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>> 1.1 Drying:
>> 3.2Injection Pressure: Ensure the "pushing force" to "fill the cavity" of the melt
● 4.Holding Pressure and Holding Time: Key to Solving "Shrinkage" in Products
The injection parameters of PEEK material need to be adjusted at different grades. Before injection, the material needs to be dried at 150-160°C for 4 hours. The mold temperature is set at 160-180°C, and the injection pressure is usually set at 80-150MPa. These parameters are only recommended values. The following text will detail how to adjust the parameters based on the characteristics of unfilled and modified PEEK.
PEEK material needs to be dried using an air circulation furnace or a hot air drying box. The thickness of the material layer should be controlled within 2.5cm to ensure uniform heating. Dry at 150-160°C for 4-6 hours to reduce the moisture content to 0.02%. Start production only when the moisture content drops below 0.02%. If the moisture content is not reduced below this level, the product will be prone to bubbles and silver streaks due to water evaporation at high temperatures, resulting in a decline in performance. After drying, it is necessary to prevent re-humidification. Quickly place the material into a dry barrel.
PEEK material is one of the plastics with the highest processing temperature. Its melting point is 343°C, and it needs to be heated to 380-390°C to achieve better processing performance. If there are other polymers remaining in the equipment, such as screws and barrel positions, if these remaining materials are not cleaned up in time, they are likely to carbonize and form black spots, ultimately affecting the quality of the product.
Temperature is crucial for the injection of PEEK material. The following are the temperature settings for each section from the barrel to the nozzle and then to the mold.
The melting temperature of PEEK is approximately 343°C, and the decomposition temperature is above 400°C. The barrel temperature needs to find a precise balance between "fully melted" and "avoid decomposition", and it must adopt the "segmental heating" mode to avoid local overheating.
The temperature setting for the feeding section: 300-320°C is recommended. This section mainly functions to preheat the material and prevent bridging. If the temperature is lower than 300°C, the material is likely to form lumps in the barrel, causing poor material feeding; if it is higher than 320°C, the material melts prematurely and may stick to the screw, affecting the conveying efficiency.
Compression Section Temperature: It needs to be raised to 340-360°C. The compression section is the key area for material melting, and the temperature must reach above the melting point of PEEK to ensure complete plasticization.
However, the temperature must not exceed 370°C; otherwise, the melt is prone to thermal oxygen aging, resulting in yellowing and a decline in mechanical properties. It is recommended to start the first adjustment at 340°C and observe the melt flow. If the melt is not uniform or has a grainy feel, gradually increase the temperature by 5°C until the melt is smooth and clean.
Homogenization Section (Metering Section) Temperature: Control at 350-370°C. This section is mainly to ensure uniform temperature and consistent viscosity of the melted material, preparing for the injection process. The temperature should be slightly higher than the compression section to ensure the melt is fully mixed, but not exceeding 370°C; otherwise, the PEEK will decompose after a long stay, forming small molecular gases in the product, causing bubbles in the mold cavity.
Here is a tip for you: Observe the melt state through the nozzle. If the melt is consecutive , without breaks, and without bubbles, it indicates that the homogenization section temperature is appropriate.
The nozzle temperature should match the homogenization section temperature and be set at380-390°C, and avoid "cold material" formation. Because the nozzle directly contacts the mold, if the temperature is too low, the melted material cools at the nozzle, turn into cold material, which will be brought into the mold cavity during injection, causing cold spots, scratches, and even blockage of the gate on the product surface.
If the temperature is too high, the molten material at the nozzle will flow and spread, causing material waste and possibly overheating at the gate, which can affect the molding of the product. It is recommended to install a heating ring at the nozzle to ensure stable temperature. Before each injection, a small amount of molten material can be manually discharged to remove the cold material and then proceed with formal production.
PEEK is a crystalline plastic, and the mold temperature directly affects the crystallinity, shrinkage rate, and mechanical properties of the product. This is much more important than for ordinary plastics. The mold temperature is usually set at 160-180°C, and the specific temperature needs to be adjusted according to the thickness of the product and the performance requirements:
If the product thickness is thin (less than 3mm), the mold temperature should be set at 160-190°C. A higher mold temperature can slow down the cooling speed of the product, allowing PEEK to have enough time to crystallize, avoiding the brittleness and strength reduction of the product due to insufficient crystallization;
If the product thickness is thick (greater than 5mm), the mold temperature can be appropriately reduced to 150-160°C to prevent the internal cooling of the product from being too slow, resulting in shrinkage cavities and depressions.(Better no lower Tg 143°C，)
For products with Uniform wall thickness,It must be emphasized that the mold temperature must be uniform, with a temperature difference between the upper and lower molds and the mold cavity areas not exceeding 10°C. Otherwise, the crystallinity of each part of the product will be inconsistent, resulting in internal stress, causing the product to warp and deform. It is recommended to use a mold temperature controller to precisely control the temperature and regularly check the circulation system of the mold temperature controller to ensure smooth flow of the heat transfer oil and avoid local temperature deviations.
