Shielded metal arc welding or SMAW is one of the most common welding methods. It is also among the earliest welding techniques to be ever developed.
Since simple equipment is used in shielded metal arc welding, it is fairly uncomplicated. Unlike TIG welding and other advanced welding methods, SMAW welding is not too hard to learn, thereby making it a good starting point for beginners.
Here, you will learn about different tips and tricks to master the art of SMAW welding.
Shielded metal arc welding also goes by different names like manual metal arc welding (MMAW), flux shielded arc welding and stick welding.
What Is Shielded Metal Arc Welding?
SMAW welding is a welding technique in which a flux covered electrode helps create a welded joint. Simply put, filler material melts to form a weld pool, which solidifies to join previously separate metal sections.
The filler material is melted by means of an electric arc. The arc is created between a metal workpiece and the consumable electrode by means of the stick welding machine, which is connected to an electrical outlet to generate DC or AC current. The AC or DC current generated by the welding machine appears in the form of an arc between the electrode and base metal. Often, the DC current provides the best welding characteristics.
The arc melts both the consumable electrode and the base metal that is being welded. The weld pool thus created is made up of molten metal. Most of the molten filler material is provided by the electrode.
As you move the electrode steadily along the surface of the base metal, a uniform layer of metal deposit called a bead is formed.
The heat generated by the arc converts the flux material into a protective gas layer, which shields the weld pool against corrosion and contamination by the atmosphere. This protective gas layer is necessary since it ensures a defect-free weld joint that is strong and reliable. As a result, a separate gas tank is not needed to supply shielding gas to protect the weld pool. In the absence of a suitable gas layer, welds tend to be weak, defective and brittle.
The molten weld pool slowly solidifies to create a solid weld joint that firmly connects separate metal sections with each other. A slag layer is also developed during this welding process. This layer has to be chipped off when it solidifies. Due to this chipping requirement, SMAW welding is more time-consuming as compared to other types of welding procedures. However, you can speed up this process by selecting a suitable electrode.
SMAW welding is most often employed for iron and steel parts. However, it is also used to some extent for aluminum and various metals.
Stick Welding Advantages
- Works well in windy and rainy conditions.
- Shielded metal arc welding equipment is inexpensive.
- No external shielding gas is required since the flux provides the protective gaseous layer – this makes stick welding cost- effective.
- Compared to other welding techniques, stick welding is less severely affected by dirt, corrosion and paint – this can save pre-welding cleaning time.
- You can change rods easily for various metals.
- You can attach the ground clamp at a considerable distance from the welding area.
Stick Welding Drawbacks
- Stick welding may be slower than other techniques.
- It is not as easy as MIG welding – operators with a higher level of skill and proficiency are needed for satisfactory stick welding quality.
- Chipping away the slag at the end of welding is time- consuming and lowers productivity.
- Stick welding is unsuitable for very thin sections.
- Compared to other welding methods, the consumable electrode needs to be replaced more frequently.
- Stick welding can produce excessive porosity, rough surfaces and spatter.
Welding Circuit Power
The power supplied by the welding circuit is most often expressed in the form of current and voltage. The voltage value depends on the arc length, which in turn is determined by the diameter and type of the electrode. Welding circuit power is usually stated in the form of amperes. Welding current depends on the welding position, thickness of metal sections being welded and electrode diameter. Thick metal sections need larger current as compared to thinner metal sections. Thicker electrodes need greater current compared to thinner electrodes.
SMAW Welding Protection
Before starting SMAW welding, you must don safety equipment to protect yourself against welding hazards. It is important to acquire protective equipment like a welding helmet and protective clothing like aprons, jackets, gloves and boots. The ultraviolet radiation generated by the electric arc is damaging to both the eyes and skin. Prolonged exposure to these hazardous rays can cause different medical conditions, including skin cancer and permanent eye damage. SMAW welding also produces high heat, hot slag and spatter in copious amounts, which can cause serious injuries. Gloves, aprons and other protective wear can be utilized for protection against these hazards.
