When welding, knowing all the different types of welds is critical. One weld that I was totally unfamiliar with, but realized how important it was was the seam weld.
So what is a seam weld? Seam welding is a resistance welding process in which suitably contoured copper electrodes apply pressure to create a region of high resistance between metal sheets. The current passed through this region generates heat due to high electrical resistance. A seam weld is created through fusion.
Read on to find out more about the details of seam welding and the different processes through which it can be carried out.
What is seam welding used for?
Seam welding is one of the most widely used welding processes. Find out about the basics of seam welding, its applications, and techniques for making high-quality seam welds.
Fabricated metal products are only as good as the welding process used to join the assembly. Engineers must know which welding methods are suitable for different situations and they should also be aware of the welding techniques that will produce the best results.
Welders and engineers have two different welding styles to choose from. These methods are stitch welding and seam welding. The basic difference between the two is that stitch welding is intermittent while seam welding is continuous.
Both techniques rely on heat input to melt and fuse metal in order to join metal pieces. This can produce changes in metal properties in the heat-affected zone in particular.
It must be kept in mind that seam welding and stitch welding techniques produce different properties. Hence, they are employed for different purposes. Making the right welding choice can be the difference between a reliable weld and a weak one.
It is basically up to the designer to determine whether seam welding or stitch welding must be utilized. Different factors must be considered, such as the required joint strength, the application of the fabricated product as well as other design factors.
The fabrication drawing will, therefore, state the welding technique that must be implemented and also list other instructions. This gives much useful information to the welder such as whether to use seam welding or stitch welding.
What is seam welding and its types?
In seam welding, a continuous weld is created along the weld joint. This procedure can be performed for both flat and corner welds.
Seam welding is almost always performed whenever pipes and tubes must be joined. Seam welds are more durable and stronger than stitch welds since they cover the entire length of the weld joint.
A uniformly welded region is created through seam welding since the surfaces are joined by fusion bonding. In fact, in many cases, the seam weld made via resistance welding may be stronger than the base metal that is joining.
Owing to these overwhelming benefits, seam welding is the default choice in welding operations where the strength of the finished weld joint is a paramount factor. However, stitch welding can save time and money for welding applications where strength requirements can be relaxed. It is also better for thinner sections since it produces less distortion as a result of lower heat input.
Seam welding is also known as resistance welding. This welding procedure employs a roller in place of the welding stick electrode.
Seam welding can be further broken down into 2 types of welding processes: friction seam welding and resistance seam welding. Keep in mind that both welding techniques can be used for joining dissimilar metals in addition to similar metals.
Resistance seam welding
Resistance seam welding bears some similarities with spot welding. The key variation is that in resistance seam welding, the welding electrodes comprise of motor-powered wheels, whereas, in resistance spot welding stationary rods are employed.
Due to the welding technique utilized, resistance seam welding is the ideal method for joining metal sheets. It is, therefore, the mainstay in sheet metal product fabrication.
Here is how it is done. In resistance seam welding, the edges to be fused together are held tightly by a strong mechanical force while current is passed through this region. A lap configuration is made between contoured copper electrodes. Since resistance welding is employed, fusion is generated where the sheets are held together under a strong force since this is the region of highest electrical resistance.
The disc-shaped electrode wheels produce heat as a result of passing current through the point of contact. Since this is the site of greatest electrical resistance, heat generation here is maximum. Metal sheets are fed between these electrode wheels. A continuous resistance weld joint is thus produced. This is also known as a non-hermetic seal weld.
Consumable copper wire
Resistance welding is also carried out with the help of a consumable wire. This alternative method has certain similarities with conventional seam welding. The key difference is that there is a groove in the electrode wheel so that a consumable copper wire can be inserted between the base metal to be joined and the electrode wheel. A spool feeds the copper wire which is ultimately discharged as scrap material. As a result of this arrangement, a clean surface is available for welding.
This welding method lends itself to the fusion of stainless steel and coated metals. The process is capable of producing consistent results and can also achieve high welding speeds that exceed 70 meters for every minute.
The consumable wire definitely adds to the cost. However, this extra expense is offset by the value of scrap copper as well as the high welding quality. There are other advantages to seam welding such as zero weld fumes and consistent quality due to automation. Besides consistent quality, productivity is also high as a result of seam welding.
What is stitch welding and how does it compare?
Stitch welding is easy to identify since it is not continuous. Rather, it is intermittent. This sets it apart from seam welding which is continuous. It involves repeating the same set of procedures throughout the length of the weld gap. The welding operator must initiate the weld, keep welding for a certain distance along the weld gap and then pause.
He must then repeat this procedure at a small distance in front of the point where the previous weld joint ended. The welding operator will keep repeating this process until the endpoint of the weld gap is reached.
Stitch welding is suitable for both flat welds and corner welds.
Stitch welding is employed in situations where the heat input must be limited in order to reduce shape distortion as a result of high heat. Large amounts of heat can lead to warping of material which will skew dimensions.
Apart from bringing undesirable changes in dimensions, high levels of heat input can also change the mechanical and chemical properties of the base material that is being welded.
The thermal effects of welding are one of the biggest challenges that welders must face. As components to be joined are heated by welding, the parts may expand. However, when the parts are joined as a result of fusion, they will start contracting due to cooling. This cooling contraction can produce a high level of stress in the weld joint and can even cause cracking. This is a major weld defect that can turn into a fracture with the passage of time.
The heat input also creates a heat affected zone where the metallurgical properties of the base metal will be different from the rest of the material. This can lead to a number of adverse material property changes that can deteriorate the quality of the joint.
In aluminum, for instance, welding heat can undo tempering so that the material reverts back to its original properties. Similarly, when welding steel, there is the risk that a brittle heat-affected zone will be created, which is more susceptible to cracking than the rest of the base metal.
High heat input is a big problem in thin metal sheets and parts. With excess heat, there is a danger of burn-through, that is, a hole will be created where the base metal has been burnt or molten away by high heat level.
Stitch welding is a practical way of alleviating these unwanted effects of high heat. This technique has other advantages as well. Stitch welding means that less filler material is consumed. This leads to savings and cost reduction.
The operation is also completed in less time because less welding is involved compared to continuous seam welding. This reduction in welding time improved productivity and expedites the welding procedure.
However, there are also major disadvantages that must be given attention. Since there is a shorter overall weld length, the strength of the weld joint is considerably lower. This is a crucial drawback especially with regard to critical applications where weld strength is a top priority.
Another big drawback is that the unwelded parts can turn into crevices that let in dirt and other foreign material. As a result, unwanted material will accumulate within the weld, which can also lead to corrosion.