Patent Publication Number: US-7591299-B1

Title: Continuous metal matrix composite manufacture

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 60/525,838, filed Dec. 1, 2003. 
    
    
     This invention was made with Government support under contract number DAAD 19-01-2-0006 awarded by the Army Research Laboratory. The Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to metal matrix composites and more particularly to methods and apparatus for the manufacture of aluminum matrix composites. 
     BACKGROUND OF THE INVENTION 
     The next generation of high technology materials for the use in, for example, aerospace and aircraft applications will need to possess high temperature capability combined with high stiffness and strength. Plates and shells fabricated from laminated composites, as opposed to monolithic materials provide the potential for meeting these requirements and thereby significantly advancing the designer&#39;s ability to meet the required elevated temperature and structural strength and stiffness specifications while minimizing weight. 
     Laminated composites of these types generally comprise relatively long lengths, preferably continuous throughout their length, of a reinforcing fibrous material such as a ceramic, carbon, and the like, in a matrix of a metal such as aluminum. 
     Currently, the metal matrix materials, so called prepegs, that form the basis for these laminated systems are very expensive to produce, and, in some cases of variable properties along the length of the laminate, both of which conditions have inhibited their proliferation and use in the aforementioned applications. 
     Accordingly, it would be highly desirable to have methods and apparatus for the manufacture of such metal matrix composite prepeg materials that is reliable, relatively inexpensive and produce a consistent product with the properties desired by aerospace and aircraft designers. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for the production of long lengths of continuous-fiber metal matrix composite prepeg ribbon or tape. The tape or ribbon is produced by the bringing together multiple fiber tows into a formed bundle of fibers and infiltrating the bundle with metal using a continuous pultrusion process. Pultrusion is a preferred method of tape or ribbon manufacture since it places the fibers in tension during manufacture and avoids subsequent issues associated with buckling stress. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the metal matrix tape or ribbon fabrication apparatus of the present invention. 
         FIG. 2  is a perspective view of the puller section of the fabrication apparatus of the present invention. 
         FIG. 3  is a perspective view of the creel section of the metal matrix tape or ribbon fabrication apparatus of the present invention. 
         FIG. 4  is a perspective view of the infiltration section of the metal matrix tape or ribbon fabrication apparatus of the present invention. 
         FIG. 5  is a partially cutaway front view of the infiltration section of the metal matrix tape or ribbon fabrication apparatus of the present invention. 
         FIG. 6  is a detailed cutaway view of the tape handling portion of the infiltration section of the metal matrix tape or ribbon fabrication apparatus of the present invention. 
         FIG. 7  is a front view of the puller section depicted in  FIG. 2 . 
         FIG. 8  is an end view of the puller section depicted in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a method for the production of long lengths of continuous-fiber metal matrix composite prepeg ribbon or tape. The tape or ribbon is produced by bringing together multiple fiber tows into a formed bundle of fibers and infiltrating the bundle with metal during a continuous pultrusion process. Pultrusion is a preferred method of tape or ribbon manufacture since it places the fibers in tension during manufacture and avoids subsequent issues associated with buckling stress. 
     The feedstocks or input materials for the production of metal matrix prepeg tapes or ribbons in accordance with the methods and in the apparatus described herein, comprise a metallic matrix material such as, in the instantly preferred case, aluminum and any of a broad variety of variety of long, continuous fibers of materials such as glass, ceramics, carbon, and the like, some of which are commonly known and to one extent or another have been incorporated into metal matrix tapes or ribbons with varying degrees of success in terms of process efficiency and the properties of the finished tape or ribbon product. It is the fibers that provide the high strength component of the material system and the matrix metal that which serves to hold the fiber bundle together and transfer the load to the fibers uniformly. Among the preferred fibrous reinforcing material are Nextel 610™ alumina (Al 2 O 3 ) commercially available from the 3-M Corporation, and various glass fibers that are supplied in long continuous lengths as strength enhancement reinforcers. 
     The fibrous input materials are commonly, and in the instant process similarly, supplied in a form referred to as roving or tow. A tow is simply an untwisted bundle of continuous filaments that form a long continuous fiber in their combined, but untwisted from. Typically, a tow would contain between several hundred up to tens of thousands of individual filaments, depending upon the composition of the tow, the desired strength/stiffness of the tape or ribbon etc. A tow is wound onto spools in much the same fashion that thread is wound onto a spool for sewing. A given spool of fiber typically contains several thousand feet of continuous fibrous material. 
     The matrix metal may be purchased commercially in any of a number of forms such as ingot, billet, pig, and the like, and is melted in a suitable furnace as described below for purposes of infiltration of the tow, also described below. 
     Referring now to  FIG. 1 , apparatus  10  of the present invention comprises a creel  12 , an infiltration section  14  and a puller  16 . Each of these apparatus sections will be described separately and in detail and then the relationships between and among the individual elements defined and the operation of the apparatus described. 
