SMAW (Shielded Metal Arc Welding) or Stick Welding is one of the most widely used welding processes. It is a manual welding process that employs electric arc that formed when the electrode maintains a contact with base metal as its source of heat to melt the consumable electrode and its protective flux shielding along with the base metal. It is known to have many names, like stick welding, manual metal arc (MMA), and flux shielded arc welding. It is also considered to be the most versatile welding process and the one that requires the least complex set-up compared to another process.
SMAW is considered versatile because of its ability to weld a wide range of material such as low alloy steel, stainless steel, cast iron, and the common carbon steel. Although it’s mainly applied to steel where it suits the material’s characteristic best. SMAW also have simple set-up, making it cheap and portable, where the limitation is only limited to the welder’s skill. In this article, we will talk about all the aspect of SMAW welding process.
Stick Welding Machine:
- Power Supply.
- Extension Cables.
- SMAW Welding Parameter.
- Welding current and voltage.
- Polarity in SMAW Welding.
- Travel Speed and Stick Welding Technique.
The basic SMAW set-up involves a simple schematic. Running from the power supply is the transformer that provides you with the electric current that you need to form the electric arc. The extension of the main transformer would be the two cables that work as the anode and cathode. One end of the polarity is connected to the base metal and the other end is extended as consumable filler metal electrode that in the end will melt and connect the separated joint. In this section, we will break down and discuss every single part of the machine schematic.
1. Power Supply
Because most of the electric grid provide 220V and 50 amps of alternating current, it would simply burn the material and the electrode before we’re able to control it. Therefore, the power source of SMAW is a step-down transformer that converts high voltage alternating current into 17 – 45 V with up to 600 Amps current. The old and traditional SMAW welding machine use coils to transform the input, while the modern welding machine also uses an inverter to provide the required current. The power supply is manipulated in such way to produce a relatively constant current with varying voltage. It is there to allow arc manipulation so that it will generate constant heat input. Because SMAW involves the use of the consumable electrode, maintaining the arc length to be constantly stable is highly impossible, and if not because the constant current setting, the heat input will vary dramatically and thus making it harder to control the arc.
2. Extension Cables
In stick welding machine, there are 2 primary cables that serve a different function. While actually, the role of anode and cathode can be a swap, the default would be the straight polarity where the electrode cable is an anode and the ground clamp is a cathode. Polarity and its effect will be discussed more in the parameter section. The cables have no other function except to extend the electric charge from the power supply.
3. Electrode Holder / Torch
While the positively charged polar is connected simply via a clamp, the negatively charged polar is connected to the electrode holder. A holder is ergonomically designed electrode handler that can be modified to hold the electrode at a different angle. Some holder model is limited particularly to 90, 45, and 0 degrees of modification, but the modern and especially expensive one has already used a rotating clamp to allow welder use more varied welding angle. While it’s not normally common, some electrode holder also has an internal cooling system. Compared to others, SMAW welding torch is so flexible and it can reach almost any corner that you find hard to reach.
The electrode is used in this process is unique and specially manufactured for this process only and it comes in the different size of diameter. Where the filler metal that’s made from the same composition of the parent metal is shielded with a layer of flux. This layer of flux will later on burnt along with the arc and the molten metal. Forming a layer of gas that will protect the molten metal from the hazardous environment. In addition to that, the protective flux also helps to stabilize the arc for easier welding, serving as deoxidizer as it solidifies and becoming a slag which is an upper layer of welding that can be chipped off and can also introduce an alloying element to the weld metal.
The American Welding Society (AWS) classify various SMAW electrodes and codified it. The codification is based on the tensile strength of the core wire, the recommended welding position, and the protective layer of flux that applied. See figure 4 for the codification.
Codification is very important. Other than for the sake of easier identification, codification is also used as the first-hand reference to pick your filler metal that will best suit your base metal. Most people will first match the tensile strength of filler metal with the tensile strength of the base metal. The basic rule of thumb is, the filler metal should have greater tensile strength than the base metal to achieve a stronger weld mix between the two. After they have found the matched tensile strength parameter, they will continue with assessing which welding position is being used. With the number 1 means that the electrode is applicable for all position, number 2 means it’s only for flat and horizontal welding, number 3 means it’s only for flat, and number 4 is for vertical down welding. Lastly, they will refer to the protective layer of flux being employed in the electrode. Because the flux can greatly affect the weld quality and some flux even require a special treatment. For example like low-hydrogen based flux, an effective hydrogen repellent flux that must be baked inside the electric oven so that it can be maximally utilized. Table 1 will give you enough explanation about the difference of each flux code.
SMAW Welding Parameter:
- Welding current and voltage.
