NO319109B1 - Apparatus and method for discontinuous reshaping of plastic materials - Google Patents

Description

The invention relates to a discontinuous reshaping process (pressing process) for plastic material according to the working principle of volume displacement in a tool's cavity by means of a differentiated pressing process, as well as a device for carrying out the method and manufactured components in accordance with the method respectively in the device. The pressing process according to the invention makes it possible to reduce the necessary high pressing forces that occur during pressing processes according to the state of the art, above all at the end of the pressing process, and thus also to reduce the material input in building the presses to a corresponding degree.

As well as when explaining the state of the art when describing the invention, certain terms will be used which will be defined in the following.

The term "cavity" used is defined as a space which changes both in terms of its surface and its volume during the forming process, and which is bounded by tool surfaces as well as by surfaces along which the tool is closed. At the end of the shaping process, the cavity formed by the tool is then identical to the geometric design of the product (component) to be manufactured. The cavity is usually bounded by the surfaces of two tool halves. Additive voids (such as flow channels) that are important to the design process but do not belong to the component geometry are not included in the term "voids".

The term "product-coated cavity" is understood to mean the part, or the partial volume of the cavity, which at any point in the shaping process is filled with material to be changed in shape.

The term "product-coated surface" refers to the surface of the cavity which, at any point in the shaping process, is in contact with the material to be reshaped.

The working principle of a reshaping process (or shaping process) by volume displacement consists in exerting pressure on a malleable mass to force it into a specific outer shape. The term "energy input into the material to be reshaped" is understood to mean the introduction of mechanical energy into the material to be caused to change shape in external aggregates or by corresponding movement of the product-applied cavity surfaces.

The discontinuous reshaping of plastic materials in a cavity starts with the cavity's reduction and ends at the time when the cavity is completely filled with the material to be reshaped (the filling phase). The repressing phase of the reshaping process to compensate for the shrinkage is not included in the term "discontinuous reshaping of plastic materials by volume displacement in a cavity".

Of prior art, FR 2529505 can be mentioned, which describes a device and a method for designing heat-setting plastic. A plastic material is introduced into a device consisting of two movable parts, where the material is formed first by means of movement of a tool half with a cavity and then by means of movement of contact pistons.

Processes according to the state of the art and to which the present invention can be applied are then: Under the term pressing processes according to the state of the art, one designates such shaping processing processes where the work pin sip for volume displacement directly takes place in the cavity. When joining inherently rigid tool halves or shaping processes, the distance between the two tool halves is reduced, so that the volume of the cavity is reduced. By reducing the tool opening, transformation energy is brought into the material to be transformed over the surfaces of the cavity that are in contact with the product.

In a pressing process according to the state of the art, the total material mass is brought into the open cavity before the beginning of the pressing process. The pressing process itself begins with movement of one or both tool halves, whereby the decisive energy input for the shaping process is brought into the material to be reshaped over the cavity surfaces that are in contact with the product. With increasing narrowing of the tool opening during the forming process, the cavity surfaces that are in contact with products are increased. The pressing process is considered finished when the movements of the tool halves have come to a standstill, and as a result, no further forming energy is introduced. During the closing movement of the tool halves, the movable tool parts of the tool halves, and which belong to the cavity surface, such as any ejectors or pushers, remain in their contour corresponding to the basic position, so that the cavity surface contour of the two tool halves during the entire pressing process can be considered unchanging.

The working principle of the volume displacement means that during the shaping process "material fitting" takes place. The order of magnitude of this material movement or also the material stress during the shaping process during the pressing process also enables a division of the pressing process into a forming pressing process and a flow pressing process.

During the compression molding process, a transformation into a compression part takes place, whereby the compression mass that is brought into the open cavity corresponds to the projected surface of the component contour as much as possible in terms of its design, so that no major flow displacements in the material to be compressed are necessary during the compression molding process. During the molding process, the press energies brought in during the closing movement of the tool halves are preferably taken up in locally limited plastic material transformations and in compression work.

