GB2198078A - A press for forming items from synthetic plastics composite plastics, or fibre reinforced synthetic plastics materials - Google Patents

Abstract

The pressing is effected between mould parts respectively carried by a press bed and by a press ram (6, Fig 2) which is movable hydraulically between a cross-head and the press bed (14), the press ram (6) being movable firstly over a non-working part of its stroke by means of a high speed hydraulic piston and cylinder assembly to an intermediate advanced posiiion adjacent the press bed, and secondly by means of a hydraulic short-stroke device (4,8, or 4',35) to a fully advanced pressing position by pressure medium admitted at passage 12. The press ram (6) is indirectly (Fig 1) or directly (Fig 3) attached to one end of a piston rod (5) having a cylinder (2, or 4') which is fixedly connected to the cross-head (15), means (3,7, or 3',7') being provided for releasably hydraulically locking the piston rod (5) to at least one part of the cylinder (2, or 2') and hydraulic pressure pad means (11) also being provided absorbing or reducing braking shock resulting from said locking of the piston rod (5), at the termination of the non-working stroke part at the intermediate advanced position. <IMAGE>

Description

APPARATUS FOR PRESS FORMING ITEMS FROM SYNTHETIC PLASTICS, COMPOSITE PLASTICS OR FIBRE REINFORCED SYNTHETIC PLASTICS MATERIALS This invention relates to apparatus for press forming items from synthetic plastics, composite plastics or fibre reinforced synthetic plastics materials.

When shaping, coating and pressing items of synthetic plastics, composite plastics or fibre-reinforced synthetic plastics materials for producing moulded or shaped parts, extremely rigid presses of high pressing accuracy and considerable operating pressures are required. In motor vehicle construction also, the tendency is for the larger shaped parts such as car doors or roofs, which were hitherto produced from steel plate, to be produced from synthetic plastics or composite plastics materials. Many new synthetic plastics and plastics combinations have been developed for that purpose which have the necessary properties. The starting material can, however, also be fibre-reinforced synthetic plastics mats or panels which are compressed and shaped in the press while cold or heated.In particular the shaping of large-area bodywork parts of extremely small cross-section calls for accurate parallel guidance of the shaped parts, so that no areas of different thickness are produced in the workpiece.

Hydraulic presses according to DE-OS 32 07 242 have become known as a means of fulfilling these general requirements.

In order to satisfy the exacting demands mentioned hereinabove, such a known press consists of a high upper cross-head which is adjustable for height on long lateral round cross-section columns and which serves as a press bed, and an undesirably highly located press base which consists of a lower cross-head with the press cylinders and press bed mounted on it. With this press, the upper cross-head which is initially clamped on the round section columns is released and drawn down the columns until it is in the lower working position. The upper cross-head is then again clamped to the columns, whereupon the lower mould half with the lower cross-head is forced via the hydro-statically mounted press cylinders upwards against the material part for the compressing and shaping stages.By reason of the necessarily considerable clearance which has to be preset in order to guide the upper cross-head on the columns, it is scarcely possible to achieve parallel guidance and adjustment of the mould halves to anything like the required accuracy.

Further developments in the processing of duroplastic and thermoplastic fibre-reinforced materials, however, also require: a) extremely short pressureless turn-round times for the relatively highly accelerated hardening material which hardens under heat, (e.g.

polyester resins for SMC large shaped parts) or even preheated thermoplastics materials which are placed in a cold tool, b) short pressure build-up times in order to have a mould removal time of less than 1 second from material contact (between male and female parts of the mould) to mould removal.

To fulfil the conditions under a) and b), it is necessary for the production of satisfactory items, for instance in the case of premature hardening or excessively rapid cooling of the as yet not mould-stripped material or in case b) in the event of rapidly reacting materials, to guarantee mould removal even with long flow paths and narrow flow crosssections.

Along with this requirement which exists for so-called 'plastics forging', it is also for high moulding accuracy and constancy of design strength or even a corresponding and regularly thin surface coating in the tool, necessary c) to ensure accurate parallel running control during the rapid movement of the press ram and during the pressing process within very narrow limits (measured over the four corners of the press bed).

