GB2338204A

GB2338204A - Locking unit for industrial machinery such as injection moulding machines and pressure die-casting machines

Info

Publication number: GB2338204A
Application number: GB9811731A
Authority: GB
Inventors: Richard Lionel Sayer
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-06-02
Filing date: 1998-06-02
Publication date: 1999-12-15
Anticipated expiration: 2018-06-02
Also published as: GB9811731D0; GB2338204B

Abstract

There is disclosed a locking unit which employs C-Frames 1 and Piston Rod Extensions 9 to accomodate the reaction to the locking force with hydraulic compensation for the difference in deflection of the C-Frames and the elongation of the piston rod extensions so maintaining parallelity of the mould mounting platens under load. The mould includes a fixed platen 2, moving platen 3 and tail stock platen 4. There are four hydraulic cylinders 6 of which the upper pair have piston rod extensions 7 which connect platen 4 to C-Frames 1 via links 8 and the lower pair have piston rod extensions 9 attached to platen 2. Platen 2 is connected to C-Frames by links 12.

Description

1 1 2338204

SPECIFICATION

LOCKING UNIT FOR INDUSTRIAL MACHINERY SUCH AS INJECTION MOULDING MACHINES AND PRESSURE DIE CASTING MACHINES DESCRIPTION

For many years the Locking Units of industrial machinery such as Injection Moulding and Pressure Die Casting Machines have incorporated three platens with four tie bars connecting the outer two platens and acting as a guide for the centre platen to slide or see Figure G - 1. Traditionally the movement of the centre platen has been achieved hydraufically either by means of a direct acting hydraulic cylinder, or indirectly via a hydraulic cylinder powering a series of levered links referred to as toggles.

More recently market requirements have demanded a greater freedom of access for mounting large, or complex moulds in the machine without the space limitations applied by the conventional four tie bars. See Figure G - 1, Several designs of machines without tie bars are now commercially available which employ a 'Horizontal C Frame' to support the two outer platens so eliminating the space limitations previously appEed by the tie bars. However, due to the fact that a 'C Frame' deflects when a force is applied across its jaws it is not possible to maintain a uniform Locking, Clamping, force distribution across the mould area resulting in flashing of the moulded components and premature mould wear.

This invention serves to overcome the problem of non-parallel platerilmould faces during locking/clamping in machines employing a 'C Frame', or 'Tie Bar Less' design, by the use of hydraulic compensation.

It should be noted that this invention may be applied to machines with both exclusive hydraulic operation for all movements and machines which use electrical drives such as A.C. servo motors for the functions of mould traverse and ejection movements. Descriptions for both applications are given in the following text.

MACHINES WITH ALL HYDRAULIC DRIVES To understand the following text reference must be made to the attached drawings Ested below:- Figure 1 - H Shows a front view of the Locking Unit - mould closed. Figure 2 - H Shows end view k and Section t-E' through the Locking Unit. Figure 3 - H Shows a plan view of the Locking Unit - mould closed. Figure 4 - H Shows a cross section through the centre line of he Locking Unit - mould open. Figure 5 - H Shows Section 'C-C' through the Locking Unit - mould closed. Figure 6 - H Shows Section'D-D' through the Locking Unit.

Construction The basic machine structure comprises of identical front and rear C- Frames (1), fixed platen (2), moving platen and tail stock platen (4), with the User's Mould' (5) being mounted on the opposing vertical faces of the fixed platen (2) and the moving platen(3).

The tail stock platen (4) is furnished with four double acting hydraulic cylinder assemblies (6), of identical diameters and strokes, with the upper pair of cylinder assemblies having piston rod extensions (7) which connect to the C-Frames (1) via links (8) and the lower pair of cylinder assemblies having piston rod extensions (9) which pass through the moving platen (3) to provide directional guidance and alignment and are attached to the fixed platen (2) at its lower corners by means of nuts (10) and retaining plates (11).

The upper corners of the fixed platen (2) are connected to the C-Frames (1) by links (12), links (8) and (12) being identical components.

Mounted on the non-mould face of the moving platen (3) are two struts (1 31) which are adjustable in length with the adjustment being effected by captive nuts (14) which are held in unison by roller chain (15) and driven by motor (16). With the mould in the open position, see Figure 4 - a adjustable struts (13) pass through holes (17) in the tail stock platen (4). At the opposite end to the moving platen (3) the adjustable struts (13) are connected to cross head (18) by studs (19).

Mounted on the upper and lower edges of the tail stock platen (4) are two double acting hydraulic cylinders (20), the piston rods of which are connected to cross head (18).

