Common Industry Applications for CBN Inserts

Cubic Boron Nitride (CBN) lathe inserts are advanced cutting tools indispensable in modern manufacturing for their exceptional hardness, thermal stability, and wear resistance. These properties make them ideal for machining hard and abrasive materials that quickly wear down traditional cutting tools like carbide. This guide explores the common industry applications where CBN lathe inserts are the preferred solution for achieving high precision, surface finish, and productivity.

Why Choose CBN Inserts for Turning?

The effectiveness of CBN inserts in lathe operations stems from their unique characteristics:

• Extreme Hardness: CBN is the second hardest material known, surpassed only by diamond. This allows CBN inserts to effectively cut materials with high hardness that are difficult or impossible to machine with other tool materials.
• High Thermal Stability: Unlike diamond, which can degrade at high temperatures, CBN retains its hardness and strength at temperatures exceeding 1000°C. This is crucial for high-speed machining where significant heat is generated.
• Chemical Inertness: CBN exhibits low reactivity with ferrous metals at high temperatures, minimizing chemical wear and built-up edge when machining steels and cast irons.
• Excellent Wear Resistance: The inherent hardness and thermal stability of CBN result in significantly longer tool life compared to carbide or ceramic inserts, leading to reduced downtime and increased productivity.
• Ability to Achieve High Surface Finish and Dimensional Accuracy: CBN inserts can maintain a sharp cutting edge for extended periods, enabling the achievement of tight tolerances and superior surface finishes, often eliminating the need for subsequent grinding operations (hard turning).

Primary Materials Machined with CBN Lathe Inserts

CBN lathe inserts are primarily used for turning operations on the following material groups:

• Hardened Steels: Steels with a hardness typically above 45 HRC, including case hardened steels, tool steels, bearing steels, and die steels.
• Cast Irons: Various types of cast iron, such as grey cast iron, nodular cast iron, chilled cast iron, and alloyed cast iron.
• High-Temperature Alloys (Superalloys): Nickel-based, cobalt-based, and iron-based alloys used in high-リーブ applications like aerospace and energy.
• Sintered Materials: Powder metallurgy parts and hardfacing alloys which are inherently abrasive.

Common Industry Applications

The unique capabilities of CBN lathe inserts make them essential in industries where the machining of hard and demanding materials is commonplace:

• Automotive Industry:

  • Hard Turning of Transmission Components: Gears, shafts, and other power transmission parts are often hardened for durability. CBN inserts are used for finish turning these components after heat treatment, replacing grinding and improving efficiency.
  • Brake Disc and Drum Machining: CBN inserts are widely used for high-speed turning of cast iron brake components, providing excellent wear resistance and surface finish.
  • Engine Component Machining: Cylinder bores in engine blocks and other cast iron or hardened steel engine parts are precisely machined using CBN inserts.

• Aerospace Industry:

  • Machining of High-Temperature Alloy Components: Turbine blades, discs, and other parts made from nickel-based and cobalt-based superalloys require tools that can withstand high cutting temperatures and abrasive wear. CBN inserts are crucial for turning these challenging materials in engine and airframe components.

• Mold and Die Manufacturing:

  • Hard Turning of Mold and Die Components: Molds and dies are typically made from hardened tool steels. CBN inserts are used for finish turning these components to achieve the required accuracy and surface quality.

• Heavy Industry and Energy Sector:

  • Machining of Hardened Rolls: Rolls used in ميلling operations and other heavy machinery are often hardened. CBN inserts provide the necessary hardness and wear resistance for turning these large, hard components.
  • Turning of Wear-Resistant Components: Parts subjected to high wear, such as pump components and valve parts made from hard cast irons or other wear-resistant alloys, are effectively machined with CBN inserts.

• Medical Device Manufacturing:

  • Precision Machining of Hardened Stainless Steels and Other Alloys: Medical implants and instruments often require high precision and are made from hardened materials. CBN inserts are used for finish turning to achieve tight tolerances and the required surface finish.

Types of CBN Lathe Inserts

CBN lathe inserts are available in various configurations to suit different applications and machining conditions:

• Solid CBN Inserts: These inserts are made entirely of CBN and offer the highest thermal stability and wear resistance. They are typically used for continuous cutting applications and when maximum tool life is required.
• Brazed/Tipped CBN Inserts: These consist of a layer or tip of CBN brazed onto a carbide substrate. They offer a balance of performance and cost-effectiveness and are suitable for a wider range of applications, including moderately interrupted cuts.
• Full-Face CBN Inserts: Similar to solid CBN, with CBN covering the entire rake face, providing multiple cutting edges.

Insert Geometries and Edge Preparation

The geometry and edge preparation of CBN lathe inserts are critical for optimizing performance and tool life in specific applications:

• Geometries: Standard ISO insert shapes (e.g., CNGA, DNGA, TNGA, WNGA) are common. The choice of geometry depends on the specific turning operation (external turning, internal turning, facing) and the workpiece shape.
• Nose Radius: A larger nose radius generally provides a stronger cutting edge and better surface finish but can increase cutting forces. Smaller nose radii are used for reduced cutting forces and in applications requiring lower surface roughness.
• Edge Preparation (Honing/Chamfer): CBN edges are typically honed or chamfered to increase their strength and prevent chipping, especially in interrupted cutting conditions. The specific edge preparation depends on the workpiece material hardness and the severity of the cut.

Considerations for Using CBN Lathe Inserts

To maximize the performance and tool life of CBN lathe inserts, several factors should be considered:

• Machine Rigidity and Stability: CBN machining often involves high cutting forces and speeds, requiring a rigid machine tool and secure workholding to prevent vibrations and ensure accuracy.
• Cutting Parameters: Optimized cutting speed, feed rate, and depth of cut are crucial for successful CBN machining. These parameters depend on the workpiece material, hardness, insert grade, geometry, and machining conditions (continuous or interrupted cut).
• Coolant: While CBN has high thermal stability, dry machining is often preferred, especially when machining hardened steels, as coolant can sometimes cause thermal shock and reduce tool life. However, in some applications, coolant can be beneficial for chip control and heat dissipation.
• Chip Control: Effective chip control is important to prevent chip entanglement and workpiece damage. Insert geometries with chipbreakers or appropriate cutting parameters can help manage chips.

In conclusion, CBN lathe inserts are powerful tools that have revolutionized the machining of hard and difficult-to-cut materials. Their exceptional properties enable increased productivity, improved part quality, and reduced manufacturing costs across a wide range of industries. Understanding the specific application requirements and selecting the appropriate CBN insert type, geometry, and cutting parameters are key to unlocking their full potential.