Patent Application
20190091906
The present invention relates to the field of devices for injection molding of a composite material comprising at least one laminate. The invention further relates to a method for injection molding of a composite material, all corresponding to the preambles of the independent claims.
Injection molding is a method of manufacturing items, in which a mold is used to impart an initially at least partially fluid material with a form or shape, whereby that form or shape is determined by the mold. A variety of complex shapes can be attained by injection molding. Furthermore, well established techniques of injection molding allow the manufacturing of forms and shapes out of composite material. This can encompass methods such as the layered injection of different materials into the mold, or the compartmentalisation of the mold and injection of the materials into the respective compartments. Injection molding can further produce composite materials by processing a variety of inlays in the mold. One particularly challenging type of injection molding the overmolding of a laminate with overmolding injection molding material. The challenge is due to the fact, that the injection process itself induces fluid dynamic forces that can have shearing effects on the laminates. In the end, this can result in a misplacement of the laminate in the resulting shape and the structural deficiencies of the letter. At the same time a fixation of the laminate inside the mold would insatiably cause spots where the overmolding would not perform in a way that the laminate is fully encapsulated.
Composite materials with laminates are useful in a variety of applications. The laminates can induce an increased stability to the product in a particular axis, while at the same time being comparatively light weight and even, if so required, be essentially stiff and equipped with a breaking point in another axis.
The document DE 10 2009 024 789 A1 (Reese, E.) describes such a process for manufacturing a form from fibre reinforced thermoplastic material by injection molding, whereby the fibre inlay is to be completely jacketed by the thermoplast. Therefore, a mold is proposed, comprising two mold portions which are equipped with fixating elements on both sides. These fixating elements are moveable towards each other. The process requires a complete closing of the mold to completely clamp and plastically deform the fibre inlay. After this closing, the fixating arms hold the fibre mesh into place as the overmolding occurs. The process is not suited for the processing of unidirectional fibres though, that do not require a pre-forming or pre-molding step.
It is thus a requirement in the art to have device and corresponding method for injection molding of a composite material with a laminate which alleviates the buckling of the laminate within the mold and at the same time ensures an encapsulation of the laminate as required by the structural demands of the resulting product.
It is therefore an object of the present invention to provide a device for injection molding of composite material which overcomes at least one disadvantage of the state of the art. In particular, a device for injection molding of a composite material shall be provided which enables the manufacture of composite materials comprising at least one laminate that is easy to use and essentially decreases relative movement of the laminate within the mold caused by an injection flow of an overmold. It is a further particular object of the present invention to provide a corresponding method for injection molding of a composite material comprising at least one laminate that is easy to execute and alleviates the event of deformations and undesirable characteristics of the resulting part. At least one of these objects has been solved with a device and a method according to the characterising part of the independent claims of the present invention.
One aspect of the present invention relates to a device for injection molding of a composite material comprising at least one laminate. In the sense of the present invention a laminate can be understood as a material which can be by itself a composite of at least two further materials of which at least one is a material that extends in the longitudinal direction of the laminate. The laminate can, but need not be inlaid in another material. One particular form of the laminate according to the sense of the present invention is a laminate comprising reinforcing fibres that extend in a longitudinal direction of the laminate. Such fibres are usually embedded into a matrix of a suitable resin. In a particular embodiment of this particular type of laminate the fibre is chosen from the group comprising glass fibre, carbon fibre, ceramic fibre, mineral fibre, nylon fibre or natural fibre, such as for example hemp fibre. Among the matrix materials most often materials from the group of duroplasts, elastomers or thermoplasts are utilised.
For the purpose of the present invention, the laminate does not need to be encapsulated in a matrix. A laminate according to the present invention can consist of the fibres as bundle per se.
In the sense of the present invention a laminate can be further define as a fibre-reinforced composite with unidirectional continuers filament.
The device of the present invention comprises a mold including a plurality of mold portions. Each of the mold portions has a first side defining a molding surface. Further, at least one of the mold portion is moveable relative to at least one other of the mold portions, such that the mold is moveable between an open state and a closed state. In which the molding surfaces of the mold portion cooperate to define a mold cavity. The device further comprises one or more retaining arms with a gripper for contacting the laminate, and the retaining arm is arranged such that this moveable between a retracted position and an extended position.
