An Informational Brief on Polymer Machining

 

Polytetrafluoroethylene (PTFE) is a fluorocarbon-based polymer, known more commonly as Dupont’s brand name Teflon®. The enhanced electrical properties, high-temperature capabilities and chemical resistances of this thermoplastic make it a favorite for backup rings, coatings, distribution valves, electrical insulation applications and more.

 

Our latest machining guide discusses what goes into machining Teflon and how its considerations differ from other manufacturing options such as metal machining, injection molding, and 3D printing.

 

Read on to learn more about Teflon’s machining, applications and properties in AIP’s informational polymer brief below, starting with the difference between working with a thermoset and a thermoplastic.

 

Machining Thermoplastics vs Thermosets

 

We’ve already said that Teflon is a thermoplastic, but what does that mean exactly?

 

All polymers can more or less be divided into two categories: thermoplastics and thermosets. The main difference between them is how they react to heat. Thermoplastics like Teflon, for example, melt in heat, while thermosets remain “set” once they’re formed. Understanding the technical distinction between these types of materials is essential to CNC machining them properly.

 

What type of thermoplastic is Teflon in particular? PTFE is a fluoropolymer, making it a semi-crystalline thermoplastic. As a fluoropolymer, PTFE possesses an inherent high resistance to solvents, acids and bases.

 

Properties & Grades of Machined Teflon

 

Teflon has excellent electric stability in a wide range of conditions and environments, and its coatings are popular in the aerospace sector. Offering excellent chemical resistance and sliding properties, PTFE finds many applications in seals, housings, linings and bearings. Teflon also maintains very good UV resistance, hot water resistance and electrical insulation at higher temperatures.

 

Unfilled PTFE is chemically inert and has the highest physical and electrical insulation properties of any Teflon grade. Mechanical grade PTFE is often made up of reground PTFE and exists as a cost-effective alternative for industries that don’t require high purity materials while providing superior compressive strength and wear resistance to virgin Teflon.

 

There are several different modified PTFE materials available with unique properties. Many of these modified grades offer greatly reduced deformation percentages under load, as well as a lower coefficient of friction. These include glass-filled, nanotube, synthetic mica and carbon-filled grades. Teflon (PTFE) is more commonly used as an additive to numerous other base polymers in order to provide reduced friction and wear properties.

 

Some of the PTFE grades we regularly machine at AIP include FLUOROSINT 207, FLUOROSINT 500, DYNEON, SEMITRON, ESD 500 HR, and SEMITRON PTFE.

 

Machining Teflon

 

Annealing & Stress Relieving Teflon

 

The process of annealing and stress-relieving PTFE reduces the likelihood of surface cracks and internal stresses occurring in the material. Post-machining annealing also helps to reduce stresses that could potentially contribute to premature failure. AIP’s special annealing process for Teflon is designed to take the specific properties of PTFE into account, and we advise anyone working with PTFE to hire a manufacturer that understands its unique demands.

 

Machining Teflon

 

PTFE’s density and softness make it deceptively easy to machine, and in virgin grade, has a temperature range from -450°F to +500°F (-267.7°C to +260°C). Teflon has low strength when compared to materials like Nylon, which has almost two to three times the tensile strength of Teflon. You’ll want to use extremely sharp and narrow tools to work with this material.

 

Teflon’s high coefficient of expansion and stress creep properties can make it difficult to achieve tight machining tolerances. It’s essential to design your application with PTFE’s inherent properties in mind, instead of trying to force the polymer to act against its nature.

 

We also suggest non-aromatic, water-soluble coolants, such as pressurized air and spray mists, to achieve optimum surface finishes and close tolerances. Coolants have the additional benefit of extending tool life as well.

 

Preventing Contamination

 

Contamination is a serious concern when machining polymer components for technically demanding industries such as medical and life sciences. To ensure the highest level of sanitation down to the sub-molecular level, AIP Precision Machining designs, heat-treats and machines only plastics, with any sub-manufactured metalwork processed outside our facility.

 

Teflon Machining Guide: Supportive Information

 

Chemical Resistant Materials

 

 

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This post was originally published in August 2017 and updated in March 2019.

 

When in need of a custom-machined component for a project, choosing a metallic material may be the instinctive consideration to the design engineer. This article is intended to provide educational insight as to a more sensible alternative for precision-machined, high-strength, durable parts: machined polymers and composites. Let’s explore the benefits of opting for a plastic material versus the more traditional metal materials for precision parts.

