Patent Application
20120038086
The invention relates to the manufacture of parts, in particular the manufacture of parts made of fiber-reinforced plastics. It relates to methods and apparatuses according to the opening clauses of the claims.
The invention can be applied in many fields, e.g., in the field of manufacturing rims or wheels, e.g., for vehicles, or in the field of aircraft production, in particular in the production of stringers used for reinforcing the fuselage. In electrical industry, the invention may be applied, e.g., for the production of glassfiber reinforced insulators from thermoplastic glassfiber prepregs.
The automotive industry has a continuous demand for very lightweight parts and parts having a good fracture behaviour combined with a high stiffness and strength. This applies, e.g., to wheels and rims. Several ways of manufacturing rims or portions thereof are known in the art.
DE 101 45 630 A1 discloses a wheel made of fiber-reinforced plastics in which the major portion of fiber strands are oriented in circumferential direction in the rim and in radial direction in the wheel spider. This is achieved, e.g., through winding of unidirectional endless fibers. This makes it difficult to implement the production method in an industrial field, in particular in case of complex part geometries.
In DE 43 35 062 A1, a method for the production of curved fiber-reinforced thermoplastic profiles is proposed. Thermoplastic pre-impregnated fibers (commonly referred to as thermoplastic “prepregs”) are heated while exposed to pressure in a forming tool. The so-shaped prepreg profile is cooled after the shaping process. Subsequently, the prepreg profile is pushed in a gliding manner through a slot between two essentially fixed tool pieces. This way, the prepreg profile is again exerted to pressure, namely to the pressure resulting from the gliding interaction with the tool pieces. The profile thereby basically adopts the cross section of the slot between the fixed tool pieces and the curvature of the curved tool pieces. A drawback of this method is that the thermoplastic profile is treated while it is moving: The layers of the prepregs may slip or bend or displace during the treatment, thus compromising the final product. Applying this method, it is furthermore difficult to keep temperatures and pressures approximately constant. Furthermore, parts of certain shapes such as ring-like parts cannot be manufactured by this method.
In EP 842 757 B1, a method for producing a preformed component (preform) of a composite material is disclosed. A fibrous pre-assembly, namely a cloth having fibres in pre-defined orientations, is used. The deformable mesh of the cloth is placed on a preforming matrix or former and then wound around this former to a depth of several layers. The winding is fixed on a larger diameter of the former, such that the fibers are orientated in a prescribed manner. The so-obtained preform can have a ring-like shape. The preform can be put into a mold, and then, a resin can be transferred through the preform under vacuum and/or with a transfer pressure, and finally, the resin can be cross-linked at a suitable temperature. The injection of a thermoplastic resin is expected to be impossible or at least very problematic due to the high viscosity of thermoplastic materials.
GB 2 010 155 A discloses a method of manufacturing seamless metallic wheel rims. The desired cross section of the rim is impressed onto a basic ring-shaped piece of metal by two profiled circular molds. This method is not readily applicable to fiber composite material since the shaping mechanisms occurring in metals do not occur in materials containing fibers.
In WO 2008 050405 A1, a process for producing seamless ring-shaped structures made of thermoplastic composite materials is described. This rather simple process is based on inserting an annular preform made of several layers of a thermoplastic composite prepreg-material between an inner and an outer ring-shaped mold. At least one of the two mentioned molds rotates such that it locally exerts a pressure on a portion of the preform, wherein the preform is heated up to a process temperature at least in the region where the pressure is applied. Apparently, problems occur when trying to automate this dynamic process. Furthermore, realizing a constant process temperature distribution while applying an appropriate pressure in order to avoid slip or overlap effects of the layers of the prepreg material of the preform is rather difficult. Even with optimized process parameters such as temperature and pressure, the repeatability and quality required for industrial scale application is hard or impossible to assure, since a constant application of these parameters throughout the process is apparently impossible to achieve in industrial production.
One object of the invention is to create a method for manufacturing parts that does not show the disadvantages or problems mentioned above. In addition, the respective apparatus for manufacturing parts shall be provided.
