Shielded Metal Arc Welding, also known as Manual Metal Arc Welding (MMA) or more commonly as Stick Welding, is a type of welding that uses a filler rod or wire as one of its electrodes. The other electrode is usually supplied by a power source connected to the work-piece through a cable. In this method, the filler rod or wire is fed into the molten pool created during the welding operation. This technique has been used for decades and it’s still widely used today. It is also known as stick welding because the filler rod or wire resembles a wooden dowel.
This welding method involves creating an arc between the electrode and a work-piece, with the heat of the arc melting the electrode coating and forming a protective slag. The weld metal is created by the core electrode wire as well as iron powder in the coating. After welding, the slag layer on top of the joint must be removed.
During the process, the flux condenses into a gas that protects the electric arc that develops between the electrode and the metal being welded. This prevents contamination from ambient gases and makes Stick Welding as opposed to MIG (GMAW), acceptable for outdoor operations.
Shielded Metal Arc Welding Equipment
Shielded metal arc welding equipment typically consists of three main components: an electrical supply unit, an electrode holder welding cables and a grounding clamp. The electrical supply unit provides the necessary current and voltage to produce the welding arc.The electrode holder secures the electrode and transfers energy from the welding machine to the electrode. Finally, a torch directs the arc onto the work piece.
The SMAW power supply provides a constant current output, which ensures that the current (and hence the heat) remains reasonably constant
This is significant since the majority of SMAW applications are manual, requiring the user to hold the torch. Sustaining a suitable continuous arc distance is challenging if a constant voltage power source is utilised instead, as this might generate extreme heat changes, making welding more challenging.
Because the current is not kept perfectly constant, expert welders executing complex welds can adjust the arc length to generate slight variations in the current.
Types Of Shielded Metal Arc Welders
There are two types of shielded metal arc welder: stick and automatic. Stick welders require manual feeding of the electrode and have no moving parts. Automatic welders use an automated feeder to position the electrode and control the welding parameters.
There are two types of cable required the Electrode Cable and the Massa Cable.
The electrode cable links the welding machine’s electricity to the electrode used to weld the base metal. The massa cable role is tp connect current from the machine to the base metal; when the base metal and electrode come into contact, the welding process begins.
Stick Welder Types
Stick welders come in different sizes, shapes and styles. Some common models include:
Single stick welders — These welders allow you to weld only one side at a time. They’re most often used for small jobs.
Double stick welders — Also called double-stick welders, these machines offer greater flexibility when compared to single stick welders. You can weld both sides simultaneously, making them ideal for larger projects.
Side stick welders — These are similar to double stick welders but they feature a longer handle so you don’t need to bend over while welding.
Stick Welding (Shielded Metal Arc Welding) Process
Stick welding is primarily used to weld iron and steels. It is also the most common form of welding used. It is also can be used to weld high-strength steels, hard-facing alloys, bronze, cast iron and aluminium.
Electrodes can be powered by both AC and DC sources. Not every DC electrode can be used with AC power sources, however AC electrodes can be used with either AC or DC power sources.
The size of the electrode determines the welding current level; manufacturers propose the usual working range and current. An electrode will require around 40A per mm as a rule of thumb for determining an acceptable current level (diameter). As a result, while 160A is the recommended current level for a 4mm diameter electrode, the permissible working range is 140 to 180A.
Reverse polarity is nearly always employed in Stick welding techniques. It aids in providing the optimum bead profile and penetration, as well as reducing excessive spatter, which are beads of liquid metal produced at or near the welding arc.
The stick welding process employs a step-down transformer and a rectifier to convert alternating power to direct current. The major rationale for employing the transformer is to enhance the current while simultaneously lowering the high voltage. An inverter and multiple coils are common types of devices used for this purpose. The coil alters the current by changing the number of turns in the coil or the spacing in between two coils. Inverters are portable and can alter current parameters quickly.
The Weld – Shielded Metal Arc Welding
An electric arc is generated between the metal and the electrode with the assistance of an electric current to connect the metal. The welding power source provides this electric current, which might be alternating or direct current.
Following the welding of a work-piece, a small pool of molten metal is created. As the weld cools a strong joint is formed between the two pieces of metal.
During the weld, the flux coating on the electrode will emit gases that act as a shielding gas and slag layer. The production of this shielding gas and slag layer protects the weld region from atmospheric gases such as nitrogen and oxygen.
To create an electric arc, an electrode is first brought into contact with the work-piece. The electrode then need to be drawn back gently and this drawing back creates the arc and transfer small amounts of electrode to the welding region or work-piece surface.
During the welding process, the welder must be conscious of the need to change the electrode on a frequent basis and to insert a new electrode carefully. The speed of the weld is determined by the welder’s abilities, electrode type, and most importantly, welding location.
Stick Welding Safety (SMAW)
If necessary measures are not followed, Stick Welding, like other welding processes, can be an extremely dangerous and harmful operation. The procedure employs an open electric arc, which increases the danger of burns.and electrocution.
In order to protect against these dangers, it is important to follow safety procedures when performing stick welding. These include:
- Using only approved electrodes
- Ensuring that all equipment is grounded before use
- Using the correct welding technique
- Preventing access to live parts during welding
- Avoiding exposure to sparks
- Keeping hands away from the welding area
- Always wearing protective clothing
- Notifying your employer about any health conditions you may have
In addition welding helmets with dark viewing windows should always be worn to protect against this exposure to the significant volumes of UV radiation that can be created during the weld.
Translucent welding curtains should also be employed to shield an spectators, especially in industrial settings. These curtains, constructed of polyvinyl chloride plastic film and protect any surrounding people from UV radiation generated by the electric arc, however these curtains should never be used to substitute the filter glass in helmets of the welder.
Advantages and Disadvantages Stick Welding:
There are various advantages and disadvantages to using the Stick welding process
Advantages Stick Welding (SMAW)
- Can be used to weld any sort of connection.
- Stick welding (SMAW) allows for the utilisation of all welding positions.
- We don’t need gas to protect the molten weld metal.
- The tools used in Stick Welding are lightweight and inexpensive.
- There isn’t much prep work required before welding.
Disadvantages Stick Welding (SMAW)
- After the welding operation is completed, you have to clear the slag.
- There tends to be a few splatters.
- Only ten to fifteen centimetres of weld metal may be produced by a single electrode.
- Can be a slower process than other types of welding because of the need to change the electrode.
- It is not an automated process, its productivity is lower than that of other welding techniques.
- Stick welding cannot be used on reactive metals such as zirconium and titanium.
I’ve been involved in the welding industry for over twenty years. I trained in various engineering shops working on various projects from small fabrication and repairs through to industrial projects.I specialize in welding aluminum and food grade stainless steel and an now run an engineering shop fabricating equipment for the food industry.