Draft angle

In practice

Forgings need more, typically 3–7°. Zero-draft walls are possible only with side actions or added cost.

Where it comes up

• Plastic injection moldingMolten thermoplastic injected into a steel or aluminum mold. Lowest piece price for plastic parts at 5,000+ a year.
• Zinc and aluminum die castingMolten zinc or aluminum injected into steel dies at high pressure. Thin walls and net shape at 2,500+ parts a year.
• ForgingClosed-die and open-die forgings in carbon, alloy, and stainless steel and aluminum, with grain flow for strength.

Related terms

Parting line

A parting line is the line on a molded or cast part where the two mold halves meet. It usually leaves a slight witness line and is where flash forms as the tool wears. Designers place it on an edge or noncosmetic surface and set draft away from it.

Core

A core is the half or insert of a mold that forms a part's inside features, such as the interior of a housing or a hole. In injection molding the core usually sits on the moving half, and the part shrinks onto it, so ejection happens from the core side.

DFM

DFM is design for manufacturability, the review of a part design against the limits of the process that will make it, before tooling is cut. It checks wall thickness, draft, radii, tolerances, and material choice. DFM changes are cheap before steel is cut and expensive after.

SPI finish

SPI finish is a mold surface finish grade defined by the Society of the Plastics Industry, now the Plastics Industry Association. Grades run from A-1, a diamond-buffed mirror, through B paper and C stone finishes to D bead-blasted textures. Glossy grades cost more to polish and maintain.