Mechanics of drilling: The primary mechanism of metal removal in drilling is

Introduction / Context:
Drilling combines cutting at the lips with severe deformation at the chisel edge. Understanding both actions explains thrust force, heat, and the need for proper point geometry and feed.

Given Data / Assumptions:

• Standard twist drill with chisel edge and two cutting lips.
• Homogeneous ductile work material.
• Normal feeds and speeds.

Concept / Approach:
At the lips, a conventional shear plane forms and material is cut (shearing). At the chisel edge, there is little true cutting because the local speed approaches zero; material is displaced plastically (extruded) and fractured, contributing to high thrust and heat.

Step-by-Step Solution:

Verification / Alternative check:
Force measurements show large axial thrust attributable to chisel-edge extrusion; split-point drills reduce it noticeably.

Why Other Options Are Wrong:

• Shearing only: ignores the chisel-edge plastic flow.
• Extrusion only: ignores true cutting action at the lips.
• Shearing and compression: compression occurs, but the defining non-cutting action is extrusion at the chisel edge.

Common Pitfalls:
Assuming more speed always fixes poor chip evacuation; geometry at the chisel and proper coolant delivery are just as critical.

Final Answer:
Shearing and extrusion