In the flow press process according to the state of the art, the total press mass before the start of the press process is brought into the cavity, whereby the mass of the introduced press material corresponds to the mass of the relevant component. During the pressing process, the fluidity of the pressed material to be compressed is utilized by the selected processing parameters (pressure, temperature, time) to fill the cavity. As the press mass that is brought into the opened cavity during the flow press process for its design is significantly smaller than the projected surfaces of the component contour, the shape change of the material brought into the tool into the manufactured component takes place during the covering of large flow distances.

In a variant of the pressing process, namely injection moulding, part of the injection cylinder surface comprises a part of a tool half. In the injection molding process, the volume of material corresponding to the completely closed cavity is introduced directly by open tool halves into the cavity which is also formed by the injection pressure cylinder. In this way, the tool halves are then closed at nominal dimensions without the introduction of transformation energy. The crucial introduction of energy into the material to be transformed then takes place exclusively over the surface in the injection pressure cylinder which is in contact with the product, and which then moves as a rigid body. The shaping process ends with movement of the injection pressure cylinder until the point where the overall geometry of the cavity surface corresponds to the desired geometry of the component to be manufactured.

In the injection molding process, which is a special case of the injection molding process, pressurized material corresponding to the intended component mass is fed via flow channels from the outside into a tool that is not yet completely closed. This takes place by supplying transformation energy to the material to be transformed in external aggregates, such as for example with the help of an injection molding machine (injection process). The further transformation of the introduced material into the cavity to the intended component geometry takes place according to the state of the art by a closing movement of one or both tool halves (embossing process). The crucial energy transfer to the introduced material during the embossing process then takes place exclusively by the closing movement of the rigid tool halves. During this closing movement of the tool halves, the per se movable tool parts of the tool halves and which belong to the surface contour of the cavity, remain in their basic position which corresponds to this contour. The cavity closing during the embossing process constitutes a flow press process.

Great difficulties with practically all of the methods indicated above condition

an optimal rheological execution of the transformation process. Under such an optimal rheological execution of the transformation process, one understands the creation of optimal flow fronts, flow path lengths and pressure conditions during the filling phase. Defined orientations are also often desired above all with fibre-reinforced construction materials, which can hardly be achieved by pressing processes according to the state of the art. For handling reasons, only a few inserts, usually only one desired, can be introduced into the open tool cavity,

and then not always in the optimal places for the float press process. Due to the production of pressed goods, one is mostly bound to a predetermined insert geometry, which makes it difficult to optimize the insert conditions.

In a pressing process, the complete filling of the cavity with the material which

must be pressed with further permissible processing parameters and with fixed pressure forces as well as mechanical or hydraulic pressure performances from the available machines, often of the greatest importance. The necessary pressure forces for closing the tool halves become extremely high at the end of the flow pressure process, so that very high press energies and, above all, press performances for complete tool fillings are extremely necessary. Therefore, the pressures that are used during the flow press process must be dimensioned based on their pressure performance, which can be achieved, among other things, by the high kinetic energy of the moving tool halves being utilized to increase the maximum pressure performance, whereby, however, considerable equipment is required for control and regulation of this energy. In addition, during the flow printing process, there is a great tendency for the tool to tip over during closing of the tool halves, and this can only be ruled out with considerable technical effort.

The discontinuous pressing process according to the known technique causes an enormous waste of press energies and press performances. This is reflected in strong technical effort and high investment costs for correspondingly large, precisely working presses as well as high energy costs for a pressing process. In addition to this, the forming process in flow press processes according to the current state of the art is largely undifferentiated with respect to the pressure control.

It has then been a task for the present invention to reduce the pressing forces, pressing energies and pressing performances that have been necessary when transforming plastic materials during pressing processes, so that considerable savings in energy and equipment effort become possible. This is achieved according to the present invention by temporally and spatially dividing the pressing process into several sub-processes.

