Patent Publication Number: US-6659160-B1

Title: Reverse break stamp hook assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a reverse break stamp hook assembly for use in breaking a biscuit from a casting and a method of breaking a biscuit from a casting using a reverse break stamp hook assembly. 
     2. Description of Related Art 
     The die casting process is used to produce accurately dimensioned, sharply defined, smooth and/or textured-surface metal parts. In the die casting process, molten metal such as, for example, aluminum and alloys of aluminum, is forced under high pressure into a cavity between two die halves. The injected molten metal quickly solidifies in the die cavity, then the two die halves are drawn apart and the casting is ejected. 
     The ejected casting typically includes extraneous material (e.g., flash, which is a thin web or fin of metal on a casting that occurs at die partings, vents and around moveable cores) that must be removed from the casting in order to obtain an acceptable part. In addition, castings formed using a cold chamber die casting machine will have a gate or biscuit, which is the excess of ladled metal remaining in the shot sleeve, that must be removed. The extraneous material and biscuit are typically removed in a stamping operation using a pair of trim dies and a die casting biscuit breaking apparatus. The trim dies include cutting/trimming surfaces as well as punches or other desired tooling. 
     FIGS. 1A and 1B show a schematic front view of a conventional die casting biscuit breaking apparatus  10 . The apparatus  10  consists of an upper trim die holder  18 , an upper trim die  20 , a lower trim die holder  28 , and a lower trim die  30 . A part  40  (or several parts) is placed between the dies  20 ,  30 , typically on the lower trim die  30 . The part  40  will typically include extraneous material (e.g., flash) that needs to be trimmed, surfaces to be punched, as well as a gate or biscuit  50  that needs to be removed. As shown in FIG. 1 B, the upper trim die holder  18  is moved downwardly to press the upper trim die  20  against the part  40  on the lower trim die  30  and thereby trim away the extraneous material from the part  40 . Conventionally, the upper trim die holder  18  also includes a stamp cutter  60  that presses downwardly against the biscuit  50  or gate to break the biscuit from the part  40 . 
     One of the problems with a conventional die casting biscuit breaking apparatus  10  is that the biscuits  50  tend to break off a distance from the part  40 , leaving a portion of biscuit material, sometimes referred to as a “high gate” 70 , remaining on the part  40 . These high gates  70  must be removed by hand, typically using angle grinders. This results in additional processing time and effort. On occasion, a high gate  70  will not be noticed upon inspection or will be improperly removed by hand. An overlooked high gate  70  can cause damage to tooling in downstream processes, resulting in machine down time and additional losses in production time due to the need to hand sort parts to find the missed high gates  70 . 
     SUMMARY OF THE INVENTION 
     The present invention provides a reverse break stamp hook assembly for use in breaking a biscuit from a casting, and a method of breaking a biscuit from a casting using the reverse break stamp hook assembly. Surprisingly, the reverse break stamp hook assembly and method according to the invention facilitate the removal of biscuits without creating a high gate. Moreover, the reverse break stamp hook assembly may be used with conventional stamping machines without modifying the operating sequence of the machine. 
     In accordance with the present invention, a reverse break stamp hook assembly is mounted in place of a stamp cutter on conventional stamping equipment. The reverse break stamp hook assembly includes a hook and a mounting bracket. The hook, which includes a downwardly extending leg and a counterweight arm, hangs from a pivot attached to the mounting bracket. A distal end of the hook leg has an angled front portion and a catch portion. 
     In further accordance with the present invention, as the upper trim die of the stamping equipment moves toward the lower trim die during the downstroke, the angled front portion of the hook contacts and slides over an edge of a biscuit, causing the hook to pivot away from the biscuit until the catch portion passes below the biscuit. The counterweight arm, which is on the opposite side of the pivot, causes the hook to pivot back toward the biscuit, positioning the catch portion under the biscuit. During the upstroke, the catch portion engages the bottom side of the biscuit and pulls the biscuit upwardly away from the part, causing the biscuit to break from the part as the upper trim die is raised. The biscuit breaks cleanly, and does not leave a high gate requiring further hand grinding. Accordingly, a rough cleaned and trimmed part results from use of the trim dies incorporating the reverse break stamp hook assembly of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and further features of the invention will be apparent with reference to the following description and drawings, wherein: 
     FIG. 1A is a schematic front view of a prior art die casting biscuit breaking apparatus prior to the stamping downstroke. 
     FIG. 1B is a schematic front view of the prior art die casting biscuit breaking apparatus shown in FIG. 1A after the stamping downstroke. 
