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Welding Processes
EN358 – Ship Structures
A Brief History of Welding
Late 19th Century
Scientists/engineers apply advances in electricity to heat and/or join metals (Le Chatelier, Joule, etc.)
Early 20th Century
Prior to WWI welding was not trusted as a method to join two metals due to crack issues
1930’s and 40’s
Industrial welding gains acceptance and is used extensively in the war effort to build tanks, aircraft, ships, etc.
Modern Welding
the nuclear/space age helps bring welding from an art to a science
Types of Welding
Weldability of a Metal
Metallurgical Capacity
Parent metal will join with the weld metal without formation of deleterious constituents or alloys
Mechanical Soundness
Joint will be free from discontinuities, gas porosity, shrinkage, slag, or cracks
Serviceability
Weld is able to perform under varying conditions or service (e.g., extreme temperatures, corrosive environments, fatigue, high pressures, etc.)
Fusion Welding Principles
Base metal is melted
Filler metal may be added
Heat is supplied by various means
Oxyacetylene gas
Electric Arc
Plasma Arc
Laser
Fusion Welding
Weld Metal Protection
During fusion welding, the molten metal in the weld “puddle” is susceptible to oxidation
Must protect weld puddle (arc pool) from the atmosphere
Methods
Weld Fluxes
Inert Gases
Vacuum
Weld Fluxes
Typical fluxes
SiO2, TiO2, FeO, MgO, Al2O3
Produces a gaseous shield to prevent contamination
Act as scavengers to reduce oxides
Add alloying elements to the weld
Influence shape of weld bead during solidification
Inert Gases
Argon, helium, nitrogen, and carbon dioxide
Form a protective envelope around the weld area
Used in
MIG
TIG
Shield Metal Arc
Vacuum
Produce high-quality welds
Used in electron beam welding
Nuclear/special metal applications
Zr, Hf, Ti
Reduces impurities by a factor of 20 versus other methods
Expensive and time-consuming
Types of Fusion Welding
Oxyacetylene Cutting/Welding
Shielded Metal Arc (“Stick”)
Metal Inert Gas (MIG)
Tungsten Inert Gas (TIG)
Oxyacetylene Welding
Flame formed by burning a mix of acetylene (C2H2) and oxygen
Fusion of metal is achieved by passing the inner cone of the flame over the metal
Oxyacetylene can also be used for cutting metals
Shielded Metal Arc (Stick)
An electric arc is generated between a coated electrode and the parent metal
The coated electrode carries the electric current to form the arc, produces a gas to control the atmosphere and provides filler metal for the weld bead
Electric current may be AC or DC. If the current is DC, the polarity will affect the weld size and application
Shielded Metal Arc (con’t)
Process:
Intense heat at the arc melts the tip of the electrode
Tiny drops of metal enter the arc stream and are deposited on the parent metal
As molten metal is deposited, a slag forms over the bead which serves as an insulation against air contaminants during cooling
After a weld ‘pass’ is allowed the cool, the oxide layer is removed by a chipping hammer and then cleaned with a wirebrush before the next pass.
Inert Gas Welding
For materials such as Al or Ti which quickly form oxide layers, a method to place an inert atmosphere around the weld puddle had to be developed
Metal Inert Gas (MIG)
Tungsten Inert Gas (MIG)
Welding Positions
Weld Defects
Undercuts/Overlaps
Grain Growth
A wide T will exist between base metal and HAZ. Preheating and cooling methods will affect the brittleness of the metal in this region
Blowholes
Are cavities caused by gas entrapment during the solidification of the weld puddle. Prevented by proper weld technique (even temperature and speed)
Weld Defects
Inclusions
Impurities or foreign substances which are forced into the weld puddle during the welding process. Has the same effect as a crack. Prevented by proper technique/cleanliness.
Segregation
Condition where some regions of the metal are enriched with an alloy ingredient and others aren’t. Can be prevented by proper heat treatment and cooling.
Porosity
The formation of tiny pinholes generated by atmospheric contamination. Prevented by keeping a protective shield over the molten weld puddle.
