CA2066937C

CA2066937C - Apparatus for high-pressure forming of plastics sheets

Info

Publication number: CA2066937C
Application number: CA 2066937
Authority: CA
Inventors: Curt Niebling
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-04-25
Filing date: 1992-04-23
Publication date: 1999-02-16
Anticipated expiration: 2012-04-23
Also published as: DE4113568C1; EP0510702A1; GB2255524A; GB2255524B; CA2066937A1; GB9208845D0

Abstract

Plastics sheets having film thicknesses between 0.05 and 2.5 mm have a fluid pressure medium applied to them at a temperature below plastics softening temperature and are isostatically formed under a medium pressure which is higher than 20 bar. An automatically working apparatus developed for this purpose comprises at least:
- a continuous string (6) of shiftable, frame-like pallets (5) which are advanced by a conveyor (11') step by step;
- a loading station (20) in which one sheet to be formed (3) each is placed on one of the pallets (5) in defined arrangement;
- a heating station (40) in which each sheet (3) is heated to a defined temperature;
- a forming station (50) with a forming tool (51) disposed in a press (70) the drive (100) of which is capable of producing a considerable mould closing force; and - an unloading station (160) in which the formed sheet (5) is removed from its pallet (5) and directed into a collecting device (163).

Description

,_ The present invention is directed to an apparatus for high-pressure forming of plastics sheets in that the sheet stock is subjected to a fluid pressure medium at a temperature which is below the softening point of that plastics material, and isostatically formed under a medium pressure higher than 20 bar.

A method of this type has already been described in EP 0 371 425 A2 which in detail describes the type of plastics material and the sheet thicknesses suitable for the process, especially the use of imprinted or coated sheets, selection of process temperature, forming pressure and type of pressure medium as well as other process steps. To avoid reiterations, reference is here expressly being made to Canadian Patent Application No. 2,004,376 in regard to these and other particulars.

The apparatus mentioned in said document for effecting isostatic forming of plastics sheets comprise a forming tool which must be loaded with sheet stock and in each single process step be controlled by an operator. Automatic production is not practicable with any of the apparatus prior known in the art.

Document US-A 4,842,668 moreover discloses a method for production of laminated plastics products. This prior known method provides for a stack of layers comprising thermosetting materials such as synthetic resin impregnated paper sheets to be arranged on a rigid, frame-like transport means. These 20 transport units each loaded with one stack are successively carried through a preheating furnace, a thermoforming press and a separator station in which the f ~

laminated product as formed, for instance a tray for serving food or the like in canteens etc., is removed from said transport means. The plastics product is placed into a collecting bin and the transport units are returned to home position for taking further stacks of formed pieces.

It is the object of the present invention to provide an automated apparatus for high-pressure forming of plastics sheets. Preferably the apparatus ensures high precision to within the 1/10 mm range and cycle times of more than 20 sheet forming operations per minute in such cases where sheets having sheet or film thicknesses between 0.05 and 2.00 mm have a fluid pressure medium applied to 10 them at a temperature below plastics softening temperature and are isostatically formed under a pressure of the pressure medium which is higher than 20 bar.

One preferred embodiment of the novel automated apparatus provides for provision of at least one additional punching press.

The present invention provides an apparatus for high-pressure forming of plastics sheets which comprises a continuous string of shiftable, frame-like pallets which are advanced by a conveyor step by step and in which each of said pallets is successively passed through:
- a loading station in which one sheet each is placed on one of the pallets in defined arrangement, said pallet keeping the sheet in said defined position and transporting it through successive stations step by step;

~ 69207-17 ~ 3 1 ~ a heating station in which the sheet stock is heated to a defined temperature;
- a forming station having a top mould table in substant-ially stationary arrangement and a shiftable bottom mould table adapted to take a closing position adjacent said top mould table and a release position distal fr-om said latter, each of said mould tables carrying one half of a forming tool against the contours of which the sheet is to be formed, wherein - a pallet with sheet on top is insertable between the spaced-apart tool halves in an initial release position, - the sheet to be formed is clamped between the two tool halves in the closing position, the tool halves are closed in a pr-essure tight manner-, and a fluid medium pressure can be introduced into a mould cavi~y in one of the tool halves which forms a sheet having a temperature below plastics softening temperature against a tool and/or mould cavity in the opposite tool half under a medium pressure higher than 20 bar; and - in a repeat release position the formed plastics sheet is separ-ated from the for-ming tool and advanced while still on the pallet;
- an unloading station in which the for-med sheet is removed from its pallet and directed into a collecting device; and - optionally at least one punch station arranged between forming station and unloading station.

The apparatus accor-ding to the present invention permits precise and automatic high-pressure forming of plastics sheets for production of deep-drawn pieces exhibiting the featur-e of permanent deformation. The starting sheets used are perfectly plane as a rule and have film thicknesses between 0.05 and 2.0 mm. Said initial sheets are preferably provided with motives, symbols or other marks which have been imprinted or applied as coatings. The specific feature of ~!_ 4 1 the high-pressure forming process under consideration is that forming can be done in the imprint or coating area without distortion of the image or motive concerned. The apparatus according to the present invention ensures auto-matic forming to a defined contour exactly in any desiredposition without distorting any existing lmage or motive and at long cycle times comprising at least 20 forming steps per minute. One exemplified embodiment of such an apparatus according to the present invention is capable of achieving cycle times of 30 forming steps per minute.
Deep-drawn pieces produced by means of the appar-atus of this invention are particularly used in motor- vehicles, for instance to provide enclosure elements, luminous display or- instrument panels, luminous pushbuttons or- switch keys, heating system screens, dashboard sections or tail light lenses and/or- the top layers of such plastic components and typically exhibit differently coloured and/or- transparent wall sections. Deep-drawn pieces produced by means of the apparatus according to the present invention can be additionally reinforced with further plastics where required.

Advantageous embodiments and improvements of the apparatus according to the present invention ar-e as disclosed in the subclaims.