     FIG. 2 is a perspective view of a preferred embodiment of a reverse break stamp hook assembly according to the invention. 
     FIG. 3A is a schematic front view of a die casting biscuit breaking apparatus according to the present invention prior to the stamping downstroke. 
     FIG. 3B is a schematic front view of the die casting biscuit breaking apparatus shown in FIG. 3A at the bottom of the stamping downstroke. 
     FIG. 3C is a schematic front view of the die casting biscuit breaking apparatus shown in FIG. 3A at the beginning of the stamping upstroke. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 2, a reverse break stamp hook assembly  100  according to the invention comprises a hook  102  and a mounting bracket  105 . The hook  102  includes a pin or pivot  104  by mans of which the hook  102  is supported and pivotally secured to the mounting bracket  105 . The hook  102  comprises a downwardly extending leg  102   a  and a counterweight arm  102   b . The leg  102   a  has a distal end with an angled front portion  106  and a catch portion  108 . The counterweight arm  102   b  extends away from the pivot  104  in a direction opposite the direction the catch portion  108  faces. Mechanical stops  107 ,  109  provided by the hook  102  and mounting bracket  105 , respectively, cooperate to limit the hook&#39;s pivotal movement toward the biscuit, and will be described more fully hereinafter. The counterweight arm  102   b  balances the leg  102   a  such that the leg  102   a  is urged into a position in which the stops  107 ,  109  are engaged with one another and the leg  102   a  hangs from the pivot  104 , preferably with a lower edge  106   a  of the angled front portion  106  disposed essentially directly below the pivot axis of the pivot  104 . As such, the counterweight arm  102   b  and stops  107 ,  109  cooperate to define and maintain the hook  102  in a desired at-rest and operating position wherein the catch portion  108  is generally horizontally oriented and positioned to engage a downwardly facing surface of the biscuit  128  in face-to-face contact. 
     In the preferred and illustrated embodiment, the mounting bracket  105  includes a solid and planar mounting plate  105 a from which a pair of spaced-apart mounting arms  105   b  downwardly extend. The mounting plate  105   a  is secured to an upper trim die holder  121 , described hereinafter. The mounting arms  105   b  define a pair of aligned openings that cooperate to receive the pivot  104 . Each of the mounting arms  105   b  rotatably supports an end of the pivot  104 , and may be either one-piece (FIG. 2) or two-piece construction (i.e., split mounting arm). The mounting arms  105   b  may optionally hold a bearing to facilitate repair and maintenance of the rotary connection between the mounting arms  105   b  and the pivot  104  of the hook  102 . 
     As noted hereinbefore, the hook  102  is generally shaped as an upside-down L such that the counterweight arm  102   b  extends at a 90° angle or less relative to the leg  102   a . The counterweight arm  102   b  is integrally formed with the leg  102   a , preferably as one piece, and a pin receiving opening (not shown) is defined generally at the intersection of the arm  102   b  and leg  102   a . The pivot  104  is received in the pin receiving opening and extends therefrom so as to fit into the openings in the mounting arms  105   b . The pivot  104  is affixed to the hook  102  so as to define a unitary structure that is adapted to pivot or rotate as one piece relative to the mounting arms  105   b . As shown in the drawing figures and described more fully hereinafter, the counterweight arm  102   b  is normally at an acute angle α to the mounting plate  105   a , and is adapted to move or rotate upwardly toward the mounting plate  105   a  as the leg  102  is pivoted outwardly from its at-rest position. 
     FIGS. 3A-3C illustrate use of the reverse break stamp hook assembly  100  in conjunction with a biscuit breaking apparatus  120 . It is noted that the stops  107 ,  109  illustrated in FIG. 2, although present in the apparatus, are not shown in FIGS. 3A-3C for purposes of clarity. 
     FIG. 3A shows a schematic front view of a modified die casting biscuit breaking apparatus  120 , which incorporates the reverse break stamp hook assembly  100  of the present invention, described hereinbefore. The apparatus  120  consists of an upper trim die holder  121 , an upper trim die  122 , a lower trim die holder  123 , and a lower trim die  124 . A part  126  (or several parts) is placed between the dies  122 ,  124 , typically on the lower trim die  124 . The part  126  will typically include extraneous material (e.g., flash) that needs to be trimmed, holes to be punched, as well as a gate or biscuit  128  that needs to be removed. The reverse break stamp hook assembly  100  is mounted to the upper trim die holder  121  in place of a conventional stamp cutter. Conventionally, flash, biscuits, and other material is trimmed, broken, or cut from the parts being worked on during the downstroke. In the present invention, described hereinafter, at least the biscuit  128  is removed or broken-off during the upstroke. 
