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CBN Indexable Inserts: The Powerhouses in Turning Operations
1 - Material Properties of CBN
Basic Characteristics
Cubic boron nitride is a synthetically produced material obtained through high-pressure-high-temperature synthesis from hexagonal boron nitride. With a hardness of approximately 4,500 HV, CBN is only slightly below that of diamond (10,000 HV on the Mohs scale), but significantly exceeds all other technical cutting materials.
Physical and Mechanical Properties
- Hardness and Wear Resistance: CBN exhibits exceptional hardness that is maintained even at high temperatures up to approximately 1,200°C. This thermal stability significantly exceeds that of diamond, as diamond begins to oxidize at 700°C. The high hardness results in excellent wear resistance against abrasive wear.
- Thermal Properties: The thermal conductivity of CBN at approximately 100-200 W/mK is significantly higher than that of carbide (50-100 W/mK), leading to better heat dissipation from the cutting zone. The thermal expansion coefficient is low, ensuring dimensional stability during temperature fluctuations.
- Chemical Resistance: CBN shows high chemical resistance to most metals and is particularly stable against ferrous materials. This property significantly reduces the tendency toward adhesive wear and built-up edge formation.
2 - Structure and Manufacturing of CBN Indexable Inserts
Structural Design
CBN indexable inserts typically consist of two components: a thin CBN layer (0.5-1.5 mm) on a carbide substrate. This construction combines the superior cutting properties of CBN with the toughness and favorable cost-performance ratio of carbide.
Manufacturing Process
Production is carried out by sintering under high pressure and high temperature. CBN crystals are bonded with metallic or ceramic binders to form a compact cutting insert layer. Common binders are titanium, aluminum, or ceramic phases, which significantly influence the properties of the final cutting insert.
Variants and Grades
Low CBN Content (50-65%):
These variants contain a higher binder content and offer a good balance between hardness and toughness. They are suitable for continuous cuts and applications with moderate requirements.
High CBN Content (85-95%):
High-purity CBN grades offer maximum hardness and wear resistance, but are more brittle and sensitive to impact loads. They are used in applications with the highest requirements for surface quality and tool life.
3 - Application Areas and Machinable Materials
Hardened Steels
CBN indexable inserts are predestined for machining hardened steels with hardness above 45 HRC. Typical applications include:
- Tool Steels: Machining of press tools, injection molds, and stamping tools after heat treatment
- Bearing Steels: Finish machining of rolling bearing rings and raceways
- Case-Hardened Steels: Post-machining of case-hardened gear wheels and camshafts
Cast Iron Materials
CBN cutting inserts show their superiority particularly when machining gray cast iron with lamellar graphite (GG) and ductile cast iron with spheroidal graphite (GGG):
- Gray Cast Iron: Cylinder head and engine block machining in the automotive industry
- Chilled Cast Iron: Rolls and wear-resistant cast parts
- Ni-Resist: Corrosion-resistant cast materials
High-Temperature Resistant Alloys
In aerospace and energy technology, CBN indexable inserts enable economical machining of:
- Nickel-Based Alloys: Inconel, Hastelloy for turbine blades
- Powder Metallurgical High-Performance Materials
- Stellite and Other Wear-Resistant Alloys
4 - Cutting Data Optimization
Cutting Speed
CBN indexable inserts work optimally at high cutting speeds between 150-600 m/min, depending on the material being machined. These high speeds are necessary to achieve the required cutting temperature and utilize thermal softening of the workpiece.
Feed Rate and Cutting Depth
Moderate feed rates (0.1-0.4 mm/rev) and low cutting depths (0.5-3 mm) are typical for CBN applications. These parameters ensure optimal chip formation and minimize mechanical loads on the brittle CBN cutting edge.
Cooling and Lubrication
Although CBN can generally be machined dry, targeted minimum quantity lubrication (MQL) or compressed air cooling is recommended for most applications to avoid temperature peaks and improve surface quality.
5 - Machine Requirements
Rigidity and Damping
CBN machining requires highly rigid machines with low vibration tendencies. Insufficient machine dynamics lead to premature cutting edge chipping and reduced tool life.
Power and Speed Range
High spindle speeds and sufficient drive power are essential. Modern turning centers for CBN applications offer speeds up to 10,000 rpm and more.
Tool Holding
Precise and vibration-free tool holding systems are critical. HSK or shrink fit chuck systems are standard for high-quality CBN applications.
6 - Economic Considerations
Tool Costs vs. Total Costs
Although CBN indexable inserts are significantly more expensive than conventional cutting materials (factor 10-50), they can reduce total machining costs through considerably longer tool life, better surface quality, and higher cutting speeds.
Tool Life and Productivity
Typical tool life of CBN indexable inserts in hard machining ranges between 30-120 minutes of active cutting time, depending on material and application. This often corresponds to 5-20 times that of conventional tools.
Quality Benefits
The achievable surface qualities (Ra 0.1-0.8 μm) and form accuracies (IT6-IT8) often eliminate downstream grinding operations and thus reduce the process chain.
7 - Limitations and Challenges
Material Limitations
CBN is not universally applicable. Aluminum alloys, titanium, and other materials can lead to chemical reactions and premature wear. Diamond is often the better alternative here.
Mechanical Sensitivity
The brittleness of CBN makes the cutting inserts sensitive to impact loads and interruptions. Vibrations and uneven cutting conditions can lead to catastrophic failure.
