Abstract:
A securing/clamping system for use with platens of a molding machine including a stationary platen having a first mold half affixed thereto, a movable platen having a second mold half affixed thereto, the movable platen travelling along a plurality of tiebars, and reciprocatively moving between a mold open and mold closed position, and a system for applying a clamping force to the movable platen.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Continuation-In-Part of U.S. patent application Ser. No. 08/743,719, filed Nov. 6, 1996 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a securing/clamping system for use with platens of a molding machine, especially an injection molding machine. 
     The prior art includes many injection molding machines which use tie bar clamping units for positioning a platen for the application of clamp-up forces. Control systems using hydraulic fluid, pressurized air and electric motors in combination with numerous switches and typically a controller unit are used to control both the positioning of the platens and the application and removal of clamp-up force for acquiring mold clamp-up and mold break. 
     Japanese Patent 61261-017 discloses a clamping mechanism for injection molding machines. The purpose of the control system therein is to maintain a parallel parting line between the molds by sensing the distance traveled by each clamping cylinder of each tie bar and maintaining the distances substantially equal. Accordingly, parallelism of the parting line between the molds can be maintained when the injection pressure of molten resin is uneven within the mold. 
     U.S. Pat. No. 4,832,884 to Speck et al. discloses a method for measuring and controlling the closing force of a plastic injection molding machine. Accordingly, for an injection molding machine, a closing force is measured for a predetermined number of operation cycles. A mean value is calculated from the measurements and if the mean value is within a predetermined tolerance, no control intervention takes place. However, if the mean value is outside the tolerance but within a zone limited by alarm units, control intervention takes place by stepwise changing the installed height of the mold until the actual value measured for closing force after each operating cycle is within the tolerance given. In this method and system, a toggle joint system serves to generate the closing force on the first and second mold parts. In this case, the force is measured and if the force is within a tolerance zone, the spacing between the first and second mold parts is altered to less than or no increase relative the old force. 
     U.S. Pat. No. 4,966,738 to Inaba et al. discloses a method for mold clamping force adjustment. Accordingly, in this method, a mold touch position is detected, at which the mold halves of a mold contact each other. The mold temperature is detected by means of thermocouples attached to the mold halves. The mold thickness is obtained based on the position where a movable platen and a stationary platen of the injection molding machine contact each other. After a molding operation is started, the mold temperature is detected and the amount of change in mold thickness during a period between a preceding cycle and a current cycle is calculated based on the change of mold temperature, the mold thickness, and the thermal expansion coefficient of the mold. A mold touch position for a current cycle is obtained based on the calculated value. Accordingly, when the mold is clamped in the current cycle, the movable platen is moved from the mold touch position toward the stationary platen by a predetermined amount to produce a predetermined mold clamping force. For this method, the measurements and adjustments are directed primarily to the mold position and not to the position of the clamping units. A clamping unit is a singular one which functions to force the movable platen against the stationary platen. That is, no tie bar clamping units are used internal to any of the platens for producing the clamp-up force. 
     U.S. Pat. No. 5,147,661 to Kurumaji et al. discloses a mold aligning device for a compression molding machine. The mold aligning device includes a plurality of mold position adjusting cylinder actuators disposed on a bed wherein position detectors are associated with the mold positioning adjusting cylinder actuators to detect the strokes thereof. The hydraulic source for driving the mold position adjusting cylinder actuators and control unit for controlling the strokes of the piston rods of the actuators with reference to zero points of the piston rods of the actuators, is determined beforehand. The zero points are decided by placing the upper mold in close contact with the lower mold and extending the piston rods of the actuators so that the piston rods are pressed against the lower surface of a slide block. The strokes of the piston rods are controlled during a compression-molding operation so that the upper mold is maintained precisely in parallel with the lower mold. This device is directly to pressure molding. The cylinder actuators are not positioned within a movable molten platen, and the actuators do not clamp onto tie bars. The main purpose of the machine is to maintain parallelism between the upper and lower molds by the actuators placing direct pressure on the upper mold supporting surface for maintaining the same parallel to the lower mold. 
     U.S. Pat. No. 5,338,171 to Hayakawa et al. discloses a die-clamping apparatus with an aligning device. The apparatus includes a stationary die plate for holding a stationary die, a movable die plate for holding a movable die, a hydraulic cylinder for moving the movable die plate forwardly and rearwardly with respect to the stationary die plate, and a tie bar for clamping by a fastening device located in the movable die plate. One or more alignment devices are provided so as to join the movable die and the stationary die in such a manner that primary alignment can be performed. The molding apparatus can be provided with a guide pin for secondarily aligning the movable die with respect to the stationary die when the stationary die and the movable die have been placed at predetermined positions. Four die clamping cylinders are provided at the corners of the stationary die plate so as to apply a clamping force to the stationary and movable dies after the fastening device has fastened to the tie bar. For this device, the tie bar fastener and clamping units, while being located on the tie bars, one adjacent the movable platen and one adjacent the stationary platen, are separate devices adding to the complexity of the machine. 
