Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-07-12
2002-03-05
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S242000, C156S245000, C264S219000, C264S220000, C264S225000, C264S226000
Reexamination Certificate
active
06352609
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to prototyping processes and, more particularly, to a composite tooling process for curing materials at elevated temperatures.
BACKGROUND OF THE INVENTION
The production of molded articles from resinous fiber materials, especially large and complex articles such as, for example, airplane fuselages, has been subject to cost, complexity, and consistency problems. Especially in a prototyping stage where few articles are produced from the mold, costs, lead-time, and accuracy of the articles produced from the mold are extremely important considerations.
An example of a current process used to produce prototyping cure tools begins by obtaining large “blocks” of 10-15 lb density urethane foam. The foam buns are attached to a base and glued together to form a generic shape. The glue used is, for example, a room temperature laminating system. The foam is then machined to the desired shape using a numerically-controlled (N/C) machine to thereby obtain the desired mold line shape of the pattern or object to be molded. The foam shape is then sealed using a room temperature resin system before the resin is sanded and coated with an automotive type paint primer. Once the master plug or facility tool is formed, two methods are typically used to fabricate the facing sheet of the bond jig or cure tool. In one method, a room temperature cure/high temperature use (RT/HT) resin is used in a pre-preg (material already impregnated with the (RT/HT) resin), wherein the pre-preg is laid up in material sheets on the facility tool and cured out at room temperature or low temperatures (less than 150° F.). A second method for fabricating a facing sheet of the cure tool is to use resin and dry cloth and hand impregnate (apply the resin to the cloth) during the lay-up process. Typically, the cure tool or bond jig is then attached to a carbon epoxy eggcrate structure and removed from the facility tool.
Several limitations and/or problems are associated with such a method for producing cure tools. For example, in the first “half” of the process, the large blocks of the urethane foam usually carry an accompanying manufacturer lead-time of up to approximately 6-8 weeks, with 3-4 weeks lead-time being about average. A further problem is that the foam generally does not machine well. This is evidenced in that measurement variances of the machine molds are often much greater than the acceptable tolerance of within 0.010 inches of the theoretical mold line. The poor machinability of the foam may be due to two different problems therewith. First, the foam structure can be considered as a plurality of foam balls glued together. As the foam structure is machined, the balls are “torn” from the glue instead of being cut to form the desired contour. Thus, in actuality, the foam balls are being pulled off the surface of the structure instead of being actually cut, thereby resulting in a rough surface finish following the machining process. A second additional problem stems from the fact that the foam balls pulled from the surface of the structure during the machining process are actually abrasive and contribute to additional machining of the foam structure from a grinding process in the vicinity of the cutter.
After the foam mold is machined, resin is applied to the foam structure to fill and smooth out the surface. The resin is added about the foam structure, sanded smooth, and coated with an automotive-type paint primer before the surface is hand worked to achieve a smooth finish. However, the dimensional accuracy of the prototype tool is typically unknown due to the extensive handwork involved in finishing the facility tool. In addition, the vacuum integrity of these foam tools is generally hard to achieve. If the tooling surface facility tool cannot be subject to a good vacuum without leakage therethrough due to poor consolidation of the tool structure or other factors, the cure tool produced from the facility tool may be unusable. Further, these foam tools are also susceptible to damage. Any loads applied to the tools must be evenly distributed in order to avoid damage to the mold. Thus, there exists a need for a method of making a cure tool wherein extensive handwork is not required to produce an acceptably smooth finish on the cure tool, thereby resulting in a more determinable dimensional accuracy thereof. Further, there exists a need for a method of forming a cure tool wherein the tools or molds used in the process have good vacuum integrity. In addition, there exists a need for a method of forming a cure tool wherein the facility tool and the cure tool are sufficiently strong to withstand damage due to uneven forces applied thereto.
Further limitations in typical prototyping processes are encountered in the fabrication of the facing sheet of the cure tool or bond jig. Typically, using a room temperature cure/high temperature use (RT/HT) material, the time required to lay-up the tool is less with the pre-preg material than with the hand-impregnated material. Further, though the curing of these materials can be performed at room temperature, this usually produces a poor quality tooling that results in poor surface quality and/or poor vacuum integrity. Curing a pre-preg tool at elevated temperatures produces a better quality tooling. However, the same problems of poor surface quality and poor vacuum integrity may still exist, albeit to a lesser extent. The best results for RT/HT tools are typically obtained by curing the tools at temperatures up to 150° F. and at an elevated pressure. However, the size of the mold may be a limiting factor in this situation where the size of the temperature/pressure chamber may be limited. In addition, foam facility tooling materials generally have a high coefficient of thermal expansion. Thus, compensation during the machining process of foam molds must be made in order to allow for expansion of the mold when cured or used at high temperatures. Further, since the foam is typically glued up from smaller pieces or buns of the foam to form the mold, the growth of the mold at elevated temperatures is not uniform. In this regard, the bond or glue lines between the foam buns will not grow at the same rate as the foam itself.
Hand impregnation using a RT/HT resin does increase the time necessary to fabricate the lay-up, but the quality of the mold produced increases accordingly. However, the hand impregnation method is also dependent on the vacuum integrity of the foam mold. If the foam is not able to pull a sufficient decreased pressure or vacuum, and maintain that decreased pressure, a poor quality cure tool will result. In addition, the hand impregnation method requires a debulk of the plies at every few layers. This increases the number of required debulks as compared to a pre-preg material. Further, the use of a vacuum bagging material around the edges of the mold can result in damage to the surface coat and necessitate additional time for repairs during the lay-up of the tool. Thus, there exists a need for a method of forming a cure tool or bond jig wherein the tooling produced has good surface quality and vacuum integrity after being cured at room temperature. In addition, there exists a need for a method of fabricating a cure tool or bond jig wherein compensation for expansion of the facility tool at high temperatures is minimal or not required. However, if the facility tool were to expand as a function of temperature, it would be preferable for the mold to expand uniformly. In addition, there exists a need for a method of forming a cure tool wherein the vacuum bagging material used to cover the facing sheet and to seal to the facility tool during the curing process for the facing sheet can be removed therefrom without damage to the facing sheet.
The fabrication of molding tools has been addressed in a number of ways. For example, U.S. Pat. No. 4,073,049 to Lint discloses a method of making a mold for vacuum thermoforming which consists of applying a gel coat to a master pattern, applying a rigidizing mixture of a thermosetting
Polus Jeffery E.
Southmayd Timothy D.
Alston & Bird LLP
Mayes Curtis
LandOfFree
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