Machining PEEK: A Plastics Guide
An Informational Brief on Polymer Machining
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
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.
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
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
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
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
• High Resistance to Creep
• Cannot Melt
• Rarely Swell in Presence of Solvents
Phenolic materials would be considered examples of a thermoset, while PEEK is an
example of a thermoplastic.
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
INDUSTRIAL GRADE VS MEDICAL GRADE
Depending on your application, you’ll want to machine either industrial-grade PEEK or
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
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.
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-
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.
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.
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.
Let’s get started.
Any Product Puzzle.
Any Customer Challenge.
AIP is the niche that you need for all of your plastic parts.
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