Abstract:
A method for operating an automated reciprocator for applying lubricant in a die casting system. As a reciprocator is moved between two die halves and a fluid is applied to the dies with the reciprocator, a safety bar is moved ahead of the reciprocator. Any objects in the path of the reciprocator are detected by contact with the safety bar. If the safety bar contacts an object as the reciprocator is moving down, a sensor signals a control system and the reciprocator is stopped.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of and claims priority from co-pending U.S. patent application Ser. No. 11/940,525, which is a divisional application of, and claims priority from, U.S. patent application Ser. No. 10/886,780, filed Jul. 8, 2004, now U.S. Pat. No. 7,299,855, issued on Nov. 27, 2007 and entitled “Die Casting Reciprocator Safety Bar,” all of which are hereby incorporated by reference for all purposes. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO A MICROFICHE APPENDIX 
       [0003]    Not applicable. 
       FIELD OF THE INVENTION 
       [0004]    The present invention relates to automated die casting systems having reciprocating spray systems, and more particularly to a method of operating a reciprocating spray system to prevent the reciprocator from injuring an operator of the die casting system. 
       BACKGROUND OF THE INVENTION 
       [0005]    Die casting is a manufacturing process for producing accurately dimensioned, sharply defined, smooth or textured-surface metal parts. A steel mold capable of producing tens of thousands of castings in rapid succession is made in at least two sections to permit removal of castings. These sections are mounted securely in a machine and are arranged so that one is stationary (fixed die half) while the other is moveable (injector die half). To begin the casting cycle, the die cavity is coated with a lubricant or mold release material. Then, the two die halves are clamped tightly together by the die casting machine. Molten metal is injected into the die cavity where it solidifies quickly. The die halves are drawn apart and the casting is ejected. 
         [0006]    Die casting cycle times vary from less than one second for small components weighing less than one ounce, to thirty seconds or more for a casting of several pounds or more. Dies are filled quickly (normally between five and forty milliseconds) and metal is injected at high pressures (1,500 to over 4,500 psi). Nevertheless, modern automation technology gives close control over these values, thus producing castings with fine detail, close tolerances and high strength. 
         [0007]    The die casting process has been automated to improve quality control, speed and safety. For example, safety interlocks prevent filling a mold with a shot of molten metal unless the mold is securely clamped shut and an outer door of a system enclosure is closed to protect the system operator. When a mold is opened after a casting cycle and the finished part is removed, an automated reciprocating sprayer or reciprocator may move down between the open die halves to spray on a lubricant on the die cavity. As the reciprocator returns to its rest position, it blows high pressure air on the mold cavity to remove excess lubricant and dry the cavity faces. The reciprocator is typically activated by the operator after opening the safety door to remove the finished die casting. Regulations have been proposed to require a safety door interlock with the reciprocator to insure that the reciprocator cannot move down when the door is open because the operator may still be in the casting enclosure. However, such an interlock arrangement would add a significant amount of time to the casting cycle time, thereby reducing the productivity of the die casting system. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a method for operating an automated reciprocator in a die casting system. As a reciprocator is moved between two die halves and a fluid is applied to the dies with the reciprocator, a safety bar is moved ahead of the reciprocator. Any objects in the path of the reciprocator are detected by contact with the safety bar. 
         [0009]    In an embodiment, the method includes stopping operation of the reciprocator when an object is detected by the safety bar. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a simplified plan view of a typical die casting system according to the present invention. 
           [0011]      FIG. 2  is an elevation view of an open mold illustrating operation of a reciprocator according to the present invention. 
           [0012]      FIG. 3  is a side view of a die casting reciprocator showing details of a safety bar according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]      FIG. 1  is a simplified plan view of a typical die casting system  10  according to the present invention. A stationary or fixed die half  12  and a moveable or injector die half  14  are shown meeting at a parting line  16 . Above the fixed die half  12  is shown a reciprocator  18 , described in more detail below. The die or mold  12 ,  14  is surrounded by an enclosure  20  having an entrance  22 . A door  24  is provided across entrance  22 . A system control panel  26  is typically located near the door  24 . A reciprocator activating switch or button  28  may be provided on the enclosure  20 , just inside the door  24 . 
         [0014]      FIG. 2  is an elevation view of the mold  12 ,  14  shown in its open position with the reciprocator  18  beginning its operating cycle. A die face  30  of moveable die half  14  is visible in  FIG. 2 . Guide pins  32  are provided to insure proper alignment of the mold  12 ,  14 , when the pins  32  engage corresponding holes in the fixed die half  12 . The reciprocator  18  includes a lubricant sprayer  34  with nozzles  36 , air nozzles  38 , and a safety bar  40  all carried on a moveable frame  42 . After the die halves  12  and  14  have opened as illustrated in  FIG. 2 , and a finished part has been removed, the reciprocator  18  moves downward as indicated by the arrow  44 . While moving downward, lubricant, which may be a mold release compound carried in water, is sprayed through the nozzles  36  onto the faces of the die cavity. After the reciprocator  18  reaches the bottom of the mold  12 ,  14 , the lubricant sprayer  34  is turned off and high pressure air is supplied to nozzles  38 , preferably through the frame  42 . The reciprocator is then move upward to a rest or storage position above the mold  12 ,  14  as indicated in  FIG. 1 . During the upward movement, the air from nozzles  38  blows off any excess lubricant and dries the faces of the mold cavity, e.g. 30. 
