Mould release — the process by which a formed plastic part separates cleanly from the tool surface — is one of the less glamorous but critically important aspects of vacuum forming. Problems with release cause surface defects, dimensional inaccuracy, and in severe cases damage to either the part or the tool. At Jabro Games, release characteristics are a key consideration in both tool design and material selection.
Draft Angle: The Primary Release Mechanism
The most fundamental release mechanism in vacuum forming is draft angle — the slight taper applied to vertical walls that allows the formed part to pull away from the tool without tearing or distortion. As a general rule, a minimum of two degrees of draft is required on all surfaces that are parallel to the direction of demoulding. Surfaces with insufficient draft cause the part to grip the tool, resulting in distortion or surface marking as it is forced off.
Tool Surface Finish and Release Agents
The surface finish of the tool affects release behaviour. Highly polished surfaces can cause suction between the plastic and the tool, making release difficult — a counter-intuitive finding for those who assume smoother is always better. A fine textured or bead-blasted surface can actually aid release by reducing the contact area between part and tool. Where release is difficult despite adequate draft and appropriate surface finish, a release agent applied to the tool surface can assist demoulding without affecting part quality.
Air Blow-Off
Most professional vacuum forming machines incorporate an air blow-off system that directs a pulse of compressed air between the part and the tool surface to assist release. The timing and pressure of this air pulse is adjusted to suit the specific tool and material combination. In some applications, strategically placed air ejection ports in the tool itself are used to assist release of particularly difficult-to-demould geometries.
Temperature at Demould
The temperature at which the part is demoulded affects both release behaviour and dimensional stability. Parts removed from the tool too early — while still warm and flexible — may distort as they cool. Parts left too long may cool to the point where shrinkage causes them to grip the tool more tightly. Optimising demould temperature for each material and tool combination is an important part of process development.
Our experienced team at Jabro Games manages all aspects of the forming process to deliver consistent, high-quality parts. Contact us at jabrogames.com.