     As best seen in  FIGS. 1 and 3 , creel  12  comprises a vertical frame  18  having a series of vertical and horizontal rows of spools  20  rotatably mounted thereon via their engagement with shafts  22  that are fixed to frame  18  in the rowed arrangement shown in  FIGS. 1 and 3 . Spools  20  contain continuous fiber tow  21  wrapped thereon (best seen in  FIG. 1 ). The tension applied to each of spools  20  is controlled by an individual spool tensioning device (not specifically shown) that may, for example comprise a magnetic clutch or the like. Such devices are well known in the art and well within the skill of the skilled artisan to fabricate and incorporate into creels of the type described herein. Tensions on the order of from about 10 to about 100 grams have been found satisfactory in the tape or ribbon fabrication process described herein. Also mounted on frame  18  are creel payout boards  24  having apertures  26  therein. Due to the manner in which tow fiber  21  is wound onto spools  20 , there is a traversing action as tow  21  is pulled off of spools  20 . In other words, the payout traverses back and forth from one end of spools  20  to the other. To eliminate the effects of this traversing action on the infiltration process described hereinafter, tow  21  is sent through a payout board  24  located several feet in front of spools  20 . This gives the individual tows  21  a consistent starting point as they enter the balance of the process. The outer periphery of apertures  26  is preferably lined or coated with a suitable abrasion resistance material such as ceramic, for example silicon carbide, boron nitride and the like that resists abrasion by the fibrous reinforcing material that is fed therethrough as described below. Creel payout boards  24  and accordingly apertures  26  are mounted perpendicular to the direction of travel of tow  21  as it travels through apparatus  10  as shown in  FIG. 1  and described below. 
     As tow  21  passes through individual apertures  26  in a single creel payout board  24  or through a multiplicity of apertures  26  in a plurality of payout boards  24 , the individual tows are aligned in the direction of infiltration section  14 . 
     Before actual entry into infiltration section  14 , however, tow fibers  21  pass through a condenser board  28  having a series of apertures  30  (see  FIG. 5 ) similar to apertures  26  therein. The purpose of condenser board  28  is to further define the shape and arrangement of the tow bundle  32  that is being formed as the individual tow fibers  21  are brought closer to infiltration section  14 . The particular profile, i.e. flat, rectangular etc., of tow bundle  32  desired will determine the shape of condenser board  28  as well as the spacing and location of apertures  30  therein. In the embodiment depicted in  FIGS. 1 and 4 , condenser board  28  is shown as arcuate with the concave side facing downstream, i.e. in the direction of the infiltration section  14 , in the fabrication process. Condenser board  28  is preferably provided with a swivel clamp or similar device to permit ready adjustment of its vertical orientation relative to infiltration section  14 . This configuration of condenser board  28  permits proper lay down of tow bundle  32 . i.e. application of proper bandwidth of tow bundle  32  on entrance roller  34  best seen in  FIGS. 5 and 6 . 
     Entrance roller  34  preferably comprises a lightweight roller of conventional design but with free rolling high-temperature bearings. Entrance roller  34  serves to flatten and redirect tow bundle  32  as it approaches the entry to infiltration section  14  that begins with entrance tube  36 . 
     Infiltration section  14  comprises two parts: 1) a furnace  38  having a molten metal well  40  and 2) a preferably moveable operating section  42  best seen in  FIG. 4  and comprising frame  48  having attached casters  49  to permit its movement as described below. Operating section  42  is best seen in  FIGS. 5 and 6 . As depicted in these Figures, operating section  42  comprises an entrance tube  36  immersed in a bath of molten metal  43  contained in metal well  40  of furnace  38 , and a pair of guide rollers  44  and  44 A that serve to guide tow bundle  32  in a planar path through molten metal  43  and beneath ultrasonic processor  46  that facilitates wetting and infiltration of molten metal into tow bundle  34 . Ultrasonic processor  46  and its associated equipment described below as well as entrance tube  36  are all carried by frame  48 . As will be apparent from a review of  FIGS. 4 and 5 , frame  48  to which ultrasonic processor  46  as well as condenser board  28  are affixed is moveable, upon casters  49  so that frame  48  becomes in effect a carriage that can be relocated away from furnace  40  during furnace charging, melting and cleaning operations. Such an arrangement simplifies considerably the actual preparation and operation of apparatus  10  and especially infiltration section  14 . 
