Clamshelling occurs when uneven pressure forces a die to warp, opening up or bulging in a shape resembling a clam shell. This deformation ruins the extrusion profile and often permanently damages the tooling. It typically happens when the material flow is unbalanced or the die design lacks sufficient structural support for the operating pressure.
Heard on the job
We had to scrap the run because the main die started to clamshell under the high viscosity resin.