Hot Working Process

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Deformation:

Hot-Working ProcessDepartment of Industrial

EngineeringUniversitas Indonesia

Classification of Deformation

• Sequence of process:

a. Primary

b. Secondary• Size and shape of work piece

a. Bulk deformation process

b. Sheet forming operations

Some of Hot-Working Process

1. Rolling

2. Forging

3. Extrusion4. Hot Drawing

5. Pipe Welding

6. Piercing

the first process that is usedto convert material into

finished wrought product1 Rolling

Slab, Bloom, Billet1. Slab• Rectangular solid where the width is

greater than twice thickness• Can be further rolled to produce plate,

sheet, and strip2. Bloom• Has a square or rectangular cross

section with a thickness greater than 15cm and a width < twice the thickness

3. Billet• Has a square or rectangular cross

section and smaller than bloom•

Produced by rolli ng or extrusion

Basic Rolling Process

Powerpoint Templates Page 7

Rolling Mill Configurations

• Forging is term applied to a family of processes where deformation is induced bylocalized compressive forces.

• The equipment can be manual or powerhammers, presses, or special forging

machines. The term forging usually implieshot forging done above the recrystaIlizationtemperature.

2 Forging

• The forging material may be – Drawn out to increase its length and

decrease its cross section, – Upset to decrease the length and

increase the cross section, – Squeezed in closed impression dies to

produce multidirectional flow.

Forging Material

FORGING• Common forging processes include:

– Open-die drop-hammer forging – Impression-die drop forging – Press forging – Upset forging – Automatic hot forging – Roll forging –

Swaging

Open Die Drop Hammer Forging

Blacksmiths use this process to reduce the thickness of bars by hammering the part on an anvil.Reduction in thickness is accompanied by barreling, as in Fig. 14.3c. (b) Reducing the diameter of abar by open-die forging; note the movements of the dies and the workpiece. (c) The thickness of aring being reduced by open-die forging.

Impression-Die Forging

(a) through (c) Stages in impression-die forging of a solid round billet. Note the formation of flash, which is excess metal that is subsequently trimmed off (d) Standard terminology for variousfeatures of a forging die.

Press Forging• Required when larger pieces or thicker products must

be formed. Deformation is analyzed in terms of forcesor pressures. Produce a more uniform deformation andflow.

Problems can arise because of longer time of contactbetween the dies and work-piece.• Heated dies are generally used to:-

Reduce heat loss – Promote surface flow – Enable production of finer details and closer

tolerances

Upset Forging• Upset-forging involves increasing diameter of material by

compressing its length

• It is the most widely used of all forging processes. Parts can

be upset forged both hot and cold on special high- speed

machines

Automatic Hot Forging•

Highly automated upset equipment in which mill-length steel bars (typically, 24 ft long) are fed into one

end at room temperature and hot-forged products

emerge from the other end at rates of up to 180 partsper minute( i.e. 86,400 parts per 8-hour shift).

• These parts can be solid or hollow, round or symmetrical, up to

12 Ib (6 kg) in weight, and up to 7 in. (180 mm) in diameter.• Small parts can be produced at up to 180 parts per minute, with

rates for larger pieces on the order of 90 parts per minute

Roll Forging• When the bar encounters a stop, the rolls rotate, and

the bar is progressively shaped as it is rolled out.

• The piece can be reinserted between the next set of

grooves and the process repeated to produce the

desired size and shape.

Swaging

Schematic illustration of the rotary-swaging process. (b) Forming internal profiles on a tubularworkpiece by swaging. (c) A die-closing swaging machine showing forming of a stepped shaft. (d)Typical parts made by swaging. Source : Courtesy of J. Richard Industries.

In the extrusion process, metal is compressedand forced to flow through a suitably shaped dieto form a product with reduced but constantcross section.

• Extrusion may be performed either hot or cold,hot extrusion is commonly employed for manymetals to reduce the forces required.

• Extrusion process is like squeezingtoothpaste out of a tube.

3 Extrusion

EXTRUSION

• Almost any cross-sectional shape can be extruded

from nonferrous metals..

Extrusions and Products Made fromExtrusions

Extrusions and examples of products made by sectioning off extrusions. Source: Courtesy of Kaiser Aluminum.

Types of Extrusion

Drawing is a plastic deformation process inwhich a flat sheet or plate is formed into arecessed, three-dimensional part with a depthmore than several times the thickness of themetal.

• As a punch descends into a mating die (or the diemoves upward over a mating punch), the metalassumes the desired configuration.

• Hot drawing is used for formingrelatively thick-walled parts of simple geometries, usuallycylindrical.

• Because the material is hot, there isoften considerable thinning as itpass es through the dies.

4 Hot Drawing of Sheet and Plate

• Large quantities of steel pipe are made by twoprocesses that use hot forming of steel stripcoupled with deformation-induced welding of itsfree edges.

• Both of these processes, utilize steel in the form of skelp-long strips with specified width, thicknessand edge configuration.

• Because the skelp has been hot rolledpreviously and welding process producesfurther compressive working andrecrystallization, pipe welded by theseproc esses tends to be v ery uniform in quality.

5 PIPE WELDING

PIPE WELDINGButt-Welded Pipe • In the butt-welding process for

making pipe, steel skelp isheated to a specified hot-working temperature by passingit through a furnace.

• Upon exiting the furnace, it ispulled through forming rollsthat shape it into a cylinder andbring the free ends into contact.

• The pressure exerted betweenthe edges of the skelp issufficient to upset the metal andproduce a welded seam.

PIPEWELDING

Lap-Welded Pipe•

Lap-welding process for making pipe differs frombutt-welding technique in that skelp now hasbeveled edges and the rolls form the weld byforcing lapped edges down against a supportedmandrel.

• This process is used primarily for largersizes of pipe, from about 2 in. (50 mm)

to 14 in. (400 mm) in diameter.• Because product is driven over a

supported mandrel, product length islimited to about 20 to 25 feet.

• Thick-walled seamless tubing can be

made by rotary piercing,• A heated billet is fed longitudinally

into the gap between two large,

convex-tapered rolls.• These rolls are powered to rotate in

the same direction, but axes of rolls

are offset from axis of billet by about

6 ° , one to right and the other to left.

6 P I E R C I N G

PIERCING

• As billet is caught by rolls, it is simultaneouslyrotated and driven forward.

• The reduced clearance between rolls forcesbillet to deform into a rotating ellipse.

• Rotation of the elliptical section causes themetal to shear about the major axis.

• A crack tends to form down thecenter axis of billet, and crackedbillet is then forced over a pointedmandrel that enlarges and shapesthe opening to form a seamless

P i t T l t P g 37

Hot Working Process

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