Cutting tool reliability: A tool can fail by which of the following mechanisms during metal cutting?

Introduction / Context:
Tool failure mechanisms determine tool life, surface finish, and productivity. Understanding the different modes—thermal cracking, chipping, and plastic deformation—guides the selection of tool materials, geometries, and cutting conditions.

Given Data / Assumptions:

• Conventional machining (turning, milling, drilling).
• Cutting temperatures and forces can be high depending on speed, feed, and material.
• Tool materials may include HSS, carbides, cermets, ceramics, and PCBN/PCD.

Concept / Approach:
Thermal cracking occurs due to cyclic thermal shocks (e.g., interrupted cuts, milling) or improper coolant application on thermal-shock-sensitive ceramics. Chipping is a brittle fracture at the cutting edge caused by impact, hard inclusions, or insufficient edge support. Plastic deformation happens when cutting temperatures and stresses exceed the hot hardness and strength of the tool, causing edge flow or crater wear acceleration.

Step-by-Step Solution:

Verification / Alternative check:
Examine a worn tool under a microscope to identify crack patterns, chipped zones, and plastically flowed edges; match with process history to confirm the mechanisms.

Why Other Options Are Wrong:
Choosing any single mechanism ignores the multifaceted nature of tool failure in real production environments.

Common Pitfalls:
Using coolant intermittently on hot ceramic tools, running too high a speed with insufficient hot hardness, or using overly sharp but weak edges on interrupted cuts can accelerate failure.

Final Answer:
All of these