We’re continuing our line of polymer machining briefs at AIP, and this month, we talk about TORLON: a PAI, or polyamide-imide. Discover AIP’s process of machining TORLON plastics in this informational polymer machining guide.

1. Machining TORLON: A Plastics Guide
An Informational Brief on Polymer Machining

2. AIP’S EXPERIENCE
AIP Precision Machining has worked
with many thermoplastics over the past
three decades, including TORLON: a
PAI, or polyamide-imide, engineered by
Solvay Specialty Polymers.
Due to its reliable performance at severe
levels of temperature and stress,
TORLON is ideal for critical mechanical
and structural components of jet
engines, automotive transmissions, oil
recovery, off-road vehicles and heavy-
duty equipment.
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AIP has over 35 years of experience machining complex components from TORLON
and various other thermoplastic materials. We are providing this Machining TORLON
as yet another insightful technical brief about our polymer component manufacturing
process, and how it differs from that of metal machining, injection molding, or 3D
printing.

3. PLASTIC CNC MACHINING
Before discussing the process of machining TORLON, 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 sheet, rod, tube or near net molded blank.
The early history of CNC machining is almost as complex as a modern CNC
system. The earliest version of computer numerical control (CNC) technology
was developed shortly after World War II as a reliable, repeatable way to
manufacture more accurate and complex parts for the aircraft industry.
Numerical control—the precursor to CNC—was developed by John Parsons
as a method of producing integrally stiffened aircraft skins.
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4. PLASTIC CNC MACHINING
Parsons, while working at his father’s Traverse City, Michigan-based Parsons Corp.,
had previously collaborated on the development of a system for producing helicopter
rotor blade templates. Using an IBM 602A multiplier to calculate airfoil coordinates, and
inputting this data to a Swiss jig borer, it was possible to produce templates from data
on punched cards.
Parsons’ work lead to numerous Air Force research projects at the Massachusetts
Institute of Technology (MIT) starting in 1949. Following extensive research and
development, an experimental milling machine was constructed at MIT’s
Servomechanisms Laboratory.
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 and thermal properties which result in
varying behavior when machined. Therefore, it’s important to understand the polymer
structure and properties of TORLON if you’re machining it.
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5. 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 these two main polymer categories react to
chemicals and temperature.
Thermoplastics soften when heated and become more fluid as additional
heat is applied. The curing process is completely reversible as no chemical
bonding takes place. This characteristic allows thermoplastics to be remolded
and recycled without negatively affecting the material’s physical properties.
• They possess the following properties:
• Good Resistance to Creep
• Soluble in Certain Solvents
• Swell in Presence of Certain Solvents
• Allows for Plastic Deformation when Heated
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6. THERMOPLASTICS VS. THERMOSETS
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Thermosets plastics contain polymers that cross-link together during the
curing process to form an irreversible chemical bond. The cross-linking
process eliminates the risk of the product re-melting when heat is applied,
making thermosets ideal for high-heat applications such as electronics and
appliances.
• They possess the following properties:
• High Resistance to Creep
• Cannot Melt
• Insoluble
• Rarely Swell in Presence of Solvents
Phenolic, Bakelite, Vinyl Ester and Epoxy materials would be considered
examples of a thermoset, while ULTEM (link to ULTEM guide), PEEK,
DELRIN and Polycarbonate materials are examples of thermoplastics.

7. THERMOPLASTICS VS. THERMOSETS
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The thermoplastic category of polymers is further categorized into Amorphous
and Crystalline polymers per the figure below:
TORLON is considered an amorphous, high-performance thermoplastic. Most
amorphous polymers are thermoform capable, translucent and easily bonded with
adhesives or solvents.

