Welding is one of the most commonly used fabrication techniques for manufacturing engineering components for power, fertilizer, petro-chemical, automotive, food processing, and many other sectors. Welding generally uses localized heating during common fusion welding processes (shielded metal arc, submerged arc, gas metal arc welding etc.) for melting the faying surfaces and filler metal. However, localized and differential heating & cooling experienced by the metal during welding makes it significantly different from other manufacturing techniques:
1) Residual stresses are induced in welded components (development of tensile residual stresses adversely affects the tensile and fatigue properties of work piece).
2) Simple shape components to be joined are partially melted.
3) Temperature of the base metal during welding in and around the weld varies as function of time.
4) Chemical, metallurgical and mechanical properties of the weld are generally anisotropic.
5) Process capabilities of the welding in terms of dimensional accuracy, precision and finish are poor.
6) Weld joints for critical applications generally need post weld treatment such as heat treatment or mechanical working to get desired properties or reline residual stress.
Advantages and Limitation of Welding as a Fabrication Technique :-
Welding is mainly used for the production of comparatively simple shape components. It is the process of joining the metallic components with or without application of heat, pressure and filler metal. Application of welding in fabrication offers many advantages, however; it suffers from few limitations also. Some of the advantage and limitations are given below.
Advantages of welding are enlisted below:
1. Permanent joint is produced, which becomes an integral part of work piece.
2. Joints can be stronger than the base metal if good quality filler metal is used.
3. Economical method of joining.
4. It is not restricted to the factory environment.
Disadvantages of welding are enlisted also below:-
1) Labour cost is high as only skilled welder can produce sound and quality weld joint.
2) It produces a permanent joint which in turn creates the problem in dissembling if of sub-component required.
3) Hazardous fumes and vapours are generated during welding. This demands proper ventilation of welding area.
Types of welding processes :-
1) Solid state welding processes.
2) Liquid state welding processes Liquid state welding processes.
3) Solid / liquid state bonding processes.
Gas Welding :-
In gas welding, the heat to produce fusion of the parent metal and filler rod is provided by burning a suitable gas in oxygen or air. A number of gases can be used but acetylene is the most popular, since it burns in oxygen and gives a high flame temperature of 3100o - 3200o. C. . . Oxygen and acetylene stored in cylinders under pressure are passed through flexible tubes to the torch, which is either hand-operated or mechanically manipulated. By adjusting the proportions of oxygen or acetylene the flame can be neutral, or have either reducing or oxidizing properties. For most materials a neutral flame is used but, for welding high carbon steel, or aluminium and its alloys an oxidizing flame is used as, by these means, the volatilization of the zinc is suppressed. The capital cost of oxyacetylene equipment is low compared with that for arc welding. The equipment is also easily portable and the process is very versatile. However, its comparative slowness means that it is more expensive than arc welding if there is a considerable amount of welding to be done.
Oxyacetylene welding requires the following equipment.
1) A cylinder of oxygen (full pressure about 15MPa).
2) A cylinder of acetylene (full pressure about 1,7).
3) Pressure regulator valves for each cylinder.
4) Hoses to transfer gas flow to torch.
5) Welding torch with various sizes of torch tips.
The gas pressures at the torch are each regulated to be about 7 to 70 KPA. Flame cutting using an oxyacetylene flame is a well-known engineering process. The cutting torch may be manually operated if low accuracy is permissible, or if higher accuracies are required, the torch is mechanically mounted and controlled numerically, or by using a tracer system. An outer oxyacetylene gas flame is used to preheat the metal to about 1000oC. An inner by a jet of oxygen is then rapidly initiated which oxidizes the red-hot metal, enabling thick sections to be cut. The cutting process is then progressed with both jets on.
Our Major Brands of Gas welding equipment are:
D.C & COMPANY Gas welding equipments