PEEK is a semicrystalline thermoplastic that can be injection molded, extruded or compression molded. It is used in a variety of applications because it is tough, rigid, has high chemical resistance and excellent fatigue resistance. It can be pigmented black, but this degrades the mechanical properties, so it is typically supplied in its natural light-brown color. PEEK can be filled with glass fiber or carbon fiber to enhance its strength and stiffness.
Peek molding is more difficult than injection molding other plastics because it requires higher injection pressures, a stable heating process and careful mold design considerations. The costs of peek molding are often higher than for other types of injection molding due to the cost of the mold.
The main costs drivers in injection molding are the tooling, materials and production costs. Tooling is the largest component of these costs, but it can be lowered by reducing the number of parts that are molded. In order to reduce the number of parts molded, the design of the part should take into account the possibility that it will need to be reworked after initial injection molding. This will allow the initial part to serve as a trial for new revisions that will lead to the final production part.
In order to reduce the number of iterations that will be needed, a part can be split into multiple components called sub-assemblies. This will allow the same injection mould to be used for different products without having to invest in new tools. This will also make it easier to maintain the integrity of the mould.
To avoid defects, injection molders should dry PEEK to a moisture content of less than 0.02%. The amount of time that it takes for the material to reach this level depends on the temperature and humidity at the injection molding plant, but it usually is less than 2 hours.
Once the injection molding machine is running, it should be maintained at a processing temperature between 350degC-400degC (662degF-752degF). This is the range that is recommended by most of the major injection molders. If possible, barrel blankets should be utilized as they provide extra heat insulation at lower energy cost.
In the mold, the rate at which the injection melt cools can affect its crystallinity. If the rate of cooling is too rapid, a mixture of amorphous and crystalline regions will occur. This is visible as uneven discoloration on the finished product. The injection molding machine should be able to control the cooling rate so that the melting point is reached in a uniform manner across the entire area of the mold.
It is important to keep in mind that PEEK has a relatively low elongation at break, which may cause warping of the finished part if the gating and clamping system is not properly designed. To mitigate this, the gating system must be designed to ensure that there is sufficient space in the corners of the cavity for the melted material to expand into. In addition, the bases of vertical features like bosses or snap-fits should be rounded so that they are as smooth as possible.