To compare two welding processes, use the same points for both, such as heat source, protection of the molten metal and hazards, and give a reason for each difference. This page covers theory only and has no welding procedure.
This lesson is part of SPM subjects and learning resources. The comparison below is original and based on classroom-style diagrams.
What terms should be clear first?
Workpiece, joint, filler metal, molten pool, flux and shielding are the terms you need for most comparisons. Your answer is only as clear as your terms.
Write one line for each, for example: the molten pool is the small region of melted metal where the joint is formed.
Worked example: arc and gas welding
An original classroom-style diagram shows an electric arc between an electrode and a plate on one side, and a torch flame on a plate on the other side.
| Point | Arc welding | Gas welding |
|---|---|---|
| Heat source | Electric arc between electrode and workpiece | Flame from a fuel gas burning with oxygen |
| How heat is applied | Concentrated at the point of the arc | Spread over a wider area by the flame |
| Protection of molten metal | Flux coating or a shielding gas limits contact with air | The flame envelope partly shields the molten pool |
| Filler metal | Often supplied by the electrode itself | Added separately as a filler rod |
| Main hazards | Intense light, sparks, electric shock | Fire, gas cylinders, flame |
A sample conclusion: “Arc welding concentrates heat at one point, so it suits joining thicker plates, while the wider flame of gas welding gives gentler heating for thinner sections.”
The mistake that loses marks
A weak answer says: “Arc welding uses electricity and gas welding uses gas, and both join metals.” It is true, but too thin to earn the comparison marks.
A stronger answer compares along a shared point and explains the effect. “Because the arc is concentrated, less of the surrounding metal is heated” is a principle, not a label.
Principles behind both processes
Both processes melt the edges of the joint so the metal can fuse, and both usually add filler metal. Both must protect the molten pool and let it cool into a sound joint.
Write the shared principle once, then the differences. This shows that you understand the topic as a whole.
Why procedures are left to the workshop
Welding involves extreme heat, intense light, fumes and electrical or gas hazards. The steps, settings and protective equipment are learned at school, with a teacher watching.
A written answer explains why a safety rule exists, for example why eye protection is needed against the arc’s light. It does not describe how to weld.
Check yourself
Give two reasons why molten metal needs protection from air, and name one way each process provides it.
Answer
Hot molten metal reacts with oxygen and nitrogen in the air, which can form oxides and gas pockets, so the joint may be weak or porous. Arc welding provides protection with a flux coating or a shielding gas, while gas welding relies partly on the flame envelope.
A careful answer states the principle first, then names the method for each process.
What to study next
Test your comparisons with the structured-answer self-review tool. It checks that you used the same points for both processes and gave a reason for each difference.
If you want a teacher to go through your theory answers with you, see online one-to-one Arc and Gas Welding tuition or the one-hour trial class (from RM50). Welding practice stays with your school.