Metal Forming Lecture Notes

Detailed vocabulary flashcards based on lecture notes covering the theory and specific processes of metal forming, including forging, rolling, extrusion, and drawing.

Deformation Processing

A forming operation also known as wrought processing where a desired shape is created on a metal sample through plastic deformation.

Plastic Deformation

Permanent deformation of a material that does not return to its original shape once the applied force is withdrawn.

Elastic Deformation

Non-permanent deformation where the material returns to its original shape after the force is removed.

Forging

A manual or mechanical process of shaping metal using compressive forces applied via a hammer or a press.

Rolling

A process where metal thickness is reduced or the cross-section is changed by passing it between two rotating rolls that apply compressive force.

Extrusion

A metal forming process where a billet is pushed by a compressive force through a die orifice to form a shape defined by the die's cross-section.

Drawing

A process similar to extrusion where a tensile (pulling) force is used to pull a metal workpiece through a die orifice, commonly used for wire manufacturing.

Slip

The primary mechanism of plastic deformation in crystals where a large segment of the crystal slides against a specific plane, known as a slip plane, creating a displacement or step.

Dislocation

A crystal defect that facilitates slip; plastic deformation occurs when these defects move across the metal and reach the surface.

Strain Hardening

The process of making a metal stronger and harder through cold working, caused by an increase in dislocation density from approximately $10^8$ to $10^{12}$.

Recrystallization Temperature

The reference temperature for metal working, defined as approximately $\frac{1}{3}$ to $\frac{1}{2}$ of the metal's melting temperature ($T_m$) in Kelvin.

Cold Working

Deformation processing performed below the recrystallization temperature, resulting in higher strength, better surface finish, and higher dimensional accuracy but reduced ductility.

Hot Working

Deformation processing performed above the recrystallization temperature, allowing for large deformations with lower forces and removal of internal pores, but resulting in poor surface finish due to oxidation (mill scales).

Annealing

A heat treatment process where a cold-worked metal is heated above its recrystallization temperature to recover ductility through three stages: recovery, recrystallization, and grain growth.

Recovery

The first stage of annealing where dislocations move and cancel each other out, softening the metal slightly without changing the grain structure significantly.

Recrystallization (Annealing Stage)

The stage where deformed grains are replaced by new, fine, defect-free grains, fully recovering the material's ductility.

Grain Growth

The final stage of annealing where, if heating continues, the new grains increase in size, further increasing ductility but potentially reducing strength.

Flow Stress

The stress required to initiate and maintain plastic flow in a metal during deformation, influenced by temperature, true strain, and strain rate.

Upsetting

An open-die forging process used to increase the diameter of a workpiece by compressing its length, commonly used for making screw and nail heads.

Flash

Excess metal that flows out between dies at the parting plane during closed-die forging; it helps ensure the metal fills the die cavity by creating resistance to outward flow.

Gutter

A space or cavity in the upper die designed to contain the flash during a forging operation.

Cluster Mill (Zezimir Mill)

A type of rolling mill using small work rolls supported by larger backup rolls to prevent deflection, ideal for producing very thin and accurate metal foils.

Tandem Rolling

A high-production rolling process using multiple sets of rolls in a series, where the speed of each set is individually controlled to synchronize with the workpiece's increasing length.

Cambering

Designing rolling rolls to be thicker at the center than at the ends to compensate for roll deflection and ensure uniform thickness in the resulting sheet.

Direct Extrusion

An extrusion process where the pressing stem and the extruded metal move in the same direction.

Indirect Extrusion

An extrusion process where the die is attached to a hollow ram and moves into the billet, causing the metal to be extruded in a direction opposite to the ram's movement, resulting in lower friction.

Hydrostatic Extrusion

A process where the billet is surrounded by pressurized fluid in a chamber, allowing for uniform pressure and the ability to extrude brittle materials.

True Strain

A measure of deformation calculated as the natural logarithm ($\text{ln}$) of the ratio of the final height (or area) to the original height (or area).