There is thus a need for a generally improved press forming apparatus which at least partially meets the above three requirements a), b) and c), and which preferably permits extremely short pressing cycles.

Accrd:p.g to the preset. .invention there s provided an apparatus for press-forming items from synthetic plastics, composite plastics or fibre reinforced synthetic plastics materials, including a press bed for carrying a first mould part, a press cross-head spaced from the press bed, a press ram for carrying a second mould part, which press ram is movable hydraulically between the cross-head and press bed towards and away from the press bed to press form material between the first and second mould parts, and which press ram is movable firstly by means of a high speed hydraulic piston and cylinder assembly operative to move the press ram quickly over the non working part of its stroke towards and away from the press bed between a fully retracted position remote from the press bed and an intermediate advanced position adjacent the press bed, and secondly by means of a hydraulic short-stroke device operative to move the press ram over the working part of its stroke towards and away from the press bed between the intermediate advanced position and a fully advanced pressing position in which material is press formed between the two mould parts, at least one piston rod and cylinder assembly having an axially movable piston rod to one end of which the press ram is indirectly or directly attached and having a cylinder which is fixedly connected to the cross-head, means for releasably hydraulically locking the piston rod to at least one part of the cylinder, and hydraulic pressure pad means for absorbing or reducing braking shock resulting from locking the piston rod to said at least one part of the cylinder during movement of the piston rod.

With an apparatus of the present invention it is possible for practical purposes to provide a jolt and wear-free coupling of the piston rod and at least one part of the cylinder due to the synchronised force-locking clamping of the piston rod in the case of small effective masses. This is made possible by the hydraulic damping and automatic compensation of the masses involved by the initially pressurised pressure pad means.

Neutralising the weight of the piston rod and of the cylinders means that by reason of the low residual masses, neutralisation of the weight of the piston rod and of the cylinder favours advantageously shorter braking times, a higher speed return stroke, and high closing speeds. This results in extremely short turn-round times of the material to be shaped from the moment it is laid into the mould until shaping begins and thus better forming properties right to the outermost corners of the workpiece.

The control and regulating technique, and also the construction of apparatus of the invention give rise to parallel running accuracy even when the female mould part enters the guides and the leading edges of the male mould part, before contact with the material to be press formed.

Advantageously the or each hydraulic pressure pad means, the or each releasable lock means and the or each hydraulic short-stroke device form a single structural unit with the or each piston rod. This allows the short pressure build-up times, with the use of the short-stroke device permitting particularly high pressing speeds. With short-stroke devices also, the necessary energy consumption and the quantities of oil to be regulated and controlled are very small and because of the low volume of oil in the device cylinder, the pressure build-up time is very small due to the low compression volume in the oil column, i.e. the quantity of oil to be compressed is about 20 times less than in the case of a fully hydraulic system.Relatively small moving quantities of oil again assist an accurate NC-controlled movement of the press ram during the closing and pressing working stroke within a narrow range of tolerances in terms of 'desired value/actual value deviation; according to predetermined velocity, braking and pressing pressure characteristics.

In comparison with other known short-stroke pressing apparatus, the high-speed apparatus of the invention requires no complicated or expensive control systems for uninterrrupted ram movement nor for synchronous movement between ram and pressing pressure system.

Thus a high-speed apparatus of the invention provides a shorter pressing cycle for the workpiece item which is to be produced and therefore a higher output with greater quality and fewer rejects, together with a longer effective life of the tools by the careful treatment of the mould leading edges.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the acompanying drawings, in which: Fig. 1 shows in vertical section an hydraulic split-taper lock means and an hydraulic short-stroke cylinder-piston device of a high-speed press apparatus according to a first embodiment of the present invention, Fig. 2 shows in part vertical section the high-speed press apparatus of Figure 1, Ay. r shows in verruca, section an hydraulic lock means and an hydraulic short-stroke cylinder-piston device of a high-speed press apparatus according to a second embodiment of the invention, Fig. 4 shows in vertical section the high speed press apparatus of Figure 3, and Fig. 5 is a path-time-pressure diagram for the apparatus of the embodiments of Figures 2 and 4.

