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The Defects of tranfer molding
Jan 29, 2018

        Limiting defects is key when commercial producing any sort of material. Transfer molding is no exception. For example, voids in a transfer molded parts significantly reduce strength and modulus. There can also be defects when fibers are used around sharp corners. The resin flow can create resin rich zones on the outside of these corners. I will focus in on the causes of these defects for the rest of the section.

 

Pressure distribution

There are several contributing factors to voids in the final product of transfer molding. One is a non uniform pressure distribution among the material being pressed into the mold. In this case the material folds in on itself and generates voids. Another is voids in the resin being forced into the mold before hand. This maybe obvious, but it is a main contributor. Things you can do to limit these molds include pressing the resin in at a high pressure, keeping the fiber distribution uniform, and using a high quality properly degassed base resin.

 

Sharp corners

Figure 3: Sharp corner generates voids in transfer molding

Sharp corners are the problems with all mold based manufacturing, including casting. Specifically in transfer molding corners can break fibers that have been placed in the mold and can create voids on the inside of corners. This effect is demonstrated in Figure 3 on the right. The limiting factor in these designs is the inner corner radius. This inner radius limit varies depending on resin and fiber selection, but a rule of thumbs is the radius though be 3 to 5 times the laminate thickness.


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