Purpose:

1. To provide a brief introduction to engineering students about metal arc welding.
2. To learn the basic techniques of welding.
3. To give a real life experience of metal arc welding to engineering students.

Equipment:

1. Welding Machine.

   Welding is a metal-joining process in which coalescence is obtained by heat and/or pressure. In arch welding, the fusion is obtained by heat produced from an electric arch between the work and the electrode. Generally, there are 2 types of welding machine:

   a) Alternating Current-AC

   This type of machine is very useful in workshop and farm workshop. It is particularly designed for small voltage work for example 37.5 amps. It is essential for welding work in all conditions without considering whether the voltage is small or large. One of its distinctive advantage is it is cheap, easy to be maintained and it does not result in a lot of noise during welding operations. Although this type of machine is mobile, it can only use limited amount of electrode. Apart from that, it does not have movable components and cannot be used on aluminum electrode. It uses only one level of electricity.

   b) Direct Current-DC

   Direct current machine is built in capacities up to 1000A, having an open circuit voltage 40 to 95 V. This type of machine is very expensive and it uses three level of electricity and it requires a generator to provide the current. The advantages of using the direct current is there is no confinement on the type of electrode being used and it is a good method to do welding operations in places with no electric supply. However, thi type of machine also has a few disadvantages. It is usually difficult to maintain and it also produces a lot of noise while functioning. Normally, high-powered DC machines use air or gasoline cooling system. The machine amps limit is between 180 –200 amps. All welding machines have their own degree of heat so that it can be used to weld metal work metal and electrode of different sizes. Apart from that, it should be kept in a safe and dry place to protect the machine. If it is stored in damp and cold places, the transformer and the generator may have a risk of damage.

2. Cables.

   Generally, there are two cables that carry the electricity from welding machine to work metal and back to welding machine and earth cable. These cables are made from small copper wire coated with strong rubber so that we can hold it without feeling the intense heat. Besides that, every cable has it own size. For instance, size No. 2 means that the cable will be able to withstand welding electricity up to 200 amps. These cables are connected to the welding machine through its copper end.

3. Electrode Holder.

   The electrode holder has a few functions. Firstly, it is used to provide the electricity from welding machine to metal work. It is also used to hold the electrode during the welding operations. One of its constructive parts is the spring where it can hold the electrode firmly and withdrawn the electrode easily after finish welding. A few important requirements for the electrode holder are the electrode holder must be lightweight, has good rubber coating and easy to handle for certain period of time. Apart from that, it must also have its own size for the amount of electric current that it can carry.

4. Earth Holder.

   The earth holder is connected to the earth cable and clamped to the work metal or to the work table. It has a spring so that is can be easily clipped and unclipped. Without this equipment, welding operation definitely cannot be done.

   4. Shield.

   It is made from inflammable material. In the middle of the shield there is a bright rectangular glass coated with dark colored glass. It is used to protect the user from fire-bolt and harmful rays during welding work. There are two types of shield, one is the helmet type and the other one is the hand held type. The sizes are No. 10 and No. 11 respectively.

5. Chipping Hammer.

   It is made from an old punch, chisel or spring metal. Shape like a chisel at one end and has a sharpened end at the other one. Its holder is made from welded soft metal. It is used commonly to remove the slag excess stringer from the surface of the work metal.

6. Wire Brush.

   It is used to clean the surface of the stringer bed after the slag is chipped away and to remove dirt from the surface of metal work before welding can be done.

7. Glove.

   It must be made from high quality leather. Use to protect your hand from fire-bolt and hot metal welding.

8. Leather jacket.

 Leather jacket is used to protect the user from the intense heat produced during welding operations. It is made of high quality leather to provide greater comfort for the user.

9. Tongs.

It is use to hold hot work metal after welding process.

Procedure:

 Connect the electrode cable and the earth cable to the Direct Current Welding Machine.

1. Clip the earth cable using its holder to the work table.
2. Clip an electrode with the holder. Make sure that the flux is not in contact with the holder. Undesired spark may occur if the flux is in contact with any metal.
3. Switch on the machine and set the dial to 90 amps.
4. Before we begin welding, we should put on our gloves and shield.
5. Take a piece of scrap metal and put it on the working table.
6. Hold the electrode about 90^o above the scrap metal. Tilt the electrode 20^o-25^o degrees to the right or left depending on which hand do you use from the work metal.
7. Scratch the front end of the electrode onto the work metal to start the burning. After the electrode has started burning, hold it at 10mm above the work metal. Try to avoid the electrode from being in contact with the surface of work because the electrode might be stucked onto the work.
8. Repeat the welding process for several times until you get a straight and firm stringer bead line when welding.
9. Next, get a cubic-shape metal block from your instructor.
10. Weld onto one side of the block to increase its thickness.
11. You must weld onto the block line by line. When you finish welding a line, use the chipping hammer to chipped off the slag and brush it off using a wire brush.
12. Stop when you have finished welding the side in three layers.

1. Please wear all the personal protective equipment recommended by OSHA.
2. Always protect your eyes from arc rays.
3. Protect your face and body from heat radiation and molten metal.
4. Move all the flammable material off the working place or cover it up using fireproof material.
5. Make sure that the welding machine is earthen.
6. Make sure that all line holder, earth clip and connection placed on good place.
7. Make sure that your working place is clean and tidy.
8. Make sure that all electric connection is tight, clean and dry.
9. Avoid pulling the cable on top or near sharp things.
10. Do not ever scratch arc on top of gas cylinder.
11. Turn off the welding machine when not in use.
12. Avoid welding cable from be in contact with hot metal, water, oil and grease.
13. Wear all safety clothing when welding.
14. All equipment such as hammer, chisel, brush and others must be well maintained.
15. A welder should not try to install or repair a welding machine.

Copyrighted^® by WEBMASTER of UNITEX