Another object of the invention is to provide a possibility to produce parts, in particular lightweight parts with superior mechanical properties, in particular parts having a good fracture behaviour and/or a high stiffness and/or a high strength.
Another object of the invention is to provide a possibility to produce parts of reinforced plastics.
Another object of the invention is to provide a possibility to provide large process windows when producing parts, in particular parts of reinforced plastics, more particularly parts of reinforced thermoplastics.
Another object of the invention is to provide a possibility to produce parts showing a particularly safe behavior in case of abrupt rupture.
Another object of the invention is to provide a possibility to produce parts showing an improved failure behaviour.
Another object of the invention is to provide a possibility to provide an improved cycle time for producing parts.
Another object of the invention is to provide a possibility to produce parts having special shapes or geometries, in particular annular or ring-like shapes or similar shapes.
Another object of the invention is to provide a possibility to produce seamless parts, in particular seamless ring-like shaped parts.
Another object of the invention is to provide a possibility to produce parts having improved insulation properties, in particular thermal and/or electrical insulation, and/or parts showing an improved chemical inertness or resistance.
Another object of the invention is to provide a possibility to more easily produce parts, in particular parts substantially made of reinforced plastics.
Another object of the invention is to provide an improved possibility to produce parts substantially made of reinforced thermoplastic, in particular of glassfiber-reinforced thermoplastic or carbonfiber reinforced thermoplastic.
Another object of the invention is to provide an improved possibility to produce rims or wheels or portions thereof.
Another object of the invention is to provide an improved possibility to produce insulators, in particular reinforced insulators.
Another object of the invention is to provide an improved possibility to produce stringers for use in airplanes as reinforcing elements of the fuselage.
Further objects emerge from the description and embodiments below.
At least one of these objects is at least partially achieved by apparatuses and methods according to the patent claims.
The method for manufacturing parts comprises the steps of
Said first and second tools can also be considered and, accordingly, can be referred to as first and second pressing tools or first and second molds.
In one embodiment, the method is a method for manufacturing parts of reinforced plastics, in particular a method for manufacturing parts of fiber-reinforced plastics, in particular of fiber-reinforced thermoplastics.
In one embodiment which may be combined with the before-addressed embodiment, said method is a method for industrially producing said parts.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said material comprises a resin, and said compressing is carried out for promoting a cross-linking of the resin.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said parts are finished products or intermediate products to be subjected to one or more finishing manufacturing steps.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said method is a method for manufacturing seamless parts.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the segments are moved along a predefined way or path.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said segments of said first and second tools, when arranged in a predefined way, referred to as closed position, form a tool surface describing the shape of a portion of a surface of said part to be manufactured; in particular, wherein said segments of said first and second tools, when arranged in a predefined way, referred to as closed position, form a tool surface substantially describing the shape of the complete surface of said part to be manufactured.
In one embodiment which may be combined with one or more of the before-addressed embodiments, step f) is carried out for forming said material (or a portion thereof) in a desired shape; the pressure applied to the material is also referred to as forming pressure.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the applied pressure mentioned in step f) causes a moving relatively to each other at least of the segments of said first tool with respect to segments of said second tool.
In fact, one can in some embodiments distinguish two phases during the compressing in step f): A compressing of the material before the closed position of all tools is reached; in this phase, at least the segments of said second set are moved; this phase can be helpful for removing from the material gases (typically air) inside the material. And a compressing while the segments of the first set and the segments of the second set of the second tool are already in the closed position; during this phase, there is no relative movement anymore of segments of said first set with respect to the segments of the second set.
In one embodiment which may be combined with one or more of the before-addressed embodiments, in step d) the at least one segments of said first set of said second tool are moved from an initial position towards and into said closed position.