The object of the present invention is therefore a method for discontinuous transformation of plastic materials by volume displacement in a cavity, during which transformation energy is introduced into the material to be transformed by means of at least two movable parts of the cavity surface, with at least one tool half comprising one or more parts which are movable in relation to the relevant tool half, at least part of the transformation energy is introduced by relative movement of these parts and the introduction of the transformation energy seen over the entire transformation process takes place under temporally and spatially differentiated control, characterized by the fact that the moving parts are controlled individually and the transformation energy - set over the entire transformation process - is introduced by only a part of the total cavity surface which is not parallel to the direction of movement on at least one tool surface, as transformation energy is introduced at each moving part by means of a single undivided - not parallel t il direction of movement horizontal - surface with product contact.

The movement of the cavity surfaces is preferably controlled so that a standstill of the flow fronts is avoided, respectively intended rheological flows and pressure conditions during the design are realized, which has positive consequences for the component qualities that can be achieved, the possible execution of the components and the overall process stability for a flow pressure process.

The described embodiments are exclusively aimed at the work process during the volume displacement inside the cavity, regardless of whether from the beginning of the reshaping process the total component-equivalent material to be reshaped is already located in the open tool cavity, or if the work process during the volume displacement inside the cavity takes place at the same time as an introduction from the outside of transformation material in the cavity. According to this, the total material to be reshaped can already be in the cavity at the beginning of the reshaping process. However, it is also possible that the material to be reshaped is brought into the cavity from outside during the reshaping process.

The mentioned embodiments thus apply both to reshaping processes whereby the reshaping material that is brought into the cavity must cover large material movements in the form of flow paths, as well as processes in which already small material movements in the form of local plastic flow, respectively local plastic deformations, are sufficient for exact complete the internal geometry of the closed cavity to nominal dimensions, so that the desired design of the relevant finished component is guaranteed.

A further preferred embodiment of the present invention consists in that the reshaping material which is in the cavity is first partially driven by movement of a tool half into a reservoir, which is formed by returning a displaced part of this cavity surface to a negative relative position, and then positive relative movement of this displaced portion of the cavity surface out from the reservoir to another area of the cavity. Below, during the closing movement of the tool, the material to be reshaped is first driven into the reservoir which, as stated above, is formed by a part of the surface of the cavity being driven back, which means it performs a negative relative movement and thereby arrives at a negative relative position , as well as finally moving again in the direction of the cavity, which means performing a positive relative movement. With the help of this positive relative movement, the material is then driven out of the reservoir to other areas of the cavity. By correspondingly determining the position and design of one or more such reservoirs, it becomes possible to completely avoid the high pressure forces towards the end of the pressing process which are necessary in pressing processes according to the known technique.

The positive relative movement of the displaced part of the cavity excess for emptying the reservoir is preferably only started when all other tool surfaces have by this time reached their final position and do not perform any further movement.

The necessary press energies, press performances and maximum permissible closing forces for the material transformation during the pressing process can be individually adapted to the available machine sizes with the help of the present invention, so that mechanical closing and locking systems can also be used, whereby the different sizes of different components can be produced with favorable costs.

The present invention also makes it possible to reduce to a minimum the technical effort of control and regulation devices required by the kinetics of the occurring energies and which is necessary to suppress the great tendency to a threatening tool tipping during the pressing process, which as a final result will drastically reduce the costs of a press device in accordance with the present invention.

Further objects of the invention are a device for discontinuous pressing of plastic materials in a cavity consisting of two tool halves in accordance with the method for material transformation according to the invention, as well as a device for injection molding of plastic materials in a cavity formed by two tool halves in accordance with the method for material transformation according to the invention, characterized in that at least one tool half has at least one movable part relative to it, while the overall cavity surface, on the other hand, has at least two movable parts, and that these at least two movable parts are arranged so that at least part of the transformation energy can be introduced into the plastic material by their relative movement, as the moving parts can be controlled individually and as each moving part has a single undivided - not lying parallel to the direction of movement - surface with product contact. Preferred additional presses are, for example, mechanical or hydraulic presses, respectively displacers or displacers.

A tool that works according to the principle of discontinuously differentiated flow pressure progression usually consists of two tool halves. The tool half on the piston side of the tool is preferably connected either with a hydraulic piston or with a mechanical locking device and performs the closing and opening movement of the press tool system. The tool half on the die side is then firmly mounted on the press.

