Welding, the process of joining materials using high heat and, often, a filler material, is a fundamental skill in the metalworking industry. It’s a craft that demands skill, precision, and the right choice of welding process. Each welding method offers unique advantages and is best suited for particular applications. Deciding which welding process to use requires a solid understanding of the available options and consideration of various factors like the material, thickness, project specifications, and environmental conditions. This comprehensive guide will delve into the various welding processes, their applications, and the factors that influence the choice, empowering welders to make informed decisions.
Understanding the Main Welding Processes
1. MIG Welding (Gas Metal Arc Welding – GMAW)
MIG welding is one of the most commonly used welding processes. It involves feeding a consumable wire electrode and an inert gas through a welding gun. The gas shields the weld from atmospheric contamination, providing a clean and strong weld. It’s versatile and ideal for various materials, including steel, aluminum, and stainless steel. This method is fast, efficient, and produces high-quality welds, making it suitable for industries like automotive, manufacturing, and construction.
2. TIG Welding (Gas Tungsten Arc Welding – GTAW)
TIG welding utilizes a non-consumable tungsten electrode to produce the weld. An inert gas protects the weld area from atmospheric contamination. TIG welding allows for precise control over the welding process, making it perfect for welding thin materials and exotic metals like magnesium and copper alloys. It produces high-quality, clean welds with no spatter, which is crucial in industries like aerospace, automotive, and artistic applications.
3. Stick Welding (Shielded Metal Arc Welding – SMAW)
Stick welding is one of the oldest and most straightforward welding processes. It employs a consumable electrode coated in flux, which produces a shielding gas when burned. This process is highly versatile and can be used in outdoor or windy conditions, making it a popular choice in construction, repair, and maintenance applications. It’s suitable for welding thick materials and works well on rusty or dirty surfaces.
4. Flux-Cored Arc Welding (FCAW)
Flux-cored welding is similar to MIG welding but utilizes a tubular wire filled with flux instead of a solid wire. It generates its shielding gas, making it suitable for outdoor and windy conditions, similar to stick welding. FCAW is fast and highly productive, making it ideal for thick materials, structural steel, and shipbuilding.
5. Submerged Arc Welding (SAW)
Submerged Arc Welding involves feeding a continuous solid or tubular electrode and a layer of granular flux over the weld area. The weld is shielded from atmospheric contamination by the flux, allowing for deep penetration and high welding speeds. It’s primarily used for welding thick materials in industries like shipbuilding, heavy equipment manufacturing, and pressure vessel fabrication.
Q: We use many welding processes in our manufacturing weld shop, including GTAW, SAW, SMAW, GMAW, and FCAW. In many instances, our welders can choose which welding process they want to use for the application. SAW is for large weld joints where we can employ automation, but there is a choice for many others. Which process consistently produces the deepest penetration and best weld deposit?
A: That is a fantastic question, considering many job shops use various welding methods.
Let’s start by addressing your direct question about depth of penetration and weld quality. Those are two separate variables and considerations that can carry equal importance.
Depth of penetration is a straightforward concept with two key components. First, if the weld joint requirement is a partial joint penetration (PJP) weld, then weld penetration should only be beyond the faces or edges of the parts being welded together. Second, penetration is not required to be set at a specific value beyond the intersecting parts. Bear in mind that the design engineer has the authority to specify a set depth, such as a percentage of the base material thickness.
Suppose the weld joint is a complete joint penetration (CJP) weld. In that case, the weld metal must fill the joint between the two intersecting components, or there must be overlapping penetration if the joint is welded from opposing sides.
Weld quality is primarily determined by the welding code you adhere to. For example, some welding codes do not allow porosity, while others allow a small amount per linear inch of weld metal. Again, the design engineer may opt for stricter guidelines since welding codes are only the minimal requirements for your welding product.
Circling back to weld penetration, the most significant variable is welding amperage. Amperage determines penetration along with heat input, which is calculated using the amperage as one of the variables. Higher amperage leads to greater penetration depth. Travel speed also plays a significant role in penetration, whereas higher travel speed reduces penetration. An important thing to keep in mind is that if travel speed is too slow with any process aside from GTAW, you may risk losing penetration because the welding arc will ride on top of the weld puddle instead of the leading edge, which will insulate the base material from the high arc temperatures and reduce penetration.
When comparing welding processes, each process uniquely attains varying penetration levels. Suppose we ignore the fact that base material chemistry can affect the weld penetration a small amount and just focus on the welding process. In that case, amperage for all processes will inflict the most significant change in penetration.
For gas-shielded welding processes, the gas type will affect the penetration profile. The two most common shielding gases are argon and carbon dioxide. Argon produces a deep penetration in the center and shallow penetration in the overall cross section, whereas carbon dioxide produces a deep, broad penetration profile. The net penetration profile for carbon dioxide is superior to other shielding gases.
The type of flux can influence weld penetration for SAW, SMAW, and FCAW processes. Additionally, most FCAW processes use a dual-shield wire, which requires an external shielding gas that is nearly always carbon dioxide or a carbon dioxide/argon blend. Self-shielded flux-core wires are typically used in field welding applications (outdoors) and are comparable to the SMAW process.
Regarding SMAW, E6010 and E6011 are the deep-penetration rods. An E6010 rod only works on direct current electrode positive (DCEP), whereas the E6011 rod can run on DCEP or alternating current (AC) power supplies. These rods are used for welding the root pass and can produce a good keyhole arc while leaving a thin, easily removable slag layer.
With the SAW process, the type of flux and its chemical makeup can affect weld penetration. The various raw materials that flux is made from and the interaction with other materials in the welding arc will affect the arc stability, weld puddle fluidity, weld metal cleaning action, weld penetration, bead appearance, and weld metal chemistry. If two different fluxes are used with the same weld settings, the weld puddle that does not wet out or produces a narrow weld bead will typically have a deeper penetrating weld. This is because the net heat input is distributed over a smaller surface area. These are just a few of the variables that affect penetration. You must consider many other variables, some of which may induce a significant effect, while others may not.
When deciding which process to use for each job, consider the amount of weld metal required to complete the job. Use the process with the highest deposition rates, allowing the most significant control to meet the required quality standards. Other things to consider may be weld fume generation, weld spatter and required postweld cleaning, welder qualifications and skills, filler metal and shielding gas costs, and operator skill.
With all things considered, this should help you choose the best process to optimize your welding demands.
