Quick coupling device for exchanging plasticizing unit of an injection molding machine

Abstract: An injection molding machine (10) comprising a drive unit (14) and a plasticizing unit (12) and includes a quick disconnect coupling mechanism for connecting the feed screw (18) of the plasticizing unit (12) to and disconnecting it from the quill (40) of the driving unit (14).

Description: BACKGROUND OF THE INVENTION The present invention relates to an injection molding machine and, more particularly, an injection molding machine provided with an improved quick disconnect coupling mechanism between the plasticizing unit and drive unit which allows for quick change of the plasticizing unit. In injection molding, it is frequently necessary to modify the thermoplastic material composition depending on the type of part being produced. In conventional machines, a change in material composition requires prolonged purging of material through the plasticizing unit when changing from one resin material to another thereby resulting in a waste of resin, energy and time. In order to avoid the disadvantages associated with prolonged purging, it is known in the prior art to simply remove the plasticizing unit, that is the barrel and screw assembly, and to substitute therefor a clean, preheated set of components for the new resin. U.S. Patents 4,704,078 and U.S. 4,708,622 to Hehl show how a quick barrel change system can be facilitated in small injection molding machines. In the '078 and '622 patents, an injection molding machine is disclosed which has an exchangeable plasticizing unit comprising a barrel and a feed screw, a drive unit includes a spindle for imparting rotation to an actual shifting of the feed screw within the barrel. A coupling assembly is provided for operatively connecting and disconnecting the spindle of the drive unit to the feed screw of the plasticizing unit. As can be seen in Figure 8 of the '078 patent, the coupling assembly for coupling the drive motor to the feed screw for supplying torque to the drive screw is transmitted through a drive dog 26. The main disadvantage of the drive dog design is that, for large machines where the power being transmitted from the drive motor to the screw is in the order of 50 hp or greater, the drive dog design is not sufficiently strong. A further prior art device is disclosed in German Offenlegungsschrift DE 32 29 223. The '223 document discloses four different species of hydraulic couplings for connecting and disconnecting the plasticizing unit of the injection molding machine to the drive unit. The disadvantage of all of the species of hydraulic couplings is that they require a supply of pressurized hydraulic fluid to act on the screw connector in order to disengage the connector and allow for automatic screw removal. In order to supply the necessary pressurized hydraulic fluid, a complicated arrangement of seals and channels are required throughout the plasticizing unit and drive unit. The requirement for rotating seals complicates and reduces the reliability of the coupling system. A further mechanism for quick changing of a plasticizing unit from a drive unit is disclosed in U.S. Patent 4,588,365. The injection molding assembly disclosed in the '365 patent includes two separate extruder units which, by way of a switching device, can be selectively coupled and uncoupled to the drive unit of the injection molding machine. This arrangement requires a relatively complicated control system for interchanging the two extruder units. Naturally, it would be highly desirable to provide a coupling mechanism for coupling the plasticizing unit of an injection molding machine to the drive unit there of which is simple of construction and strong enough to allow for power transmission between the drive unit and the plasticizing unit in the order of 50 hp or more. A further device for exchanging the plasticizing unit of an injection molding machine is disclosed in German Patent Application DE-A-38 08 769. This document discloses an apparatus comprising a collar with inwardly radially depending portions that extend beyond the minor diameter of the male spline used for driving the screw. The collar is rotatable between positions of alignment and non-alignment with slots on the screw corresponding to the depending positions of the collar. The slots are a number of spline teeth wide. An inconvenience due to this arrangement is that modifications are required to the end of the screw for obtaining said slots, and therefore standard screws cannot be used. Moreover, the broadness and depth of the slots reduce the strength of the spline drastically. In addition, as the DE '769 coupling apparatus comprises numerous components for coupling the screw to the machine, it results rather complicated to operate. Accordingly, it is the principle object of the present invention to provide an injection molding machine provided with an improved coupling mechanism between the plasticizing unit and drive unit which allows for quick change of the plasticizing unit from the injection molding machine. EP-A-0 266 709 discloses an apparatus having a screw coupling with two recesses in the drive unit, of which a longer recess is splined in order to transmit torque to the screw, while the shorter recess accommodates a mechanism to either retain the male spline in engagement with the female drive spline, or to allow the male spline on the screw to disengage. This is accomplished by moving two blocks radially into and out of engagement behind the male