Manual Welding 1st Yr 2013 Jul

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Subject: Workshop Practice-I and II

WS-171 &172 L-T-P: 0-0-3 2 credits 1st and 2nd Semester, All Branches

Welding shop

GENERAL INSTRUCTIONS TO STUDENTS

1. Students are required to come in proper dress while attending the Workshop practical class.

They should wear apron (available in the workshop) and full shoes. Without full shoes no one

will be permitted to enter into the shop.

2. Students are required to come on time as per the timetable. They shall be marked late if they do

not turn up within five minutes of the scheduled time. Those who come late are to take

permission from Prof.-in-Charge to enter into the shop. No one will be allowed if they are late

by 15 minutes in any case.

3. Students are required to follow the instructions given by the teacher concerned or instructor

strictly. They should remain present in their place of working for the whole class unless

otherwise instructed.

4. Students are required to handle only those machines allowed to them by the instructors. Under

no circumstances any student should handle machines not assigned to him.

5. Students are required to fill in Workshop Card each day before entering the shop. At the time of

leaving student must ensure that it is signed by the instructor and a grade is given.

6. Students are required to complete the job within the time allotted to them. They should do the

job by themselves. Instructors would only help them in difficulty. Students should gather as

much information about the machine tools; power tools, hand tools, gauges, processes and other

details as possible from the instructors.

7. In case of any dispute, misunderstanding or difficulty, they may meet the Prof.-in-Charge or

Head of the Central Workshop.

8. Every student is required to clean the machine and return the tools issued to them after each

day’ work.

9. Students are required to appear for the Quiz Test/Viva-voce examination as and when notified

or instructions given by the Coordinator, Workshop Practice.

10. Assessment shall be done on the basis of regularity in attendance, discipline, attitude of the

student, quality of jobs done, report and performance in the Quiz Test/Viva-voce test.

11. After each class, they are required to submit the record (one bound volume for entire semester)

when they report for next class.

On completion all classes in a shop, all students are required to submit the record and all jobs made by

them for evaluation. Each class shop record should consist of the following:

i. Task to be done

ii. Raw materials used.

iii. Tools used

iv. Description of tools and instruments used with neat sketch

v. Procedure

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Welding Safety and Precautions

Perform welding only in designated areas.

Operate welding equipment after getting training from the instructor.

Wear protective clothing to cover all exposed areas of the body for protection sparks,

hot spatter, and radiation.

Protective clothing should be dry and free of holes, grease, oil, and other substances

which may burn.

Wear flame proof gauntlet gloves, a leather apron, and high-top shoes to provide good

protection against sparks and spatter.

Wear specifically designed, leak-proof helmets equipped with filter plates to protect

against ultraviolet, infrared, and visible radiation.

Never look at the flash, even for an instant.

Keep your head away from the plume by staying back and to the side of the work.

Never touch the job with bare hand just after the welding.

Use your helmet and avoid inhalation of fume.

Make sure there is good local exhaust ventilation to keep the air in your breathing

zone clear.

Don’t perform welding in wet areas, or with wet hands.

If others are working in the area be sure they are warned and protected against arcs,

fumes, sparks, and other welding hazards.

Don’t coil the electrode cable around your body.

Ground both the frame of the welding equipment and metal being welded.

Check for leaks in gas hoses using an inert gas.

Check area around you before welding to be sure no flammable material or degreasing

solvents are in the welding area.

Keep a fire watch in the area during and after welding to be sure there are no

smoldering materials, hot slag or live sparks which could start a fire.

Locate the nearest fire extinguisher before welding.

Deposit all scraps and electrode butts in proper waste container to avoid fire and toxic

fumes.

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Practice Schedule and Record Submission Details

1st Class

A. Task

a) Practice – melting a welding track by gas welding on 3 mm thick MS plate

b) Bead formation using filler rod on the opposite side of the plate

B. Record Submission Draw the schematic diagram of gas welding equipment

Raw material, Equipments used and procedure for doing the job

2nd Class

A. Task

Practice – Butt joint of 3 mm thick plate using gas welding

B. Record Submission

How heat is generating in gas welding?

