There are several welding processes available that help us to fuse parts together to create a joint. Some processes are complicated, and only skilled welders can perform them to achieve perfection. Other processes are rather simple and mark as a starting point for beginners. The Shielded Metal Arc or SMAW Welding falls under the simple welding process, and it is one of the most popular welding techniques used all around the world. In this article, we will have a comprehensive look at SMAW welding process. We will see how SMAW works, its applications, advantages, and limitations.
What is SMAW Welding (Stick Welding)?
Shielded Metal Arc Welding (SMAW) is the most common arc welding process worldwide, in use since the early 20th century. Commonly known as Manual Metal Arc welding (MMA) or Stick Electrode Welding, SMAW uses a covered electrode for welding. It is the most versatile
welding method that can be used to weld most materials in a wide range of thicknesses and in all welding positions.
This process requires no external shielding gas, making it convenient and versatile. The electrode rods have a wire core with an external coating containing chemicals, minerals, and iron powder. Manufacturers produce the electrode covering through extrusion and baking processes, offering various core diameters for specific current ranges.
The primary function of the electrode covering is to decompose under arc heat, forming a CO2 shielding gas. This gas protects the weld joint as it solidifies and cools from atmospheric contamination and makes it highly durable.
During welding, an arc strikes between the electrode and workpiece, melting the electrode coating. This melting forms a protective slag that floats to the top of the weld puddle and solidifies. The weld metal comes from both the core electrode wire and the iron powder in the coating. After welding, one must remove the slag layer from the joint.
SMAW is mostly a manual process that offers greater versatility compared to other arc welding processes like Gas Metal Arc Welding (GMAW) and Submerged Arc Welding. While these processes may have higher productivity, SMAW’s adaptability suits both shop and field fabrication.
Additionally, the power supplies and other equipment needed for SMAW are relatively minimal, inexpensive, portable, and robust making it is one of the most popular welding processes to date.
The welder has more control over the process starting from dimensions of weld bead, penetration of weld as well as spatter quantity. Moreover, SMAW is inexpensive in comparison to other welding processes such as MIG and TIG.
Principle of Operation of SMAW
The heart of the SMAW process is the power source, which supplies continuous and steady electrical current. This power source can be an AC supply (a transformer) or a DC supply (transformer-rectifier or a generator). Two cables extend from the power source’s output terminals: one is the ground cable, and the other is the welding cable. The ground cable attaches to the workpiece with an earth-clamp, while the welding cable connects to the electrode holder.
To start welding, the welder fixes the bare end of a flux-coated electrode into the holder. Next, they strike an arc by touching or scratching the workpiece with the electrode’s arc-striking end. Then, the welder withdraws the electrode slightly to maintain a short arc. The arc’s heat consumes the electrode, converting it into weld metal and slag. The welder manually guides the electrode, controlling its direction and arc travel speed. They skillfully feed the electrode into the workpiece to maintain a steady arc length. To end the operation, the welder withdraws the electrode suddenly, breaking the arc.
How SMAW Works?
SMAW needs minimum investment behind equipment requirements. The following is a complete illustration of the working of SMAW.
Process
As stated earlier, the electric arc generates enough heat to melt the base metal and the top of the electrode. The welder has to set up an electric circuit consisting of the power source, an electrode holder with electrode, workpiece, the welding cable, and the ground clamp. The power source should have a connection to both the electrode and the workpiece.
As soon as the electricity starts flowing, an electric arm forms between the electrode and the workpiece. This starts generating heat, and the temperature can reach higher than 9000-degree Fahrenheit. This heat melts the surface of the workpiece as well as the tip of the electrode. Then the filler material is deposited with electrode melting.
Voltage Variation
The voltage needs to be varied in SMAW welding in order to control the width and height of the weld deposit. It is true that there are some welding processes where you can maintain a present voltage throughout the process. In SMAW, the welder can regulate voltage manually, and he needs to move the stick close or farther from work for the temperature regulation.
Welding Current
The power supply in SMAW has constant current output, which means it stays constant throughout the process (more or less). Therefore, the welders do not have to bother about current regulation, instead, they have to focus more on voltage regulation for perfect welding.
Polarity
In the SMAW process, reverse polarity (DCEP – DC Electrode Positive) is commonly used. There are various advantages of using reverse polarity. It ensures that you get the desired bead profile and penetration. Most importantly, it reduces the droplet deposition of molten material near the welding arc.
Components
- Welding machine containing arc power source
- An electrode with appropriate flux covering
- An electrode holder
- Adequate welding cables and connectors
- A workpiece (base metal)
- Ground clamp
Apart from these, the welder must-have safety equipment, starting from helmets and goggles to gloves and safety clothes.
SMAW Electrodes (Sticks)
SMAW electrodes come in various types to meet diverse requirements. The wire core coating contains finely powdered chemicals and minerals held by a binder. This coating performs crucial functions, including protecting metal droplets and the weld pool from air reactions. The molten slag and emitted gases provide this protection.
