Chapter 6 - Metal Work

© Mechanical Engineering Department

CHAPTER 6:

METAL WORK

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CONTENTS

JF302 – MATERIAL TECHNOLOGY 1 CHAPTER 6: METAL WORK

Cold Work 1

2

Hot Work 2


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COLD WORK

• plastic alterations carried out at a temperature

below the recrystallization of metal

• conducted at room temperature

• crystal structure (lattice) is changed, become

distorted and elongated in the direction of worked

• internal stresses, strength and electrical resistance

will increase and decrease the ductility criteria

• metal becomes harder and brittle after workable

cool



COLD WORK

Cool job functions are to:

• Allows exact dimensions available on the work.

• Getting a clean and smooth finish.

• Obtain various degrees of hardness by applying

different types of cold work.

• Improve facilities machined and yield point.



TYPE OF COLD WORK


(Drawing) (Rolling)


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(DRAWING)

• metal forming process which involves attracting

workpiece through a die (die) resulting in reduced

cross-sectional area of the workpiece

• metal to be pulled through a tapered diameter mold



(DRAWING)

• usually metal was annealed and have only high

ductility can be processed.

• friction, the effect of strong shear and pressure

occur divided by the contact between the mold and

the material heats the next part

• Tungsten Carbide is commonly used as a `die-insert

'at the end of the mold



(DRAWING)

• a metal should have dikerjasejuk with completeness

and cool quickly so that there is distortion

(elongated) and broken

• produce a good surface quality and dimensional

tolerances are very low

• used for the production of wire (under 2μm

diameter), tubes, rods and other products from

copper and steel



(DRAWING)



(ROLLING)

• a process of reduction in cross-sectional area or

shape a piece of metal through deformation caused

by a pair pengolek rotating in the opposite direction



(ROLLING)

• operations performed on

the mill roll 4 rolls.

• small diameter rollers are

moved to thin metal

material

• Large rollers serve as

rollers supporters



(ROLLING)

lubrication materials are sometimes given to the

workpiece before and after rolled

This type of work berkemampauan produce sheets

thickness (0.008mm-0.009mm) and a very thin

named 'Foil'.

usually performed after hot rolling on a good surface

quality and low thickness tolerance required

used in the manufacture of the sheets and strips



(ROLLING)



COLD WORK

ADVANTAGES

• Good surface finish.

• Relatively high

measurement accuracy.

• Inflated kemesinan

features a good metal to

finish and improve

strength and rigidity.


DISADVANTAGES

• Higher costs compared

to hot working

processes.

• Material becomes less

ductile due to work

hardening.


HOT WORK

• metal formation performed slightly above the

recrystallization temperature.

• this causes the plastic deformation on the

recrystallization of the crystal structure but will

restore it to the original lattice



HOT WORK

• if high heating temperature, recrystallization will

occur in a short time, and the resulting materials

more easily workable without the risk of aggravating

crack

• if low heating temperature, recrystallization will

occur slowly and require more power (compression)

to mengerotkan metal and cracking risk-prone.

• if dipanaslampaukan metal material, the oxidation

will occur at grain boundaries and this will weaken

the material



TYPES OF HOT WORK


(Forging) (Rolling) (Extrusion)





(ROLLING)

• intended to dilute the hot metal bars or thick

sections, until we get the desired thickness.

• special-shaped section of railway crossings, and

round bar frame construction can be obtained by

using specially shaped rollers.



(ROLLING)

• pig goes through two large cylindrical rollers and

then through some other rollers



(FORGING) • forming metal materials

(sheets and ingots) with

impact hammer / punch

• material will be placed

between the two parts of

each mold tied hammer and

anvil.

• when the force is given, both

mold material will stick

together to form a complete

mold



(FORGING)

• mold type is called a closed mold (closed die)

• to ensure filling of the mold is full, the quantity of

material must be more than a little blank space

availability at the mold.

• excess quantity will flow out of the mold and mold

flash.

• Examples of use in the manufacturing process are

spanner, connecting rod and bolts



(FORGING)



(EXTRUSION)

• involves a rejection of

the hot billet through a

die with hydraulic

power.

• Through this process

ingots (ignot) pressed

until the flow under

high pressure through

an orifice `channel 'or'

die '



(EXTRUSION)

• The advantage is the ability to produce a variety of

complicated shapes with high dimensional accuracy

and good housekeeping

• Production can also be run continuously but metal

materials that can be processed is limited to metals

with a low melting point and good liquid such as

copper, brass alloys, aluminum and its alloys.



(EXTRUSION)



(EXTRUSION)



HOT WORK

ADVANTAGES

• Can break coarse crystalline

structure found in pig

• Fine grain structure

• Cavities (blow holes) present in

the ingots will be removed

• Strength, ductility and hardness of

workpiece produced from hot

working processes are better

compared to workpiece as a result

of cold working process


DISADVANTAGES

• Exact final dimensions for

workpiece is quite hard to come by

• End surface of the workpiece has

a messy


Documents

Chapter 6 - Metal Work