In the sense of the present invention, the retaining arm is found to be in an extended position, when it is further form the molding surface of the respective mold portion then when in the retracted positions and extends into the mold cavity. Analogously the gripper is in the retracted position, when it is relatively closer to the surface of a respective mold portion than in the extended position.
In a particular embodiment, the gripper part of the retaining arm is flush with the surface of the respective mold portion the retaining arm is associated with when in the retracted position.
In a particular embodiment, the plurality of mold portions comprises at least one pair of mold portions which are essentially complementary to each other. In the sense of the present invention, the pair of mold portions is essentially complementary to each other, when both mold portions are arranged, such as to form a cavity when they interact with each other, respectively when the mold is in the closed state and the molding surfaces of both mold portions of the pair of mold portions define a cooperatively formed mold cavity. In a particular embodiment, a first mold portion is a core mold portion and a second mold portion is a cavity mold portion.
In a further particular embodiment, the molding surfaces are arranged such as to face each other when in open state.
In a particular embodiment of the present invention, the retaining arm(s) is slideably coupled to the respective mold portion. In a further particular embodiment the retaining arm(s) are arranged at either one of the mold portions, such that they extend through the mold surfaces into mold cavity, respectively into a distance between the mold portions prior to closing the mold.
In the sense of the present invention, a gripper shall encompass any means suitable for preventing the laminate from shifting or buckling from its position in the course of the injection molding. In particular, such a gripper shall not be construed as being limited to a device performing a gripping function by itself. In the most basic embodiment, the gripper according into the present invention is configured as a bracket which interacts with a second gripper bracket of a further retaining arm, such that the laminate is held in position.
In a further embodiment of the present invention, the gripper is configured as flat front edge with structures for increased friction with the laminate to be retained. In a particular embodiment, the flat front edge has channels for the flow of overmold during the overmold injection step.
In a particular embodiment, the gripper has an essentially oblong contact surface for contacting the laminate to be held. In a further embodiment, the long dimension of the essentially oblong contact surface of the gripper is chosen such as to have a dimension larger than the width of the laminate to be held.
In a particular embodiment, the gripper is configured with a ridged surface for contacting the laminate.
In a most basic embodiment, the gripper is arranged, such as to hold the laminate by contacting it and retaining it either with an opposing gripper, a plurality of opposing grippers or an opposite molding surface formed by a first side of a mold portion arranged opposite to said gripper.
In a further particular embodiment, the gripper is arranged such as to enable a gripping, clamping or pinching movement upon the laminate by contacting the laminate. In a particular embodiment the gripper is formed integrally and from one piece.
In a particular embodiment, the gripper, preferably the front end surface of the gripper adapted for contacting the laminate, is either one of serrated, ridged, chamfered or traversed with furrows. In a further preferred embodiment, the said serrations, chamfers or furrows are adapted to allow an overmold material to flow through during the injection molding procedure.
In a particular embodiment of the present invention, the retaining arm(s) includes at least one shaft that is coupled to the gripper and is slideably received by the respective mold portion. The respective mold portion can be equipped further guidance, such as to enable a linear movement of the retaining arm(s) from the retracted into the extended position. In a further particular embodiment, the retaining arm(s) include a plurality of shafts each one either ending in an individual gripper or collectively ending into one integral gripper.
In a particular embodiment, the gripper is integral with the at least one shaft. In an alternative embodiment, the gripper and the at least one shaft(s) are separate elements joined together to form a retaining arm.
In a particular embodiment, each gripper is held by at least two shafts that are slideably retractable into the respective mold portion. This enables a precise steering and therefore dosage of the retaining force of the gripper in respect to the laminate.
In a particular embodiment, the shafts of the retaining arm(s) are chosen in length to correspond to a first stroke of an actuator actuating the retaining arm(s) in question. In a particular embodiment, the shaft is telescopic, such as to accommodate at least a second stroke and whereby the sum of strokes is larger than the length of the drawn in telescopic shaft, but equal to the fully extended telescopic shaft.
