What is a CBN Insert (PCBN)?
PCBN (Nicknamed CBN) stands for “Polycrystalline Cubic Boron Nitride”, the second hardest material, second only to diamond. In addition to its high hardness[1] (4,500 HV[2]), it also has excellent hot hardness and chemical stability. Therefore, it can successfully machine Steel[3] up to 70 HRC[4] and other hard-to-machine materials.
![CBN Inserts 2 CBN Insert](https://www.machiningdoctor.com/wp-content/uploads/2021/06/CBN-Insert.png)
![CBN Inserts 3 chart of The hardness of CBN relative to other cutting materials](https://www.machiningdoctor.com/wp-content/uploads/2021/06/CBN-Hardness-300x258.png)
What are CBN inserts used for?
- Machine Steel heat treated to 50-70 HRC. (Coated carbide inserts cannot machine materials above 45 HRC)
- Machine Cast Iron[5] 3 times faster compared with coated carbide inserts. (~ 1,500 mm/min, 5,00 SFM[6])
- Machine Titanium[7] and Inconel (HRSA[8]) 5 times faster compared with coated carbide (~350 mm/min, 1,100 SFM)
CBN inserts working materials and cutting speeds
PROPERTY | CARBIDE | CERAMIC | CBN | PCD |
---|---|---|---|---|
Hardness [HV] | 1,300-1,800 | 2,100-2,400 | 4,500-5,000 | 5,000-6,000 |
Price per Cutting Edge [USD] | 4$ | 10$ | 40$ | 160$ |
Machining Hard Steel |
|
|
|
N/A |
Machining Cast Iron |
|
|
|
N/A |
Machining Super Alloys |
|
|
|
N/A |
Machining Aluminum |
|
N/A | N/A |
|
Machining Hardened Steel with CBN inserts
![CBN Inserts 4 Hard Steel ISO H](https://www.machiningdoctor.com/wp-content/uploads/2021/06/Hard-Steel-ISO-H.png)
Advantages:
- Excellent wear resistance.
- Long tool-life
- High cutting speeds[6]
- Maintaining close tolerances.
- High surface finish[9]
- It can replace grinding in many applications.
Disadvantages:
- High price.
- Low depth of cut. The depth of cut is limited by the size of the brazed CBN tips.
- Solid CBN, which enables heavier machining, is far more expensive.
Machining Cast Iron with CBN inserts
![CBN Inserts 5 Cast Iron ISO K](https://www.machiningdoctor.com/wp-content/uploads/2020/12/Cast-Iron-1.jpg)
The more popular solution for fast metal removal on Cast Iron is with Ceramic inserts[10]. Ceramic inserts cost less and can work in a higher depth of cuts. CBN inserts are used only for finishing operations that require higher surface finish and accuracy that cannot be obtained with Ceramic Inserts[10].
Machining Super Alloys (Nickel Based) with CBN inserts
![CBN Inserts 6 Super Alloys ISO S](https://www.machiningdoctor.com/wp-content/uploads/2021/05/ISO-S.jpg)
The more popular solution for fast metal removal on Nickel Based Alloys is with Ceramic inserts. Ceramic inserts cost less and can work in a higher depth of cuts. CBN inserts are used only for finishing operations that require higher surface finish and accuracy that cannot be obtained with Ceramic Inserts.