Nylon injection molding

This guide provides a comprehensive overview of PA injection molding and polyamide molding, covering material behaviour, tooling considerations, processing parameters, common challenges, and real-world applications. It is designed to help engineers, designers, and buyers optimize the injection molding process for efficient, reliable production of high-quality nylon components.

What Is Nylon Injection Molding?

Nylon injection molding is a specialized manufacturing process in which molten polyamide resin is injected into a mold cavity under high pressure, cooled, and then ejected as a finished part. This method is widely used to make nylon components that require durability, precision, and strong mechanical performance.

As a high-performance thermoplastic, nylon delivers excellent tensile strength, wear resistance, and heat resistance, making it ideal for engineering applications.

The nylon molding process is commonly applied to both standard and reinforced nylon molding grades, including glass-filled nylon, nylon 6 molding, and nylon 66 injection molding. These materials allow manufacturers to create molded nylon components with superior rigidity, reduced shrinkage, and enhanced stability.

Because nylon is hygroscopic and sensitive to processing conditions, the operation demands precise control over moisture content, elevated mold temperatures, and optimized cooling cycles. Compared with commodity thermoplastics, engineering plastic molding with nylon requires tighter parameter control to avoid defects, maintain part accuracy, and ensure optimal performance.

Overall, molded nylon offers excellent dimensional stability, supports complex geometries, and delivers long-lasting, high-quality parts for a wide range of industries.

Properties of Nylon

Nylon’s unique properties make it ideal for engineering applications. Its key characteristics include:

Mechanical Properties
Nylon is widely valued in thermoplastic injection molding because of its strong and reliable mechanical performance. With a typical tensile strength of 60–80 MPa, depending on the type of nylon and fillers, it is ideal for plastic part manufacturing where durability is essential.

The material offers excellent impact resistance, high fatigue resistance, and good creep performance. In precision nylon molding, these qualities help produce wear-resistant nylon parts that maintain their integrity under repeated mechanical stress.

Thermal Properties
As a high-temperature thermoplastic, nylon offers a heat deflection temperature between 80–180°C, depending on whether it’s unfilled or reinforced nylon. Its glass transition temperature sits around 45–50°C for PA6 and 50–60°C for PA66. These thermal characteristics allow nylon to maintain mechanical strength during molding with nylon and in applications exposed to heat, making it a preferred injection molding material for automotive and industrial components.

Chemical Resistance
Nylon plastic resists hydrocarbons, oils, greases, and diluted acids, making it suitable for demanding plastic injection molding with nylon applications. However, it remains sensitive to strong acids, alkalis, and oxidising chemicals. Engineers must understand nylon material compatibility during nylon mold design to ensure long-term part stability.

Electrical Properties
With strong insulating performance, nylon is valuable for electrical housings and connectors. Its low dielectric constant makes it ideal for electronic components produced via injection molding service.

Hygroscopic Nature
Nylon absorbs moisture readily, which affects dimensional stability, mechanical behaviour, and the overall molding process. Proper drying is essential before processing in an injection molding machine, as moisture can cause bubbles, splay, brittleness, or inconsistent injection speed during production.

Types of Nylon Used in Injection Molding

Several grades of nylon are commonly selected in injection molding, each offering different performance advantages based on application and processing requirements.

PA6 (Polyamide 6)
PA6 provides excellent toughness and strong mechanical properties of nylon, making it ideal for gears, bearings, and dynamic mechanical parts. With a moderate nylon melt temperature, it processes easily and delivers good wear resistance. However, the shrinkage rate of nylon must be considered when setting nylon part tolerances.

PA66 (Polyamide 66)
PA66 offers a higher melting point and better heat resistance than PA6, giving it superior stiffness and structural performance. It is widely used in automotive and industrial components exposed to elevated temperatures. Higher injection pressure for nylon is often required due to increased viscosity, and mold cooling for nylon must be controlled carefully to achieve consistent dimensional stability.

PA12
PA12 absorbs far less moisture than PA6 or PA66 and provides excellent chemical resistance, making it suitable for fuel lines, pneumatic systems, and flexible components. Its low water absorption also improves tolerance stability across varying environments.

Filled Nylons
Reinforced grades—such as glass-filled nylon—offer increased stiffness, reduced shrinkage, and excellent dimensional control. Mineral-filled grades provide lower cost and moderate rigidity, while internally lubricated grades reduce friction for sliding parts. These materials require specific nylon tooling requirements due to their abrasive nature and altered flow characteristics.

