Patent Application
20190351647
The present application claims priority to U.S. Provisional Patent Application No. 62/674,124 filed on May 21, 2018. The entire disclosure of the foregoing application is hereby incorporated herein by reference.
The present invention relates to the field of composite materials. In particular, the present application relates to thermoplastic composite materials. More specifically, the present invention is directed toward a method and apparatus for forming composite laminates having low porosity.
Composite materials have been used in a wide variety of applications in which the benefit of low weight high strength materials outweigh the cost of the materials. For instance, historically, aerostructures have been formed of lightweight metals, such as aluminum and more recently titanium. However, a substantial portion of modern aircraft is formed from composite materials. A commonly used material in the aerospace industry is carbon fiber reinforced thermoplastic. The known manufacturing processes have the potential for causing porosity, which is the presence of small voids or air pockets in the thermoplastic matrix material. Porosity can adversely affect the mechanical properties of the composite materials. Accordingly, it is desirable to minimize the porosity of a composite laminate.
Porosity can be a concern in applications in which the laminate is being formed on a tool, such as a mold intended to give the laminate a shape. When the laminate is a relatively small flat laminate, the layers can be laid up and then the entire laminate can be heated up under pressure at the same time, thereby reducing porosity. However, when the laminate is laid up over a mold the laminate is formed layer by layer. As a layer is added, the new layer is heated and pressure is applied to fuse to the new layer to the underlying layer(s). In such situations, pressure is only localized rather than being applied to the entire laminate. As such, the potential for porosity in increased.
Accordingly, there is a need for a system for forming low porosity laminates.
In view of the shortcomings of the prior art, according to one aspect, the present invention provides a method and apparatus for producing low porosity composite laminates.
According to one aspect, the present invention provides an apparatus for forming a multi-layer carbon fiber reinforced thermoplastic laminate on a form. The apparatus includes a holder configured to hold a length of carbon fiber reinforced thermoplastic tape and a feeder for advancing the tape from the holder toward an intersection where the tape intersects with the form or the laminate. The apparatus also includes a tape heating device, a compaction device and a laminate heating device. The tape heating device is configured to heat the tape and a top layer of the laminate to a first temperature that is above the melting point of the tape thermoplastic. The tape heating element directs the heat at the intersection across substantially the entire width of tape. The compaction device is configured to apply pressure against the tape adjacent the intersection to fuse the tape with the laminate after the tape heating element heats the tape and the top layer of the laminate to the first temperature. The laminate heating device includes an induction heating device and is spaced apart from the compaction device so that the laminate heating device is positioned so that the laminate heating device heats the laminate without heating the tape being applied to the laminate. The apparatus may also include a drive assembly connected with the tape heating device, compaction device and laminate heating device. The drive assembly may be configured to control the position of the tape heating device, compaction device and laminate heating device to displace the tape heating device, compaction device and laminate heating device along X, Y and Z axes.
According to another aspect, the present invention provides an apparatus for forming a multi-layer carbon fiber reinforced thermoplastic laminate on a form. The apparatus includes a drive assembly and a tape laying assembly. The drive assembly is configured to displace the tape laying assembly along at least two axes. The tape laying assembly includes a feed module a tape heating module, a compaction module and a pre-heating module. The feed module is operable to feed carbon fiber reinforced tape toward the form or onto a top surface of one or more layers of carbon fiber reinforced thermoplastic laid on the form. The tape heating module is configured to heat the tape and the top surface at a point where the tape is laid on the top surface. The compaction module is positioned downstream from the point where the tape heating module heats the tape and the top surface and is configured to apply pressure to the tape to fuse the tape with the top layer. The pre-heating module is positioned upstream from the point where the tape heating module heats the tape and the top surface and the pre-heating module is configured to heat a plurality of the layers on the form prior to the tape being laid onto the plurality of layers.