Residual Stresses
Rapid heating and cooling results in thermal stresses detrimental to joint strength.
Prevention
Edge Preparation/Alignment – beveled edges and space between components to allow movement
Control of heat input – skip or intermittent weld technique
Preheating – reduces expansion/contraction forces (alloys) and removes moisture from the surface
Peening – help metal stretch as it cools by hitting with a hammer. Use with care since it may work harden the metal
Heat Treatment – “soak” the metal at a high temperature to relieve stresses
Jigs and Fixtures – prevent distortion by holding metal fixed
Number of Passes – the fewer the better.

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PROJECT REPORT ONWELDING
INTRODUCTION TO WORK SHOP:-
Jhansi workshop is the biggest wagon repair workshop of Indian railways.
It undertakes POH of 605 vehicle units (VUs) per month which constitutes 18% of the wagon POH done in Indian railways. Over 400 BOXN wagon per month undergo POH in Jhansi workshop.
In addition, Jhansi workshop also undertakes rehabilitation of BOXN wagons.
HISTORY:-
Jhansi workshop has a great historical value as it was established by Indian midland railways in 1895
1930- Loco 1989- Commencement of construction of Jhansi workshop.
1995- Steam loco, coach and wagon repair activities started.
repair transferred from Jhansi to parel workshop.
1961- Introduction of incentive scheme.
1990- Introduction of POH of BOX ‘N’/BCN wagons.
1997- Discontinuation of coach POH.
2001- ISO 9001:2000 Certificate awarded to Jhansi workshop.
2008- Rehabilitation of BOXN wagons using mild steel POH of tower wagons 2009.
2009- Rehabilitation of BOXN wagons using stainless steel
REPAIRING AGE OF WAGONS:-
POH:- ( periodic over hauling) in this routine newly manufactured wagon comes for repairing after 6 year. And after repairing wagon comes for repairing after 4.5 years. In POH whole wagon repair.
ROH:- ( routine over hauling ) duration is 18 month.
For each wagon. In this checking of wheels, brakes, brake pipes etc done.
N-POH:- (no duration) in this category those wagon comes which are damaged in sudden accident. If these wagon repairable than comes under this NPOH.
INTRODUCTION TO WELDING
Welding process can be defined as the process of metallurgical joining two pieces of metals by fusion to produce essentially a single piece of the metal. Welding technology is more than 2500 years old.
VARIOUS WELDING SHOP:-
In Indian railway wagon repair workshop Jhansi. Welding section is divided into four shops they are as follows.
Re-hab.
Booth.
BNR-1
BNR-2
RE HAB:- 
In this section making of side wall or side fixture and end wall or end fixture are manufactured. with help of welding. Commonly (MAG and MMAW ) used. than assembled to the wagon base or wheel pad. Thickness of the sheet wall is 5mm to 8mm. 
BOOTH:-
In this section doors, pillars are manufactured. For the BOXN wagons. In a one side wall six pillars are used these pillars made from this booth shop.
BNR 1 :-
In this section only those parts will be repaired which are damaged or defected. due to
Corrosion
Accident
Excessive load.etc
BNR 2 :-
The process in BNR 2 as similar as BNR 1. It is used to distribute the work of BNR section.
POSITION OF WELDING
There are four types of welding position.
Down hand welding.
Vertical welding.
Horizontal welding.
Over head welding.
TYPES OF JOINT:-
T- joint.
Lap joint.
Corner joint.
Butt joint.
POWER SOURCE:-
Jhansi workshop mostly used DC type arc welding because it has following advantage. They are as follows.
DC arc welding can be weld both ferrous and non ferrous metal. But AC arc only weld ferrous metal.
 In DC maintenance of short arc is easier. but in AC except in case of iron powder electrodes, maintenance of a small arc is difficult.
In DC it is easier to strike an arc, even with thin electrodes. But in AC striking of arc, particularly with electrodes, is relatively difficult.
TYPES OF WELDING USED:-
Indian railway wagon repair workshop, Jhansi used mainly two types of welding they are as follows.
 MAG (metal active gas welding) or MIG (metal inert gas welding).
