Thermoforming against Injection for Volumes below Fifty Thousand Units
Thermoforming delivers lower total landed cost below fifteen thousand units by saving upfront tooling capital, beyond which injection piece price efficiency dominates.
Demolding Draft
Meaning
Tapered angles are incorporated into the vertical walls of a mold cavity to facilitate the ejection of the plastic part. This design feature, known as demolding draft, reduces the friction between the polymer and the steel walls as the mold opens and ejects the molded object. It applies to all surfaces parallel to the direction of mold opening.
High draft is required for deep-draw parts but is restricted where straight vertical walls are functionally necessary.
Friction Reduction
As the polymer cools, it shrinks onto the steel core of the mold and creates a clamping force. Introducing a demolding draft allows the molded part to break free from the steel surface almost instantly upon the start of the ejection stroke. This design prevents the ejector pins from pushing through the hot plastic.
Texture Requirement
Textured surfaces on a molded part increase the resistance to ejection and require additional clearance. To avoid drag marks on a leather-grain or matte finish, the demolding draft must be increased by approximately one degree for every twenty-five micrometers of texture depth. Smooth, polished surfaces can function with much smaller angles.
Part Defect
Insufficient taper leads to high ejection force and cosmetic damage. It results in scuffing or stress whitening on the part walls. In severe cases, the part sticks to the core and stops the automatic cycle of the machine.