According to a further aspect, the present invention provides a method for forming a multi-later carbon fiber reinforced thermoplastic laminate The method includes the steps of A) providing a form having a shape and B) feeding a first layer of carbon fiber reinforced thermoplastic material into engagement with the form so that the first layer is a top layer. According to step C) a subsequent layer of carbon fiber reinforced thermoplastic material is fed onto the top layer so that the top layer becomes the second layer and the subsequent layer becomes the top layer. In step D) the top layer and the second layer are heated to a temperature above a first temperature as the top layer is fed onto the second layer. In a step E) pressure is applied to the top layer and the second layer after the step of heating, wherein the pressure fuses the top layer with the second layer. Steps C through E are repeated a plurality of iterations to form a laminate having a plurality of layers. The second layer and layers below the second layer are heated during each iteration before the step of heating the top layer.
According to still another aspect, the present invention provides a method for forming a carbon fiber reinforced thermoplastic laminate including the step of applying a first layer of unidirectional carbon fiber reinforced thermoplastic having a fiber direction in a first direction. A second layer of unidirectional carbon fiber reinforced thermoplastic material is applied onto the first layer, wherein the second layer has a fiber orientation that is transverse the fiber orientation of the first layer. The first and second layers are heated at an intersection that extends across a width of the second layer. Pressure is applied to the first and second layers across the width of the second layer to fuse the second layer with the first layer. A third layer of unidirectional carbon fiber reinforced thermoplastic material have a fiber direction that is transverse the fiber direction of the second layer is applied onto the second layer. The first and second layers are heated after the step of applying pressure to the first and second layers and prior to the step of applying the third layer. Additionally, the second and third layers are heated at an intersection of the second and third layers during the step of applying the third layer. Pressure is then applied to the third layer after the step of heating the second and third layers to fuse the third layer to the second layer.
While the methods and apparatus are described herein by way of example for several embodiments and illustrative drawings, those skilled in the art will recognize that the inventive methods and apparatus for sorting items using a dynamically reconfigurable sorting array are not limited to the embodiments or drawings described. It should be understood, that the drawings and detailed description thereto are not intended to limit embodiments to the particular form disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the methods and apparatus for sorting items using one or more dynamically reconfigurable sorting array defined by the appended claims. Any headings used herein are for organizational purposes only and are not meant to limit the scope of the description or the claims. As used herein, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including, but not limited to.
The foregoing summary and the following detailed description of the preferred embodiments of the present invention will be best understood when read in conjunction with the appended drawings, in which:
Referring now to the figures in general, a system for forming a composite laminate is designated generally 10. The system 10 is an automated tape laying machine designed to lay a composite laminate on a form 5 so that the composite laminate conforms to the shape of the form. The form may any of a variety of elements, including, but not limited to a mold or a mandrel. Additionally, the form may be a plate so that the laminate is generally planar. The tape laying machine includes a control arm 20 and a tape laying head 30 connected with the control arm. The control arm 20 is moveable to displace the tape laying head 30. The control arm 20 repeatedly displaces the tape laying head 30 to lay a series of layers onto the form 5 to build up the laminate layer by layer.
The tape laying head 30 is configured to lay any of a variety of composite materials. However, in the present instance, the head is configured to lay down carbon fiber reinforced thermoplastic material. In particular, the head 30 is configured to handle strips of carbon fiber reinforced thermoplastic material. The strips may be any of a variety of widths. For instance, the width of each strip may be as narrow as ¼″ or as wide as 6 or 12″. Accordingly, the tape laying head is not limited to include any particular composite material or any particular width of material. Accordingly, in the following description, although the head 30 is referred to as a tape laying head, the term as used herein is defined broadly enough to include any system for laying down carbon fiber reinforced composite materials, including, but not limited to systems referred to as automated tape laying heads or automated fiber placement heads.
Referring to
It should be understood that the form 5 may have any of a variety of shapes. Although the form 5 is illustrated as a flat panel for clarity of the illustrations, the form may be any of a variety of shapes and sizes. The form may be concave so that the strips are deposited into the form to create a convex laminate. Similarly, the form may be concave so that the strips are laid over the form to create a concave laminate. In this way, the finished laminate may have a complex three-dimensional geometry. For instance, the laminate may be used in a variety of structures in a variety of fields and may have particular application in the field of aerospace to provide a variety of components, including, but not limited to airframes, nacelles and airfoils, such as wings, elevators etc.
