I'm working on a project that involves pressing a softened thermoplastic sheet in a two-part mold to form a part 0.090" thick. None of us at our small company are experts in matched molds, and we've come up against a question that must be answered before we put more financial resources into the project.

The shape that we are working with can be approximated as an arc, with the open side up. That makes a female mold with a cupping shape and a male mold with a rounded shape. Our question resides in the pressures that we can achieve along the side walls that approach vertical. In my mind, this is a simple statics problem. Assuming there are no other significant effects besides the normal force between the mold faces, then if $F$ is the pressing force and $\theta$ is the angle of the sidewall, measured from horizontal, the sidewall normal force $N$ will simply be $N=F\sin(\theta)$.

If my assumptions are good and shear doesn't play a significant effect on the final geometry, then $N$ is reduced to below 20% of $F$ when $\theta=10^{\circ}$. That has potential to heavily influence the quality of part in those regions. My question is, as someone with no prior molding experience, is the normal force the only significant player when it comes to pressing a part at steep angles?


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