Molding Wet Lay-up

Contact molding is the process of applying reinforcement, preferably pre-cut to size, onto a mold treated with a release agent to produce a molding, which will have only one smooth 

RIFT Resin fusion under flexible tooling 

SCRIMP Seemann composite resin infusion molding process 

SMRIM Sequentiai muiti port resin injection system 

TERTM Thermai expansion resin transfer molding 

---

The process allows panels measuring several meters in each dimension to be infused with resin quickly and thoroughly, to give more rapid and consistent production. It can be controlled more closely than open-mold wet lay-up, giving parts of higher consistency and reproducibility. Structures, which are both thick and complex, can be impregnated and... 

Random planar Sheet molding compound resin transfer molding wet lay-up 0.30 0.30... 

Part Design Blow Molding Casting Compression Extrusion Filament Winding Injection Matched Die Molding Rotational Thermo- forming Transfer Compression Wet lay-up (Contact Molding)... 

Compression Molding Flexible Plunger Flexible Bag Molding Laminate Hand Lay-Up Vacuum Bag Molding Vacuum Bag Molding and Pressure Pressure Bag Molding Autoclave Molding Autoclave Press Clave Wet Lay-Up... 

One way to apply such moderate pressure is to enclose the wet-liquid resin material and mold in a flexible membrane or bag, and draw a vacuum inside the enclosure. Atmospheric pressure on the outside then presses the bag or membrane uniformly against the wet lay-up. An effective pressure of 69-283 kPa (10 to 14 psi) is applied to the product. Air is mechanically worked out of the lay-up by hand usually using serrated rollers. The vacuum direcdy helps to remove air in the wet lay-up via techniques such as using bleeder channels within the bag (using material such as jute, glass wool, etc.) to aid in the removal of air and also to permit drainage of any excess resin. This layup is than exposed to heat using an oven or heat lamp. 

Pari design Casting Compression Filament winding Injection Matched die molding Rotational Transfer compression Wet lay-up (contact molding)... 

Wet lay-up" refers to a process in which liquid resin systems of low viscosity are used to impregnate the reinforcements, either before or after the reinforcements have been laid in place. The liquid resin penetrates the fibers and displaces the air. The distinctive feature of this method is that the composite object is shaped into its final configuration while the resin component of the lay-up is still liquid (uncured). Cure is effected after the lay-up is completely in place and conforms exactly to the mold. 

Wet Lay-Up Process. Formulations are impregnated by hand or sprayed into fibers that are in the form of woven, knitted, stitched, or bonded fabrics. This is usually accomplished by rollers or brushes. Spray-up is a partly mechanized version of the hand lay-up process. The thermoset precursor is applied by means of a spray gun to the mold surface simultaneously with the chopped glass-fiber roving. Laminates are left to cure under standard atmospheric conditions. 

In pressure-bag molding the reinforcement and the resin mixed with catalyst are placed in a mold, and a flexible bag is placed over the wet lay-up after a separating sheet (such as cellophane) is laid down. The bag is then inflated with an air pressure of 20-50 psi (1.4—3.5 kg/cm ). The resin and reinforcement follow the contours of the mold (Figure 2.47). After the part is hardened, the bag is deflated and the part is removed. The technique has been used to make radomes, small cases, and helmets. 

Prepregs have advantages over resin wet lay-up fabrication systems (Chapter 5). The wet lay-up places the reinforcement in a mold cavity followed with literally pouring resin over the reinforcement. Resin or a gel coating can be applied to the mold surface prior to placement of the reinforcement to provide an improved molded part surface. The main advantages of prepregs over wet lay-up fabrication are ... 

Vacuum bag film is usually a polypropylene film, modified to resist elevated temperatures. The elastic nature of the film offers high formability and resistance to puncture, also permitting the film to be stretched over complex molds without need for a large number of tucks and folds, so improving the efficiency of the vacuum. The film is suitable for use with prepreg and wet lay-up laminating systems in an autoclave. 

Breather/bleed fabric is a 5 mm or 10 mm thick uncompressed felt of temperature-resistant synthetic fibers, treated with mold release. The material has good drapability, allowing use with large and complicated mold patterns. It can be used also as a bleed fabric to absorb excess resin from wet lay-ups. 

Conyplex in the Netherlands, like many series production boatbuilders uses glass fiber constructions, including in its latest Contest 44 and 50 yachts, to achieve easily driven hulls of modest displacement. Performance of its new-generation boats is further enhanced by wing keels, an RP wet lay-up appendage. The company has been transitioning to resin injection molding techniques. 

The primary structural role of the face/core interface in sandwich construction is to transfer transverse shear stresses between faces and core. This condition stabilizes the faces against rupture or buckling away ftom the core. It also carries loads normally applied to the panel surface. They resist transverse shear and normal compressive and tensile stress resultants. For the most part, the faces and core that contain all plastics can be connected during a wet lay-up molding or, thereafter, by adhesive bonding. In some special cases, such as in a truss-core pipe. 

Wet lay-up or contact molding Not economical for large volume production uniformity of resin distribution difficult to control only one good surface limited to simple shapes... 

Filament winding is basically a simple process, although numerous modifications have been developed to improve product quality. Moldings can be produced by either a wet lay-up process or from prepreg. 

Hand Lay-uplSpray up Spray up and open contact molding (hand lay-up) in one-sided molds is one of the cheapest and most common process for making fiber composite products. Typical products are boat hulls and decks, truck cabs and fenders. In a typical open mold application, the mold is first waxed and sprayed with gel coat and cured in a heated oven at about 49°C. In the spray up process, after the gel coat is cured, catalyzed resin (usually polyester or vinyl ester at 500-1,000 cP viscosity) is sprayed into the mold, along with chopped fiber. A secondary spray up layer imbeds the core between the laminates (sandwich construction). Then it is cured, cooled, and removed from the reusable mold. In hand layup processing, continuous fiber strand mat and other fabrics such as woven roving are manually placed in the mold. Each ply is sprayed with catalyzed resin (1,000-1,500 cP) and the resin is worked into the fiber with brush rollers to wet-out and compact the laminate. 

Fabrics Yams woven into a multiplicity of cloth styles with various thicknesses and strength orientations. D to K fibers, 2.5-40 oz/yd in weight. Starch size removed and compatible finish applied after weaving Wet lay-up for open molding, prepreg, high pressure lamination, and also some press molding. 

---