Interview questions on Welding Technology For Mechanical Students

In this article we wills see frequently asked questions related to welding while interview for mechanical Engineering Students and Welding related job posts.

1.What is Difference Between TIG and MIG ?

While Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG) are both shielded arc welding applications, they are very different from one another. MIG welds are created with a consumable electrode, while TIG welds are created with a non-consumable electrode. TIG welding typically includes filler metal as well.

TIG and MIG arc welding can both be automated. However, TIG is a more complicated process so the equipment is more expensive and difficult to set-up.

2 . Why carbon dioxide is used as a shielding gas as it dissociates during welding and may contaminate the weld?

Carbon dioxide has similar penetration characterstic as helium and is much cheaper when compared to inert gases. It is used in welding of ferrous metals only, mainly carbon steel( mild steel).

Due to arc heat co2 disassociate into carbon monoxide and oxygen. The oxygen is released in small quantities and it’s strength may vary a bit and co is released into atmosphere which is hazardous to the welder. Hence co2 has it’s advantages and disadvantages

3. How does seam welding is differ from spot welding?

Spot Welding

Spot welding is most often used to connect metal parts that are usually around 3 mm thick. The material to be welded is put between two copper electrodes. Electric current flows through the material to weld the two metals while pressure on them is maintained.

Seam Welding

Seam welding is more complicated than spot welding. Two copper wheels replace the electrodes present in spot welding. The wheels create seams along two pieces of metal that bind them together. Seam welding is used to make items such as fuel tanks.

Seam & Spot Welding comes under resistance welding .The principle of operation is based on the joules law H= I^2Rt. The principal of operation remains same for both spot & seam welding but the method of application differentiates each other.

4. What is fusion welding?

In case of fusion welding the metal to be welded, is heated up to molten state and re solidification results in completion of the weld. Examples: Arc welding, Gas welding, TIG welding, MIG welding etc.

5. What is GTAW welding?

GTAW is an abbreviation of Gas Tungsten Arc Welding. It is a type of arc welding in which the non consumable tungsten electrode is used.
The gas is used for shielding welding from atmosphere.the gas mostly used for this purpose is either argon or helium which are chemically inert.
There is no need for filler metal for welding thin materials but additional filler material used for welding thick plates.
Mostly pure tungsten is used as electrode because it has high melting point(3422 degree Celsius) .But for some cases the electrode contain 1 to 2% thorium this electrode is known as thoriated Tungsten electrode this electrode is manitain the arc stable.

6. What are the main factors affecting the welding design?

Several factors affect the design of any weldment or any welding process, to be rather specific.

These include:
1. The material going to be welded. In this context, several other interlinked issues also come into play, like, is it going to a weld between similar materials, are they homogeneous etc.

2. Nature of the process: like RSW, FSW, Manual Metal Arc, MIG etc.

3. Dimensions of the workpiece

4. Length of the weldment etc.

5. Will filler materials be used?

6. The orientation of the joint: Overhead or vertical or transverse?

7. What are the different reasons for welding defects?

Most weld defects are the welders fault at the end of the day, and I would say almost all weld defects are from inexperience. Things like being able to control:

undercut (incorrect amp settings/rod angle or inclination)

porosity (dirty base metal/too long of an arc/environmental factors like wind)

cold lapping/lack of fusion (not keeping the arc on the leading edge of the puddle with MIG. Or not maintaining the proper arc length with stick)

Incomplete penetration (caused by improper fit up, too tight of a gap. Or too low of an amp setting

Slag inclusion (trying to fill too much at once, or weaving a bead too wide, not maintaining proper arc length)

All of these problems (especially improper fit up) will go away as you learn and grow in the trade. And with enough experience most defects can be avoided. The most important things to keep in mind are rod angle/inclination, good gap/fit, and proper settings.

8. What is the difference between SMAW and MIG?

SMAW means Shieled Metal Arc Welding and MIG means Metal Inert Gas welding .

In SMAW flux cored electrode is used for welding and when arc generates , gases generated by burning of flux protects Arc of the welding and

In MIG Inert gas is flowed around the arc generated by bare electrode of same as metal being welded. Inert gases are like argon and helium is used for shielding .

9. What do you mean by cold welding?

Cold welding or contact welding is a solid-state welding process in which joining takes place without fusion/heating at the interface of the two parts to be welded. Unlike in the fusion-welding processes, no liquid or molten phase is present in the joint.

Cold welding was first recognized as a general materials phenomenon in the 1940s. It was then discovered that two clean, flat surfaces of similar metal would strongly adhere if brought into contact under vacuum. Newly discovered micro- and nano-scale cold welding has already shown great potential in the latest nanofabrication processes.

10. What is the meaning of slag when welding?

Its is the combo of carbonate and silicate material, when the heat produces and reaches to the weld zone then slag formed in flux and produce gases that push it back , preventing purpose.