Jawaharlal Nehru Technological University Hyderabad B.Tech III MACHINE TOOLS Previous Question Paper (October - 2020 - R13)

A single point cutting tool geometry is defined by several specific angles that control the cutting action. The key elements include the back rake angle, side rake angle, end relief angle, side relief angle, end cutting edge angle, side cutting edge angle, and nose radius. These angles are measured relative to the tool base and the shank axis.

The geometry is typically represented by the American Standards Association (ASA) system, which defines the tool signature as: Back Rake Angle - Side Rake Angle - End Relief Angle - Side Relief Angle - End Cutting Edge Angle - Side Cutting Edge Angle - Nose Radius. The back and side rake angles control the chip flow and cutting force, while the relief angles prevent rubbing between the tool flank and the workpiece. The cutting edge angles determine the chip thickness and the direction of chip flow, and the nose radius improves surface finish and tool strength.

The selection of cutting speed and feed is critical for optimizing tool life, surface finish, and production rate. The primary factors influencing these parameters include:

• Workpiece Material: Harder and tougher materials require lower cutting speeds to prevent excessive heat generation and rapid tool wear.
• Tool Material: High-speed steel (HSS) tools operate at lower speeds compared to carbide or ceramic tools, which can withstand higher temperatures.
• Surface Finish Requirements: Finer surface finishes generally require lower feed rates and higher cutting speeds to minimize built-up edge formation.
• Depth of Cut: A larger depth of cut increases cutting forces, necessitating a reduction in feed rate or speed to avoid tool deflection or chatter.
• Machine Tool Rigidity: The stability and power capacity of the machine limit the maximum speed and feed; less rigid setups require more conservative parameters to prevent vibrations.
• Tool Life Criteria: If the objective is maximum tool life, lower speeds are selected. If the objective is maximum production rate, higher speeds are chosen despite increased tool wear.
• Coolant Application: The use of effective cutting fluids allows for higher cutting speeds by facilitating heat dissipation and reducing friction.