     Ultrasonic processor  46  further comprises a cooling chamber  50  for the upper portion of the ultrasonic waveguide  52  and transducer  54 . Cooling chamber  50  is preferably double walled and with a continuous gas purge therethrough. Cooling chamber  50  extends the life of transducer  54  and maintains the temperature and hence the acoustic impedance of the ultrasonic processor consistent. This control is very important for reducing process variability. A screw drive  58  is provided for raising and lowering, i.e. adjusting the locations of ultrasonic processor  46  and entrance tube  36  in metal bath  43  or for withdrawing this piece of equipment when not in use to prevent damage thereto by accident or extended and unnecessary exposure to the high temperature conditions and the erosive effects of molten metal. Ultrasonic waveguide  52  may be fabricated from any number of materials, such as titanium and niobium, however, the use of niobium is particularly preferred as it is highly resistant to the action of, for example, molten aluminum. An ultrasonic waveguide that operates in the range of about 20 kHz and a power output of about 1500 Watts have proven satisfactory in the production of a metal matrix composite tape or ribbon. 
     After passing in the area of ultrasonic waveguide  52  between rollers  44  and  44 A the now molten metal infiltrated tow bundle  56  is passed through a die  60  to impart the desired final shape to infiltrated tow bundle  56  thereby producing reinforced metal matrix tape/ribbon  62  that passes over exit guide roll  34 A toward puller  16 . According to a preferred embodiment of the present invention, the die is fabricated from graphite although it could be similarly fabricated from a suitable ceramic or refractory material. A preferred dimension for tape or ribbon  62  is 0.25 inches wide by 0.015 inches thick. Other “shaping or forming” devices could also be used in place of die  60 , for example a pair of facing rollers or the like. Die  60  is located such that it lies in line with infiltrated tow bundle  56  as it exits molten metal bath  43 . The particular configuration of die  60  will vary widely depending upon the particular shape of the metal matrix tape or ribbon being fabricated, and, as such, its configuration in the overall metal matrix fabrication process is not particularly critical although the design or configuration of die  60  may be highly important in the fabrication of a particularly shaped metal matrix tape or ribbon. 
     After exiting die  60  and over exit guide roll  34 A tape/ribbon  62  then passes into puller  16 . Puller  16  preferably comprises a commercially available dual belt pulling system. According to a highly preferred embodiment of the present invention, puller  16  is equipped with a set of air amplifying nozzles  66  that cool tape/ribbon  62  before it comes into contact with rubber belts  68  and four-roller centering mechanism  70  of puller  16 . Four-roller centering mechanism  70  maintains tape/ribbon  62  centered on belts  68 . 
     It is puller  16  in combination with the tensioning devices associated with shafts  22  described above that maintain tension throughout apparatus  10  and that result in the production of a pultrusion effect as infiltrated fiber tow bundle  56  is drawn through die  60  by the action of puller  16  to yield tape/ribbon  62 . As will be obvious to the skilled artisan, although perhaps more difficult to control a variety of devices might be substituted for puller  16 . For example a sophisticated and highly automated coiling system might be used to “pull” the fiber tow through the apparatus described herein. 
     Upon exiting puller  16 , tape/ribbon  62  can be coiled using a conventional coiling device not shown. 
     In practice, the apparatus just described operates as follows: spools  20  of a suitable ceramic, glass, carbon, and the like, continuous fiber are mounted in creel  12  as shown in  FIGS. 1 and 3 . Depending upon the size, type, strength etc., of the composite tape being produced, any number of continuous fibers may be applied from creel  12 . The individual continuous fibers  21  are passed through creel payout boards  24  via apertures  26  or some other suitable alignment apparatus and then through condenser board  28  to be brought into a suitable arrangement for application to entrance roll  34 . From entrance roll  34  the now bundled tow  32  passes into entrance tube  36  wherein it is placed below the surface of molten metal bath  43 , generally at a depth of from about 1 to about 2 inches, and passes over guide roll  44 , is impacted by ultrasonic emissions generated by waveguide  52  that assists infiltration of molten metal into tow bundle  32 , passes over guide roll  44 A and thence through die  60  where infiltrated tow bundle  56  is formed into an appropriately shaped tape/ribbon  62  that passes over exit roll  34 A and enters puller  16  after being subjected to cooling by the impingement of air from air amplifying nozzles  66 . The product tape/ribbon  62  is then coiled or otherwise collected for use. 
     Operating speeds on the order of from about 5 to about 15 feet per minute have been found suitable for the production of satisfactory product, although it is anticipated that operation of the apparatus described herein outside of this range is entirely feasible. 
     There have thus been described both an apparatus and a method for the production of continuous fiber reinforced metal matrix composites. The method described and claimed herein is relatively simple to implement, is highly reproducible and produces very consistent product over relatively long production runs. 
     While similar apparatus has been used to produce coated and other products in the past, applicants are not aware of any single process or combination of processes that utilize the apertured creel payout boards, apertured condenser boards, ultrasonic assisted infiltration technique, air cooling and pultrusion effects of the present invention that are described herein. 
     As the invention has been described, it will be apparent to those skilled in the art that the same may be varied in many ways without departing from the spirit and scope of the invention. Any and all such modifications are intended to be included within the scope of the appended claims.