What problems should be paid attention to in PEEK injection molding process?

There are many problems needing attention in the process of PEEK injection molding, including material handling, equipment selection, mold design, process parameter setting and quality control, as follows:

material processing

Drying treatment: PEEK material has low hygroscopicity, but in order to ensure the processing quality, it still needs to be dried before processing. It is generally recommended to dry at 150-180℃ for 4-8 hours, so as to remove the water that may be absorbed and prevent bubbles, crazing and other defects caused by evaporation of water during injection molding.

Material storage: the dried PEEK material should be stored in a dry and sealed environment to avoid re-absorption. Drying box or sealed bag can be used, and desiccant can be put in to ensure that the material is kept in a good dry state before use.

equipment selection

Type of injection molding machine: Due to the high processing temperature of PEEK, it is necessary to choose an injection molding machine with sufficient heating power and temperature control accuracy. Screw injection molding machine is usually more suitable for PEEK injection molding because it can better realize plasticization and metering.

Screw parameters: The length-diameter ratio (L/D) of the screw is generally between 20 and 25, and the compression ratio is between 2.5 and 3.5. Such screw parameters are helpful to the uniform plasticization and transportation of PEEK materials.

mold design

Mold material: Considering the high temperature and high pressure during PEEK injection molding, the mold material should have good strength, hardness and thermal stability. High-quality die steel, such as P20 and H13, can be selected, and appropriate heat treatment can be carried out to improve the service life of the die.

Demoulding mechanism: PEEK products are difficult to demould, so it is necessary to design a reasonable demoulding mechanism. Commonly used methods are ejector pin demoulding and push plate demoulding. The proper demoulding method should be selected according to the shape, structure and size of the product, and the demoulding force should be evenly distributed to avoid deformation and cracking of the product during demoulding.

Process parameter setting

Temperature control: the temperature of the barrel is generally set between 380-420℃, and the temperature of the nozzle can be slightly lower than the temperature of the front end of the barrel, within the range of 370-410℃. Mold temperature is usually controlled at 150-200℃, which is helpful to improve the crystallinity and dimensional stability of products.

Injection pressure and speed: the injection pressure is generally between 80 and 150 MPa, and the injection speed depends on the shape and structure of the product. For thin-walled products, a higher injection speed, generally 50-100 mm/s, can be adopted; For thick-walled products, the injection speed can be reduced appropriately, between 20 and 50 mm/s.

Holding pressure and time: The holding pressure is generally 60%-80% of the injection pressure, and the holding time depends on the thickness and size of the product, generally between 10-30s.

Cooling time: the cooling time should be long enough to ensure that the product is fully cooled and shaped. The cooling time is generally between 15-60s, which can be adjusted according to the thickness of the product and the cooling efficiency of the mold.

quality control

Appearance inspection: check whether there are defects such as bubbles, silver lines, lack of materials and flash on the surface of the product. For products with high surface quality requirements, optical microscope or electron microscope can be used for microscopic inspection.

Dimensional accuracy control: measure the dimensions of products regularly to ensure that the dimensions of products meet the design requirements. Calipers, micrometers, three-coordinate measuring instruments and other measuring tools can be used to measure key dimensions.

Performance test: the mechanical properties and thermal properties of the products are tested, such as tensile strength, bending strength, thermal deformation temperature, etc., to ensure that the properties of the products meet the requirements of use.