Top 5 tips for carbon fibre machining

The rise in the demand of carbon fibre products in recent decades has driven the need for more effective and efficient carbon fibre machining methods.

The development of such manufacturing techniques, combined with the attractive properties of carbon fibre, has resulted in a rapid growth in production. In 2006, the global carbon fibre market was valued at $1.3 billion with a total output of 27 thousand tonnes. In 2018 this value almost doubled to $2.5 billion, and the compound annual growth rate between 2019 and 2025 is estimated at 11.2%.

Carbon fibre, also referred to as graphite fibre or carbon graphite, consists of thin strands of molecules made from organic polymers. These strands are 5-10 microns in diameter and are bonded together via carbon atoms. Several thousand strands bonded together form a tow, which can then be woven to form a cloth.

Typically, other materials such as resin or graphite are combined with the carbon fibre cloth to produce a composite material. When cured, this composite material has the desirable properties carbon fibre is known for:

• High stiffness
• Increased chemical resistance
• Low weight
• High melting point
• High tensile strength
• Relatively low thermal expansion

These properties lead to carbon fibre being embraced by many industries. Most notable is commercial flight and aerospace, where weight is money. Carbon fibre’s high strength-to-weight ratio is ideal in this regard. Reducing the weight of aeroplane components not only saves the company money by either increasing the payload weight or decreasing the fuel requirements, but it also has environmental benefits thanks to reduced fossil fuel emissions.

An example of an aircraft that makes extensive use of low-weight composite materials is the Boeing 787 Dreamliner. First flown in 2009, the aeroplane is made from roughly 50% composite materials including carbon fibre.

Other carbon fibre applications include:

• High-performance vehicles
• Sporting equipment
• Musical instruments
• Wind turbines
• Natural gas storage
• Deep-water drilling platforms

The challenges of carbon fibre machining

Machine shops have had to adapt to the new challenges that come with carbon fibre machining. Precise and repeatable machining results require a change of approach when compared to machining traditional materials such as metal.

Below is a list of challenges associated with carbon fibre machining.

• Carbon fibre relaxes when cut – Relaxation of the material causes machined holes and pockets to be undersized or misshapen. The fibre orientation is unpredictable, so the effects of machining are difficult to predict. Extensive inspection and adjustment are needed to overcome this problem and maintain the required tolerances, something that is harder if the machining process requires the use of multiple machines.
• High cost of scrapping – Manufacturing and custom moulding of the carbon fibre material is an expensive process, so machinists have very little room for error and the cost of mistakes is much higher.
• Abrasive – Carbon fibre is an abrasive material, and increases the rate of wear on the tools used. This is exacerbated by the increased heat associated with carbon fibre machining – the material has low thermal conductivity and very little heat is carried away in chips. Additionally, using a dull edge for carbon fibre machining causes the delamination of the material’s layers.
• Dust – carbon fibre machining produces more dust compared to metal machining. The carbon dust produced is harmful to the lungs and skin, and since it conducts electricity, it can also cause shorts in electrical equipment.

Carbon fibre machining tips

1. Water jet machining – Whenever possible, carbon fibre machining should be performed using water jet cutting as opposed to rotary machining. It doesn’t generate the dust or heat that causes so many challenges in carbon fibre machining. When performed correctly, it will also not cause the delamination of the material’s layers.
2. PCD tools – If rotary machines must be used, polycrystalline diamond (PCD) tools offer better abrasion resistance than carbide. PCD tools can operate at triple the spindle speed and last up to 25 times longer than similar carbide alternatives.
3. Reduce tool lifetime – Even if you are using PCD tools, their overall lifespan will be reduced when used for carbon fibre machining. The usage of each tool should be monitored and its sharpness inspected before each use to prevent delamination.
4. Lower feed rates – To reduce the build-up of heat and the resulting damage to the tool, carbon fibre machining requires lower feed rates compared to other materials.
5. Dust mitigation – The dust must be vacuumed frequently to prevent harm to the machinist and any surrounding electrical equipment. Proper safety equipment such as gloves, goggles, and dust masks must be worn to protect the operator’s lungs and skin

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