Injection molds made in PEEK for silicone parts
23 July 2018
Besides hobbyists, makerspaces and laboratories, fused deposition modeling (FDM) can be employed for professional applications with a variety of different thermoplastics. Fabru GmbH demonstrates the use of FDM to manufacture injection molds in PEEK.
3D printers based on Fused Deposition Modeling (FDM) are commonly employed by hobbyists, makerspaces and laboratories for the fast and cheap manufacturing of prototypes. Print material in the form of filament is heated in a nozzle and applied layer by layer to form a part. Frequently used materials are PLA and ABS. These materials represent, however, only a small fraction of the available thermoplastic materials in the field of modern plastics processing.
There exists a large number of thermoplastics with various properties that can be utilized for different applications. The targeted use of such materials results in profes-sional applications for FDM. In this context, the company Fabru GmbH is developing printers and filament for FDM. The goal is to be able to process a wide range of thermo-plastic materials without the necessity to make changes on a 3D printer, including its printing head. An application example of Fabru GmbH demonstrates the use of FDM for processing PEEK (polyether ether ketone). In this case, molds are made of PEEK for injection molding of silicone parts, in this case a sealing ring.
Advantages of PEEK in FDM process
There are several reasons for manufacturing the molds in PEEK within an FDM process. In order to crosslink the silicone part, the injection molds have to be heated to a temperature of up to 200 °C. In this temperature range, almost all thermoplastics fail due to their heat resistance. In addition, the molds are exposed to high mechanical stress during injection molding. Therefore, prototype molds are often produced from metallic materials instead. However, this results in long lead times and high manufacturing costs. The use of PEEK within an FDM process avoids these disadvantages. The material has a high mechanical strength and heat resistance. Using the FDM process, molds can be fabricated comparatively quickly and cheaply with a sufficiently good surface finish. This approach is therefore particularly advantageous for prototyping and small-series production.
The Plasjet 3C-855 Printer
The Plastjet 3C-855 printer from Fabru GmbH is employed for processing PEEK. The challenge lies mainly in the high processing temperatures required for printing PEEK filament. The heating bed is heated up to 210 °C and the nozzle set to 420 °C to bring the filament into a thermoplastic state. By heating the build space, which has a dimension of 800 X 500 X 500 mm, shrinkage effects of the plastic are minimized. In this case, the temperature of the filament must not be too low, as otherwise the layer adhesion is insufficient and individual layers will then separate from each other. However, the filament must also not be heated up too much, as the material will then not be applied in a sufficiently defined manner.
To control the temperature in the printing head and achieve thermal separation, an internal water cooler with a closed cooling water cycle is utilized. As adhesion between building base plate and PEEK filament is relatively high, removal from the base plate represents another challenge within the manufacturing. Advantages of processing PEEK are that the material possesses a good layer adhesion and shows relatively low distortion values.
Production process of PEEK moulds for a sealing ring
The fabrication of the PEEK molds for a sealing ring takes a few hours. The required tolerances are within a range of +/– 0.05 mm. Further post-processing of the surface can be done, but is optional. To save material, the molds use integrated honeycomb structures. Although the honeycombs are enclosed, such a geometry can be imple-mented with the FDM process, since no openings are required in comparison to powder-based or liquid-based additive manufacturing processes. The high mechanical properties of PEEK and its high temperature resistance lead to tough molds. Injection molding can be used to produce a small series of components. Further improvements of the material properties of PEEK are possible if short fibers are added to the filament. All in all, applying PEEK in combination with the FDM process allows producing complex and robust molds for prototypes or a small series in a fast and cost-effective way.
Use of other plastic materials
In the area of modern plastics technology, PEEK is used in addition to many other thermoplastic materials. Several other plastics are nowadays also produced as filament for additive manufacturing and processable with FDM. For instance, in comparison to expensive PEEK, PEI (polyetherimides) or polycarbonates (PC) are also suitable as temperature-resistant materials for molds. These materials can also be processed with the Plastjet 3C-855 printer from Fabru GmbH. In principle, depending on the application, the right material has to be combined with the right design for FDM in order to achieve an added value. In this respect, FDM offers many advantages and besides the common materials PLA and ABS, it offers a wide range of other plastics for innovative applications.