Key facts
Injection mold design guide: draft angles, wall thickness, gate selection, ejection and cooling rules from a China mold maker that builds 2,000+ molds a year.
Good parts start with a good mold, and good molds follow a few non-negotiable rules. This guide collects the design rules our engineers apply to every project – so your part is moldable, durable and cost-effective before steel is cut.
Draft Angles
Every vertical face needs draft: 1-2 degrees for textured surfaces, 0.5 degree minimum for polished cores, more for deep ribs. Without draft, parts scuff on ejection and cycle times stretch. If your product cannot show draft, we design ejector placement and polish direction to hide it – but tell us early.
Wall Thickness and Uniformity
Keep walls uniform: 1.5-3.0 mm for most resins. Thickness changes sink and warp. Where structure demands thickness, core it out and add ribs at 50-60% of the adjoining wall so they do not sink on the show face.
Gates, Ejection and Cooling
- Gates: place where vestige is acceptable and filling is balanced; submarine gates hide under the parting line, hot tips land on non-cosmetic zones
- Ejection: ample ejector area on ribs and bosses prevents push marks on cosmetic faces
- Cooling: uniform baffle and bubbler layouts cut cycle time more than any other single factor
- Venting: vent at fill ends to prevent burns and short shots
Get a Free DFM Review
Upload your 3D files and our engineers will mark up draft, thickness, gate and ejection issues in a free DFM report within 24 hours – before you commit to tooling.
Features that look free but are not
Some design details cost nothing to draw and plenty to mold. Zero-draft cosmetic walls need lifter or slide mechanisms on every side. Text that sits on a draft-facing surface fills poorly and wears the steel fast. Sharp internal corners concentrate stress in the part and cracking risk in the mold – a 0.5 mm radius costs nothing and removes both problems. Rib-to-wall ratios above 60 percent guarantee sink marks opposite every rib.
None of this means the design must be boring – it means the moldable version of your idea should be decided before quoting, not discovered during trials. Send the part early: the DFM report prices each risky feature separately, so you choose with numbers. Everything above feeds directly into steel decisions and the simulation stage.