Chapter 2: Arc welding¶

Introduction in brief/ History¶

As we are familiar with the common welding activity which involves joining of two metals using filler or heat or pressure in order to create a whole object.

Welding is hugely applied industrial practice for joining metals. From joining the frame of your study table to build huge transportation things, welding is inevitable in every construction and manufacture.

Definition of welding¶

The American Welding Society (AWS) has given the most satisfying definition for the term welding which is:

“Welding is a materials joining process which produces coalescence of materials by heating them to suitable temperatures with or without the application of pressure or by the application of pressure alone and with or without the use of filler material”.

Applications of welding¶

Repairs
Aeronautical Industry:
To build the body of airplanes and other components
Automobile Industry:
To build the vehicles like Bus, car, bicycle, bike etc.
Railways:
To construct body of rail, tracks and stations
Machine Industry or Workshops:
When machines are prepared welding is necessary to make the component.
Building Industries:
To build big industries also welding is necessary
Construction of Bridge and Dams
Utensils making Industries
Ornament making Industries
Ship making Industries
Ordnance Factories etc.

Advantages of welding¶

1) Welding is more economical and much faster process than other process like riveting, bolting, casting etc.

2) If properly done, it results in permanent joints having strength equal or sometimes more than base metal.

3) General Welding equipment is not very costly

4) Welding permits considerable freedom in design

5) Welding can also be mechanized

6) Leakage proof (both liquid and gas) joints can be made.

7) Different metals can be joined as a whole in simple ways

8) If welded place does not look good, then welded metal can be removed using machine and taken back to previous form

Disadvantage of welding¶

1) It results in residual stresses and distortion of the work pieces.

2) Welded joint needs stress relieving and heat treatment

3) Welding emits harmful radiations, fumes and spatter harmful for your eyes and skin.

4) Smoke coming out while welding is harmful for our respiration.

5) Skilled welder is required for production of good welding.

6) Edges preparation of the welding jobs are required before welding

7) Jigs and fixtures are needed to hold and position the parts to be welded

8) Heat treatment is necessary after welding of metals.

Basic requirements for a good weld¶

1) Heat Energy¶

In order to join two metals together they must be melt first near to their melting point. So, to melt those metals we need a heat source. Commonly used heat sources are – Gas Flame, Electric Arc, Blacksmith, Radiant energy, Laser beam and so on.

2) Protection¶

We have to think in long term protection of our welded material. When we left the welded surface or joint exposed to environment then dirt as well as atmospheric gases like oxygen, carbon dioxide, hydrogen and other gases reacts with metal and forms oxidization layer. Therefore, to keep our joint safe we commonly use techniques like

Flux coating in metal surface
Applying inert gases
Applying non-reactive substances

3) Cleaning¶

Before welding any metal surface, we must ensure that metal does not have any oxidization and dirt in its surface. If we weld metal with oxidized or dirty surface, then weak joint is formed. Dirt can be like oil, dust, lubricants, gas or rust. So, we use techniques like Wire brushing, Filing, using Machine and so on to clean the metal surface before they are subjected to welding.

4) Mixing¶

A good welding should possess the same qualities as that of base metal. The more quality of joint differs from metal quality the weaker welded joint becomes. The best practices we apply mixing for good weld are as follows:

By using De-oxidizer
By performing pre heat and post heat.
By using good filling material.
By controlling the mixture used in base metal.

Ways of joining metals¶

To assemble the different parts of machines different types of joining methods are needed and some are discussed below:

1) Riveting: A rivet which is a metal fastener that has a cylindrical post with a head is placed in a drilled or punched hole to join two metals. Applications: Channel gates, aircrafts and ships, bridges etc.

2) By using nut and bolt or screw joints: Metal are often joined using nuts and bolt and it is popular form of joining metals. Applications: turbines, hand pumps, vehicles etc.

3) Joints by folding: Applications: bridges and vehicle wheels.

4) Soldering: In soldering, metals are joined by heating filler metal below 427 degree Celsius. Applications: Consumer electronics, automotive and photovoltaic industries.

5) Brazing: Metals are joined by heating filler metal above 427 degree Celsius. Applications: Electronics, automotive and heavy transport industries.

6) Glue: Some special glues used to join metals are epoxy, silicone, polyurethane and tapes. It joins metal but is not as durable and strong as welding. Surface preparation is necessary before applying glue for joining metals. Applications: Pipe thread sealant, thread locker, toys etc.

7) By welding: Welding is the common way of joining metals. It provides simple, durable and strong weld. Applications: Vehicles, home decoration and doors, ships and aircrafts etc.

What’s Next¶

chapter3