In a particular embodiment, the respective mold portion defines a recess for a least one of the retaining(s) configured to receive at least a portion of the gripper when the retaining is in the retraced position.
In a further particular embodiment, the mold portion defines a recess for at least one of the retaining arm(s) at the molding surface, such that when the retaining arm is in the retracted position and outer surface of the gripper is substantially flush with a portion of the molding surface that borders the recess. With other words, during operation the front edge of the gripper can be said to form part of the molding surface of the form to be thus produced. In an alternative embodiment, though, the recess is formed in a way that part of the front edge of the gripper, i.e. parts of the gripper that contact the laminate, are completely retracted into a recess of the mold portion.
In a particular embodiment of the present invention, the retaining arms are arranged in pairs. Each retaining arm has an opposite retaining arm, such that the grippers of the pair of retaining arms are adapted at holding a laminate in place. In a particular embodiment, the grippers are arranged as complementary brackets that upon being brought into an extended position both engage a laminate located between the brackets in a way, that the laminate is held into place. Such engagement can, but need not encompass a clamping of the respective laminate.
In a particular embodiment, the pairs are configured such as to be symmetrical in respect to each other. In an alternative embodiment, the pairs are structurally different from each other. In a further particular embodiment, the pairs can have analogous strokes, moving towards each other. In an alternative embodiment, the strokes the pair of gripping arms have towards each other are different. In a further particular embodiment, a retaining arm can be paired with a plurality of retaining arms on the opposite side, each with an individual stroke towards that said first retaining arm.
In a particular embodiment the retaining arms with their respective grippers are arranged such as to provide shape to the form to be achieved. Opposite grippers can be arranged such as to interlock with each other in manner that a particular geometry is achieved in the desired form.
In a particular embodiment the device compromises at least two retaining arms, whereby a first retaining arm is movably coupled to a first mold portion and a second retaining arm is movably coupled to a second mold portion. They are movably coupled such that, when the mold is in a closed state, the gripper of the first retaining arm opposes to the gripper of the second retaining arm.
In a particular embodiment the gripper of at least one of the retaining arm(s) defines one or more channels extending through gripper and configured to receive overmolding material.
In a particular embodiment, the mold comprises at least one injection gate. In a further particular embodiment, the mold comprises a plurality of injection gates. In an even further particular embodiment, the injection gates are arranged on or at least near one of the mold portion. In the sense of the present invention, an injection gate is adapted at injecting an overmold material into the mold cavity once the mold is moved into a closed state. For that and, the mold need not be in a completely closed state. That means an injection can already take place when the mold is moving from the open state into a closed state. In a particular embodiment, an injection gate is formed by a recess that is formed by at least two mold portions being the closed position. This can be achieved by equipping the mold portion with respective furrows that are complementary to each other and form a channel for low through of an overmold, once the mold parts are interlocked.
In a particular preferred embodiment of the present invention, the plurality of injection gates is arranged such, that each injection gate is distanced from another injection gate.
In a particular preferred embodiment, the injection gates are arranged, such as to be operated individually.
In a particular embodiment the retaining arms are individually activated. Preferably, they are actuated such that at least one retaining arm is capable of performing a multi-level stroke. In the sense of the present invention, a multi-level stroke can, but need not be a gradual multi-level stroke but can mean that the retaining is capable performing at least two successive strokes. In a preferred embodiment, the at least one drive is chosen from the group consisting of: hydraulic drive, pneumatic drive or electro-mechanical linear actuator. For the purposes of the present invention, a stroke can be defined as at least a linear motion of the thus actuated item which is essentially reversible. Accordingly for the particular embodiment described further above, a multi-level stroke can be defined as the capability of performing at least two, preferably a multitude of successive translational movements. For this purpose the retaining arms can be individually actuated by either a drive capable of performing such a multi-level stroke, or alternatively be actuated by a multitude of drives according to the number of strokes required for the retaining arm. In a device according the present invention, the different ways of actuating a retaining arm can be individual for each retaining arm. This means that retaining arms adapted at performing only one stroke can come paired or simply just appear in the same embodiment as with retaining arms capable of performing a multi-level stroke.
