Rolling-forging

Bulk Deformation Processes

Metal forming operations causing significant shape change by plastic flow of bulk forms like bars, billets, or slabs.

Basic Bulk Deformation Processes

The four processes are rolling, forging, extrusion, and wire and bar drawing.

Hot Working

A bulk deformation process that allows significant shape change due to reduced strength and increased ductility.

Cold Working

Enhances bulk deformation parts by increasing strength through strain hardening.

Near Net Shape

Parts that require little or no subsequent machining after bulk deformation.

Typical Starting Forms for Bulk Deformation

Cylindrical bars, billets, rectangular billets, and slabs.

Rolling

A metalworking process where slab or plate thickness is reduced by compressive forces between opposing rolls.

Percentage of Deformed Materials Undergoing Rolling

Over 90% of deformed materials undergo rolling.

Flat Rolling

Used for reducing the thickness of a rectangular cross section.

Shape Rolling

Forming a square cross section into shapes like I-beams or rails.

Backing Rolls in Four-High Rolling Mill

Support smaller work rolls and reduce deflection.

Tandem Rolling Mill Operation

Uses a sequence of two-high mills for continuous reduction.

Common Defect in Flat Rolling Due to High Friction

Wavy edges caused by uneven material flow.

Alligatoring in Rolling

Surface splitting caused by excessive deformation or sticking.

Role of Camber in Rolling Mills

Compensates for roll bending to ensure uniform strip thickness.

Hot Rolling vs Cold Rolling

Hot rolling is more common because it allows large deformations due to lower material strength.

Cold-Rolled Sheet Improvements

Improvements in surface finish and dimensional tolerances compared to hot-rolled.

Thread Rolling

A cold working process to form threads on cylindrical parts using dies.

Advantage of Thread Rolling Over Machining

Stronger threads due to work hardening.

Ring Rolling

Produces thin-walled rings of larger diameter from thick-walled rings.

Roll Piercing

Creating seamless tubes by exploiting internal cracks in a compressed bar.

Controls Hole Size in Roll Piercing

A mandrel controls the hole size during the process.

Roll Forging

Also known as cross-rolling, it's used to shape materials by rolling them.

Examples of Roll-Forged Products

Tapered leaf springs and knives.

Ball Rolling Process

Steel balls are formed by skew-rolling or upsetting for bearings.

Forging Definition

Controlled plastic deformation of metal into a predefined shape by pressure or impact.

Age of Forging Process

The forging process dates back to about 5000 BC.

Advantage of Forging Over Casting

Work hardening increases strength in forged parts.

Main Types of Forging Dies

Open-die, impression-die, and flashless forging dies.

Open-Die Forging

Also called upsetting or upset forging, allows metal to flow freely.

Barreling in Open-Die Forging

Caused by friction between work and die surfaces leading to a barrel shape.

Role of Flash in Impression-Die Forging

Constrain metal flow to fill the die cavity.

Impression-Die Forging Requirement

Often requires skilled operators under adverse conditions.

Limitation of Impression-Die Forging

Not capable of close tolerances; machining is often needed.

Flashless Forging Characteristics

No excess flash is created; the work is fully constrained.

Coining in Forging

A flashless process used to mint coins with sharp details.

Upsetting Process in Forging

Used to form heads on nails, bolts, and similar hardware.

Swaging Process

Using rotating dies to taper a workpiece radially.

Typical Swaged Product

Tapered rods or tubes produced through swaging.

Forging Equipment Impact Load Application

Drop hammers (gravity or power) apply the impact load in forging.

Speed Range of Hydraulic Forging Press

0.06-0.30 m/s is the speed range for hydraulic forging presses.

Highest Speed Range Forging Equipment

Counterblow hammer with a speed range of 4.5-9.0 m/s.

Why Hydraulic Presses are Expensive in Forging

High initial cost, though easier to maintain.

Forging Economics Compared to Casting for Connecting Rods

Forging is more economical for large quantities.

Reducing Setup and Tooling Costs in Forging

Increasing the number of pieces forged with the same die reduces costs.

Extrusion Process Definition

A process forcing metal through a die opening to form a uniform cross-sectional shape.

Two Basic Types of Extrusion

Direct (forward) and indirect (backward/reverse) extrusion.

Butt in Direct Extrusion

The small portion of billet that cannot be forced through the die.

Limitation of Indirect Extrusion

Limited by lower rigidity of the hollow ram and difficulty supporting the extruded product.

Grain Structure Enhancement in Cold Extrusion

Work hardening enhances the grain structure of the material.

Disadvantage of Cold Extrusion

High stresses on machinery and die wear without lubrication.

Defect in Extrusion with High Friction

Pipe (extrusion) defect can occur under these conditions.

Impact Extrusion Definition

A high-speed cold extrusion process, often for collapsible tubes.

Avoid in Extruded Cross-Section Design

Sharp corners and non-uniform thicknesses should be avoided.

Wire Drawing Difference from Extrusion

Work is pulled through the die instead of pushed.

Typical Cross-Sectional Shape in Wire Drawing

The typical cross-sectional shape is circular.

Wire Drawing vs Bar Drawing

Wire drawing uses smaller diameter stock down to 0.03 mm.

Maximum Reduction Limitation in Drawing

Draw stress exceeding the yield strength causes elongation instead of reduction.

Purpose of Annealing in Wire Drawing

To relieve work hardening between dies.

Common Product of Bar Drawing

Metal bars for machining or forging.