Designing plastic parts for injection molding is both a science and an art. From material selection to part geometry and tooling strategies, every detail impacts the final part’s performance, quality, and manufacturability. At Crescent Industries, we bring over 70 years of experience to help our partners navigate these critical design choices, especially in high-stakes industries like medical, defense, and pharmaceutical.
In this guide, we explore proven strategies for successful injection molding design and why collaborating with an experienced partner like Crescent Industries can make all the difference.
1. Material Selection: The Foundation of Success
The choice of resin determines much of a part’s characteristics—strength, chemical resistance, temperature tolerance, and even aesthetics. Whether you're producing rugged military components or FDA-compliant medical devices, choosing the right material is critical.
Common materials used for molding include but are not limited to these:
- Polycarbonate (PC)
- Polypropylene (PP)
- Polyethylene (PE)
- ABS
- Nylon (PA)
- Thermoplastic Elastomers (TPE/TPU)
- Medical-grade and UV-stable resins for specialized applications
📘 Explore this Resin Raw Material Selection Guide for more information on all types of resins.
2. Design for Manufacturability (DFM): Saving Time and Cost
Design for Manufacturability is the process of optimizing a part’s geometry for efficient, defect-free production. At Crescent, we utilize DFM analysis and simulation tools to validate flow patterns, shrinkage rates, and warpage—before tooling ever begins.
Key DFM elements include:
Wall Thickness & Uniformity: Prevent Warping and Sink Marks
Maintaining a uniform wall thickness is essential for proper cooling and consistent material flow. Inconsistent thickness can lead to warping, voids, or weak points.
Tips: Ideal wall thickness: 0.080–0.160 inches (depending on material)
Gradual transitions between thick and thin areas
Use ribs (70% of adjacent wall thickness) to maintain strength
Ribs, Bosses, Fillets & Radii: Strength Without Excess Weight
Strategic design features improve mechanical performance while maintaining manufacturability:
Ribs: Add strength without thickening walls (keep height ≤ 3x wall thickness)
Bosses: Provide mounting or fastening points; support them with gussets
Fillets & Radii: Reduce stress concentrations and material flow issue
Gate, Runner, and Cooling Design: Efficiency Starts Here
Proper gate and runner design ensures the molten plastic flows evenly, fills all cavities, and cools uniformly. Gate size, location, and type (e.g., tunnel, edge, fan) directly affect flow quality and visual appearance.
Cooling system considerations: Peripheral and ejector pin venting
Cycle time reduction strategies
🎯 Get our full DFM Checklist to evaluate your part design readiness.
3. Avoiding Common Defects: Knit Lines, Flash & Warping
Design plays a huge role in reducing injection molding defects:
- Short Shots can result for material viscosity or not enough injection pressure.
- Flash results from poor clamping or venting.
- Warping often stems from uneven wall thickness or inconsistent cooling.
Simulations and iterative prototyping help resolve many of these before production.
📽️Watch the video on common injection molding defects.
4. Tooling Considerations: Getting the Mold Right the First Time
Mold quality is directly linked to part performance and production speed. Our tooling specialists consider:
- Number of cavities
- Cooling and ejection system design
- Tolerances based on resin shrink rates
- Compatibility of steel and resin materials
⚙️ See how Crescent delivers precision through our in-house Mold Building Capabilities.
Why Choose Crescent Industries?
As an employee-owned company with deep expertise in regulated industries, Crescent Industries provides more than manufacturing—we deliver true engineering partnerships. Our vertically integrated model allows us to control every aspect of your project from concept to production, ensuring:
- Consolidation of supply chain – build molds, molding, and post-processing work
- Reliable, compliant parts
- Full traceability and quality assurance
🏆 Discover how we serve Medical Device, Defense, Industrial markets with precision.
If you’re designing a new injection-molded product or revising an existing one, reach out to our expert team. Crescent Industries is here to help you engineer success.
📩Contact us today to get started on your next project.