My presentation-welding

Advanced metallic Materials, Summer Semester 2015 1

Welding

Presented By: Niranjan Ramakrishnegowda

History of Welding The first metal to be shaped in welding history is thought to be copper since it can be

hammered and bent.B.C. Welding History

4000 B.C: Welding history is thought to begin in Egypt in the starting of 4000 B.C. In general, civilizations started with copper and then progressed to bronze, silver, gold and iron.

1000 B.C: Gold boxes found in Ireland that were fabricated by hammering lapped joints (form of pressure welding).

589 B.C: The Chinese during the Sui Dynasty developed the ability to turn wrought iron into steel in 589 A.D. The Japanese manufactured steel through a welding and forging process to produce Samurai swords.

A.D. Welding History

310 A.D: The Iron Pillar of Delhi is fabricated using iron billets. Blacksmiths forge welded the structure that is approximately 25 feet high and weighs 6 tons.



History of Welding1375 A.D: The Middle Ages (5th to 15th century) brought a phase in welding history where forge welding was front and center. Blacksmiths pounded hot metal until it bonded.

19th Century1800: Sir Humphrey Davy invented the electric arc. The arc was created between 2 carbon electrodes that were powered by a battery.1838: Patent issued to Eugene Desbassayrs de Richemont for fusion welding.1903: Thermite welding is invented, another process, oxyfuel welding, also became well established as a commercial process.1943: Gas Metal Arc Welding was invented.1950: Shielded Metal Arc Welding.

Modern WeldingFriction stir welding, Magnetic Pulse welding

Iron Pillar of Delhi, India.

Welding For Ships Was Not Reliable due to Cracking Until World War I.


Introduction

Definition: Welding is a technique of joining similar and dissimilar metals and plastics by adopting ways which do not include adhesives and fasteners. From Wikipedia: Fabrication or sculptural process to join materials (Usually metals or thermoplastics).High temperature metal joining technique (Heated till the fusion point).Filler material is often used addition to melting of the base metal.Permanent joints are produced.Localized coalescence in the weld pool caused by suitable combination of temperature, pressure and metallurgical conditions.

Basics


Distinction Between Welding, Soldering and Brazing:

Soldering: Soldering differs from welding in that soldering does not involve melting the work pieces.Brazing: Brazing differs from welding in that it does not involve melting the work pieces and from soldering in using higher temperatures for a similar process, while also requiring much more closely fitted parts than when soldering.

https://www.youtube.com/watch?v=c3mnk_rqGMc

Heat Sources


Variation of heat input to the work piece with power density of the heat source.

Weld DesignJoint Type: 5 Basic Joint Types


Welds are made at the junction of all the pieces that make up the weldment (assembled part).Butt Joint: A joint between two members aligned approximately in the same plane.Corner Joint: A joint between two members located approximately at right angles to each other in the form of an L.Lap Joint: Between two overlapping members located in parallel.T Joint: A joint between two members located approximately at right angles to each other in a form of a T.Edge Joint: Between the edges of two or more parallel or nearly parallel members

Weld Design


Weld Type:

•Fillet weld: On the Joint.•Groove weld: In the Joint.•Back weld: Made on the backside of the joint.•Slot weld: Used with prepared holes.•Spot weld: Weld at the interface of the members.•Seam weld: Without prepared holes.•Stud weld: Welding a metal stud.•Surface weld: Weld beads deposited on the base metal or broken surface.

Weld Design- Fillet Weld


Fillet weld on corner joint Fillet weld on lap joint Fillet weld on T-joint

• Triangular shaped weld having concave, convex or flat surface.

Example: Connecting flanges to pipes.

http://www.lincolnelectric.com/en-us/support/process-and-theory/Pages/weld-fusion-weld-penetration.aspx


Weld Design- Groove Weld

• There are seven basic groove welds: square, V, bevel, U, J, flare V and flare bevel.


Classification Various welding process differ in a manner in which temperature and pressureare combined and achieved, classification can also be done on the source of energy.