8. VARIOUS GRADES OF MACHINED TORLON
What makes TORLON unique is how it possesses both the incredible performance of
thermoset polyimides and the melt-processing advantages of thermoplastics. The
compressive strength of (unfilled) TORLON PAI is double that of PEEK and 30% higher than
that of ULTEM PEI. In fact, TORLON is considered the highest performing, melt-
processible plastic.
High-strength grades of TORLON retain their toughness, high strength and high stiffness up
to 275°C. This and its impressive wear resistance allow TORLON to endure in hostile
thermal, chemical and stress conditions considered too severe for other thermoplastics.
TORLON is also resistant to automotive and aviation fluids, making it a favorite of
aerospace and automotive engineers.
One concern of using TORLON is that its moisture absorption rate is not as low as other
high-performance plastics, so special care should be taken when designing components for
wet environments.
There’s more than one particular type of TORLON PAI you can machine, and each has
slightly different properties for perfecting this material’s use in different applications.
Following are several grades of TORLON PAI we machine regularly at AIP Precision
Machining.
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9. VARIOUS GRADES OF MACHINED TORLON
TORLON 4203
TORLON 4203 is the unfilled or natural
grade of TORLON PAI that outperforms
other grades with the best impact
resistance and the most elongation.
TORLON 4203 PAI can be used for a
variety of applications but due to its good
electrical properties, it is commonly
machined for electronic equipment
manufacturing, valve seals, bearings and
temperature test sockets.
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10. VARIOUS GRADES OF MACHINED TORLON
TORLON 4301
TORLON 4301 is a wear-resistant grade
of TORLON PAI containing PTFE and
graphite. It has high flexural and
compressive strength with a low
coefficient of friction, as well as good
mechanical properties. Typical
applications of 4301 are anything that
requires strength at high temperature
with wear resistance and low friction.
This material is useful for parts such as
thrust washers, spline liners, valve
seats, bushings, bearings and wear
rings.
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11. VARIOUS GRADES OF MACHINED TORLON
TORLON 4XG
TORLON 4XG is a 30% glass-
reinforced extruded grade of PAI well
suited to higher load structural or
electronic applications. When you
need a high degree of dimensional
control, this grade offers the high-
performance you need. Various uses
of TORLON 4XG include burn-in
sockets, gears, valve plates, impellers,
rotors, terminal strips and insulators,
among others.
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12. VARIOUS GRADES OF MACHINED TORLON
TORLON 4XCF
TORLON 4XCF is a 30% carbon-
reinforced extruded grade of PAI that
has the lowest coefficient of thermal
expansion and the most impressive
fatigue resistance of all plastic
materials. This uncommon grade works
well as a replacement for metal
applications as well as mission-critical
aerospace components, in addition to
impellers, shrouds and pistons.
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13. VARIOUS GRADES OF MACHINED TORLON
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14. MACHINING TORLON
Annealing TORLON
TORLON PAI can be received in the form of rods, sheets, tube or film. 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.
This also helps prevent any warping or distortion of your plastic materials.
TORLON additionally benefits from post-machining annealing to reduce any stress
that could contribute to premature failure. Extruded TORLON parts, such as those
machined from TORLON 4XCF and TORLON 4XG, benefit from an additional cure
after machining to further enhance wear resistance; this is unique to PAI. Proper
annealing of Torlon can require more than seven days in special ovens at AIP.
If the machine shop you are working with does not have a computer controlled
annealing oven for plastics, then “head for dee hills” as they are obviously not
TORLON machining experts.
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15. MACHINING TORLON
Machining TORLON
An important consideration to have when machining TORLON PAI is how abrasive it
is on tooling. If you’re machining on a short run, carbide tooling can be used, but
polycrystalline (PCD) tooling should be considered for lengthier runs, machining for
tight tolerance and any time you are working with reinforced grades.
Another thing to keep in mind when machining extruded TORLON shapes is that they
have a cured outer skin, which is harder than interior sections. The outer skin offers
the best wear and chemical resistance. If wear resistance and chemical resistance
needs to be optimized, extruded TORLON should be re-cured.
TORLON PAI will nearly always require the use of coolants due to its stiffness and
hardness. Non-aromatic, water soluble coolants are most suitable for ideal surface
finishes and close tolerances. These include pressurized air and spray mists.
Coolants have the additional benefit of extending tool life as well.
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16. MACHINING TORLON
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.
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Many metal shops use petroleum-based
coolants, but these types of fluids attack
TORLON. Many past experiences have
shown parts going to customer without
cracks, only to develop cracks over time
due to exposure to metal machine shop
fluids. Be sure to use a facility like AIP who
machines polymers and only polymers.

17. TORLON Machining Guide: Supportive
Information
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Supportive Guides
• Medical Sector Biomaterials Guide
• Energy Sector Materials Guide
• Aerospace Sector Materials Guide
• Amorphous Materials
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.

18. Let’s get started.
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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
AIP.Sales@AIPprecision.com
AIPprecision.com