Milling mechanics: In down milling (climb milling), how does the cutting force vary during a tooth’s engagement?

Introduction / Context:
Understanding chip thickness variation is crucial in milling. In down (climb) milling, the cutter rotation is in the same direction as the table feed. This reverses the chip formation pattern compared to up (conventional) milling and strongly affects forces and surface finish.

Given Data / Assumptions:

• Standard slab or end milling.
• Rigid setup with minimal backlash or compensated backlash.
• Normal feeds and depth of cut.

Concept / Approach:
Chip thickness h varies along the tooth path. In down milling, the tooth first meets the work at maximum chip thickness and exits at zero thickness. Cutting force is roughly proportional to instantaneous uncut chip thickness (and width and shear strength), so the force peaks at entry and decays to near zero at exit.

Step-by-Step Solution:

Verification / Alternative check:
Force dynamometer traces show a descending force profile for each tooth engagement in climb milling; the inverse occurs in up milling.

Why Other Options Are Wrong:

• Minimum-at-entry profile describes up milling, not down milling.
• Constant or zero force is unrealistic in metal cutting.

Common Pitfalls:
Using climb milling on machines with backlash can cause a pull-in effect. Modern CNCs compensate backlash and often prefer climb milling for better finish and tool life.

Final Answer:
Correct: maximum at entry, reducing to minimum at exit