Chip formation and built-up edge (BUE) Under which cutting conditions are continuous chips with a built-up edge most likely to form during metal cutting?

Introduction / Context:
Built-up edge (BUE) is a transient layer of work material that adheres to the tool rake face and cutting edge, altering geometry and degrading finish. Controlling BUE is key to consistent surface quality.

Given Data / Assumptions:

• Ductile materials, moderate to low cutting temperatures.
• Ordinary tool surfaces without special coatings or lubrication.

Concept / Approach:
BUE tends to form when friction and adhesion dominate, which occurs at low cutting speeds (insufficient temperature to stabilize a shear zone and promote clean separation) and with small rake angles (higher normal pressure on the rake face). This increases sticking and promotes accumulation of welded material at the edge.

Step-by-Step Solution:
Low speed → lower shear-zone temperature → higher adhesion and friction.Small rake angle → larger negative normal force on rake face → more sticking.Result: continuous chip with BUE is likely.

Verification / Alternative check:
Raising cutting speed, using sharper (larger positive rake) tools, or adding cutting fluids reduces BUE occurrence, which aligns with shop practice.

Why Other Options Are Wrong:

• Large rake or high speeds reduce contact length and adhesion, mitigating BUE.
• Very high speed with sharp rake and coolant typically yields continuous chips without BUE or even discontinuous chips depending on material.

Common Pitfalls:
Confusing BUE with serrated chips at very high speeds; ignoring tool coatings that also suppress BUE.

Final Answer:
Low cutting speed and small rake angle