Plastic CNC machining

The CNC technology is compatible with an extensive range of materials, metals, alloys, plastics, composites, wood, and many more. However, most CNC machining projects utilize metal and plastics. PEEK is one of the frequently used plastics that offer various advantageous properties, suitable for different applications.

In this article, we will discuss the properties of PEEK, the stages involved in PEEK CNC machining, several considerations & tips, and applications.

What is PEEK Plastic?

Polyetheretherketone (PEEK) is a popular engineering thermoplastic created with step-growth polymerization. It consists of repeating monomers, two ether, and a ketone group, resulting in semi-crystalline manners. Although PEEK is a colorless plastic, PEEK is predominantly available in three colors, brown, tan, and black. These colors are the results of mixing pigments during the molding.

PEEK at a glance

Common grades of PEEK plastics

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What are the properties of PEEK plastic?

PEEK is considered the “superior plastic family” in the manufacturing industry because of its excellent strength-to-weight ratio, dimensional stability, and stiffness. Let’s go through some fundamental properties of PEEK in detail.

• Excellent mechanical properties

PEEK is superior to other thermoplastics in terms of mechanical properties. It is a strong material with high fatigue resistance, impact strength, creep resistance, and wear resistance, and it can withstand high machining stress.

• Thermal resistance & Flame retardant

The capacity to work at high temperatures is the property that makes PEEK unique among the thermoplastics family. It can withstand temperatures up to 260° C and have a melting point of 350 ° C (Ranvijay Kumar, 2022).

It is also flame retardant and prevents the fire from spreading. At high temperatures, PEEK produces fire-resistive compounds like CO, CO2, Phenoxyphenol, and Diphenoxybenzene. This nature of PEEK makes it suitable to use as building & vehicle material.

• Chemical inertness

PEEK shows excellent inertness when coming in contact with dilute acids, alkalis, organic solvents, oils, hydrocarbons, and alcohol. So, it remains unaffected by these chemicals and does not go under corrosion and any degradation.

• Low friction coefficient

If you are wondering why PEEK is a low-wear plastic & used heavily in bearings, because of its low friction characteristic. The lubricity of PEEK does not let it wear and change in physical conditions while used in rotating & stress applications.

• Moisture & radiation resistance

PEEK almost absorbs zero water and withstands harsh environmental conditions. The chemical structure allows it to sustain wet operating conditions, making it ideal for marine and water pressure applications. In addition, It does not get affected by UV exposure and ionizing radiations.

• Electrical insulation

It is capable of absorbing high-voltage shocks without losing any properties. The zero electrical conductivity and high dielectric strength of PEEK make it an excellent electric insulation.

Some of the other essential properties are;

• It does not emit any toxic emissions and can be recycled after the lifespan of manufactured parts.
• It is highly bio-compatible and suitable for medical applications.
• Excellent peel resistance, thin parts can be machined with our warpage.

How to process PEEK with a CNC machine?

PEEK CNC machining

Converting the 3D model into accurate PEEK parts using CNC technology involves several steps and considerations.

Step 1: Review your 3D model

Simplify all of the complexity in a 3D model of the part. Maintain a decent thickness (a minimum of 0.8 mm is recommended). Before finalizing the design, check the tolerance to ensure whether it is possible to achieve or not. Over-tolerancing might cause defects and failure. Review all the features present in a design, such as edges, cavities, undercuts, and many more.

Step 2: Finalize the tool-path

After analyzing the 3D model, decide on the necessary CNC operations (milling, turning, drilling, etc.). Next, you need to fix and optimize the tool path. Avoid any intersections and long-complicated paths. The CAM software can simulate and find the best route for machining PEEK parts.

Step 3: Digital instructions & machining parameters

Upload the digital instruction (G-code) into the computer that will dictate the tools to move according to the finalized tool path.

Additionally, you should input machining parameters, such as cutting speed, feed rate, cutting depth, and more. Only correct machining parameters can produce the best result with PEEK plastic. So, select the cutting speed and feed rate according to the type of CNC operation.

