Vacuum assisted resin transfer molding (VARTM) is likely the most common acronym of all used in the discussion of low pressure closed mold reinforced composite molding. The often used VARTM acronym is most accurately applied to the process of vacuum infusion, that is where the composite is molded using a rigid mold to provide part geometry and a thin flexible membrane over the fiber, with outer atmospheric pressure compressing the fiber tight against the rigid mold surface. It should be noted however that VARTM simply means to add vacuum at the exit vent of the molding tool, thus any form of resin transfer molding in which vacuum is applied to the vent would qualify for the VARTM association. Often, the aerospace industry will have very high fiber volume composites molded within a rigid matched mold set in which the fixed cavity mold is clamped closed using a press and the resin injection pressures typically range less than 100 psi, yet could be as high as 600psi as used to fill the mold encapsulating the dry fiber within.

Required Strengths:

Reviewing the fact that the vast majority of molded parts have over the years adopted the typical fiber loading of 30% by weight as sufficient for most all applications, variations of resins have then enhanced the fiber properties for specific needs of heat or corrosion, as well as, surface finish. The other factor that is common to the most applications is the need for “stiffness” or “flex modulus”. Here in lies the issue with the VARTM process, by the fact that there is only one mold surface and the amount of fiber loaded upon that surface sets the part thickness, using the same fiber loading value per square area in the VARTM process as would be used for the other molding process, yields a much thinner laminate and thus a much more flexible laminate.