Abstract:
A punch is provided with a detection system for evaluating crack defects in waste material removed during a clipping operation. The punch includes a clip ring and a clip insert for shearing excess material from a part processed therein. The excess material is engaged around the clip ring when sheared from the part. Frictional resistance between the waste material and the clip ring is evaluated in determining potential crack defects in the waste material.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to parts and pieces made by stampings and/or progressive stampings; and, more particularly, the invention relates to devices and procedures for testing the integrity of stamped flanges. 
     BACKGROUND OF THE INVENTION 
     Parts and pieces of many different types and shapes are made by stampings and progressive stampings for use in a variety of different assemblies and constructions. Metal can be shaped into many different forms and configurations by the application of force causing a metal blank to conform to the shape of a die used while applying the force. Simple parts and pieces can sometimes be made by a single stamping. In a single stamping, force is applied in a single event so that the metal conforms to a die used while applying the force. For more complex parts or parts taking a shape quite different from the original metal blank, progressive stampings are used. In progressive stampings, a series of dies are used in a series of stamping events, with each die and each stamping event forming the metal in stages from the original blank to the desired final formation. 
     The loads applied to the metal in a stamping process can cause a variety of flaws to form in stamped metal pieces and parts. For example, the metal may not conform as desired to the die used in the stamping process. Further, the force applied can cause cracks and other flaws in the metal. It is necessary to remove defective parts so that the defective parts are not incorporated into a final assembly. While visual inspection can be used for some defects, visual inspection by individuals is slow and not completely reliable if the defects are small. 
     Stamping is often used to make parts and pieces inexpensively, since a stamping event is a rapid occurrence. Accordingly, parts can be formed quickly and inexpensively, with minimal waste. To ensure a high percentage of quality parts are shipped to customers cost effectively, testing procedures for stamped parts must be performed rapidly and reliably. Preferably, a testing method occurs as quickly as the stamping process so that testing or inspection does not slow the overall process of making the part. 
     It is known to use stamping techniques to form a variety of parts having a head or a flange at an end thereof. For example, a substantially cylindrical or tubular part can be stamped to have a peripheral flange at one end. The stamping process may include a first formation process to form the flange in a gross, oversize configuration. A more precise clipping process is then used to ensure a reliable diameter by shearing away any excess material in the preformed flange. In a clipping process a peripheral portion of the stamped flange is removed as an annular ring so that the remaining portion on the part is of the desired diameter, and is positioned properly in the part. 
     A process to form a flange as described above can cause cracks to occur in the flange portion of the part. Cracks can cause the part to seal inadequately causing leaks, or to support inadequately and cause failure. Further, cracks can migrate over time, causing the part to fail prematurely. Accordingly, it is desirable to identify parts in which even small cracks have occurred before the part is put into use and fails. While complex, detailed metal analysis could be performed on each part, such testing is cost prohibitive for many parts that must be supplied inexpensively. 
     Accordingly, it is desirable to provide a device and process for testing stamped flange parts to reliably identify parts in which cracks have been created during the formation process. 
     SUMMARY OF THE INVENTION 
     The present invention provides a process and apparatus for determining if cracks have occurred in a stamped, clipped flange by testing the annular ring of waste material removed during the clipping step. 
     In one aspect thereof, the present invention provides a process to evaluate a part with steps of preforming the part, clipping the preformed part to generate a finished part and a waste piece, evaluating the waste piece for the presence of crack defects; and rejecting the finished part when the waste part exhibits crack defects. 
     In another aspect thereof, the present invention provides a process for forming a head on a part and evaluating the head for crack defects. The process has steps of pre-forming the head on the part, clipping a peripheral portion of the head to provide a finished head while generating a generally annular waste piece, providing the waste piece about a body; sliding the waste piece from the body; evaluating the frictional resistance between the waste piece and the body; and rejecting the part with the finished head if the frictional resistance between the annular waste piece and the body is less than a pre-established threshold. 
     In a still further aspect thereof, the present invention provides a clipping assembly with a die block supporting a clip insert and a punch assembly including an axially translatable plunger having a clip ring receivable in the clip insert for shearing material between the clip ring and the clip insert. A floating punch has an end in the plunger and is biased in the plunger away from the clip insert. A proximity detector determines a position of the end. A grasping means captures waste material on the clip ring as the plunger is moved away from the clip insert. 