Other Specialty Grades
Specialty nylons include flame-retardant formulations for electronic housings, UV-stabilized grades for outdoor applications, and additive-enhanced materials modified with lubricants, impact modifiers, or gas-resistant properties. These variants support cycle time optimization and improve part performance across diverse industries.

Nylon Injection Molding Process

The injection molding process for nylon involves several critical polymer processing steps, each essential for maintaining the material’s mechanical properties, dimensional stability, and long-term performance in engineering applications. Because nylon is one of the most hygroscopic plastics, strict moisture control in nylon is necessary to prevent defects and degradation during molding.

Material Drying
Nylon resin must be thoroughly dried because absorbed moisture can cause bubbles, splay, and reduced impact strength. Typical pre-drying nylon resin conditions are 80–100°C for 4–6 hours, ensuring moisture content drops below 0.2%. Proper drying is especially important for parts like nylon gears and bushings or nylon automotive components.

Melting and Plasticising
Nylon’s relatively high melting point (220–280°C depending on grade) requires elevated barrel temperatures compared with commodity plastics. Stable melt temperature prevents thermal degradation and maintains abrasion resistance for components such as bearing surfaces and sliding mechanisms.

Injection
The molten material is injected into the mold under pressures typically between 70–150 MPa. Controlling shear rate is essential to preserve polymer chains and ensure consistent strength for parts like nylon fasteners, electrical housings, nylon clips, and nylon clips and brackets.

Packing and Holding
Packing pressure compensates for nylon’s natural shrinkage and helps avoid voids. Holding pressure is kept at 50–70% of injection pressure, with holding time ranging from 5–20 seconds, depending on wall thickness.

Cooling
A high-temperature mold—80–100°C for PA6 or 90–120°C for PA66—improves crystallinity and enhances stiffness and dimensional stability. Cooling duration varies with part geometry, especially for thicker engineering applications nylon.

Ejection
Early ejection may lead to warpage or distortion. Adequate draft angles (1–3°) and polished surfaces ensure clean release, protecting the final mechanical properties of the molded nylon component.

Common Defects and Solutions in Nylon Injection Molding

Defects in nylon plastic injection molding often arise from the material’s semi-crystalline structure, its strong tendency to absorb moisture, and the higher temperature control requirements of resins such as nylon 6 and nylon 66, nylon 46, nylon 11, and nylon 12.

Understanding nylon’s material properties—including high tensile strength, fatigue resistance, wear resistance, and low friction—is essential for producing reliable molded nylon parts across various injection molding projects.

Warpage
Warpage is common because nylon cools at different rates due to its crystalline nature. Uneven cooling or non-uniform wall thickness can distort the part.
Solution: Improve mold venting, use uniform wall thickness, optimize cavity layout, and increase mold temperature for better crystalline stability in injection-molded nylon.

Bubbles or Voids
Voids often result from moisture or insufficient packing during molding. Since nylon tends to absorb moisture, improper drying leads to trapped steam and bubbles.
Solution: Dry resin to the recommended drying temperature (usually 80–100°C), maintain <0.2% moisture, and ensure proper packing pressure to enhance mechanical strength in nylon products.

Splay Marks
Splay appears as silvery streaks and is mainly caused by moisture in hygroscopic PA 6 or other grades.
Solution: Fully dry the resin, reduce injection speed, and stabilise barrel temperature to prevent moisture flashing at high temperatures.

Short Shots
These occur when molten nylon cannot fill the mold completely, often due to insufficient flow or low melt temperature.
Solution: Increase melt temperature, raise injection pressure, improve venting, or adjust gate size to maintain good flow in nylon plastic used in injection molding.

Flow Lines
Visible lines on the surface can come from improper injection speed, temperature imbalance, or inconsistent filling patterns.
Solution: Optimize process parameters on injection molding machines, balance injection speed, increase resin temperature, and improve gate design to ensure smooth filling.

By addressing these issues with correct processing strategies, manufacturers can achieve consistent, high-quality performance from nylon’s exceptional high-temperature resistance and engineering-grade properties.

Advantages of Nylon Injection Molding

Nylon injection molding provides a wide range of performance benefits that make it a preferred solution for demanding engineering applications. Its exceptional chemical resistance (nylon), strong mechanical behaviour, and excellent durability enable manufacturers to create fatigue-resistant nylon parts suitable for both industrial and consumer environments. Below are the key advantages, expanded with design and processing considerations important in modern production.