     U.S. Pat. No. 5,370,518 to Sasaki et al. discloses an apparatus for injection and compression molding. The apparatus includes and injection device and a compression molding device wherein the compression molding device includes a stationary die plate for holding a stationary die, a movable die plate for holding a movable die, means for rapidly extending and retracting the movable die plate relative to the stationary die plate and means for locking the movable die plate to the tie bars at a position where the movable die plate approaches the stationary die plate. Means for fastening the dies after the movable die plate is locked to the tie bars is also provided. An injection device for feeding a molten plastic material into a mold cavity between the stationary die and the movable die initiates feeding of the molten plastic material into the mold cavity when the stationary die and movable die are parted from each other by a predetermined distance. The plastic material is compressed and drawn while the movable die is moved towards the stationary die after a predetermined quantity of molten plastic material has been fed into the mold cavity. The apparatus includes a device in a movable die plate for clamping onto the tie bars. However, the device does not include a combined means for providing the clamping force between the platens and fastening to the tie bars, as the clamp force is provided by separate die fastening cylinders which are positioned on the tie bars but separate from the fasteners. 
     U.S. Pat. No. 5,133,655 to Schad et al. shows a clamp mechanism for an injection molding machine in which four columns attached to the moving platen are individually gripped by fluid actuated cylinders which also act as clamp force pistons. While this design is effective, it requires very close tolerances to be maintained between the columns and the inner bores of the cylinders since the amount of deflection of the cylinder walls to achieve sufficient gripping on the columns is small. Thus, manufacturing this clamp is expensive and in operation maintaining these small clearances imposes costly maintenance procedures. 
     Copending U.S. patent applications Ser. Nos. 08/482,869, 08/482,870 and 08/486,600 to Glaesener now U.S. Pat. No. 5,624,695, 5,645,875 &amp; 5,620,723, respectively, show a novel lock nut arrangement for engaging the tiebars of a two platen injection molding machine clamp, for example. The locking nuts also act as clamp force pistons acting on the tiebars to clamp the mold between the platens. 
     It is an object of the present invention to provide a fast acting, energy efficient injection molding machine clamp assembly. 
     It is a still further object of the present invention to provide an injection molding machine clamp assembly with low construction cost, low maintenance and good reliability. 
     It is a still further object of the present invention to provide an injection molding machine clamp assembly which occupies less floor space than conventional designs. 
     Further objects and advantages of the present invention will appear hereinbelow. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the foregoing objects and advantages are readily obtained. 
     The present invention provides a securing/clamping system for use with platens of a molding machine, especially an injection molding machine. The system of the present invention includes a stationary platen having a first mold half affixed thereto and a movable platen having a second mold half affixed thereto, with the movable platen travelling along a plurality of tiebars. Means are provided for reciprocatingly moving the movable platen between a mold open and a mold closed position. The present invention includes means for applying a clamping force to the movable platen in the mold closed position comprising at least one and preferably a plurality of columns having a first end affixed to the movable platen and a second end spaced from the movable platen with a plurality of spaced teeth on the second end, a clamp piston adjacent the second end of the column, and lock means as lock nuts engaging the clamp piston operative to engage and disengage the circumferentially spaced teeth. 
     Further features of the present invention will appear hereinbelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more readily understood from a consideration of the following illustrative drawings, wherein: 
     FIG. 1 is a section view of a clamp mechanism of the present invention. 
     FIG. 2 is a detailed section view of a locking nut of the present invention; 
     FIG. 3 is a perspective view of a locking nut and bearing assembly of the present invention; 
     FIG. 4 is a section view of an alternate embodiment of a clamp mechanism of the present invention; 
     FIG. 5 is a section view of an additional alternate embodiment of a clamp mechanism of the present invention; and 
     FIG. 6 is a section view showing an alternate embodiment of a clamp mechanism of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a high speed clamp mechanism  10  for an injection molding machine including a fixed platen  12 , a movable platen  14  and a clamp block  16 . Tiebars  18  connect fixed platen  12  and clamp block  16  while supporting the movable platen  14  which is free to slide along the tiebars. Generally four of the tiebars are used with only two being shown in FIG.  1 . Moving platen  14  is moved from a mold closed position shown in FIG. 1 to a mold open position by cylinders  20  which may be supported by clamp block  16 . One cylinder  20  is shown in FIG. 1, but of course two or more of the cylinders may be used depending on requirements. The cylinders are actuated by a suitable motive means, not shown. 
     First mold half  22 , such as a cavity half, is affixed to movable platen  14 , and second mold half  24 , such as a core half, is affixed to fixed platen  12 , with the mold halves together forming mold  26  in the mold closed position. As indicated above, movable platen  14  moves on tiebars  18  between a mold open and mold closed position. Only one mold  26  is shown in FIG. 1 for simplicity, but naturally a plurality of the molds can readily be provided. 