One or both tool halves have one or more tool contour feeders

moving parts that can perform relative movement in relation to their tool half, so that it will be a draw which part of a tool half will perform the movement. All moving parts that belong to the tool contour are referred to as additive presses when, during the transformation process, they perform relative movements in relation to their associated tool halves, and thus with their movement bring transformation energy into the pressed object, regardless of the size of the descriptive contour.

The positive relative position of an additional press vis-a-vis other additional presses on its tool half can already be present at the beginning of the pressing process, or possibly achieved by relative movement during the differentiated floating press process. The positive relative position between an additive press and its tool half is used during the cavity filling during the differentiated flow press process so that a smaller wall thickness of the cavity is first simulated within the contour area of the additive press, which will be useful for the formation of intended flow courses at the beginning of or during the differentiated flow press processes.

The negative relative position of an additional press above further additional presses on a tool half can already be present at the beginning of the pressing process, but possibly also achieved by relative movements during the differentiated floating press process. The purpose of a negative relative position between an additive press and its tool half during mold filling during the differentiated flow press process is that during the filling phase additional volumes are produced in the tool cavity for temporary material reservoirs, as a greater cavity wall thickness is simulated in the contour area of the additive press.

Additional cavities in a corresponding tool and which do not form any part of the tool's cavity, but are connected to it and over which, during the molding process, neither pressing mass nor energy is introduced into the present pressing mass in this product-affecting tool cavity, can then serve to compensate for variations in the embedded pressing compound.

The main task of an additive press is that the cavity contour is not rigidly maintained during the filling phase of the differentiated flow press process, but that intentional cavity volumes are also sought to be formed in the tool cavity with the help of possible movements of the additive presses, so that these volumes can serve as temporary material reservoirs. During the positive relative movement of an additional press, the pressed material is compressed, and the displaced pressed material then serves for a design of the corresponding tool cavity, as well as possibly for filling one or more additional material reservoirs, which are formed by the negative relative positional displacement of the present additional presses. The closing movement of an additive press ends in a position that corresponds to the desired component thickness or slightly beyond this (shrinkage). The further sub-cavity filling takes place in an analogous way by the positive relative movement of the individual additional presses, during which the individual movements of the additional presses can take place temporally simultaneously, mutually overlapping or also in sequence. The overall shaping of the component in question during the differentiated flow pressing process is finished when any arbitrary place on the component surface matches the surface contour of the tool, and any partial pressing process is finished, which will be the case with an accurate mass dosage and introduction of the flowable mass to be compressed into the open tool cavity at the beginning of the differentiated flow press sequence. At this point, the entire cavity surface is in contact with the product.

The necessary force application for the movements and for securing the static equilibrium for the individual additional presses during the differentiated flow press sequence can take place either mechanically or hydraulically. The mechanical movement of the additional presses takes place over corresponding weight bars (knee bars) or spring elements. One can naturally also imagine that the corresponding lifting functions for integrated ejectors or pushers in the tool take over the function of the additional presses. However, the necessary power input for the individual additional presses can also take place hydraulically.

The control or regulation of the individual movements of the additional presses can take place either from the piston path or also be pressure time dependent. This control or regulation of the movements of the additional presses can alternatively also take place on the basis of measured mechanical or hydraulic closing forces or also on the basis of measured internal forming pressures at suitable locations in the tool cavity.

In fig. 1 to 4 shows a preferred embodiment of the device used for carrying out the method, which means that the tool is shown in four typical positions corresponding to the course of the process in the method for discontinuously differentiated flow pressing. The introduced compact material mass in the cavity at the beginning of the differentiated pressing process corresponds to the component mass, so that during the differentiated pressing process no further pressing mass is introduced into the cavity. Since at the beginning of the pressing process the surface of the cavity that is in contact with the product is significantly smaller than the overall surface of the cavity at the end of the reshaping process, the reshaping takes place to a large extent due to the flowability of the pressing mass, as relatively large flow stretches occur.