Arc Welding Gas metal arc welding (GMAW) :

• Also called Metal inert-Gas welding.• Weld area is shielded by an inert gas like argon, helium or carbon dioxide.• Consumable bare wire with de-oxidizers are fed automatically into weld area by wire feed drive motor. • Suitable only for thin sheets and sections less than 6mm. (Otherwise Incomplete fusion, spatter losses are more)

(1) Torch handle, (2) Molded phenolic dielectric (shown in white) and threaded metal nut insert (yellow), (3) Shielding gas diffuser, (4) Contact tip, (5) Nozzle output face

Arc Welding Gas tungsten arc welding (GTAW):


• Also called Tungsten Inert Gas welding (TIG).• Non-Consumable tungsten electrode.• Filler metal normally used.• Weld area is protected by Shielding gases like Argon or Helium.• Not safe- protective clothing needed.• Difficult of all the welding techniques known since a short arc length has to be maintained.• A high frequency generator is used to strike electric spark, this arc is the conductive path for the welding current through the shielding gas while the electrode and the work piece are separated (1.5-3mm).• Filler rod is always withdrawn every time the electrode advances but never taken out of the weld pool in order to avoid the oxidation.

Arc Welding Shielded Metal Arc Welding (SMAW):

• Electrode and the work piece melts forming the weld pool that cools to form a joint.

• The flux coating disintegrates giving raise to the vapor which serve as a shielding gas and forming a layer of slag later which acts as a shield for the atmospheric contamination.


Electron Beam welding-Major Breakthrough


• Beam focus and beam deflection are a part of todays weld schedule and can be programmably varied.

• Small Heat affected Zone.

Electron Beam welding


• Formation of a Key Hole in EBW, the high energy density instantly vaporizes the material forming a key hole as shown in figure.

Possibilities:•Depth-to-width ration of 40:1 have been achieved in production for many years.•Conduction mode welding produces a wide and shallow welds, this can be done by lowering the beam power and either defocusing the e-beam or widening the beam by using deflection pattern.

Electron Beam welding


Weld with root porosity. Pattern generator-A unique e-beam welding parameter.

Manual Transmission gear component.

Solid State Welding-Major Breakthrough Friction Stir Welding (FSW):

• A non consumable rotating tool with a pin and a shoulder is inserted into the abutting edges of the plates.

• The tool heats up (by friction) the work piece and moves the material to produce joint.

• It is a ‘‘green’’ technique, due to its energy efficiency, environment friendliness, and versatility.



Defects in WeldmentsA welding defect is any flaw that compromises the usefulness of a weldment. There is a great variety of welding defects.

Misalignment

Geometric Imperfections

Undercutting

Convex and Concave welds

Porosity

Weld Metallurgy


Presentation of the various constituent parts of a welded joint.

• Welding metallurgy can be considered a special branch, since reaction times are in the order of minutes, seconds, fraction of seconds, whereas in the other branches reactions are in hours and minutes.

• Welding metallurgy deals with the interaction of different metals and interaction of metals with gases and chemicals of all types.


Weldability of Steels

• Iron-carbon equilibrium diagram provides an insight of the behavior of steels in connection with welding thermal cycles and heat treatment. This diagram represents the alloy of iron with carbon, ranging from 0% to 5% carbon.



• 0% carbon, pure iron, above 1540ºC, in liquid state, no crystalline structure

• 1540 ºC, solidification starts, BCC structure, Delta iron• 1400 ºC, transformation occurs, FCC structure, Gamma iron• 910 ºC, iron back to BCC, alpha iron until room temp

• Iron and carbon form a compound known as iron carbide (Fe3C) or cementite.• When iron carbide or cementite is heated above 1115 ºC, it decomposes into liquid

iron saturated with graphite, which is a crystalline form of carbon.

Martensite Formation:

• At fast cooling rates, the austenite might not have sufficient time to transform completely to ferrite and pearlite and will provide a different microstructure. In this case, some of the untransformed austenite will be retained and the carbon is held at supersaturated state. This new structure is called ‘martensite’.

• If the cooling rate is sufficiently fast, the austenite might transform completely into martensite. It is harder than pearlite or ferrite-pearlite structure and it has lower ductility.


Hardenability:

Hardness mainly depends on the carbon content but cooling rate also influences the microstructure and causes higher hardness. This is because the crystal lattice is changed or distorted and this hardens the material. By adding different alloys to the steel, the tendency of austenite to transform into martensite upon cooling increases, which is the basis of hardening steels. Carbon, manganese, chromium, molybdenum etc. The amount of alloys and their power to create this microstructure transformation are known as hardenability. Grain size and microstructure relate directly to hardness and strength. Fine grain size promotes both increase in strength and hardness. This is an advantage for heat treatment but it can be detrimental to welding since high hardness is not desired in welds of softer materials.


