TIG

TIG Welding (Tungsten Inert Gas Welding)

 TIG is technically stands for GAS Tungsten Inert Gas Welding.

TIG is also a type of welding process, which is known as tungsten inert gas welding. In this Process arc is produced between non-consumable tungsten electrode and base metal and simultaneously consumable filler metal filled at the welding spot. Filler metal are consumable TIG filler in the forms of rods in different different diameter.
The weld area is protected is protected from atmospheric contamination by an inert shielding gases such as helium and argon, and filler metal is feeded separately to weld .TIG is commonly used to weld thin section of stainless steel and non ferrous metal such as aluminium, magnesium, and copper alloy.

TIG process requires continuous movement of two hand, first hand to feed the filler metal in weld area and other to manipulate the torch in required direction. The important factor in to be maintain arc length and preventing the contact between electrode and work piece

Once the arc is struck, welder moves the torch in a small circle to create welding pool, size of which depends on size of electrode and amount of current. while maintaining a constant separation between the electrode and workpiece, the operator then moves the torch back slightly and tilts it backward about 10-15 degree from vertical. Filler metal is added manually to the front end of weld pool as it is needed.

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TIG always gives a better result in quality aspect, because it affords better control over the time of welding process thru the welding area. For better quality always it requires a very skill operator, Cleanness, Surfaces & equipment's should free from oil, grease, dirt, impurities and contamination for a better result in the form of welding strength.

Shield gases always plays a vital role in welding process, it covers the welding pool by shield gas that prevent the welding pool from atmospheric contamination such gases are nitrogen and oxygen. Argon is most commonly used gas for GTAW for high quality welding and HELIUM is often used for high penetration.

Submerged Arc Welding (SAW)

Submerged Arc Welding (SAW)

SAW is a type of welding process that means submerged arc welding process. This welding process remains continuous in which Arc is submerged in flux and welding take place.

This is an arc welding process in which the heat for welding is supplied by an arc developed between a consumable solid wire or flux cored wire and the job. The arc is shielded by a layer of granular fusible flux which covers the molten weld metal and the base metal near the joint. The arc being submerged in flux is not seen easily from outside.

Required basic equipments for SAW are:

1. Power Source
2. Wire Feeder
3. Wire Reel
4.  Wire feeding control system
5. Flux Hopper
6. Flux Torch
7. Welding Holder
8. Welding Wire
9. Base Plate

Submerged Arc Welding is either used in semi-automatic or fully automatic mode.

The process gives very high deposition rates (upto 40 kg/hr.) and can be used for welding very thick sections. It is use for both joining and overlaying. Due to high current employed, the heat input is large and the flux cover gives a slow cooling rate. The combination of high heat input and low cooling rate makes this process more suitable for high hardenability metals like Ni-Hard than manual arc welding. As the flux is deposited in granular form prior to arcing, SAW is suitable only for downhand welding. SAW is also not suitable for welding plates less than 5mm in thickness as it might result in burn through.

Every welding process has their own advantage and limitations, If we talk about Submerged arc welding the major advantage of this process is massive buildup. It is suitable for big HRC roller and for that component which required continuous  heavy buildup.

Advantage of Submerged Welding Are:

• Very high deposition rate (40-50 kg/hr).
• No spatter of welding because Arc is covered with flux
• Deep penetration of arc 
• Can be use in indoor and out door activity
• High operation feature in mechanised applications.
• Welding fumes and are light emission is very low.
• 70% or more than 70% flux recoverable.

Limitation:

• Limited to some nickle base alloy and limited to (ferrous) steel and stainless steel.
• Limited to high thickness end sheets.
• Backing strips required for good penetration.
• Limited to Down-hand welding process.

Manual Metal Arc Welding

MMAW (Manual Metal Arc Welding)
or
SMAW(Shield Metal Arc Welding)

Shield or Manual metal arc welding is a process, in which the heat for welding is generated by an electric arc, established between a flux covered consumable electrode and the workpiece. The electrode rod is made of a material that is compatible with the base material being welded and covered with a flux that gives off vapors that serve as a shielding gas and provides a layer of slag both of which the protect the weld area by atmospheric contamination.

Types of welding:-

• Autogenous Welding- It is a kind of welding in which only similar metal parts can be welded. e.g. mild steel to mild steel, brass to brass, copper to copper.  
• Heterogeneous Welding- It is a kind of welding in which only dissimilar parts can be welded. e.g. mild steel to copper, cast iron to mild steel, stainless steel to mild steel, etc.

Advantage of Shielded Metal Arc welding-

1. This is the simplest among all arc welding processes.
2. It is portable.
3. This process is the benchmark for all arc welding processes.
4. Cost economical.
5. This can be used outdoor and indoor.
6. Welding can be carried in any position.
7. This process finds countless applications because of the availability of a wide range of electrode. 
8. A big range of metal and their alloys can be welded.
9. The power cable of SMAW can be extended, that's why it can be used for long-distance and height process.

Application:-

SMAW is used both in fabrication and maintenance repair job. This process finds application in 

• Tank, boilers, and pressure vessel fabrication.
• Shipbuilding
• Pipes and penstock joining
• Building and bridge fabrication
• automotive and aircraft industry etc.

Equipment required for shielded metal arc welding:-

• Arc welding power source 
• Welding cables 
• Electrode holder
• Earth clamp
• Welding electrode
• Welding helmet and hand shield
• Protective coating including hand gloves
• Chipping hammer, wire brush, etc.
• PPE (Personal protective equipment)

Power sources for SMAW:
In SMAW both AC and DC power sources can be used. All of them supply the high current used for welding at a sufficient safe lower voltage. The output requires is either AC or DC. Welding current plays a significant role in deposit quality and deposition rate.
In manual metal arc welding, short circuit voltage can fluctuate due to arc length changes. Hence if a constant voltage power source is used, current will fluctuate with arc gap in manual arc welding.
To overcome this problem a constant current power source is used in manual arc welding. In direct current, the current flows continuously in one direction and hence welding arc is relatively steady and smooth. DC is superior to AC especially while welding with lower currents.

Polarity in DC welding:- 

Polarity indicates the direction of current flow in the welding circuit.

The flow of electrons is always from negative to positive.

Kinds of polarity

1.  Straight polarity
2. Reverse polarity

Straight polarity:- In straight polarity, the electrode is connected to the negative and the work to the positive terminal of the power source.

Reverse polarity:- In reverse polarity, the electrode is connected to the positive and work to the negative terminal of the power source.

Why polarity is important in welding:

In DC welding, 2/3 of the heat is liberated from the positive end and 1/3 from the negative end. To have this advantage of unequal heat distribution in the electrode and base metal, the polarity as an important factor for successful welding.

Straight polarity is used for:

• Welding with bare light coated and medium coated electrodes.
• Welding the thicker sections to obtain more fusion and penetration.

Reverse polarity is used for:

• Welding of non-ferrous metals.
• Welding with heavy and super-heavy coated electrodes.
• Position welding 
• Sheet metal welding

ARC Lenght:-
Arc length is known as the gap or distance between the tip of the electrode and the workpiece during welding.

Types of arc length:

1. Standard arc length
2. Short arc length
3. Long arc length

Advantage of standard arc length:

1. Good weld joint
2. Good penetration
3. Maximum strength
4. Less chance of porosity
5. Metal deposition as per standard
6. Maximum ductility
7. Lessor no oxidation