Mounted on the inside vertical face of the tail stock platen (4) is the shutter plate assembly which comprises of shutter plate (2 1), mounted on pivot (22) and support plate (23)) which acts to support and guide adjustable struts (13). Shutter plate (2 1) is connected to double acting hydraulic cylinder (24) which controls its radial position. EE:- with the hydraulic cylinder (24) fully retracted as shown in Figure 2 - H the shutter plate (2 1) assumes a position where by the holes (17) in the tail stock platen (4) are uncovered, whereas when the hydraulic cylinder (24) is fully extended shutter plate (2 1) assumes a vertical position and shadows holes (17) in tail stock platen (4).

Also mounted on the non-mould face of moving platen (3) is a hydraulic ejection system (25) similar to that used on traditional Injection Moulding and Pressure Die Casting Machines.

Mounted below the platens are two support bars (26) which serve to support moving platen (3) via support shoes (27) in the event that heavy moulds are mounted in the machine. The support bars (26) are connected to the under side of fixed platen (2) by means of pivot joint (28) and to the under side of tail stock platen (4) by sliding joint (29).

0 Operation To understand the operating cycle of the Locking/Clamping Unit it is first necessary to verify the 'Start of Cycle Conditions', which are:- Mould open as shown in Figure 4 -R but note that that shown in Figure 4 - H is with the mould opened through its maximum stroke and under production conditions the actual mould open stroke will be limited to the minimum necessary to remove the components from the mould in order to achieve the minimum possible cycle time.

Shutter plate (21) in the open position as shown in Figure 2 - R 'Section E-E'.

The four hydraulic cylinders (6) in tail stock platen (4) pressurized at their 'Y' ports, so ensuring the maximum possible distance between the fixed platen (2) ad tail stock platen (4).

The length of the adjustable struts (13) will have been adjusted to a position where by the distance between the opposing faces of the fixed platen (2) and the moving platen (3) when the machine is in the closed position is equal to the thickness of the mould mounted in the machine.

The hydraulic ejection system (25) will be in its retracted position.

Upon receipt of the start cycle signal hydraulic fluid is directed to the rod side of the double acting hydraulic cylinders (20) so causing them to retract until their pistons reach the mechanical end of stroke, IE - the piston contacts the end cap of the cylinder. The rate of fluid flow to the cylinders through out the set stroke length is controlled by electronic ramps to give gentle acceleration and deceleration, with displacement transducer (30) feeding position data to the control system. As the cylinders (20) retract they cause the moving platen (3) to move towards the fixed platen (2), via the connection through cross head (18), studs (19) and adjustable struts (13), so closing the mould.

With the mould in the closed position the end of the adjustable struts (13) at stud (19) end have passed out of holes (17) in tail stock platen (4) and stopped at the '0' position shown on Figure 4 - H, which is some 0,25 mm clear of stopper plate (21). It is important to note that the sarne'O' position applies in all cases, Upon receipt of the 'mould closed signal' from linear transducer (30) hydraulic fluid is directed to the full bore side of the double acting hydraulic cylinder (24) so causing it to extend and move the shutter plate (2 1) into its closed, vertical position, so closing the entry to holes (17) in tail stock platen (4) for the adjustable struts (13).

With the shutter plate in its closed position pressurized hydraulic fluid is switched from port 'Y' to port 'Z' of the cylinders (6) in tail stock platen (4), see Figure 5 - R so causing the tail stock platen (4) to move towards fixed platen (2), so compressing shutter plate (2 1), adjustable struts (13), moving platen (3), mould (5) and fixed platen (2). The reaction to this compressive force, Locking Force, is transmitted between the upper pair of hydraulic cylinders (6) in tail stock platen (4) and the upper corners of the fixed platen (2) via links (8) and (12) to the CFrames (1) and from the lower pair of cylinders (6) in tail stock platen (4) and the lower corners of fixed platen (2) by piston rod extensions (9).As the applied Locking Force increases the C-Frames (1) will start to deflect with their jaws opening at the upper end the piston rod extensions (9) will extend. The deflection of the C-Frames (1) and the elongation of the piston rod extensions (9) will be of dissimilar values, but this will automatically be compensated for by different stroke lengths of the upper and lower pair of hydraulic cyfinders(6) in tail stock platen (4), as all four cylinders are subject to a common hydraulic pressure. To eliminate any mechanical restriction to the upper connections to the C-Frames links (8) and (12) are so designed that the have a horizontal moment of inertia sufficient to support the mass of the components they connect to, directly and indirectly and to transmit the Locking Force, but which enables them to deflect when subject to bending forces associated with the deflection of the C-Frames. During the period the Locking Force is applied the mould is compressed by equal forces acting across the mould base area, hence the paraflefity of the platens (2) and (3) will follow the parallelity of the mould.

