Custom sheet metal working requires impressive skills that professional craftspersons acquire after years of trade training and practical experience. Metal working might be intimidating for the novice, but few people look at a custom-built piece without noticing the smooth joinery and precise seams you’ll see in a finished product. Most impressive of all are flawless welds that seem almost magical.
In theory, welding sounds simple. The welding process joins metal parts through fusion. That involves extremely high temperatures that melt metal and fuse the joints together. In practice, welding can be complicated. There are so many different metal types as well as differing welding techniques. No doubt you’ve heard terms like arc welding, mig welding, tig welding and gas welding.
If you’re planning to have a sheet metal project custom-built, it’s very important to understand what welding techniques your fabricator might use. That way, you’ll be in the best-educated position to approve a welding process that your fabricating company recommends. Custom metal work is a serious investment, and you need assurance you’re doing it right.
It’s easy to be confused about welding terminology. There are so many acronyms and abbreviations used in the sheet metal fabrication and welding business, and each term has its meaning and application. To help educate you on welding forms employed in custom metal work, here is a detailed explanation of welding types, terms and techniques.
Shielded Metal Arc Welding (SMAW)
Shielded metal arc welding, or SMAW, is the oldest metal bonding form next to the ancient heating and pounding method used by blacksmiths. For countless centuries, metal workers fused their pieces together by heating them to a cherry-red temperature in a forge and then hammering seams on an anvil. That ancient technique still exists in small craft and hobby shops, but electric welding replaced blacksmith skills in the late 1800s.
By the early 20th century, electric welding reached a technological sophistication where it became mainstream in metal joinery. According to the Fabricators & Manufacturers Association, shielded metal arc welding is still the most popular form of electric welding despite many high-tech advancements made in the welding field. SMAW is easy to learn and highly versatile for a variety of metals. It’s also a very portable process, so it can be used everywhere from shops to the field.
Shielded metal arc welding is commonly called "stick welding." That’s due to the simple welding electrode, or stick component, that distinguishes it from other welding types. The term "shielded" comes from the part of this welding process where particular gasses from the melting electrode shield the fresh weld from common atmospheric gasses like oxygen and nitrogen that threaten a new weld’s integrity.
SMAW welding works on a simple principle. Positive high-voltage electric current electricity from a power grid or generator flows through heavy welding cables and into a welding electrode, or stick, mounted in a hand-held grip. The metal work surface has a grounded negative charge. Once the positive charge in the electrode makes close contact with the work surface, a blindingly bright electric arc flashes.
This energy arcing creates enormous heat in the 7,000-degree-Fahrenheit range. That causes both the welding rod and the work surface to melt and bond together. As the electrode stick dissolves into a liquid, its flux coating changes to a gas state protecting or shielding the weld pool from atmospheric forces. A slag coating forms over the cooling weld joint as it turns back to solid form. Usually, the slag gets chipped or brushed away to expose a shiny new weld.
Welders and custom sheet metal fabricators normally use stick or SMAW welding on routine jobs involving carbon steel and stainless steel. SMAW welding allows joining reasonably thick metal components due to the immense heat generation. High-quality stick welding equipment lets the welder adjust temperatures depending on the size of their work and the metal composition. Many welders claim their welded joints have stronger tensile strength than the parent or native material.
Gas Metal Arc Welding (GMAW)
Gas metal arc welding, or GMAW, is the second most popular welding form used in custom sheet metal fabrication. You’ll usually hear GMAW welding called "MIG welding," which comes from "metal inert gas" (MIG). In fact, the term "MIG" is so familiar in the welding world that using the acronym GMAW might puzzle even the most experienced welder. They’d probably recognize the term “heliarc” welding in place of GMAW due to the helium gas once used when the MIG process started.
The big difference between SMAW and GMAW welding is the electrode composition. Both welding forms rely on high-voltage current to create an electrically charged arc that melts both the electrode and the work surface to form a bond. However, with the GMAW or MIG welding process, the atmospheric shielding gas is artificially introduced by a separate feed rather than gassing-off from the melting electrode.
