Patent Application
20170189958
The present invention relates to fabrication of a composite material. In particular, the present invention relates to a method and a machine for manufacturing of a micro/nanofiber based composite material.
Composite films consisting of a micro- and/or nanofibrous film and an infiltrated metal matrix can be manufactured to have advantageous thermal and mechanical properties. In particular, such thermally conducting films may be used at the interface between two surfaces to facilitate thermal transport. One interesting application area concerns high performance microelectronic components where efficient cooling of components is essential. A thermally conductive film may then be placed between the active component and a cooling device, or between a chip and a heatspreader/lid, to facilitate heat conduction away from the component.
However, at the present time, it is difficult to infiltrate materials into films consisting of micro and nanofiber films. This is due to the high pressure required to penetrate small pore sizes. It is particularly difficult to form composites which are void free, when there is a large difference in surface energy between the fibers and the metal/alloy matrix material, such as carbon based fibers with metal/alloy matrix, or polymer based fibers with metal/alloy matrix.
Existing continuous processes based on lamination techniques cannot achieve sufficient pressure to infiltrate the small pores of micro and nanofiber based films, and result in unwanted pores.
In order to provide such composite materials, a commercially viable process for the infiltration of micro and/or nanofiber networks with metallic/alloy matrix materials is desirable.
In view of the above-mentioned desired properties of infiltration of nanomaterials, and the above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide an improved method and apparatus for manufacturing of an infiltrated fiber-based composite film.
According to a first aspect of the invention, it is therefore provided an apparatus for manufacturing of an infiltrated fiber-based composite film. The apparatus comprises: two tool blocks arranged opposite each other enabling a fiber-based film to be arranged between the tool blocks, wherein at least one of the tool blocks comprising a recess; wherein at least one of the tool blocks is movable towards the opposing tool block such that the recess form a sealed cavity configured to enclose a portion of the film when the tool blocks are in contact with each other; and wherein at least one of the tool blocks comprises: a vacuum channel in a first end connected to the recess and in a second end connectable to a vacuum pump for drawing a vacuum in the cavity; a melt channel in a first end connected to the recess and in a second end connected to a source of molten material; the melt channel comprising a valve arrangement configured to control delivery of the molten material to the cavity; pressure means configured to achieve an elevated pressure within the cavity such that a fiber film in the cavity is infiltrated by the molten material; and an ejection piston configured to eject an infiltrated fiber film from the cavity, when the tool blocks are in a retracted position spaced apart from each other.
The tool blocks are movable towards each other, either by moving only one of the tool blocks towards the other or by moving both tool blocks towards each other. Accordingly, one or both of the tool blocks may comprise a recess forming the cavity when the tool blocks are pressed together. The tool blocks may for example be moved by means of one or more actuators. Furthermore, the tool blocks may comprise inserts which define the recess. If inserts are used, the inserts may be removable so that the size and geometry of the recess determining the configuration of the cavity may be easily varied in the apparatus by changing inserts.
The apparatus according to embodiment of the present invention allows for sequential manufacturing of a composite film consisting of a micro/nanofiber-based film infiltrated with a metal-based matrix, thereby enabling a more efficient manufacturing method. Moreover, the apparatus enables uniform and complete infiltration of the molten material into the fiber film to achieve advantageous composite properties.
According to one embodiment of the invention, the recess may have a depth in the range of 5 to 500 micrometers to enable manufacturing of infiltrated films having a corresponding thickness.
According to one embodiment of the invention, the valve arrangement may advantageously comprise a channel valve configured to control the delivery of molten material from the source to the melt channel and an injector valve configured to control the delivery of molten material from the melt channel to said cavity. Thereby, the amount of molten metal to be delivered to the cavity can be controlled by the channel valve, and the injector valve controls the injection of molten metal into the cavity.
In one embodiment of the invention, the pressure means are advantageously configured to provide a pressure within the cavity higher than 30 MPa. Such a pressure will act to force the molten material into the pores of the film so that the film is fully infiltrated. The force pressing the two tool blocks towards each other must be controlled so that the cavity remains sealed also when the high pressure is applied to the cavity in order to avoid any leakage from the cavity during infiltration.
