metal forming – 1 · 2017-09-30 · 8/11/2008 1 sme 2713 manufacturing process metal forming –1...
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SME 2713 Manufacturing Process
METAL FORMING – 1(Introduction)
Assoc Prof Zainal Abidin Ahmad
UTM, Skudai
4.1 Introduction
1. Classification of metal forming processes
2. Definition
3. Plastic deformation
4. Competitive characteristics
5. Hot and cold working
6. Recrystallization
7. Strain hardening
8. Process variables11 August 2008 Assoc Prof Zainal Abidin Ahmad 2
Forming Processes
Sheet Bulk Powder
Sheet metal forming
Vacuum forming
Blow moulding
Sheet
Forging
Rolling
Extrusion
Bulk
Slip csting
Pressing & sintering
Isostatic pressing
Powder
Superplastic forming Drawing
Metal Metal &Polymer
Ceramic Ceramic & Metal
Polymer
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Primary working
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Bulk Metal Forming
Rolling Forging
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Extrusion Drawing6
Sheet Metalworking
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2. Metal Forming Definition
• A group of manufacturing processes in which the material is shaped to a certain geometry by applyingmaterial is shaped to a certain geometry by applying external forces large enough to cause a permanent deformation. The deformed material experienced plastic deformation, i.e. it will not return to its original shape after the forces are released.
• The external forces can be in the form ofThe external forces can be in the form of compression, tension, torsion, shearing, bending, drawing or a combination of the various forces.
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Various types and combination of forces
Stresses in theStresses in the form of compression, tension, shear and others
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3. Plastic Deformation
• Elastic Deformation ‐ If a metal deformed b f t t it i i l by a force return to its original dimensions when the force is removed; the metal undergo elastic deformation
• Plastic deformation (metals) Permanent deformation of metals Permanent deformation of metals due to the movement of dislocations on slip system.
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bonds
1. Initial 2. Small load 3. Unload
F
δ
stretch
return to initial
F Linear
2
Elastic means reversible!
F
δ
Linear- elastic
Non-Linear-elastic
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1. Initial 2. Small load 3. Unload
planes still
bonds stretch & l
F
still sheared
δelastic + plastic
& planes shear
δplastic
3
Plastic means permanent!
F
δlinear elastic
linear elastic
δplastic
F
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4. Competitive Characteristics
• Mass conservation– material formed into different shapes without changing its volume, or minimum volume changes, thereby little waste or scrap.
• Better material properties – grain structure or fibre
• Very fast production
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Manufacture of a spark plug body : (left) by machining from hexagonal bar stock; (right) by cold forming. Note the
reduction in waste17
Comparison of microstructure
CASTINGPoor microstructure
MACHININGGrain structure
FORMINGFibrous grain structure Poor microstructure
with high porosityGrain structure being cut through
ggiving good mechanical properties
Mechanical properties improving
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Grain structure or fiber of machined vs rolled component
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Parts produced within seconds
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What about Disadvantages?
• Please state a few disadvantages as compared ith th f t iwith other manufacturing processes
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5. Hot and Cold Working
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Hot Working
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Cold Working
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Temperature effect on Metal Working
Melting temperatureSteel
1500 0C
Hot working
Recrystalisation range
Warm working
700500
1500 0C
Cold working
g
Ambient temperature
200
20
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Temperature in Metalworking
• Hot working ‐ Deformation at temperature b t lli ti t t t i llabove recrystallization temperature typically between 0.5Tm to 0.75Tm– Pros
• larger deformation possible
• lower forces and power
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• forming of room temperature low ductility material is possible
• isotropic properties resulted from process
• no work hardening27
Temperature in Metalworking• Warm working ‐ temperature between room temperature and recrystallization
hl b 0 3 Ttemperature, roughly about 0.3 Tm– Pros against cold working
• Lower forces and power
• more intricate work geometries possible
d f li b d d/ li i t d
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• need for annealing may be reduced/eliminated.
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Temperature in Metalworking• Cold working
– Pros• better dimensional control and accuracybetter dimensional control and accuracy• Fine grain ‐ better surface finish• strain hardening increases strength and hardness• grain flow during deformation provides directional properties
• no heating is needed, easier handling (low operating temperature
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temperature
– Cons• higher forces and power are required, therefore bigger capacity machines
• ductility and strain‐hardening limits the extent of forming 29
Temperature in Metalworking
• Isothermal Forming ‐ preheating the tools to th t t th k t l Thithe same temperature as the work metal. This eliminates the surface cooling and the resulting thermal gradient in the workpart.
• Normally applies to highly alloyed steels, titanium alloys and high‐temperature nickel y g palloys.
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6. RecrystallizationThe process in which, at a certain temperature range, new strain-free grains are formed, replacing the older grains.
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6. Recrystallization
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Properties of steels (C10) after hot and cold working
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7. Strain Hardening
• Berlaku apabila logam dikerjakan dalam keadaan sejuk di mana kekuatan logamkeadaan sejuk, di mana kekuatan logam bertambah dan pada masa yang sama kekerasan meningkat.
• Juga dinamakan pengerasan kerja• Kesan langsungKekerasan dan kekuatan meningkatWujud tegasan tinggal/bakiKemuluran berkurang
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8. Process Variables ‐ independent
• Starting material ‐ types
• Starting work piece geometry
• Tool and die geometry
• Lubrication
• Starting temperature
• Speed of operation
• Amount of deformation
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• Dependent Variables– Force or power required
– Nature of material flow
– Material properties
– Exit temperature
– Surface finishSurface finish
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• Outcome– Experience
– Experiments
– Theory
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