     An advantage of the present invention is providing an apparatus and process for reliably determining the possible presence of cracks in an annular flange formed by stamping or progressive stamping processes. 
     Another advantage of the present invention is providing a crack detection process which operates quickly in conjunction with a stamping process used to form a part so that testing is performed quickly and reliably without slowing the stamping process. 
     Another advantage of the present invention is providing a crack detection process for stamped flanges which does not add significant cost to the manufacturing process to make the stamped part. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a press prepared to clip a flange on a part, all in accordance with the present invention; 
         FIG. 2  is a cross-sectional view similar to that of  FIG. 1 , but illustrating the press and part as crack testing begins after the clipping step has been completed; 
         FIG. 3  is an enlarged fragmentary cross-sectional view of a portion of the press shown in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view similar to  FIGS. 1 and 2 , but illustrating the press in a later stage of the process, when the integrity test of the present invention is being performed; and 
         FIG. 5  is an enlarged fragmentary cross-sectional view of a portion of the press as shown in  FIG. 4 . 
     
    
    
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use herein of “including”, “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof, as well as additional items and equivalents thereof. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now more specifically to the drawings and to  FIG. 1  in particular, a punch press  10  in accordance with the present invention is shown. Press  10  is configured for processing a part  12  in clipping and crack detection processes also in accordance with the present invention. Press  10  is configured to clip a peripheral edge of a preformed head or flange  14  on part  12 . 
     Part  12  includes a tubular shank  16  from which preformed flange  14 , at one end thereof, may have been formed in a previous stamping process, prior to processing in press  10 . Punch press  10  is configured and operated to clip a peripheral annular ring waste segment  18  from preformed flange  14  to thereby form a finished flange  20  ( FIGS. 2 &amp; 3 ) from preformed flange  14 . Accordingly, finished flange  20  has a precise diameter and is positioned accurately, which may be difficult to achieve the initial stamping of preformed head or flange  14 . 
     In the exemplary embodiment, part  12  further includes an end flange  22  opposite preformed flange  14 . However, it should be understood that the present invention can be used for stamping processes forming other types of parts than part  12  shown. The exemplary embodiment having a relatively long shank with flanges on both ends is merely exemplary. For example, as those skilled in the art will understand readily from the following description, the present invention can be used also when forming flanges on parts of other shapes or when forming other parts, perhaps even flat parts, having a clipping process in which a continuous annular waste piece is generated. For example, the present invention can be used if head or flange  14  is an outwardly extending head of a part having a solid shank. 
     Punch press  10  includes a die block  30  having a clip insert  32  therein. Die block  30  supports a guide block  34  having a guide ring  36 . A punch assembly  38  is configured and arranged for operating together with guide block  30  and the equipment supported thereby for clipping the peripheral edge from preformed flange  14 . Accordingly, punch assembly  38  is in axially translatable toward and away from clip insert  32  through guide block  34  and guide ring  36  therein. 
     Punch assembly  38  includes a pilot  40  which is inserted into shank  16  for centering part  12  relative to press  10 , as can be seen most clearly in  FIG. 2 . A clip ring  42  is forced against preformed flange  14 , and in cooperation with clip insert  32  cuts the peripheral waste ring  18  from preformed flange  14 , thereby forming finished flange  20 . 
     Pilot  40  and clip ring  42  are held in a floating punch  44  retained by a punch chuck  46  in a plunger  48 . A cylinder  50  in plunger  48  applies a continuous force pulling floating punch  44  into punch chuck  46 . A steel rod  52  extends from cylinder  50  toward a proximity switch  54  configured to detect the presence of steel rod  52  within a prescribed axial range. Punch chuck  46  defines a cavity  56  receiving a head  58  of floating punch  44 , and provides axial space as shown whereby head  58  can move relative to punch chuck  46 . 
     A waste ring removal assembly  60  is provided for removing waste ring  18  from clip ring  42  as punch assembly  38  is retracted. Transfer fingers  62 ,  64  include notches  66 ,  68  for grasping waste ring  18 , stripping it from clip ring  42  and transferring waste ring  18  to scrap processing. As shown in  FIGS. 4 and 5 , waste ring  18  is caught in notches  66 ,  68  for stripping from clip ring  42  as punch assembly  38  is retracted. 
