Design for Manufacturability (DFM) is one of the most critical steps in ensuring injection molded parts are produced efficiently, cost-effectively, and with consistent quality. Catching design issues at the CAD stage can save weeks of lead time and thousands of dollars in tooling rework. This guide expands on key DFM checks, material considerations, and practical tips to help engineers and buyers specify parts that moldmakers can build right the first time.
Top 5 DFM Checks
- Draft Angles: Provide at least 1–2° on polished surfaces, 3–5° on textured surfaces, and more for deep ribs or slides.
- Uniform Wall Thickness: Avoid thick masses; use ribs and coring to maintain consistent cooling and shrinkage.
- Gate Location: Place gates away from cosmetic surfaces and minimize weld lines in critical areas.
- Ejection Strategy: Add draft and ejector land to reduce scuffing; plan steel-safe areas where adjustments may be needed.
- Shrink & Tolerance: Account for resin shrinkage values and tolerance stack-up during CAD design.
Material-Specific Guidelines
- ABS: Good dimensional stability; requires 1–2° draft.
- Polypropylene (PP): Higher shrink; use uniform walls to reduce warpage.
- Glass-Filled Nylon: Very abrasive; plan for higher draft and steel wear protection.
- Polycarbonate (PC): High cosmetic requirements; surfaces often require SPI A/B finishes.
Tooling Implications
- Undercuts without draft may require slides, lifters, or collapsible cores.
- Thick sections increase cycle time and may require copper alloy inserts to improve cooling.
- Lack of venting around gates can cause burn marks or short shots.
Cycle Time & Cost Impact
Bad DFM not only increases tooling cost, but it also directly impacts production cost. Thicker walls or poor venting mean longer cycles and higher press tonnage requirements. Optimizing design upfront shortens cycles and reduces scrap.
Case Example
A customer designed a consumer part with 0° draft and 4 mm thick walls. Without intervention, the tool would have required lifters and experienced long cooling times. After a DFM review, adding 2° draft and coring the walls down to 2.5 mm eliminated lifters, cut cycle time by 25%, and reduced press requirements by 50 tons.
5 Key Takeaways
- Always add a draft early in CAD design.
- Use ribs and coring to reduce thick walls.
- Gate away from cosmetic areas.
- Plan for resin shrinkage and tolerance stack-up.
- Work with your moldmaker early to validate assumptions.
Work with Brown Tool & Mold
Send your CAD model for a free DFM pre-check. Our engineers will provide annotated feedback and recommendations to optimize your design before tooling. Contact us today to accelerate your project and reduce risk.