     In FIG. 3A, the upper trim die  122  and lower trim die  124  of the modified die casting biscuit breaking apparatus  120  are separated from each other. In FIG. 3B, the upper trim die holder  121  has been moved downwardly to press the upper trim die  122 , part  126 , and lower trim die  124  together. The upper trim die holder  121  conventionally includes a resilient mount (i.e., die springs  121   a ) for the upper trim die  122  that is compressed during the downstroke as the upper trim die  122  engages the part  126 /lower trim die  124  and is de-compressed during the upstroke as the upper die holder  121  is moved away from the lower die holder  123 . 
     As will be appreciated by those skilled in the art, there is a period of lost motion at the end of the downstroke and the beginning of the upstroke in which the upper die holder  121  moves relative to the upper trim die  122 , lower trim die  124 , and lower trim die holder  123  while the upper trim die  122  is stationary relative to the lower trim die  124  and lower trim die holder  123 . The present invention takes advantage of this period of lost motion to properly locate and implement the reverse break stamp hook assembly  100  relative to the biscuit  128 , described hereinafter. 
     Toward the end of the downstroke, the part  126  is sandwiched between the upper trim die  122  and the lower trim die  124 , the upper trim die holder  121  is moving toward the lower trim die holder  123 , the die springs  121   a  are being compressed, and the angled front portion  106  of the hook  102  contacts an edge  128   a  of the biscuit  128 . The contact between the biscuit edge  128 a and the angled front portion  106  of the hook  102 , together with continued downward motion of the upper trim die holder  121  and reverse break stamp hook assembly  100 , causes the hook  102  to rotate or pivot away from the biscuit  128 . As viewed in FIGS. 3A-3C, the hook  102  rotates in a clockwise direction. The angled front portion  106  of the hook  102  slides along the edge  128   a  of the biscuit  128 , without breaking it down, until the catch portion  108  passes below the biscuit  128 . When the catch portion  108  passes below the biscuit  128 , the hook  102  pivots or rotates in the counter-clockwise direction back toward the at-rest position in which the stops  107 , 109  engage one another. 
     In other words, after the catch portion  108  of the hook leg  102   a  passes below the edge  128   a  of the biscuit  128 , the counterweight arm  102   b  on the opposite side of the pivot  104  causes the hook  102  to rotate back toward the biscuit  128 , positioning the catch portion  108  under the biscuit  128 , as shown in FIG.  3 B. Rotation of the hook  102  in the clockwise direction is limited to the angle a (by possible engagement of the arm with the plate), while the return rotation or pivot in the counter-clockwise direction is limited by engagement of the stops  107 ,  109 . Preferably, when the stops  107 ,  109  are in engagement with one another the catch portion  108  of the hook  102  is directly under the pivot axis of the pivot  104  and thereby prevents the catch portion  108  from slipping off of the biscuit  128  during the upstroke. 
     The catch portion  108  passes beneath the biscuit  128  just prior to the upper trim die holder  121  reaching the bottom position of its downstroke (i.e., wherein the die springs  121   a  have been fully compressed), so that there is minimal clearance between the catch portion and the biscuit  128 . In tests conducted by the inventors, the spacing between the catch portion and the biscuit is preferably between about 10-20 mm. Accordingly, it will be appreciated that the spacing between the biscuit  128  and the hook catch portion  108  is exaggerated in FIG. 3B for purposes of clarity. 
     At the beginning of the upstroke, which is shown in FIG. 3C, the upper trim die holder  121  initially moves upwardly and the springs  121   a  decompress while the upper trim die  122  remains stationary. During this initial period the force of the springs  121   a  holds the upper trim die  122  stationary while the hook  102  moves upwardly relative to the upper trim die  122 , the catch portion  108  engages the bottom side of the biscuit  128 , and applies sufficient force to break the biscuit  128  from the part  126 . It has been found that using the present invention reliably breaks the biscuit  128  cleanly from the part  126 , and does not leave a high gate condition. 
     Almost immediately after breaking the biscuit, continued upward movement of the upper trim die holder  121  causes the springs  121   a  to completely decompress and, as the upper die holder  121  moves further away form the lower die holder  123 , the upper trim die  122  moves with the upper die holder  121  away from the lower trim die  124 . Because the reverse break stamp hook assembly  100  according to the invention does not create high gates, very little if any hand trimming is needed and the resulting trimmed and rough cleaned or finished part is immediately available for further processing. Accordingly, the present invention reduces production time and manual inspection and hand grinding, and protects downstream tooling from damage. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and illustrative examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.