Bulk deformation processes — accurate definition of extrusion Which statement best describes the extrusion process used to produce uniform sections such as rods, tubes, and profiles?

Introduction / Context:
Extrusion is a primary metalworking process used to create long products with constant cross-sections, from window frames to heat-sink fins and seamless tubes. Understanding what extrusion is (and what it is not) helps in selecting processes for cost, tolerances, and mechanical properties.

Given Data / Assumptions:

• We compare multiple manufacturing operations that may appear similar.
• Target is a constant cross-section produced continuously or in long lengths.
• Material may be hot- or cold-extruded depending on alloy and reduction ratio.

Concept / Approach:
In extrusion, a billet is confined in a container and forced through a die opening. Because volume is conserved, the exit material takes the exact die profile, producing uniform solid or hollow sections. This is fundamentally different from heading (for bolts), rotary swaging (impact radial forging), peening (a surface treatment), and thermoforming (a polymer process).

Step-by-Step Solution:
Identify defining features: confinement in a container + pressure-driven flow through a die.Relate to product: constant cross-section equal to die orifice shape.Select the statement matching those features.Option (d) precisely describes extrusion.

Verification / Alternative check:
Direct vs. indirect extrusion, hot vs. cold; all share the same core principle: billet is forced through a die opening.Industrial examples: aluminium window frames, copper bus bars, seamless tubes (via extrusion + mandrel/piercer).

Why Other Options Are Wrong:
Heading makes bolt heads; it is a specific upsetting process, not extrusion.

Rotary swaging uses oscillating dies to reduce diameter; it does not push a billet through a fixed-profile die orifice.

Peening is a surface strengthening treatment, not a shaping process.

Vacuum forming applies to thermoplastics, not bulk metal extrusion.

Common Pitfalls:
Confusing drawing and extrusion (drawing pulls material through a die; extrusion pushes). Ignoring container/billet friction which influences load; neglecting die angle and bearing length which control surface finish and dimensional accuracy.

Final Answer:
It presses metal inside a chamber and forces it out through a shaped orifice under high pressure to obtain the desired cross-section