In this Series of discussions, we will explore some past projects that involved some trouble shooting and some machining tips that were learned along the way. This might help you set your mind when certain problems arise in your next project.
Machining PEEK:
PEEK (Polyetheretherketone) semi-crystalline thermoplastic that is high temperature resistant, excellent chemical, wear and stability properties. High long term operating temperature
and excellent resistance to high energy radiation. PEEK has very little moisture absorption and a working temperature range of about 480°F but is capable in steam and pressure environments to resist over 550°F. PEEK grades offer chemical and hydrolysis resistance similar to PPS, but can operate at higher temperatures. PEEK is also FDA compliant, making it a good choice for demanding food contact, medical applications, is an excellent material for machining, and is also available in standard shapes. For hostile environments, PEEK is a high strength alternative to fluoropolymers and carries a V-O flammability rating and exhibits very low smoke and toxic gas emission when exposed to flame.
We have seen and worked with standard sizes that range 0.030" to 2" thick sheets, rods and tubes from 0.025" to 6" in diameter. PEEK is a great high strength alternative replacement for fluoropolymers and can be filled with glass or carbon fiber. A word of caution when using filled materials, do a machine wash down before and after machining with dedicated tooling sets and fixtures to prevent or reduce contamination in parts machined in plastic for the food processing and medical industries. When machining PEEK we use moderate cutting speeds with fast feed rates, recommended tooling is diamond filmed, PCD and polished carbide. PCD cutters are the best choice for glass filled PEEK, use tools with small radii corners to help avoid chipping of the material and finish. Keep moderate feed rates to avoid excess heat accumulation and rubbing. Average surface feet per minute for sawing is about 2400, milling 400 - 800, turning 800 - 1400, and drilling 200 - 400 roughly speaking. Again, these are things for you to experiment with, but this should work well as a starting point in most cases.
Sawing Tip: Rip and combination blades with a 0° tooth rake and 3° to 10° tooth set are best for general sawing in order to reduce frictional heat. Use hollow ground circular saw blades without set will yield smooth cuts up to 3/4” thickness. Tungsten carbide blades wear well and provide optimum surface finishes. Another blade range setting we have used for PEEK with great results is blades with a 10° to 15° relief angles and 0° to 15° tooth rake angles, tooth pitch from 5/16" to 1" and cutting speeds from 39 to 118 in/min. If using a band saw use blades with 25° to 40° tooth relief angles and 0° to 8° rake angle range, tooth pitch from 5/64" to 1/8" and cutting speeds from 2 to 8 in/min.
Drilling Tip: The insulating characteristics of plastics require consideration during drilling operations, especially when hole depths are greater than twice the diameter. High speed steel twist drills are generally sufficient for small holes. To improve swarf removal, frequent pull-out (peck drilling) is suggested. A slow spiral (low helix) drill will allow for better swarf removal.
For large diameter holes a slow spiral (low helix) drill or general purpose drill bit ground to a 118° point angle with 9° to 15° lip clearance is recommended. The lip rake should be ground (dubbed off) and the web thinned. It is generally best to drill a pilot hole (maximum 1/2” diameter) using 600 to 1,000 rpm and a positive feed of 0.005” to 0.015” per revolution. Avoid hand feeding because of the drill grabbing which can result in micro cracks forming. Secondary drilling at 400 to 500 rpm at 0.008" to 0.020” per revolution is required to expand the hole to larger diameters. A two step process using both drilling and boring can be used on notch sensitive materials and glass reinforced materials. This minimizes heat build-up and reduces the risk of cracking.
Threading and Tapping Tip: Threading should be done by single point using a carbide insert and taking four to five 0.001” passes at the end. Coolant usage is suggested. For tapping, use the specified drill with a two-flute coated tap. Remember to keep the tap clean of chip build-up. Use of a coolant during tapping is also suggested. Use of a coated tap will create radii at the root of the threads resulting in a stronger and tougher thread which is less prone to cracking from over-torquing.
Turning Tip: Turning operations require inserts with positive geometries and ground peripheries. Ground peripheries and polished top surfaces generally reduce material build-up on the insert, improving the attainable surface finish. Fine grained C-2 carbide is generally best for turning operations.
Post Machining Annealing: In our experience and parts we have produced this step was avoidable with a roughing in machine stage and leaving parts unclamped for 1 to 2 days. This worked great for critical tolerance work. Here is some information on the annealing process that we feel is important to at least mention.
Common Applications for PEEK:
Aerospace Components
Electric Components
Food Processing
Machinery
Pumps and Valves
Semiconductor Equipment
Case Study #Reduce Part Distortion: PEEK 1000
We manufacture many components for the food processing equipment industry around the United States. Many of components are under high temperatures, and new processing machines move higher volumes and run even higher temperatures than previous models. The high temperatures on this client's new machines caused several plastic components to warp, leading to positioning and staging inaccuracies which lead to further problems of part breakage going down the line. Client was having product not placed correctly and was being rejected as the temperature reached its operating efficiency specifications.
Challenge: Improve or eliminate positioning inaccuracies, part binding and staging problems at operating temperatures.
Solution: These machines tend to be large and in complex processing lines, so a visit was in order at the site to see and review all of the customer's concerns. After a surface temperature reading on the failed components was performed, we had to further investigate what are these components made of. A review of the Dynamic Modulus for the current material must be studied. It was discovered that the material currently in use was not able to operate at that high temperature for a prolonged amount of time, the parts would soften, creep, and distort to the point that their original shape and dimensions where altered. We decided on using PEEK 1000 because of its ability to withstand high temperatures for prolonged periods of time without distortion. We machined the PEEK 1000 components and had the customer's maintenance crew tear down and replace the components with our PEEK components for a trial run. The machine did reach and maintained its operating temperature which improved the efficiency of the production line, the parts made in PEEK 1000 did not distort so positioning and staging remained accurate throughout the trail run. The processing unit did stop eventually due to part breakage, but we are proud to say it was not the PEEK 1000 components that we machined that failed.
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