The system 10 the control arm 20 and the tape laying head 30. The head 30 includes a tape heating module 60 for heating the tape as it is applied to the laminate and a compaction module 50 for applying pressure to the tape to fuse the tape with the laminate. Additionally, the tape laying head 30 includes a laminate heating module for heating the laminate prior to depositing a new layer of tape onto the laminate. By heating the laminate prior to applying the new layer, the compaction module is able to compact multiple layers of the laminate, thereby minimizing the presence of gas pockets throughout the laminate to reduce the laminate's porosity.
The control arm 20 may be any of a variety of moveable systems designed to move the tape laying head 30. For instance, the control arm 20 may comprise a multi-arm linkage configured to provide three degrees of freedom of translator motion and three degrees of freedom of rotation motion. However, the control arm may provide fewer degrees of freedom of motion. In this way, the control arm is operable to control the position and orientation of the tape laying head 30. Additionally, although the control arm 20 is illustrated as a multi-bar linkage, the control mechanism may incorporate alternate structures, such as a rail or a gantry. Accordingly, the control arm 20 can be any structure connected with the tape laying head that provides for the controlled displacement of the tape laying head. The system also includes an electronic controller configured to control the operation of the control arm to control the position and orientation of the tape laying head. For instance, the controller may be a microprocessor programmed to control the operation of the control arm. The controller may also be configured to control operation of the tape laying head as the control arm moves the head. For instance, the controller may be configured to control the displacement of the tape laying head so that the head follows a predetermined path when laying down a series of lengths of carbon fiber reinforced thermoplastic material.
As noted previously, the system 10 is operable in connection with a plurality of materials. However, in the particularly suited for forming laminates of a plurality of layers of carbon fiber reinforced thermoplastic materials. A variety of such materials can be used. Depending upon the application, the reinforcing elements may be any of a variety of reinforcing materials. By way of example, the reinforcing elements may be elongated strands or fibers of glass or carbon, however in the present instance the reinforcing elements are conductive materials, such as carbon fiber. For instance, an exemplary carbon fiber is a continuous, high strength, high strain, PAN based fiber in tows of 3,000 to 12,000. In particular, in the present instance, the reinforcing elements are carbon fibers produced by Hexcel Corporation of Stamford, Conn. and sold under the name HEXTOW, such as HEXTOW AS4D. These reinforcing fibers may be treated with a surface treatment and may be sized to improve its interlaminar shear properties with the matrix material. However, it should be understood that these materials are intended as exemplary materials; other materials can be utilized depending on the environment in which the laminate is to be used.
The reinforcing elements are embedded within a matrix material, such as a polymer. Depending on the application, any of a variety of polymers can be used for the matrix material, including amorphous, crystalline and semi-crystalline polymers. In the present instance, the matrix material is a thermoplastic material, such as a thermoplastic elastomer. More specifically, the thermoplastic material is a semi-crystalline thermoplastic. In particular, the thermoplastic may be a thermoplastic polymer in the polyaryletherketone (PAEK) family, including, but not limited to polyetheretherketone (PEEK) and polyetherketoneketone (PEKK).
As noted above, the material laid by the tape laying head may be carbon fiber reinforced thermoplastic composites. In particular, the lamina may be thermoplastic prepregs, which are laminae in which the reinforcement materials have been pre-impregnated with resin. For instance, the prepreg may be thermoplastic prepregs produced by coating reinforcement fibers with a thermoplastic matrix. Such a prepreg lamina has the ability to be reheated and reformed by heating the lamina above the melting point of the thermoplastic matrix. Several exemplary prepreg materials that may be used to form the structural elements 25, 26 include, but are not limited to, materials produced by TenCate Advanced Composites USA of Morgan Hill, Calif. and sold under the name CETEX, such as TC1200, TC1225 and TC1320. TC1200 is a carbon fiber reinforced semi-crystalline PEEK composite having a glass transition temperature (Tg) of 143° C./289° F. and a melting temperature (Tm) of 343° C./649° F. TC1225 is a carbon fiber reinforced semi-crystalline PAEK composite having a Tg of 147° C./297° F. and a Tm of 305° C./581° F. TC1320 is a carbon fiber reinforced semi-crystalline PEKK composite having a Tg of 150° C./318° F. and a Tm of 337° C./639° F.