You must ensure that the surface of the metal being welded is clean prior to starting stick welding. Compared to other welding techniques, shielded metal arc welding is less affected by surface impurities. However, there is still a possibility that these impurities can lead to serious defects in the weld joint. Hence, it is necessary to clean the surface before welding.
After cleaning the surfaces, fit the most appropriate electrode into the welder. Configure the current settings according to the guidelines mentioned in the user manual of the welding machine. You are now ready to perform SMAW welding.
Initiating the Electric Arc
You can initiate the arc with one of the two methods: scratch start and tapping.
To develop a steady welding arc through the scratch start method, you must first scratch the workpiece surface with the electrode and move it away. You have to drag the electrode on the metal surface in the same way that you strike a match. If this movement is done correctly, an arc will be initiated and you can perform your welding job. Developing this welding arc can be rather tricky and will require some practice to perfect.
If the arc disappeared after striking the electrode on the workpiece, then it implies that you lifted the electrode too far away from the surface. Try to keep the electrode as close as possible to the metal surface without making contact. If there is prolonged contact, then the electrode may stick firmly to the base metal owing to current flow. If this happens, a quick twist is enough to free the electrode.
In essence, the tapping method is not too different from the scratch start method. For the tapping method, you must bring down the electrode straight onto the base metal while keeping it at 90 degrees to the surface. As soon as the electrode touches the surface, lift it slightly. An arc will be initiated as the electrode rises. If the arc is interrupted, then you must have lifted the electrode too high. If you are not quick enough and there is prolonged contact between the electrode and the surface, then the electrode may stick to the metal section. Give the electrode a quick twist to pull it free.
Besides knowledge of the right technique – which is not too difficult – initiating an arc requires deftness, which can be attained through practice. You can practice on scrap flat metal pieces to learn how to sustain an arc in one go. Once you master this process, you can also practice moving the electrode along the metal surface at a constant rate to apply the weld bead evenly.
While you practice making weld beads, remember that the electrode should be nearly perpendicular with respect to the metal surface. It is best to tilt the electrode by 10 to 30 degrees in the direction of weld travel for the most consistent results.
Different Welding Positions
Before adopting any welding position, you must think about the effect of gravity on the molten weld pool. Since this is a pool of liquid metal, it will behave similarly to other liquids. Taking this effect into consideration, you must adopt the most appropriate position to weld effectively and safely.
Vertical and horizontal welds can receive support from beveled edges and backing plates. For both kinds of welds, orient the electrode at a 90-degree angle to the base metal surface.
Overhead welding can be considerably difficult due to the hazard posed by spatter that is raining down. A backing plate can be helpful in this situation. For flat welds, the electrode should be oriented at a 90-degree angle with respect to the metal surface. Wherever possible, you should also try to tilt the electrode slightly, so that drops don’t fall onto any equipment.
For the thinner metals, you can rely on a square groove weld. But for metal sections thicker than 3/16 inch, you must employ a grinder or plasma cutter to cut beveled edges.
For both v-groove welds and square groove welds, you must position the electrode at 90 degrees to the base metal section. For better results, lean it slightly in the direction of weld travel. Tilting in other directions may render the welds ineffective.
When doing fillet joints, you should orient the electrode at 45 degrees with respect to the weld. On the other hand, you can reduce the angle while working on lap joints. To increase the strength of the joint thus formed, give circular motion to the electrode. For both kinds of joints, it is best to weld both sides in order to ensure maximum durability and strength.
Troubleshooting Hints and Tricks
You might encounter a number of problems while you are learning the basics of shielded metal arc welding. You will become much better at welding by practicing consistently and trying out new things to improve. In case you run into problems, you can apply the following troubleshooting tricks to resolve those issues.
Initiating the arc can be challenging, especially for beginners. As you scratch the surface to develop the arc, the electrode can stick to the metal surface. Don’t get worried. All you need to do is to twist the electrode sharply. This will loosen the electrode from the surface. You can then resume working with the electrode.