Each pallet for instance may preferably and substantially consist of a flat, frame-like rectangular plate having at least one recess which by its opposite narrow sides is supported against one pallet holder each and secured thereto with a detachable fixing means. Such fixing means part-icularly comprise quickly and easily detachable fixing elements such as quarter-turn fasteners because a mould change normally requires all pallets of the apparatus to be exchanged and adapted also. The two opposite and relatively spaced pallet holders are each secured to an endless chain, said chains being disposed in parallel and ~,~ 5 1 and spaced apart. They are preferably driven by means of step gear and threephase AC motor.

Each pallet is provided with at least one recess which is covered up by the sheet to be formed. The pallet as such is not clamped into the forming tool, but by bringing segments on the outer circumference of the forming tool into engagement with corresponding segments on the inner circumference of the pallet recess is centered relatively to the forming tool and precision arranged to within just a few 1/10 millimeters in relation thereto. A pallet may have one recess or several recesses for concurrent forming of one or several sheet section(s). Typically, the pallets may consist of steel plate which is beaded in the area of the two longitudinal margins extending cross to the convey-ing direction to pr-ovide higher stability.

Preferably, two centering pins at least protrude from the top of the metal frame of each pallet which (pins) engage into suitable apertures or recesses in the sheet to be formed to ensur-e a defined ar-rangement of the ~heet relative to the pallet. Two centering pins will do to arrange the sheet on the pallet in a manner preventing displacement.

Precise arrangement of a sheet on each of the p?llets is;
effected in the loading station for which purpose the pallet r-ow or string advanced step by step is momentarily stopped and a sheet is placed on the pallet in the loading station. This loading can be done manually.

An automatic loading station is preferably provided, however, which comprises a magazine containins a plurality of sheets and a rotatable and swingable device with suction elements.
In each work cycle, this device seizes the exposed sheet in the magazine, takes said sheet from the magazine and places it on the pallet positioned in the loading station. Precise arrangement in defined position is ensured by the centering pins on the pallet and corresponding apertures/recesses in the sheet.

. ~ ..~. ~ .

1 It is desirable to feed the sheet to be formed to the isosta-tic high-pressure forming unit at a defined temperature. F~r this purpose, the apparatus of the present invention is provided with a heating station disposed along the pallet string route between Ioading and forming station. Typically, the sheets are introduced into the forming station at a temperature of about 30 to 40~C, though sheet temperatures of 60~C and over, for example, can also be provided in specific cases.

Preferably, a heating station is provided which is capable of taking several pallets each with one sheet to be formed per working cycle. A heating station comprising three pallets, for instance, has been found advantageous. In spite of the relatively high cycle speed and cor-respondingly shor-t time of retention in the heating station it is practicable to set any desired sheet temperature to within about 1~C to 2~C.

Also, the heating station pr-eferably comprises several heating zones, for instance three, which in turn are each fitted with a defined number of infrar-ed large-area r-adiation heaters. Each heating zone has at least a few separately contr-ollable infrared radiators. The marginal heater- units, for- instance, can be of separ-ate contr-ol type. In addition, the heating station comprises at least one pilot radiator whose surface temper-ature can be kept within narrow limits with the aid of a thermocouple. This pilot radiator gives out control pulses for activation of the separately controllable infrared radiation heaters.
These heating zones are preferably arranged on a heating box which is disposed above the pallet string track. The arrangement of that heating box relative to the pallet route can be varied in several ways: it is for instance possible to change the vertical spacing of the box relative to the pallet flow which facilitates the setting of a defined sheet temperature. Also, the heating box can be shifted from a position above the pallet string to a later-al position relatively offset therefrom in which the heating =~ .. .

~ 7 1 zones are adjustable to a defined temperature. In addition, a reflector spaced from the heating zones can be fitted in that heating box rest position to thereby reduce energy consumption.
The sheet heated to defined temperature inside the heating station then gets into the forming station where high-pressure forming of the initially flat sheet takes place while the sheet is still being held by the pallet carrying it. As stated previously, the forming station comprises at least:
- a top mould table in substantially stationary arrangement;
- a shiftabl-e bottom mould table adapted to take a closing position adjacent said upper- mould table and a release position distal therefrom; and - a forming tool having one half attached to the top and the other half to the bottom mould table wherein:
- a pallet with sheet on top is insertable between the two spaced-apart tool halves in an initial release position - the sheet to be formed is clamped between the two tool halves in the closing position, the tool halves are hermetically closed and a fluid pressur-e medium can be introduced into a forming or mould cavity in one of the tool halves which gets imparted to the sheet and contour-s said sheet to a mould and/or forming cavity in the other tool half, and - in another release position the formed plastics sheet is separated from the forming tool and advanced while still on the pallet.
Preferably, this forming station comprises a pillar type frame with a plurality of upright pillars. The top mould table is secured to said pillars in substantially stationary arrangement, though for adjustments it may be slightly shiftable in vertical direction. The bottom mould table is guided shiftably along said pillars. Adjustments of .. ~_ . .

1 the bottom mould table are effected by means of a drive com-prising geared brake motor, crank mechanism, connecting rod with vertically readjuable bearing assembly and double toggle lever assembly. Each s ngle toggle lever arrangement of said double toggle lever assembly has three arms disposed on one common toggle lever shaft. The geared brake motor is stoppable exactly in closing position, i.e. in the top deadcenter position of the bottom mould table adjusting system, and in release position, i.e. the bottom deadcenter position of that system. Advantageously, each mould table is of substantially square shape as seen in plan view and pro-vided with extended corner areas. Four pillars are provided and run through holes which are disposed in the four- corner-areas of each mould table. Adjustment of the bottom mould table via toggle lever- assembly and cr-ank mechanism provides a sinusoidal drive ensuring that the bottom mould table will just gradually take the top deadcenter position (closing position) as well as the bottom deadcenter- position (release position) in its adjusting motion. Ver-y substantial mould closing pressures are achieved at low noise development.

Ver-tical adjustment of the top mould table is preferably accomplished via synchronizing chains along a thr-eaed joint for which purpose the upper end portions of each pillar are provided with a male thr-ead section. The top mould table as seen in plan view is of substantially square configuration and has a hole recessed in each corner area to receive a rotatable bush with corr-esponding female thread. Each bush is moreover provided with a toothed rim. A driven chain permits each bush to be turned in an equal amount to thereby raise or lower the top mould table.