In the following discussion, the composite material being laid by the tape laying head 30 will be referred to as tape, which as discussed above includes any length of composite material regardless of the width of the material.
The system 10 includes a tape storage module 40 for storing a supply of tape 35 that is to be fed to the tape laying head 30. For instance, the system 10 may include a reel or spool 42 and the tape 35 may be wound or coiled around the reel. The storage reel 42 may be connected with the tape laying head 30 so that the reel moves along with the head as shown in
The number of structural plies and the orientation of the plies in the laminate may vary depending on the application. It should be understood that the number of plies, the orientation of the plies, as well as the number and location of the insulating layers 60 are only an example; the invention is not limited to the lay-up illustrated in this exemplary laminate.
The laminate includes a plurality of structural layers designated 102, 105, 106 and 107 in
It should be noted that the thickness of the layers in the Figures are not to scale and in some instances the thickness is exaggerated for illustration purposes only. For instance, in
The details of the tape laying head will now be described in greater detail. As noted above, the system may include a storage module 40 for storing a length of tape 35 and the storage module 40 may be part of the tape laying head 30 or it may be a separate element. The tape 35 is fed from the storage reel 42 through a series of guide elements and deposited at a discharge nip 55. At the discharge nip the tape is laid onto an underlying structure. In most instances, the underlying structure is either the form 5 or a previously laid layer of composite material.
As shown in
From the drive roller 48, the tape 35 advances toward the form 5 if the tape forms the first layer, or the top layer 105 of the laminate 100 if one or more layers have already been deposited or laid on the form. The point where the tape first comes into contact with the form or the top layer 105 of the laminate is referred to as the intersection and in the present instance the intersection is at or adjacent the nip 55 formed between the compaction roller 52 and the form or the laminate.
The tape laying head 30 include a tape heating module 60 for heating the tape 35 at the intersection of the tape and the form or the laminate. In particular, the tape heating module is configured to direct a heat source at the intersection to heat both the tape 35 and the top layer 105 of the laminate. In particular, the tape heating module is configured to rapidly heat the tape and the top layer of the laminate to a temperature at or above the melting point of the matrix material of the tape. For instance, as described above, the tape may have a thermoplastic resin, such as PEEK, so the tape heating module may heat the tape and the top layer of the laminate to a temperature over 650° F.
Since the tape is moving, the tape heating module provides a concentrated heat source focused on a small area at the intersection of the tape and the top layer 105. The small area at the intersection at which the heat is directed is referred to as the welding zone 67. The weld zone 67 extends across the entire width “w” of the tape 35. The tape heating module is configured to provide focused heat simultaneous across the entire weld zone to melt the tape and the top layer across the width of the tape and across a width of the top layer corresponding to the width of the tape. In particular, in
The tape heating module may incorporate any of a variety of heating elements operable to provide a focused heat source. For instance, heating elements such as hot gas heaters, flames, ultrasonic, infrared or induction heaters may be used to heat the tape in the weld zone. However, in the present instance, the tape heating module incorporates a laser heating assembly. For example, an exemplary laser heating module may comprise a plurality of laser diodes disposed in one or several rows, such as laser diodes that emit radiation having a wavelength of between 880 and 1030 nm. An exemplary laser heating assembly is a fiber coupled diode laser having two stacks, such as the LDF 6000-100 6,000 watt laser manufactured by Laserline Inc. of Santa Clara, Calif. Alternatively, the laser heating module may incorporate an optical fiber laser or a YAG laser. Accordingly, it should be understood that the tape heating module may include any of a variety of heating elements configured to provide focused heat.
