A Comprehensive Analysis of the Injection Molding Process for PA66 Plastic Materials
- A Comprehensive Analysis of the Injection Molding Process for PA66 Plastic Materials
- What is nylon material?
- What is Nylon PA66?
- Basic chemical and physical properties of PA66 plastic
- Characteristics of PA66 plastic after injection molding
- Details to consider when injection molding PA66
- Main difficulties in PA66 injection molding process
- Why do most injection-molded plastic products use PA66 material?
- Applications and Industry Use Cases of PA66 Material
- Elimold is your best partner for PA66 injection molding projects.
- in conclusion
Polyamide (PA), commonly known as nylon, is a widely used semi-crystalline thermoplastic, renowned for its excellent abrasion resistance, low density, and high thermal stability. This material, depending on the carbon number of the diamine and diacid, is synthesized from two monomers, resulting in nylon varieties such as PA46, PA66, PA610, PA612, and PA1010. PA66, due to its superior mechanical properties, heat resistance, and chemical stability, is widely used in the automotive, electronics, and machinery industries. To fully understand the injection molding manufacturing of PA66 plastic material, it is first necessary to understand its basic physicochemical properties and the technical details that need attention during the injection molding process.
What is nylon material?
First, let’s briefly understand what nylon is. Nylon is a man-made fiber and one of the most commonly used polyamides. This material refers to a class of synthetic polymers composed of polyamides. Nylon is a silk-like material made from petroleum and is typically melted into films, various shapes, or fibers. By adding other properties or additives, nylon can be derived into many different types. Currently, nylon is widely used in almost all industries. You can use it to make a variety of plastic products. It is lightweight, durable, strong, and wear-resistant.
What is Nylon PA66?
Nylon has many variants. Generally, nylons synthesized from two monomers based on the number of carbon atoms in the diamine and diacid are: PA46, PA66, PA610, PA612, PA1010, etc. They are also named according to the number of carbon atoms in the monomers: Nylon PA6, PA11, PA12, etc. One such variant is PA66, also known as Nylon PA66. It is one of the earliest nylon materials. Wallace Hume Carothers invented it in 1935 at the DuPont research center. To date, it has become the most widely used nylon material in the world. Companies use PA66 plastic to manufacture products because of its excellent performance balance and relatively low price. Furthermore, it has high rigidity and toughness, as well as excellent tensile strength.
Basic chemical and physical properties of PA66 plastic
PA66 plastic has a relatively high melting point among polyamide materials. It is a semi-crystalline material. PA66 plastic maintains high strength and stiffness even at high temperatures. Moreover, the melting point of PA66 is between 250-265℃, significantly higher than many general-purpose plastics such as PP and PE. This high melting point directly affects the selection and control of processing temperature. Its glass transition temperature (Tg) is approximately 50-60℃, a parameter that determines the critical point of morphological change during processing. The crystallinity of PA66 is typically between 35-50%, and its crystallization behavior has a significant impact on the shrinkage rate, dimensional stability, and mechanical properties of the finished product.
From a molecular structure perspective, PA66 is formed by the condensation polymerization of hexamethylenediamine and adipic acid. The amide bonds (-CONH-) in the molecular chain can form strong hydrogen bonds, which endows the material with high mechanical strength, but also leads to significant hygroscopicity. The equilibrium water absorption rate of PA66 can reach 2.5-3.0%, and the presence of moisture will significantly affect the melt viscosity and processing behavior.
Characteristics of PA66 plastic after injection molding
PA66 retains its hygroscopic properties after molding, the degree of which depends primarily on the material composition, wall thickness, and environmental conditions. The impact of hygroscopicity on geometric stability must be considered during product design. Various modifiers are frequently added to improve the mechanical properties of PA66 plastic. Glass is the most common additive; sometimes synthetic rubbers such as EPDM and SBR are added to improve impact resistance. PA66 plastic has low viscosity, resulting in good flowability (though not as good as PA6). This property allows for the processing of very thin components. Its viscosity is highly sensitive to temperature changes. The shrinkage rate of PA66 plastic is between 1% and 2%, which can be reduced to 0.2% to 1% by adding glass fiber additives. The difference in shrinkage rate between the flow direction and the direction perpendicular to the flow direction is significant. PA66 plastic is resistant to many solvents, but its resistance to acids and some chlorinating agents is relatively weak.
Details to consider when injection molding PA66
Our engineering team has accumulated extensive experience in the injection molding of PA66 plastic materials (having manufactured over 10,000 different nylon plastic products to date). Below are the lessons learned from our daily experience in manufacturing nylon plastic products.
