Materials / Non-Metallic Materials

The Challenges of Machining Non-metallic Materials

The type and structure of the bond between the atoms in a material are critical in determining its properties. This is an area where metallic and non-metallic materials differ fundamentally. Another difference is that non-metallic materials come in two forms: inorganic and organic. Glass and ceramic are two of the most common inorganic non-metallic materials used in industry, whereas organic materials encompass plastics of all types.
Composition materials are used in industrial applications to combine certain specific properties available with different materials. This is done, for example, to shed weight and hence conserve resources in the production of cars and other types of vehicles. This group includes carbon fibre, glass fibre or aramid fibre reinforced polymer (CFRP, GFRP and AFRP). To create each of these materials, fibres are embedded in a plastic matrix.

Non-Metallic Materials: Plastics, Ceramics, and Beyond

Replacing metal parts with plastic components has become increasingly common in efforts to reduce the weight of electric vehicles and develop more fuel-efficient aircraft. Composites like CFRP (Carbon Fiber Reinforced Polymer) and GFRP (Glass Fiber Reinforced Polymer) are favored for their high mechanical stability and low specific weight. However, the unique properties required for specific applications present challenges in machining these materials. This also applies to ceramic components like zirconium dioxide used in dental prostheses.

Here is a short list of non-metallic materials that are difficult to machine:

  1. Kevlar: Kevlar, a brand name of DuPont, is made from aramid fibers (aromatic polyamide). It boasts high tensile strength and impact resistance, making it suitable for components subject to impact and shock. Kevlar is light and highly vibration-absorbent. However, machining Kevlar Reinforced Polymer (KFRP) can lead to delamination, where the cut edges fray, causing damage. The abrasive fibers also wear down cutting tools if they are not specifically designed for this purpose.
  2. CFRP: The properties of CFRP can be influenced by the choice and alignment of carbon fibers. With a density roughly 20% that of steel, CFRP can achieve comparable strengths with an 80% reduction in weight. The fibers are embedded in thermoset or thermoplastic (re-fusible) plastic. CFRP is used in automotive, aerospace, and medical equipment sectors due to its high fatigue resistance. Machining CFRP poses challenges like delamination and high abrasiveness.
  3. GFRP: Glass fibers embedded in plastic create GFRP, which is relatively stable and less expensive than CFRP. GFRP is used in similar applications as CFRP but also presents issues like delamination and tool wear due to the hardness of the glass fibers.
  4. Zirconium Dioxide: Also known as zirconia, this material is used in dentistry for implants, dental crowns, root posts, and overdentures. The extreme hardness of zirconia makes it particularly difficult to machine.

Machining non-metallic materials poses unique challenges. Fiber-reinforced plastics are prone to delamination, especially when the tool is plunged in and out, causing fraying and splintering. Hard materials like zirconia cause significant tool wear. However, with high-quality cutting tools from ZCC-CT, it is possible to overcome these material-specific challenges in milling, turning, and drilling operations.