Apparatus for press-forming items from synthetic plastics, composite plastics or fibre reinforced synthetic plastics materials according to a first embodiment of the invention is shown in Figures 1 and 2 and its operating sequence illustrated in Fig. 5.

As shown in Fig. 2 the apparatus is a hydraulic high-speed press of window frame design, comprising a press frame 1 with an upper cross-head 15 and a press bed 14 spaced from the cross-head 15. Between the crosshead 15 and the bed 14 there is a press ram 6 which carries an upper tool half or female part 28 (see Fig. 5) of the mould and which can be raised and lowered quickly by means of a hydraulic high-speed piston and cylinder assembly. The high speed piston and cylinder assembly consists of a piston rod 9 attached at one end centrally on the ram 6 and a cooperating hydraulic cylinder attached at one end to the cross-head 15. The press ram 6 is fixed on at least one, and preferable two or four (according to the type of press) piston rods 5 slidably guided in the cross-head 15.An hydraulic releasable split-taper lock means 3, 7 and 13 and an hydraulic short stroke press device 2, 4, 8, 11 and 12 operatively connected to it form a structural unit with the piston rods 2.

Fig. 1 shows in vertical section, in more detail, the disposition of a piston rod 5, the hydraulic split-taper lock means 2, 3, 7 and 13 and the hydraulic short-stroke device 4,8, 11 and 12 for the working pressing stroke.

As pressurised hydraulic medium is introduced into a feed line 13, a diaphragm 7 is urged away from a bore in a cylinder 2 in which the piston rod slides, to urge a split clamping sleeve 3, housed in a recess in the bore in the cylinder 2, into releasable locking engagement with the piston rod periphery to lock the piston rod together with the cylinder 2. Since the cylinders 2 are fixedly attached to the cross-head 15, the piston rods 5 are therefore also in this way releasably fixed to the cross head.At the commencement of or prior to the lowering of the ram 6, pressurised hydraulic medium is drawn from a pressure storage means and introduced into hydraulic medium is drawn from a pressure storage means and introduced into hydraulic pressure pad means in order to generate an initial pressure therein which is sufficient to raise the weight of all the piston rods 5 and all piston heads 8 relative to the cross-head 15.

The hydraulic pressure pad means for absorbing or reducing braking shock resulting from locking the piston rods 5 to the cylinders 2 during downward movement of the piston rods 5 includes a respective piston head 8 fixedly attached to the end of the associated piston rod 5 nearest to the press bed 14 and a cylinder head 4 having a bore opening through one end thereof into which bore the piston head 8 slidably projects. The cylinder head 4 is fixedly attached, at its closed end remote from the end through which the bore opens, to the press ram 6 as can be seen in Fig. 2.

The synchronised locking of the piston rods 5 with the cross-head 15 thus produces a shock-free absorption of the moving masses. After the locking stage, by further introduction of pressurised hydraulic medium through a feedline 12 into the cylinder head bore between the closed end of the cylinder head 4 and the facing end of the piston heed 8, the necessary pressure for the working stroke of the pressing process is exerted, with the piston heads 8, and ram 6 being displaced to press the female mould part 28 against the male mould part 29 and the press bed 14.

At the start of a pressing cycle, in the upper position of the piston rod 9, the split-taper lock means 2, 3, 7 and 13 is released. With commencement of the controlled downwards movement of the piston rods 5 and press ran 6 caused by the hydraulic cylinder 10 and piston 9, the piston rods 5 with the press ram 6 and the female mould part 28 are lowered.