In one embodiment which may be combined with the before-addressed embodiment, at least one of said segments of said second set of said second tool is, when said second tool is in said closed position, arranged between more than one neighboring segments of said first set of said second tool, and an opening between said more than one neighboring segments of said first set of said second tool is, from said initial position up to an intermediate position reached by the first set before reaching said closed position, too small for said at least one of said segments of said second set of said second tool to penetrate on its way towards said closed position.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the direction of pressure applied to a segment of said second tool at least substantially coincides with the direction of the moving of the respective segment mentioned in step d) and e), respectively, at least when close to said closed position. In particular, wherein said moving mentioned in step d) and e), respectively, is accomplished at least substantially along a straight line, and wherein said direction of pressure at least substantially coincides with the respective direction of the moving.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said parts are predominantly, in particularly substantially, continuous-fiber reinforced parts (and said material correspondingly comprises continuous-fiber reinforced plastics). Parts reinforced with such substantially uninterrupted fibers have extraordinary properties.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said parts comprise fibers which are predominantly, in particularly substantially, oriented fibers (and said material correspondingly comprises oriented fibers). Parts reinforced in such a way can have extraordinary properties. The orientation of the fibers is selected according to desired properties of the part to be manufactured. E.g., calculations/simulations can be carried out for finding an optimum fiber orientation. Usually, there are comprised in the material several layers one or more of which will have the same and one or more of which will have a different fiber orientation.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said parts are rims or wheels or portions thereof.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said parts are insulators, in particular reinforced insulators, in particular substantially cylindrically-shaped insulators.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said parts are stringers used in airplanes as reinforcing elements of the fuselage.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said first set of said second tool is brought into contact with said material before said second set of said second tool is brought into contact with said material. In particular, pressure is applied to said material by said second set of said second tool only after pressure has been applied to said material by said first set of said second tool. And more particularly, said first and second sets of said second tool are structured and arranged and moved in such a way that whenever pressure is applied to said material by said second set of said second tool, pressure is also applied to said material by said first set of said second tool.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said first tool is an outer tool and said second set is an inner tool, or vice versa, in particular wherein the inner tool is, during said moving steps, located generally inside a shape generally described by said outer tool.
Usually, said first tool, more particularly its segments, are kept in position during the movements of the sets of the second tool. This can be accomplished by applying corresponding forces to the segments of said first tool and/or by fixing the segments of the first tool with respect to one another. Particularly interesting is the case that the first tool is the outer tool and the second tool is the inner tool. In this case, fibers, in particular continuous fibers comprised in the material will, at least predominantly, be stretched during the described compressing action, which usually leads to particularly advantageous material properties.
In one embodiment which may be combined with one or more of the before-addressed embodiments, at least one of (in particular each of) said sets of segments comprises at least two, in particular at least three, more particularly at least four segments.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the method comprises moving all segments of one of said sets (be it a set of said first tool or a set of said second tool) at least substantially simultaneously during said compressing, in particular wherein this applies to each of the sets of an inner tool or to each of the sets. In particular wherein for said moving of all segments of said one of said sets is driven by one and the same drive.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the method comprises moving all segments of one of said sets (be it a set of said first tool or a set of said second tool) at substantially the same speed during said compressing, in particular wherein this applies to each of the sets of an inner tool or to each of the sets.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said material is provided, in particular inserted between said first and second tools, substantially in form of foils or sheets or stripes.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said material as well as said part comprise or are at least substantially made of reinforced plastics, in particular of fiber reinforced plastics.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said material inserted between said first and second tools comprises a thermoplastic. Thermoplastics enable a more rapid production (shorter production cycle time), they have a high fracture toughness and a good recycleability and some show a high temperature resistance.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said material substantially is a preform or a prepreg material.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said material is inserted manually between said first and said second tools.
In one embodiment which may be combined with one or more of the before-addressed embodiments except for the before-mentioned embodiment, said material is inserted automatically between said first and said second tools, in particular by a robot.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the method comprises heating said material before said compressing, and in particular after inserting the material between said first and said second tools. For thermoplastics, heating is important, whereas in case thermosets and elastomeres, it can be possible to dispense with heating.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the method comprises heating said material during said compressing.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the method comprises monitoring, in particular controlling the temperature of said material, in particular before and/or during said compressing.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said parts comprise a portion describing
In one embodiment which may be combined with one or more of the before-addressed embodiments, said parts comprise a portion having a substantially ring-shaped or ring-like structure, or wherein said parts substantially have a ring-shaped or ring-like structure.
