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Machining PEEK: A Plastics Guide


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An Informational Brief on Polymer Machining and Machining PEEK.

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Machining PEEK: A Plastics Guide

  1. 1. Machining PEEK: A Plastics Guide An Informational Brief on Polymer Machining
  2. 2. THE VERSATILITY OF PEEK The recent popularity of PEEK (polyetheretherketone) in complex industries such as Aerospace & Defense and Medical & Life Sciences is well documented, and for good reason: this lightweight thermoplastic bears properties that make it ideal for a variety of specialized applications. This versatility makes PEEK equally capable of being used for implants and custom medical devices or machined components for aircraft interiors. What is less known, however, is the process that goes into machining this plastic material. With over 35 years of experience machining this thermoplastic material, we at AIP have written a brief introduction to machining PEEK. We hope this gives you some insight into our polymer machining process, and how it differs from that of metal machining or injection molding. 2
  3. 3. PLASTIC CNC MACHINING Before discussing the process of machining PEEK, it’s important to understand exactly what plastic machining is. CNC (Computer Numerical Control) machining is a process in the manufacturing sector that involves the use of computers to control machine tools. In the case of plastic machining, this involves the precise removal of layers from a plastic material. The technique of utilizing drilling tools to carve plastics was introduced by MIT during the 1950s, and because this process is computer- controlled, products with extremely precise tolerances can be achieved. 3 Due to the many different kinds of polymers and composites, it’s important to have strong technical expertise of polymer materials when machining plastic components; some plastics are brittle, for example, while others cut similarly to metal. The challenge of plastics is their wide range of mechanical properties and varying behavior when machined. Therefore, it’s important to understand the polymer structure of PEEK if you’re machining it.
  4. 4. THERMOPLASTICS VS. THERMOSETS When it comes to polymers, you have two basic types: thermoplastics and thermosets. It’s crucial to know which one you’re working with due to distinct differences between how those polymers react to heat and temperature. Thermoplastics are capable of being repeatedly softened and pliable when temperature increases, meaning that when heat is applied, that results in a physical change for the polymer. They possess the following properties: • Good Resistance to Creep • May Melt Before Turning to Gaseous State • Soluble in Certain Solvents • Swell in Presence of Certain Solvents • Allows for Plastic Deformation when Heated 4
  5. 5. THERMOPLASTICS VS. THERMOSETS Thermosets in contrast turn into an infusible and insoluble material when cured by application of heat or chemical means, making for poor elasticity. They possess the following properties: • High Resistance to Creep • Cannot Melt • Insoluble • Rarely Swell in Presence of Solvents Phenolic materials would be considered examples of a thermoset, while PEEK is an example of a thermoplastic. 5 In particular, PEEK is considered a semi-crystalline, high- performance thermoplastic. This gives it enough elasticity to be machined to various custom designs, with strong mechanical properties that provide resistance to fatigue and stress-cracking, as well as a good structure for bearing, wear, and structural applications.
  6. 6. INDUSTRIAL GRADE VS MEDICAL GRADE Depending on your application, you’ll want to machine either industrial-grade PEEK or medical-grade PEEK. Industrial-grade PEEK is a strong, flame-retardant and abrasion resistant thermoplastic with high impact strength and a low coefficient of friction. It’s known for retaining its mechanical properties, even at elevated temperatures. As suggested by its name, this grade is most commonly used in aerospace, automotive, chemical, electronics, petroleum, as well as food and beverage industries. Medical-grade PEEK adds biocompatibility per ISO 10993, high chemical resistance, and sterilization compatibilities to the above list of qualities. In addition, this thermoplastic is radiolucent, meaning it is not visible under X-ray, MRI or CT. Medical- grade PEEK includes polymers suitable for implants, such as PEEK Optima and Zeniva PEEK, which can stay in contact with blood or tissue indefinitely while mimicking the stiffness of bone. Other variations of medical-grade PEEK can be used for custom medical components and applications, such as articulating joints and spinal devices. 6
  7. 7. MACHINING PEEK Annealing PEEK Most shops receive PEEK in the form of rods of various lengths, ranging from 6mm to 150mm in diameter. Stress-relieving before machining through an annealing process is crucial, as it reduces the likelihood that surface cracks and internal stresses will occur from the heat generated. Additional benefits of annealing include increased levels of crystallinity and the opportunity to limit dimensional changes. If your PEEK components will undergo long stretches of machining time, it is likely you will require additional intermediate annealing steps to assure the ability to maintain critically tight tolerances and flatness. 7
  8. 8. MACHINING PEEK 8 Machining Industrial-Grade & Medical-Grade PEEK Both industrial-grade and most medical-grade PEEK machine similarly, save for PEEK reinforced with carbon fiber. Silicon carbide cutting tools work well for natural PEEK, while diamond tools work well for PEEK reinforced with carbon- fiber. For medical-grade PEEK applications, the best way to avoid jeopardizing the biocompatibility of the material is to machine dry. However, PEEK doesn’t dissipate heat the way that metals do, so often a coolant is necessary. In that case, air is the coolant option least likely to affect medical-grade PEEK’s biocompatibility. Any chips that are a result of machining medical-grade PEEK can be reused for industrial applications.
  9. 9. MACHINING PEEK 9 Preventing Contamination Contamination is a serious concern when machining polymer components for technically demanding industries such as aerospace and medical. 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.
  10. 10. We Satisfy Tight Tolerances in Plastic Parts AIP has well over three decades of expertise with thermoplastic materials, and understands how plastics react when machined. We are one of a very select few companies able to hold incredibly tight tolerances in plastic parts. AIP has been successfully audited by some of the most stringent OEMs and are ISO 13485:2016, ISO 9001:2015, IS9100 and FDA registered. 10
  11. 11. Let’s get started. 11 Any Product Puzzle. Any Customer Challenge. AIP is the niche that you need for all of your plastic parts. 724 Fentress Boulevard, Daytona Beach 32114 +1 386.274.5335