Welding has always been an important topic in many industrial activities. What is welding? Of course, most people “understand in the abstract” what welding is. Welding is the process of joining one metal to another. This is a process that was discovered thousands of years ago by blacksmiths although, of course, they were not as sophisticated as they are today.
Since the 19th century, welding has completely changed and that century can perhaps be considered the starting point for the transformation of welding technology, from “primitive welding to modern welding”, characterized by the use of oxygen and acetylene gases to produce flames with very high temperatures. Much higher than what was possible before. And not long after the introduction of the application of oxygen and acetylene, a newer welding method was also introduced, which used electrical energy (electric welding).
What Is Sheet Metal Welding?
Welding is a process of joining one metal to another and “metal” here mostly refers to sheet metal. Sheet metal has the meaning of metal that has been processed into sheet one. It is a kind of flat and thin piece of metal. Usually, sheet metal is made from the main types of metals such as aluminum, stainless steel, bronze, brass, and of course steel. Today there are various online fabrication services that can be accessed by many industries at various scales to meet their needs for sheet metals.
Sheet metals are very popular in various metal hardware production processes because of their thin dimensions. The category of a metal object that can be classified as sheet metal varies but generally, it is not more than 6 mm or 0.25 inch thick. Sheet metal with a thickness greater than that is usually considered plate metal. Sheet metal often comes in two forms; flat cut and circular strip. They are formed by a steel coil slitter that “grinds the metal material” continuously, sheet by sheet.
Welding is all about joining one metal to another and the product of that process is a welded joint. There are at least four welding methods; MIG, TIG, Stick, and Flux-cored. The first two are more widely used. For additional information, it is recommended that you check MIG vs TIG welding processes.
Common Welding Joints
But what are the common welding joints used on sheet metal welding? Keep reading!
There are at least three types of welded joints that are common for sheet metal welding. They are:
1. Butt Joints
Butt joints are the simplest example of welded joints. They are formed by joining two pieces of metal on the same surface. One side of the first metal is connected to one side of the second one. As simple as that. What’s the method? The metal sides to be joined are melted first to form welding surfaces which are commonly called faying surfaces. Faying surfaces can be shaped as required but are usually shaped based on factors such as increased strength, codes and standards to comply with, penetration, etc.
Common techniques used to shape Butt Joints are:
Square-groove Butt joint technique:
This is the simplest and most commonly used technique for strong penetration under great pressure. Starting from the root opening, the edges of the weld are not modified and in welding, the alignment of the two metals on the same plane is the most important factor.
Single (and double) Bevel Butt joint technique:
In this technique, one of the plates must be tilted at a certain angle. The second metal is not beveled and in practice, the Bevel angle is determined by the thickness of the metal and the size of the weld bead.
Single (and double) Butt V joint technique:
Has similarities with the single (and double) Bevel Butt joint but the two metal sheets are angled so as to form a V-shaped gap. Usually used for thick sheet metals.
The advantages and limitations:
This type of joint works by joining two metal sheets into one welded joint so that it is very strong. It’s also simple and practical. Butt joints have limitations in that they only work well on flat surfaces and two sheet metals of the same thickness.
Usually, this type of welded joint is often found in the welding of piping systems and steel structures. It can also be used to repair metal surfaces that have surface damage.
2. Lap Joints
The Lap joint is a further modification of the Butt joint. The difference is that the two metal sheets are superimposed on each other (overlapping).
There are several popular types of Lap joints, namely Slot, Flare-Bevel-Groove, Spot, J-Groove, and Bevel-Groove.
What are the explanations for Lap joint welding methods? Basically, the surfaces of the two metal sheets are overlapped. The consideration for determining the amount of overlap is important and the thicker the sheet metals used, the more overlap is required. Making sure there are no gaps between the two sheet metal planes is key. If the sheet metals being connected tend to be thin, it is necessary to reduce the amperage coupled with an increase in travel speed to minimize the risks of burn-through and distortion.
The advantages of this type of joint are that it is stronger than a butt joint (allows more weld material to be used), is easier to fabricate, tends to be flexible, and has a “cleaner look”. But the “disadvantages” are that it is more difficult to inspect, has more limited applications, and is more prone to leaks.
Usually used for engineering constructions such as cranes, load-bearing frames, bridges, and equipment with consistent heavy load pressure.
3. Corner Joints
Corner joints are two sheet metal joints where the two are joined together to form a right angle. Their combination forms the “letter L”. The key to this welding joint technique is the 90-degree angle formed by the two welded objects. Any connection that does not form a right angle cannot be classified as an angle joint (eg 45 degrees or 135 degrees).
The welding method for this type of welded joint can be carried out by not pre-preparing the surfaces of the objects to be joined, except for some types of corner joints, for example, T corner joints. If working on relatively thick sheet metal, layered welds may be required.
How about factors influencing the choice of welding method for corner joints? Depending on the sheet metals to be joined, if they tend to be thin, a T-type connection may be considered. As for thick sheet metals, the fully open corner joint type is the best option because this type exerts a greater force on the weld material than the two metals combined. As for the results of a cleaner weld, a half-open corner joint is considered better.
The advantages of using this type of corner joint are accommodation for two dissimilar metal sheets, “cleaner” weld results, and more suitable for two metal sheets that cannot be “adjusted” perfectly. The limitations however are that it is not suitable for holding very large forces on a regular basis, is more difficult to inspect, and in many cases tends to be time-consuming.
Comparison and selection of welding joints on sheet metals
When compared broadly, butt joints can be applied to piping constructions or repair damaged workpiece surfaces. Meanwhile, Lap joints are recommended for constructions that consistently withstand heavy loads, such as bridges and cranes. The corner joint is better for connecting two types of metal that are not the same and for producing a more aesthetically pleasing weld.
Sheet metal is an important component of modern metal-based industries and combining them with each other is inevitable. Appropriate welding processes are needed so that ineffective welds and weld failures can be minimized. The three types of welded joints above are the three most commonly used when people come to sheet metal welding. Each has its own advantages and limitations and the selection of all three should take into account the required weld strength, aesthetic factors, and production efficiency which includes the amount of weld material used and welding time.