nylon injection molding

What Is Nylon?

Nylon is a semi-crystalline thermoplastic known for its:

• High tensile strength and mechanical performance

• Impact resistance and fatigue endurance

• Excellent wear and abrasion resistance

• Good chemical and thermal stability

Nylon can be unfilled or reinforced with glass fiber, mineral fillers, or other additives to enhance mechanical strength, stiffness, or dimensional stability in molded nylon parts.

Common Types of Nylon for Injection Molding

Several types of nylon are widely used in plastic injection molding with nylon:

Nylon 6 (PA6)

• High strength and toughness

• Good chemical resistance

• Moderate water absorption

• Excellent abrasion resistance

Nylon 66 (PA66 / nylon pa66)

• Higher heat resistance than PA6

• Excellent nylon material properties for mechanical parts

• Slightly lower moisture absorption than PA6

• Ideal for load-bearing nylon products

Nylon 12 (PA12)

• Low moisture absorption

• Flexible and fatigue-resistant

• High chemical resistance

• Often used in automotive fuel and fluid systems

Reinforced Nylons

• Glass-filled nylon (PA6 GF, PA66 GF)

  • Increased stiffness and strength

  • Reduced creep

  • Higher-dimensional stability

• Mineral-filled Nylon

  • Enhanced heat distortion resistance

  • Better dimensional stability

  • Slightly lower impact toughness than glass-filled grades

Choosing the right nylon resin grade is critical for achieving performance, durability, and manufacturability in injection-molded nylon parts.

Key Properties of Nylon Relevant to Injection Molding

When designing nylon injection molded parts, engineers must consider:

Mechanical Strength

• Excellent tensile strength and impact resistance

• High fatigue resistance, especially in glass-filled nylon and unfilled grades

Thermal Properties

• Heat deflection temperature ranges from 50°C (PA12) to 260°C (reinforced PA66 / nylon 66)

• Can withstand moderate continuous temperatures for industrial and automotive nylon plastic parts

Moisture Absorption

• Nylon absorbs moisture from the air, affecting dimensions, mechanical properties, and processability

• Unfilled nylons: up to 2–3% moisture by weight

• Glass-filled nylons: less moisture absorption, more dimensional stability nylon

Wear and Abrasion Resistance

• Excellent sliding wear performance

• Ideal for gears, bearings, bushings, and other moving nylon parts

Chemical Resistance

• Resistant to oils, fuels, greases, and some solvents

• Susceptible to strong acids or concentrated alkalis

Design Considerations for Nylon Injection Molding

Wall Thickness

• Uniform wall thickness is critical to avoid warping, sink marks, or voids in injection-molded nylon

• Recommended: 1.5–4.0 mm for standard nylon; thinner sections may be possible for PA12

Draft Angles

• Minimum 1°–2° for smooth ejection from the mold

• Textured surfaces require more draft

Rib and Boss Design

• Rib thickness: 50–60% of wall thickness

• Rib height: up to 3× wall thickness

• Boss wall: 50–60% of nominal wall

• Use fillets to reduce stress concentration in nylon injection-molded parts

Shrinkage Compensation

• Nylon shrinks 1–2% in the molding process, depending on grade and moisture content

• Glass-filled nylon shrinks less, ~0.2–0.8%

Processing Tips for Nylon Injection Molding

Drying

• Moisture must be removed before injection molding machines process the resin to avoid hydrolysis

• Typical drying conditions:

  • Temperature: 80–90°C (drying temperature)

  • Duration: 4–6 hours for unfilled nylon, 6–8 hours for glass-filled nylon

Melt Temperature

• PA6: 240–270°C (melting temperature)

• PA66: 260–280°C

• PA12: 210–250°C

• Glass-filled grades may require slightly higher temperatures

Mold Temperature

• 80–100°C for unfilled nylon

• 90–120°C for reinforced nylon

• Higher mold temperature helps reduce internal stress and shrinkage variations

Injection Speed and Pressure

• Moderate injection speed to prevent jetting and burn marks

• High injection pressure for glass-filled nylon due to higher viscosity

Gate Design

• Gates should feed thicker sections to avoid voids and sink marks

• Tunnel or edge gates are common

• Multiple gates may be needed for large, complex nylon parts

Common Challenges in Nylon Injection Molding

Warping and Shrinkage

• Caused by uneven cooling and moisture variation

• Minimized by uniform wall thickness, proper mold temperature, and reinforced nylon grades

Moisture-Related Defects

• Hydrolysis can cause discoloration and brittleness

• Moisture affects dimensional accuracy in nylon injection molding

Surface Finish Issues

• Flow lines and weld lines can appear in high-viscosity or improperly gated parts

• Polishing mold surfaces and adjusting the injection speed can improve the appearance

Tool Wear

• Glass-filled nylons are abrasive and may require hardened steel inserts

• Proper tool maintenance extends molding machine life

Applications of Nylon Injection Molding

Nylon’s versatility allows it to be used across many industries. As a thermoplastic engineering resin, nylon is commonly used in demanding plastic mechanical parts and industrial nylon components where mechanical strength and durability are critical.