In a particular embodiment of the present invention, the retaining arms are actuated by at least one hydraulic drive, preferably by two hydraulic drives such that the retaining arm in question is capable of performing at least a two-level stroke.
It is thus provided a device with a variety of advantageous embodiments, that is capable of injection molding of a composite material comprising at least one laminate and essentially ensuring, that the laminate surface suffers as little shift during the overmolding as possible, while at the same time being highly customisable in regard to the geometry of the desired form and the placement of the laminate in the mold.
It is evident for a person skilled in the art, that all the above described embodiments can be realised in an execution of the present invention in any combination, as soon as they are not explicitly exclusive. It is further evident for the skilled artisan that many of the embodiments described above providing further advantageous implementations are by themselves facultative for the execution of the basic inventive concept of the present invention.
Another aspect of the present invention is a method for injection molding of a composite material comprising at least one laminate. That method comprises placing a laminate relative to a plurality of mold portions of a mold, where at least one of the mold portions is moveable relative to at least one other of the mold portions, such that the mold is movable between an open state and a closed state in which the molding surfaces of the mold portions cooperate to define a mold cavity. Further the method comprises the step of placing the laminate such that, when the mold is in the closed state, the laminate is at least partially disposed within the mold cavity. The method according the present invention comprises the further step of moving at least one gripper that is moveably coupled to the first side of a respective one of the mold portions into contact with the laminate by moving the gripper between a retracted position and an extended position in which the gripper is further from the molding surface of the respective mold portion than when in the retracted position. The method required further injecting the mold cavity with an overmolding material and moving the grippers from the extended position to the retracted position.
In a particularly embodiment of the present invention, the method requires further the providing of a device as described above.
In a further embodiment of the present method the step of moving the grippers from the extended position to the retracted position is a sequential movement and comprises in particular sequentially moving the grippers from the extended position to the retracted position.
In the sense of the present invention a skilled artisan can define a sequentially moving of the grippers as a movement that begins with one gripper, preferably one inside of the mold closed to an injection gate, and ends after a series of grippers have performed that retracting steps. The sequence need not be in the sequence of arrangement of the injection gates on the mold surfaces. For complex forms, which comprise a variety of cavities and chambers it might be beneficial to start the injection from to opposite sides, additionally from the middle of the mold and sequentially removing the grippers as the overmold reaches the place where the grippers contact the laminate.
In a particular embodiment the method comprises the step of moving the grippers from the extended to the retracted position as the overmold advances during the injection step. In a further particular embodiment, the injection of the overmold is synchronised with the moving of the grippers from the extended position to the retracted position. In a further particular embodiment of the present invention the latter step is also synchronized with closing movements of the mold portion. In an even further particular embodiment, the latter step is synchronized with the actuation of a further stroke of the respective retaining arm on which the gripper in question is affixed.
In an alternative embodiment, the grippers are not sequentially moved from the extended to the retracted position but synchronically.
In a particular embodiment of the matter according to the present invention, a further step is required that comprises applying tension to the laminate. Said tension can be applied by two neighbouring retaining arms, whose strokes can be arranged such as that they move on essentially parallel axes. In the sense of the present invention, an axis is essentially parallel to another one when the angle both axes enclose is not larger than 5 degrees. This deviation might be required to adjust particular geometries of the intended form and is tolerable for applying said tension.
The tension means, in the sense of the present invention, that a force is applied between two points along the laminate which acts in essentially opposed direction, so that the laminate is better adapted at resisting any sheering forces apply during the overmold injection.
In a particular embodiment, the tension in the laminate is applied by using gravity of the laminate. The laminate is first retained in a first set of grippers and let loose on one side, where it is pulled downwards by gravity. Then a second set of retaining arms downstream from the first is extended to retain the hanging part of the laminate. It has been surprisingly found, that this amount of tension resulting from two sets of distanced retaining arms can suffice to significantly reduce shifting of the laminate due to forces from the fluid during the injection molding step. The mold need not be maintained in the same orientation once tension is such applied to the laminate, but can be turned, moved, or otherwise handled.