GMAW/MIG welding also employs a different electrode type. Instead of the consumable stick that melts and fumes, the MIG electrode is a continuous feed of wire from a pre-stocked spool. This metal filler is automatically fed to the weld joint and runs at a steady rate. Where the SMAW welding electrode melts down and needs constant replacement, the GMAW process allows continuous joint and seam welding.
There are no breaks or gaps in the MIG welding process. The weld is smooth and uniform, which presents far better on the finished product that the stop-and-go stick arc welding process. You get a faster and more dependable product with the gas metal arc welding technique than with the shielded metal arc welding process.
GMAW systems operate on a steady shielding flow of argon, carbon dioxide or helium gas. Some use a blended mixture of two or all three. These safe and common gasses effectively shield the new weld from oxygen and nitrogen, which immediately compromise a fresh weld and cause it to oxidize or prematurely rust as it sets up. Because argon, carbon dioxide and helium are common, they’re also inexpensive, which lowers overall welding costs.
Larger MIG welding equipment utilizes multiple electrode wire spools. You’ll find the multi-spool approach in big shops that mass-produce products. However, you’ll also find compact MIG or GMAW outfits in small fabrication facilities. Besides being economical equipment to buy, the MIG welding technique is easy to learn and highly dependable for producing cleanly welded joints.
Gas Tungsten Arc Welding (GTAW)
Gas tungsten arc welding is also called "tungsten inert gas arc welding" or "TIG arc welding." Like the SMAW and GMAW welding techniques, GTAW uses high-voltage electricity to heat the work and a metal filler rod to extremely high temperatures, causing both the work and filler to melt, pool and fuse once cooling. The primary difference with TIG welding is that it utilizes inert tungsten gas to shield the weld as it forms.
GTAW/TIG welding can also perform without fillers. Some GTAW equipment has wire reels similar to those you’d see in a heliarc or MIG system. Instead of utilizing low-cost helium, carbon dioxide or argon gasses, the TIG welding system relies on tungsten gas, which is considerably more expensive for a fabrication shop to source.
Tungsten gas has a superior advantage over its competitors. Although more expensive, tungsten gas is stable at all heat levels. GTAW welding can achieve temperatures far greater when shielded with tungsten. This makes a GTAW welding system versatile for operating outside a welding electrode or wire reel filler.
Some TIG welding processes eliminate any consumable wire, filler or electrode. They employ a non-consumable electrode that creates an immensely hot arc that causes the metal surfaces to bond or blend without an additive. Tungsten gas injection around the electrode’s tip shields the fusing metal from oxygen and nitrogen contamination.
With no filler or auxiliary material introduced to the meld, all that’s left is the original metal, now seamlessly fused together. The weld retains the same tensile strength of its native metals and is practically invincible to breakage. Because TIG welds are so precise and use original metal if operated without a filler, the welded joint is practically invisible.
The TIG or GTAW welding technique is ideal for thin and specialized metals. You’ll find TIG welders often working with aluminum projects, as aluminum is a notoriously difficult metal to weld. GTAW welding also suits brass, copper, magnesium, titanium and high-strength alloys. As a rule of thumb, TIG, or tungsten inert gas welding, suits more expensive materials and more complex metal joinery requirements.
Oxygen-Acetylene Welding (Oxy-Acetylene)
Most welding students cut their teeth on oxy-acetylene welding equipment. The oxy-acetylene process works on combustible gas heat rather than harnessed electricity. Here, a welder lights an open flame using a blended ratio of compressed oxygen and acetylene emitted from a torch head mounted on hoses connecting the gas cylinders. The torch flame heats the work surface to temperatures slightly lower than those found in SMAW and GMAW processes.
All oxygen-acetylene welding processes require fillers. With oxy-acetylene operations, that’s usually a welding rod made of metal like brass or steel. There’s no gas shielding with oxy-acetylene welding. This technique isn’t designed for the same oxygen and nitrogen protection you find in regular arc, MIG and TIG welding.
