PTFE Auto Molding
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

All About Automolding

PTFE is an excellent material for many different applications and operating environments. Its low friction, chemical compatibility, and ability to maintain key properties at extreme temperatures has made it ideal for everything from seals in sterile food handling equipment to sleeve bearings in the harsh world of oil and gas. 

And there are several different options when it comes to manufacturing PTFE components, but not all methods are the same. In this blog post, we will be discussing auto molding in the context of manufacturing PTFE components.

What is Auto Molding?

Auto molding, as known as compression molding, is a popular manufacturing technique for making thermoset and thermoplastic parts–and one of the oldest plastic forming methods still in use. In short, auto molding uses compression and dies to form a near net shape polymer part. 

Where is Auto Molding Used?

There are numerous industries that depend on auto molded parts, such as aerospace, chemical processing, and the manufacture of semiconductors.

Auto molding is used to manufacture a wide range of parts, as well. These include …

  • Bearings
  • Bushings
  • Piston rings
  • Sleeves
  • Seals
  • Gaskets
  • Valves
  • Valve Seats
  • Diaphragms
  • Bellows
  • Electrical components

When compression molding of a PTFE part is done correctly, then you can depend on key aspects such as specific density, strength, elongation, and flex life as well as permeation resistance.

How Auto Molding Works

In the auto molding process, the raw materials are in the form of molding compounds. These molding compounds may be preforms (which is already shaped somewhat like the final part), granules, or putty-like masses. 

The basic design for the mold is usually generated from a 3D CAD file, and the tool and die maker will then base the mold design on that file. However, the mold designer must account for shrinkage, molding compound flow, size and positioning of channels to carry away excess material, and achieving uniform curing temperatures for the part. It is also important to ensure that the part can be removed from the mold, and there may be a need for ejector pins to achieve this. Needless to say, the mold is the most expensive aspect of auto molding.

Once the mold design is complete, it is manufactured out of steel using a CAD/CAM (Computer-Aided Design / Computer Aided Manufacturing) system and a CNC (Computer Numeric Control) milling machine. Additional features and surface finishes may require post-processing of the mold.

Once the mold is ready to go, the amount of compound needed for the part is carefully measured out and placed in the pre-heated open mold cavity. Once in place, the other side of the mold closes over the mold cavity and pressure is applied (most often by a hydraulic ram) in one direction to force the raw materials to fill up all cavities within the mold. Any excess material is carried away from the mold via overflow grooves.

Heat and pressure are both maintained until the polymer has completely cured. Once the part has cured and cooled, it is removed from the mold, and this part of the process may require the use of part ejection pins to completely free the newly cured part from the mold. After the part is removed, any flash can be easily trimmed away and precision machining can be used to ensure the part meets necessary tolerances.

Auto Molding PTFE

There are certain key aspects to auto molding PTFE compounds, including …

  • Pressure (usually between 3,000 and 4,500 psi)
  • Sintering temperature (in the range of 685°F – 720°F)
  • Dwell time (how long the part is held at the sintering temperature)

Pressure and dwell time are dependent on the volume and geometry of the part, as well as the machine being used.

Benefits of Auto Molding 

Auto molding PTFE has numerous benefits:

  • Range of geometries and shapes are possible
  • Can produce larger parts than possible with extrusion
  • Minimal waste material
  • Very cost-effective when compared to injection molding
  • Good surface finish
  • Close tolerances
  • Avoids defects associated with machining a polymer (e.g., internal stresses, warping)

In addition, auto molding can be used with both virgin and filled PTFE. Fillers can include both those that enhance structural and material properties (e.g., carbon fiber, molybdenum disulfide MoS2) and colors. Depending on the size and geometry of the part, it may be possible to compression mold multiple parts simultaneously. In such cases, a multi-cavity die would be used.

Disadvantages of Auto Molding

However, there are pros and cons to every PTFE manufacturing process. In the case of auto molded PTFE, the production speed is slower compared to injection molding (due to longer cycle times). Flash will always form and needs to be removed before the part can be considered finished, and this can also add a bit to the production time. While compression molding can be used to manufacture complex parts, there can be issues, such as underfilling in certain areas and the inability to achieve undercuts.

Auto Molding Costs

The most expensive aspect of auto molding, aside from the machinery needed, is the compression molds. Mold cost depends in part on the size of the component, but is more heavily influenced by the complexity of the die. The more complex the geometry of a part, the more expensive the die will be. However, the cost of a compression molding die is significantly less than that of an injection molding die. This is mostly due to the fact that compression molds do not require a complicated system of gates and runners that are necessary in injection molds.

Conclusion

Auto molding works well for manufacturing PTFE components that are not overly complex, have no undercuts, and involve a medium to large production run. In addition, the auto molding process is generally far more cost effective than injection molding. However, for PTFE parts to be high quality and durable, you need a company that is familiar with the process.

At Advanced EMC, we have the knowledge and experience to assist you with auto molding PTFE parts for your applications. Contact us today if you have any questions or are interested in obtaining a quote.

