Polyetheretherketone (PEEK), as a high-performance thermoplastic engineering plastic, boasts excellent mechanical properties, high-temperature resistance, chemical stability, and fatigue resistance. It finds wide applications in numerous fields such as aerospace, automotive manufacturing, and electronics and electrical engineering. However, the special properties of PEEK materials also pose many challenges to injection molding. To achieve high-quality PEEK injection molding, it is necessary to precisely grasp the following key points.
Raw Material Pre-treatment
Sufficient Drying: Although PEEK materials have relatively low hygroscopicity, even trace amounts of moisture can trigger hydrolysis reactions during high-temperature injection molding, leading to a decline in material properties and defects such as silver streaks and bubbles in the molded parts. Therefore, it is essential to fully dry the PEEK raw materials before injection molding. It is generally recommended to use a desiccant dryer, set the drying temperature at 150℃ - 180℃, and the drying time for 4 - 6 hours to ensure that the moisture content of the raw materials drops below 0.02%. In actual operations, a high-precision moisture detector can be equipped to monitor the drying effect in real time and ensure sufficient drying of the raw materials.
Raw Material Screening and Preheating: Carefully inspect the PEEK raw material pellets, remove impurities, discolored, or deformed pellets to ensure uniform raw material quality. For cases where fillers or additives need to be added, ensure thorough mixing. A high-speed mixer can be used to precisely control the proportion of each component according to the formula, with a mixing time usually ranging from 15 - 30 minutes, so that the additives are evenly dispersed in the PEEK raw materials, avoiding inconsistent properties of the molded parts due to uneven mixing. In addition, preheat the raw materials to a certain temperature before they enter the barrel of the injection molding machine, which helps reduce the heating time in the barrel, improve plasticization efficiency, and thus speed up production.
Optimization of Injection Molding Process Parameters
Temperature Control: PEEK has a relatively high melting temperature, generally between 340℃ - 400℃. During the injection molding process, the barrel temperature needs to be precisely controlled, with the front section temperature slightly lower than the rear section to ensure uniform plasticization of the raw materials and avoid overheating and decomposition. The mold temperature is also crucial for PEEK injection molding, usually controlled at 180℃ - 220℃. An appropriate mold temperature can improve the melt flowability, reduce the internal stress of the molded parts, and enhance product dimensional accuracy and surface quality. When injection molding PEEK gears, stabilizing the mold temperature at 200℃ can effectively reduce the roughness of the gear tooth surfaces and improve the transmission accuracy of the gears.
Pressure and Speed Adjustment: Reasonable injection pressure and speed are key to ensuring good cavity filling. Too low pressure can easily lead to problems such as insufficient filling and short shots; too high pressure may cause flash and mold bulging. Excessive injection speed can cause air entrapment and scorching; too slow speed will affect production efficiency. In actual production, it is necessary to determine the optimal pressure and speed curves through trial molding according to factors such as the shape, size, and wall thickness of the molded parts. For PEEK molded parts with uneven wall thickness, multi-stage injection can be adopted, increasing the injection speed at the thin-walled sections and appropriately reducing the pressure at the thick-walled sections to ensure uniform filling.
Setting of Holding Pressure and Cooling Time: Holding pressure can supplement the material required for melt cooling shrinkage and prevent shrink marks on the molded parts. The holding pressure is generally 60% - 80% of the injection pressure, and the holding time depends on the thickness of the molded parts, usually ranging from 10 - 30 seconds. The cooling time should be long enough to ensure that the molded parts are fully cooled and set, avoiding deformation during demolding. The cooling time can be determined based on factors such as the volume of the molded parts, the cooling area, and the efficiency of the mold cooling system, generally ranging from 20 - 60 seconds.
Key Points of Mold Design
Optimizing Mold Structure: The gate and runner design of the mold has a significant impact on the flow of the PEEK melt. Due to the high viscosity and poor flowability of the PEEK melt, large-sized gates and short and thick runners should be used to reduce flow resistance. A hot runner system can reduce the generation of cold material, improve the uniformity of the melt temperature, lower the injection pressure, and at the same time shorten the molding cycle and improve production efficiency. For molded parts with complex shapes, reasonably design the parting surface and demolding mechanism to ensure smooth demolding of the molded parts and avoid production interruptions and product damage due to difficult demolding. When designing molds for PEEK molded parts with deep cavities, side core-pulling mechanisms such as sliders or inclined tops can be used to achieve smooth demolding.
Strengthening Cooling System Design: An efficient cooling system can accelerate the cooling speed of PEEK molded parts and shorten the molding cycle. According to the mold structure and the shape of the molded parts, reasonably arrange the cooling water channels to ensure uniform cooling. Conformal cooling technology can be adopted to make the cooling water channels conform to the contour of the molded parts and improve cooling efficiency. Increasing the diameter and quantity of the cooling water channels and improving the flow rate of the cooling fluid can also effectively enhance the cooling effect. In large-scale PEEK injection molds, a circulating cooling system equipped with a cooling medium temperature controller can be used to precisely control the temperature of the cooling fluid and ensure stable cooling effects.
Equipment Selection and Maintenance
Equipment Selection: PEEK injection molding places high demands on the performance of the injection molding machine. An injection molding machine with sufficient injection pressure and clamping force should be selected to meet the requirements of high-viscosity and high-pressure injection molding of the PEEK melt. The screw of the injection molding machine should be made of special materials, such as a nitrided screw, to improve its wear resistance and corrosion resistance. At the same time, the temperature control system of the injection molding machine should be precise and reliable to accurately control the temperatures of the barrel and the mold.
Equipment Maintenance: Regularly conduct comprehensive inspections and maintenance on the injection molding machine, including components such as the screw, barrel, hydraulic system, and electrical system. Timely replace worn screw tips, check rings, and other parts to ensure stable plasticizing and injection performance. Clean the filters of the hydraulic system to prevent blockage by impurities and ensure the cleanliness and stable pressure of the hydraulic oil. Inspect the electrical system to ensure that all electrical components are reliably connected and the temperature control is accurate. Regular equipment maintenance can reduce the probability of equipment failures and avoid production interruptions caused by equipment failures.
Quality Inspection and Control
Process Inspection: During the PEEK injection molding process, strengthen real-time monitoring of key parameters such as temperature, pressure, and speed. Install sensors to transmit the data to the control system, and issue alarms and make adjustments in a timely manner if any parameters are abnormal. At the same time, conduct real-time visual inspections of the molded parts. If defects such as flash, bubbles, or deformation are found, analyze the causes in a timely manner and take measures to solve them.
Finished Product Inspection: Conduct comprehensive quality inspections on the PEEK molded parts after injection molding, including dimensional accuracy, appearance quality, and mechanical properties. Use high-precision measuring instruments such as coordinate measuring machines to detect whether the dimensional accuracy of the molded parts meets the design requirements. Through visual inspection, ensure that the surface of the molded parts is free of defects and has a uniform color. Conduct mechanical property tests such as tensile and bending tests on the molded parts to verify whether they meet the usage requirements. Establish a complete quality traceability system to record and analyze the quality data of each batch of products, continuously optimize the production process, and improve the stability of product quality.
PEEK injection molding is a complex process. It is necessary to precisely control multiple aspects such as raw material pre-treatment, optimization of injection molding process parameters, mold design, equipment selection and maintenance, and quality inspection and control to produce high-quality PEEK molded parts and meet the demands of various industries for high-performance plastic products.