Immediately prior to the two tool halves - female mould part 28 and male mould part 29 - coming n contact with each other, when matching contact 18 strikes an abutment 16, the downwards movement of the press ram 6 and of the piston rods 5 which are fixedly connected to it is braked. With the synchronised coupling of the piston rods 5 to the cylinders 2 fixed to the cross head 15, only the relatively small mass of the piston heads 8 and the piston rods 5 connected form-lockingly to it have to be accelerated from the speed V=O mm/sec to the braking speed of the press ram 6 against the pressure pads 11 which are slightly pre-pressurised according to the inherent weight of the rods 5 and heads 8. The force-locking coupling by the split.

r?=er ISC' means 39 8 and 15 can nus, HishUut interrupeing he movement of the press ram, take piace in shock-free fashion for the mass of the piston heads 8 and of the piston rods 5, in a damped manner. When the abutment 17 comes into contact with the matching contact 18, the build-up of pressing pressure is initiated and the parallel movement control started. Directly associated with each cylinder head 4 and serving as a positioning member is a servo-switching valve which reacts proportionally to the volume of infed pressurised medium.The mechanical abutments 16 and 17 are adjustable in guide rails 19 so that shaped items 31 of various thicknesses can be produced. The travelling movement of the piston rod 9 can also be controlled and regulated via a central time and/or path measuring system.

Fig. 5 is a path-time-pressure-diagram which diagrammatically shows the mould parts 28 and 29 to illustrate the production cycle according to the invention in respect of a workpiece 31 from the start of movement of the piston rod 9 and 21 as far as the end of the compression time at 33. Plotted as the abscissa is the piston rod stroke while the closing speed is plotted as the ordinate. The speed profile curve shows at 22 the start and at 23 the end of coupling between the cylinder 2 and the piston rods 5. At the same time, parallel running control starts at 23. While material contact starts at 25, the arrows at 26 show the short pressure build-up time by virtue of the short-stroke version of the cylinder heads 4. After pressure build-up 26, the actual pressing pressure also starts at 25, as shown over on the right as a pressure curve.The time related pattern of a pressing cycle is shown right at the bottom by the arrowed markings 'return stroke' and 'pressing stroke' with the pressure build-up time, 0.3 seconds still showing the time for locking or coupling of the piston rods 5. Reference numeral 27 denotes the necessary return stroke as clearance for loading and unloading robots. The high-speed piston rod movement of approx. 1000 mm/sec closing speed is carried out shortly prior to contact with the leading edges 20 of the mould parts via exactly predetermined speed and braking characteristics.

Reference numeral 24 denotes the travel in the assumed example for a parallel regulated press stroke as far as the end of forming of the pressing material or shaped part 31 to the thickness 32.

The second embodiment of the invention illustrated in Figures 3 and 4 is basically similar to that of Figures 1 and 2 and like reference numerals will be used for like parts which will not be further described in detail. The second embodiment also operates according to the diagram of Fig. 5 and this operation likewise will not be further described.

In the second embodiment the piston rods 5 are fixedly secured at one end to the press ram 6. The hydraulic short-stroke device includes an annular intermediate cylinder 2' having an enlarged head portion 35 slidably housed in a bore through the cylinder 4', which cylinder 4' is fixed to the cross head 15. The hydraulic pressure pad means is in the form of an annular chamber 11 provided between the bore of the cylinder 4' and the cylinder head portion 35 to receive hydraulic medium under pressure to exert a preloading pressure between the cylinder 4' and cylinder head portion 35 to resist advancement of the cylinder head portion 35 out of the cylinder 4'. The piston rod 5 is slidably mountd in a bore through the cylinder 2'.

The releasable lock means is a two section sleeve lock housed in the bore of the cylinder 2'. It has two sleeves 3, 3' each surrounding the piston rod 5 at axially spaced locations therealong and each housed in an associated annular recess in the bore of the cylinder 2'. A flexibl2 diaphragm 7, 7' is located between each sleeve 3, 3' and the bore in the cylinder 2'.

The hydraulic short-stroke device is operative to advance the enlarged head portion 35, and the piston rod 5 when locked thereto, out of the cylinder 4' by hydraulic medium under pressure supplied into the bore in the cylinder 4' via line 12 to act in an annular chamber 8' against the enlarged head portion 35 on a shoulder face thereof located upstream of the chamber 11.

