Metal forming practice — terminology of forging operations In hot or cold forging, the specific operation that increases the cross-sectional area (diameter or thickness) of a bar or rod at the expense of its length is called:

Introduction / Context:
In manufacturing and metal forming, precise terminology helps technicians select the right process. When a bar's cross-section must be enlarged while its length decreases, the classic forging operation is known by a specific name. Distinguishing this from drawing, swaging, spinning, or peening avoids design and shop-floor errors.

Given Data / Assumptions:

• Work material is a ductile metal bar/rod worked hot or cold depending on alloy.
• Objective is to increase cross-sectional area while sacrificing overall length.
• No change in material volume (plastic deformation is volume-conserving).

Concept / Approach:
Plastic deformation in forging conserves volume, so any increase in area must be balanced by a reduction in length. The operation that thickens or bulges the workpiece by end pressure or hammer blows is called upsetting. In contrast, drawing down or swaging reduces cross-section and lengthens the piece; spinning is a sheet process; peening modifies surface properties rather than bulk dimensions.

Step-by-Step Solution:
Identify desired effect: larger diameter/thickness with shorter length.Match with forging operations: end compression → bulging → upsetting.Confirm alternatives are incompatible: drawing/swaging cause thinning and elongation.Conclude the correct operation is upsetting.

Verification / Alternative check:
Practical example: forming bolt heads. A heated rod is placed in a header; axial force upsets metal to create a head while shank shortens slightly.Engineering check: volume before ≈ volume after (Area_before * Length_before ≈ Area_after * Length_after).

Why Other Options Are Wrong:
Drawing down and swaging reduce area and increase length; they are the geometric opposite of the requirement.

Spinning shapes sheet over a mandrel and does not apply to solid bars.

Peening changes surface residual stresses/hardness; it does not intentionally thicken the bar.

Common Pitfalls:
Confusing upsetting with heading (heading is a specific application of upsetting for fasteners). Assuming temperature is irrelevant—many alloys require hot upsetting to avoid cracking. Neglecting die constraint, which controls upset height and final shape.

Final Answer:
upsetting (increasing section and reducing length)