Abstract:
Disclosed is a method for producing a three-dimensional composite structure and a method for producing the mold for the three-dimensional composite structure. The mold is formed of at least one rigid die member and a second thermoplastic die member. The second thermoplastic die member is formed by coupling a rubber flexible pattern to a surface of the first die member. Vacuum or pressure is applied to a heated thermoplastic sheet to cause the heated thermoplastic sheet to deform about the flexible pattern, thereby forming the second die. Strips of reinforced polymer thermoset pre-preg material are then positioned within the cavities formed by the flexible pattern and are allowed to cure. Optionally, heat, pressure, and vacuum may be applied to the mold construction to facilitate the curing of the thermoset materials.

Description:
[0001]     This application is a divisional of U.S. patent application Ser. No. 10/603,477 filed on Jun. 25, 2003, which claims the benefit of U.S. Provisional Application No. 60/391,995, filed on Jun. 25, 2002. The disclosure of the above applications is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to composite materials and to methods of manufacturing the composite materials. In particular, the methods of manufacturing the composite materials of the present invention include a method of creating a mold, and more particularly, a method produce a three dimensional mold for use in forming a customized composite knee brace.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is known that knee braces can be produced by the use of composite materials are coupled together by metallic hinges. Typically, complex three-dimensional die cavities are formed by complex cuttings of metal die materials. These die cavities correspond to the leg shape as well as to the exterior shape of the leg brace. Obviously, these tools are very expensive and time consuming to produce. As such, the use of customized composite leg braces is significantly limited.  
       SUMMARY OF THE INVENTION  
       [0004]     Accordingly, it is an object of the present invention to provide a method of manufacturing the composite material which includes creating a custom mold. The method produces an three dimensional mold having a thermoplastic die for use in forming a customized thermoset composite knee brace.  
         [0005]     In one embodiment of the present invention, a method for producing a three-dimensional composite support structure for a body is provided. The method begins with a coupling of a flexible pattern to an exterior surface of a three-dimensional model of the body. The model of the body and the flexible pattern are then coated with a deformable polymer layer. Either gas pressure or a vacuum is applied to the polymer layer so as to cause an imprint of the flexible pattern to be formed onto the polymer layer, thereby forming a cavity in the polymer layer when the flexible pattern is removed. The polymer layer is then allowed to harden into a splash mold. Strips of reinforced polymer thermoset pre-preg material are positioned into the flexible pattern of the splash mold. The splash mold is then re-coupled to the model of the body and pressure and/or vacuum are applied to the model and the splash molds in the presence of heat so as to cure the reinforced polymer pre-preg material.  
         [0006]     In another embodiment of the present invention, a method for producing a custom knee brace is disclosed. The method comprises providing a three-dimensional model of a knee and leg structure. A flexible pattern corresponding to a portion of the knee brace is positioned on the surface of the knee model. The knee model and flexible pattern are then covered with a deformable polymer layer. Pressure or vacuum is applied to the polymer layer so as to cause an imprint of the flexible pattern onto the polymer layer. The polymer layer is allowed to harden into a splash mold. The splash mold of the knee brace is removed from the model and strips of reinforced polymer thermoset pre-preg material is positioned into the imprint of the flexible mold. The splash mold and thermoset pre-preg are then coupled to the model of the knee. Either gas pressure or vacuum are applied to the splash mold in the presence of heat so as to cure the reinforced polymer material.  
         [0007]     In yet another embodiment of the present invention, a die for a reinforced composite structure is disclosed. The die comprises a first die member having a first die surface, and a second die member being formed of a thermoplastic material having a second die surface. The first and second die surfaces define a cavity configured to mold thermoset polymer materials.  
         [0008]     In yet another embodiment of the present invention, a method for producing a die for reinforced thermoset polymer materials is disclosed. The method comprises providing a mold base having a first die surface. A flexible die pattern is positioned onto the first die surface. A heated thermoplastic splash mold sheet is positioned over the first die surface and the flexible pattern. Pressure or vacuum are applied to the thermoplastic sheet to cause it to deform over the flexible pattern, thereby forming a cavity conforming to the shape of the flexible pattern. The thermoplastic sheet is then cooled until it is solid and removed from the mold base to form the second die member.  
