JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III Year METROLOGY AND MACHINE TOOLS Previous Question Paper (October - 2020 - R16)

Chips formed during metal cutting are generally classified into four types: Continuous chips, Continuous chips with built-up edge (BUE), Discontinuous chips, and Segmented or non-homogeneous chips.

• Continuous chips: Formed during the machining of ductile materials at high cutting speeds with a small feed and a positive rake angle.
• Continuous chips with BUE: Occur when high friction at the tool-chip interface causes work material to weld to the tool tip, creating a built-up edge that periodically breaks off.
• Discontinuous chips: Formed when machining brittle materials or ductile materials at low cutting speeds with large feeds and negative rake angles, causing the material to fracture ahead of the tool.
• Segmented chips: Formed at very high cutting speeds where thermal softening leads to periodic shear localization.

Factors influencing chip formation include: Workpiece material properties (ductility, hardness, and brittleness), Cutting parameters (cutting speed, feed rate, and depth of cut), Tool geometry (rake angle and nose radius), and Frictional conditions at the tool-chip interface, often mitigated by the use of cutting fluids.

The engine lathe operates on the principle of generating a surface of revolution by rotating the workpiece about its axis while a single-point cutting tool is fed against it. The workpiece is held securely between centers or in a chuck mounted on the headstock spindle, which is driven by an electric motor through a gear train to provide specific rotational speeds.

The cutting tool is mounted on a tool post situated on the carriage, which can move longitudinally along the bed (parallel to the axis of rotation) or transversely (cross-slide movement perpendicular to the axis). As the workpiece rotates, the tool removes metal in the form of chips, thereby reducing the diameter or creating various profiles. The feed rate is controlled by the lead screw or feed rod, which is synchronized with the spindle speed to ensure precise material removal. This combination of rotary motion of the work and linear motion of the tool allows for operations such as turning, facing, threading, and drilling.