     Part  12  is formed by a stamping or the like, with a gross formation of preformed flange  14 . During the formation of preformed flange  14 , or during the subsequent clipping operation performed by press  10  to separate waste ring  18  from finished flange  20  cracks may form in preformed flange  14 . In most circumstances, annular waste ring  18  will exhibit cracks if cracks are present in the region of finished flange  20 . Accordingly, detecting defects or flaws such as cracks in waste ring  18  indicates that similar cracks or flaws may exist in finished flange  20 . Similarly, if waste ring  18  exhibits no cracks or flaws it is very unlikely that any crack or flaw will exist in finished flange  20 . Accordingly, the present invention takes advantage of the ability to evaluate a condition of waste ring  18  to determine the possibility of defects in finished flange  20 . Although an occasional part  12  having an acceptable finished flange  20  may be rejected because of cracks found only in waste ring  18 , such occurrences are unlikely and rare and the occasional waste therefrom is acceptable. 
       FIG. 1  illustrates punch press  10  and part  12  prior to commencement of a flange clipping operation. Part  12  is positioned to start the clipping process, and punch assembly  38  is retracted. 
     In  FIG. 2 , part  12  is guided through clip insert  32  as any excess material of preformed flange  14  is sheared away as waste ring  18 , to size and position finished flange  20  properly and accurately. Waste ring  18  remains positioned about clip ring  42  from the clipping process. As shown in  FIG. 4 , finished part  12  falls from die block  30  as the press returns to its starting position. 
     When waste ring  18  is continuous, solid and intact without cracks, waste ring  18  is engaged around clip ring  42  with some frictional resistance. Resistance to the upward movement of floating punch  44  is created as transfer fingers  62 ,  64  hold waste ring  18 . The resistance is in the opposite direction of the normal biasing force exerted by cylinder  50 . The frictional resistance overcomes the biasing force supplied by cylinder  50  and thereby causes a brief displacement of floating punch  44  relative to plunger  48  during the return step. For a brief time, floating punch  44  remains in a substantially fixed position while plunger  48  continues along its path of retraction and punch chuck  46  moves relative to head  56  as permitted by the size of cavity  56 . Rod  52  also remains substantially fixed as plunger  48  moves, causing a relative axial displacement between the end of rod  52  and proximity switch  54 . Proximity switch  54  detects an absence of steel rod  52  and allows press  10  to continue the return stroke. The relative displacement between floating punch  44  and plunger  48  is limited by the difference in axial lengths of head  58  and cavity  56 , so that at some point in the return stroke of punch assembly  38  the frictional resistance of waste ring  18  on clip ring  42  is overcome, stripping waste ring  18  from clip ring  42 . The momentary absence of steel rod  52  from detection by proximity switch  54  is an indication that waste ring  18  is solid and intact, in the that it provided a predetermined frictional resistance to movement on clip ring  42  sufficient to overcome the biasing force of cylinder  50 . This interpretation is extrapolated to the condition of finished flange  20 , and part  12  is determined to be acceptable. 
     If preformed flange  14  includes cracks or similar defects, or if cracks are created during the clipping process described the defects extend into waste ring  18 . As a result, waste ring  18  will fit more loosely around clip ring  42  than if waste ring  18  is without defects. As plunger  48  is returned to the start position, the frictional resistance of waste ring  18  on clip ring  42  is insufficient to overcome the biasing force of cylinder  50 . Accordingly, in this condition, no relative movement occurs between floating punch  44  and plunger  48 . Proximity switch  54  fails to detect an absence of steel rod  52 , and a signal is sent to terminate operation of punch press  10 . A light or other indicator can be used to alert an operator that part  12  may contain a defect, and/or press  10  can be shut down. Part  12  can be removed from the stream of parts being produced or part  12  can be flagged for later removal as normal operation of press  10  continues. 
     Defect detection in waste ring  18  is performed as part of the routine stroke of punch press  10 . Accordingly, evaluation of part  12  is performed immediately as finished flange  20  is formed, and no delay occurs. No additional time is required to complete the testing or evaluation since the evaluation occurs during a normal return stroke of punch press  10 . 
     Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art. 
     Various features of the invention are set forth in the following claims.