Week8

WEEK -8

S E P 3 0 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

2 Solid State Welding

Application of Heat or Pressure or only Pressure leads to welding

Localized melting is possible or melting may not even occur

Filler metal is not used

Metallurgical bond is created with almost no melting

Advantages:

Welding with little melting or no melting

Metallurgical purity is maintained

No HAZ

Dissimilar metals can be bonded

Example: Forge welding, Roll welding, Cold welding, Diffusion welding

Explosion welding (Cladding)

TA 201 Dr. Shashank Shekhar

2014-15 Semester-I

Forged Welding • Forging welding is one of the oldest joining process. • In this process, components to be welded is heated to the temperature

(lower than melting temperature) and then forged together by hammer

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2014-15 Semester-I

4

Roll Welding


• It is used in cladding stainless steel to mild steel for corrosion resistance

• Making bimetallic strips • Producing sandwich strips which

can be later punched to obtain coins

2014-15 Semester-I

5 Friction Welding

Applications:

Welding various shafts and tubes

Automobile, Aircrafts


Flash produced is removed later on by trimming process

Short time cycle of this process is suitable for mass production

Applied in the welding of various shafts and tubular parts of similar or dissimilar metals

2014-15 Semester-I

6 Weld Quality: Residual stresses and distortions

Remedy: 1. Welding fixture 2. Heat sinks (heat removal from all sides) 3. Preheating


2014-15 Semester-I

7

Welding cracks

Incomplete fusion

Weld Quality: Welding defects


2014-15 Semester-I

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Weldability

Ability of a metal to get welded easily with absence of weld defects, acceptable strength, ductility and toughness in the welded joint.

Factors that affect weldability: 1.Base metal properties 2.Welding process 3.Filler metal 4.Surface conditions


2014-15 Semester-I

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Brazing

Soldering

Adhesive bonding

Brazing, Soldering and Adhesive joining


2014-15 Semester-I

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Brazing and Soldering

Filler metal used for joining

Filler metal melts but base metal does not

Falls in between complete fusion and solid state welding

Metals with poor weldability can be joined

Dissimilar metals can be joined

High strength is not a requirement


2014-15 Semester-I

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Brazing Filler metal melts and gets distributed due to capillary force

between the facing surfaces

Filler metal melts but base metal does not

Melting temperature of filler metal > 4500C but must be

below the melting point of base metal

Advantages of Brazing:

Any metals can be joined even dissimilar metals

Quick and consistent

Joining thin walled part

Less heat and power requirement (less HAZ problem)

Difficult to access parts can be joined (because of Capillary force)


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

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Butt Joints and its variants

Lap Joints and its variants


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Filler Metals 1. Melting temperature must be compatible with base metal 2. Surface tension of the liquid must be low to increase the

wettability 3. Fluidity for penetration must be high 4. Should impart adequate strength 5. Avoidance of chemical interaction. No galvanic effect

should be there.

Shape of the Filler metal: Wire, rod, strips

2014-15 Semester-I

Brazing fluxes: 1. Facilitates wetting 2. Protect the joint until the solidification of the filler metal 3. Low viscosity so that it can be displaced by filler metal 4. Flux should be easy to remove after brazing 5. Low melting temperature materials are used as fluxes 6. Common Fluxes are Borax, Borates, fluorides, Chlorides

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Brazing Processes Torch Brazing Furnace Brazing Induction Brazing Resistance Brazing

2014-15 Semester-I

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Brazing

Limitations to Brazing 1. Joint strength is less than welded joint

2. Although strength of a good brazed joint is greater than

that of a filler metal, it is less than base metal

3. High service temperature may weaken a brazed joint

4. Aesthetic disadvantage - Color of brazed metal may not match with base metal


2014-15 Semester-I

Soldering

1. Similar to Brazing 2. Filler metal used and melting point of filler metal is less than

4500C 3. Capillary action distributes the molten filler metals into the

surfaces of the metal parts being joined. 4. No melting of the base metal 5. Filler melts, wets and combine with base metal to give strength

because of metallurgical bond. 6. Cleaning of the surfaces are necessary to increase the

wettability. 7. Filler metal is called Solder 8. Electronic industry finds great use of soldering. 9. Most Solders are alloys of tin and lead, since both metals have

low melting points.

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2014-15 Semester-I

Advantages of Soldering

1. Low energy input relative to brazing and fusion welding.

2. Good electrical and thermal conductivity in the joint.

3. Capability of making air tight and liquid tight seams for

container

Disadvantages

1. Low joint strength unless reinforce by mechanical means

2. Possible weakening or melting of the joint in elevated

temperature service.

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Solder alloys

2014-15 Semester-I

Soldering fluxes

1. Remove oxide films and tarnish from the base metal surfaces.

2. Prevent oxidation during heating

3. Promotes wetting of the faying surfaces.

4. Be molten at soldering temperature

5. Be readily displaced by the molten solder during process.

6. Leaves a residue that is noncorrosive and non-conductive.

Example: 1. Resin 2. Alcohol, organic acids 3. muriatic acid 4. Salts ( Zinc and ammonium chloride )

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2014-15 Semester-I

Soldering Joint 21



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Differences between Brazing and Soldering - Brazing is done between 450 C and the melting temperature of the alloy to be joined Brazing filler materials are usually copper alloys (eg. brass whose m.p. is 950 C) Soldering is carried out below 450 C Soldering filler materials are usually tin alloys (M.P. 180 to 300 C) Brazing provides better strength than soldering

2014-15 Semester-I

Adhesive Bonding

Adhesive bonding is a joining process in which a filler material is used to hold two (or more) closely spaced parts together by surface attachment .

Filler material: Adhesive ( Generally nonmetallic substance-

Polymer)

Parts to be joined: Adherands

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2014-15 Semester-I

Strength of the attachments is due to either-

1. Chemical bonding – adhesives unite with the adherands by

forming primary chemical bonding, upon hardening

2. Physical Interaction: Secondary bonding results between atoms

of opposite surfaces

3. Mechanical interlocking: in which the surface roughness of the

adherand causes the hardened adhesive to become entangled

or trapped in its microscopic surface asperities

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2014-15 Semester-I

Conditions to get better result from adhesive bonding-

1. Clean surface – free from oil, dirt- oxide film.

2. Better wetting of the adherends by the liquid adhesive.

3. Little rough surface of the adherends is better – promotes

mechanical interlocking.

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Major Applications

1. Aerospace

2. Automotive

3. Packaging industry


27 Joint Designs

2014-15 Semester-I

Advantages:

1. This process is applicable to a wide variety of materials.

2. Parts of different sizes and cross sections ca be joined-

fragile parts can be joined by adhesive bonding.

3. Bonding occurs over the entire surface area of the joint

4. Low temperature curing avoids damage to parts being joined.

5. Sealing as well as bonding can be achieved

6. Simplified joint design

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2014-15 Semester-I

Limitations:

1. Joining is not as strong as other joining methods

2. Adhesive must be compatible with adherends

3. Service temperature is limited

4. Cleanliness and surface preparation is very crucial

5. Curing time imposes production rate

6. Inspection of bonding joint is difficult

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2014-15 Semester-I

Differences between adhesive bonding and Brazing and Soldering are- a. In adhesive bonding, the filler material is not metal.

b. Adhesive bonding takes place at room temperature or

moderately high temperature.

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