In a particular embodiment, the overmolding material comprises a thermoplastic material. Injection molding with a thermoplastic material, which essentially receives fluid properties once heat above a certain temperature is known in the art and can easily be adapted to the present invention by a skilled artisan. In an alternative to a purely thermoplastic injection molding, a chemical induced hardening might be used, where a multitude of materials is used that upon contact engage in a chemical reaction hardening the overmold into its final form.
In a further particular embodiment, the overmolding material comprises a plurality of fibres. In a particular example of this embodiment the plurality of fibres can consists of chopped glass fibres.
In a particular embodiment, the injection molding is synchronized with sequentially moving from the extended position to the retracted position of a series of retaining arms as the injected overmold reaches them.
In a further particular embodiment of the present invention, the method comprises moving the at least one gripper out of contact with the laminate to allow overmolding material to flow within the gripper and the laminate. In a preferred embodiment, this step is performed as the overmolding material flow reaches the said gripper. In a particularly preferred method according to the present invention the sequence of retracting the gripper is predetermined and chosen according to the geometry of the mold and the viscosity and fluid dynamics of the injected overmold. In a particular embodiment a steering control is used to perform the required synchronization of injection and retracting of the grippers.
With this method a method for injecting molding a composite material comprising a laminate is provided, which enables the handling of unidirectional fibre composites in various complex mold form. The problem of bulking and shifting and ultimately loss of quality in the resulting mold by sheering forces and material instability of the unidirectional fibres in one direction of force is thus alleviated. For a person of ordinary skill in the art, the above methods steps are evidentially adapted to be performed in any combination to achieve the solution of the present invention, as long as they are not mutually exclusive.
In the following, the present invention shall be illustrated by means of particular examples and schematical illustrations, without being restricted thereto though. For the sake of understanding analogous elements have been provided with same references number in the different schematical drawings.
The drawings show:
To establish full contact with the laminate in a particular embodiment of the present invention shown in
As it becomes easily evident to a person skilled in the art based on the description of
For the production of even more complex forms the mold 2 can be adapted with arrangements and the required retaining arms to suit such geometry.
The arrangement is analogous in the core mold portion 4. There four retaining arms 8, 8′, 8″ and 8′″ each and in an individually shaped gripper 10, 10′, 10″, 10′″ with each and building an individual gripper surface 12′, 12″, 12′″, 12″″. Analogously, each of the retaining arms 8, 8′, 8″, 8′″ are shown as being actuated by a single actuator 13, which has already explained for the cavity mold portion 3 can be replaced by a multitude of actuators for each retaining arm.
The materials used in compass as a laminate a material that has one or more layers of material in itself. For instants a laminate can be unidirectional fibre either continues or uncontinuous that is joined together using a matrix material. Suitable matrix materials are epoxy, resin or other thermoplastic materials. The fibres can comprise layers of carbon fibres, glass fibres, basaltic fibres, fabric, textile, natural fibres or any combination of these types of fibres.
Further details of the grippers are shown in
The same embodiment of
The canals can further help at insuring a flow of overmold material during the injection molding. Further it can help with increasing the grip on the laminate.
Set forth below are some embodiments of the device and method disclosed herein.
Embodiment 1: A device for injection molding of a composite material comprising at least one laminate, the device comprising: a) a mold including: a plurality of mold portions, each having a first side defining a molding surface, and where at least one of the mold portions is movable relative to at least one other of the mold portions, such that the mold is movable between an open state and a closed state in which the molding surfaces of the mold portions cooperate to define a mold cavity; and b) one or more retaining arms with a gripper for contacting the laminate and whereby the retaining arm is arranged such that it is movable between a retracted position and an extended position.
Embodiment 2: The device of Embodiment 1, where at least one of the retaining arm(s) is slidably coupled to the respective mold portion.