Such kinds of parts are difficult to produce otherwise, in particular when the material substantially is reinforced thermoplastics, in particular thermoplastics reinforced with fibers, in particular reinforced with continuous fibers.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said parts comprise a portion having a substantially annular shape, or wherein said parts substantially have an annular shape.
In one embodiment which may be combined with one or more of the before-addressed embodiments, during said compressing said material, an area of said material which is in contact with said first set of said second tool is larger than, in particular is at least two times, more particularly at least three times as large as the area of said material which is in contact with said second set of said second tool.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said first and second tools are tools the shape of which determines the shape of said parts, in particular wherein the shape of said first and second tools are tools describing, when they are arranged in a predefined way referred to as closed position), a shape corresponding to the shape of the part to be produced.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the tools form, when arranged in a predefined way, a cavity corresponding at least substantially to the shape of said part to be manufactured.
In one embodiment which may be combined with one or more of the before-addressed embodiments, for said first set of said second tool and/or for said second set of said second tool, the segments of the respective set are moved such that a pressure onto said material to be compressed exerted by one of the segments of said respective set is at least approximately the same for each of said segments.
In one embodiment which may be combined with one or more of the before-addressed embodiments, at least one of said segments of said second set of said second tool is tapered in the direction of the movement of said segment. In particular, each of said segments of said second set of said first tool is tapered in the direction of the movement of respective segment.
In one embodiment which may be combined with one or more of the before-addressed embodiments, at least one of said segments of said second set of said second tool is shaped such that when compressing said material, forces are exerted by said segment onto at least one segment of said first set of said second tool. In particular, wherein each of said segments of said second set of said second tool is shaped such that when compressing said material by moving said segments, forces are exerted by said segments onto at least one segment of said first set of said second tool, in particular onto each segment of said first set of said second tool.
In one embodiment referring to the before-addressed embodiment, said exerted force is transferred from said segment or from said segments onto said at least one segment of said first set of said second tool or onto each segment of said first set of said second tool via—in particular substantially solely via—at least one contact surface of said segment or segments interacting with at least one contact surface of said at least one segment of said first set of said second tool or interacting with contact surfaces of said segments of said first set of said second tool. In particular, such interacting contact surfaces are mating surfaces.
In one embodiment referring to the last-mentioned or to the before-last mentioned embodiment, said exerted forces are directed substantially in the direction of said movement of said segment or nearly perpendicularly thereto or a superposition of such forces.
In one embodiment which may be combined with one or more of the before-addressed embodiments, by said compressing, a pressure of at least 5 bar and in particular of at most 50 bar is exerted on said material. More particularly, a pressure of between 10 and 30 bar is exerted on said material by the segments of the tools.
In one embodiment which may be combined with one or more of the before-addressed embodiments, the method comprises the step of heating said material before and/or during and/or after said compressing, in particular heating at least substantially all of the material inserted between said first and second tool. In particular, namely most prominently in case of (reinforced) thermosets, said material comprises a resin, and said heating is carried out for promoting a cross-linking of the resin. In case of (reinforced) thermoplastics, said heating brings the thermoplastic into a well-formable state.
The apparatus for manufacturing parts (in particular of parts substantially made of reinforced plastics) comprises
Such an apparatus can allow to carry out the above-described methods.
In one embodiment, said drive unit is a drive unit for driving at least said first set and said second set of said second tool towards said first tool; in particular, said drive is structured and configured for said driving.
In one embodiment of the apparatus which may be combined with one or more of the before-addressed embodiments, the segments of said first tool are shaped such that, when arranged in a predefined way referred to as closed position, they form a an at least substantially continuous surface corresponding to a first partial surface of a part to be manufactured, and wherein the segments of said second tool are shaped such that, when arranged in a predefined way referred to as closed position, they form an at least substantially continuous surface corresponding to a second partial surface of said part to be manufactured, in particular wherein these two partial surfaces complement each other such that they form substantially the whole surface of said part to be manufactured.