The bottom mould table preferably has a lower tool half attached to it which comprises:
- a bottom plate with heating and constant-temperature control , . _ . .

.,, 9 1 - a tool against the contours of which the sheet is to be formed, and - a spring-mounted mould closely encompassing said tool.

The bottom plate is secured to the forming or mould table with a thermal insulation interposed between table and bottom plate. The tool is secured to the bottom plate such as by means of screws. When the springs are compressed, the top of said mould is substantially flush with the contour and/or the bottom of a mould cavity on the tool. On reopen-ing the complete forming tool after the high-pressure forming operation, the springs react to raise the mould which thereby separates the formed sheet from the tool. The spring-mounted mould facilitates the removal of the formed deep-drawn piece.

An outward opening allround step is preferably provided on the top of the spring-mounted mould whose dimensions are adapted to those of the recess provided in each pallet. The pallet conveyor carries the pallet together with the sheet to be formed into a position above the mould. Vertical upward adjustment of the bottom mollld table concurrently entails a vertical upward adjustment of the mould to thereb~y make the allround projecting edge portion slide into the pallet recess. This way, the pallet gets centered and the sheet to be formed exactly takes the very position relative to the forming tool that is needed for the high-pressure forming operation involved. The sheet to be formed gets positioned to within just a few 1/]0 millimeters.

The other, corresponding tool half is secured to the top mould table in which a mould cavity is provided for intro-duction of a fluid pressure medium thereinto. This other tool half has an allround lower marginal or edge portion fitted with a sealing element such as an O-ring.

As the vertically upward directed adjusting movement of the bottom forming or mould table continues, the mould surrounded by the pallet gets into contact with the allround marginal or edge portion of the top tool half. The springs carrying the mould are gradually compressed and the entire forming tool is closed with the sealing means ensuring a pressure-tight joint. Following this, the fluid pressure medium is intro-duced into the mould cavity, gets imparted to the sheet and orms said latter against the contours of the tool.
In this high-pressure forming process, the sheet stock is directlv exposed to the fluid pressure medium. The fluid pressure medium preferably to be used is compressed air. It is within fractions of a second after opening a pressure medium inlet valve that the sheet is shaped against the contours of the tool and the forming operation is ended. Petarded pressure buildu via throttled pressure medium feed may be advisable for certain sheet materials withstanding lesser mechanical loads. In the case of larger-size repeat-use tools, too, complete removal of the entire sheet may take a little longer. But in these cases as well is the forming process termlnated within a time that is less than 2 seconds.

Pressure medium feed is stopped on termination of the forming operation, the mould cavity relieved and the bottom mould table lowered again. The springs supporting the mould frame react to raise said latter so that the formed sheet gets separated from the tool. Further lowering of the mould table makes the pallet clear the mould. The pallet conveyor drive is restarted and the pallet with formed sheet is carried on, clearing the forming station.

On reaching the unloading station, the formed sheet piece is separated from its pallet and directed into a collectinq device. The simplest design version provides for the pallet string to be carried over deflector rolls in which case the sheet separates from the pallet under the action of 11 .

1 gravity and drops into a collecting bin. Alternatively, it is possible to remove the sheet from the pallet and place it into a collecting bin manually. A final approach provides for the sheet to get separated from the pallet and introduced into the collecting bin by means of compressed air and/or suction elements.

It is preferred to provide an unloading station which com-prises a reciprocable stem and a stacking trough arranged in a spaced relation therefrom. The pallet string is carried over a deflector roll and then run through a gap between stem and stacking trough in substantially vertical direction.
Each forward movement of said stem forces a sheet out of one of the pallets and into the stacking trough. Preferably, the stacking trough should have a slight upward slope relative to the horizontal to keep the sheets from toppLing over.

After separation of a sheet from its pallet, said pallet is recycled into the loading station along a pallet transport route so that another sheet to be formed can be placed thereon.
The high-pressure forming operation calls for the sheet to have a fluid pressure medium imparted to it which has a pressure of at least 20 bar. Compressed air is preferably used as pressure medium and dependent on the type of sheet stock, sheet thickness and/or tool configuration and area to be formed this air has pressures between about 60 and 300 bar. Allocated to the apparatus of the present invention is a compressed air generator comprising a multi-stage compressor to produce compressed air having a pressure of about 330 bar. The compressed air is passed through a condensation drier for separation of water from the air. Dried compressed air is collected in a storage bottle from which it is directed into the forming tool. One pressure reducer or several such reducers are fitted in that pressure line. The compressor units are restarted automatically whenever the pressure in the storage or accumulator bottle has dropped to a defined level.

2~66937 1 The drive motor and the various return pulleys for the pallet string as well as the components of the stations hereinbefore described and explained are mounted on a frame structure which is arranged on a foundation with rubber-metal vibr-a-tion dampers interposed. These feet with vibration damp-ing rubber elements are fitted with adjusting spindles for parallel setting of the processing units. They absorb a major part of the shock vibrations that are produced dur-ing operation of the forming station. The frame is lined as customary in this art and access is afforded through doors secured with limit switches.

The apparatus of the present invention can additionally be equipped with a punch station arranged between forming and unloading station. If a punch station is provided, the pallet string is appropriately extended by an additional number of pallets. The punch station may have separ-ate punch units in the form of a hole punch on one hand and as drop-through type cutting punch. Preferably, a combined punch unit is provided which is fitted with both a hole and a dropoff cutting punch tool.

