We are often asked why high performance turning inserts should use a more traditional carbide substrate. Our range includes CBN, PCD and ceramic turning inserts, and in this article we will describe them and tell you why you need them.
What is CBN?
CBN stands for Cubic Boron Nitride, and CBN turning inserts are designed specifically for cutting ferrous metals. Typically, these inserts are used especially for hardened steels up to Rockwell hardness 70. But they are also suitable for wear-resistant cast iron and heat-resistant super alloys (such as Inconel).
CBN is made by combining ceramic material with micron-sized cubic boron nitride fragments under high pressure and temperature. It is almost as hard as diamond, so it is the second hardest material in the world with a hardness of about 70GPa. These properties ensure low wear and can guarantee tolerances during machining.
As technology advances in various industries, more and more manufacturers use CBN turning inserts when machining harder materials that are more heat-resistant and wear-resistant. These industries include automotive, aerospace, oil and gas, and medical industries.
What are the Main Advantages of CBN Turning Inserts?
- Greatly increases cutting speeds and feeds.
- Higher metal removal rates.
- Provides an exceptional surface finish.
- Excellent wear resistance.
- Maintains tight tolerances during machining.
- Greatly extends tool life compared to standard carbide turning inserts.
CBN inserts also do not require additional grinding when machining. They are a cost-effective alternative to diamond tools.
What are PCD Turning Inserts?
PCD, or polycrystalline diamond, PCD turning inserts are designed for high-performance turning of non-ferrous metals and composites. This includes aluminum alloys, brass, carbon fiber, fiberglass, composites and wear-resistant plastics. PCD is an advanced material, similar to CBN, made by bonding selected diamond particles together under high pressure and temperature. These types of inserts have extremely high hardness because their composition contains (90-95%) diamond, the hardest material in the world. Therefore, they can maintain a sharp cutting edge for a long time and have good thermal conductivity.
What are the Main Benefits of Using PCD Inserts?
- Excellent performance.
- Extra long tool life.
- Provides a mirror finish.
- High precision, high wear resistance.
- Lower cutting forces Higher speeds, greater feeds and cutting depths.
So overall, PCD inserts offer greatly improved performance and tool life compared to standard carbide inserts.
What are Ceramic Turning Inserts?
Ceramic turning inserts are made of aluminum oxide or silicon nitride. They are also the most popular solution for fast metal cutting with nickel-based alloys. Ceramic inserts cost up to three times more per cutting edge than carbide inserts. However, the greatly increased cutting speeds shorten the machining cycle, which means significantly lower production costs.
Ceramic turning inserts are often used in aerospace to machine large components due to their high cutting speeds.
What are the Main Benefits of Using Ceramic Inserts?
- Significantly reduced machining cycle times.
- Lower production costs.
- Excellent thermal shock resistance.
- Excellent tool life and wear resistance.
- Precise cutting with high surface finish.
In summary, ceramic inserts are a recognized alternative to standard carbide inserts. Because of their high heat resistance, service life, and overall machining performance is improved.
What Tool Holders Should be Used?
To get the best results with CBN and PCD turning inserts, you can use standard boring bars for machining IDs and dual clamping module locking turning tools for machining ODs. The dual clamping system minimizes vibrations and maximizes tool life. Chip cleaning and tool life are also improved by coolant.
For ceramic turning inserts, there are dedicated turning tools and boring bars that will allow you to achieve maximum cutting data and tool life. Since the geometry of ceramic inserts does not utilize the standard clamping methods of conventional toolholders, wedge or top clamping methods are used to firmly clamp the insert in place.
Tips for machining CBN, PCD and ceramic inserts
PCD is 95% diamond bonded to a tungsten carbide matrix, however, the diamond portion is essentially pure carbon. Therefore, it is important not to use it to machine ferrous materials such as steel and cast iron, as at high temperatures the carbon atoms react with the part material to form iron carbide and can cause the diamond structure to collapse.
PCD is very hard, but it is also very brittle. This means it is not suitable for unstable machining conditions where vibration may occur. In addition, we generally recommend the use of coolant when machining with PCD tools.
Ceramic inserts are not a panacea and require special care when machining. Since ceramics are more brittle (relative to materials such as carbides), it is wise to choose thicker inserts where possible. Ceramic inserts also require very high cutting speeds and enhanced geometry designs, which can be used for both roughing and finishing. Wedge-shaped or top-clamp-type toolholders are used to securely hold ceramic inserts. Coolant can be used, but is also not recommended for certain applications.
The main element in CBN is boron. These inserts are mainly suitable for cutting hardened steel (HRc50-70) and are best suited for high-finish machining. No coolant is required when machining CBN inserts.
PCD (Polycrystalline Diamond) inserts are best suited for machining non-ferrous materials. Although PCD has higher toughness than natural diamond, it is still very brittle compared to other cutting materials.
The most commonly used PCD machining material is aluminum, followed by plastics and brass.