Fig. 1 shows the necessary tool technical components for the differentiated flow press process as well as the starting position for such a differentiated flow press process. The tool half 1 on the die side is in itself rigidly made and firmly mounted, and its tool surface contours are identical to the intended component geometry. The tool half on the piston side consists of tool parts 3,4 and 5 which form the movable cavity surfaces. The pressed material to be pressed and which has been brought into the open tool cavity, and whose mass corresponds to the desired mass of the relevant component, is denoted by 2. The introduced pressed material is available in flowable form under the selected process parameters.

In the aforementioned embodiment, the necessary force input for the movements and for ensuring the necessary closing force for the individual movable tool parts can be both mechanical and hydraulic in nature. The individual movements of the tool parts 3,4 and 5 can be controlled either simultaneously, overlapping or in sequence.

Fig. 2 schematically shows the beginning of the discontinuous differentiated pressing process. During the closing movement of the tool parts 3, reshaping energy is brought into the pressed material to be reshaped, so that a reshaping of the pressed material placed in the press is produced. The closing movement of the tool parts ends in this case in the position corresponding to the desired component thickness and remains in this position during the remaining shaping during the differentiated pressing process. The movable tool part 4 which is built into the tool part 3 performs in this phase of the differentiated pressing process the same closing movement as the moving tool part 3. Based on the negative relative position of the tool part 4 in relation to the tool part 3 at the beginning of the differentiated pressing process, it possible to produce a temporary material reservoir in the corresponding cavity area of the tool part 4. The movable tool part 5 performs no movement in the first phase of the differentiated pressing process.

The next process phase of the discontinuous differentiated pressing process is shown in fig.

3. The closing movement of the movable tool portion 5 produces a positive fit between the tool half on the piston side and the tool half on the die side to guarantee the tightness of the cavity, which is necessary for the complete reshaping process. When achieving a corresponding early sealing of the cavity at the form closure of the movable tool part 5 on the piston side above the tool half part 1 on the die side, there is no need for a submerged edge tool. During the closing movement of the tool part 5, transformation energy can, but not necessarily, be brought into the pressed product over any surfaces with product contact. The other movable tool parts 3 and 4 perform no movement in this phase of the described course of the differentiated pressing process and thus bring no transformation energy into the pressed material.

The still remaining transformation of the pressed material into a finished component by the differentiated pressing process takes place in accordance with fig. 4 exclusively at the final movement of the movable tool part 4 on the piston side. When introducing the reshaping energy seen over the overall reshaping process, only a part of the cavity surface that does not run parallel to the direction of movement within at least one tool half participates.

Application of a necessary back pressure (shrinkage) takes place by means of additional small closing movements of all movable tool parts on the piston side, and which are not in contact with the tool half on the die side above a direct mold closure.

Both the size and shape of the individual movable tool parts on the piston side can be individually adapted based on tool technical reasons and rheological conditions. The individual movement sequences of the displaced tool parts on the piston side can also be controlled separately. These conditions open up a multitude of degrees of freedom for creating the ideal shaping process within a discontinuously differentiated press process. In this way, in practice, the closing phases of the movement sequences described here are found in strict sequential order by simultaneous closing movements of the individual movable tool parts. In accordance with the present invention, however, it is in accordance with the preferred embodiment of the discontinuous differentiated pressing process that the last phases of the reshaping process, namely the complete mold filling, take place by introducing reshaping energy over the cavity surfaces of the movable tool parts which have the smallest cavity surfaces.

The method according to the invention as well as the corresponding device are suitable for pressing all pressable plastic materials, and in particular those which are plastic or flowable under the pressing conditions. Duromers or thermoplastic plastic materials are preferred, such as, for example, urea, melamine or phenolic resins, epoxides, polyolefins, such as, for example, polyethylene or polypropylene, polyamides, polyimides, polyesters, polyether ketones, polyester ketones, polysulfides, polysulfones or aramids. The aforementioned plastic materials can be unfilled as well as filled by adding common additives. The method according to the invention as well as the corresponding device are also suitable for pressing metals and ceramic materials.