         [0009]     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0011]      FIG. 1  depicts a customized molded plaster cast according to the teachings of the present invention;  
         [0012]      FIG. 2  teaches the preparation of offset material used according to the present invention;  
         [0013]      FIG. 3  depicts the application of a stockinet over a cast model;  
         [0014]      FIGS. 4-6  depict the application of the offset material to the cast model according to the teachings of the present invention;  
         [0015]      FIGS. 7 and 8  depict the offset material over the cast model according to the teachings of the present invention;  
         [0016]      FIG. 9  depicts positioning a hinged template onto a rotational axis of the cast model according to the teachings of the present invention;  
         [0017]      FIG. 10  depicts the cast model coated by a stockinet according to the teachings of the present invention;  
         [0018]      FIG. 11  depicts flexible templates used to produce the knee brace;  
         [0019]      FIGS. 12-15  depict the application of the flexible templates to the cast model;  
         [0020]      FIGS. 16-18  depict the formation of a splash mold according to the teachings of the present invention;  
         [0021]      FIGS. 19-23  depict the removal of and preparation of the splash mold;  
         [0022]      FIGS. 24-26  show the fixturing of the splash mold;  
         [0023]      FIGS. 27 and 28  depict the composite pre-preg materials used to form the knee brace according to the teachings of the present invention;  
         [0024]      FIGS. 29 and 30  depict the application of woven pre-preg material and metal hinges into the cavity of the splash mold;  
         [0025]      FIG. 31  shows the application of a balsa wood core according to the teachings of the present invention;  
         [0026]      FIGS. 32 and 33  depict the application of a foam filler and carbon fiber cord into the composite construct;  
         [0027]      FIG. 34  depicts the application of steel washers into the composite structure;  
         [0028]      FIG. 35  depicts the application of woven pre-preg material to the splash mold;  
         [0029]      FIGS. 36-38  depict the edge preparation and subsequent application of a final layer according to the teachings of the present invention;  
         [0030]      FIG. 39  depicts the use of a vacuum bag to remove air from between the layers of the uncured composite materials;  
         [0031]      FIGS. 40   a - 40   d  depict the splash molds with uncured composites according to the teachings of the present invention;  
         [0032]      FIG. 41  depicts the application of the uncured splash molds onto the offset layer of the plaster cast according to the teachings of the present invention;  
         [0033]      FIGS. 42 and 43  show the preparation of the hinge area prior to autoclaving;  
         [0034]      FIGS. 44-46  depict the preparation of the mold prior to autoclaving; and  
         [0035]      FIG. 47  depicts a three-dimensional knee brace produced according to the teachings of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]     The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. Specifically, described is a method for forming three dimensional composite structure. Whereas the three dimensional structure described is a knee brace, the application of these principles are equally applicable to any number of three dimensional composite structures formed of thermoset or thermoplastic polymers.  
         [0037]      FIG. 1  depicts a customized plaster cast model  50  according to the teachings of the present invention. The custom plaster cast model  50  is formed from a negative cast (not shown) of a patient&#39;s extremity, which is provided by a treating physician. This negative cast has important landmarks, such as a joint rotational axis  52 , called out. Typically, the cast model  50  of a knee will be about 20″ long, and specifically, plus and minus 10″ in the proximal and distal directions from the axis of rotation  52  of the joint.  
         [0038]     Upon receipt of the negative cast, the three-dimensional cast model  50  of the joint is produced. The exterior surface  54  of the cast model can be modified prior to the formation of the three-dimensional composite structure  56 . Offsets or cutouts and landmarks and fixation points can be formed into the exterior surface  54  of the cast model  50 . For example, to produce a knee brace  58 , a pair of generally parallel planes  60  are formed on the medial and lateral sides  62  and  64  of a knee joint. These parallel planes  60  are used to align a pair of knee braces&#39; parallel knee joint hinges  66 . Additionally, a hole  68  is bore into the cast model  50  at the axis of rotation  52  of a knee joint.  
         [0039]     Optionally, the cast model  50  can be formed of urethane foam which is shaped utilizing computer bioscanning system. The computerized bioscanning system creates a three dimensional computer model of the patients leg utilizing lasers. The lasers scan the plaster cast provided by the physicians. The three dimensional computer model is then modified to provide Offsets or cutouts and landmarks and fixation points. A 5-axis cutting tool can be coupled to the computer to produce the model  50  which is used to form the composite structure.  