Investment Costs
The high tool costs require careful economic consideration and are only justified with corresponding production volumes or high quality requirements.
8 - Future Perspectives
The further development of CBN indexable inserts focuses on improved binder systems, optimized coatings, and new manufacturing processes. Trends such as additive manufacturing open up new possibilities for customized cutting edge geometries and graded materials.
At the same time, digital technologies such as process monitoring and machine learning expand the possibilities for optimized use of these high-performance tools.
Conclusion
CBN indexable inserts today represent the spearhead of machining technology and enable economical machining of the hardest materials. However, their use requires a holistic consideration of tool, machine, and process. When properly applied, they offer unmatched performance in terms of tool life, surface quality, and productivity, making them an indispensable tool in modern precision manufacturing.
Related Products
Indexable CBN-Insert - CNGA 1204..-2N RTC20T
| Shape | CNGA |
| Scope of application | Hard turning |
| Cutting edges | 2 |
| Grade | RTC20T : TIN-coated CBN for full to slightly interrupted cuts in hardened steels |
| Packaging unit | 2 Pc |
| I.C. | S | r | d | L | |
| CNGA 120404-2N RTC20T | 12,7 | 4,76 | 0,4 | 5,16 | 2,2 |
| CNGA 120408-2N RTC20T | 12,7 | 4,76 | 0,8 | 5,16 | 2,2 |
Indexable CBN-Insert - CCGW ...-2N RTC20T
| Shape | CCGW |
| Scope of application | Hard turning |
| Cutting edges | 2 |
| Grade | RTC20T : TIN-coated CBN for full to slightly interrupted cuts in hardened steels |
| Packaging unit | 2 Pc |
| I.C. | S | r | L | |
| CCGW 060202-2N RTC20T | 6,35 | 2,38 | 0,2 | 2,2 |
| CCGW 060204-2N RTC20T | 6,35 | 2,38 | 0,4 | 2,2 |
| CCGW 060208-2N RTC20T | 6,35 | 2,38 | 0,8 | 2,2 |
| CCGW 09T302-2N RTC20T | 9,525 | 3,97 | 0,2 | 2,2 |
| CCGW 09T304-2N RTC20T | 9,525 | 3,97 | 0,4 | 2,2 |
| CCGW 09T308-2N RTC20T | 9,525 | 3,97 | 0,8 | 2,2 |
| CCGW 09T312-2N RTC20T | 9,525 | 3,97 | 1,2 | 2,2 |
| CCGW 120404-2N RTC20T | 12,7 | 4,76 | 0,4 | 2,2 |
Indexable CBN-Insert - DNGA 1506..-2N RTC20T
| Shape | DNGA |
| Scope of application | Hard turning |
| Cutting edges | 2 |
| Grade | RTC20T : TIN-coated CBN for full to slightly interrupted cuts in hardened steels |
| Packaging unit | 2 Pc |
| I.C. | S | r | d | L | |
| DNGA 150604-2N RTC20T | 12,7 | 6,35 | 0,4 | 5,16 | 2,2 |
| DNGA 150608-2N RTC20T | 12,7 | 6,35 | 0,8 | 5,16 | 2,2 |
Indexable CBN-Insert - DCGW ...-2N RTC20T
| Shape | DCGW |
| Scope of application | Hard turning |
| Cutting edges | 2 |
| Grade | RTC20T : TIN-coated CBN for full to slightly interrupted cuts in hardened steels |
| Packaging unit | 2 Pc |
| I.C. | S | r | d | L | |
| DCGW 070204-2N RTC20T | 6,35 | 2,38 | 0,4 | 2,8 | 2,2 |
| DCGW 070208-2N RTC20T | 6,35 | 2,38 | 0,8 | 2,8 | 2,2 |
| DCGW 11T302-2N RTC20T | 9,525 | 3,97 | 0,2 | 4,4 | 2,2 |
| DCGW 11T304-2N RTC20T | 9,525 | 3,97 | 0,4 | 4,4 | 2,2 |
| DCGW 11T308-2N RTC20T | 9,525 | 3,97 | 0,8 | 4,4 | 2,2 |
Indexable CBN-Insert - WNGA 0804..-3N RTC20T
| Shape | WNGA |
| Scope of application | Hard turning |
| Cutting edges | 3 |
| Grade | RTC20T : TIN-coated CBN for full to slightly interrupted cuts in hardened steels |
| Packaging unit | 2 Pc |
| I.C. | S | r | d | L | |
| WNGA 080404-3N RTC20T | 12,7 | 4,76 | 0,4 | 5,16 | 2,2 |
| WNGA 080408-3N RTC20T | 12,7 | 4,76 | 0,8 | 5,16 | 2,2 |
Grooving insert - MGGN ...-CBN RTC20
| Grooving Insert | MGGN |
| Workpiece Materials | Hard Materials |
| Grade | RTC20=CBN fine grain grade for grooving in hardened steel, also in interrupted cut |
| Grooving system | MGM./MRM.-System |
| Packaging unit | 1 Pc. |
| B | R | L | S | |
| MGGN 200-CBN RTC20 | 2 | 0,2 | 16 | 4,8 |
| MGGN 300-CBN RTC20 | 3 | 0,4 | 21 | 4,8 |