Embodiment 3: The device of any of the preceding embodiments, where at least one of the retaining arm(s) includes at least one shaft that is coupled to the gripper and is slidably received by the respective mold portion.
Embodiment 4: The device of any of the preceding embodiments, where, for at least one of the retaining arm(s), the molding surface of the respective mold portion defines a recess configured to receive at least a portion of the gripper when the retaining arm is in the retracted position.
Embodiment 5: The device of any of the preceding embodiments, where, for at least one of the retaining arm(s), the molding surface of the respective mold portion defines a recess configured to receive the gripper when the retaining arm is in the retracted position such that an outer surface of the gripper is substantially flush with a portion of the molding surface that borders the recess.
Embodiment 6: The device of any of the preceding embodiments, where the retaining arms are arranged in pairs, with each retaining arm having an opposite retaining arm, such that the grippers of the pair of retaining arms are adapted at holding a laminate in place.
Embodiment 7: The device of any of the preceding embodiments, comprising at least two retaining arms, whereby a first retaining arm is movably coupled to a first mold portion, and a second retaining arm is movably coupled to a second mold portion, such that when the mold is in the closed state, the gripper of the first retaining arm opposes the gripper of the second retaining arm.
Embodiment 8: The device of any of the preceding embodiments, where the gripper of at least one of the retaining arm(s) defines one or more channels extending through the gripper and configured to receive overmolding material.
Embodiment 9: The device of any of the preceding embodiments, where the mold comprises at least one injection gate, in particular a plurality of injection gates, and further in particular at least one of the mold portions comprises an injection gate.
Embodiment 10: The device of any of the preceding embodiments, whereby the retaining arms are individually actuated, in particular are actuated such that at least one retaining arm is capable of performing a multi-level stroke, the retaining arms being actuated by at least one drive chosen from the group consisting of: hydraulic drive, pneumatic drive or electromechanical linear actuator.
Embodiment 11: The device of Embodiment 10, whereby the retaining arms are actuated by at least one hydraulic drive, in particular by two hydraulic drives such that the retaining arms are capable of performing a two-level stroke.
Embodiment 12: A method for injection molding of a composite material comprising at least one laminate, comprising: in particular, providing a device according to any of the preceding embodiments; placing a laminate relative to a plurality of mold portion of a mold, where: at least one of the mold portions is movable relative to at least one other of the mold portions such that the mold is movable between an open state and a closed state in which the molding surfaces of the mold portions cooperate to define a mold cavity; and the placing the laminate is such that, when the mold is in the closed state, the laminate is at least partially disposed within the mold cavity; and moving at least one gripper that is movably coupled to the first side of a respective one of the mold portions into contact with the laminate by moving the gripper between a retracted position and an extended position in which the gripper is further from the molding surface of the respective mold portion than when in the retracted position, injecting the mold cavity with an overmolding material and moving the grippers from the extended position to the retracted position, in particular sequentially moving the grippers from the extended position to the retracted position.
Embodiment 13: The method of Embodiment 12, comprising applying tension to the laminate inside the mold.
Embodiment 14: The method of any of Embodiment 12 or 13, where the overmolding material comprises a thermoplastic material.
Embodiment 15: The method of any of Embodiments 12-14, where the overmolding material comprises a plurality of fibers.
Embodiment 16: The method of any of Embodiments 12-15, comprising moving the at least one gripper out of contact with the laminate to allow overmolding material to flow between the gripper and the laminate.
Embodiment 17: Use of a device according to any of Embodiments 1-11 for the overmold injection molding of a strand of unidirectional fibre material, in particular a laminate comprising a strand of unidirectional fibre material.
For a person are skilled in the art it is perfectly evident, that all the shown particular embodiments and examples are in no way limiting to the scope of the present invention and you can easily adopt the general disclosure to the particular embodiments, such that further advantages embodiments maybe realised. The present application claims priority to Application No. CH: 00291/16, filed on Mar. 7, 2016, by Georg Kaufmann Formenbau AG, which is incorporated herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 00291/16 | Mar 2016 | CH | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2017/051334 | 3/7/2017 | WO | 00 |