Once the set Locking force has been achieved the Injection Moulding, or Pressure Die Casting Machine will continue its cycle by injecting synthetic resin, or metal alloys into the mould and the cooling time will then commence to run, this being a function of the Injection Unit which is not the subject of this speeffication.

Upon expiration of the cooling time the mould unlock signal is generated which causes decompression of the hydraulic fluid in the four cylinders (6) in tail stock platen (4) via ports 'Z', see Figure 5 -R so removing the Locking Force. Hydraulic fluid is next directed to ports 'Y' of the four cylinders (6), so causing the tail stock platen (4) to move to its maximum distance from the fixed platen (2), resulting in a small gap, 0, 25 mm, between the stud (19) end of the adjustable struts (13) and shutter plate (21).

With the tail stock platen (4) at its maximum distance from the fixed platen (2) hydraulic fluid is directed to the rod side of double acting hydraulic cylinder (24) causing it to retract and move the shutter plate (21) to its open position, see Figure 2 - H.

With the shutter plate (2 1) in its open position hydraulic fluid is next directed to the full bore side of the two double acting hydraulic cylinders (20) causing them to extend so opening the mould due to the mechanical connections via cross head (18), studs (19), adjustable struts (13) and moving platen (3). After the initial moud half separation hydraulic fluid is also directed to the rod side of hydraulic cylinders (20) so that they continue to open the mould under regenerative conditions at a higher speed and a reduced force. The flow of hydraulic fluid to cylinders (20) is controlled through out the opening stroke with electronic ramps controlling acceleration and deceleration and linear transducer (30) feeding position data to the control system. When the linear transducer (30) reads a value equivalent to the set mould opening stroke the mould open movement is arrested.

Upon completion of the mould open movement the hydraulic ejection system (25) extends and retracts through its set stroke to eject the products from the mould as with conventional Injection Moulding and Pressure Die Casting Machines.

MACHINES WITH ELECTRICAL DRIVES FOR MOULD TRAVERSE, SHUTUR PLATE MOVEMENTS, DIE HEIGHT ADJUSTMENT ANDJJECTION FACILITIES.

To under stand the following text reference must be made to the attached drawings listed below.- Figure 1 - E Shows a front view of the Locking Unit - mould closed. Figure 2 - E Shows end view A' and Section t-E' through the Locking Unit. Figure 3 - E Shows a plan view of the Locking Unit - mould closed. Figure 4 - E Shows a cross section through the centre fine of the Locking Unit - mould open. Figure 5 - E Shows Section 'C-C' through the Locking - mould closed. Figure 6 - E Shows Section 'D-D' through the Locldng Unit.

Construction The basic machine structure comprises of identical front and rear C- Frames (1), fixed platen (2), moving platen (3) and tail stock platen (4), with the Cser's Mould' (5) being mounted on the opposing vertical faces of the fixed platen (2) and the moving platen (3).

The upper corners of the fixed platen (2) are connected to the C-Frames (1) by links 12, links (8) and (12) being identical components.

Mounted on the non-mould face of the moving platen (3) are two struts (13) which are adjustable in length with the adjustment being effected by captive nuts (14) which are held in unison by roller chain (15) and driven by motor (16). With the mould in the open position, see Figure 4 - E, adjustable struts (13) pass through holes (17) in the tail stock platen (4). At the opposite end to the moving platen (3) the adjustable struts (13) are connected to cross head (18) by studs (19).

Mounted on the upper edge of cross head (18) is A. C. servo motor (3 1) which is connected to ball screw (32) via toothed belt drive (321). Ball screw (32) is retained in cross head (18) by combination bearing (33) and extends to engage in ball nut (34) which is secured to the tail stock platen (4).

Mounted on the inside vertical face of the tail stock platen (4) is the shutter plate assembly which comprises of shutter plate (35) and support plate (36) which acts both as a radial bearing for the shutter plate (3 5) and as a support and guide for the adjustable struts (13). Mounted on the face of support plate (36) is AC. servo motor (37) which drives pinion (38), which is engaged in gear teeth (39) cut on the circumference of shutter plate (3 5). The A. C. servo motor (3 7) serves to move the shutter plate (3 5) through its open and closed positions as shown on Figure 2 - E. In the open position shutter plate (35) exposes the holes (17) in the tail stock platen (4) and in the closed position shutter plate (3 5) shadows the holes (17) in the tail stock platen (4).