         [0040]     As can be seen in  FIG. 1 , the cast model  50  is positioned onto an integral support member  70 . In this instance, the support member  70  is a hollow aluminum tube which is configured to support the cast model  50  as well as to draw a vacuum during processing as is described in further detail below. Coupled to and disposed about the support member is a flexible seal  72 , which is used to seal a vacuum enclosure about the cast model  50  during various processing steps.  
         [0041]      FIG. 2  shows a sheet of thermoplastic material  74  disposed within an oven  76 . The thermoplastic material  74  is coupled the surface of the cast model  50  and functions as a constant thickness offset layer  78  from the exterior surface  54  of the cast model  50 . Specifically, the offset layer  78  functions to provide the gap and spacing needed between the knee brace  58  and the patient&#39;s leg for soft internal knee brace structures. It is envisioned that the thickness of the offset layer  78  can be adjusted in the different areas along the cast model  50  to allow for different spacing of a solid brace and the surface of the patient&#39;s skin. Specifically, different thicknesses can be used in areas where increased padding or hinge thickness is necessary.  
         [0042]     The thermoplastic material  74  shown is a ⅛″ layer of polyethylene material. Both sides of the polymer offset layer  78  are cleaned with alcohol and checked for defects. The polymer offset layer  78  is then placed in an oven  76  having a temperature of 400° F. maximum. At this point, three layers of stockinet  80  are positioned over the cast model  50 . A knot is tied to the stockinet  80  and trimmed to the length of the cast model  50 . The stockinet  80  functions as an air passage between the cast model  50  and the polymer offset layer  78  during processing.  
         [0043]     As best seen in  FIG. 4 , the polymer offset layer  78  is removed from the oven  76  after it turns clear (approximately 5 minutes). The polymer offset layer  78  is transported to the cast model  50  and is subsequently applied over the stockinet layers. As best seen in  FIG. 5 , the bottom  82  and ends  84  of the polymer offset layer  78  are sealed. A vacuum is drawn through the support member  70  to pull the polymer offset layer  78  onto the surface of the stockinet  80  disposed about the cast model  50 .  FIG. 6  depicts the trimming away of the polymer offset layer  78 .  
         [0044]      FIGS. 7 and 8  show the polymer offset layer  78  disposed over the cast model  50 . As can be seen, modifications formed on the exterior surface  54  of the cast model  50  are transferred to the outer surface of the offset.  FIG. 7  shows the flattened hinge accepting portions  60  as well as the bore defined at the knee joint rotation axis  52 .  
         [0045]      FIG. 9  depicts the fixation of a hinge jig  82  into the knee axis hole. The hinge jig  82  is aligned along the rotational axis  52  of the leg and is traced with a marker to form a hinge pattern outline  83 .  FIG. 10  depicts the pattern outline  82  of the hinge jig  82  about the knee hole axis. The hinge pattern outline  83  is used to align flexible patterns  84 , which will eventually define a three dimensional composite frame  86 .  
         [0046]     Two layers of stockinets  80  are then applied over the polymer offset layer  78 . Upon the application of each stockinet  80 , the ankle end of the stockinet  80  is tied into a knot while the thigh end is trimmed to fit the length of the casting. The stockinet  80  material functions as an air passage way between the offset layer  78  and a thermoplastic layer  88  which will form a thermoplastic splash mold  90 .  
         [0047]      FIG. 11  depicts a set of flexible patterns  84  which will be applied to the cast model  50 . The flexible patterns  84  are formed of polyurethane material or silicon having a durometer of about 10, but can be any compressible elastic material which maintains is configuration under processing parameters. It should be noted that a full set of thigh  92  and calf  94  patterns are available. The process of the present invention allows for the intermingling of different flexible thigh  92  and calf  94  patterns as are required by the specific geometry of the cast model  50 .  
         [0048]      FIG. 12  depicts the application of the flexible patterns  84  onto the cast model  50 . First, a thigh pattern  92  that fits the leg is chosen and placed onto the cast model  50 . The traced hinge jig  82  is used to align the flexible pattern  84  onto the cast model  50 . A tracing of the thigh pattern  92  is then made onto the stockinet  80 . A flexible calf pattern  94  is chosen and placed onto the cast model  50 . Again, the flexible calf pattern  94  is aligned with the exterior profile of the hinge jig  82  and is traced.  