Once you start welding, you must move your hand smoothly and steadily to sustain the arc. If you move the electrode too far away from the surface, the arc might disappear. Simply resume welding from the same position on the base metal where the weld was interrupted. You only need to ensure that the correct distance is maintained between the surface and the electrode.
Understanding the most suitable arc distance may be helpful. Peruse industry manufacturer instructions to find out more. A 1/8 inch arc length is normally suitable for electrodes that have a 1/8 inch diameter. Thinner electrodes will work well at 1/16 inch arc length.
If there is insufficient penetration, then you will have to consider several possible factors to determine the actual cause. One of these factors is travel speed. If the electrode moves too rapidly, then the weld thickness will be too inconsistent and narrow. If the electrode travels too slowly, then excessive molten metal will accumulate, which is unnecessary and wasteful.
With practice, you can move the electrode at the right speed. You will attain the best results in a horizontal or flat position. But if you have to weld in an overhead or vertical position, the current must be less than that for the horizontal position. The best weld joint is formed by keeping short arc lengths and moving the electrode at a constant rate.
If you find that the welds are too weak and breaking, you should test them using a hammer before putting away the welding gear. You do not need to strike the welds directly. The hammer impact should be 2 to 3 inches away from the weld.
Prior to continuing welding or completing multiple passes, you have to chip off the slag for a smooth surface.
Shielded Metal Arc Welding Best Practices
You can also take the following steps to ensure the best quality welds from the shielded metal arc welding technique.
Choose Steel from the Normal Range
Selecting steel from the normal range will produce good stick welding results. This includes steels ranging between AISI-SAE 1015 and 1025. For these steels, the sulfur content is less than 0.035 percent and the silicon content has a maximum value of 0.1 percent. Stick welding process with these steels is easier and more convenient since they allow faster welding speeds. The tendency for cracking is also minimized due to the desirable metallurgical properties of these steels.
If you have to weld carbon steels and low alloy steels whose chemistry is beyond the normal range, then there will be a greater likelihood of weld defects. These steels are more likely to crack with stick welding. The risk for this kind of defect increases even further for stick welding of rigid structures and heavy plates made from these steels.
Owing to these issues, you must take certain countermeasures. Steels with high phosphorus and sulfur content, in particular, are not ideal for stick welding. If you must stick weld these steels, then make sure that you utilize low hydrogen and narrow diameter electrodes. It is better to weld at a slower travel rate so that the weld pool remains molten for longer. As a result, there will be enough time for gas bubbles to boil out. These bubbles would otherwise be trapped within the weld pool if it solidifies too quickly, which would cause porosity.
Select the Best Joint Position
The finished weld quality is greatly influenced by the joint position. For steel sheets between 10 to 18 gauge thickness, you will be able to attain the fastest welding rate at a downhill angle between 45 and 75 degrees. There is no need to overweld or lay a weld that is bigger than what is needed. This will produce too much molten metal that can lead to burnthrough.
For low alloy and high carbon steel plates, perform stick welding by keeping the pieces in a level position.
Select the Most Appropriate Electrode Size
Bigger electrodes carry larger currents and deposit filler metal at a higher rate. For high weld quality, you should make use of the largest electrode that is practical. However, the electrode size may have to be kept small for root passes and sheet metal to avoid burnthroughs. The electrode diameter may also be limited by joint dimensions.
Shielded Metal Arc Welding Defects and Their Remedies
Here are some of the most common stick welding defects, along with their possible solutions.
Cracking is an involved topic since many different kinds of cracks can develop at various locations along the weld. All cracks pose a serious risk as there is always the possibility that they will increase in size and turn into fractures. Alloy, high sulfur or high carbon content in base metals is most often responsible for cracking.
In order to minimize the risk of cracking, you should follow these steps during stick welding:
- Use low hydrogen electrodes.
- For rigid joints and heavy plates, employ high preheats.