     Attached to the back side of movable platen  14 , i.e., the movable platen side opposed to mold  26 , is at least one column  28 , generally a plurality of columns and preferably four columns, with two of the columns shown in FIG.  1 . Columns  28  have a first end  30  affixed to movable platen  14  and a second end  32  spaced from the movable platen. A plurality of teeth  34  are provided on second end  32 . Circumferentially spaced between teeth  34  is at least one axial groove  36  and generally three or more of said grooves as clearly shown in FIG.  3 . Columns  28  pass through corresponding holes  38  in clamp piston  40 , with the clamp piston  40  housed in clamp block  16  as shown in FIG.  1 . Bearing  42  in clamp piston  40  support the columns in holes  38 . 
     Lock nuts  44  mounted on or with clamp piston  40  and carrying lock nut teeth  45  are rotatable to engage or disengage teeth  34  on column  28 . The lock nuts may be any desired locking means and engage clamp piston  40  or are retained inside or on a face of clamp piston  40 , as by bearings  42  as shown in FIGS. 2,  3  and  5 , or by retaining caps  46  as shown in FIGS. 1 and 4. Clamp piston  40  is retained inside clamp block  16  by front cap  48  or other desired retaining means. Lock nuts  44  are caused to rotate by cylinder  50  via linkage  52 . In an alternate embodiment shown in FIG. 4, lock nuts  44  have gear teeth  54  cut in their external perimeter and these are engaged by a central gear  56  which is driven by motor  58  via drive shaft  60  that passes through clamp piston  40 . The shaft  60  is splined so that it can move axially with respect to motor  58  when the clamp piston  40  carrying gear  56  moves within clamp block  16 . 
     Sleeves  62 , which can be an integral part of lock nut  44  as shown in FIGS. 2 and 5, or separate pieces as shown in FIGS. 1 and 4, use seals  64  to prevent fluid in the clamp cylinder from escaping during operation. 
     Ejector plate  66  carry ejector pins  68 , is mounted on columns  28  to eject molded articles from mold  26  in a conventional manner. 
     In operation, movable platen  14  carrying first mold half  22  is moved to the mold closed position shown in FIG. 1 to form mold  26  by cylinder(s)  20 . Lock nuts  44  are rotated so that lock nut teeth  45  engage column teeth  34 . High pressure fluid is directed into clamp cylinder  14   41 to cause clamp piston  40  to press against lock nuts  44  and thereby against columns  28 . This action clamps mold  26  between fixed platen  12  and movable platen  14 . After injection and cooling of the plastic is complete the clamp is opened by first directing pressurized fluid against the “mold break” side of clamp piston  40  into cavity  70 . This causes clamp piston  40  to pull lock nuts  44  away from the movable platen  14 , they act on the back side of teeth  34  on column  28  and cause mold  26  to be forced open a short distance. Next, the lock nuts  44  are rotated out of engagement with columns  28 , and cylinders  20  complete the opening of the mold. The molded parts are ejected from the mold  26  in a conventional manner and the clamp is ready to repeat the cycle. 
     The alternate embodiment of FIG. 6 shows a single column  72  having a first end  74  affixed to movable platen  14  and a second end  76  spaced from the movable platen. Column  72  is provided with a plurality of teeth  78  adjacent second end  76  which may be along the length of column  72  as shown in FIG.  6 . Teeth  78  engage corresponding teeth  80  in bore  82  through single clamp piston  84  in locked relationship as shown in FIG.  6 . Clamp piston  84  is rotated to engage/disengage teeth  78  and  80  by cylinder  86  which may be mounted onto clamp block  88 . Teeth  78  on column  72  are interrupted by slots as shown in the other embodiments, see slots  36  in FIG. 3, so that in the disengaged position the teeth  80  in piston  84  are cleared in the slot permitting column  72  to move freely through bore  82  in piston  84 . Column  72  is fixed to the back of movable platen  14 , as by bolts  90 , which is moved to open and close by cylinders  92  (one shown in FIG.  6 ). Cylinder  92  is mounted to moving platen  14  and its rod  94  is mounted to clamp block  88 . Alternatively, the cylinder may be mounted to the clamp block and the rod to the moving platen. The operation of the embodiment of FIG. 6 is essentially as the previous embodiments. An advantage of the embodiment of FIG. 6 is its reduced cost and greater simplicity and hence greater reliability. 
     The design of the clamping system of the present invention uses very little pressurized fluid to cause its motions for securing and clamping and consequently is a very energy efficient and fast acting clamp system. 
     The simplicity of the system of the present invention has the advantages of low construction cost, less maintenance and good operating reliability when compared to conventional systems. When compared to a conventional column blocking style of clamp design, the present design of smaller, lighter and less costly components are mounted on the clamp piston face. Also, the distance between the back face of the moving platen and the front face of the clamp block can be reduced without reducing platen opening stroke because the shutter plate assembly has been eliminated. Thus, the overall build length of the present clamp system is shorter and thereby reduces the footprint of the clamp which reduces the required floor space in the operating plant. 
     It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.