“Brown Tool & Mold is a custom injection mold manufacturer and mold maker in Nebo, North Carolina.”
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- 86 Waterfall Trail Nebo, NC 28761
- 937-620-4261
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Material selection is one of the most critical decisions in any injection molding program. The resin you choose directly affects shrinkage, cooling strategy, gate design, steel selection, draft requirements, and long-term part performance.
Material selection is critical because it directly affects part strength, durability, shrinkage, surface finish, and overall performance. It also drives key mold design decisions — the wrong material creates problems that cannot be fixed after the mold is built.
Shrink rate drives cavity dimensions. Viscosity determines gate size and runner design. Thermal properties determine cooling circuit layout and mold temperature requirements.
Materials with lower thermal conductivity or higher melt temperatures require longer cooling cycles. Proper cooling design must be matched to the selected material to optimize production.
Material properties such as shrink rate, stiffness, and thermal conductivity influence wall thickness requirements, warpage risk, draft angle minimums, and dimensional stability in production.
The following table covers commonly specified injection molding materials across commodity, engineering, and reinforced resin categories. Consult your material supplier datasheet for specific grade properties.
| Material | Shrink Rate | Key Properties | Common Applications | Mold Design Notes |
|---|---|---|---|---|
| PP | 0.010–0.025 in/in | Flexible, chemical resistant, low cost, semi-crystalline | Caps, closures, containers, living hinges, automotive | High shrink variation — cooling uniformity critical. Living hinge requires gate-to-hinge orientation. |
| PE | 0.015–0.040 in/in | Tough, flexible, excellent chemical resistance, semi-crystalline | Containers, industrial components, pipe fittings | High shrink — parts must be designed with generous draft. Slow crystallization requires adequate cooling time. |
| ABS | 0.004–0.008 in/in | Strong, impact resistant, good surface finish, amorphous | Consumer electronics, enclosures, automotive trim, appliances | Low shrink, predictable behavior. Good for tight tolerances. Susceptible to sink on thick sections. |
| Nylon (PA6/PA66) | 0.007–0.022 in/in | High strength, wear resistant, moisture sensitive, semi-crystalline | Structural components, gears, automotive, industrial hardware | Moisture absorption affects dimensional stability. Mold temperature control critical. High shrink variation. |
| PC | 0.005–0.007 in/in | High impact strength, heat resistant, optical clarity, amorphous | Lenses, medical devices, safety equipment, automotive lighting | High melt temperature and viscosity — requires robust gating. Sensitive to stress concentration and gate vestige. |
| Acetal (POM) | 0.018–0.025 in/in | Low friction, high dimensional stability, fatigue resistant, semi-crystalline | Gears, bearings, fasteners, precision components | High shrink — critical for tight tolerance parts. Formaldehyde off-gassing requires adequate venting. |
| Glass-Filled Nylon | 0.003–0.010 in/in | High stiffness and strength, improved dimensional stability vs. unfilled | Structural automotive, electrical connectors, industrial | Abrasive — consider tool steel hardness and gate design. Fiber orientation affects anisotropic shrinkage. |
| PEEK | 0.010–0.015 in/in | Extreme temperature resistance, chemical resistance, biocompatible grades available | Medical implants, aerospace, high-performance industrial | Very high melt temperature. Requires heated mold and specialized processing. Abrasive in filled grades. |
Note: Shrink rate ranges are typical for unfilled grades. Filled, reinforced, or specialty grades will vary. Always use the specific material datasheet for mold design calculations.
Material selection drives mold design decisions across every major engineering system. Brown Tool & Mold evaluates material properties during DFM to ensure the mold is designed correctly for the specified resin.
Different materials transfer heat at different rates. High-viscosity or high-melt-temperature materials require longer cooling cycles. Semi-crystalline materials like PP and nylon require adequate time for crystallization before ejection. Cooling design must account for the thermal properties of the specific material.
Material viscosity determines gate type, size, and injection pressure requirements. High-viscosity materials require larger gates and higher pressure. Shear-sensitive materials need careful gate sizing to avoid degradation. Glass-filled materials require gate design that manages fiber orientation.
Stiff or grippy materials require additional draft to release cleanly from the mold. Textured surfaces increase draft requirements further. Materials with high shrink may grip cores more aggressively, requiring careful ejection design to prevent part distortion.
Abrasive materials such as glass or mineral-filled resins accelerate gate and cavity wear. These applications require harder tool steels, carbide gate inserts, or surface treatments. Corrosive materials such as PVC or flame-retardant grades require stainless or nickel-plated steel.
Material selection is critical because it directly affects part strength, durability, shrinkage, surface finish, and performance. It also drives mold design decisions — shrink rate determines cavity dimensions, viscosity determines gating, and thermal properties determine cooling strategy. Choosing the wrong material creates problems that cannot be corrected after the mold is built.
Different materials transfer heat at different rates. Materials with lower thermal conductivity or higher melt temperatures require longer cooling times. Semi-crystalline materials require adequate time for crystallization. Proper cooling design must be matched to the specific material to optimize cycle time without compromising part quality.
Material viscosity and flow characteristics determine gate design including gate type, size, and location. High-viscosity materials require larger gates and higher injection pressure. Glass-filled materials require careful gate design to manage fiber orientation and avoid excessive wear at the gate land.
Engineering-grade materials should be used when parts require high strength, heat resistance, chemical resistance, or tight tolerances that commodity plastics cannot meet. These materials improve performance but require more precise mold design, tighter tolerances, and more controlled processing parameters.
Brown Tool & Mold evaluates material properties during DFM analysis — including shrink rate, viscosity, thermal properties, abrasiveness, and chemical behavior. Moldex3D simulation is used to validate fill and cooling performance for the specified material before mold design is finalized.
Common mistakes include selecting material based only on cost without considering shrinkage behavior, ignoring moisture sensitivity on hygroscopic resins, specifying filled materials without adjusting gate and steel design for abrasion, and failing to consider environmental exposure requirements for the finished part.
Contact Brown Tool & Mold to review your part and material specifications. Our engineering team evaluates material properties during DFM to ensure the mold is designed correctly for your resin.
Contact Our Engineering Team
“Brown Tool & Mold is a custom injection mold manufacturer and mold maker in Nebo, North Carolina.”