Weldability of Aluminium alloy

Parameters Controlling Microstructure and Hardness during Friction-Stir Welding of Precipitation-Hardenable Aluminum Alloy 6063.


Relationship between the welding rotation speed and the maximum temperature of the welding thermal cycle.

Cross sections perpendicular to the welding direction of the welds of Al alloys 6063-T5 and T4.



Optical microstructures in the stir zones in the welds of Al alloys 6063-T5 and T4.

OIM images in the stir zones in the welds of Al alloy 6063-T5.



Relationship between the grain size and the maximum temperature of the welding thermal cycle.

Horizontal hardness profiles of the welds of Al alloy 6063-T5 (a) in the as-welded condition and (b) in the postweld-aged condition.

Applications


Aircraft industry Ship building

Automotive industry

References

Gourd, L.M., Principles of welding technology, 3rd edition, 1995, Edward Arnold, ISBN 0 340 61399 8.

Parameters Controlling Microstructure and Hardness during Friction-Stir Welding of Precipitation-Hardenable Aluminum Alloy 6063 by YUTAKA S. SATO, MITSUNORI URATA, and HIROYUKI KOKAWA.

Microstructural investigation of friction stir welded 7050- T651 aluminium by J.-Q. Su a, T.W. Nelson a, , R. Mishra b, M. Mahoney.∗

www.Wikipedia.com Cary, H.B., Modern welding technology, 4th edition, 1998, Prentice Hall,

ISBN 0-13-241803-7. Welding metallurgy by American Welding Society.


http://www.wikipedia.com/

Questions?


Smart Mater. Ex. WS 2012, Name, Title 31

Fume extraction arm


Defects in Weldments Weld Damage


Spatter

Welding Safety

Mention about the lung damage caused by fumes. Mention about use of welding helmet (cost online lol)


Solid State Welding-Major Breakthrough Magnetic Pulse Welding (MPW) and Explosion Welding: MPW and Explosion welding are alike but not the same.

MPW System Explosion Welding


Weld Metallurgy

GrainsThe size of the crystals and grains depends on the rate of growth of the crystal. The rate of crystal growth depends on the rate of cooling of the molten solidifying metal. When the rate of cooling is high, the solidification process occurs more rapidly and the crystal size and grain size tend to be smaller and vice versa. MicrostructuresThe overall arrangement of grains, grain boundaries, phases present in an alloy is called its microstructure. It is largely responsible for the properties of the metal. The microstructure is affected by the composition or alloy content and by other factors such as hot or cold working, straining, heat treating etc.The microstructure of weld metal and adjacent metal is greatly influenced by the welding process, which influence the properties of the weld.


Microstructure of a weld used in stainless steel Microstructure of base metal of the same stainless steel.

39

Weld Metallurgy-Crystal Structures

• The structure of metal is complex. When metal is in a liquid state, usually hot, it has no distinct structure or orderly arrangement of atoms. So that atoms move freely since they have high degrees of mobility due to the heat energy involved during melting process.

• As the metal cools, atoms loose their energy and their mobility. When temperature is further reduced, the atoms are no longer able to move and attracted together into definite patterns.

• These patterns consist of three-dimensional lattices, which are made of imaginary lines connecting atoms in symmetrical arrangements.

• Metals in a solid state possess this uniform arrangements, which is called crystals. All metals are crystalline solids made of atoms arranged in a specific uniform manner.

40

Weld Metallurgy-Phase Transformation

Some metals change their crystallographic arrangement with changes in temp. Iron has a BCC lattice structure from room temp. up to 910ºC, and from this point to 1388 ºC it is FCC. Above this point to melting point, 1538 ºC it is again BCC. This change is called as phase transformation or allotropic transformation. Like, titanium, zirconium and cobalt.

Transformation occurs when metal melts or solidifies; In melting, arrangement of atoms disappears and atoms move

randomly. In solidifying, crystalline arrangement reestablish itself.

Pure metals melts or solidify at a single temperature, while alloys solidify or melt over a range of temperature with a few exceptions.

Phase changes can be related to alloy compositions and temp when they are in equilibrium, and shown on a diagram (known as phase diagrams, alloy equilibrium diagrams or constitution diagrams).

My presentation-welding

Documents

Transcript of My presentation-welding