Draft angle

Part features cut into the surface of the mold perpendicular to the parting line require taper or draft to permit proper ejection. This draft allows the part to break free by creating a clearance as soon as the mold starts to open. Since thermoplastics shrink as they cool they grip to cores or male forms in the mold making normal ejection difficult if draft is not included in the design. If careful consideration is given to the amount of draft and shutoff in the mold it is often possible to eliminate side actions and save on tool and maintenance costs.

For untextured surfaces generally a minimum of 0.5 deg draft per side is recommended although there are exceptions when less may be acceptable. Polishing in draw line or using special surface treatments can help achieve this.

For textured sidewalls use an additional 0.4 deg draft per 0.1mm depth of texture.

Draft (A) in mm for various draft angles (B) as a function of molding depth (C).

Typically 1 to 3 deg draft is recommended. As the draft increases ejection becomes easier but it increases the risk that some sections may become too heavy.

Try to keep features in the parting line or plane. When a stepped parting line is required allow 7 deg for shutoff. 5 deg should be considered as a minimum. Drag at the shutoff will cause wear over time with the risk that flash will form during molding. More frequent maintenance will be required for this type of tooling if flash free parts are to be produced.

Parting line.