 

Benefits Across the Board

 

Machined polymer and composite components are the most cost-effective solution when compared to metal.

 

Machined plastic parts are lighter and therefore provide immense advantages over metals by offering lower lifetime freight costs for equipment that is regularly transported or handled over the product’s lifetime. In bearing and wear applications, polymers provide extensive advantages over metals by allowing for lower power motors for moving parts due to lower frictional properties of polymer wear components compared to metals. The low frictional properties provide for less wear as well. The lower wear rates allow for less maintenance-related downtime. Now your equipment can be online longer producing you more profit. Not only are plastics lighter, but they’re also less expensive than many raw metal materials used for parts. Plastics are produced in faster cycles than metals which helps keep manufacturing costs down as well.

 

Plastics are more resistant to chemicals than their metal counterparts.

 

Without extensive and costly secondary finishes and coatings, metals are easily attacked by many common chemicals. Corrosion due to moisture or even dissimilar metals in close contact is also a major concern with metal components. Polymer and composite materials such as PEEK, Kynar, Teflon, and Polyethylene are impervious to some of the harshest chemicals. This allows for the manufacture and use of precision fluid handling components in the chemical and processing industries which would otherwise dissolve if manufactured from metallic materials. Some polymer materials available for machining can withstand temperatures over 700°F (370°C).

 

Plastic parts do not require post-treatment finishing efforts, unlike metal.


Polymer and composites are both thermally and electrically insulating. Metallic components require special secondary processing and coating in order to achieve any sort of insulating properties. These secondary processes add cost to metallic components without offering the level of insulation offered by polymer materials. Plastic and composite components are also naturally corrosion resistant and experience no galvanic effects in a dissimilar metal scenario that require sheathing. Unlike metals, plastic materials are compounded with color before machining, eliminating the need for post-treatment finishing efforts such as painting.

 

Let’s Break It Down by Industry

 

The benefits and features of plastic materials over metals discussed above span across multiple industries, showcasing the utility and versatility that plastic brings to the table.

 

Aerospace & Defense

 

  • Lightweight: Polymer and composite materials are up to ten times lighter than typical metals. A reduction in the weight of parts can have a huge impact on an aerospace company’s bottom line. For every pound of weight reduced on a plane, the airline can realize up to $15k per year in fuel cost reduction.

 

  • Corrosion-Resistant: Plastic materials handle far better than metals in chemically harsh environments. This increases the lifespan of the aircraft and avoids costly repairs brought about by corroding metal components an in-turn reducing MRO downtime provides for more operational time per aircraft per year.

 

  • Insulating and Radar Absorbent: Polymers are naturally radar absorbent as well as thermally and electrically insulating.

 

  • Flame & Smoke Resistances: High-performance thermoplastics meet the stringent flame and smoke resistances required for aerospace applications.

 

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Medical & Life Sciences

 

  • Sterility: In the medical industry, cleanliness is vital when it comes to equipment. Infection is the greatest threat facing hospital patients. Polymer and composite materials are easier to clean and sterilize than metal.

 

  • Radiolucency: Radiolucency is the quality of permitting the passage of radiant energy, such as x-rays, while still offering some resistance to it. Surgical instruments and components manufactured from polymer materials allow the surgeon a clear unobstructed view under fluoroscopy. This allows for safer, more precise surgeon outcomes in the OR. Metal instruments impede the surgeon’s view.

 

  • Lightweight: Plastic and composite surgical components allow orthopedic OEMs to meet ergonomic weight limits for surgical trays. Each metallic instrument adds weight and strain to the surgical team carrying and using metal instruments.

 

  • Reduced Stress-Shielding: Stress shielding occurs when metal implants and bone don’t become one nor work in unison. In medical-grade polymers like PEEK, however, its similar modulus to bone “fuses” with the bone into a single construct.

 

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Specialized Industrial

 

  • High Tensile Strength: Several lightweight thermoplastics can match the strength of metals, making them perfect for industrial equipment metal part replacement.

 

  • Chemical & Corrosion Resistances: Semiconductor equipment and electronics require survival in extreme, high-pressure environments.

 

  • Flexibility & Impact Resistance: Polymers are resistant to impact damage, making them less prone to denting or cracking the way that metals do.

 

  • Excellent Bearing & Wear Properties: Bearing-grade plastics can withstand repeated friction and wear for your high-load solutions.