Such a combination punch can prefer-ably take two pallets each with a formed sheet and comprises a bottom table which is electric motor driven via a double toggle lever assembly.
Associated therewith is a top punch table which is vertically adjustable to a minor- extent by means of synchr-o-nizing chains the way as described for the top mould table of the forming station. The cutting tools are preferably of slide-in design to permit quick tool changes. The cutting tools ar-e secured to the top table. Clamp ledges are preferably used for attachment of these tool components which are prestressed under the action of cup springs when in arrested condition. In addition, a number of pneumatic operated piston/cylinder assemblies are provided which through one stem each raise the clamp ledge and move it into a tool changing position. Accidental detachment of the ~r 1 clamp ledges with tool position changes for consequence is prevented even in case of pressure supply failure. Center-ing of the pallet holding the sheet already formed and to be punched with a punch tool bottom plate is provided the way as previously described for pallet centering with the mould of the forming tool.

If a dropoff type cutting punch is used, then the bottom table is additionally fitted with a pneumatic ejector- which in each punch cycle moves the punched deep-drawn piece through the die and into a stacking cage fitted in the top table.
Final takeoff of the punched pieces is by hand. The punch screen remains with the pallet and is finally removed in the unloading station. This combination punch is preferably provided with a drive comprising geared motor, crank mecha-nism and double toggle lever assembly which is capable of producing a punch force of 0.3 Mega-Newton and over-, for instance 0.4 Mega-Newton.

Preferred embodiments of the appar-atus according to the present invention shall now be explained in detail with reference to the drawings in which:
Figure 1 is a schematic side elevation of a first embodiment of the apparatus according to the present invention;
Figure 2 is a schematic side elevation of a second embodiment of the apparatus according to the present invention which comprises an automatic loading and an automatic unloading station;

Figure 3 is a schematic side elevation of a third embodiment of the apparatus according to the present invention which additionally comprises a combination punch unt;
Figure 4a is a schematic longitudinal section and Figure 4b is a perspective view of the loading station in the apparatus according to the present invention;

, .. ,.~-- . . .

~66937 Figure 5 is a schematic side elevation of the heating station in an apparatus of the present invention;
Figure 6a is a schematic longitudinal section, Figure 6b is a schematic cross-section and Figure 6c is a cutaway perspective view showing the double toggle lever assembly of a forming station in an apparatus of the present invention;

Figure 7a shows a forming tool of the forming station acc.
to Fig. 6a in open condition and Figure 7b shows a forming tool of the forming station acc.
to Fig. 6a in closed condition;
Figure 8a is a schematic side elevation of a punch station in an apparatus of the present invention and Figure 8b is a detail from Fig. 8a representing the attach-ment of the clamp ledges in arrested or in tool changing position;
Figure 9 is a schematic side elevation of the attachment of a pallet to a transport chain; and Figure 10 is a perspective rear view of an appar-atus accord-ing to the pr-esent invention which particularly shows the pallet conveyor- and the compressed air generating system.

As schematically represented in Figs. 1, 2 and 3, the apparatus according to the present invention comprises a machine frame 1 disposed on feet 2 with vibration dampers on a ~oundation.
Mounted on said frame 1 are a loading station 20, a heat-ing station 40, a forming station 50 and an unloading station 160. In addition, an optional punch station 120 also can be fitted to it the way as represented in Fig. 3. In the embodiment according to Fig. 1, the sheets to be formed 3 are loaded manually and the formed sheets 4 are unloaded auto-matically undeI the action of gravity.

2~66~37 ,, 1 A plurality of pallets 5 are arranged ln a closed and virtually endless pallet string 6, each of sald pallets 5 serving to transport one sheet 3 to be formed or one sheet 4 already formed through selected work stations of the apparatus. Each pallet 5 consists of a rectangular frame-like plate having at least one recess 7 which is covered up by the sheet to be formed. Two centering pins 8 protrude from the pallet 5 which engage into corresponding recesses in the she2t to be formed to ensure a defined arrangement of the sheet 3 relative to said pallet 5. Each pallet 5 is kept by a pallet holder 9 in the area of the two narrow-side marginal or edge portions and that holder in turn is hinged to the links of an endless chain 10. Two such chains 10 ar-e provided parallel to and spacea apart from each other and carried over r-eturn pulleys 11, 11', 11" and 11"'. Typically, r-eturn pulleys 11' are driven, for which purpose an electric motor- 15 and a spur gear are provided (see Fig. 10). The pallets 5 are advanced step by step in the direction of arrow "A" and this advance movement is specifically adapted to the working cycle of forming station 50.

One sheet 3 to be formed is precision arranged on each pallet 5 in the loading station 20. Typically, said sheet 3 to be formed is provided with a multi-colour-ed imprint or- any other type of coating consistent with the intended use of the deep-drawn piece to be produced. In the simplest of all cases, the sheets 3 are applied or placed manually the way as outlined in Fig. 1, though it is preferred to provide an automatic loading station 20 as schematically represented in Figs. 4a and 4b.
The essential components of said loading station 20 comprise an adjustable magazine 21 containing a plurality of parallelly disposed sheets 3, two parallel and spaced-apart, synchronized loading arms 30 rotatably holding a suction manifold 31 to which a number of adjustable suction units 32 are fitted, and a drive 36 for at least one of said loading ar~s 30.

,.~

1 Suction manifold 31 is reciprocally turned section-wise so that the suction units 32 perform a swivel movement as per arrow "B" (see Fig. 4a).

Magazine 21 is provided with a vertically adjustable bottom 22 and laterally adjustable magazine si~e walls 23. The magazine bottom 22 has an upward slope, preferably of 30~
relative to the horizontal. A vertically adjustable retainer rod 24 at the magazine top and the laterally adjustable magazine side walls 23 enable said magazine 21 to be set for any sheet size. Suction manifold 31 is in communication with a vacuum source (not shown) via a controllable valve assembly 33. The positions of the suction units 32 can be easily adapted to any actual sheet size or- format. Valve assembly 33 imparts vacuum to the suction units 32 or feeds air thereto as a function of the particular working step involved of each loading cycle. Suction units 32 seize the sheet 3 in each case exposed in magazine 21, transport said sheet to the pallet 5 disposed inside loading station 20 and place said sheet on said pallet. As will be particularly seen from the sectional representation in Fig. 4a, one end of loading arm 30 is guided in a gap 34 while the opposite end is held by a rocking lever 35. The rocker dr-ive 36 compr-ises a cr-ank mechanism 37 and a connecting rod 38. Crank mechanism 37 is driven by a motor (not shown) and in each work cycle performs one revolution. Limit switches, setscrews and sensor-s for oper-ational monitoring ar-e provided in addition.