High Mechanical Strength
Nylon delivers outstanding tensile strength, impact toughness, and abrasion resistance (nylon). When combined with glass fibres and additives, it forms highly reinforced polymer parts ideal for gears, bearings, structural components, and high-load assemblies.

Thermal Resistance
Nylon maintains mechanical performance at elevated temperatures, with stable strength and stiffness even during continuous use. Proper gate design for nylon, controlled runner system for nylon molding, and optimised melt management help retain performance and minimise thermal degradation.

Chemical Resistance
Its excellent chemical resistance allows nylon to withstand oils, fuels, greases, and solvents, making it highly suitable for automotive and mechanical applications. Compared with Nylon vs ABS molding, nylon offers superior chemical durability and higher temperature capability.

Dimensional Stability
Filled grades—especially glass-filled nylon—offer reduced thermal expansion (nylon), lower shrinkage, and improved tolerance control. Designers must incorporate correct nylon wall thickness considerations, and molders often use specialised mold release agents for nylon to ensure consistent results.

Versatility in Processing
Nylon supports overmolding, multi-material molding, colour customization through color additives for nylon, and different surface-level outcomes from matte to polished nylon surface finish. Both hot runner systems (nylon) and cold runner molds can be used, depending on part size, flow requirements, and cost targets.

Long Service Life
Nylon’s exceptional fatigue resistance, abrasion performance, and long-term stability contribute to parts that can endure years of stress and mechanical loading. Robust process control and injection molding troubleshooting help manufacturers minimise defects and ensure reliable nylon part assembly.

With its combination of strength, chemical durability, and manufacturing flexibility, nylon continues to outperform many traditional materials and remains a core engineering thermoplastic for high-performance molded components.

Cost Considerations in Nylon Injection Molding

Material Cost
Nylon is a synthetic engineering polymer with superior physical properties, including heat resistance, temperature resistance, and a low coefficient of friction. Because of these engineering-grade characteristics, the material cost is usually higher than general plastics. When manufacturers make nylon injection molding parts, they must also account for the fact that nylon absorbs moisture; its rate of water absorption affects processing stability. Properly drying nylon before production is essential to maintain quality.

Mold Cost
Precision molds are required to produce high-performance injection molded nylon parts, especially for applications demanding tight tolerances. Tooling cost can increase further depending on nylon resin selection, reinforced materials, or advanced part geometry. Projects involving nylon thin-wall molding or nylon thick-wall molding may require specialised gate and cooling layouts to manage nylon’s flow behaviour and shrinkage. As a result, mold cost is generally higher than for standard plastics.

Cycle Time
Cycle time tends to be longer because nylon requires high melt and mold temperatures. Stable quality control and proper temperature management are essential, especially since nylon is prone to moisture-related defects if not processed correctly. Longer cooling and drying cycles directly affect overall production efficiency.

Secondary Processing
Additional operations such as machining, painting, assembly, or overmolding increase total cost. However, many injection molding applications benefit from nylon’s tensile and flexural strength, chemical resistance, and durability. These advantages often outweigh the extra secondary processing expenses.

Production Volume
Total nylon molding cost decreases significantly at higher volumes. For large-scale manufacturing solutions, nylon remains a strong choice because nylon resists wear, chemicals, and high temperatures. Nylon injection molding applications across automotive, electronics, and consumer products demonstrate that although initial cost may be higher, long-term performance provides excellent value.

Conclusion

Nylon injection molding remains a core process in the production of high-performance molded plastics. Because nylons are semi-crystalline materials within the broader polyamide family, they offer a wide range of properties, including high tensile strength, excellent wear resistance, and a high melting point that makes them suitable for applications requiring durability and heat stability.

During production, molten resin is fed from the machine hopper into precision tooling that often requires a higher mold temperature compared with commodity plastics. Although nylon is prone to shrinkage, proper process control ensures dimensional accuracy and consistent results.

The technology supports a wide variety of demanding sectors—nylon for industrial components, gears, bushings, and mechanical parts, as well as nylon for consumer goods such as housings, fasteners, and everyday durable products. With grades ranging from standard PA6 to engineered PA66, manufacturers often compare nylon 6/6 vs nylon 6 to match performance with cost and design needs.

As industries move toward sustainable nylon molding, automation, and improved resin technology continue to advance the efficiency and quality of applications that require precision and reliability. Overall, nylon injection molding delivers strong, versatile, and long-lasting solutions that remain essential across modern manufacturing.