RTM Library Articles:

What is RTM?

Resin Transfer Molding (RTM) is a low pressure, closed molding process which offers a dimensionally accurate and high quality surface finish composite molding, using liquid thermoset polymers reinforced with various forms of fiber reinforcements. Typically polymers of Epoxy, Vinyl Ester, Methyl Methacrylate, Polyester or Phenolic are used with fiberglass reinforcement. Other reinforcements, are offered for more demanding applications such as Arimid, Carbon and Synthetic fibers either individually or in combination with each other.

The matrix selection of polymer and reinforcement dictates both molding material cost, as well as molding mechanical and surface finish performance. Along with the polymer and reinforcement the addition of mineral fillers may be added to enhance fire retardancy, flex modulus and surface finish.

Reinforcements are presented in their dry form to the mold in either binder-bound chopped mat, random-continuous strand mat or woven cloth format. The fiber has been either "preformed" to the exact shape of the molding tool in a previous operation or is hand-tailored during the loading process in the molding tool. After the fiber is installed into the mold, a premixed catalyst and resin is injected into the closed mold cavity encapsulating the fiber within. The primary surface of the molding may be gel-coated, a process of spraying the mold surface before installing the fiber. If a gel coat is not required, the exterior finish would be the same from the front to back of the molded part. The RTM process has the inherent advantage of low-pressure injection, it usually does not exceed 100 psi of resin injection pressure during the mold-fill process. The most common application of JHM Technologies is molded with a cross-sectional thickness of 3mm or 1/8th” with 30% fiber content by weight of the total laminate.

The RTM Process

Resin Transfer Molding (RTM) is a low pressure, closed molding process, where a mixed resin and catalyst are injected into a closed mold containing a fiber pack or preform. After the resin has cured, the mold can be opened and the finished component removed.

A wide range of resin systems can be used including: polyester, vinylester, epoxy, phenolic and methyl methacrylates, combined with pigments and fillers including aluminum trihydrates and calcium carbonates if required. The fiber pack can be glass, carbon, arimid, or a combination of these.

The Benefits of using RTM

 Closed Molding process is cleaner and healthier which attracts higher skilled employees.

 Closed Molding operator turn-over is dramatically reduced through improved working conditions.

 Closed Molding area has organized process flow to maximize throughput efficiency.

 Moldings can be manufactured to close dimensional tolerances.

 Components will have good surface finish on both sides.

 Selective reinforcement and accurate fiber management is achievable.

 Ability to build-in fiber volume fraction loadings up to 65%.

 Consistency in thickness and fiber loading, resulting in uniform shrinkage.

 Inserts may be incorporated into moldings.

 Tooling costs comparatively low compared to other manufacturing processes.

 Uses only low pressure injection.

 Low volatile emission during processing.

 Ability to produce near net shape moldings, reducing material wastage.

 Process can be automated, resulting in higher production rates with less scrap.

 Ability to mold complex structural and hollow shapes.

 Low resultant voidage in molded components.

 Ability to achieve from 0.1mm to 90mm laminate thickness.