It is desirable to carry out high-pressure forming on a sheet 3 which has a defined temperature. To this end, the sheet 3 is heated to a predetermined temperature which is typically in the range between 30 and 40~C, but in exceptional cases may also be 60~C and over. Heating of each sheet 3 disposed on a pallet 5 takes place in heating station 40.

Fig. 5 schematically shows the design and arrangement of a heating station 40. Typically, said heating station 40 has three heating zones 41, 41' and 41" which are arranged above the track of pallet string 6 in a spaced-apart relation.

_ 17 1 Each of said heating zones 41, 41' and 41" has a ~lurality of infrared large-area radiation heaters 42 of which some are separately controllable. Preferably, the marginal heater units 42' are of separate control type. A pilot radiator 43 is provided with sensors to detect ambient and surface temperature. The surface temperature of said pilot radiator 43~can be kept constant witkin close limits. Said pilot radiator ~3 gives out control pulses for control of the separately activating IR radiation heaters 42'. Heating zones 41, 41' and 41" are preferably arranged on a heating box 44 which is vertically adjustable relative to the path of movement of the pallet string 6 and which is shiftable to aside said track. An additional reflector (not shown) is provided in this lateral rest position in a spaced relation from the IR radiation heaters 42, 42'.

The sheet 3 heated to defined temperature gets into the form-ing station 50 and has a fluid pressure medium applied to it therein to perform the high-pressure forming operation. One preferred forming station 50 is shown in Figs. 6a, 6b and 6c.
The essential components of said forming station 50 comprise a press 70, a drive 100 for said press 70 and a forming tool 51 against which the forming process is effected. The press 70 includes a top mould table 80, a bottom mould table 90 and a pillar type frame structure with four upright pillars 71 to afford guiding action to mould tables 80, 90. Each upper end portion of each pillar 71 is provided with a male thread portion 72. Each of the mould tables 80, 90 is of substant-ially square configuration in plan view (Fig. 10) and provided with extended corner areas each having a throughhole 84, 94 provided therein to receive one pillar 71 each.
Each mould table 80, 90 has one table plate 81 and/or 91 which is seated against a supporting structure 82, 92 each which (supporting structure) in turn comprises several 3~ carrier beam members 83, 93. As will be generally seen from Figs. 6a and 6b, the press 70 is of heavy and rugged design 2~66937 .

_ 18 1 which is capable of taking or exerting considerable forces.
One exemplified press having a mould area for approx. 240 cm2 is rated for a maximum forming pressure of approx. 300 bar and with the type of drive still to be described of producing a mould closing force of 300 Mega-Newton minimum.

The top mould table ~0 is substantially stationary, though for adjustments it is slightly shiftable in vertical direction. A synchronizing chain assembly is provided for this purpose. A rotatable bush 85 is fitted in each of the throughholes 84 in the top mould table 80 and on its inner circumference has a female thread portion 86. In addition, each bush 85 is provided with a toothed rim 87.
A motor driven chain 18 successively engages eac~h of said rims 87 to rotate each of said bushes 85 by an equal amount which results in a vertical adjustment of the top mould table 80 along thread portions 72/86.

The bottom mould table 90 is vertically adjustable along pillars 71. The design of drive 100 for adjustment of the bottom mould table 90 is particularly evident from Figs. 6b and 6c where the left-hand part representation in Fig. 6b shows the top deadcenter position of the mould table adjusting system (closing position) while the right-hand portion of Fig. 6b represents the bottom deadcenter position thereof (release position).

This drive 100 comprises an electric spur gear type brake motor 101 driving a crank mechanism 102. Crank 103 through a connecting rod 104 acts on a shiftable connecting rod bearing 105 which is vertically shiftable on guide rods 106. A double toggle lever assembly 110 has three pivotably coupled arms 111, 112 and 113 which are all mounted on said common toggle lever shaft 114. The first arm 111 1 extends between toggle lever shaft 114 and a shaft 107 on con-necting rod bearing 105; the second arm 112 between toggle lever shaft 114 and a backing shaft 108 supported against the press frame; and the third arm 113 between toggle lever shaft 114 and a shaft 115 supporting against the support beam members 93 of lifting frame 92 of the bottom mould table 90.

As can be seen from the partial representation on the left of Fig. 6b, the first arm 111 extends substantially horizontal while the second and the third arms 112 and 113 are extending in vertical direction parallel to the pillars 71 of the pillar type frame - all referred to the top deadcenter position of the crank. The spur gear type brake motor can be stopped exactly in that position conforming to the closing position of the bottom mould table 90. This is the position in which the drive 100 can exert and/or take a particularly high forming pressure. Said drive 100 operates very quietly due to the sinusoidal adjustment via crank drive 102 and double toggle lever assembly 110 and the bottom mould table 90 takes its top or bottom end and/or deadcenter position gradually. The heaviest forces are always acting in vertical direction, parallel to pillars 71, and any damages to the pillars 71 and the guides 94 on the bottom mould table are definitely prevented. The high mould closing force desired of 300 ~ega-Newton and over can be obtained with such a drive 100 which is of relatively small size.

The motor 101 can be controlled and operated to raise the bottom mould table 90 until it reaches its top deadcenter and hence closing position, and/or to lower said table until the bottom mould table 90 has reached its bottom deadcenter and hence taken a release position. It is exactly in these end positions that the gear type brake motor 101 can be stopped.

1 A chain guard structure 12 shielding each of the chains 10 holding and transporting the plurality of pallets 5 is run through the work space confined on the one hand by the forward and rearward pillars 71 and on the other hand by the bottom and top mould table 80, 90.