By introducing pressurised medium into the feed line 13, the diaphragms 7 and 7' generate pressure n the clamping sleeves 3 and 3' and the piston rod 5 is force-lockingly locked to the annular cylinder 2' of the differential cylinder 4'. Since the differential cylinders 4 are fixedly attached to the cross-head 15, the piston rods 5 are therefore also connected to it. At the commencement of or prior to the lowering of the ram 6, pressurised medium is fed out of pressure storage means and into the pressure pad chambers 11 in order to set up an initial pressure therein which is adequate to cancel out the weight of all the-piston rods 5 and all the annular cylinders 2' in relation to the cross-head 15.The synchronous locking of the piston rods 5 to the cross-head 15 thus produces a shock-free Lorptcr J oS tbe z v5n5 mdsses. aster rhe lockrnr, process, the introduction of pressurised medium through the feedline 12 into the cylinder chamber 8' exerts the necessary pressure for the pressing process, the annular cylinders 2, via the piston rods 5, pressing the ram 6 with the female mould part 28 against the male mould part 29 and press bed 14. At the start of a pressing cycle, in the upper position of the piston rod 9, the splittaper lock means 3, 7 and 13 is unlocked. At the commencement of the controlled downwards movement by the hydraulic piston 9 and cylinder 10, the piston rods 5 move downwards, together with the ram 6 and the female mould part 28.Immediately before contact is made between 29 - the rapid downwards movement of the ram 6 and of the piston rods 5 connected to it in form-locking manner is braked when contact 18 strikes abutment 16. With the synchronised coupling, only the relatively small mass of the annular cylinders 2' has to be accelerated from speed V=O mm/sec to the braking speed of the ram 6 against the pressure pad chambers 11 which are slightly prepressurised according to their inherent weight. Force-locking coupling by means of the split-taper lock means 2', 3, 7 and 13 can thus be applied in a damped manner jolt free for the masses of the annular cylinders 2' and without interruption of the press ram movement. When the abutment 17 is contacted by the matching contact 18, the build-up of pressing pressure is initiated and the parallel running control is started. Directly associated with each differential cylinder 4' and serving as a positioning member is the servo-switching valve which reacts proportionally to the infed volume of pressurised medium.

Claims (12)

1. Apparatus for press-forming items from synthetic plastics, composite plastics or fibre reinforced synthetic plastics materials, including a press bed for carrying a first mould part, a press cross-head spaced from the press bed, a press ram for carrying a second mould part, which press ram is movable hydraulically between the cross-head and press bed towards and away from the press bed to press form material between the first and second mould parts, and which press am Is movable firstly by means of a high speed hydraulic piston and cylinder assembly operative to move the press ram quickly over the non-working part of its stroke towards and away from the press bed between a fully retracted position remote from the press bed and an intermediate advanced position adjacent the press bed, and secondly by means of a hydraulic short-stroke device operative to move the press ram over the working part of its stroke towards and away from the press bed between the intermediate advanced position and a fully advanced pressing position in which material is press formed between the two mould parts1 at least one piston rod and cylinder assembly having an axially movable piston rod to one end of which the press ram is indirectly or directly attached and having a cylinder which is fixedly connected to the cross-head, means for releasably hydraulically locking the piston rod to at least one part of the cylinder, and hydraulic pressure pad means for absorbing or reducing braking shock resulting from locking the piston rod to said at least one part of the cylinder during movement of the piston rod.

2. Apparatus according to claim 1, wherein the piston rod is slidably mounted in the cylinder, wherein the releasable lock means is a split-taper lo !s ul?tofl5Hin9 the piston. rcd and housed ir. the ylinder bore for releasably locking the piston rod to the cylinder, and wherein the hydraulic short-stroke device is a piston head fixedly attached to the end of the piston rod nearest to the press bed and a cylinder head having a bore opening through one end thereof into which bore the piston head slidably projects, said cylinder head being fixedly attached, at its closed end remote from the end through which the bore opens, to the press ram, said hydraulic pressure pad means being in the form of an annular chamber provided between the piston head and cylinder head behind an enlarged diameter part of the piston head to receive hydraulic medium under pressure to exert a preloading pressure between the cylinder head and piston head tending to resist advancement of the cylinder head away from the piston head, and said hydraulic short-stroke device being operative to advance the cylinder head away from the piston head for the working stroke by hydraulic medium supplied under pressure into the cylinder head bore between the closed end of the cylinder head the the facing end of the piston head.