spline. The radial disengagement is accomplished by moving two cam plates in unison between the blocks forcing them apart so that the male spline can pass between them. Movement of the cam plates is done with motive means to ensure that the blocks are moved evenly and without rotation, otherwise the blocks would bind on the pins on which they slide. The coupling must also withstand axial tensile forces, particularly when suck back during the molding cycle. This occurs when the piston is reversed and pulls the screw backward to create a negative pressure in the barrel head and so to minimise drooling. The guide pins in the EP-A- 266 709 apparatus must withstand these forces, and therefore could be bent or otherwise damaged when used in this manner. Axial tensile forces could also force the blocks apart if there is a chamfer on the back of the spline as is normally the case. This would cause unexpected disengagement of the coupling. To overcome this, a square shoulder is provided, possibly requiring modification to existing screws in order to practice the apparatus. It is an object of this invention to provide a solid ring located behind the spline, so a chamfer would not result in unexpected disengagement of the coupling. By providing a collar retained on the drive quill by a threaded locking plate, as better described hereinafter, the collar can withstand much higher tensile forces than the apparatus disclosed in EP-A-0 266 709. It is a further object of the present invention to provide a coupling mechanism as aforesaid which is sufficiently strong for use on large injection molding machines. It is a still further object of the present invention to provide a coupling mechanism as aforesaid which is of simple construction, economic to manufacture and easily used with a high degree of reliability. Further objects 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 by providing an injection molding machine comprising: a plasticizing unit removably fastened to said molding machine, said plasticizing unit including a barrel and a screw mounted in said barrel along an axis of injection, said screw having a shank portion; a drive unit including driving means mounted along said axis of injection for rotating and axially moving said screw within said barrel, said driving means having an end face; coupling means for selectively securing said shank portion of said screw to said end face of said driving means; said coupling means including: a first recess of depth X having a female spline located in said end face of said driving means about said axis of injection; a second recess of depth Y located in said end face about said first recess wherein X is greater than Y; a male spline located on the shank portion of said screw wherein said male spline and female spline are matching splines; characterised in that collar means are mounted in said second recess and are rotatably movable between a first position and a second position; said coupling means including means for releasably locking said collar means in said first and second positions; said collar means including an internal bore having a female spline substantially identical to said female spline in said end face of said driving means such that when said collar means is in said first position, said female splines are aligned thereby allowing said male spline on said shank portion of said screw through said female spline on said collar means and into and out of said first recess so as to facilitate removal of said plasticizing unit from said molding machine, and when said collar means is in said second position, said female splines are non-aligned thereby locking said male screw spline in engagement with said female spline of said first recess. In accordance with the preferred embodiment of the present invention, a locking member is provided for holding the collar within the second recess and includes a detent mechanism for holding the collar in either its first or second position. The device of the present invention offers significant advantages over couplings heretofor known. First, by way of the spline connection between the feed screw and the quill of the drive unit, a strong coupling is made which can withstand the torque required by large injection molding machines without damaging the coupling connection. In addition, as the coupling mechanism is of simple construction, there is a high degree of reliability which is heretofor, not obtainable by prior art coupling devices. Further objects and advantages of the present invention will appear hereinbelow. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration in cross section of an injection molding machine employing the quick disconnection coupling mechanism of the present invention; and Figure 2 is a partial exploded view illustrating the mechanism for coupling and uncoupling the feed screw from the driving unit of the injection molding machine of Figure 1. DETAILED DESCRIPTION While the quick disconnect coupling mechanism of the present invention is described with reference to an injection molding machine and, particularly, the coupling of a plasticizing unit of the injection molding machine to the drive unit to the injection molding machine, it should be appreciated that the coupling mechanism may be employed in other embodiments without departing from the scope of the instant invention. With reference to the drawings, an injection molding machine 10 comprises a plasticising unit 12 and a drive unit 14. The plasticizing unit 12 is adapted to be removably