Angles 99, 89 are in pairs disposed on plate 91 of the bottom mould table 90 and plate 81 of the top mould plate 80; each of said angles confine a guide groove into which a carrier element 53, 61 each of the top and the bottom tool half 52, 60 is insertable. An arresting means (not shown) keeps said inserted tool half 52, 60 in its defined position.
The resultlng push-in provision enables said tool halves 52, to be quickly changed.
Fig. 7a shows a formling tool 51 in the open condition while Fig. 7b reflects said forming tool 51 in closed state on com-pletion of an isostatic high-pressure forming operation. As may be more closely seen from Figs. 7a and 7b, the forming tool 51 substantially consists of a-top portion 52 and a bottom tool half 60. The top portion 52 comprises a projecting reta-iner flange 53 and an allround web 54 having a sealing element such as an O-ring 56 in it~;unde~side 55. ~aid top portion 52 confines a mould cavity 57 into which a port 58 is opening for a fluid pressure medium to be fed and a5 discharged. Control elements 59 which are just schematically outlined are taking care of pressure medium suppl~.

The bottom tool half 60 substantially comprises a carrier plate 61, a bottom plate 63, a tool 64 as such having contours 65, 65' 65" just schematically represented for example, and a spring-supported mould 66 surrounding said tool 64. The bottom plate is preferably fitted with a heating device such as heating wires and a regulating system for keeping temper-ature constant. This arrangement permits the temperature of the bottom tool half 60 to be adapted to the temperature of the sheet. A layer consisting of heat insulating material 62 is interposed between carrier plate 61 and bottom plate 63.

~.. . ~ . .

~_ 21 1 Carrier plate 61 is held in position by means of the angles 99 on bottom mould table 90.

Mould 66 comprises a frame 67 which is resiliently supported by springs 68. An allround, outwardly opening ste 69 is recessed in the upper end face of said frame 67. This step 59 is adapted to engage into a recess 7 of a pallet 5 which (recess) is provided between top portion 52 and bottom tool half 60 to thereby center the pallet 5 relative to the form-ing tool 51. The sheet 3 to be formed gets perfectlyarranged in a defined position relative to tool 64.

The bottom mould table 90 takes a closing position on reaching its top deadcenter position during adjustment. To definitely reach said closing posi~tion~, the pallet 5 disposed inside press 70 can be slightly raised, for example by about 3 to 4 mm, so that positive forming of the sheet also can be accomplished when required. Forming tool 51 is sealed in that closing position the way as reflected by Fig. 7b. The springs 68 holding the mould 66 are compressed and the lower e~d face of frame 67 of said mould 66 is in contact with the bottom plate 63. The sheet 3 carried by pallet 5 is inititally just a slight distance above tool 64. The bottom end face 55 of top portion 52 is in contact with the top end face of mould 66 and sealing means 56 provides a pressure-tight seal. A fluid pressure medium is introduced into mould cavity 57 through the port 58 and instantaneously forms said sheet 3 against the contours 65! 65', 65" of said tool 64. Control elements 59 then react to relieve mould cavity 57 and make the bottom mould table 90 go down again. Springs 68 respond to raise mould 66 whereupon the formed sheet 4 will be released and/or separated from the tool 64.

The formed sheet 4 is advanced on its pallet 5 to finally get into unloading station 160. As will be seen from Fig. 1, the formed sheet 4 can get loose from pallet 5 under the action of gravity and drop into a collecting bin 163 through a shaft means in the simplest of all cases. Separation of 1 of said formed sheet 4 can be assisted by application of com-pressed air and/or vacuum. Manual removal is another alter-native.

Preferably, the unloading station 160 provided is of auto-matic type the way as schematically outlined in Fig. 2.
This unloading station 160 as shown comprises a pneumatically or mechanically driven stem 161 and a stacking trough 162 in spaced relation therefrom. Said stack;ng trough 162 has a slight ascending slope relative to the horizontal. The pallet string 6 is routed between deflector rolls 11' and 11"
through a gap between 161 and stacking trough 162 on a substantially vertical path. Each time said stem 161 advances it exerts pressure on the formed sheet 4, releases same from centering pins 8, removes it from pallet 5 and pushes same into stacking trough 162. A defined number of formed sheets 4 are finally removed from stacking trough 162.

A punch station 120 may additionally be arranged between for~-ing station 50 and unloading station 160 the way as shown in Fig. 3. In any such case the number of pallets 5 in the cycle should be increased and the chains 10 carrying and transporting said pallets 5 be increased in length. Punch station 120 may comprise a hole punch to provide holes in said formed sheet 4. An alternative solution provides for the punch station 120 to be equipped with a dropoff type cutting punch to perform contoured cuts. Preferably, said punch station 120 comprises a combination punch 121 which consists of a hole punch 135 and a dropoff type cutting punch 140. One exemplified embodiment of such a combination punch assembly 121 is shown in Fig. 8a.

As can be seen from Fig. 8a, the combination punch unit 121 comprises a pillar type frame with four upright pillars 122 in which a top table 123 and a bottom table 124 are guided.
The spacings as viewed in pallet flow direction between the first and the second pillars as well as the dimensions of tables 123, 124 have been amply selected for accommodating two pallets 5. Top table 123 is vertically shiftable for , ~ .

1 adjusting purposes to which end there are motor operated syn-chronizing chains provided of the type previously described with reference to the top mould table 80 of press 70 in the forming station 50. Bottom table 124 is vertically adjust-able along the pillar-s 122. Starting from a release position distal from the top table 123 said bottom table 124 passes throuqh a punching position adjacent said top table 123 to then take the release position again.

Adjustment of bottom table 124 is effected by means of a drive 125 with a geared motor 126 which positively acts on a crank mechanism 128 via worm gear 127 with hollow shaft and flywheel transmission. Crank 129 thereof is connected to a vertically adjustable connecting rod bearing 131 by means of a connecting rod 130. Further, a double toggle lever assembly 132 with toggle lever shaft 133 is provided to which a plurality of arms are fitted the way as earlier described in closer detail for the double toggle lever assembly 110 of drive 100 for the press 70. It is due to said double toggle lever assembly 132 that the punch unit 121 is also operable on one side with just one of the tools 135 or 140 fitted. A punch force of 0.4 Mega-Newton can be produced with a drive power of 3 kW for geared motor 126.

