Semi-automatic welding in protective gas environments today is the most advanced technological approach to the implementation of metal compounds. But even this group of welding methods is not free from the disadvantages that are manifested both in the spraying of the melt and in the difficulties of maintaining the standard parameters of the arc. Pulse welding, which requires the use of special equipment and observance of special organizational rules, helped to solve these problems in many respects, but from the point of view of the quality of the seam fully justifies itself.
Technology features
The method provides an overlay on the basic welding seam of additional current pulses, the frequency of which can reach tens of hertz. What is noteworthy, the percentage of pulse current relative to the main indicator is up to 15%. Today, technologies for the supply of double pulses in modulation conditions are also being developed. This makes it possible to change the angles of inclination of the thermal effect, shape and pediments. For the operator, this means increasing the functionality of the process in terms of the ability to control small-drop metal transfer. In other words, pulsed arc welding does not minimize the same melt spraying effect with an increase in electrode powder consumption, but provides more means for its regulation. If we talk about the differences from conventional semi-automatic welding, then the pulse-arc technique also eliminates the need for stripping the work area, is characterized by a lower burnup of the metal, and also gives more space for the direction of the current. And all this is achieved in the same temperature conditions.
What equipment is used
Mostly these are devices operating in MIG / MAG welding modes and supporting the possibility of smooth adjustment of currents. There are two groups of pulse welding machines:
- Models with integrated gas-cooled (automatic) wire feed system.
- Models with optional (plug-in) wire feed system. In this case, liquid cooling is provided.
In both cases, the operator can count on the possibility of precise control of the frequency and size of the drops of metal melt, which are transferred to the weld pool. Similar functions are present in standard semiautomatic devices, but there is a fundamental difference in two points. Firstly, the current adjustment range extends from minimum to maximum. Secondly, a pulsed arc, regardless of operator control, prevents short circuits and almost eliminates spatter. In working with non-ferrous metals, the possibilities of detailed adjustment of the apparatus for specific operating modes are especially evident. For example, a modern semiautomatic device with a pulsed mode for aluminum welding supports synergistic control, which allows you to perform auto-tuning according to the thickness of the workpiece and the speed of the wire. The new MIG-Pulse modes, for example, also prevent sagging due to crushing of crystals in the melt zone.
Preparing the device for work and setting up
First of all, the main components of the welding station are connected. The design will include directly the inverter, transformers or converters from the power source, gas bottle and burner. Next, the optimal modes are set. For example, how to adjust the pulse mode of TIG welding? This is done through the control panel of the device, where you can set the type of welding process, as well as specific parameters for current strength, wire thickness, etc. By the way, the frequency pulse range is usually from 0.5 to 300 Hz. The higher the frequency, the more operational effects can be realized automatically. In particular, this concerns the reduction of pore size in the weld structure and the narrowing of the arc. Conversely, in the low range, more effective control is realized in terms of position selection. Thus, experienced welders consider the direction of the bottom-up arc to be the most optimal (PF mode).
Benefits of contact surge current
This type of frequency-controlled welding is also called resistive or fusion welding. It differs from techniques using an arc in that the current with the support of pulses passes through two separated products. What are the benefits of this? New opportunities and advantages of pulsed contact welding are caused by an increase in the current strength that occurs at the point of contact between the two products. To melt the metal, less load is required on the equipment, and the current strength and temperature regime increase. As a result, a reliable and point connection is formed with a neat seam. By the way, all regulatory possibilities when performing resistive welding are preserved.
Advantages of TIG welding with impulses
The combination of pulsed current mode and TIG welding method is used infrequently, but it has a number of important advantages. To the greatest extent, they relate to the possibility of reducing heat input, but are not limited to this. When working with thin sheets of stainless steel at high frequencies, you can achieve the accuracy of the formation of the seam. Changing the current parameters during TIG welding from maximum to minimum with pauses also allows you to minimize heating the workpiece and its warpage. At medium frequencies, a more efficient concentration of currents can be achieved, which contributes to deep penetration at standard rates of heat input. Also, due to the fine-crystalline structure, welding of stainless steels at an average pulse frequency provides high corrosion resistance of the weld. In the future, there is no need to apply special protective coatings, since the structure of the material itself does not support the development of rust.
Advantages of MIG welding with impulses
The main feature of this method is the non-contact method of transferring the melt from the wire to the welding zone. In combination with a pulsed current mode, this approach provides the following advantages:
- Save gas and wire resources. Consumables with smaller parameters are used, and the protective gas environment can be used for different tasks without selecting additional burners and tips.
- Low smoke and spatter. Again, due to a higher degree of control and power costs, in principle, the process of thermal exposure is optimized and negative factors are reduced.
- High performance. In MIG mode, pulsed welding provides higher melt efficiency with the same technical and operational parameters of the equipment.
- Reliability and safety. Comprehensive control of the welding process is expressed not only in the regulation of spatter and automation of individual functions, but also in the support of a whole set of protective options with shutdown during overheating.
When applying pulsed current welding
The technology was developed primarily for stainless steel and today is one of the most effective methods for welding such steels. Moreover, the scope of its application has expanded significantly, covering operations related to the processing and joining of low-carbon steels, aluminum, copper, as well as silver and titanium. Pulse spot welding also works well when connecting thin-walled parts made of both ferrous and non-ferrous metals. Especially the combination of pulsed current with a tungsten electrode can minimize the risk of burn-through of blanks in the form of thin sheets from 1 to 50 mm.
Impulse welding weaknesses
Like all welding technologies, including modern ones, the pulse method is not free from disadvantages. Despite the expressed advantages, it is rarely used in solving typical problems due to the high cost of equipment, increasing organizational costs and a number of negative technological nuances. In particular, the TIG mode of pulsed welding is characterized by low productivity and low wire feed speed. The use of other modes is limited by high requirements in terms of the choice of mixtures with shielding gases. That is, the method is for the most part highly specialized and is suitable only for use in certain operations with certain conditions.
Conclusion
The ability to precisely control the current is a logical continuation of the concept of inverter semi-automatic welding, which makes welding processes more flexible and more functional. Another thing is that, along with the extension of the optional, various restrictions on the use of the method are also imposed. At the amateur level, of course, the need for pulsed welding, with all its advantages, is still not so obvious. The same investments in equipment and consumables are unlikely to be justified even taking into account the receipt of a high-quality seam. The situation is different in industry and professional construction, where minimizing melt spatter in the continuous welding mode justifies organizational difficulties.