How to improve the surface quality of PEEK injection molded products?
To improve the surface quality of PEEK injection-molded products, we can start with optimizing material treatment, adjusting process parameters, improving mold design and maintenance, and strengthening equipment maintenance. The specific methods are as follows:
Material handling
Strict drying treatment: Ensure that the PEEK material is fully dried before processing, and dry it at appropriate temperature and time according to the suggestions of the material supplier, such as drying at 150-180℃ for 4-8 hours, using desiccant and sealing for storage, so as to prevent the dried material from absorbing moisture again and reduce the defects such as surface bubbles and silver wires caused by moisture.
Material screening and inspection: each batch of PEEK material shall be strictly inspected for its particle size distribution, impurity content and other indicators, so as to ensure the uniform and stable quality of the material and avoid the surface quality of the product being affected by the quality problems of the material itself.
Optimization of process parameters
Precise temperature control
Cylinder temperature: According to the characteristics of PEEK material and product requirements, accurately adjust the cylinder temperature, generally controlled at 380-420℃, to ensure uniform plasticization of the material, and avoid the surface quality being affected by poor plasticization caused by material decomposition due to too high temperature or too low temperature.
Mold temperature: Setting the mold temperature reasonably, usually at 150-200℃, is helpful to improve the fluidity and filling of the melt, make the surface of the product smoother, promote the crystallization of the material, and improve the dimensional stability and surface quality of the product.
Optimizing injection parameters
Injection pressure: Select an appropriate injection pressure, generally between 80-150MPa, to ensure that the melt can fully fill the mold cavity, avoid defects such as lack of materials and bubbles, and at the same time prevent flash caused by excessive pressure from affecting the surface smoothness of products.
Injection speed: adjust the injection speed according to the shape and wall thickness of the product. For thin-walled products, a higher injection speed of 50-100mm/s can be adopted to make the melt fill the cavity quickly and reduce the surface flow marks; For thick-walled products, the injection speed can be controlled at 20-50mm/s to avoid the turbulence of melt in the cavity.
Reasonable pressure keeping and cooling
Holding pressure and time: Generally, the holding pressure is 60%-80% of the injection pressure, and the holding time is 10-30s. It should be adjusted according to the actual situation of the product to ensure that the product is fully replenished during cooling and shrinkage, and to reduce surface shrinkage marks and depressions.
Cooling time: ensure sufficient cooling time, generally between 15-60s, so that the product can be fully cooled and shaped, and prevent deformation due to insufficient cooling after demoulding, which will affect the surface quality.
Mould design and maintenance
Optimize mold structure
Gate design: design the location, number and size of gates reasonably, so that the melt can fill the mold cavity evenly and reduce the occurrence of weld marks. For products with complex shapes, multiple gates or point gates can be used to improve the melt flow state.
Runner design: Smooth and reasonable runner structure is adopted to reduce the flow resistance of the melt, ensure the uniform flow of the melt in the runner, and avoid stagnation or eddy current. Hot runner system can be adopted to improve the temperature uniformity and fluidity of the melt.
Improve mold precision and surface quality
Machining accuracy: improve the machining accuracy of the mold, ensure that the dimensional accuracy and surface roughness of the mold cavity meet the requirements, and the surface roughness of the mold is generally controlled at Ra0.8-Ra1.6μm, so as to reduce the defects such as scratches and strains on the product surface caused by the unsmooth surface of the mold.
Mould polishing: Fine polishing is carried out on the surface of mould cavity to improve the smoothness of mould surface, make products easier to demould and reduce surface defects. Mechanical polishing, chemical polishing or electric spark polishing can be adopted, and appropriate polishing process can be selected according to mould materials and surface requirements.
Regular mold maintenance: clean, lubricate and maintain the mold regularly, check the wear of the mold, repair or replace the worn parts in time, and prevent the surface quality of products from being affected by mold damage or dirt.
Equipment maintenance
Check the injection molding machine regularly: check the wear of the screw, barrel and other parts of the injection molding machine regularly, replace the seriously worn parts in time, ensure the plasticizing effect and measurement accuracy, ensure the uniform plasticization and accurate injection of materials, and thus improve the surface quality of products.
Calibration of temperature and pressure sensors: calibrate the temperature and pressure sensors of injection molding machine regularly to ensure the accuracy of temperature and pressure control, provide guarantee for stable injection molding process, and avoid product surface defects caused by inaccurate temperature or pressure control.