Material drying
For PA66 material, drying before molding is necessary. Generally, drying in an 85°C hot air oven is required before molding to remove moisture. However, if the material’s moisture content is greater than 0.2%, it should be vacuum dried at 105°C for 12 hours. This will ensure optimal product results.
Mold temperature control
Mold temperature affects the appearance of the final molded product from PA66 material and can alter its crystallinity. Therefore, Elimold’s engineering team typically recommends a mold temperature of 80°C. If the manufactured product has a thin-walled design, annealing may be necessary to maintain dimensional stability. Especially at mold temperatures below 40°C, the crystallinity can change over time, so the mold temperature must be carefully evaluated based on the mold components and material.
Injection speed control
Injection speed is crucial. Improper operation can ruin the entire molding process. Too high a speed can cause material overflow and damage. Too low a speed can lead to air bubbles in the mixture, resulting in uneven material mixing. Therefore, this aspect is critical. For PA66, the injection speed should be relatively high. However, if the grade is reinforced, the injection speed should be slightly lower.
Melt temperature control
Melt temperature is another critical factor to consider when injection molding PA66 . Remember, as we mentioned earlier, this process requires heating. That is, the material being molded needs to be heated. Typically, PA66 is heated to a liquid state for molding. Melt temperature refers to the temperature at which PA66 melts. If the temperature is too low, it will melt slowly and unevenly. However, if the temperature is too high, it may damage the material. Therefore, two melt temperatures are recommended: 275-280°C or 260-290°C. However, please note that this depends on the properties of PA66. If you are modifying these parts and they are glass fiber reinforced PA66, then we recommend a melt temperature below 300°C.
Injection pressure control
Injection pressure is crucial for the shaping of PA66 plastic products , primarily because it affects the shrinkage or deformation of the molded product . The key is finding a balance. Typically, we select an appropriate pressure based on both the characteristics of the PA66 material and the mold design . The injection pressure is determined by utilizing their properties. Furthermore, we can follow some basic standards. Generally, the pressure should be between 75-125 MPa.
Gate and runner design
Gates and runners are also crucial for PA66 material molding. The gate’s location is vital for controlling product cooling, which helps manage the rapid cooling phase. While you can use any type of gate, we need to ensure its location is correct . Additionally , we need to pay attention to the gate opening size. Ensure it is no less than half the part’s thickness. Once these conditions are met, production can begin. When using cold runners, the gate can be larger. However, when using hot runners, the gate should be smaller. For submersible gates, the gate diameter should be 0.75 mm.
Main difficulties in PA66 injection molding process
PA66, as a high-performance engineering plastic, presents processing challenges primarily due to its stringent drying requirements, narrow processing window, high shrinkage rate, and sensitivity to shear history. These challenges necessitate a multi-pronged approach, including material modification, process optimization, and equipment improvement. Below, Elimold’s engineering team summarizes the main difficulties in PA66 injection molding based on the material’s characteristics and their experience manufacturing over 10,000 PA66 plastic products.
Strict moisture control requirements
The primary challenge in processing PA66 is its extremely high hygroscopicity. Undried PA66 undergoes hydrolytic degradation during melting, leading to a decrease in molecular weight and a significant reduction in the mechanical properties of the finished product. Studies have shown that when the moisture content exceeds 0.2%, noticeable defects such as bubbles and silver streaks will occur during processing. Precise control of drying process parameters is necessary: typically, drying at 80-90℃ for 4-6 hours is required to reduce the moisture content to below 0.1%. Dried material that cannot be used immediately must be properly sealed and stored. In actual production, this requirement increases equipment investment and energy consumption, and also extends the production cycle.
Narrow molding temperature window
PA66 has a relatively narrow processing temperature window, typically controlled between 270-290℃, a range only about 20-30℃ higher than its melting point. Too low a temperature leads to poor melt flow and difficulty in mold filling; too high a temperature causes thermal degradation, resulting in yellowing and decreased mechanical properties. Therefore, controlling the melt temperature is crucial. Studies show that when the temperature exceeds 300℃, the molecular weight of PA66 decreases rapidly, and its intrinsic viscosity can drop by more than 20% in a short period. This sensitivity requires processing equipment with a precise temperature control system, increasing both the technical difficulty and equipment cost.
High shrinkage and dimensional stability issues
PA66 has a molding shrinkage rate between 1.5% and 2.5%, higher than many engineering plastics. This high shrinkage stems from its crystallinity; as it cools from the molten state, the molecular chains tend to become more ordered, resulting in significant volume shrinkage. The shrinkage behavior exhibits marked anisotropy: shrinkage in the flow direction is typically 0.3-0.5% less than that in the perpendicular direction. This difference can cause warping and deformation of the finished product, especially for thin-walled or complex-shaped parts. This characteristic must be considered during mold design, often requiring multiple trial molding adjustments to obtain a satisfactory product.
