View
87
Download
3
Category
Tags:
Preview:
Citation preview
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
3
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I
4
Roll Welding
TA 201 Dr. Shashank Shekhar
• 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
TA 201 Dr. Shashank Shekhar
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
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I
7
Welding cracks
Incomplete fusion
Weld Quality: Welding defects
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I
8
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
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I
9
Brazing
Soldering
Adhesive bonding
Brazing, Soldering and Adhesive joining
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I
10
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
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I
11
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)
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I TA 201 Dr. Shashank Shekhar
12
Butt Joints and its variants
Lap Joints and its variants
2014-15 Semester-I TA 201 Dr. Shashank Shekhar
13
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
14
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I TA 201 Dr. Shashank Shekhar
15
Brazing Processes Torch Brazing Furnace Brazing Induction Brazing Resistance Brazing
2014-15 Semester-I
16
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
TA 201 Dr. Shashank Shekhar
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.
17
TA 201 Dr. Shashank Shekhar
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.
18
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I TA 201 Dr. Shashank Shekhar
19
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 )
20
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I
Soldering Joint 21
TA 201 Dr. Shashank Shekhar
2014-15 Semester-I TA 201 Dr. Shashank Shekhar
22
2014-15 Semester-I TA 201 Dr. Shashank Shekhar
23
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
24
TA 201 Dr. Shashank Shekhar
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
25
TA 201 Dr. Shashank Shekhar
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.
26
TA 201 Dr. Shashank Shekhar
Major Applications
1. Aerospace
2. Automotive
3. Packaging industry
2014-15 Semester-I TA 201 Dr. Shashank Shekhar
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
28
TA 201 Dr. Shashank Shekhar
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
29
TA 201 Dr. Shashank Shekhar
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.
30
TA 201 Dr. Shashank Shekhar
Recommended