Patent Publication Number: US-7222405-B2

Title: Device for determining axial alignment or misalignment of a punch with respect to a die

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of Japanese Patent Application No. 2003-148921 filed May 27, 2003, incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   This invention relates to determining alignment or misalignment of a punch with respect to a die, in an apparatus in which workpieces are joined by self-piercing rivets, for example. One such apparatus is disclosed in U.S. Pat. No. 5,277,049 issued Jan. 11, 1994. 
     FIG. 1  shows an example of another self-piercing rivet setting apparatus in which the present invention may be employed. Typically, the apparatus  1  comprises a rigid C-shaped support frame  2 , and a spindle unit  3  fixed to a first end (upper end in  FIG. 1 ) of the C-shaped support frame. The spindle unit  3  holds an elongated tubular nosepiece  5  axially slidable through an end of the spindle unit (lower end in  FIG. 1 ). A receiver  7  is fixed to the nosepiece  5  to receive self-piercing rivets supplied from a feed tube  6 . A rod-shaped punch  9  is slidable axially in the nosepiece  5 . A replaceable die  10  is seated at a position on the frame  2  facing the punch  9 . The die has a portion centrally fitted in a bore  11 . 
   Workpieces to be joined are placed between the punch and the die. A main shaft (not shown) axially movable in the spindle unit  3  is driven by a servomotor  13  and a reduction gear mechanism  14  to move the nosepiece  5  and the punch  9  toward the die  10 . When the nosepiece  5  is brought into contact with a workpiece, the movement of the nosepiece toward the die is discontinued, but the punch  9  continues to move toward the die to press a self-piercing rivet, held axially at the end of the nosepiece, into the workpieces to be joined. 
     FIG. 2  shows the state after two workpieces  17  and  18 , such as panels, are joined by a self-piercing rivet  15 . As shown, the rivet includes a head  19  and a hollow smaller diameter leg  21  (typically of cylindrical shape) extending from the head toward the die  10 . The rivet  15  is driven into the workpieces in such a manner that the leg  21  is expandingly deformed by the die while piercing the workpieces. The self-piercing rivet  15  penetrates the workpiece  17  located on the side of the punch  9  but stays in the workpiece  18  adjacent to the die  10  without penetrating that workpiece. Thus, no opening is formed in the exposed surface of the workpiece  18 , preventing appearance degradation and blocking passage of noise and rainwater, for example. Panels typically joined in this manner are aluminum body panels employed in automobiles (e.g., to reduce weight) which are not easily welded. 
   If, during setting of a self-piercing rivet, as above described, the axis  23  of the punch and the rivet and the axis  25  of the die are aligned as shown in  FIG. 2 , a central protrusion  26  of the die  10  will be located at the center of the hollow leg  21 , and the splayed portions of the leg will be symmetrically disposed with respect to the axis  25  of the die, whereby the workpieces  17 ,  18  are strongly connected. If, on the other hand, the axis  25  of the die  10  is misaligned with respect to the axis  23  of the punch and the rivet  15 , as indicated by reference numeral  27  in  FIG. 3 , and if the misalignment is in excess of a tolerance, the expandingly deformed portion  22  of the leg  21  will not reliably join the workpieces  17 ,  18 . More particularly, the tensile shear strength and peel strength of the workpieces will become unreliable. Furthermore, the leg  21  may protrude outside of the workpiece  18 , forming an opening through which rainwater, for example, may pass, which may cause a corrosion problem. 
   Because of the manner in which each self-piercing rivet  15  is held in the nosepiece  5 , there is little likelihood of misalignment between the punch  9  and the rivet. However, the die  10 , located at a position away from the nosepiece  5 , may become axially misaligned with respect to the punch and a rivet. The manufacturer of the riveting apparatus will take appropriate steps to avoid such misalignment. However, occurrences at a user&#39;s job site may cause misalignment beyond the control of the manufacturer. Resulting defective riveted joints may not be easily detected by the user of the riveting apparatus. Moreover, returning the riveting apparatus to the manufacturer to check alignment is burdensome and may, undesirably, require use of standby apparatus. 