 

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Power & Energy

 

  • Weight, corrosion, and sealing: Plastic materials allow the oil and gas industry to explore deeper depths than ever before by offering tool weight reduction without a loss of strength as well as materials which offer superior sealing attributes.

 

  • Superior Insulation: Naturally insulating plastics provide for superior thermal and electrical insulation over metals, which is a must for power generation equipment that deals with electrical currents.

 

  • Chemical, Wear & Corrosion Resistances: Plastic components with a strong chemical, wear and corrosion resistances reduce downtime and yield long-lasting performance and reliability.

 

  • Extreme Water & Earth Depth Capabilities: These qualities are necessary for high pressure and temperature applications that involve surviving extreme environments.

 

Learn More

 

As you can see, plastics have a variety of unique attributes which place them above metals in terms of utility, cost-effectiveness and flexibility for precision-machined components. Search specific plastic materials and their applications per industry with our useful material search function.

 

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An Informational Brief on Polymer Machining

 

Delrin®, also commonly known as an acetal (polyoxymethylene) homopolymer, is an impact and wear resistant semi-crystalline thermoplastic popular for a broad range of machining applications. To list just a few of its impressive qualities, Delrin offers great stiffness, flexural modulus, and high tensile and impact strength.

Our latest machining guide discusses what goes into machining Delrin and how its considerations differ from other manufacturing options such as metal machining, injection molding, and 3D printing.

How does AIP approach Delrin and its machining process? To start, we’ll explain the difference between machining Delrin, a thermoplastic, and machining thermosets.

 

Machining Thermoplastics vs Thermosets

 

We’ve already said that Delrin is a thermoplastic, but what does that mean exactly?

All polymers can more or less be divided into two categories: thermoplastics and thermosets. The main difference between them is how they react to heat. Thermoplastics like Delrin, for example, melt in the heat, while thermosets remain “set” once they’re formed. Understanding the technical distinction between these types of materials is essential to CNC machining them properly.

What type of thermoplastic is Delrin in particular? Acetal homopolymer is a semicrystalline, engineering thermoplastic.

 

Properties & Grades of Machined Delrin

 

This strong, stiff and hard acetal homopolymer is easy to machine and exhibits dimensional stability and good creep resistance, among several other desirable qualities. Delrin is also known for its superior friction resistance, high tensile strength, and its fatigue, abrasion, solvent and moisture resistance.

The latter quality allows Delrin to significantly outperform other thermoplastics like Nylon in high moisture or submerged environments without losing high-performance in the process. In other words, Delrin can retain its low coefficient of friction and good wear properties in wet environments.

One of the main reasons for Delrin’s popularity is its sheer versatility. The above blend of unique qualities makes Delrin broadly applicable to various industries in the medical, aerospace and energy sectors. For example, you can machine Delrin for medical implants and instruments, or for industrial bearings, rollers, gears, and scraper blades. It is ideal for smaller applications at temperatures below 250 °F (121°C) and can have centerline porosity.

Some of the Delrin grades we regularly machine at AIP include:

 

PTFE-Filled Acetals

 

PTFE (polytetrafluoroethylene) filled grades of Delrin is ideal where impact strength and wear capability are of the highest importance.

 

Glass-Reinforced Acetals

 

Acetals that are reinforced with glass have a much higher strength and greater heat resistance than other grades of Delrin.

 

FDA-Compliant Acetals

 

There are FDA-compliant grades of Delrin available for use in medical and food-related applications.

 

Machining Delrin

 

Machining Delrin

 

It’s true that Delrin is an easy material to work with in terms of machining. It is a very stable material, which makes precise, tight tolerances easier to achieve for this thermoplastic.

While machining, keep in mind that Delrin is sensitive to heat at or above 250 °F (121°C).

Balance the material removal as best as you can to keep your dimensions stable.

We also suggest non-aromatic, air-based coolants to achieve optimum surface finishes and close tolerances. Coolants have the additional benefit of extending tool life as well.

 

Preventing Contamination

 

Contamination is a serious concern when machining polymer components for technically demanding industries such as medical and life sciences. To ensure the highest level of sanitation down to the sub-molecular level, AIP Precision Machining designs, heat-treats, and machines only plastics, with any sub-manufactured metalwork processed outside our facility.

 

Delrin Machining Guide: Supportive Information

 

General Engineering Materials

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