Also mounted on the non-mould face of moving platen (3) is the ejection system (40) which is powered by a linear A.C. servo motor.

Mounted below the platens are two support bars (26) which serve to support moving platen (3) via support shoes (27) in the event that heavy moulds are mounted in the machine. The support bars (26) are connected the under side of the fixed platen (2) by means of a pivot joint (28) and to the under side of the tail stock platen (4) by sliding joint (29).

Operation To understand the operating cycle of the Locking/ Clamping Unit it is first necessary to verify the 'Start of Cycle Conditions', which are:- Mould open as shown in Figure 4 - E, but note that that shown in Figure 4 -E is with the mould opened through its maximum stroke and under production conditions the actual mould open stroke will be limited to the minimum necessary to remove the components from the mould in order to achieve the minimum possible cycle time.

Shutter plate (3 5) in the open position as shown on Figure 2 - E, 'Section E-E'.

The four hydraulic cylinders (6) in tail stock platen (4) are hydraulically locked in their midstroke position as shown in Figure 5 - E.

The ejection system (40) will be in its retracted position.

Upon receipt of the start cycle signal AC. servo motor (3 1) is powered up to drive ball screw (32) in a clock-wise direction, as viewed from the drive end, so pulling the cross head and A.C. servo drive assembly, (18) (3 1) (3 2 1) and (3 3) towards the tail stock platen (4). Due to the mechanical connection between the cross head (18) and the moving platen (3) via studs (19) and adjustable struts (13) the movement of cross head (18) is transferred to the moving platen (3), so causing it to move towards fixed platen (2), so closing the mould.

With the mould in the closed position the end of the adjustable struts (13) at stud (19) end have passed out of holes (17) in tail stock platen (4) and stopped at the '0' position shown on Figure 4 - E, which is some 0.25 min clear of stopper plate (3 5). It is important to note that the same '0' position applies in all cases and is measured by the absolute encoder incorporated in the A.C. servo motor (3 1).

Upon receipt of the 'moWd closed signal' from the absolute encoder incorporated in A. C. servo motor (3 1) the shutter plate (3 5) is moved from its open position, to its closed position, see Figure 2 - E, Section E-E, by means of A.C. servo motor (37) and the gear drives (38) and (39), so closing the entry to holes (17) in tail stock platen (4) for the adjustable struts (13). An absolute encoder incorporated in A.C. servo, motor (37) feeds back positional data of the shutter plate (35) to the control system.

With the shutter plate in the closed position pressurized hydraulic fluid is directed to ports 7' of cylinders (6) in tail stock platen (4), see Figure 5 - E, so causing the tail stock platen (4) to move towards fixed platen (2), so compressing shutter plate (3 5), adjustable struts (13), moving platen (3), mould (5) and fixed platen (2) The reaction to this compressive force, Locking Force, is transmitted between the upper pair of hydraulic cylinders (6) in tail stock platen (4) and the upper corners of fixed platen (2) via links (8) and ( 12) to the C-Frames (1) and from the lower pair of cylinders (6) in tail stock platen (4) to the lower corners of fixed platen (2) by piston rod extensions (9). As the applied Locking Force increases the C-Frames (1) will start to deflect with their jaws opening at the upper end and the piston rod extensions (9) will extend. The deflection of the C-Frames (1) and the elongation of the piston rod extensions (9) will be of dissimilar values, but this will automatically be compensated for by different stroke lengths of the upper and lower pair of hydraulic cylinders (6) in tail stock platen (4), as all four cylinders are subject to a common hydraulic pressure. To eliminate any mechanical restrictions to the upper connections to the C- Frames links (8) and (12) are so designed that they have a horizontal moment of inertia sufficient to support the mass of the components they connect to, directly and indirectly and to transmit the Locking Force, but which enables them to deflect when subject to bending forces associated with the deflection of the C-Frames. During the period the Locking Force is applied the mould is compressed by equal forces across the mould base area, hence the parallelity of the platens (2) and (3) will foHow the parallelity of the mould.

Once the set Locking Force has been achieved the Injection Moulding Machine, or Pressure Die Casting Machine will continue its cycle by injecting synthetic resins, or metal alloys into the mould and the cooling timewill then commence to run, this being a function of the Injection Unit which is not the subject of this specification.

