Manufacturing Processes — Cold Working vs. Hot Working State whether the following statement is correct: “Cold working (performed below the recrystallisation temperature) requires much higher pressure/force than hot working for the same amount of plastic deformation.”

Introduction / Context:
Cold working and hot working are two fundamental metal-forming routes. The key difference lies in temperature relative to the material's recrystallisation temperature, which strongly affects flow stress, required force, and resulting properties such as strain hardening and grain refinement.

Given Data / Assumptions:

• Cold working occurs below recrystallisation temperature; hot working occurs above it.
• We compare the force/pressure needed for the same plastic deformation magnitude.
• Friction conditions and tool geometry are assumed comparable.

Concept / Approach:
Flow stress rises as temperature decreases. At cold-working temperatures, dislocation mobility is reduced and dynamic recovery/recrystallisation do not occur, so the metal work-hardens quickly. Hot working benefits from thermal softening and dynamic restoration processes, dramatically lowering the flow stress for a given strain, thus reducing forming loads.

Step-by-Step Solution:
Define flow stress σ_flow as the stress required to continue plastic deformation.At low temperature (cold work), σ_flow is high due to limited dislocation motion and rapid work hardening.At high temperature (hot work), σ_flow decreases due to thermally activated slip and dynamic recovery/recrystallisation.Forming load P roughly scales with σ_flow * projected area → higher at cold conditions for the same geometry and reduction.

Verification / Alternative check:
Compare forging press capacities: hot forgings require substantially lower tonnage than cold-forged equivalents of the same size reduction.

Why Other Options Are Wrong:
Incorrect: contradicts the temperature dependence of flow stress.Non-ferrous only / high strain rate only / thin sheets only: the principle is general and not limited to these cases.

Common Pitfalls:
Confusing improved surface finish/tolerances in cold work with reduced force; in reality, force typically increases.

Final Answer:
Correct