• Milling: Feed rate 0.05 – 0.02 mm/ tooth, cutting speed 50- 300 m/ minute.
• Turning: Feed rate 0.1 – 0.5 mm/ tooth, cutting speed 150- 500 m/ minute.
• Drilling: Feed rate 0.1 – 0.3 mm/ tooth, cutting speed 50- 100 m/ minute.

Source: (Machining Guidelines – PEEK)

Step 4: Start the machining

Finally, hold the workpiece & position the cutting tool, and start the machining operation to convert the Raw PEEK into functional parts. Keep a close eye on the control panel and CNC machine to ensure everything is going according to planning.

Considerations for Accurate PEEK Machining

Minor considerations during the machining of PEEK can significantly impact the quality of the final result. Following are some crucial considerations for PEEK CNC machining.

1. Consider heat treatment with the workpiece.

Consider the annealing heat treatment before proceeding with the raw material of PEEK plastic. The internal build-up stress of the sheet, rod, or bar of PEEK might cause cracking during CNC machining. Hence, heating it for a specified temperature and cooling it at room temperature release the stress and prevent possible cracking.

2. Choose the appropriate machining tools.

PEEK is a rigid thermoplastic, as was already explained. The tools that can process the workpiece without wear are necessary. It is best to utilize poly-crystalline tools for long-run machining and carbide tools for general operations.

3. Use suitable coolants.

Coolants are mandatory in CNC machining because PEEK does not dissipate heat efficiently. Use air, oil, or water as coolant to eliminate the risk of deformation because of thermal stress. Although medical-grade PEEK requires extra attention when choosing the coolant, go with biocompatible coolants like pressurized air.

Tips for PEEK CNC Machining

Here are some tips you can follow during PEEK CNC machining to obtain the desired quality.

• Avoid deep drilling holes since the PEEK workpiece might crack due to low elastic properties.
• While machining the medical grade PEEK, wear clean gloves and handle the parts maintaining hygiene to avoid possible contamination.
• Use soft jaws or pie jaws for the creation of thin walls.
• Spiral carbide taps with two flutes are the best choice for the tapped hole.

Applications of PEEK CNC machining

CNC-machined PEEK parts

PEEK plastics come in various grades and can be precisely machined to meet the needs of multiple industries. It can be utilized for everything from large-scale production to quick prototyping. Let’s go further into the PEEK CNC machining applications.

Conclusion

PEEK is a superior thermoplastic with versatile physical, mechanical, and chemical properties. It is considered a metal replacement in many applications. The capability of working at high temperatures and high mechanical strength makes it a go-to option for different CNC machining projects.

CNC machining of PEEK requires several considerations regarding tool selection, cutting parameters, and coolants. ProlenaTech can do your best job with advanced CNC technology and a team of experienced engineers. We offer the precision CNC machining service for various materials, including the PEEK. Our quality control team closely monitors each manufacturing step to meet all your expectations.

FAQ’s

Why is PEEK considered the superior thermoplastic?

PEEK can work at high temperatures without losing any properties, while other thermoplastics are unable to do. It offers excellent mechanical strength, stiffness, impact resistance, abrasion resistance, and chemical inertness.

Is it easy to process PEEK with CNC machining?

Yes, PEEK has decent machinability. It can be processed with CNC machining operations like milling, turning, routing, drilling, and more. However, PEEK machining requires several considerations, from tool selection to the use of coolants.

What are the essential factors for precision PEEK machining?

Precise machining of PEEKs demands few considerations. Carbide tools are suitable for PEEK machining. The selection of coolants needs to be done with a grade of PEEK. Machining variables need to fix according to the type of operations and require annealing of the workpiece before machining begins.

What are the applications of PEEK CNC machining?

PEEK CNC machining has a significant role in manufacturing parts for automotive, aerospace, medical, electrical & electronics, food processing, oil & gas, and other industries.

Bibliography

1. (n.d.). Machining Guidelines – PEEK. DRAKE plastics.
2. RanvijayKumar, R. (2022). Thermoplastic Containers for Disposal of Radioactive Waste. ScienceDirect.