- Make use of small diameter electrodes and low currents to reduce penetration. This will reduce the number of alloys that are included in the weld pool from the base metal.
- For filler or multiple pass welds, be certain that the weld bead has the right size and shape to prevent cracking. You may add further layers if you are sure about this. You may increase the size of the bead by welding 5 degrees uphill, using a short arc and slow travel speed. Carry out welding while the workpiece is hot.
Rigid parts have a greater tendency to crack. Weld in the direction of the unclamped end if this is possible. There should be a gap of at least 1/32 inch between plates to allow shrinkage while the weld is cooling down. You may also peen the weld beads while they are hot to reduce stress.
Penetration is the depth that the weld goes to in the base metal. This is usually not easily visible. For high strength welds, full penetration is necessary to the lowest point of the joint. If you notice low penetration problem, then try slower travel speeds and higher currents. Small electrodes are more likely to go penetrate all the way in narrow deep grooves.
Remember to maintain some gap at the joint’s lower part.
Proper fusion exists when a solid bead is formed through the full length of the joint and the weld pool has solidified to strongly bond both sides of the joint. Poor fusion is easily visible and should be resolved for strong joints. You can employ the stringer bead method and higher currents to treat poor fusion. Ensure that the joint edges are free from dirt. You can also use 11 electrode or AWS E6010, which can cut into the impurities. If there is too much gap, then you must employ the weave technique to close the gap.
Porosity is not usually visible, which is unfortunate considering how common and serious it is. To minimize the risk of porosity, clean up the base metal surface prior to stick welding. Make sure that the weld pool remains molten for a longer time. This will give gas bubbles enough time to escape. These bubbles may become trapped if the weld pool solidifies too quickly. These bubbles create holes in the solid structure, which gives rise to porosity.
Use a low hydrogen electrode for steel with phosphorus, sulfur, manganese or low carbon content. Free machining steels may have excessive sulfur, which prevents proper stick welding. In such cases, you should try to minimize the amount of base metal that melts into the weld pool by using fast travel speeds and low current. You can also employ a shorter arc length as well.
While using low hydrogen electrodes, the light drag method is advisable. You can also deploy the same countermeasures for surface holes.
If you are performing DC stick welding, then the arc can begin wandering from its intended course due to interference by stray magnetic fields. This issue is more likely in complicated joints and higher currents. The best way to control wandering arc issue is to switch to AC. If this method fails, then use smaller electrodes, shorter arc length and lower current.
You can also modify the current path by transferring the work connection towards a different section within the workpiece. You can also try making connections in different locations. You may also try run-out tabs, welding towards finished joints and placing steel blocks to alter the electrical path. You can also attach small plates along the seam at the ends of the weld.
If the current and polarity are in accordance with manufacturer guidelines, but the arc is still unstable, then it could be a case of wet electrodes. Open a fresh container for dry electrodes. If the problem is recurring frequently, then you should place open electrode containers within heated cabinets.
Undercutting may seem to be an appearance issue only, but it can deteriorate weld strength if the weld suffers fatigue or a tension force. You can minimize the possibility of undercuts by slowing down the travel speed and lowering current. You may also employ a smaller electrode for a weld pool size that you can manage. Also, try varying the electrode angle. Avoid too much weaving and move the electrode at a uniform travel speed.
Spattering does not have much of an effect on weld strength. However, it does lead to poor surface finish and therefore higher cleanup costs. You can control excessive spatter in a number of different ways.
The first method is to keep the current relatively low. However, ensure that this reduced current is within the range for the given electrode size and type. The current should have the right polarity.
You can also reduce spatter by reducing the arc length. If the weld pool is spreading in front of the welding arc, then adjust the angle of the electrode slightly. Be careful about arc blow conditions. This is called a wandering arc. The electrode must be completely dry.
Not only have you learned the basics of stick welding and its techniques, you have also learnt about stick welding defects and their remedies. This will help you create high quality welds that are free from defects.