1. Automotive Industry

• PA6 and PA66: under-the-hood components, engine covers, connectors, and structural brackets

• PA12: fuel lines, tubing, and flexible automotive nylon parts

• Glass-filled nylon: gears, clips, and reinforced brackets for higher tensile strength and creep resistance

Nylon injection molding allows plastic alternatives to metal in lightweight, high-performance automotive parts.

2. Electrical and Electronics

• Connectors, switches, and enclosures for electrical nylon components

• Excellent impact strength, low coefficient of friction, and chemical resistance

• Flame-retardant and transparent nylon grades are available for specialized molded nylon parts

3. Industrial Components

• Nylon gears and bearings, bushings, rollers

• High wear resistance and durable nylon materials

• Suitable for long-life polymer materials and demanding mechanical applications

4. Consumer Goods

• Sports equipment, handles, and clips

• Appliance components

• Injection-molded nylon offers durability, lightweight performance, and chemical resistance

5. Medical Applications

• Nylon grades approved for medical and food contact applications

• Surgical instrument handles, tubing, and housings

• Toughened nylon and nylon 11 can be used where biocompatibility and sterilizability are required

Advantages of Nylon in Injection Molding

• High mechanical strength, toughness, and impact-resistant nylon

• Excellent wear and fatigue resistance

• Good chemical resistance

• Lightweight compared to metals

• Can replace metal parts in many molded nylon products

• Available in reinforced nylon grades (glass-filled, mineral-filled) for better dimensional stability

Limitations and Considerations

• Nylon tends to absorb moisture, requiring drying of nylon before molding

• Shrinkage and warpage must be managed with proper molding design and temperature control

• Abrasive glass-filled nylon and mineral-filled nylon increase tool wear

• Not suitable for very high-temperature continuous service above ~200°C unless specialized grades like nylon 46 or high-temperature nylon plastics

Tips for Successful Nylon Injection Molding

• Material Selection – Choose the correct nylon material or PA nylon grade (PA6, PA66, PA12, PA11, reinforced) for mechanical properties and processing

• Drying – Always dry nylon according to manufacturer recommendations to avoid hydrolysis and poor surface finish

• Gate Design – Feed thicker sections to reduce voids; avoid cosmetic surfaces

• Uniform Walls – Minimize thick and thin sections for thin-walled parts to prevent warping

• Mold Temperature – Maintain proper mold temperature, increasing the mold temperature if needed to control shrinkage and improve surface quality

• Processing Parameters – Adjust melt temperature, injection speed, and appropriate injection pressure according to reinforced nylon or toughened nylon grades

• Post-Mold Conditioning – Some custom-molded nylon parts benefit from conditioning to stabilize dimensions

Nylon vs Other Engineering Plastics

Nylon is also preferred where strength, wear resistance, and flexibility are critical, especially in moving molded nylon parts or components under load.

Sustainability Considerations

• Recycling: Nylon can be recycled mechanically, but reinforced nylon grades require careful handling

• Bio-based nylons: Nylon 11 and PA610 derived from castor oil offer more sustainable alternatives

• Lightweighting: Nylon reduces part weight, contributing to fuel efficiency in automotive nylon parts

Future Trends in Nylon Injection Molding

• Advanced Reinforcements: Carbon fiber, nano-fillers for improved stiffness, conductivity, and high-stiffness nylon plastics

• High-Temperature Grades: PA46, PA66 high-temperature grades for engine components

• Bio-Based Nylons: More sustainable sources and production methods

• Hybrid Materials: Nylon blends with elastomers or additives for multifunctional plastic parts for industrial equipment

Final Thoughts

Nylon injection molding combines mechanical strength, durability, and versatility, making it one of the most widely used engineering plastics in injection molding. Proper material selection, design, and processing of nylon are essential to achieve high-performance, reliable molded nylon parts.

From automotive nylon parts and precision nylon gears to electrical nylon components, nylon enables manufacturers to create lightweight, durable, and cost-effective nylon products while meeting demanding application requirements.

Understanding nylon’s material properties, the nylon injection molding process, and its range of applications is critical for successful design, prototyping, and scaling of plastic injection molded nylon parts.