In one embodiment of the apparatus which may be combined with one or more of the before-addressed embodiments, the segments of said first tool are shaped such that, when arranged in a predefined way, they form a continuous surface, and the segments of said second tool are shaped such that, when arranged in a predefined way, they form another continuous surface, and wherein these two continuous surfaces complement each other such that they form substantially the whole surface of a pre-defined volume when arranged with respect to each other in a predefined way.
In one embodiment of the apparatus referring to one or both of the two last-addressed embodiments, said at least one segments of said first set of said second tool comprise at least one mating surface each, mating, when said second tool is in said closed position, with at least one mating surface of said at least one segment of said second set of said second tool, wherein the mating surfaces of said first set of said second tool each form, in said closed position, an acute angle with said second partial surface.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said apparatus comprises a control unit configured to control a movement of said first and of said second set of said second tool in such a way that said segments of said second tool are moved such that continually during moving the at least one segments of said second set of said second tool towards said closed position, a momentary travel distance up to said closed position for the at least one segments of said second set of said second tool exceeds a momentary travel distance up to said closed position for the at least one segments of said first set of said second tool. In particular, the control unit controls said drive unit in the described way.
In one embodiment which may be combined with one or more of the before-addressed embodiments, said apparatus comprises a temperature change unit structured and configured for heating or cooling or for both, heating and cooling, material inserted between said first and second tools. In particular, at least a portion of said temperature change unit is integrated in at least one of said tools.
The invention comprises apparatuses with features of corresponding methods according to the invention, and vice versa.
The advantages of the apparatuses basically correspond to the advantages of corresponding methods and vice versa.
In one aspect of the invention, the method for manufacturing parts comprises the steps of
The subsequent movements of said first set of said second tool and said second set of said second tool (which movements are typically carried out exerting pressures of at least 5 bar) makes it possible to form ring-shaped and ring-like shaped parts from preforms such as prepreg material. It is possible to apply pressures very homogeneously to the material.
In one embodiment of this aspect, said moving at least said first set of said second tool towards said first tool takes place still (i.e. continuedly) or again (i.e. renewedly) during said moving at least said second set of said second tool towards said first tool.
This aspect may be combined, as far as principally compatible, with any other herein disclosed embodiment and with any feature of any other herein disclosed embodiment.
Further embodiments and advantages emerge from the dependent claims and the figures.
Below, the invention is described in more detail by means of examples and the included drawings. The figures show schematically:
The reference symbols used in the figures and their meaning are summarized in the list of reference symbols. The described embodiments are meant as examples and shall not confine the invention.
Parts, for instance ring-shaped structures, made of reinforced plastics can be manufactured since overlapping layers of a preform, usually made of prepreg material, merge during a production process involving pressing and usually also heating such that no more relevant intersections between the layers exist in the so-produced (seamless) part. Forces applied to a so-obtained part are transferred from one fiber strand to the next in the overlapping areas through shear forces in the matrix, and thus, the resulting structural impairment is very small compared to weld seams or glued surfaces.
Various semi-finished products can be used as a preform to be processed afterwards. For example: different fiber matrix combinations, or pre-impregnated (prepreg) non-consolidated fiber semi-finished products, or non-impregnated semi-finished products combined with films of not-reinforced polymer. Even thermoset or elastomer matrix systems can be processed in the proposed method.
For example, the following fiber materials can be used: carbon fibers, glass fibers, aramide fibers, basalt fibres, Poly p-phenylene benzobisoxazole (PBO) fibers, boron fibres, polyamide fibres, flax fibres, hemp, cotton, or combinations thereof. In general, as long as process pressure, time and temperature do not deteriorate the properties of the fibers in the produced part, any type of fiber can be used. Selection is made by most importantly considering by means of which fiber the desired properties of the produced part can be achieved.
