If you love DIY or work in an industrial laboratory, you will have often used a welding machine, i.e. that tool needed to permanently join two different materials. Welding machines are a very versatile tool and thus are used by a multitude of artisans or workers who need to model metals or tin alloys, speeding up and optimizing every step of the process. Depending on which welding machine and working technique you use, the materials that you can weld will be different, starting from metal sheets or tin or tungsten, but some models of welding machine also allow you to weld plastic.
Arc welding machines
Arc welding machines are among the most widely used and differ in the melting process, which is carried out by means of electrodes that act as filler material. Using an arc welding machine, the fusion between the materials takes place by reaching very high temperatures; the name is given by the electric arc that is created between the electrode and the part of the material to be welded. However, for optimal welding success, the so-called melting pool must be protected from contact with the air in order to prevent oxidation, and this can be managed thanks to inert gases that the welding machine injects directly onto the electrode coating.
Technically, arc welding is divided into two types: electric or coated arc welding and submerged arc welding. The main difference lies in the basic mechanism, in the environment the welding takes place in and in the chemical process that results from it, but both can be carried out on small and large surfaces.
Electric arc welding
In an electric arc welding machine, the elements that allow welding are the electric welding machine itself, the electrode holder clamp, the clamp that connects the machine to the workpiece and the metal workbench. In electric arc welding, the connection between the pieces to be welded is obtained through their fusion and the subsequent solidification of the two edges, where a filler metal is added. The fusion process between the two ends occurs through the electric arc, i.e. an electric discharge generated by the electrode in contact with the pieces to be welded. What characterizes the electric arc is its very high temperature, reaching up to 4000° C, thanks to which welding takes place very quickly.
The electrode usually consists of a so-called “metal core” coated with a mixture of special substances. The first element has the task of forming the filler metal, while the mixture serves to form a sort of gas dome that envelops the electric arc and avoids oxidation of the melting pool. This gas, however, produces slag that must be removed as soon as the weld solidifies, and it is advisable to do so with a slag hammer and a metal brush. Finally, when performing electric arc welding, it is very important to wear protective equipment, because during this process UV and IR radiation are emitted. For this reason, it is essential to use protective glasses and visors for welders, but also gloves to protect hands and a work suit.
Submerged arc welding
As far as submerged arc welding is concerned, it involves a more advanced and at the same time faster technique, because there is no need to replace the electrodes like in electric arc welding, but a continuous wire is used which is consumed as the welding progresses. In this welding technique, the melting pool is protected by a special powder that creates a sort of protective screen, avoiding contact with air. Submerged arc welding is, therefore, a technique that can be made automatic, being able to perform both circumferential welding on positioners and longitudinal welding on flat surfaces. The name “submerged arc” derives from the movement of the arc of the electric welding machine which, when it strikes below the melt pool, is hidden from the human eye.
A submerged arc welding machine consists of a current generator, a wire feeder moving at constant speed along the entire welding line, a hopper containing the flux, and a possible device for the recovery of the unmelted flux. Unlike electric arc welding, in this case a granular flux is required to protect the weld pool, so this welding machine can only be used in a flat position. Specifically, although longitudinal joints can be made, circumferential joints can only be made by joining positioning machines to the welding machine, capable of placing the joint to be welded in a flat position.
Types of arc welding machines
As said, arc welding machines are divided into two macro categories: electric arc and submerged arc. However, they contain other subcategories, starting with the MMA electrode welding machine or coated electrode welding machine (SMAW), considered ideal if you need to start this type of work and have little experience. If you are, therefore, a beginner, the advice is to opt for this arc welding machine which has a ground cable to connect directly to the workpiece and a cable complete with electrode holder clamp. The welding process takes place as described above, i.e. with the electrode melting after a short circuit and its distribution along the entire area to be welded, waiting for it to cool down to clean it. During melting, you must pay particular attention not to bring the electrode too close to the piece to be welded, because if it sticks to the surface, you risk preventing the formation of the electric arc essential for welding. In addition, you must keep an adequate distance between the arc and the workpiece to be welded, adapting every time the electrode wears out. Other types of arc welding machine are the MMA inverters, which have an electrical circuit from which they take direct current and allow the power to be adjusted as required. Precisely because of this feature, they ensure a better quality welding, but they are also light and compact, so they are very comfortable to use in any place and are equipped with a safety system that allows the current to be interrupted in case the electrode should stick to the piece to be welded. If you use the welding machine for small manual or DIY jobs, this model is ideal, because it costs less than the others and is so handy that it can be used in any place, even the narrowest one. If, on the other hand, you are an expert welder, the TIG model may be more suitable, because it uses an inert gas, an infusible electrode and a filler metal in the process. Thanks to this type of welding machine you can, therefore, weld pieces of even very thin materials and make use of its semi-automatic operation in which the tow-wire system for the filler metal allows you to have a free hand. It is the ideal welding machine if you are used to melt non-ferrous metals, such as titanium or aluminum, and guarantees a high quality and watertight result. The only contraindication is that in this model the welding torch must be cooled, otherwise the machine will malfunction or break. This is because the gas-induced cooling is sufficient only when you need to carry out low current intensity welds; therefore, if you need to carry out welds that require a higher current intensity, it is better to direct you towards a model with a liquid-cooled torch. Finally, there are MIG/MAG arc welding machines that are suitable both if you already know the job and if you want to take your first steps in the field. This model is characterized by the absence of a coated electrode, replaced by a coil of metal wire that unrolls by hand and, passing through the welding torch, wears out during the welding process. Moreover, the classic electrode coating is also absent, in whose place there is a gas (argon or helium, usually) spread by the torch itself when you are welding. It is a perfect machine if you have to weld materials such as stainless steel or light alloys or non-ferrous metals and it also uses a mixture of argon and carbon dioxide (or argon and oxygen), thanks to which the welding quality is improved.
How to choose the best electric arc welding machine
Many welding products and many models of arc welding machine are on sale on the market, but none can be defined as universal, so when you have to choose the perfect one for your professional or hobby needs, you will have to take into account several factors and compare advantages and disadvantages. The first discriminating factor is, of course, your budget, on the basis of which you will be able to establish the quality level of the electric welding machine, but it will not be difficult to find an arc welding machine on offer at competitive prices, especially on specialized online shops; then the use you must make of it, if you will use it occasionally or for long-term projects; it is also important to note what maintenance it requires and whether you will be able to ensure it; moreover, the type of production you will be dealing with and, above all, the materials to be used. In this regard, an MMA welding machine, for example, can weld most existing materials, but it is not the best with aluminum. MIG/MAG welders, on the other hand, weld the most common metals, while TIG welders are perfect for any metal, including titanium. Another element to take into consideration before purchasing your electric welding machine is the thickness of the parts to be welded, because the thicker they are the more current you will need, so you should always opt for a welding machine that can ensure the necessary current intensity. In this regard, know that single-phase welding machines are able to deliver a max intensity of 200A, while three-phase models can reach up to 600A. Finally, there is the so-called service factor, i.e. a selection criterion that takes into account the ability of a welding machine to work for a long time without overheating. This data is usually expressed as a percentage, which indicates the time of use of an electric welding machine at a specified current in relation to a standard period of ten minutes. In practice, for your choice you must take into account that the higher the current supplied, the higher the temperature of the welder will increase and the lower the service factor will be.