According to one embodiment of the invention, the pressure means may advantageously comprise an injector piston connected to the melt channel such that the molten material is infiltrated at an elevated pressure into the fiber film in the cavity by means of actuation of said injector piston. The injector piston, actuated by a suitable actuator enables application of sufficiently high pressure onto the molten material to achieve infiltration of the molten material into the film.
In one embodiment of the invention, the tool block and/or the tool inserts may advantageously comprise a heater configured to heat the cavity to a temperature exceeding a melting temperature of the molten material. By heating the cavity prior to injection of the molten metal, the metal will not solidify in the cavity which enables the infiltration. The heater may advantageously comprise one or more heating elements having an effect of several kW.
According to one embodiment of the invention, the tool block may advantageously comprise cooling means configured to cool the cavity to a temperature lower than said meting temperature of said molten material after injection of the metal and infiltration of film. Through the cooling means, the infiltrated film can be rapidly cooled down so that the metal solidifies enabling the infiltrated film to be removed from the cavity. This improves the cycling time thereby providing a faster manufacturing process. Heating and cooling the cavity should in the present context be understood as heating and cooling the portions of the apparatus forming the cavity, such that any material, i.e. film and/or metal, located in the cavity is heated or cooled.
In one embodiment of the invention, the cooling means may advantageously comprise a cooling channel containing a fluidic cooling medium such as oil or water. Preferably, cooling channels and heating elements are provided to enable process cycle times less than 3 minutes. The cycle time is preferably as short as possible to provide an efficient process. In general, the cycle time is related to the heating and cooling capabilities of the apparatus.
According to one embodiment of the invention, the molten material may advantageously be selected from the group comprising SnAgCu, Sn, SnBi, SnBiAg, SnZn, In, BiSnAg, and eutectic InSnBi.
According to one embodiment of the invention, the each tool block may advantageously comprise a recess, and the tool blocks may thus be arranged such that the recesses face each other so that a cavity is formed when the two tool blocks are pressed together.
In one embodiment of the invention, there is provided an assembly for reel-to-reel manufacturing of an infiltrated fiber-based composite film. The assembly comprises an apparatus according to any one of the embodiments discussed above, a micro/nanofiber film, a storage reel holding the film, and a collecting reel configured to receive the film. The film is arranged between the storage reel and the collecting reel such that a path of the film from the storage reel to the collecting reel runs between the tool blocks. Through the above discussed assembly reel-to-reel manufacturing is enabled meaning that an entire roll of infiltrated film preforms may be sequentially manufactured without interruptions. In such a process, the film is unwound from the storage reel and passed through the tool and then stored on the collecting reel.
According to one embodiment of the invention, the micro/nanofiber film may advantageously comprise fibers selected from the group comprising polyimide, polyurethane, polyacrylonitrile, polyaramid, high density polyethylene, PEEK, Kevlar, polyester, boron nitride, carbon fibers, carbon nanotubes, inorganic fibers and graphene coated fibers. Microfibers refer to fibers having a diameter on the order of micrometers, and nanofibers refer to fibers having a sub-micrometer diameter.
In one embodiment of the invention, the film may advantageously have a surface which is modified to facilitate wetting of the molten material to the film. In particular, the fibers of the film may be coated with Ag, Cu, Au, Ni, Pd, Ti and/or Pt or a combination thereof.
According to a second aspect of the invention, there is provided a method for reel-to-reel manufacturing of a composite film, consisting of a micro/nanofiber-based fiber film with a metal-based matrix, the method comprising the steps of; arranging micro/nanofiber-based film between a storage reel holding the film and a collecting reel receiving the film; enclosing a portion of the film in a cavity formed by pressing together a first and a second tool block arranged opposite each other, wherein at least one of the tool blocks comprises a recess forming the cavity; providing a molten material to the cavity; elevating a pressure onto the molten material such that a fiber film in the cavity is infiltrated by the molten material; and cooling the cavity to a temperature below a melting temperature of the molten material; and releasing the composite film by moving apart the tool blocks. The infiltrated portion of the film is then ejected it using an ejection mechanism.
Effects and features of this second aspect of the present invention are largely analogous to those described above in connection with the first aspect of the invention.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.
These and other aspects of the present invention will now be described in more detail with reference to the appended drawings showing an example embodiment of the invention, wherein:
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person. Like reference characters refer to like elements throughout.