         [0049]     As is shown in  FIG. 13 , the flexible patterns  84  are removed from the cast model  50 . Contact cement  96  is brushed inside the traced flexible pattern area  98  as well as metallic hinge jigs  82 . The hinge jigs  82  are placed at the knee axis while the flexible thigh and calf patterns are positioned in their respective locations.  
         [0050]      FIGS. 14 and 15  show the fixed flexible patterns  84 . At this point, the flexible patterns  84  are checked for proper alignment, and the flexible calf pattern  94  is checked for proper tibia crest alignment. The flexible patterns  84  define the location of the three dimensional members, as well as the placement of hinges and mounting features.  
         [0051]      FIG. 16  shows the initial step for producing the splash mold  90 . Similar to the formation of the offset layer  78 , a ⅛″ sheet of polyethylene  100  is cleaned with alcohol and checked for defects. The polyethylene sheet  100  is then placed within a 400° F. oven  76 . Two layers of stockinet  80  are again placed over the cast mold  50 . In this regard, the stockinet  80  layers are placed over the flexible patterns  84 . As is best shown in  FIG. 16 , the polyethylene sheet  100  is removed from the oven  76  after it turns clear (approximately 5 minutes) and placed over the cast model  50 . The polyethylene sheet  61  is sealed on the ends  102  and the bottom  104 . Vacuum is applied to the cast model through the mounting tube. Excess plastic is trimmed from the ends and the bottom of the polyethylene sheet  61 . As is shown in  FIG. 18 , the thigh portion  104  and calf portion  106  of the splash mold  90  are labeled.  
         [0052]      FIG. 19  shows the splash mold  90  being cut away from the casting along the back side of the cast model  50 . The splash mold  90  is subsequently removed from the cast model  50 . The flexible pattern  84  and stockinet  80  are subsequently removed from the cast model  50 .  
         [0053]      FIGS. 20-22  depict the preparation of the splash mold  90  for its use. Shown is the removal of excess polymer from the splash mold  90 .  FIG. 23  depicts the punching of mounting holes  108  in the outside periphery of the splash mold  90 .  
         [0054]      FIG. 24  depicts the fixturing of the splash mold  90 . The splash mold  90  is shown being fixed by jig bolts through the mounting holes  108 . Nuts  110  are placed onto the bolt and tightened to hold the splash mold  90  in place. The interior  112  of the mold is then cleaned with isopropyl alcohol which is evaporated using a heat gun as is shown in  FIG. 25 .  
         [0055]      FIG. 26  depicts the application of carbon fiber starter strips  114  to the hinge area. Additionally, glass scrim  124  reinforcing material is applied to the hinge area  116 .  FIG. 27  depicts a prefabricated carbon fiber kit  118 . The carbon fiber kit contains precut strips of a woven carbon fiber pre-preg material  120  and precut balsa wood core  122 . The carbon fiber pre-preg material  120  is generally a very resin rich material. Preferably, having a 55% resin content is used in order to achieve a resin rich surface. The pre-preg material  120  is formed of woven carbon fiber. The fiber is preferably oriented in 90° and 60° orientations. Optionally, glass-fiber reinforced resin or KEVLAR reinforced resin can be used.  
         [0056]     An example of the carbon fiber pre-preg material  120  are models DA 4090 and DA 4092 Modified Pre-Impregnated Systems available from Adhesive Pre-pregs for Composite Manufacturers of Plainsfield, Conn. This pre-preg material  120  is curable at 250° F. for 1 hour. The material has a tensile strength of about 63 ksi and flexural modulus of about 3×10 6  psi. The pre-preg material  120  optionally will have a curing cycle of 5-10° F. per minute temperature rise from room temperature to 180° F. while under a 25 Hg vacuum. Once at 180° F., 50 psi of pressure is applied to the exterior surface of the material and the temperature is increased at a rate of 5 to 10° F. per minute rise to 250° F. The construct is then held at 250° F. for one hour. Optionally, the pre-preg material  120  can be cured simply in an oven at 250° F. for about 10 hours under vacuum as opposed to in a pressurized autoclave.  
