What are the factors that affect the quality of PEEK injection-molded products?

The quality of PEEK injection-molded products is influenced by many factors. The following aspects are analyzed in detail: raw materials, equipment and molds, process parameters, environment, etc.

Raw material factor

Material quality: the purity, molecular weight and distribution of PEEK raw materials have a significant impact on the quality of products. If the purity is not high and contains impurities, it may lead to defects such as bubbles and cracks in the products, and reduce the mechanical properties and appearance quality of the products. If the molecular weight distribution is too wide, the processability of materials and the properties of products will be unstable.

Drying degree: Although the hygroscopicity of PEEK material is relatively low, if it is not fully dried before processing, water will vaporize to form bubbles during high-temperature injection molding, which will affect the strength and appearance of the product and cause problems such as silver wire and pockmarks on the surface of the product. Usually it needs to be dried at 150-180℃ for 4-8 hours.

Use of additives: In order to improve some properties of PEEK, glass fiber, carbon fiber and other reinforcing materials or other additives may be added. However, the type, content and dispersion uniformity of additives will affect the quality of products. If the additive is unevenly dispersed, it will lead to local performance differences of products and reduce the overall performance.

Equipment and mold factors

Performance of injection molding machine: Plasticizing ability, temperature control accuracy and pressure control stability of injection molding machine are very important. Insufficient plasticizing ability will cause uneven plasticization of PEEK materials, which will affect the mechanical properties and appearance of products. Inaccurate temperature control may lead to poor material decomposition or plasticization; Unstable pressure control will cause problems such as dimensional deviation and uneven density of products.

Mold design and manufacture

Mold structure: A reasonable mold structure is the basis to ensure the quality of products. Improper gate position and size will lead to uneven melt flow, resulting in weld marks, bubbles and other defects; Unreasonable runner design will increase the melt flow resistance and affect the filling effect.

Mold accuracy: the manufacturing accuracy of mold directly affects the dimensional accuracy and surface quality of products. The size deviation and surface roughness of the mold will lead to the product size not meeting the requirements and the surface is not smooth.

Mold cooling system: Unreasonable design of cooling system will lead to uneven cooling of products, internal stress, deformation and cracking of products. A good cooling system should be able to ensure the uniform temperature of all parts of the mold, so that the products can be cooled quickly and evenly.

Process parameter factor

Temperature control

Cylinder temperature: If the cylinder temperature is too high, the PEEK material will decompose, producing gas and impurities, which will affect the product quality; Too low temperature, poor plasticization and poor fluidity of materials lead to problems such as lack of materials and rough surface of products.

Mold temperature: mold temperature has an important influence on the crystallinity and dimensional stability of products. The mold temperature is too low, the crystallinity of the product is low and the mechanical properties are poor; If the temperature is too high, the cooling time will be prolonged, the production efficiency will be reduced, and it may lead to the difficulty of demoulding the products.

Injection pressure and speed

Injection pressure: the injection pressure is insufficient, and the material can't fill the mold cavity, which leads to the lack of material in the product; Excessive pressure will cause problems such as flash and increased residual stress.

Injection speed: if the injection speed is too fast, the melt will be turbulent, and air will be involved to form bubbles, which may also lead to flow marks on the surface of the product; If the speed is too slow, the melt will be cooled too fast during the flow, resulting in insufficient filling.

Holding pressure and time: if the holding pressure and time are insufficient, the product can't get enough supplementary material during cooling and shrinkage, and there will be defects such as shrinkage marks and depressions; If the holding pressure is too high or the holding time is too long, the internal stress of the product will increase, and cracking will easily occur.

Cooling time: the cooling time is too short, the product is not fully cooled and shaped, and it is easy to deform after demoulding; Too long cooling time will reduce production efficiency.

environmental factor

Temperature and humidity in the production workshop: the change of temperature and humidity in the workshop will affect the properties of PEEK material and injection molding process parameters. Too high temperature or humidity will increase the moisture absorption of materials and affect the quality of products.

Cleanliness of workshop: Dust and impurities in the workshop will be mixed into materials, which will affect the appearance and performance of products. Especially for some products that require high surface quality, workshop cleanliness is particularly important.