- Polarity in SMAW Welding
- Travel Speed and Stick Welding Technique
Welding parameters are variables that can be manipulated to achieve the desired result of welding. Even among arc welding process, the variables may vary with each different process. The following list is the important variables in SMAW welding process and a short explanation of the effect of a parameter change.
1. Power Supply
As mentioned above, SMAW welding process uses the constant current electricity, so the parameter that can be modified is only electrical current. The voltage is allowed to fluctuate in order to compensate the arc length so in the end when the arc length changes the voltage will also change to keep the heat input as constant as possible. The variation is between the ranges of 17 – 45 volt, where outside of that range the arc will simply disappear. The modification of welding current is more flexible in this term. The factors that are taken into consideration when deciding how much amperage that a welder going to use are: electrode’s diameter, base metal’s thickness, and welding position. Some welders will also recommend using a slightly higher welding current than estimated to allow extra penetration and faster welding to get the job done faster. Incorrect setting of welding current can be disastrous, whether it’s too low or too high. If the welder cannot anticipate compensating for the uncontrollable arc, discontinuity or even defect can occur.
A relatively low welding current will result in lower heat input, although it would be easier to control the arc, there’s also a risk to have discontinuities like slag inclusion, porosity, incomplete penetration, and lack of fusion. Those discontinuities are mostly not acceptable, therefore it has to be reworked by removing the weld and then re-welded which is another extra effort that you really need to avoid. Using a higher welding current will surely help you avoid those discontinuities. However, it doesn’t necessarily free you from defect, because when you use higher welding current the electric will be more volatile, making it hard to control. The excessive heat input is also proven to be equally problematic. An unnecessarily high welding parameter will result in discontinuities like undercut, excessive spatter, burn through, and deformation. The key to determining the best welding current is to be moderate and know your limits.
2. Polarity in SMAW Welding
Electric polarity affects the location of the heat concentration. Because electron flows from negative to positive polarity, the heat will be concentrated to which part is being subjected to positive polarity. Polarity manipulation can be very helpful in some case of welding especially welding aluminum. In SMAW and most of the welding process, there are 3 kinds of polarity: Alternating Current (AC), Electrode Positive (DCEP), and electrode Negative (DCEN). Let’s talk about DC polarity first, in here we can either choose DCEP or DCEN. DCEP or Direct Current Electrode Positive is also known as DCRP or Direct Current Reverse Polarity, it’s when you put positive polarity in your electrode so 2/3 of the heat will be concentrated in your electrode. With such condition, the heat will allow greater penetration in the exchange of narrower bead.
DCEN or Direct Current Electrode Negative is also known as DCSP or Direct Current Straight Polarity, it’s when you put negative polarity in your electrode so 2/3 of the heat is concentrated in the base metal. It doesn’t provide great penetration, but the weld bead will be wider. Meanwhile, AC or Alternating Current is kind of the mix between the 2 DC polarities. Because the polarity in AC is constantly shifting around 50 – 100 times per second. Providing a moderate penetration combined with a moderate width of molten metal. Although the variation of polarity is not so important in SMAW process, in another type of welding like aluminum GTAW welding, different polarity can help the welding process.
3. Travel Speed and Stick Welding Technique
Travel speed and welding technique is a parameter that doesn’t have any switch to change, it solely relied on the performance of the welder. However, it’s still worth mentioning because it can also affect the result of welding. Incorrect welding current coupled with incorrect welding technique will result in catastrophic welding visual and will certainly contribute to why you’re fired from your welding workshop.
To summarize, SMAW welding process is your best friend when you need to finish a welding job with the least effort. It has a relatively simple schematic, so it will certainly won’t hinder you if you need high mobility when welding on site. You just have to disconnect some cable, move the machine, reinstall the cable, then you’re good to weld just like a plug n weld device. The parameters are also relatively easy to master, a minute after reading the machine manual will indulge you with all the information you need to operate the machine. Despite all that, SMAW is not your dream welding machine because of its flaws. Just like how everything is flawed, so do this welding process.
SMAW welding process is a fully manual process, therefore it will take you some practice before you’re able to produce some quality weld. The length of the single weld is also limited to the length of the electrode. Once you’re running out of electrode you have to stop to “refill” your burnt electrode. Not to mention that this is a fairly dirty process with all the solidified slag on top of your weld metal. You really want to remove that slag before starting another pass above the said weld or you’ll have a bad time dealing with slag inclusion. Another downside is the excessive spatter in this process. So you have to reconsider when you’re about to use high parameter because it will incite more spatters. With all being said, it doesn’t stop SMAW from being the most awesome welding process. That has a good price per quality ratio and versatility. I’ll bet that this process will not be abandoned in the foreseeable future and developments will increase the survivability of this reliable welding method.