Different type of flame used in gas welding


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3rd Class

A. Task

Practice – corner joint using gas welding

B. Record Submission Raw material, Equipments used and procedure for doing the job

What are the common defects occur during gas welding

What are the advantages and disadvantages of gas welding

4th Class

A. Task

Practice- butt joint of two plates (5 mm thick) using arc welding


Draw the schematic diagram of arc welding equipment

How arc is generated?


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5h Class

A. Task Practice- Lap joint of two plates (5 mm thick) using arc welding



Type of electrodes, function of electrode coating

What is the function of flux? What is slag?

6h Class

A. Task

Practice- T joint using arc welding

B. Record Submission Raw material, Equipments used and procedure for doing the job

What are the common defects occur during arc welding

What are the advantages and disadvantages of arc welding

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INTORDUCTION ABOUT WELDING

Welding is a process of metallurgical joining of two pieces of metals by the

application of heat with or without the application of pressure and addition of filler

metal. The joint formed is a permanent joint.

Various types of welding process:

Arc welding Gas Welding Resistance

Welding

Solid State

Welding

Advanced

welding Carbon arc

Metal arc

Metal inert gas (MIG)

Tungsten inert gas (TIG)

Plasma arc

Submerged arc

Electro-slag

Oxy-acetylene

Air-acetylene

Oxy-hydrogen

Spot

Seam

Projection

Friction

Ultrasonic

Diffusion

Explosive

Electron beam

Laser beam

Different types of joint:

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Oxy-acetylene Gas Welding

• In oxy-fuel gas welding the heat is obtained from the combustion of a fuel gas such as

acetylene in combination with oxygen

• The process is a fusion welding process wherein the joint is completely melted to obtain the

fusion.

• The heat produced by the combustion of gas is sufficient to melt any metal and as such is

universally applicable

• The fuel gas generally used is acetylene because of the high temperature generated in the

flame. This process is called oxy-acetylene welding

Equipment

Oxy-acetylene Gas Welding Equipment

1. Welding torch & tip

2. An acetylene cylinder – 15.5 bar, red or maroon

3. An oxygen cylinder – 125 bar. Blue or black

4. Pressure regulator – Cylinder pressure to delivery pressure

5. Pressure gauge- One shows cylinder pressure & the other shows the working or

delivery pressure

6. Rubber hoses - black/green hose for oxygen & red/orange hose for acetylene

7. Safety devices – Goggle, hand gloves, helmet, apron, sleeves, shoes etc.

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GAS WELDING FLAMES (Based on Gas Ratio)

The maximum temperature of the oxy-acetylene flame is 3100-3500 oC.

Centre of heat concentration is near the extreme tip of the white cone.

Inner Cone:

2C2H2 + 2O2 (cylinder) = 4 CO + 2H2 + heat

Outer envelope:

4CO + 2H2 + 3O2 = 4 CO2 + 2H2O + heat

1. Neutral Flame: (Gas ratio is 1:1)

2. Carburizing or Reducing Flame: ( Gas ratio 0.95 to 1)

3. Oxidizing Flame: (Gas ratio 1.15 to 1.5)

Advantages of Oxy-acetylene Gas Welding:

The equipment is inexpensive, simple and is easily portable.

Useful for welding light metals such as automobile bodies and repair works.

A large variety of material can be welded.

Welds can be produced at reasonable cost.

Compared to electric arc welding this provides greater flexibility with respect to heat impact

and cooling rates.

Disadvantages of Oxy-acetylene Gas Welding:

Equipment must always be handled carefully as in certain circumstances acetylene is

explosive as oxygen when used in an oily atmosphere (such as an old dirty garage floor pit).

A high temperature flame from a hand held torch is dangerous when handled carelessly.

It is much slower than electric arc welding and does not concentrate the heat close to the

weld. Thus, the heat treated area is larger, which causes more distortion.

