Tool life factors: If the shear angle is large and the chip–tool contact length is small, how does this affect tool life?

Introduction / Context:
Tool life is governed by cutting temperature, stresses at the cutting edge, and friction on the rake face and flank. Shear angle and contact length directly influence chip formation, heat generation, and frictional work, thereby affecting wear mechanisms such as crater and flank wear.

Given Data / Assumptions:

• Larger shear angle implies thinner shear plane and lower shear deformation energy.
• Smaller chip–tool contact area reduces friction and heat on the rake face.
• Other parameters (speed, feed, tool material) remain comparable.

Concept / Approach:
Cutting power roughly partitions into shear work in the primary zone and frictional work on the rake face. With a larger shear angle, the primary shear work decreases. With reduced contact length, frictional work and heat generation at the tool–chip interface decline. Both effects lower temperature and stress at the cutting edge, promoting longer tool life, all else equal.

Step-by-Step Reasoning:

Verification / Alternative check:
Empirical relationships (e.g., Merchant’s theory trends and observed crater wear vs. contact length) support increased tool life with higher effective rake (higher shear angle) and shorter contact length.

Why Other Options Are Wrong:
Saying tool life decreases contradicts the well-established reduction in heat and friction when shear angle is high and contact is short.

Common Pitfalls:
Assuming shear angle can be increased indefinitely; excessive rake may weaken the edge. Balance rake with edge strength and work material behavior.

Final Answer:
Correct: tool life will be more