Peek is an engineering thermoplastic that exhibits superior mechanical properties. The material is often used as an alternative to machined metal components in demanding applications such as aerospace and medical devices. Peek is a member of the polyaryletherketone (PAEK) family of high-performance plastics, which have been designed to keep their integrity in extreme conditions. Peek injection molding is a specialty process that requires higher injection pressure, stable heating and careful consideration of the mold design.
The primary issue facing peek molding is the need to maintain precise temperatures throughout the injection process. The crystalline PEEK and its compounds will quickly quench into an amorphous state if the temperature is not kept in a precise range. This can lead to voids, sink marks and warping of the finished part.
Fortunately, this can be avoided by using electrical or oil heaters to precisely control the temperature of the mold. Injection speed should also be carefully controlled to prevent over-injection, which can damage the molecular structure of the polymer.
Injection of the peek polymer is similar to that of other plastics, but it is important to remember that this is a semi-crystalline material that tends to have more shrinkage than an amorphous plastic. This increased shrinkage may require an increase in the injection pressure or the use of carbon fiber fillers to reduce it.
The sprue is the channel through which the melted plastic flows as it enters the mold cavity. This is a critical area in any injection molding operation, but especially so with PEEK, as it is sensitive to contamination. A contaminated sprue will cause black specks to appear on the finished product. To prevent this, it is important to thoroughly clean all drying ovens, hoppers and injection machines prior to molding with peek. The sprue should also be properly sized to accommodate the desired final component.
When the sprue is sized properly, the flow of the molten plastic into the cavity will be gradual and uniform. This will help to minimize the formation of knit lines, small hair-like discolorations that occur when 2 separate flows of melted plastic meet. These lines can decrease the strength of the finished part, and they are most common on parts with abrupt geometry changes or holes. Trapped air in the sprue can also inhibit the flow of the plastic and lead to short shots.
The best way to avoid these issues is to work with a specialty injection molding company that has experience working with peek and understands the challenges involved. It is also essential to follow established procedures that have been proven to be effective in the manufacture of parts molded from this highly engineered resin. With proper attention to detail, these companies can create products that are durable, strong and beautiful. They can also provide an effective return on investment by reducing manufacturing costs while enhancing part performance and functionality. For more information about how these experts can help, please contact us.