There are various ways for manufacturing a preform, in particular a ring-like shaped preform. Here are some examples:
Monitoring and/or controlling the temperature of the preform before and/or during exposing it to pressure in an apparatus with tools is recommended at least for thermoplastics in order to have a well-defined and stable process. The tolerance of the process temperature may be 10° C. to 20° C. or even around 50° C., or even more, depending on the material to be processed and with the process temperature chosen sufficiently high above TM and TG, respectively.
In case of reinforced thermoplastics as matrix material in which the fibers are embedded, it is the thermoplastic material which basically defines the relevant process temperatures.
For semi-crystalline thermoplastic materials, the crystalline melting temperature TM (e.g., 162° C. for polypropylene) and the crystallization temperature TC are relevant. TC can be more than 40° C. lower than TM, depending on the specific thermoplastic material.
A preform has to be heated at least up to its crystalline melting temperature TM. This can be accomplished by direct heating, e.g., using strip heaters, by radiation, e.g., using infrared radiators, by hot air convection, or by indirect heating through a tool in which the preform is pressed. A combination of two or more of these heating methods is also possible.
The arrangement of the heating devices is preferably chosen such that the preform is heated uniformly and quickly to a temperature higher than TM, in particularly to a process temperature clearly above TM, in most cases it will be chosen at least 20°, at least 50° C., or at least 75° C. above TM.
In the case of amorphous thermoplastic materials, there are no distinct temperature limits aside from the so-called glass transition temperature TG. The processing temperature has to be above TG, in particularly clearly above TG, in most cases it will be chosen at least on 20° C., at least 50° C., at least 100° C. or at least 150° C. above TG. Likewise, there is also no crystallization temperature TC for amorphous thermoplastic materials (because they remain amorphous). For the solidification of the material, the solidification temperature Ts (which usually is slightly higher than TG, typically by between 10° C. and 40° C.) is of importance.
The principles of the processing methods are the same for amorphous and for semi-crystalline thermoplastic materials; but definitions and denotations of the temperature limits vary.
The following table shows some exemplary thermoplastic polymer materials usable in the proposed process. The temperature ranges are merely a reference for the corresponding bulk polymers. Depending on the specific modification of the polymers, the values can strongly deviate from the values in the table.
Elastomers and thermosetting plastics have a low viscosity, allowing to inject them into a mold cavity (formed by tools of the apparatus), e.g., in a resin transfer molding (RTM)-like process. It is also possible to use prepregs based on thermosets or elastomers as a preform.
The apparatus (equipment) suitable to perform the proposed method comprises an inner and an outer tool (or inner and outer “mold”), wherein the total number of segments comprised in both tools is at least three. In a very simple configuration, this means that either the outer tool comprises exactly one segment and the inner tool comprises exactly two segments, or the outer tool comprises exactly two segments and the inner tool comprises exactly one segment.
At least one of said tools is arrangeable in an open position in which a preform can be inserted into the apparatus before the preform is pressed in a pressing step and/or in which a pressed part can be released from the apparatus after said pressing step, and arrangeable in a closed position in which the pressing step/the forming process takes place. The outer and inner tools are reciprocally movable with respect to one another either by moving only one of them or by moving both.
In particular, if parts shall be produced having more complex shapes, like for instance open or closed ring-shaped structures, the inner and the outer tools are preferably each composed of two or more tool segments. This enables or facilitates to remove the part from the tools.
The tools can be made of the same or of different material. Metals and alloys, e.g., steel or aluminum, are suitable as materials for tools, because they are resilient and at the same time cost-effective and easily workable into the needed shape required in order to obtain the desired part.
If necessary, adhesion between matrix material of the preform and a tool surface can be avoided in that the surface of the tool is treated, e.g., with a commercial grade releasing agent.
In case of too little adhesion between matrix material of the preform and a tool surface, gluing substances or the like can be applied between matrix material of the preform and the tool surface in order to avoid uncontrolled/undesired mutual sliding of different layers comprised in the preform.