         [0015]      FIG. 3  provides a side view of a die casting reciprocator  18  showing more details of a safety bar  40  according to the present invention. Parts shown in  FIGS. 1 and 2  are given the same reference numbers in  FIG. 3 . The frame  42  of the reciprocator  18  may be made of square cross section hollow tubing which may be used to convey high pressure air to the blow off nozzles  38 . Suitable hoses may be provided to convey lubricant to the sprayer  34  and through it to the sprayer nozzles  36 . Conventional automated or robotic systems may be provided for lowering and raising the frame  42  as needed. 
         [0016]    As shown in the figures, the safety bar  40  is a simple rectangular element having length and width dimensions at least as large as the plan view dimensions of the reciprocator as shown in  FIG. 1 . The safety bar  40  may be a solid sheet of a suitable material or may be made from a framework of individual parts leaving some open spaces. It is preferred that the all edges of the safety bar be continuous so that it moves through or sweeps out a space having plan view length and width dimensions at least as large as the space through which the reciprocator  18  moves in its downward travel. 
         [0017]    The safety bar  40  is movably supported from the lower side of the reciprocator  18 , e.g. by a pair of bolts  46  attached at their upper ends to the frame  42 . The safety bar  40  may have clearance holes for receiving the bolts  46 . A nut  48  or other retainer means may be attached to the lower end of each bolt  46  below the safety bar  40  to suspend the safety bar  40  at a selected distance below the reciprocator  18 . While gravity tends to hold the safety bar  40  in its lowermost position on the bolts  46 , it is preferred to provide springs  50  around the bolts  46  to further urge the safety bar  40  into this position. 
         [0018]    In this embodiment, a proximity sensor  52  is carried on each end of the safety bar  40 , to detect upward movement of the safety bar  40  relative to the reciprocator  18 . The proximity sensor may be an inductive sensor sold by Turck, Inc. of Minneapolis, Minn. under the Part Number Bi 2-EG08K-AP6X-V1131 and ID Number S4669450. A metal extension  54  may be provided on the frame  42  proximate each of the proximity sensors  52  when the safety bar  40  is in its lowermost position. The hall effect sensors  52  provide a closed circuit between its wire leads  56  when they are near a metal object and an open circuit between leads  56  when they move away from the metal object. In this embodiment, the leads  56  of both sensors  52  are connected in series and the circuit is connected to an input of the control system  26 . 
         [0019]    As noted above, in normal operation of the die casting system of  FIGS. 1 and 2 , the operator prefers to activate the reciprocator  18  cycle as he enters the door  22  to remove the just cast part. The reciprocator would then begin it downward travel before the operator can completely remove the finished part and exit the enclosure  20 . During normal operations there is sufficient time for the operator to exit. By following this procedure, a finished part, e.g. a gas grill top or bottom housing, may be cast in a 25 second cycle time. If the operator is required to exit and close the door  24  before the reciprocator can start its cycle, at least 5 more seconds will be added to the cycle time, reducing system productivity by about twenty percent. 
         [0020]    With the system of the present invention, the operator may activate the reciprocator as he enters the enclosure  20  to remove a finished part without danger of being injured by contact with the reciprocator as it cycles. If for any reason the operator does not exit the enclosure  20 , but remains in the travel path of the reciprocator  18 , the safety bar  40  will contact the operator before any other part of the reciprocator can reach the operator. With only slight force on the safety bar  40 , it will move upward relative to the reciprocator  18  and one or both proximity detectors  52  will move away from its corresponding post  54 . The circuit in one or both detectors  52  will open and the control system  26  will instantly stop movement of the reciprocator bar  18  and stop the flow of lubricant through the nozzles  36 . If desired, the control system may be programmed to return the reciprocator to its uppermost or rest position above the mold  12 ,  14 . In a preferred embodiment, the control system  26  is programmed to not allow the operator to restart the reciprocator by pushing the button  28 , but to instead require the operator to physically go to the control system  26  and reset the reciprocator. 
         [0021]    While a particular proximity sensor, a hall effect device, was used in the preferred embodiment, it is apparent that many other devices could be substituted. For example, magnetic relays such as those used on home security systems could be used. The metal extensions  54  could be magnets positioned to close such relays carried on the safety bar  40 . Various optical sensors may also be used. Mechanically operated switches or relays may be coupled between the safety bar  40  and the reciprocator  18  to close or open a circuit in response to movement of the safety bar  40  relative to the reciprocator  18 . In the preferred embodiment, the proximity sensor is carried on the safety bar  40  and the material being sensed, e.g. bars  54 , is carried on the reciprocator frame  42 . It is apparent that the sensors  52  could be mounted on the frame  42  and the material being sensed, e.g. a magnet, could be carried on the safety bar  40 . 
         [0022]    While the bolts  46  are shown as fixed to the frame  42  and slidably coupled to the safety bar  40 , it is apparent that the bolts could be fixed to the safety bar  40  and slidably coupled to the reciprocator  18 . 
         [0023]    While the present invention has been described in terms of preventing injury to the operator of the die casting system, it is also useful for preventing property damage. For example, there could be a malfunction of the system which results in the movable die half  14  failing to move to its fully open position. In that case, the reciprocator may collide with the die half  14  damaging the die and/or the reciprocator itself. Damage to either would be expensive to repair and may result in extended downtime for the die casting system. The present invention reduces the chances of such system damage by stopping the reciprocator if it contacts any other part of the die casting system as it cycles downward. 
         [0024]    While the present invention has been illustrated and described with reference to particular components and methods of operation, it is apparent that various substitutions of components and changes in methods of operation can be made within the scope of the present invention as defined by the appended claims.