Metal spinning — primary deformation mode During conventional metal spinning of circular blanks over a mandrel, the principal mode of deformation is:

Introduction / Context:
Metal spinning forms axisymmetric parts (lampshades, cookware, cones) by forcing a rotating sheet blank over a mandrel with a roller tool. Understanding how the sheet deforms helps in predicting thickness changes and avoiding tearing.

Given Data / Assumptions:

• Conventional manual or CNC spinning of ductile sheet metals.
• Blank rotates on a lathe-type machine; roller tool applies local pressure.
• No intentional through-thickness compression like deep drawing with a punch/die pair.

Concept / Approach:
In spinning, the material near the tool undergoes localized bending as it conforms to the mandrel curvature and simultaneous in-plane stretching (tensile) causing some thinning. The overall deformation is a combination of bending and membrane stretching along the meridian of the part.

Step-by-Step Solution:
The tool forces material over changing curvature → bending occurs.Material flows along the surface lengthening in the meridional direction → stretching occurs.Therefore the correct description is 'bending and stretching'.

Verification / Alternative check:
Thickness measurements of spun parts typically show thinning at high curvature regions, corroborating stretching; spring-back after unloading confirms bending recovery effects.

Why Other Options Are Wrong:
Bending only ignores thinning; stretching only ignores curvature change; rolling/stretching without bending is unrealistic; pure compression does not describe spinning, which mainly uses tensile membrane forces.

Common Pitfalls:
Over-thinning due to excessive passes; wrinkling at flanges from insufficient support; tearing near the nose from high tensile strain without proper lubrication.

Final Answer:
bending and stretching