MMAW (manual metal arc welding).
These welding used for joining purpose while for cutting the metal. Indian railway workshop used. Gas cutting .(mixture of oxygen and acetylene.) and plasma cutting used
Automatic pillar welding machine.
MAG or MIG:-
Gas metal arc welding (GMAW), sometimes referred to by its subtypes, metal inert gas (MIG) welding or metal active gas (MAG) welding, is a semi-automatic or automatic arc
welding process in which a continuous and consumable wire electrode and a shielding gas are fed through a welding gun.
MMAW (Manual metal arc welding):-
A manual process using a flux coated electrode.
Alternating current or direct current forms an arc between the electrode and the base metal.
The flux coating disintegrates and gives off vapors that serve as a shielding gas , provide a protective layer of slag
Indian railway workshop Jhansi having 2 types of power source for the arc welding. single rectifier and multiple rectifier.
In the multiple rectifier six welder can weld at a time with a single source. Because these type of rectifier connected with six voltage regulator so six welder can weld at a different amp at a time according to their used.
In single rectifier one welder can weld at a time.
These rectifier are air cooled rectifier.
SEMI AUTOMATIC PILLAR WELDING MACHINE:-
It is design for BOXN body side stanchion both side at a time by Co2 welding process.
In this welding machine pillars are weld for the side fixture or end fixture. For the wagon.
This semi automatic machine contains two. MIG . which weld the pillars simultaneously
TYPES OF ELECTRODE USED:-
DEFECTS AND REMEDIES:-
POROSITY :-
This defect is caused in welding surface as well as internally, it is caused due to
(a)- by gases released during melting of the weld area but trapped during solidification,
(b)- by chemical reactions during welding, or by contaminants.
©- moisture in electrode.
(d)- high sulphur content of base metal.
(e)- long arc length.
(f)- higher travel speed. Or high solidification rate.
Remedies against porosity-
(a)- Clean joint area.
(b)- Proper selection of electrode.
©- Improved welding techniques, such as preheating of the weld area or in increase in the rate of heat input.
(d)-Store electrode properly. Follow manufacture recommended parameters
SLAG INCLUSION :-
Slag inclusion are compounds such as oxides, fluxes and electrode-coating materials that are trapped in the weld zone. Or slag remains on the surface of bead. Due to…
(a)- Excessive current.
(b)- High travel speed of welding.
©- If shielding gas are not effective during welding, contamination from the environment may also contribute to such inclusion.
Remedies against slack inclusion:
(a)- Cleaning the weld-bead surface before the next layer is deposited, by means of a wire brush (hand or power).
(b)- Use proper current.
©- Use accurate weaving technique.
(d)- Electrode should be heated at 250c in electrode oven.
CRACKS :-
Cracks may occur in various location and directions in the weld area
(a)-change the joint design ,to minimize stresses from shrinkage during cooling .
(b)-preheat the components to be welded.
©-Avoid rapid cooling of the welded component.
LACK OF FUSION :-
It is caused when joint is not prepared properly.
(a)- Excessive travel speed of welding.
(b)- Use lack of current.
©- Higher arc length. 
Remedies against lack of fusion:-  
(a)- Clean the joint before welding.
(b)- At every run clean the slug than do the next run.
©- Increase included angle of grove joint.
(d)- Maintain proper electrode position
SUGESSTION:-
Welder should be skilled. Because welding is mostly depend on the welder. If he is using correct technique and working under given specification which is recommended by RDSO. Than defects almost removed which comes during welding process.
Selection of proper electrode.
Proper cooling rate.
The electrode feed rate and welding voltage are set to the recommended values for the electrode size and material.
A trial bead weld should be made to establish proper voltage (arc length) and feed rate values.
CONCLUSION :-
At last I conclude that welding is a process of joining two metal. But during joining process many defects occurs due to using wrong technique. Wrong parameters, so the welding qualities decrease and joint become poor.
I suggest that by given proper training to welder so he can use proper method, accurate parameters that is (current, arc length, position of welding, travel speed etc). welding quality can be increased.
It was the good experience for me to completed my project on the welding.