Since some materials and/or geometries may require a controlled cooling procedure or a thermal post-treatment, the presence of at least one heating and/or cooling device is recommended not only during pressing and/or before pressing has started (in order to reduce the pressing time), but also afterwards. E.g., a heating and/or cooling device can be incorporated directly into the apparatus, more particularly into one or both tools. And/or another heating and/or cooling device can be provided separately from the tools. Ways of accomplishing heating have been cited above. With respect to cooling, the same principles can be applied, but inversely, e.g., by using cold water serpentines or similar means well-known in the art.
In order to achieve a forming pressure suitable for both, the employed preform matrix material (mainly composing the preform), and for the shape of the part to be produced, different methods can be used, e.g., mechanically, hydraulically or electromechanically exerting a force on an external surface of at least one of the inner and outer tools. In order to achieve a very good fit between all of the tool segments and/or between the tools and the preform arranged between the tools, and in order to ensure a suitable direction of the applied force and a suitable pressure distribution, it is advisable to suitably guide the applied force, e.g., by using push rods or pull rods, wherein many alternatives are known to a person skilled in the art.
The process, or at least the pressing step (and therefore the movement of the segments) and preferably also the heating, is preferably automatically controlled, e.g., using a suitable software running in a controller or in a computer, e.g., the software controlling important parameters as for instance times for cooling, for heating and for pressing, temperature and pressure.
In particular, oriented continuous fibers are used as reinforcement. The
The outer tool comprises a set of segments comprising four segments 1 which are pair-wise clamped to each other by clamps 6.
The inner tool comprises a first set of segments comprising four segments 2a and a second set of segments comprising four segments 2b.
First tool (outer tool) and second tool (inner tool) are shown in closed position.
In
In
In order to increase the stiffness of the outer tool in the closed position 4, clamps 6 are applied to the outer tool, see
It is possible to start at this point a heating of the inner and/or of the outer tools (preferably both). A person skilled in the art will recognize that the heating process and the start of the heating can be scheduled earlier or later depending in particular on requirements given by the process and by the material or materials of the preform 3.
In
In
It shall be mentioned that the contacting interfaces 13 (cf.
The contact interfaces 13 (cf.
Segments 2a and 2b are pulled (by pull-rods 8 and 11, respectively) toward the preform 3 until they reach a preset position (closed position). In that position, the cavity between outer tool and inner tool equals the shape of the part to be manufactured, i.e. the rim shape. Together, the outer surfaces of the segments 2a and 2b now have the shape of and form the inner surface of the part to be manufactured.
The pressure (forming pressure) exerted onto the preform 3 through segments 2a and 2b is upheld for between 2 seconds and 2 minutes, preferably between 20 seconds and 1 minute, for a consolidation of the thermoplastic resin in the layers of the preform 3. In the present example, the process pressure has to be between 5 bar and 50 bar, preferably between 8 bar and 20 bar. These wide time and pressure ranges are one of the great advantages of the presented process, making it easier to run-in a new part geometry, and a new part geometry usually has one main variable: the number of prepreg material layers.
For example, in case of a rim for a bike wheel, only very few layers are needed, and therefore 10 seconds pressing time can already be sufficient, whereas in case of a wheel for a car, the number of layers is substantially higher, e.g., a few dozens, and thus, the pressing time rises to, e.g., 20 or 30 seconds.
The pressing time and the pressure are roughly proportional to the number of layers in the preform 3, although other factors such as the complexity of the geometry of the part to be formed do also influence these parameters, but usually less strongly.
At this point, cooling of the inner and outer tool usually will be commenced, while still maintaining the pressure of the tools on the preform 3. From now on, the preform 3 can be referred to as part 16, in the present example: the rim 16. Cooling can of course be accelerated by, for example, cooling serpentines in the tools.
While cooling, after having reached a temperature where the chosen material is solid, the pressure on the rim 16 will be reduced by loosening the rods 11. The segments 2b are moved away from the rim 16.
In
With the rim 16 removed from the tools, the apparatus is ready for the next production cycle.