   BRIEF DESCRIPTION OF THE INVENTION 
   The present invention provides a simple device and method for determining whether axial misalignment, if any, of a die relative to a punch is within an acceptable range. The invention uses a jig that substitutes for a replaceable die and that permits viewing of the relationship of the punch with respect to a punch-receiving axial hole in the jig. If the punch can enter the hole, any axial misalignment is within tolerance. If the punch cannot enter the hole, axial misalignment is excessive. Axial misalignment can be readily determined without disassembly of the rivet setting apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be further described in conjunction with the accompanying drawings, which illustrate a preferred (best mode) embodiment, and wherein: 
       FIG. 1  is a perspective view of a self-piercing rivet setting apparatus in which the present invention may be used; 
       FIG. 2  is a sectional view showing the state after a plurality of workpieces are properly joined using a self-piercing rivet; 
       FIG. 3  is a sectional view showing the state after a plurality of workpieces are improperly joined due to axial misalignment of a die relative to a punch and a self-piercing rivet; 
       FIG. 4  is a perspective view of an axial misalignment determination jig according to one embodiment of the present invention; 
       FIG. 5  is a vertical sectional view of the jig in  FIG. 4 ; 
       FIG. 6  is a sectional view showing the state before a nosepiece and a punch are moved toward an axial misalignment determination jig according to one embodiment of the present invention; 
       FIG. 7  is a sectional view showing the state after the nosepiece is moved from the position in  FIG. 6 , and brought into contact with a head of the jig; and 
       FIG. 8  is a sectional view showing the state after the punch is moved from the position in  FIG. 7  so as to protrude from the nosepiece, and is inserted into an axial hole in the head of the jig. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 4 and 5  show an axial misalignment determination jig  30  according to one embodiment of the present invention. The jig  30  can be used, for example, in the rivet setting apparatus  1  in  FIG. 1 , but is not limited to use in that apparatus. In the form shown, the jig  30  comprises a shank  31  and a head  33 . In the preferred form, both the shank  31  and the head  33  of the jig are cylindrical, as shown in  FIG. 4 . The jig  30  is preferably molded of metal or hard plastic and can be readily reproduced at low cost. 
   The shank is adapted to be inserted into the die-receiving bore  11  of the C-shaped support frame  2  of the apparatus  1 , with the head adjacent to the frame and facing the punch  9 . The head is formed with an axial hole  35  for receiving the punch  9 . The hole has an axis that is aligned with the axis of the die-receiving bore  11 . The height H of the head above the frame  2  is approximately equal to the height of a portion of a die  10  protruding from the frame when the die is inserted in the bore  11 . 
   The upper portion of the head  33  is constructed to permit viewing of the relationship between the punch  9  and the axial hole  35 . For this purpose, a large notch  37  is provided at a single position of the head, but the shape and number of notches may vary, so long as the relationship between the punch  9  and the hole  35  can be viewed. Preferably, the axial hole is designed to have a diameter D satisfying the following formula: 
   D=the diameter of the punch+[the tolerance (or the allowable range) of the misalignment  27  between the axes of the punch (and the rivet) and the die]×2. 
   For example, given a punch diameter of 8 mm, and the tolerance of axial misalignment  27  of 0.5 mm, the diameter of the axial hole is set at 9 mm. 
     FIGS. 6–8  show the manner in which the jig  30  can be used to determine axial misalignment. The shank  31  of the jig is inserted in the die-receiving bore  11  of the support frame  2  (absent a die) to locate the head  33  in opposition to the punch  9  and the nosepiece  5 , as shown in  FIG. 6 . Then the rivet setting apparatus  1  is activated to move the nosepiece  5  and the punch  9  toward the jig  30  until the nosepiece abuts a surface  34  of the head  33 , whereupon movement of the nosepiece toward the jig is discontinued, as shown in  FIG. 7 . However, the punch  9  continues to move toward the jig, and if the axial alignment of the punch  9  and the hole  35  is within an acceptable range, the punch enters the opening, as shown in  FIG. 8 . If it is observed through the notch  37  that the end of the punch  9  is not received in the axial hole  35 , then it will be evident that the misalignment between the axis  25  of the die and the axis  23  of the punch (and the rivet) is out of tolerance. Suitable adjustments can then be made to correct such misalignment. 
   While a preferred embodiment of the invention has been shown and described, it will be apparent that changes can be made without departing from the principles and the spirit of the invention, the scope of which is defined in the accompanying claims. For example, the invention may be used in clinching apparatus.