PROTOTYPE-MODEL MAKING

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AIM: construction of an effective load bearing structureJOINING TECHNIQUE: Manual TIG(Tungsten

Inert Gas) welding was used as the joining technique as it provides better strength and higher quality welds

JOINT DESIGN: There are several Joint designs as shown in figure. But we have used Butt Joint because it gives better strength and high resistance to impact and cyclic stress.To minimize weld distortions and residual stresses, the heat input is minimized

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Tungsten inert gas welding Non consumable electrode processArc heat melts the filler rod and gets

deposited in weld joint as shown in figureTouching of tungsten electrode to base

metal prohibited otherwise:1. Strength of arc will decrease2. Tungsten inclusion To prevent touching we require HIGH FREQUENCY UNIT.

Precise angle required for concentrated arc

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Continued…Requires significant operator skillAccomplished at relatively low speedsSafety measures:- Protective clothing including light and thin

leather gloves- Opaque full face and neck Helmets with dark

eye lenses are worn to prevent exposure to ultraviolet light

- Proper ventilation and protection from dangerous gases

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WELDING PARAMETERS:Current-Too much current can lead to splatter and

workpiece damage. Too little current can lead to sticking of the filler wire

Voltage-A high initial voltage allows for easy arc initiation and allows for a greater range of working tip distance.

Gas flow and composition- Choice of gas important; affects production costs, electrode life, weld temperature, arc stability and also the mechanical properties..

Welding Speed--Increasing welding speed for the same current and voltage reduces the heat input and produces a decrease in weld cross sectional area and consequently D and W also decreases.-Normal welding speeds are from 100 to 500 mm/min depending on current, material type and plate thickness.

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EQUIPMENTSWelding torch-Two basic types:1-Air cooled2-Water cooled-Collet is used to hold the electrode in a GTAW torch - Gas nozzle is fastened to the torch body by threaded connection.Power supply--Both dc and ac power supply are used with static volt-ampere characteristics of the drooping type.-A.C.,DCEN,DCEP power sources can be used.

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Electrode--Either pure tungsten electrode, thoriated W electrode or zirconated W electrode can be used.-Preparation of electrode is important to achieve a strong, clean and quality welds.Shielding Gas--Usually an inert gas like argon or helium is used. The gas selection is based on the metal to be welded. Some of the examples are:1-Stainless steel and high temperature alloys: Ar is mainly used while hydrogen upto 25% is added to Ar or He for mechanised welding of these alloys

2-Titanium:Ar is used for section thickness upto 3mm.However, He is found better for deeper penetration in thick sections

3-Aluminium:Ar is generally used but Ar-He mixtures can also be used.

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Advantages of TIG• versatile and uses less energy than other welding

methods• Produces high quality welds and stable arc• No slag is produced• TIG Welding can be done in any position• Weld composition is close to that of the parent metal• Thermal distortions of work pieces are minimal• No filler rod required for thin plates (autogenous). Often

used in THIN SHEET WELDING(1-2 mm)• Provides precise control of welding variables• process grants the operator greater control over the

weld than competing processes

Applications of TIGTIG Welding is used for welding a variety of metals.Frequently applied to stainless steel and light

metalsAerospace industry, space vehicles and bicycle

industryIn maintenance and repair work, commonly used to

repair tools and dies, especially components made of aluminium and magnesium

It is preferred for joining thin gage metal and to produce weld close to heat sensitive components

Also used in nuclear industry

• It can be also be used for spot welding in sheet metal applications.

• TIG is also widely applied in mechanised systems either autogenously or with filler wire.

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