Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Laser
Reexamination Certificate
1999-10-02
2001-04-10
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Laser
C264S040100, C264S308000, C264S483000, C264S485000, C264S488000, C264S489000, C264S492000, C264S494000, C347S001000, C425S135000, C425S141000, C425S145000, C425S375000, C700S119000
Reexamination Certificate
active
06214279
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a computer-controlled process and apparatus for fabricating reinforcement preforms for composite parts and, in particular, to an improved process and apparatus for building a three-dimensional composite preform in a layer-by-layer fashion.
BACKGROUND OF THE INVENTION
The process of liquid composite molding (LCM), including resin transfer molding, to produce structural composites has gained considerable attention over the last decade. One barrier to the process gaining further acceptance has been the lack of adequate knowledge and expertise in the cost-effective production of reinforcement preforms. If the LCM process is to remain economically viable, low-cost methods of preform production must be further advanced. At present, two basic input forms of fiberglass are available to the LCM molder for producing a stiff three-dimensional (3-D) preform: a thermoformable continuous strand mat and a multi-end roving.
Three basic routes are available for fabricating LCM preforms from the two basic input forms of reinforcement (mats and rovings). These are cut-and-sew preforming, directed fiber spray-up, and stamping of thermoformed mats. Cut-and-sew preforming is utilized in aerospace and low-volume applications. In a cut-and-sew preform, areas of material are defined based on the requirements determined in a finite element analysis. In this process, the general size and shape of each area is cut from a conformable material and fit to the part mold or a part model; this is then cut, trimmed and sewn to fit the desired dimensions. A final template is built and the actual reinforcement is cut and sewed on the preform. This process is slow and labor intensive.
The directed fiber spray-up process utilizes an air-assisted chopper/binder gun which conveys glass and binder to a perforated metal screen shaped identical to the part to be molded. The chopped fibers are held in place on the screen by a large blower drawing air through the screen. Once the desired thickness of reinforcement has been achieved, the chopping system is turned off and the preform is formed by polymerizing or curing the binder. Once stabilized, the preform is cooled and removed from the screen. A pre-shaped screen or perforated mold is required in this process.
The thermoformed mat process requires an oven to heat the mat, a frame to hold it while being stretched into shape, and a tool to form the mat into a preform. In a typical process, several plies of mat would be cut to the approximate desired shape of the molded part, allowing extra material to be held in a frame. The frame containing the material is then placed in an oven to be heated (up to 170° C.) and then quickly transferred to the forming tool. The tool is closed, forming and cooling the mat for a short period of time. After removing the frame and trimming the waste fibers clamped in the frame, the preform is ready for molding. Both thermoplastic and thermoset binder systems are available to retain the formed shape. Again, a pre-shaped tool or mold is required in this process.
The preparation of fiber preforms for metal matrix composites (MMCs) or ceramic matrix composites (CMCs) is often accomplished by machining blocks or sheets of fibers (e.g., preforms used in U.S. Pat. No. 4,141,948, Feb. 27, 1979 to W. Laskow and C. Morelock). A preform can also be made by pouring a curable mixture of carbon fiber and binder into a mold, followed by the removal of excess binder by the application of reduced pressure or vacuum pumping (e.g., U.S. Pat. No. 4,320,079, Mar. 16, 1982 to W. Minnear and W. Morrison). In a similar approach, a fiber preform precursor is impregnated with a colloidal suspension of inorganic material. This impregnated preform precursor is cooled to precipitate the inorganic material from the suspension and then dried to form a rigidized fiber preform (U.S. Pat. No. 4,902,326, Feb 20, 1990 to D. Jarmon). Other methods of making composite preforms may be found in the following U.S. Patents: U.S. Pat. Nos. 5,346,774 (Sep. 13, 1994 to K. Burgess), U.S. Pat. No. 5,350,545 (Sep. 27, 1994 to H. Streckert, et al.), U.S. Pat. No. 5,456,981 (Oct. 10, 1995 to P. Olry, et al.), U.S. Pat. No. 5,571,628 (Nov. 5, 1996 to L. Hackman), U.S. Pat. No. 5,529,620 (Jun. 25, 1996 to W. Gorbett, et al.), U.S. Pat. No. 5,705,008 (Jan. 6, 1998 to D. Hecht), and U.S. Pat. No. 4,659,610 (Apr. 21, 1987 to S. George, et al.). A common shortcoming of these preform making methods is the need to have a pre-shaped mold or tool against which a preform structure of a desired shape is made. Otherwise, the preform must be made into a larger-than-necessary shape and then machined down to the desired shape.
Solid freeform fabrication (SFF) or layer manufacturing (LM) is a new fabrication technology that builds an object of any complex shape layer by layer or point by point without using a pre-shaped tool (die or mold). This process begins with creating a Computer Aided Design (CAD) file to represent the geometry or drawing of a desired object. As a common practice, this CAD file is converted to a stereo lithography (.STL) format in which the exterior and interior surfaces of the object is approximated by a large number of triangular facets that are connected in a vertex-to-vertex manner. A triangular facet is represented by three vertex points each having three coordinate points: (x
1
,y
1
,z
1
), (x
2
,y
2
,z
2
), and (x
3
, y
3
,z
3
). A perpendicular unit vector (i,j,k) is also attached to each triangular facet to represent its normal for helping to differentiate between an exterior and an interior surface. This object image file is further sliced into a large number of thin layers with the contours of each layer being defined by a plurality of line segments connected to form polylines. The layer data are converted to tool path data normally in terms of computer numerical control (CNC) codes such as G-codes and M-codes. These codes are then utilized to drive a fabrication tool for building an object layer by layer.
This SFF technology enables direct translation of the CAD image data into a three-dimensional (3-D) object. The technology has enjoyed a broad array of applications such as verifying CAD database, evaluating design feasibility, testing part functionality, assessing aesthetics, checking ergonomics of design, aiding in tool and fixture design, creating conceptual models and sales/marketing tools, generating patterns for investment casting, reducing or eliminating engineering changes in production, and providing small production runs. The potential of adapting SFF technology for the preparation of reinforcement preforms from fibers and/or particulates for composite applications has been largely ignored.
The SFF techniques that potentially can be used to fabricate short fiber- or particulate-reinforced composite parts or their precursor preforms include fused deposition modeling (FDM), laminated object manufacturing (LOM) or related lamination-based process, and powder-dispensing techniques. The FDM process (e.g., U.S. Pat. No. 5,121,329; 1992 to S. S. Crump) operates by employing a heated nozzle to melt and extrude out a material such as nylon, ABS plastic (acrylonitrile-butadiene-styrene) and wax in the form of a rod or filament. The filament or rod is introduced into a channel of a nozzle inside which the rod/filament is driven by a motor and associated rollers to move like a piston. The front end, near a nozzle tip, of this piston is heated to become melted; the rear end or solid portion of this piston pushes the melted portion forward to exit through the nozzle tip. The nozzle is translated under the control of a computer system in accordance with previously sliced CAD data to trace out a 3-D object point by point and layer by layer. In principle, the filament may be composed of a fiber or particulate reinforcement dispersed in a matrix (e.g., a thermoplastic such as nylon). In this case, the resulting object would be a short fiber composite or particulate composite. The FDM method has been hitherto limited to low
Jang Bor Z.
Liu Junhai
Wu Liangwei
Yang Junsheng
NANOTEK Instruments, Inc.
Tentoni Leo B.
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