Injection Molded and Machined PEEK Components
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Injection Molded and Machined PEEK Components

PEEK (polyetheretherketone) is a high-performance thermoplastic available in various grades to suit a wide variety of applications. It is commonly used in bushings, medical implants, gears, gaskets, and more. However, what one of the aspects of PEEK that makes it stand out from other engineering polymers is that it can be machined or injection molded, making it suitable for the manufacture of an even more diverse group of components.

PEEK Components

There are a number of different types of parts and applications where machined or injection molded PEEK are used. These include …

It is also a common material in a variety of industries, including …

  • Oil & gas
  • Renewable energy
  • Nuclear energy
  • Chemical processing
  • Food & dairy
  • Medical
  • Pharmaceutical
  • Transportation
  • Electronics (including semiconductors)
  • Aerospace

PEEK: High Performance Polymer

PEEK is both stiffer and stronger than most plastics, retaining its mechanical strength even at high temperature. It also provides key characteristics such as dimensional stability, excellent wear resistance, and hydrolytic stability. It is also known for having a low coefficient of friction, self-lubrication, and a very low tendency to form stress cracks. PEEK also provides very good chemical resistance and is insoluble in most solvents. In addition, it provides both environmental and regulatory benefits because it is fully recyclable. Furthermore, PEEK lends itself to various processing methods.

PEEK is available in FDA-approved grades as well as implantable grades, where its biocompatibility makes it highly desirable for medical applications. In addition, PEEK grades are available that can handle gamma radiation exposure and even autoclaving as part of sterilization processes. It is ideal for very harsh, high temperature environments, including those found in the petrochemical industry and aerospace. Its low particle generation and outgassing make it well adapted to applications involving semiconductors where high purity is critical.

Fillers can also be added to PEEK to improve properties such as abrasion resistance, surface hardness, and friction. Common fillers include glass, carbon, and graphite fibers as well as PTFE and silicon dioxide. Glass fibers can increase compressive strength and enhance heat resistance while carbon and graphite fibers reduce weight while increasing overall strength. Adding PTFE to PEEK further reduces friction while silicon dioxide can be used to increase strength.

Injection Molded PEEK

Injection molding involves raising the temperature of a polymer to the point where it almost melts, which allows it to be injected under high pressure into a mold. Once the polymer has cooled, the components are removed from the mold and typically require minimal post-processing to prepare them for use.

Injection molding PEEK is much cheaper than machining for larger  production runs around 10,000+ components, and is a near-net-shape manufacturing method that results in minimal waste. It works extremely well when parts are needed that are too complex to machine efficiently. The most costly aspect of injection molding lies in the design and execution of the molds required; however, depending on the size of the part and the machine used, multiple parts can be injection molded with a single die.

When used in connection with PEEK, injection molding is often used to manufacture a replacement for metal bushing. Injection molded PEEK bushings can be found in various applications, including …

  • Citrus processing, where exposure to the acids in the fruit can lead to chemical compatibility issues
  • Pumps used in harsh environments that include aggressive chemicals and high temperatures
  • Applications where the presence of vibration accelerates wear

Note, however, that injection molding PEEK involves very high processing temperatures that not all facilities are equipped to handle. In addition, to achieve reliable part fabrication, there are certain cooling requirements that must be met to prevent issues such as warping and annealing may be required to eliminate residual stresses. Injection molding is also limited in its capabilities when there is a need for high precision parts or large parts.

Machined PEEK

Machining using cutting and grinding tools to remove unwanted material from a solid blank in order to produce the desired component. Most facilities use CNC (Computer Numeric Control) machining, which ties in well with CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) that allows a part to be first designed on a computer and then machined using tools that are computer controlled.

Machining is typically used when dimensions need to be extremely precise, the geometry of the PEEK component does not lend itself to injection molding, thin walls are needed, or the desired components are relatively large.

Machining is also more economical when a short production run (<5,000) is involved, which means it is also ideal for developing prototypes. It is faster than injection molding because there is no significant upfront time required for tooling such as molds / dies. In addition, machined PEEK parts usually have much better wear and mechanical properties than injection molded PEEK. And, unlike many thermoplastics, PEEK is easy to machine. Machining also works extremely well for achieving thin walls and fabricating parts with non-standard dimensions or shapes.

There are several industries that make use of machined PEEK components, including …

  • Oil and gas industry, where large PEEK bushings are often required
  • Medical applications where an FDA-approved material must be combined with high precision, customized parts
  • Arctic wind turbines, which require large bushings that can handle the aggressive environment 

Machining can be challenging when working with a filled grade of PEEK and not all machining companies have the skills and knowledge needed to fabricate a machined PEEK component. Finally, annealing may be needed to stress relieve machined parts.

Conclusion

For PEEK parts with a short production run that require a short lead time, machining works extremely well. It is also recommended when there is a need for thin walls or extreme tolerances. On the other hand, high-production volumes will benefit from the lower costs involved with injection molding. 

Advanced EMC has the skill and equipment needed for precision machining and injection molding of PEEK components. To learn more about what we have to offer or to get advice on which process would work best for your application, contact us today.