fastened to the housing 16 of the injection molding machine 10 in known manner. The plasticising unit 12 of the injection molding machine includes a feed screw 18 which is rotatably and axially displaceable within a barrel 20 along an axis of injection X. The feed screw 18 comprises a screw portion 22 and a shank portion 24. A hopper 26 loaded with the material to be extruded is mounted on the injection molding machine and delivers the material to be extruded to the barrel 20 and the feed screw 18 via passage 28. The shank portion 24 of feed screw 18 is provided intermediately with a groove 30 which receives an arresting bolt 32 under the influence of spring 34 for reasons to be made clear hereinbelow. The underside of the arresting bolt 32 is connected with a pressure source via passage 36 in opposition to spring 34. The drive unit 14 of the injection molding machine 10 includes a quill 40 rotatably mounted in a piston 70 for driving feed screw 18 in a rotatable and axial manner. The quill and piston are driven in a manner which is well-known in the art as, for example, disclosed in U.S. Patent 4,731,005 and for the sake of simplicity is neither illustrated in the drawings nor will be described in detail herein. The coupling mechanism of the present invention for securing the feed screw of plasticizing unit 12 to the quill 40 of drive unit 14 is described in detail with reference to Figures 1 and 2. The coupling mechanism comprises a first recess 42 provided in the end face 44 of quill 40 about the axis of injection X. Recess 42 is provided with a female spline which is adapted to receive the shank portion 24 of feed screw 18 which is provided with a male spline 38. The end face 44 of quill 40 is provided with a second recess 46 which receives a collar 48. The collar 48 is held in place within the recess 46 by means of a locking plate 50 which is threaded into threading recess 46 and secured therein. Locking collar 48 is mounted within recess 46 with the locking plate 50 so as to allow the collar 48 to rotate within the space defined by the recess 46 and locking plate 50. In order to allow for rotation of the collar, the collar 48 is mounted with an axial clearance within the space defined by recess 46 and locking plate 50 of approximately no greater than 0.127 mm (.005") in order to minimize the axial clearance of the spline 38 provided on feed screw 18 and the female spline 52 provided in an internal bore formed on the collar 48. In accordance with the present invention, female splines 42 and 52 are identical and match male spline 38 provided on feed screw 18. The external peripheral surface 54 of collar 48 is provided with first and second indents 56, only one of which is illustrated in Figure 1, which receive detent 60 provided in locking plate 50 for holding the collar in a first position or in a second position as will be discussed hereinbelow. In addition, as is illustrated in Figure 2, the collar is provided with several wrench slots 62 which are adapted to receive a holding arm 64 which is selectively pivotable into and out of a wrench slot 62 by means of a motor mechanism 66 which is schematically illustrated in Figure 2. The operation of the quick disconnect mechanism of the present invention is as follows. With reference to Figure 1, spline portion 38 of shank portion 24 of feed screw 18 is illustrated as being locked in position within the recess portion 42 of quill 40. In this position, the spline connection between the quill 40 and the feed screw 18 allows for the quill 40 to drive the feed screw 18 both rotatably and axially. When the feed screw 18 is locked in place, the collar 48 assumes its first position wherein the spline 52 is non-aligned with the spline in recess 42. The collar is held in this first position by the detent 60 engaging indent 56. When it is desired to remove the plasticizing unit 12 from the drive unit 14, the motor mechanism 66 is actuated so as to engage arm 64 within a wrench slot 62. Quill 40 is then rotated relative to collar 48 as collar 48 is held stationary by arm 64. The rotation of quill 40 causes detent 60 to disengage from first indent 56 as locking plate 50 rotates with quill 40 relative to collar 48. The quill is rotated until detent 60 engages second indent 56 at which point the female spline provided in the quill 40 aligns with the female spline provided on collar 48. In order to again lock the feed screw 18 to the quill 40, the quill need only be rotated counter back to its original position wherein detent 60 again engages first indent 56. When the coupling is in its unlocked position, that is, when the female splines on quill 40 and collar 48 are in alignment, the feed screw can be disconnected from the quill 40 and thus the drive unit 14. In order to allow the plasticizing unit to be removed as a unit, hydraulic pressure is relieved from line 36 under detent pin 32. Thus allowing detent pin 32 to be biased by spring 34 into engagement with groove 30 provided on the shank portion 24 of feed screw 18. When in this position, the plasticizing unit may be removed as a whole from the drive unit of the injection molding machine. As can be seen from the foregoing, the coupling mechanism of the present invention offers a simple construction which is economic to manufacture, exhibits a high degree of reliability and satisfies the object set out hereinabove. In addition, the system is readily adaptable to be semi or fully automatic as the flexibility of its design is easily adaptable to either construction.