Upon expiration of the cooling time the mould unlock signal is generated which causes decompression of the hydraulic fluid in the four cylinders (6) in tail stock platen (4) via ports 'Z', see Figure 5 - E, so removing the Locking Force. Hydraulic fluid is next directed to ports 'Y' of the four cylinders (6), so causing the tail stock platen (4) to move to its maximum set distance from the fixed platen (2), resulting in a small gap, 0,25 mm, between the stud (19) end of the adjustable struts (13) and shutter plate (35).

With the tail stock platen (4) at its maximum set distance from fixed platen (2) A. C. servo motor (3 7) is powered up to move the shutter plate (35) from its closed to open position, see Figure 2 -E, Section EE, via gear drives (38) and (39).

With the shutter plate (3 5) in its open position A. C servo motor (3 1) is powered up to drive ball screw (3 2) in a counter clockwise direction, as viewed from the drive end, so causing the cross head (18) to move away from the tail stock platen (4) so pulling the mould open through its set stroke due the mechanical link via studs (19), adjustable struts (13) and moving platen (3).

Upon completion of the mould open movement the ejection system (40) extends and retracts through its set stroke to eject the products from the mould as with conventional Injection Moulding and Pressure Die Casting Machines.

Claims

1 A locking unit comprising of three platens with four hydraulic cylinders incorporated in the tail stock platen the upper pair of which are connected to the fixed platen by means of two C-Frames and the lower pair of which are connected to the fixed platen by extensions to the piston rods of the lower cylinder assemblies.

2 A locking unit which incorporates C-Frames to accommodate 50% of the reaction to the locking force and piston rod extensions to accommodate the remaining 50% of the locking force reaction, with two pairs of hydraulic cylinders applying the locking force and providing hydraulic compensation for the difference in the deflection of the C-Frame and elongation of the piston rod extensions when the locking force is applied to ensure that the parallelity of the fixed and moving platens for mounting the mould follows exactly the parallefity of the mould.

7 A locking unit substantially as described herein with reference to Figures 1 - R 2 - R 3 4 -R 5 -R 6-R 1 -E, 2 -E, 3 -E, 4-E, 5 -E and 6-E of the accompanying drawings.

- q_ Amendments to the claims have been filed as foflows 1. An injection moulding or pressure die casting machine having:

a pair of C-frames; and a headstock platen and a tailstock platen disposed between the ends of the C's of the C-ftames and facing each other for receiving a mould therebetween; the headstock platen being connected adjacent its top to the headstock ends of the C-frames; the tailstock platen being connected adjacent its top by an upper, first pair of hydraulic pistonand-cylinder assemblies to the tailstock ends of the C-frames; and the headstock and tailstock platens being connected adjacent their bottoms by a lower, second pair of hydraulic piston-and-cylinder assemblies and respective piston rod extensions.

2.

An injection moulding or pressure die casting machine having:

a pair of C-frames; a headstock platen and a tailstock platen disposed within the C's of the C-frames and facing each other for receiving a mould therebetween; and a hydraulic arrangement for forcing the headstock and tailstock platens towards each other to apply a locking force to such a mould; the hydraulic arrangement comprising:

a first pair of piston-and-cylinder assemblies acting between the headstock and tailstock platens via the C-frames; and a second pair of piston-and-cylinder assemblies, each with a piston rod extension, acting directly between the headstock and tailstock platens; and the machine being such that, in use, half of the locking force is reacted by the first pair of pistonand-cylinder assemblies and the C-frames, and the remaining half of the locking force is reacted by the second pair of piston-and-cylinder assemblies and their piston rod extensions.

-to- A machine as claimed in any preceding claim, wherein the four piston-and- cylinder assemblies have equal cylinder working areas and are connected to a hydraulic source arranged to apply equal pressures thereto.

4. A machine as claimed in any preceding claim, wherein each of the piston rods extends in a direction parallel to a longitudinal axis of the machine between the platens.

5. A machine as claimed in any preceding claim, wherein a first plane containing the axes of the first pair of piston-and-cylinder assemblies is parallel to a second plane containing the axes of the second pair of piston-and-cylinder assemblies.

6. A machine as claimed in claim 5, wherein the tailstock and headstock platens are mounted so that they can flex with respect to the tailstock ends and headstock ends, respectively, of the C-frames about respective transverse axes lying in the first plane.

7. A machine as claimed in any preceding claim, further including a movable platen disposed between the headstock and tailstock platens so that the mould can be received between the movable platen and the headstock platen, and means for adjusting the spacing between the movable platen and the tailstock platen.

8. A machine as claimed in claim 7, wherein the movable platen is slidably mounted on the piston rod extensions.

9. An injection moulding or pressure die casting machine, substantially as described with reference to Figures 1-H to 6-H, or Figures PE to 6-E, of the drawings.