 8 ) is determined with a curve fitting algorithm (10-3) to fit the nominal curve for the face of the welding electrode used to the B-scan top surface profile and to the C-scan. The indentation depth calculation 10-4 uses the couplant velocity and the time differences measured for the front surface of plate  12  and the maximum distance to the electrode impression fit from 10-3. Distortion calculation 10-5 uses the areas of the scan to compute a reference plane through representative points from the image, then locates and removes the weld tool impression so that variations from the plane can be calculated ignoring the tool impression. Yield calculations 10-6 report the number of welds tested, passed, and the types of failures, and flag changes in the statistics of the measurements. Weld defects can also be detected using various classification criteria to identify the presence of each type to manufacturing (e.g., excessive inclusions in plate  12  causing bad welds). Item 10-7 is included to indicate that the probe of the present invention can be used with presently available ultrasonic test equipment to detect weldment cracks, holes, porosity, non-metallic inclusions, and indentations.
   
               

   As discussed above the methods and apparatus of the present invention present may advantages and is capable of making calculations not heretofore possible. In the above discussion an embodiment of the invention has been provided together with several examples of calculations that are possible with the present invention and suggested formulas for making those calculations. One skilled in the art will recognize that the same results provided by the present invention could be achieved with different or modified formulas. It is to be understood that the present invention is not limited to only that discussed above, and that it also includes equivalents of those disclosed. Therefore the present invention is only to be limited by the scope of the claims.