Secured to bottom table 124 are the cutting or punch tool 136 for the hole punch 135 and the cutting or punch tool 141 for the dropoff cutting punch 140. Fitting counterbearings or counterpieces 137 and/or 142 are attached to the top table 123. All tool components 136, 137 and/or 141, 142 are fixed to holding plates 138, 138' and/or 143, 143' which while of slide-in design can be clamped and/or arrested against bottom table 124 or top table 123.

Detail features of said slide-in type fixing assembly are shown in Fia. 8b. Each profiled clamp ledge 150, 150' sur-rounds a marginal portion each of a holding plate 138, 138';
143, 143', forcing same against the plate of bottom table 124 or top table 123. Clamp ledge 150 can take an arrest 1 position (as shown on the left in Fig. 8b) and/or clamp ledge 150' a tool change position (as shown on the right in Fig.
8b). Holes 151 extend vertically through clamp ledges 150, 150' at regular spacings. Each bolt 152 has a projectina head 153 on one end and a male thread portion 154 on the other. Said bolts 152 are run through said holes 151 and by their thread portions 154 screwed into mating female thread portions 156 which are provided in plate 124. ~ cup spring 155 is interposed between bolt head 153 and clamp ledge 150, 150' to force said clamp ledge 150, 150' against holding plate 138.

There are a plurality of stems 158 provided to bring clamp ledge 150' from its fixed position into the tool change position against the action of cup spring 155. These stems 158 extend through apertures 157 provided in plate 124 and act on the underside of clamp ledge 150'. Each stem 158 communicates with a piston of a hydraulically operable piston/
cylinder assembly 159. Each stem 153 will only be moved to and retained in the clamp ledge release or tool change position when pressure medium is applied to the piston/cylinder assembly 159.

Bottom table 124 comprises a recess in the area of dropoff cutting punch 140 to accommodate a pneumatically operated ejector 145 with vertically adjustable ram 146. This ram 146 can pass through aligning bores in the table plate of bottom table 124, the cutting or punch tool 141 or the adjusted die 142 of the dropoff cutting punch 140 to thereby push stampings 4' punched from the formed sheet 4 into a stacking type magazine 147 which is inserted in top table 123. The stacking magazine 147 is sugstantial~y ~-er~ical and confines a stacking cage in which the stampings 4' are collected. An operator removes them from said cage from time to time. The punch screen remains on the pallet 5 to be conveyed to the unloading station 160 therewith where it gets into a collecting bin 160 (see Fig. 3).

~- 25 1 Centering of the pallets 5 with the cutting or punch tool 136 of the hole punch and/or with the cutting or punch tool 141 of the dropoff cutting punch 140 inside punch station 120 is accomplished in the same way as described for centering the pallets 5 with the forming tool 51 inside the formina station 50.

Fig. 9 schematically represents the attachment of a pallet 5 to a transport chain 10. A pallet holder 9 made from plastics material is ~ivotablv secured to a link of chain - -10 and in a spaced relation therefrom engages another chain link so that the pallet holder 9 is adapted to also follow the path of movement over the periphery of a return pulley. A frame-like rectangular plate panel is secured to the pallet holder 9 with the aid of quick-release fixing means 14 such as quarter-turn fasteners. Two centering pins 8 project vertically from the top of the pallet 5.

Fig. 10 shows in perspective representation a forming station 50, part of the pallet string 6 passing through said forming station and an adjacent compressed air source 170. Each pallet 5 is supported against a pallet holder 9 by each of its opposite narrow sides, said pallet holder being secured to a link of one driven endless chain 10 each. The two chains are parallel and in a spaced relation carried over return pulleys ll' and 11". An electric motor 15 is provided to drive return pulley 11'. As can be seen, the pallet string 6 attached to chains 10 is fed to the forming station 50 through the work space between top mould table 80 and bottom mould table 90. A chain guard 12 is for each of the chains provided in spaced relation from the moving pallet string 6.

Disposed aside the forming station 50 is a compressed air generator 170 (shown in schematic representation) which com-prises a multistage compressor in a casing 171, a conden-.~ ,~

~ 26 1 sation drier 172, a compressed air accumulator bottle 173, pressure reducing means 174 as well as customary regulating elements 175 and indicators or displays 176. A line (not shown) leads to the control elements 59 on the forming station 50 to enter com~ressed air into the mould cavity57 provided in the forming 51 whenever needed.

... .. .. .

Claims

1. An apparatus for high-pressure forming of plastics sheets comprising a continuous string of shiftable, frame-like pallets which are advanced by a conveyor step by step and in which each of said pallets is successively passed through;
a) a loading station in which one sheet each is placed on one of the pallets in a defined arrangement, said pallet keeping the sheet in that defined position and transporting it through successive downline stations step by step;
b) a heating station in which each of the sheets is heated to a defined temperature;
c) a forming station having a top mould table in substantially stationary arrangement and a shiftable bottom mould table adapted to take a closing position adjacent said top mould table and a release position distal therefrom, each of said mould tables carrying one half of a forming tool comprising given contours, wherein at least one half of the forming tool is additionally provided with means for the introduction of a fluid pressure medium which will press and form the sheet against the contours of the other half of the forming tool, and wherein a said pallet with a sheet on top is insertable between the spaced-apart tool halves in an initial release position, the sheet to be formed is clamped between the two tool halves in the closing position, the tool halves are closed pressure tight, and a fluid pressure medium can be introduced into at least one of a mould cavity in one tool half which contours a sheet having a temperature below plastics softening temperature against a tool and a mould cavity in the other tool half, at a fluid pressure higher than 20 bar, and in a repeat release position the formed sheet is separated from the forming tool and advanced while on the pallet; and d) an unloading station wherein the formed sheet is separated from the pallet and is directed into a collecting device.

2. Apparatus as claimed in claim 1, wherein each pallet substantially consists of a flat, frame-like rectangular plate panel having two oppositely arranged long frame sides and two oppositely arranged narrow frame sides defining at least one aperture and adapted to support one sheet to be formed;
further providing two endless chains arranged parallel and distantly to each other, and adapted to be driven in the same manner, wherein each chain carries a number of pallet holders attached at regular spacing on the chain for common movement therewith; wherein each pallet is supported by its opposite narrow frame sides each on a pallet holder and secured thereto by a detachable fixing means.