The invention relates to a process for making complete and uniform infiltration of a metal/alloy matrix material into films of continuous micro and/or nanofibers. More specifically, this invention relates to the process and tool for forming such composite in a reel-to-reel production.
The film that is infiltrated in the described process can comprise continuous micro and/or nanofibers made of a polymeric, boron nitride or carbon based composition. The film can be formed through, but not limited to, an electrospinning process, followed by additional processes such as nitration or carbonization. Typically the films have a porosity of 60±20%, a total thickness of 5-200 μm, and are made from fibers with diameters of 100 nm-15 μm. The film can also have an additional layer such as a thin coating on the fibers to facilitate the wetting of the molten material, which can be formed through both dry and wet deposition techniques, such as CVD, sputtering, electroplating, and electroless plating. In an example embodiment the reel/spool/roller 124 is carrying a 30 meter long continuous film of continuous polyimide submicron fibers coated with Ag particles. Movement of the film from the storage reel 124 to the collecting reel is controlled by a motor.
In one embodiment, the tool blocks 102a-b are made from aluminum alloy, and incorporate electrical heating elements with several kW heating effect, channels for oil cooling, and with a geometry that allows an ejection piston. The tool blocks 102a-b comprises insert blocks 128a-b made from stainless steel, having polished surfaces and a cavity of a geometry that corresponds to the desired geometry of the final composite film. The tool blocks and tool inserts have channels connected to an injection piston 116 which can push liquid melt into the tool insert cavity with high pressure.
First 202, the tool blocks 102a-b closes around the film 106 with a sufficiently high locking force and the recesses 104a-b forms a cavity 150 which is sealed in part by the film itself and in which cavity a portion of the film is in a non-compressed state
Next, 204, the vacuum valve 120 is opened and the vacuum pump 118 is activated to draw vacuum in the cavity. The vacuum valve 120 is then closed.
After vacuum is formed in the cavity, heating elements heats 206 the tool blocks 102a, 102b and in particular the inserts 128a, 128b so that the temperature in the parts forming the cavity reaches a temperature of 247° C., which is 30° C. higher than the melting temperature of the metal to be used, in this example a SnAgCu alloy.
Next 208, the channel valve 112 is opened to allow molten metal to flow from the molten metal container 108 into the melt channel 110. The channel valve 112 is open until the melt channel 110 is filled. Filling of the melt channel may include retracting the injector piston 116 to facilitate additional filling of molten metal in the channel system. The melt channel 110 may also be fully or partially filled with a molten material from a previous cycle. The heating elements for heating the cavity are thus arranged to also ensure that the melt channel is sufficiently heated to enable a flow of molten material through the channel.
After delivery of molten metal to the melt channel 110, the injector valve 114 is opened so that the molten metal flows into the cavity 150, helped by the vacuum in the cavity 150, to fill 210 the cavity and to enclose the film. After filling of the cavity, the channel valve 112 is closed.
In the next step 212, a high pressure, typically above 30 MPa, is applied by the injection piston (116) to force infiltration of the melt metal/alloy matrix material into the pores of the film. The force applied on the injection piston is then reduced and the injector valve is closed.
After infiltration of the film, the tool blocks and inserts are cooled 214 down to a temperature of about 187° C., which is 30 degrees below the melting point of the SnAgCu alloy, by flowing oil in the cooling channels in the tool, the tool inserts and ejection piston 122.
Once the cavity and the film therein has reached the target temperatures, the tool blocks 104a-b are moved apart and the infiltrated portion of the film is ejected 216 by the ejection piston 122. After ejection of the film, the film may be moved a distance and a new film portion may be infiltrated by restarting the cycle.
Through the above described method consecutive portions of the film can be sequentially infiltrated in an efficient manner. If reel-to-reel production is undesirable, the apparatus 100 may equally well be used for infiltration of individual pieces of film.
Even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. For example, the channels and valves may be arranged in a different manner, while still achieving the same effect as the above described apparatus. Also, it should be noted that other parts of the system may be omitted, interchanged or arranged in various ways, the apparatus yet being able to perform the functionality of the present invention.
Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2014/060567 | 5/22/2014 | WO | 00 |