As noted above, in the present instance, the laser heating assembly provides a focused high intensity laser operable to provide a sheet of heat 65 focused on the weld zone 67. In this way, the tape heater rapidly heats the portion of the top layer 105 and the tape 35 adjacent the nip 55 so that the tape and the top surface have reached the melting point of the thermoplastic before the tape and the top layer pass under the compaction module 50. The tape laying head 30 moves relative to the laminate, so the tape and the top layer of the laminate are heated as the tape is being laid on the top layer of the laminate. In this way, the speed at which the tape can be laid is limited by the speed at which the tape heating module can heat the tape and the top surface of the laminate to the temperature need to melt the thermoplastic resin in the tape and the laminate to fuse the tape to the top layer of the laminate. Accordingly, it is desirable to configure the tape heating module so that the heating element is able to elevate the material in the weld zone to the melting temperature in a short period of time. In particular, the tape heating module 60 is configured to heat the material in the weld zone to over 650° F. in less than a second. Further still, the tape heating module may be configured to heat the material in the weld zone to over 650° F. in less than 0.5 seconds and in some instance the tape heating module may be configured to heat the material in the weld zone to over 650° F. in less than 0.1 seconds.
The tape laying head 30 also includes a compaction module 50 positioned adjacent the weld zone 67. The compaction module 50 is configured to apply pressure to the newly applied tape and the top layer of the laminate 100 below the newly applied tape. The compaction module may incorporate any of a variety of elements for applying pressure to the tape as the tape is fed under the compaction module. For instance, the compaction module may a plate, fence or guide, such as a rounded guide. In the present instance, the compaction module includes a roller 52 that extends across the width of the weld zone 67. For example, as shown in
The compaction module 50 also includes a biasing element 58 for biasing the compaction roller 52 toward the form 5 or the laminate. The biasing element provides the downward force against the tape 35 and the laminate to provide the requisite pressure for fusing the tape with the top layer of the laminate. The biasing element 58 provides sufficient force to provide pressure along the entire weld zone 67. The biasing element may be any of a variety of elements, including but not limited to hydraulic, pneumatic, elastomeric and spring elements.
The tape laying head 30 may also include a cutting device 49 for severing the tape 35 as the tape is advanced along the path toward the nip 55. The cutting device 49 may be any of a variety of elements configured to sever a length of carbon fiber reinforced thermoplastic tape, including, but not limited to mechanical knives, shears, ultrasonic knife and lasers.
To improve compaction and reduce porosity, the tape laying head also includes a pre-heating module 70 for heating the laminate 100 before the tape 35 is laid onto the laminate. In particular, the pre-heating module is configured to be able to rapidly heat at least several layers of the laminate prior to the laminate being compacted by the compaction module 50. In the present instance, the pre-heating module 70 includes an induction heating head in the form of an induction coil 72. The coil 72 provides an electromagnetic field 75 and a flux concentrator 74 focus the electromagnetic field to provide inductive heating in the laminate. In particular, the inductive heater 70 heats the top layer 105 and one or more of the lower layers 106, 107 by electromagnetic induction, through heat generated by eddy currents. The pre-heater includes an electronic oscillator that passes a high-frequency alternating current through an electromagnet. The rapidly alternating magnetic field then penetrates the laminate to generate the eddy currents which in turn heat the top layer 105 and one or more layers below the top layer.
In this way, the pre-heating module 70 is configured to heat the laminate including at least one or more layers below the top layer and up to all of the layers in the laminate before the tape 35 is laid onto the laminate. By using an induction heating element, the pre-heater 70 directly heats one or more layers below the top layer 105 rather than applying heat to the top layer that then conducts through the layers.
An induction welding head 100 is then brought into operative engagement with the laminate to induce an electromagnetic field through the thickness of the laminate. In particular, the induction welding head 100 travels over the top surface of the laminate. The weld head need not contact the upper surface; however, the weld head is sufficiently close to the top surface of the laminate to induce an electromagnetic field through the thickness of the laminate having sufficient strength to weld the bottom layer 58a and the connecting element 39.