Sensitivity of melt viscosity to shear rate
PA66 is a pseudoplastic fluid, meaning its apparent viscosity decreases significantly with increasing shear rate. While this characteristic is beneficial for improving mold filling performance by increasing injection speed, it also introduces complexity into process control. In actual injection molding, the shear rate of the melt passing through the gate can reach as high as 100,000 s⁻¹, at which point the viscosity can decrease by 2-3 orders of magnitude compared to low shear rates. This drastic change requires precise control of injection parameters; otherwise, defects such as flash and underfilling can occur. Furthermore, high shear can also cause molecular chain breakage, affecting the final product’s performance.
Why do most injection-molded plastic products use PA66 material?
Nylon exhibits unique flow properties in injection molding, making it easy to manufacture complex plastic products using this process. PA66 boasts a melt flow rate (MFR) of up to 30 g/10 min (275℃/5 kg). This honey-like flow pattern ensures complete filling of complex structures while avoiding defects such as jetting. In micro-connector injection molding, nylon melt can precisely fill needle-like cavities with a wall thickness of 0.15 mm and an aspect ratio exceeding 20:1—a precision unattainable by most engineering plastics.
Precise control of mold temperature over the crystallinity of nylon creates a new dimension in performance regulation. When the mold temperature rises from 40℃ to 120℃, the crystallinity of PA6 can increase from 20% to 45%, and the tensile strength increases by 30% accordingly. A certain automotive turbocharger pipeline uses gradient temperature control technology to maintain a high-temperature mold at the end of the flow channel, thereby doubling the pressure resistance of key connection parts.
The intricate interplay between material shrinkage and mold compensation showcases the ingenuity of nylon injection molding. The molding shrinkage of ordinary PA66 ranges from 1.5% to 2.5%, decreasing to 0.3% to 0.8% after glass fiber reinforcement. Nippon Seiko’s gearbox bearing cage, through a 0.05mm-level mold compensation design, controls the roundness error of 50mm diameter nylon parts to within ±5μm.
Applications and Industry Use Cases of PA66 Material
PA66 material is indispensable in many industries due to its versatility. Here are some typical applications:
| Industry | PA66 Injection-Molded Products |
| Automotive | Engine covers, air intake manifolds, radiator end tanks, fuel system components, cable ties, connectors, clips, gears |
| Electrical & Electronics | Electrical connectors, terminal blocks, circuit breaker housings, coil bobbins, switch components, wire management parts |
| Industrial Machinery | Gears, bushings, bearings, wear pads, rollers, housings, guides, pulleys |
| Consumer Appliances | Washing machine parts, dishwasher components, fan blades, motor housings, pump components, structural brackets |
| Aerospace | Cable clamps, fasteners, interior structural supports, electrical connector housings |
| Medical Devices | Surgical instrument handles, diagnostic device housings, medical-grade connectors (non-implantable) |
| Construction & Infrastructure | Cable ties, anchors, fasteners, pipe fittings, mounting brackets |
| Energy & Power | Insulating components, connector housings, sensor housings, switchgear parts |
| Consumer Goods | Power tool housings, sports equipment components, zippers, buckles, mechanical fasteners |
| Telecommunications | Antenna components, connector shells, fiber optic hardware, protective enclosures |
Elimold is your best partner for PA66 injection molding projects.
Are you looking for and want the best PA66 injection molding services? Elimold boasts state-of-the-art manufacturing equipment and extensive experience, offering flexible options and optimal injection molding solutions. You can choose services based on your budget and part geometry. Furthermore, we provide product design and mold design optimization consulting services; our engineers will thoroughly analyze your PA66 part geometry and recommend the most suitable manufacturing solution for your project.
In addition, Elimold offers an integrated service from validation to production. This is a complete solution covering every step from design to mold making to mass production, all handled in one stop. Therefore, this will save you time, money, and costs.
in conclusion
PA66 is an excellent material with a wide range of applications. It is not only one of the oldest nylon materials but also the most widely used. It is lightweight, has high chemical strength, and is very inexpensive compared to other materials. Therefore, almost all companies want to use PA66, especially those that need to mass-produce, utilize limited resources, and reduce costs.
Nylon PA66 is an ideal choice. Combined with injection molding, it yields superior finished products. However, incorrect operation can affect the quality of the final product. By paying attention to the manufacturing details mentioned in this article, you can certainly obtain high-quality nylon products. If you require products manufactured using PA66 material and injection molding, please contact Elimold. To date, we have manufactured over 10,000 nylon injection molding projects.