A further object of the invention are components made of plastic materials, and which are produced in accordance with the method according to the invention, which means components which are produced in the device according to the invention. Such components are, for example: Machine parts and components for the motor vehicle industry, such as car bodies, doors, engine hoods, mud flaps, tailgates, roof pieces, side sills, bumper carriers, engine caps, spare wheel molds, front ends, battery carriers, underbody liners, instrument panels, seat pans, the cover part inside and on the outside of cars, steering wheel covers etc.

Machine parts and components for air and space transport, as well as shipping: Structural components, seat bowls, luggage racks, covers, transport containers, etc.

Components for the electrical and electronics industry:

Housing parts, covers, household appliances, switch cabinets, lamp fittings, housings and structural components for the computer industry, support structures for electronic components, etc.

Building components for the construction industry, the furniture industry and the household industry: Shower enclosures, swimming pools, bathtubs, wash basins, chemical containers and chemical equipment, drains, containers, troughs, kitchenware, facade structures, gardener's benches, roof domes, tool boxes, transport containers, semi-finished products etc.

Claims (12)

1. Method for discontinuous transformation of plastic materials by volume displacement in a cavity, during which transformation energy is introduced into the material to be transformed by means of at least two movable parts of the cavity surface, with at least one tool half comprising one or more parts which are movable in relation to the relevant tool half, at least part of the transformation energy is introduced by relative movement of these parts and the introduction of the transformation energy seen over the entire transformation process takes place under temporally and spatially differentiated control, characterized by the fact that the moving parts are controlled individually and the transformation energy - seen over the entire transformation process - is introduced by only a part of the overall cavity surface that is not parallel to the direction of movement on at least one tool surface, as transformation energy is introduced at each moving part by means of a single undivided - not lying parallel to the direction of movement - surface with per oduct contact. 2. Method as stated in claim 1, characterized in that the total material to be reshaped is already in the cavity at the beginning of the reshaping process. 3. Method as specified in claim 1, characterized in that material to be reshaped is supplied to the cavity from the outside during the reshaping process. 4. Method as set forth in claims 1 to 3, characterized in that the material to be reshaped and which is located in the cavity is first partially driven by movement of a tool half into a reservoir, which is formed by retraction of a moved part of the surface of the cavity to a negative relative position, and the material then by positive relative movement of this moved part of the cavity surface is driven out of the reservoir to other areas of the cavity. 5. Method as stated in one of the claims 1 to 4, characterized in that long flow paths for the material are produced during the transformation process. 6. Method as stated in one of claims 1, 2 or 4, characterized in that the transformation essentially takes place by local plastic material flow, as long flow paths are largely avoided. 7. Device for discontinuous pressing of plastic materials (2) in a cavity consisting of two tool halves (1; 3,4, 5) as stated in one of claims 1 to 6, characterized in that at least one tool half (1; 3, 4, 5) has at least one relative to this movable part (3,4,5), while the overall cavity excess, on the other hand, has at least two movable parts (3,4, 5), and that these at least two movable parts ( 3,4,5) is arranged so that at least part of the transformation energy can be introduced into the plastic material by their relative movement, as the movable parts (3,4,5) can be controlled individually and as each movable part (3,4, 5) has a single undivided - not lying parallel to the direction of movement - surface with product contact. 8. Device for injection embossing of plastic materials (2) in a cavity formed by two tool halves (1; 3,4, 5) as specified in one of claims l to 6, characterized in that at least one tool half (1; 3, 4, 5 ) has at least one movable part (3,4, 5) in relation to the relevant half, that the overall cavity surplus, on the other hand, has at least two movable parts (3,4, 5), and that these at least two movable parts (3,4,5) is arranged in such a way that at least part of the transformation energy is brought into the plastic material by means of the relative movement of these parts, whereby the movable parts (3,4,5) can be controlled individually and in that each moving part has a single undivided - not lying parallel to the direction of movement - surface with product contact. 9. Device as specified in claim 7 or 8, characterized in that the movable parts (3,4, S) are designed as additive presses. 10. Device as specified in claim 9, characterized in that the additional presses are made up of hydraulic presses. 11. Device as specified in claim 9, characterized in that the additional presses are made up of mechanical presses. 12. Device as stated in claim 9, characterized in that the additional presses are made up of displacers or displacers.