In the present instance, the weld head induces an electromagnetic field through the laminate and the connecting elements, so that the adjacent layers having transverse carbon fibers heat up in response to the electromagnetic field. In particular, in the present instance, the electromagnetic field produced by the preheater 70 is sufficient to heat the top layer 105 and one or more of the layers beneath the top layer. In the present instance, the coil 72 induces an electromagnetic field through the entire thickness of the laminate including layers 105, 106 and 107. However, it should be understood that the pre-heater may be configured and positioned to heat more than three layers. Similarly, the induction heater may be configured and positioned to heat only a few of the layers of the laminate rather than heating the entire laminate. In either instance, the layers are considered to be heated when the layer is heated to a temperature above the melting point of the resin that forms the matrix material for the layer. For instance, the matrix material may be PEEK material and the layer is considered to be heated if the pre-heater 70 heats the layer to a temperature above approximately 650° F. The pre-heater may be configured so that part of the electromagnetic field 75 extends into layers so that there is some heating effect on the layers but not sufficiently to heat the layer above the melting point of the matrix for the layer. Such a rise in temperature is not considered to be heated for purposes of this process.
A shown in
The details of forming a laminate 100 will now be described. Referring to
A plurality of layers of carbon fiber reinforced thermoplastic tape are laid over top of one another to form a plurality of plies that are structural layers. The fiber orientation in the plies may be varied and insulating plies may be positioned in the interface of plies having transverse fiber orientations. For example, the layers may be formed of five structural plies oriented at 90°, 0°, 45°, 0°, 90°. In this exemplary laminate, the carbon fiber layers of the structural layers are formed of PEEK/AS4 carbon fiber reinforced unidirectional tape.
The structural are consolidated to form a laminate by heating the assembled plies under pressure. For instance, the assembly may be heated up to a temperature above the melting temperature. In the present instance, the assembled layers are heated to approximately 725° under a pressure of approximately 100 psi. The consolidated laminate is then cooled to ambient temperature.
The laminate is formed by an additive process of laying down carbon fiber tape piece by piece to build up a plurality of layers. In
Referring to
While laying the fourth layer 102, the control arm 20 displaces the tape laying head along a path to lay one or more lengths of tape 35 onto the top layer 105 so that the fiber orientation of the fourth layer is transverse the fiber orientation of the top layer 105. The pre-heating module is actuated as the tape laying head 30 is moved over the top layer 105. The pre-heating module 70 induces an electromagnetic field through the laminate, so that the adjacent layers having transverse carbon fibers heat up in response to the electromagnetic field. In particular, in the present instance, the electromagnetic field produced by the heating head is sufficient to heat the top layer 105 and lower layers 106, 107 above the melting temperature of the thermoplastic matrix material in the layers. Further, the pre-heating module extends across the entire width of the tape so that the pre-heating module heats the portion of layers 105, 106 and 107 corresponding to the width of the tape being laid. The head lays the tape 35 onto the heated laminate and the tape heating module 60 heats the tape and the top layer 105 in the weld zone 67. The tape heating module may heat the tape and the upper layer 105 to a temperature higher than the temperature that the pre-heating module heats the laminate.
From the weld zone, the tape and the laminate pass under the compaction roller 52. The roller applies pressure against the newly laid tape to press the new tape against the top layer 105 to fuse the tape onto the top layer so that the tape become the new top layer 102. The pressure applied by the compaction roller compacts the layers in the laminate that were heated above the melting point. In particular, the pressure of the compaction module is applied across the width of the tape and the force is applied to all of the layers below the tape. The pressure squeezes the layers together and the layers that were heated to a temperature above the melting point of their matrix material are free to flow under the pressure. Additionally, the pressure operates on the melted layers to squeeze gas pockets that may remain within the melted layers to transport the gas pockets out of the laminate to reduce voids in the matrix material.
In accordance with the following process, the control arm moves in a direction, such as direction “A” indicated in
It will be recognized by those skilled in the art that changes or modifications may be made to the above-described embodiments without departing from the broad inventive concepts of the invention. It should therefore be understood that this invention is not limited to the particular embodiments described herein, but is intended to include all changes and modifications that are within the scope and spirit of the invention as set forth in the claims.
| Number | Date | Country | |
|---|---|---|---|
| 62674124 | May 2018 | US |
