Welding Processes

Welding provides joining of metals, their alloys, plastics and other materials. All types of welding may be divided into 3 groups:

• pressure welding;

• fusion welding;

• fusion-pressure welding.

Among the main types of welding we can mention hammer welding in which two metal pieces are joined and forced together by force from hammer; thermit welding which includes a chemical reaction obtained by igniting finely divided aluminium and iron oxide; electric welding utilizing the heat of electric current for heating metal parts; gas welding in which the source of heat is the gas flame obtained from a gas (acetylene).

Now we are going to dwell upon some welding processes most widely used in modern industry.

Resistance welding (RW). One of the main parameters of RW is the contact resistance at the interface of the surfaces to be joined. The most widely spread kind of RW is spot welding. Typically, there are between 3000 and 4000 spot welds in every passenger vehicle.

Friction welding (FSW – friction stir welding) provides forged bonds between similar and dissimilar materials. It’s suitable for such products where one component to be welded can be rotated at high speed before making contacts with other part.

Tungsten inert gas (TIG) welding process is a simple easy maintained process. The 60000 to 80000F (33150 to 44270C) arc provides a concentrated heat source to melt the edges of the parts and fuse them together without a flux or added material. The high concentration of heat in the TIG arc permits joining metals very close to heat affected zone (HAZ).

Metal-arc inert gas (MIG) welding is usually chosen for joining heavier sections in which filler metal is added because of its higher strength, speed and economy.

Gas tungsten arc (GTA) and gas metal arc (GMA) processes are widely used for welding aluminium.

Laser beam welding (LBW) is used in construction for ease of assembly, economy of machining operations before and after welding, structural strength, easy inspection of the joint or other purposes. The joint must be accessible for the focused laser beam.

Plasma arc welding utilizes a stable unidirectional high intensity plasma jet as the heat source. It offers a number of advantages over the TIG process from which it was developed:

1) the ability to weld at high speeds;

2) reduced joint preparation and filler metal consumption;

3) elimination of tungsten inclusions.

Language study

1. Make nouns from the verbs:

to weld, to join, to alloy, to fuse, to press, to machine, to heat, to resist, to fill, to rotate, to replace, to produce, to manufacture, to cost, to construct, to vary, to coat, to result, to prepare, to consume, to eliminate, to react, to inspect.

2. Combine the following words to receive proper terms:

added fillet weld spot plasma sheet laser heat filler welding

speed alloy source beam steel arc welding face weld material

3. Fill in the gaps using the following words: advantages, aluminium, electric, flux, friction, fuses, hammer, joining, melts, resistance, welding.

1. Welding provides … of metals.

2. All types of … may be divided into 3 groups.

3. In … welding two metal pieces are joined by force from hammer.

4. In … welding the heat of electric current is used to heat metal parts.

5. The most widespread kind of … welding is spot welding.

6. … welding is suitable for such products where one component can be rotated.

7. A concentrated heat source … the edges of the parts and … them.

8. TIG arc permits joining metals without a … or added material.

9. GTA and GMA processes are used to weld … .

10. Plasma arc welding offers a number of … over the TIG processes.