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7/28/2019 Hot Working Process
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Deformation:
Hot-Working ProcessDepartment of Industrial
EngineeringUniversitas Indonesia
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Classification of Deformation
• Sequence of process:
a. Primary
b. Secondary• Size and shape of work piece
a. Bulk deformation process
b. Sheet forming operations
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Some of Hot-Working Process
1. Rolling
2. Forging
3. Extrusion4. Hot Drawing
5. Pipe Welding
6. Piercing
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the first process that is usedto convert material into
finished wrought product1 Rolling
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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
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Basic Rolling Process
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Rolling Mill Configurations
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• 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
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• 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
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FORGING• Common forging processes include:
– Open-die drop-hammer forging – Impression-die drop forging – Press forging – Upset forging – Automatic hot forging – Roll forging –
Swaging
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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.
2a
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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.
2b
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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
2c
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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
2d
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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
2e
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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.
2f
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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.
2g
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•
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
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EXTRUSION
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EXTRUSION
• Almost any cross-sectional shape can be extruded
from nonferrous metals..
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Extrusions and Products Made fromExtrusions
Extrusions and examples of products made by sectioning off extrusions. Source: Courtesy of Kaiser Aluminum.
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Types of Extrusion
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•
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
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• 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
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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
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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.
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• 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
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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
tube.
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P i t T l t P g 37