A short simplified version of the proposed process can be roughly summarized by the following steps in the following order:
Note that applying the full forming pressure only after the material has reached a process temperature above TM and TG, respectively, will usually result in better quality parts than applying that full forming pressure already before the material reached that temperature.
While the first example presented above in conjunction with
Also another process is possible: A robot keeps the preform 3 in position, and both, the inner tool and the outer tool, substantially simultaneously move from the opened position into the closed position represented by
In case of the tools and a ring-like part according to the first example, the minimal number of segments of the inner tool (2a and 2b, together) is four. In general, if a perfectly cylindrical or conical part has to be produced, one single cylindrical segment for the outer tool is in principle sufficient. But if the radial cross section of the rim presents at least one undercut in axial direction, at least two segments have to be used for the outer tool in order to remove a manufactured stiff part from the tools.
In case of the aforementioned chronologically inversed or simultaneous movement of the segments of the tools, these minimal numbers of segments may change accordingly.
If the cross-section of the preform 3 perpendicular to its axis is not perfectly circular, as for instance in an open ring-shaped structure or in an elliptical structure, the process can be adapted by replacing the perfectly circular inner and outer tools with correspondingly shaped other inner and outer segments having the suitable curvature and/or shape, cf. the various examples illustrated in
The segments 2a and 2b of the inner tool are mounted on pantograph 17. While turning pantograph bolt 18, the segments 2a and 2b move, since mounted on one and the same pantograph 17, towards the closed outer tool, thus applying the desired pressure on the preform 3. E.g., the segments 2a,2b are moved such that firstly, segments 2a get into contact with the inserted material, and then segments 2b get into contact with the inserted material, or segments 2a are moved earlier and/or at a different speed than segments 2a. Generally, segments 2b will never be closer to the material 3 than segments 2a on their respective way towards and into the closed position. Suitably designing the pantograph arms allows to achieve such movements. After heating and pressing, the part can be extracted from the tools by turning the pantograph bolt 18 in the opposite way.
A third example of a method and of an apparatus for manufacturing parts is described in conjunction with
This third example refers to a method and an apparatus for manufacturing carbon fiber reinforced polyetheretherketone (PEEK) open profiles 19, for instance a stringer for reinforcing aircraft fuselages (cf.
And profile 19 can have continuously changing bending radii (cf. R1 and RN in
The process parameters of temperature, pressing time and pressure of the first example (see above) can also be applied in this case.
In general, the process also works in substantially the same way as the above-described first example and with a principally equivalent or at least similar apparatus. A main difference is the number of segments: in this case, the inner tool has to comprise at least one central segment 20 and two lateral segments 21, while the outer tool has to comprise at least two segments 22.
The particular example of
In general, in practice the minimal number of segments is basically given by two factors:
Note that the interface 13 and the mating surfaces 13a and 13b do not necessarily have to be plane. As indicated by the dotted line in
It will be appreciated that the segment(s) 2b (first and second example) and 21 (third example) of the second set are (is), on their way towards the closed position always farther away (along their travel path) from their (its) position when in closed position than—at the same time—the segment(s) 2a (first and second example) and 20 (third example) of the first set (along their travel path) from their (its) position when in closed position.
One can, somewhat sloppily, say, the segment(s) 2b, 21 of the second set cannot pass by or “overtake” the segment(s) of the first set on their respective way into the closed position.
This allows to form parts with narrow concave surfaces. A limited space available for the segments is cleverly used. Different sets of segments are moved at different times and/or at different speeds to overcome geometrical limitations. Note that, similarly to what was discussed above in conjunction with the second example (cf.
The described method and apparatus is excellently suited for the manufacture of pressure-formed fiber-reinforced plastics parts from preforms, in particular for such parts which have or comprise a portion having a shape which is ring-like or nearly-closed or is rather complex with concave portions, in particular wherein continuous fibers and/or oriented fibers are used as reinforcement.
| Number | Date | Country | Kind |
|---|---|---|---|
| 61151985 | Feb 2009 | US | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2010/051647 | 2/10/2010 | WO | 00 | 10/14/2011 |
