Week12

WEEK -12

O C T 2 8 T H 2 0 1 4

2 0 1 4 - 2 0 1 5 S E M E S T E R - I

TA201 Manufacturing Processes

2014-15 Semester-I

Announcements

TA 201 Dr. Shashank Shekhar

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Please come prepared for your project evaluation starting from 10th November. You should be prepared for a total of 10-15 min presentation for

interaction with the committee members

Bring report on cost estimate. Materials cost of various materials will be sent by mail and will be available on course website

Also note that each member of a group need not get the same marks for the project. Individuals will be awarded marks based on their contribution and their ability to answer the questions posed to them.

Note: You MUST NOT touch other's project

Endsem Syllabus All topics covered so far (from start of the semester)

Objective + Subjective + Numerical problems

2014-15 Semester-I

3 Powder characterization

Particle size and distribution

Particle shape and structure

Particle surface area

TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Powder fabrication Classification 4

These can be classified into following main categories Mechanical

Milling Attritioning and Mechanical alloying

Physical Atomization

Chemical Decomposition of a solid by a gas Thermal decomposition Solid-solid reactive synthesis

Other Electrolytic techniques Microorganism Synthesis

TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Ball Milling 5

Milling implies mechanical impaction using hard balls, rods, or hammers and is a classic approach to fabricating ceramic powders

Material must be brittle. [What can you do if a material is ductile like metal?]

The impact stress required for fracture increases with decreasing particle size

[So How should the size vary with time?]

[What will happen if the speed of the mill is too low or too high?]

TA 201 Dr. Shashank Shekhar

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2014-15 Semester-I

Ball Milling 6

Ball milling is inefficient because most of the energy goes into noise and heat

For optimal milling The ball diameter should be approximately 30 times the

diameter of the powder

The balls should fill about half of the jar volume

The particles should be about 25% of the jar volume

Fluids or protective atomosphere are used to reduce oxidation and aid grinding

When wet, liquid clings to the media surface. How can this influence the particle size that can be obtained?

TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Ball Milling 7

TA 201 Dr. Shashank Shekhar

Grain size variation with milling time. [What will be the change when you add liquid to increase adhesion?]

2014-15 Semester-I

Atomization Techniques 8

Relies on disintegration of melt into droplets that freeze into particles

Commercial atomization units operate at production rates as high as 400 kg/min

Mostly used for metals, alloys and intermetallics with recent applications in polymers and ceramics

Two main method of atomization Gas atomization

Liquid atomization

TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

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Gas Atomization

Powder production Water Atomization

Rotating disc Atomization

TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Gas vs Liquid Atomization 10

Difference due to turbulent vs not-so-turbulent flow of gas from the nozzle Turbulence causes particles to reenter the gas expansion zone, leading to the formation of satellite particles

TA 201 Dr. Shashank Shekhar

Liquid Atomization: As round as it gets

2014-15 Semester-I

Electrolytic Technique 11

TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Electrolytic Technique 12

Elemental powders can be deposited at the cathode of the electrolytic cell

Raw metal is dissolved at the anode and deposited at the cathode

After deposition, the cathode deposit is washed, dried, ground, screened, and annealed to form a powder

Very high purity particulates are obtained

Most common examples are palladium, chromium, copper, iron, zinc, manganese, and silver

TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

13 Compaction (Dry Pressing)

TA 201 Dr. Shashank Shekhar

Green compact Green strength

2014-15 Semester-I

14 Stages of compaction and density of green compact

1. Loose compact after filling 2. Rearrangement 3. Particle deformation and

reduction in pores [How will the plot be different for ceramics?]

Associated density variation

Increasing pressure

TA 201 Dr. Shashank Shekhar

Green density

2014-15 Semester-I

Compaction Pressure

TA 201 Dr. Shashank Shekhar

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2014-15 Semester-I

Single Action Compaction Double Action Compaction

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Die-wall friction

TA 201 Dr. Shashank Shekhar

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2014-15 Semester-I

Cold Isostatic Compaction

TA 201 Dr. Shashank Shekhar

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2014-15 Semester-I

19 Sintering (Firing)

• It is an heat treatment process for attaining strength and density in the green compact

• Sintering - Green compacts are heated in a furnace to a temperature below melting point (0.7-0.9Tm)

• Improves the strength of the material

• Proper furnace control is important for optimum properties

• Part shrinkage occurs during sintering due to pore size reduction

Solid phase sintering (all in solid state)

Liquid phase sintering (One is in liquid state) Example: WC+Cu Cu-Sn bearings

TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

20 Sintering stages

Particle bonding is initiated at contact points

Contact points grow into necks

Reduction in pore size

Grain boundaries develop between particle TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Initial stage: formation of interparticle neck intermediate stage: transition occurs from open porosity to closed porosity. Typically, when the overall porosity in the compact is less than 8%, the pores are predominantly closed type final stage: reduction/ elimination of closed pores.

Solid –State Sintering

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Dr. Shashank Shekhar

2014-15 Semester-I

Solid-State Sintering Stages

• W powder size: 5 µm • green density: 58% theoretical • sintering temp.: 1750°C

initial intermediate final

Note that despite sintering at such high temperature, there is still some residual porosity

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Dr. Shashank Shekhar

2014-15 Semester-I TA 201 Dr. Shashank Shekhar

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Typical Sintering Operation

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Spark Plasma Sintering

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Dr. Shashank Shekhar

2014-15 Semester-I

Pressure-assisted sintering

TA 201 Dr. Shashank Shekhar

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2014-15 Semester-I

Design Considerations for P/M

Design principles to consider

Shape of the compact must be simple and uniform

Bulk production must be met

Provision must be made for the ejection of the part

Wide tolerances should be used whenever possible

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TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Process Capabilities

It is a technique for making parts from high melting point refractory metals and ceramic materials

High production rates

Good dimensional control

Wide range of compositions for obtaining special mechanical and physical properties

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TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Process Capabilities

Limitations

High cost

Tooling cost for short production runs

Limitations on part size and shape

Mechanical properties of the part Strength

Ductility

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TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Freeform Fabrication: 3-D printing

TA 201 Dr. Shashank Shekhar

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2014-15 Semester-I TA 201 Dr. Shashank Shekhar

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