Basic Welding : Manual Metal Arc Welding

Manual Metal Arc Welding
Overview: Perhaps the most primitive of welding processes, this process involves a metal rod with flux coating to give a protective gas shield. When an arc is struck between the metal rod (electrode) and the work piece, both the rod and work piece surface melt to form a weld pool. Simultaneous melting of the flux coating on the rod forms gas and slag which protects the weld pool from the surrounding atmosphere. The slag solidifies and cools and must be chipped off the weld bead once the weld run is complete (or before the next weld pass is deposited).

The process allows only short lengths of weld to be produced before a new electrode needs to be inserted in the holder. Weld penetration is low and the quality of the weld deposit is highly dependent on the skill of the welder.

Applications of MMA Welding: Due to the simplicity of apparatus, this process is widely used for welding applications in difficult locations, like at heights or where the joint is in abnormal welding position. This process is normally used where the weld metal deposition is less than 20Kg. If the deposition is more than 20 Kg, MMA will be used only if automated processes like MIG / SAW cannot be utilized.

Hazards in MMA Welding: The following hazards are common for MMA process:

a) Welders’ Eye or Arc Eye: This normally happens dues to accidental or inadvertent eye contact with the welding arc. Operators & people in close vicinity of the weld process must wear suitable glasses to safeguard from this hazard.

b) Fumes: The flux coating on the electrodes create gas fumes that protect the weld pool from environmental hydrogen. However these fumes are harmful to the health of the welder. Sufficient air draft has to be provided such that while the fumes protect the weld pool, they do not come in the respiratory zone of the welder.

c) Electric Shock: This may be caused due to improper welding cable connections, improper grounding of workpiece, damaged insulations of power cables etc. thw welder has to check for these points, every time he starts a fresh job, to safeguard against this hazard.

d) Burns: This happens due to contact with hot metal surfaces, contact with flying weld spatters, contact with molten slag etc. Welders must use appropriate clothing, gloves & guards so as to prevent burn injuries.

e) Fire: Since the process involves a naked arc & flying spatters, a danger of fire is always present. There shall be no flammable articles near the welding process. Also the welder has to be cautious enough to see where the spatters & electrode stubs are falling so as to prevent occurrence of a fire.

f) Fall: When working at heights, the falling hazard is eminent. Relevant fall arrestors have to be worn, if proper platform cannot be provided.

What is fabrication ?

What is Fabrication ?

The definition of the word “Fabrication”, as per the Oxford Dictionary is “ to construct or manufacture an industrial equipment”. That is the simplest way to define fabrication for industry.

A fabrication engineer will put to use a variety of processes in his armoury to construct an equipment as desired by his customer. Even as the fabrication technology has developed considerably over past 2 decades, the basic processes involved in fabrication of equipment remain the same.

The core processes involved in fabrication are Gas Cutting, Plasma Cutting, Welding, Plate bending & rolling, Hot / Cold Forming, grinding, heat treatment, surface treatment & coating. This list is however only indicative. Each of these processes has many variants. Also this list is not exhaustive. There are a lot of support processes in fabrication which may not be termed as core processes though. It can be noted that there is huge element of human involvement in these processes. A workshop that carries out such processes will normally be termed a fabrication shop or fab shop for short. A fab shop will typically employ fitters (some times called fabricators), welders and grinders (small tool operators).

However, machining processes too are integral part of construction of equipments. In industry these processes are collectively termed as machining. It may include operations like turning, milling, drilling, tapping, thread whirling. Machines used may vary from simple lathes & ,milling machines to sophisticated CNC machines.

While customers will normally refer to their equipment manufacturer as fabricator, the manufacturer may have distinct shops for fabrication and machining.

Therefore hereon I will be refering manufacturer as fabricator, shop that builds an equipment by manual / semi-automatic processes mentioned above as fab shop and shop that carries out major machining operations as machine shop.

I will be discussing each of the core fabrication processes to the details that I have in my limited knowledge, in future posts.