The impact of the electric arc on the structure of the material is one of the oldest ways to obtain a strong connection between metal billets. The first technological approaches to this welding method had a lot of disadvantages associated with the porosity of the weld and the formation of cracks in the working area. To date, manufacturers of equipment and accessories have significantly optimized the method of conducting electric arc welding, expanding the scope of its use.
Technology Overview
The method is called MMA (Manual Metal Arc), which can be decoded as manual welding with piece electrodes. The working process is based on the control of electric current supplied to the target zone by a special source connected to the network. The current is supplied to the parts being welded by two cables of different polarity. Actually, the closure of the electric circuit provokes the formation of an arc, the thermal effect of which melts the metal and forms a weld pool.
After the completion of the heat attack, the working zone cools, and its structure crystallizes. An important component of the technology of electric arc welding is the electrode. As a rule, this is a steel rod provided with a coating with a certain chemical composition. As the arc is affected, the structure of the bar also melts and drops into the working zone, forming a uniform material with the workpiece.
Arc ignition as the first work step
As already mentioned, the initiation of thermal exposure occurs as a result of the closure of the electrical circuit. The arc itself, depending on the current source used, can be characterized by dipping, steeply dipping, or hard current-voltage characteristics. It arises as a result of supplying current to the electrode and the surface of the workpiece. Current is passed through both objects, after which an electric arc forms between them.
The excitation of the process itself occurs in various ways. In one case, electric arc welding is initiated by briefly touching the bar with a working part with a quick break. And in another - striking touches are performed with the same margins at certain distances. In this case, the stability of welding will depend precisely on the exposure to an acceptable distance between the electrode and the workpiece. If you exceed this distance, the burning of the arc will stop. Conversely, too close to the rod to be welded can cause adhesion of materials. The choice of the optimal indentation depends on the degree of elasticity of the arc itself, which is also determined by the current-voltage settings of the equipment. Experienced craftsmen can adjust the distance within the acceptable range, thus affecting the efficiency of the melt, and the penetration of the metal.
Welding process
The work involves the already mentioned current source, the types of which will be considered separately, and two cables with different polarity. One cable ends with an electrode holder, and the other with a terminal clamp, which is fixed to the workpiece. As a result of the thermal effect of the initiated arc, the metal melts in the weld pool. As this process progresses, droplets of the melting electrode are also transferred - small-droplet and large-droplet. Here it is necessary to emphasize the importance of coating the bar. The chemical composition of the coating is determined not so much by the requirements for interaction with the electric arc, but by the effect on the structure of the weld, which will absorb the coating components through melting drops.
In the process of electric arc welding, the outer layer of the electrode is also burned, as a result of which gaseous protective compounds are formed. The formation of a cloud that does not allow harmful effects from the environment is a fundamental difference between the modern approach to MMA welding. After stopping the supply of the electric arc, the process of solidification and crystallization of the formed compound begins.
Types of welds
There are several classifications of welds that can be obtained during this welding. For example, according to the position, ceiling, vertical and horizontal connections are distinguished. In turn, the vertical seams differ depending on the direction - on the descent and ascent. Horizontal joints are perhaps the most complex, since from the welding zone the metal will fall on the lower edges of the workpiece. For the same reason, the top edge can get a cut.
In length, intermittent and continuous connections are distinguished. The former are often used for the reason that they save resources and time. Continuous seams of electric arc welding are used in those cases when it is necessary to provide a high degree of reliability when pairing two critical structures. An intermittent connection is less durable, but under certain conditions it justifies itself.
There is a classification for convexity. This parameter depends on the volume of deposited metal. There are convex, normal and concave seams. At the same time, one should not expect that the presence of a large amount of surfacing as such ensures the strength and durability of the connection. Under the action of high loads and vibrations, such a seam loses the joint of a normal structure.
Transformers for welding MMA
This is a universal source and converter of electric current, which is also used for flux welding and plasma cutting of metal. Such devices are simple in device, unpretentious in maintenance and reliable. Management of even modern models is mostly mechanical. The stuffing of the equipment is a coil with a wound wire - a core that converts the mains electric current into the voltage necessary for specific tasks. It is important to note that working with electric arc welding under transformer power supply involves the use of alternating current, which requires professional skills from the operator.
Invertors
The most technologically advanced, easy-to-use and functional device to support modern welding. It provides work in direct current conditions, increasing the chances of getting a smooth and clean seam even for a beginner. More importantly, electric arc welding with an inverter allows you to use a household network for power supply, if it is capable of providing a current strength of 16 A to 25 A. In general, this is the optimal solution for private needs when processing parts in a garage, laying metal coatings, etc. etc. Specialists can use the resources of the inverter for argon-arc welding, expanding the capabilities of equipment operation.
Arc Welding Rectifiers
Such devices serve to convert the mains current from AC to DC, also contributing to the implementation of high-quality seams. The main difference between this type of current source is the coordination of interaction with different types of electrodes. With this support, electric arc welding machines can be used for operations in protective gas environments, for example, if the bar is made of steel or colormet. The disadvantages of rectifiers include large sizes, large mass and, as a result, difficulties with transportation. Therefore, manufacturers as an addition offer running platforms with wheels for convenient movement of the device.
Technology advantages
The configuration of this welding method against the background of many alternative methods may seem outdated and ineffective, nevertheless, within the framework of this concept, it is possible to organize the possibility of processing almost all common types of metals. Versatility is the main advantage of the MMA method. A plus is also noted in terms of physical ergonomics of work. This is not to say that manual arc welding is comfortable, but the very ability to perform operations in any position and in confined spaces is very valuable.
Separately, it is worth emphasizing independence from external atmospheric and temperature operating conditions. The process can be organized both indoors and outdoors. If we are talking about increased requirements for weld quality, the technology allows the use of protective media to prevent air from entering the weld pool, which minimizes the risks of defects.
Cons of technology
The method is very cheap in terms of organization, which cannot but determine a number of negative factors. For example, the exclusion of modern methods of process automation and electronic control of individual parameters of the current source transfers responsibility for the quality of the seam to the operator. The characteristics of the resulting compound structure will depend more on his skills. Easy-to-perform electric arc welding of metals cannot be called either. The difficulty lies in the process of ignition of the arc, which, again, is controlled by the user "by eye" without auxiliary systems. If you compare the method with semi-automatic welding, you will also find a lack of productivity.
Conclusion
Due to its versatility, MMA technology has embraced and stably holds many fields of application. In households, in workshops and garages, in industries and in construction, electric arc welding finds its place, making it possible to make welds of various types. As for the limitations, they are mainly determined by ergonomics. Due to their convenience, alternative concepts of semi-automatic welding are also in considerable demand, in some areas crowding out the principles of MMA. On the other hand, arc welding outperforms many competitive technologies due to the increased strength of the weld being formed and minimal resource investments in the organization of work.