         [0057]     A glass scrim  124  layer is attached to a carbon fiber pre-preg material  120 .  FIG. 29  shows the placement of the first pre-preg layer  120  of carbon fiber with the glass scrim layer face down into the splash mold  90 . The first pre-preg layer  126  is centered within the mold and pressed into position. A second pre-preg layer  128  with a 60° orientation is placed into the splash mold  90  with the adhesive side down.  
         [0058]     Next, a third pre-preg layer  130  having a 90° orientation is prepared and placed onto the splash mold  90  adhesive side down. With reference to  FIG. 30 , at this point, hinge bars  132  are identified for the splash mold  90  and placed into proper position.  
         [0059]      FIG. 31  depicts the insertion of the balsa wood core material  122  into the splash mold  90  with its mesh side  134  up. The core material is a scored balsa material  122  having a mesh backing. The excess core material is trimmed and removed.  
         [0060]      FIG. 32  depicts the insert of carbon fiber braid material  136  into the hinge area. The braid material  136  is inserted between the outside edge  138  of the balsa wood core material  122  and the mold inside edge  140 . The braid material  136  is applied to both the inside and outside edges from hinge to hinge  132 .  
         [0061]      FIG. 33  shows the insertion of expanding foam  142  between the braid material and the mold edge. The expanding foam is cut into 0.25″ strips. Any void surrounding the hinge is filled with expandable foam  142 .  
         [0062]      FIG. 34  shows the application of metal washers  143  within the composite lay-up. These metal washers  135  are used as fixation points for the padding and harness (not shown) to be disposed within the three-dimensional frame  144 .  
         [0063]      FIG. 35  shows the insertion of three layers of carbon fiber pre-preg ( 146 ,  148 ,  150 ). Specifically a 60° small layer  146  is placed into the mold adhesive side down. Next, a 90° carbon fiber layer  148  is placed into the mold adhesive side down. Lastly, a second 60° layer  150  is placed on top.  FIG. 36  depicts folding bottom carbon fiber tabs  152  towards the center of the brace to enclose the pre-preg construct. The starter strips are folded towards the interior of the brace.  
         [0064]      FIG. 37  depicts the application of another layer  154  of 90° orientated fibers over the composite covering the folded tabs.  FIG. 38  depicts the folding of the hinge starter strip  156  inward to form a straight seam along the hinge. As best seen in  FIG. 39 , the entire assembly  158  is placed within a rubber bag  160  and a vacuum is pulled on the splash mold  90  for 15 minutes to remove as much air as possible from between the pre-preg laminate layers.  
         [0065]      FIGS. 40   a - 40   d  show the filled splash molds  90  after they are removed from the rubber bag  160  and are trimmed using a manual cutter.  FIG. 41  shows the packed thigh mold  162  being positioned onto the cast Model  50 . Straps  163  are used to hold the thigh mold  162  into position. Next, the packed calf mold  164  is positioned onto the cast model  50  and a strap  163  is used to hold the padded calf mold  164  into position. In  FIG. 42 , a utility knife is used to trim the thigh and calf molds  152  and  164  away from the hinge areas.  
         [0066]      FIG. 43  shows the hinges being applied to the calf side  164  of the uncured structure. The hinges  166  are secured to both sides of the brace using hinge holders (not shown).  FIG. 44  depicts the assembly being wrapped with rubber material  168  while  FIG. 45  shows the assembly now being wrapped with breather material  170  which is used to degas the structure while it is being processed. At this point, the rubber sealing member  72  is again placed onto the aluminum supporting member  72 . A portion of the breather material  170  is placed under the rubber sealing member to ensure proper gas flow during the processing of the material. The assembly is then placed within a vacuum bag  172  and sealed using sealing tape. A vacuum is then applied to check for leaks with any leaks being sealed.  
         [0067]     The entire assembly is then placed into an oven  76  with a vacuum line attached to the vacuum hose. The construct is cured for ten hours at an oven temperature of 250° F.  
         [0068]      FIG. 47  discloses a brace produced according to the process of the present invention. A significant advantage of the present system is the ability to produce a customized three-dimensional composite structure without using metal tooling plates. The splash mold  50  functions as a thermoplastic pressure plate. Of particular note is the ability to use a polyethylene thermoplastic sheet as a pressure plate/mold without the use of release film or release materials.  
         [0069]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.