Design Smarter. Manufacture Better.
Injection molding is one of the most efficient, scalable, and cost-effective manufacturing methods for plastic parts. But the success of any injection molding project hinges on one thing: great mold design.
Whether you’re launching a new product or refining an existing one, this guide walks you through essential principles, best practices, and engineering tips to help you create molds that perform reliably, minimize production issues, and maximize part quality.
Why Mold Design Matters
A well-designed injection mold delivers:
- Consistent part quality
- Faster cycle times
- Lower manufacturing costs
- Longer mold life
- Minimal post-processing
Poor mold design, on the other hand, can result in warping, sink marks, short shots, flashing, or even costly mold rework. Investing time in design up front pays dividends in every production run.
Key Elements of Injection Mold Design
1. Part Geometry
Start with the part. The geometry of your component dictates many aspects of mold design:
- Wall thickness: Uniformity reduces shrinkage and warping.
- Draft angles: Necessary for easy ejection; typically 1–2° for most surfaces.
- Radii and corners: Sharp corners increase stress concentration and can cause flow problems.
2. Material Selection
Different resins behave differently. Consider:
- Flow characteristics
- Shrinkage rates
- Cooling requirements
- Chemical resistance
The mold must be designed to accommodate the unique properties of your chosen plastic.
3. Gate Design
Gates control how molten plastic enters the cavity. The right gate design affects:
- Fill pattern
- Pressure distribution
- Aesthetic finish
- Cycle time
Common types include edge gates, pin gates, and hot tip gates—each with pros and cons depending on part design and material.
4. Cooling System
Efficient cooling is key to fast cycle times and dimensional accuracy.
- Use conformal cooling where possible for complex shapes
- Optimize channel diameter and placement for uniform temperature
- Balance cooling to avoid warping
5. Ejection System
Proper ejection ensures the part is released without damage:
- Ejector pins
- Sleeves
- Stripper plates
- Air assist
Placement and timing are critical to avoid visible marks or part deformation.
6. Venting
Air and gas must escape as the cavity fills. Poor venting leads to:
- Short shots
- Burn marks
- Incomplete fills
Vents are typically small (0.001″–0.003″) and placed at end-of-fill areas.
7. Mold Materials and Finishes
Mold base and cavity materials affect tool life and surface finish. Options include:
- P20 steel (pre-hardened)
- H13 steel (high durability)
- Aluminum (for prototyping and short runs)
Surface textures or coatings may also be applied to improve release or aesthetics.
Design Tips for Manufacturability
- Minimize undercuts: These complicate mold action and add cost
- Design with consistent wall thickness to avoid sink and warp
- Use ribs and gussets for structural support without bulk
- Avoid deep cores unless necessary—they can increase cycle times
- Incorporate self-locating features like snap fits or alignment tabs
- Plan for assembly and downstream processes during early design
Common Design Mistakes to Avoid
- Neglecting draft angles
- Using overly tight tolerances
- Overcomplicating part geometry
- Poor gate or runner placement
- Inadequate cooling or venting
- Ignoring resin-specific needs