For products with uneven wall thickness, it is best to use zone-controlled mold temperature. In thinner areas, a higher mold temperature should be used, while in thicker areas, a lower mold temperature should be employed. This helps to balance the crystallization rate at each part, thereby suppressing warping and shrinkage.
The viscosity of PEEK melt is high, so the injection speed cannot be too fast or too slow. It needs to be "progressively increased". Usually, it is set at 30-90mm/s. The specific speed is adjusted according to the product structure:
For simple structures without thin walls or complex cavities, the injection speed can be set at 30-40mm/s, filling uniformly to avoid turbulence of the melt in the cavity, which can lead to air bubbles;
For products with thin walls (less than 2mm) or complex cavities, the injection speed needs to be appropriately increased to 50-60mm/s, filling quickly to prevent the melt from cooling too quickly during filling, resulting in under-filling, but the speed cannot exceed 90mm/s, otherwise the melt will flow too fast, generating shear heat, causing local overheating and decomposition, and it may also cause flash edges.
Please pay attention to observing the filling process of the product: if there is a shortage of material at the end of the cavity when filling, the injection speed can be appropriately increased; if there are flash edges or the gate area turns white, it indicates that the speed is too fast, and it needs to be reduced.
The ESD PEEK injection speed will affect the surface resistance it need higher speed，see how to injection ESD PEEK？
The injection pressure should be coordinated with the injection speed. It is typically set between 80-150 MPa. PEEK has a high melt viscosity, so sufficient pressure is needed to push the melt to fill the cavity. However, excessive pressure can lead to increased internal stress in the product, causing warping, cracking, and even damaging the mold. Insufficient pressure will result in under-filling and a lack of fullness on the product surface.
During the debugging process, you can start with a lower pressure (such as 80 MPa). If the product is underfilled, gradually increase the pressure, raising it by 10 MPa each time, until the product is fully filled. If the product has flash edges, it indicates that the pressure is too high, and the pressure needs to be reduced. At the same time, the injection pressure should be coordinated with the barrel temperature: if the barrel temperature is low, the melt viscosity is high, and the injection pressure can be appropriately increased; if the barrel temperature is high, the melt viscosity is low, and the injection pressure can be reduced to avoid over-filling.
PEEK materials need to be debugged according to different grades. Fibre-reinforced PEEK materials have a higher melt viscosity than un-reinforced PEEK materials, requiring a greater injection pressure.
| Material | Injection pressure | Typical adjustment |
| Unfilled PEEK | 100-110Mpa | Increase for long/thin flow paths |
| Glass fiber filled PEEK | 110-135Mpa | Adjust for fiber loading and flow resistance |
| Carbon fiber filled PEEK | 120-140Mpa | Balance filling pressure with fiber orientation/shear |
For pure PEEK raw material injection molding, the standard injection pressure range is between 90 MPa and 130 MPa. For general components with regular structure and uniform wall thickness, setting the pressure at 100 MPa to 110 MPa can achieve stable filling and ensure a full and defect-free product formation.
For thin-walled, long flow channels, and complex precision parts, the injection pressure can be appropriately increased, within the range of 110 MPa to 130 MPa. It is important to note that the pressure should not be pulled all the way up at once to avoid causing process problems such as burrs, flash, and internal stress cracking in the product.
The fluidity of glass fibre-reinforced PEEK materials slightly decreases, and the filling resistance increases. Injection molding requires an appropriate increase in pressure, with a reasonable range of 110 MPa to 135 MPa. Increasing the pressure appropriately can improve the dispersion effect of glass fibres and avoid surface defects and uneven strength caused by fibre agglomeration.
Carbon fibre-modified PEEK materials have greater rigidity and higher melt viscosity, making the molding the most difficult. The injection pressure is recommended to be controlled within 120 MPa to 140 MPa. This parameter range can ensure the rapid filling of the mold by the melt and meet the molding requirements for high-end precision components.
During the cooling process of PEEK, the shrinkage rate is relatively high. Therefore, it is necessary to use holding pressure to replenish the material and prevent the products from developing shrinkage cavities or depressions.
Holding Pressure: It is usually set at 50%-80% of the injection pressure, which is 40-120 MPa. If the holding pressure is too high, it will cause an increase in internal stress in the product, resulting in stress concentration at the gate and easy cracking; if the holding pressure is too low, it will not be able to replenish the material, and the product will develop shrinkage cavities. It is recommended to start from 50% of the injection pressure and observe the surface of the product. If there is a depression, gradually increase the holding pressure by 5%-10% until the depression disappears.
Holding Time: It is set at 5-10 seconds, mainly adjusted according to the thickness of the product. Thick-walled products cool slowly, so the holding time needs to be longer (10-20 seconds) to ensure sufficient time for material replenishment; thin-walled products cool quickly, so the holding time can be shorter (5-10 seconds) to avoid overheating at the gate. The method to determine if the holding time is appropriate: when the material at the gate solidifies, continuing to hold pressure has no obvious effect, this is the optimal holding time. An excessively long holding time will increase the production cycle and reduce efficiency.