Highly skilled operators are required to produce a good weld.

If electric arc welding is available gas welding is seldom used for work over 3.2mm thick.

The process is not satisfactory for heavy sections

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Arc welding

An electric arc is a discharge of electric current across a gap in a circuit

It is sustained by an ionized column of gas (plasma) through which the current flows

To initiate the arc electrode is brought into contact with work and then quickly separated from

it by a short distance

The arc must be shielded because as it hardens the molten metal combines with oxygen and

nitrogen to form impurities that weaken the weld.

The electrodes are usually coated with a flux. This coating forms a gaseous cloud that shields

the molten metal from the atmosphere.

The coating also forms a protective slag. The slag floats on the molten pool and hardens as

the weld cools. This keeps impurities out of the weld.

Arc welding setup

ARC WELDING MACHINE:

AC Arc Welding Machine:

• A step down transformer receives the AC supply between 200 to 440volts and transforms it

to the required low welding voltage in the range of 80 to 100volts.

• A high current of 100 to 400A will be suitable for general arc welding work.

• In AC arc welding, there is no choice of polarity since they change in every cycle.

DC Arc Welding Machine:

• In DC welding, the work-piece is connected to the positive pole of a DC generator and the

electrode to the negative pole in order to melt greater mass of the metal in the base material.

This is called straight polarity.

• When the less heat is required at the base material, the polarity is reversed. This is called

reversed polarity.

• We can select the polarity depending upon the type of the job. Hence, in DC arc welding, it is

possible to melt many metals which require more heat to melt.

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ARC WELDING ELECTRODES

Consumable Electrodes: Melt along with the work-pieces & fills the joint (Bare or Coated)

When the bare electrodes are used, the globules of the molten metal while passing from the

electrodes absorb oxygen and nitrogen from the atmospheric air to form non-metallic constituents

which gets trapped in the solidifying weld metal and thereby decreasing the strength of the joint.

Coated Electrodes facilitate:

Protection of molten metal from oxygen and nitrogen of the air by providing a gaseous shield

around the arc and the molten metal pool

To establish & maintain the arc throughout welding

The formation of slag over the joint, thus protects from rapid cooling

Addition of alloying elements

Advantages of Arc Welding:

1. Applicable to an infinite variety of work & can be executed in any position.

2. There is less buckling and warping of the work.

3. It produces strong sound and ductile welds.

4. Satisfactory welds can be produced in heavy & light sections.

5. Low cost process & Low accuracy in setting up required.

6. Excellent joint properties can be obtained in mild, low alloy and stainless steels, nickel and

copper-base alloys.

GENERAL WELDING PROCEDURE

1. Marking and cutting: mark the work-piece as per requirement and cut it with Cut-off saw.

2. Edge Preparation: Edges preparation of the pieces to be joined should be done by grinding

wheel. It may involve beveling or grooving. This is done in order to get the fusion or

penetration through the entire thickness of the member.

3. Checking and setting of welding machine: check the welding machine and do proper

current setting (for arc welding); check the cylinder regulator pressure, hose pipe and blow

pipe (for gas welding).

4. Safety Devices: Goggles & shields to protect the eyes, Apron to prevent the sparks and flying

globules of molten metal, shoes, hand gloves etc.

5. Initial Weld: Initial welding spot are done at the opposite corners of the joint to secure the

pieces together.

6. Intermediate and Final Welding: The weld joint is formed through various weaving

movements (weld beads). During this process, filler metal and a suitable flux are used. After

the intermediate run of welding, final run is taken.

7. Removal of Excess Material: Extra material on the weld surface can be removed using tongs

and chipping hammer. The weld is allowed to cool and then cleaned.

Reference Book:

1. Manufacturing Technology Volume 1 (Foundry, Forming and Welding), P. N. Rao

2. Elements of workshop technology Vol-1 Manufacturing process, Hajra & Choudhury

Manual Welding 1st Yr 2013 Jul

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