3. Apparatus as claimed in claim 2, further comprising at least two centering pins which protrude from the top of each pallet and which engage into suitable apertures or recesses in the sheet to be formed to ensure a defined arrangement of said sheet relative to the pallet.

4. Apparatus as claimed in claim 1, wherein an automatic loading station is provided comprising a magazine containing a plurality of sheets, and a shiftable arm bearing a rotatably arranged suction pipe provided with a plurality of suction elements and performing a shifting movement per each work cycle, wherein each sheet arranged in a final position is taken away from the magazine and is placed on the pallet positioned in the loading station.

5. Apparatus as claimed in claim 1, wherein the heating station is adapted to take a plurality of pallets, each with one sheet to be formed, and comprises several heating zones which are each fitted with a number of infrared large-area radiation heaters; each heating zone has at least a plurality of separately controllable infrared radiators; and the heating station comprises at least one pilot radiator whose surface temperature is kept within narrow limits; and said pilot radiator gives out control pulses for activation of said separately controllable infrared radiation heaters.

6. Apparatus as claimed in claim 5, wherein the heating zones are arranged on a heating box which is vertically adjustable relative to the path of movement of the pallet string and which is shiftable into a rest position aside said flow route of the pallet string.

7. Apparatus as claimed in claim 6, wherein the heating station additionally comprises a reflector which is spaced from the heating zones when the heating box is in the rest position.

8. Apparatus as claimed in claim 1, wherein the forming station comprises a press with a pillar frame structure with a number of upright pillars; the top mould table on said pillars is substantially stationary, though for adjustments it is slightly shiftable in a vertical direction; the bottom mould table is guided shiftably along said pillars; and a drive is provided to adjust the bottom mould table which comprises a spurgear type brake motor, a crank mechanism, a connecting rod with a shiftable connecting rod bearing and a double toggle lever assembly.

9. Apparatus as claimed in claim 8, wherein the drive is rated for a mould closing force of at least 300 Mega-Newton.

10. Apparatus as claimed in claim 8, wherein a lower tool half is fixed to the bottom mould table which tool half comprises a bottom plate, a tool and a spring-mounted mould closely encompassing said tool.

11. Apparatus as claimed in claim 10, wherein an outward opening all round step is provided on the top of the spring-mounted mould whose dimensions are adapted to those of the recess provided in each pallet.

12. Apparatus as claimed in claim 11, wherein in raising the bottom mould table, at least a portion of said all round step is pushed into said recess in the pallet to thereby centre the pallet and make the sheet to be formed take the very position relative to the tool that is required for the forming operation.

13. Apparatus as claimed in claim 12, wherein, in raising the bottom mould table, the pallet holding the sheet to be formed is raised for positive forming of said sheet to take place.

14. Apparatus as claimed in claim 10, wherein the spring-mounted mould is supported against springs which untension as the forming tool opens to thereby raise the mould relatively to the tool for detaching and/or separating the formed sheet from said tool.

15. Apparatus as claimed in claim 1, wherein the unloading station comprises a reciprocating stem and a stacking trough; pallets with formed sheets on top are run through a gap between the stem and the stacking trough on a substantially vertical path of movement; and each forward movement of the stem forces one formed sheet from its pallet and into the stacking trough.

16. Apparatus as claimed in claim 15, wherein the stacking trough has a slight upward slope relative to the horizontal.

17. Apparatus as claimed in claim 1, wherein at least one punch station is interposed between the forming station and the unloading station in the path of movement of the pallet string.

18. Apparatus as claimed in claim 17, wherein the punch station comprises a pillar type frame having a plurality of upright pillars to which a top table is fixed in substantially stationary arrangement and in which a bottom table is shiftably guided which can take a release position distal from said top table and starting from that release position passes through a punching position adjacent said top table to then take the release position again; and at least one hole punch and/or one drop-off type cutting punch attachable to the bottom table which in the punch position cuts at least one desired piece from the formed sheet positioned inside the punch station.

19. Apparatus as claimed in claim 17, wherein the punch station comprises a combination punch unit equipped with a hole punch and a drop-off type cutting punch; and the combination punch unit can take two pallets each carrying one formed sheet per work cycle.

20. Apparatus as claimed in claim 18, wherein a drive is provided for adjustment of the bottom table which drive comprises a geared motor, a crank mechanism, a connecting rod with a vertically adjustable connecting rod bearing and a double toggle lever assembly; and wherein said drive is rated for a punch force of at least 0.4 Mega-Newton.

21. Apparatus as claimed in claim 19, wherein the hole punch is fitted with one cutting or punch tool and provided with one counterbearing or counterpiece; the drop-off cutting punch is fitted with one cutting or punch tool and provided with one counterbearing or counterpiece; the cutting or punch tool of the hole punch and the drop-off cutting punch, and the counterbearing or counterpiece of the hole punch and the drop-off cutting punch are fixable to the bottom table or the top table by means of clamp ledges; and said clamp ledges are retained in a tool arrest position by cup springs and movable into a tool change position by means of pneumatically operated piston/cylinder assemblies.

22. Apparatus as claimed in claim 20, wherein a pneumatically operated ejector with a vertically adjustable ram is arranged in the area of the drop-off cutting punch which is inserted in the bottom table; a stacking magazine is inserted in the top table which confines a stacking cage; and the ram acts to push a stamping punched from the sheet into the stacking cage on the occasion of each stroke.

23. Apparatus as claimed in claim 1, wherein a source of a fluid pressure medium under increased pressure is provided, and said pressure medium source comprises a compressed air generator with a multistage compressor which produces compressed air having a pressure of about 330 bar.

24. Apparatus as claimed in claim 23, wherein the source for a fluid pressure medium under increased pressure is a compressed air generator which comprises a multistage compressor, a condensation drier and a compressed air accumulator bottle, and which is rated for producing compressed air having a pressure of about 330 bar.