What is MMA in a welding machine?

Dec. 02, 2024

Manual Metal Arc Welding (MMA, SMAW or Stick Welding) - TWI

Manual metal arc welding (MMA or MMAW), also known as shielded metal arc welding (SMAW), flux shielded arc welding or stick welding, is a process where the arc is struck between an electrode flux coated metal rod and the work piece. Both the rod and the surface of the work piece melt to create a weld.

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Manual metal arc welding was first invented in Russia in . It involved a bare metal rod with no flux coating to give a protective gas shield. The development of coated electrodes did not occur until the early s when the Kjellberg process was invented in Sweden and the Quasi-arc method was introduced in the UK. It is worth noting that coated electrodes were slow to be adopted because of their high cost. However, it was inevitable that as the demand for sound welds grew, manual metal arc became synonymous with coated electrodes. When an arc is struck between the metal rod (electrode) and the workpiece, both the rod and workpiece surface melt to form a weld pool of molten metal. Simultaneous melting of the flux coating on the rod will form gas and slag which protects the weld pool from the surrounding atmosphere. The slag will solidify and cool 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 welding electrode holder. Weld penetration is low and the quality of the finished weld deposit is highly dependent on the skill of the welder.

Types of flux/electrodes

To strike an arc between the electrode and base metal, such as carbon steel, and to produce a good quality weld, a stick welder must ensure that their welding machines are fitted with suitable electrodes. Arc stability, depth of penetration, metal deposition rate and positional capability are greatly influenced by the chemical composition of the flux coating on the electrode. Electrodes can be divided into three main groups:

Cellulosic
Rutile
Basic

Cellulosic electrodes contain a high proportion of cellulose in the coating and are characterised by a deeply penetrating arc and a rapid burn-off rate giving high welding speeds. Weld deposit can be coarse and with fluid slag, deslagging can be difficult. These electrodes are easy to use in any position and are noted for their use in the 'stovepipe' welding technique.

Features:

deep penetration in all positions
suitability for vertical down welding
reasonably good mechanical properties
high level of hydrogen generated - risk of cracking in the heat affected zone (HAZ)

Rutile electrodes contain a high proportion of titanium oxide (rutile) in the coating. Titanium oxide promotes easy arc ignition, smooth arc operation and low spatter. These electrodes are general purpose electrodes with good welding properties. They can be used with AC and DC power sources and in all positions. The electrodes are especially suitable for welding fillet joints in the horizontal/vertical (H/V) position.

Features:

moderate weld metal mechanical properties, such as tensile strength
good bead profile produced through the viscous slag
positional welding possible with a fluid slag (containing fluoride)
easily removable slag

Basic electrodes contain a high proportion of calcium carbonate (limestone) and calcium fluoride (fluorspar) in the coating. This makes their slag coating more fluid than rutile coatings - this is also fast-freezing which assists welding in the vertical and overhead position. These electrodes are used for welding medium and heavy section fabrications where higher weld quality, good mechanical properties and resistance to cracking (due to high restraint) are required.

Features:

low hydrogen weld metal
requires high welding currents/speeds
poor bead profile (convex and coarse surface profile)
slag removal difficult

Metal powder electrodes contain an addition of metal powder to the flux coating to increase the maximum permissible welding current level. Thus, for a given electrode size, the metal deposition rate and efficiency (percentage of the metal deposited) are increased compared with an electrode containing no iron powder in the coating. The slag is normally easily removed. Iron powder electrodes are mainly used in the flat and H/V positions to take advantage of the higher deposition rates. Efficiencies as high as 130 to 140% can be achieved for rutile and basic electrodes without marked deterioration of the arcing characteristics but the arc tends to be less forceful which reduces bead penetration.

If you are looking for more details, kindly visit mma 500 welding machine.

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Electrodes can be operated with AC and DC power supplies. Not all DC electrodes can be operated on AC power sources, however AC electrodes may be used on either AC or DC.

Welding current

MMA Welding: What You Need to Know | HARtech

Welding is vital to many industries, from skyscraper construction to car manufacturing. And among the various welding techniques available, MMA welding or Manual Metal Arc Welding stands out for its versatility and efficiency.

Join us as our industrial welding professionals in Quebec present MMA welding (also called stick welding), explaining how it works, its benefits, and why it remains the technique of choice for professionals and hobbyists worldwide.

MMA welding definition

Welding dates back to ancient times, and welding techniques have been constantly refined and adapted over the centuries according to the changing needs of industry. MMA welding occupies a prominent place among the many welding techniques that exist today.

MMA stands for 'Manual Metal Arc'. As the name suggests, this is a manual welding technique that relies on an electric arc to fuse metals. 'Manual' refers to the fact that the welder will guide the electrode by hand, 'Metal' refers to the base material used, and 'Arc' refers to the electrical phenomenon that generates the heat required to fuse the metals.

Examples of MMA welding projects

Pipeline construction: MMA welding is often used to join sections of pipe with watertight, pressure-resistant welds.
Agricultural machinery repair: Agricultural equipment is often subjected to hard use. MMA welding is a good choice for repairing these tools, as it produces exceptionally sturdy welds.
Metal furniture manufacturing: MMA welding is used to create sturdy, attractive furniture or every kind, from chairs to tables.
Shipbuilding: In shipyards, trained professionals use MMA welding to join large sections of ship hulls and other marine structures.

How does MMA welding work?

MMA stick welding involves a symphony of elements working in concert to create a strong metallic bond. To really understand how it works, let's break down the process, step by step.

Creating the arc

It all starts with the electric arc. When the electrode is brought close to the workpiece and a current is applied, it creates a nearly complete circuit. By moving the electrode slightly away from the workpiece, a gap is formed, where the electric arc appears. This spark generates a tremendous amount of heat, which melts the metal on contact.

Role of the coated electrode

The electrode plays a dual role in this process. First, it acts as a conduit for the current, allowing the electric arc to form. Second, as it melts, it provides the filler metal needed to form the weld. But that's not all: the electrode coating is crucial. As it melts, it generates gases that surround the weld zone, creating a protective atmosphere. This contributes to the formation of a layer of slag on the weld, which can be removed after cooling.

Protection against oxidation and contamination

It is important to protect the weld, otherwise the molten metal will be exposed to oxygen in the air, which could lead to rapid oxidation and compromise weld quality. Other airborne contaminants, such as nitrogen, can also affect the weld. The protective atmosphere generated by the electrode coating prevents these harmful elements from coming into contact with the molten metal, ensuring a clean, strong and long-lasting weld.

Advantages of MMA welding

Despite the emergence of new welding technologies and techniques (such as MIG/MAG welding and laser welding), MMA welding remains a preferred choice for many professionals. But what makes this process so attractive? Here are some of the major advantages of MMA welding.

Versatility

One of the major advantages of MMA welding is its versatility. It can be used on a variety of metals, from common steels to more specialized alloys. Whether you're working on mild steel, stainless steel, cast iron or even aluminum, MMA welding will do the job well. If you need help with projects that involve working with different types of materials, contact us!

For more information, please visit builders warehouse welding machine.

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