Furthermore, the coating containing substances like titanium, zirconium, and magnesium, stabilizes the arc. These arc-stabilizing elements prevent excessive spatter and arc extinguishing, especially with AC welding. Additionally, the coating shapes the weld surface and facilitates slag removal, using tools like a chipping hammer or wire brush.
Moreover, the coating, often containing iron powder to improve efficiency, applies alloying and anti-oxidizing substances to the weld pool. It also ensures sufficient penetration into the base material, releasing hot gases from carbonates or cellulose compounds.
Types of SMAW Electrodes
Electrodes classify into three main types based on flux covering: cellulosic, rutile, and basic. Cellulosic electrodes have high cellulose content, providing excellent penetration and hydrogen content in the arc. These electrodes suit welding oil or natural gas pipelines in any position.
Rutile electrodes contain 25-45% rutile (TiO2), making them easy to strike and use. They produce neat welds with easily removable slag but introduce higher hydrogen content, limiting use to specific carbon steel types. These electrodes are ideal for standard structural and shipbuilding steel.
Basic electrodes feature calcium fluoride (CaF2) in their coating, resulting in strong, tough welds with low sulfur and oxygen content. They offer high resistance to hot cracking and low hydrogen content, suiting positional welding. However, they produce coarser weld surfaces and require dry storage conditions. Typical applications include structural, shipbuilding, and pressure-vessel steel.
What are the Applications of SMAW?
SMAW welding finds its application in a variety of metals, starting from ductile and cast iron to carbon steel to welding stainless steel. Among the non-ferrous metal, SMAW is suitable for nickel and copper.
Apart from direct metal, the process is applicable to alloys. SMAW is inexpensive, and the equipment is easily transportable. Welders can weld any part in indoor as well as outdoor environments. As far as industrial applications go, SMAW is quite regularly used in
- Mining and pipeline projects
- Shipbuilding and marine projects
- Machinery manufacturing industry
- Steel fabrication and structural welding works
- Nuclear and aerospace projects
- Construction industry
- Locomotive and defense industry
Advantages of SMAW
- Total Control: A welder can easily control the following parameters using SMAW, which are not possible with other welding processes at once.
- The size of the electrode to control the amount of deposition.
- Type of electrode to get desired property after welding.
- Electrode angle to control the penetration level.
- Speed of travel for deposition speed.
- Weld width, amperage, arc length, and polarity.
- Simple: Among all the other welding processes, SMAW is the simplest process to set up and operate. There is no requirement for extremely high skills and experience initially, though they are essential for perfection.
- Low Cost: SMAW has the lowest cost requirement for setting up the equipment in comparison to all other welding methods. To put it in percentage, it costs near 40%-50% less in equipment costing.
- Portable: SMAW equipment is lightweight and hence, easy to transport. The welder can work on it in any place and environment.
- Positional Variety: A welder can do SMAW arc welding in any position he wants to, which is not possible in other welding methods. Starting from flat and vertical position to horizontal and overhead position, all possibilities are there. It is also one of the reasons for its versatile application.
- Less Requirements: There is no need for shielding gas during the process. The process is not sensitive to air, and hence, no special arrangement is required.
- Alternate Power Supply: While almost all other welding processes cannot run without electricity, SMAW can run on gasoline and diesel. Therefore, it is applicable in those remote areas where electricity is not available.
Disadvantages of SMAW
- Low Productivity Rate: Since the entire SMAW process is manual, the productivity level is low, unlike other welding processes that are either semi-automatic or automatic. Therefore, the deposition per unit time is going to be lower.
- Cleanup: Splatter formation is higher in SMAW than in other welding processes. Hence, you have to spend some time cleaning up the slag and splatter after the welding process is over.
- Heat and Spark: SMAW produces more heat and spark than other welding processes. Since the process is manual, the welder is subjected to harmful gases and particles.
- Welding Halts: If the welding needs thicker deposition and the welding area is long, one needs to halt welding in between to replace the electrode when it reaches the last 2 inches. If the halts are long, the welding will not be uniform and there could be issues in the welded part in the future.
Frequently Asked Questions
SMAW is referred to as stick welding due to the presence of a stick or metal rod at the core of the electrode.
In Gas Metal Arc Welding(GMAW), the arc is formed between the base metal and a wire electrode. It relies on external shielding gas for protection against contamination. In SMAW, the flex-covered electrode produces the shielding gas when melted and hence, no external requirement.
On the other hand, GMAW uses a wire electrode that can be fed automatically without halting the process. In SMAW, the welder may need to halt the process in order to replace the electrode.
This is because it involves 6 steps precisely, and they are:
- Preparation of the base metal and electrode.
- Taking safety precautions rigorously as the process is manual.
- Setting up the machine and forming the circuit with components.
- Striking the arc and control the variables.
- Start welding the beads and finish the process as required.
- Remove the slag and splatter and get the finished product.
Conclusion
There is no doubt that SMAW is the most popular welding method, especially for ferrous metals and alloys. Even though the process is simple, it takes considerable skill and experience to achieve perfection consistently. Always remember to take safety precautions as the entire process is manual and involved a considerable amount of risk when distracted during the process.