3. Apparatus according to claim 2, wherein the split-taper lock is in the form of a split sleeve surrounding the piston rod and housed in an annular recess in the cylinder bore, there being a flexible diaphragm between the cylinder bore and the sleeve so that hydraulic medium supplied under pressure between the cylinder bore and diaphragm displaces the diaphragm towards the piston rod and thereby releasably urges the sleeve into locking contact with the piston rod periphery.

4. Apparatus according to claim 1, wherein the piston rod is fixedly secured at one end to the press ram, wherein the hydraulic pressure pad means is in the form of an annular chamber provided between the cylinder bore and the intermediate cylinder head portion to receive hydraulic medium under pressure to exert a preloading pressure between the cylinder and intermediate cylinder head portion tending to resist advancement of the intermediate cylinder head portion out of the cylinder, wherein the piston rod is slidably mounted in a bore through the annular intermediate cylinder, wherein the releasable lock means is a two section sleeve lock housed in the intermediate cylinder bore for releasably locking the piston rod to the intermediate cylinder, and wherein the hydraulic short stroke device is operative to advance the enlarged head portion of the intermediate cylinder, and the piston rod when locked thereto, out of the cylinder bore by hydraulic medium supplied under pressure into the cylinder bore to act on the enlarged head portion on a shoulder face thereof located upstream of the pressure pad means.

5. Apparatus according to claim 4, wherein the two section sleeve lock is in the form of two sleeves each surrounding the piston rod at axially spaced locations therealong and each housed in an annular recess in the intermediate cylinder bore, there being a flexible diaphragm between each sleeve and the intermediate cylinder bore so that hydraulic medium supplied under pressure between the intermediate cylinder bore and diaphragm displaces the diaphragm towards the piston rod and thereby releasably urges the sleeve into locking contact with the piston rod periphery.

6. Apparatus according to claim 4 or claim 5, wherein the hydraulic pressure pad means is constructed such that a pre-loading pressure greater than the total weight of the piston rod and intermediate cylinder can be exerted on the intermediate cylinder enlarged head portion.

7. Apparatus according to any one of claims 2 and 3 and claims 4 to 6, including at least two said piston rod and cylinder assemblies and at least two said hydraulic short-stroke devices.

8, Apparatus according to any one of claims 2 and 3, 4 to 6 and 7, wherein the or each hydraulic pressure pad means, the or each releasable lock means and the or each hydraulic short-stroke device form a single structural unit with the or each piston rod.

9. Apparatus according to any one of claims 2 and 3, 4 to 6, 7 and 8, including guide rails extending between the press cross head and press bed, infinitely variable mechanical contact in or on the guide rails, and highly sensitive measuring systems for controlling a common hydraulic switching device for the serial triggering of the central build up of initial hydraulic pressure in the hydraulic pressure pad means, in the hydraulic lock means, and the hydraulic pressure build-up in the short-stroke device, accompanied by simultaneous parallel-running control of the press ram, by controlling the volumetric synchronism of the hydraulic medium content of the short-stroke device.

10. Apparatus according to any one of claims 1 to 9, including a numerically controlled computerised system working to an exactly predetermined velocity and braking graph for operating the high-speed hydraulic piston and cylinder assembly for the return stroke until just shortly before contact with a leading edge of the first mould part.

11. Apparatus according to Claim 9, including for parallel-running control, a proportionally reacting servo-switching valve associated directly with the or each short-stroke device to act as a positioning member.

12. Apparatus for press forming items from synthetic plastics, composite plastics or fibre reinforced synthetic platics materials, substantially as hereinbefore described and as illustrated in Figures 1 and 2 or Figures 3 and 4, as modified by Figure 5 of the accompanying drawings.