"Brazing" and "soldering" are two terms you’ll often hear used to refer to oxy-acetylene welding. Brazing is a moderate heat application where the metal work surfaces get heated at the same time a brazing rod melts and pours into the joint gap. Because of lower temperatures and a more gradual heating time, the weld strength is nowhere near what you’ll get with fast-acting SMAW, GMAW and GTAW welds. Brazing strength is mostly in the filler rather than the native material. It’s often employed in quick repairs rather than in custom sheet metal work.
Soldering requires even less heat. Solder is a soft metal product containing an interior liquid flux. As solder melts, the flux drips into the work joint and cleans it from dirt, oil and oxidation. Rather than repair work like brazing, you’ll find solder often used on metal joins in electrical and plumbing work. It’s almost unheard of to find solder in sheet metal fabrication.
Although oxygen-acetylene welding is suited more for light construction and metal work where the finished appearance isn’t important, there is one clear advantage to an oxy-acetylene outfit. This equipment excels at cutting metal where arc welding processes don’t. All oxy-acetylene sets have two torch heads. One is a low-heat configuration for welding, brazing and soldering. The second head is a cutting nozzle.
Types of Welding Joints and Positions
Just as there are different welding forms and equipment types, there are various welding joint types and application positions to be aware of. You’ll find these joints and positions spread across most welding facilities and applications. That ranges from custom sheet metal fabrication shops to large industrial and manufacturing facilities.
Not every piece of welding equipment works with all joints and positions. SMAC, or stick welding, is the most versatile form. But it doesn’t produce the perfection that MIG or TIG welding does. Generally, there are four welding positions where you can have any number of joint types:
Flat Welding: These work surfaces lay like a bench or table top. The welder approaches them from a top-down position and lets gravity help with molten flow. Flat surfaces really suit MIG and TIG welding equipment, where wire feed and gas flow works best on a straight and level surface.
Horizontal Welding: This position refers to welding on a line of sight position like across an upright wall. SMAW welding using a stick electrode works well in horizontal positions where it’s more challenging to get a MIG or TIG welder balanced. Oxy-acetylene welding is also tougher on horizontal surfaces than on flat ones.
Vertical Welding: Like horizontal welds, running beads on a vertical or up-and-down surface has its problems. It’s simple for a SMAW welder to strike vertical beads but not so simple for the TIG and MIG people. When possible, metal fabricators adjust their horizontal and vertical work to a flat position.
Overhead Welding: By far, overhead welding is the toughest task for any welder. Fortunately, you’ll rarely have this need in a custom sheet metal fabrication facility. Overhead welds show up in factories and industrial sites that have suspended equipment. Conventional SMAW welding equipment is the only practical solution for overhead problems.
Regardless of what welding position you might have, you’ll have some basic welding joint types or styles that regularly appear. Each joint has its procedures that metal welders learn proficiency at. These are the most common joints in welding:
Butt joints have their work surfaces facing each other from end to end.
Lap joints have overlapping surfaces with mating faces on each work side.
T-joints intersect each other on 90-degree angles in a T-shape.intersect each other on 90-degree angles in a T-shape.
Corner joints touch at inside and outside corners, usually forming a right angle.
Edge joints are similar to butt joints but have more metal face connecting the work.
Custom Sheet Metal Fabrication Welding
APX York Sheet Metal is your premium metal fabrication company serving central Pennsylvania and northern Maryland. Since 1946, we’ve built a reputation for dependability and excellence in welding and fabricating outstanding custom sheet metal work as well as customer service. We’ve accomplished this by using the highest-quality materials, the best cutting-edge technologies and the most efficient welding processes.
For a request for quote (RFQ) on your custom fabricated metal projects and parts, call APX York Sheet Metal today at 717-767-2704. You can also reach us for a quote through our online contact form.