1. Field
The present disclosure generally relates to the fabrication of fiber reinforced thermoplastic parts, and deals more particularly with a method and apparatus for compression molding such parts, especially those having complex shapes.
2. Background
In the aircraft and other industries, a variety of parts and structures are fabricated from composites or combination of composites and light weight metals because of their relatively high strength-to-weight ratios. In the case of parts having contours or relatively complex geometries, the parts are often fabricated using thermoset pre-preg tape layup techniques, and autoclave curing. Bandwidths of pre-preg tape or tows are laid up side-by-side to form a multi-ply laminate. In those applications where the part requires fittings at load input locations along the part, custom metal fittings are separately machined and then fastened to the composite laminate part. Depending upon the geometry of the part, fillers, sometimes referred to as “noodles”, must be installed in gaps or cavities in the part in order to strengthen joints.
The composite laminate fabrication process described above is time-consuming, labor intensive and requires expensive capital equipment such as automatic fiber placement machines. Moreover, these composite laminate parts may be heavier than desired because pad-ups required for localized strengthening must be formed gradually, thus requiring placement of the of additional ply materials. Also, composite laminate parts may exhibit notch sensitivity around openings in the laminate, such as around lightening holes that are drilled or cut in the laminate part after it has been cured.
Thermoplastic parts having discontinuous fiber reinforcement may be molded into a variety of shapes, however the ability to integrate part features is limited due to the high viscosity of the melted thermoplastic resin which limits resin flow. The ability to flow resins is particularly limited where the reinforcement fibers are relatively long, the fiber content is high, and the required flow distances are long. Also, molding techniques such as injection molding may have a tendency to damage the fibers, thereby affecting the strength of the molded part. Other molding techniques, such as extrusion molding are limited to producing a single, straight part having a uniform cross-sectional shape.
Accordingly, there is a need for a method and apparatus for fabricating composite parts having curves, contours or complex geometries which obviate the need for laying up lamina, and which reduce touch labor as well as expensive capital equipment. There is also a need for composite parts with complex geometries having integrated features and fittings that can be quickly and economically fabricated in high rate production environments.