Claims: An injection molding machine (10) comprising: a plasticizing unit (12) removably fastened to said molding machine, said plasticizing unit including a barrel (20) and a screw (18) mounted in said barrel along an axis of injection, said screw having a shank portion (24); a drive unit (14) including driving means (40) mounted along said axis of injection for rotating and axially moving said screw (18) within said barrel (20), said driving means (40) having an end face (44); coupling means for selectively securing said shank portion (24) of said screw (18) to said end face (44) of said driving means (40); said coupling means including: a first recess (42) of depth X having a female spline located in said end face (44) of said driving means (40) about said axis of injection; a second recess (46) of depth Y located in said end face (44) about said first recess wherein X is greater than Y; a male spline (38) located on the shank portion (24) of said screw (18) wherein said male spline (38) and female spline (42) are matching splines; characterised in that collar means (48) are mounted in said second recess (46) and are rotatably movable between a first position and a second position; said coupling means including means (56,60) for releasably locking said collar means (48) in said first and second positions; said collar means (48) including an internal bore having a female spline (52) substantially identical to said female spline (42) in said end face (44) of said driving means (40) such that when said collar means (48) is in said first position, said female splines (42,52) are aligned thereby allowing said male spline (38) on said shank portion (24) of said screw (18) through said female spline (52) on said collar means (48) and into and out of said first recess (42) so as to facilitate removal of said plasticizing unit (12) from said molding machine (10), and when said collar means (48) is in said second position, said female splines (42,52) are non-aligned thereby locking said male screw spline (38) in engagement with said female spline (42) of said first recess. An injection molding machine according to claim 1, characterised in that said second recess (46) is threaded so as to receive a threaded locking plate (50) for mounting said collar means (48) within said second recess. An injection molding machine according to claim 1, characterised in that said collar means (48) includes locking means (62,64) for holding said collar means (48) against rotation upon rotation of said driving means (40) for moving said collar means to said first and second positions. An injection molding machine according to claim 3, characterised in that said locking means includes a slot (62) provided in said collar means (48) and motor actuated detent means (64) for selectively engaging said slot (62). An injection molding machine according to claim 2, characterised in that said collar means (48) is mounted by said locking plate (50) in said second recess (46) so as to allow for an axial clearance less than or equal to 0.127 mm (0.005"). An injection molding machine according to claim 2, characterised in that said second recess (46) is threaded so as to receive a threaded locking plate (50) for mounting said collar means (48) within said second recess. An injection molding machine according to claim 1, characterised in that said shank portion (24) of said screw (18) is provided with a groove (30) and said plasticizing unit (12) includes detent means (32) for selectively engaging said groove so as to allow removal of said plasticizing unit from said molding machine (10) as a unit when said collar means (48) is in said first position.

Inventors: COSMAN JOHN, SILAGHI VICTOR, COSMAN, JOHN, SILAGHI, VICTOR
Applicants: HUSKY INJECTION MOLDING, HUSKY INJECTION MOLDING SYSTEMS LTD.
Application year: 1991
Main classification: B29C45
IPC codes: B29C45