Many product designers don’t realize that a seemingly small design decision can either double mold costs or save tens of thousands of dollars. Today, I’m sharing 5 simple yet highly effective design details—real cases we see every day in mold manufacturing.
The Problem: No draft angle or too small of an angle can cause the part to scratch during ejection. In severe cases, the part may get stuck in the mold.
How to Fix:
1°-2° draft angle for cosmetic surfaces
3°-5° for non-cosmetic surfaces
For deep cavities (>50mm depth), use 1° + 0.5°/25mm increment rule
How Much You Save: Proper draft angle design eliminates post-mold polishing and even mold rework. A mold modification caused by ejection issues can cost anywhere from hundreds to thousands of dollars.
The Problem: Undercut features (such as internal ribs or snap hooks) require additional sliders or lifter mechanisms. A single slider can cost thousands of dollars and increases mold failure risk.
How to Fix:
Position snap hooks on external surfaces or in the draw direction
Design internal features with an angle that allows forced ejection (>10°)
If unavoidable, evaluate whether post-processing can replace complex mechanisms
How Much You Save: Eliminating just one slider mechanism reduces mold cost by 10%-20% and shortens lead time by 7-10 days.
The Problem: Significant wall thickness variations cause sink marks, warpage, and residual stress concentration. In severe cases, parts deform beyond usability.
How to Fix:
Maintain uniform wall thickness, with variations within 20%
Use gradual transitions between thick and thin sections, with transition length at least 3 times the thickness difference
Keep rib thickness at 0.5-0.7 times the main wall thickness
How Much You Save: Proper wall thickness design reduces trial shots by 2-3 rounds, saving trial costs and material while improving yield rates.
The Problem: Sharp internal corners are stress concentration points prone to cracking. They also require special machining (such as EDM), which is time-consuming and costly.
How to Fix:
Add R0.5-R1.0 fillets to all internal corners
Maintain consistent radii on cosmetic surfaces
Ensure radii near parting lines don’t affect sealing
How Much You Save: Adding fillets reduces EDM time by up to 30%, significantly lowering machining costs.
The Problem: Parting lines (the seam where mold halves meet) placed on cosmetic surfaces affect appearance and may require post-polishing or painting.
How to Fix:
Position parting lines along product edges or corners
Place them on non-cosmetic surfaces or areas hidden after assembly
If a parting line must be on a cosmetic surface, ensure it’s on a flat area that will be covered or decorated
How Much You Save: Smart parting line placement eliminates post-processing steps like polishing and painting, reducing per-part cost by 15%-30%.
Each of these 5 points seems simple on its own, but combined, they can reduce mold costs by 20%-30% and shorten lead time by 15-20 days.
The key is: these optimizations cost almost nothing when done at the design stage. If done after the mold is already built, every single change adds expense.
If you’re designing a product that will go into molding, feel free to talk with us before finalizing your drawings. We can help identify potential issues upfront—saving costs right at the design phase.
