JNTU B.Tech III MACHINE TOOLS Previous Question Paper (May-2018 - R13)

The factors responsible for the formation of a Built-Up Edge (BUE) in cutting tools include:

• Friction: High friction between the chip and the tool face causes workpiece material to adhere to the tool.
• Temperature: Elevated temperatures at the chip-tool interface soften the workpiece material, making it more prone to adhesion.
• Pressure: High pressure at the interface also contributes to the plastic deformation and welding of workpiece material to the tool.
• Workpiece Material Properties: Ductile materials, especially those with a tendency to weld, are more likely to form a BUE.
• Cutting Speed: Moderate cutting speeds often promote BUE formation as there is sufficient time for material transfer and adhesion.

The various cutting tool materials are:

• High-Speed Steel (HSS): A common and versatile material, good toughness and wear resistance.
• Carbides (Cemented Carbides): Sintered materials with high hardness, strength, and wear resistance, suitable for high-speed machining.
• Ceramics: Extremely hard and brittle, offer excellent wear resistance and high-temperature strength, used for high-speed finishing.
• Cubic Boron Nitride (CBN): Second hardest material, used for machining hardened steels and cast irons.
• Diamond (Polycrystalline Diamond - PCD): The hardest known material, used for machining non-ferrous metals and non-metallic materials.

Important characteristics of cutting tools include:

• Hardness: Resistance to plastic deformation, crucial for maintaining cutting edge integrity.
• Toughness: Ability to withstand shock and vibration without fracturing.
• Wear Resistance: Ability to resist gradual removal of material from the cutting edge.
• Hot Hardness: Ability to retain hardness at elevated cutting temperatures.
• Chemical Stability: Resistance to chemical reactions with the workpiece material at high temperatures.
• Redness Resistance: Ability to maintain hardness at high temperatures.