How to choose a welding machine
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How does a welding machine work?
A welding machine is, roughly speaking, a device for powering a welding arc with electric power. It takes electricity from the network (single-phase 230 V or three-phase 400 V) and increases the power strength - up to the very high values necessary for welding metal.
Previously, transformers were mainly used in welding - relatively simple and inexpensive devices that had many disadvantages (heavy weight, large size, instability of the output power, “drawdowns” of the electrical network and unsuitability for certain types of work). Now they are almost completely replaced by welding machines with inverter power circuits. Their design includes diode rectifiers, blocks of transistors with a high switching frequency and high-frequency transformers of reduced size. Due to more complex circuitry and the abundance of electronics, inverter machines for manual and semi-automatic welding are more expensive than classic transformers. But this drawback is more than compensated by improved characteristics of the welding arc, improved quality of welds and the possibility of finer and more precise adjustment of the equipment. Therefore, inverter machines are better suited for both beginners taking their first steps in welding and experienced professional welders.
Types of welding
There are various ways to join metals by welding. Each technology has its own advantages, disadvantages and optimal areas of application.
Manual arc welding (MMA)
Welding using stick electrodes coated with a special coating is used primarily for joining parts made of carbon steel. This method is widely used for welding metal structures and pipelines, as well as connecting parts of machines and mechanisms.
Advantages of manual arc welding:
- low cost of equipment and consumables;
- you can quickly master the technology at a level sufficient to perform simple tasks;
- work is performed without the use of gas cylinders.
Flaws:
- low productivity compared to semi-automatic welding;
- The quality and strength of the weld depend very much on the skills and competence of the welder.
Argon arc welding (TIG)
Shielded gas welding using a non-consumable (tungsten) electrode is used to join parts made of stainless steel, cast iron, non-ferrous metals (aluminum, copper, titanium, magnesium, nickel, etc.) and alloys based on them. Since the electrode does not melt during TIG welding, special filler materials in the form of metal rods or wires, which are selected for a specific task, are used to form and fill the seam.
Advantages of argon-arc welding:
- you can cook almost any metals and alloys;
- technology allows you to carefully weld thin metal and parts of complex shapes;
- high quality welds and joint strength are ensured.
Flaws:
- low productivity due to the need to accurately control the welding process;
- high qualifications and a good level of training of the welder are required;
- the need to use an argon cylinder, which increases the cost of welding and limits mobility.
Semi-automatic welding (MIG/MAG)
In semi-automatic welding, which is performed in a protective gas environment, instead of stick electrodes, wire is used, which is continuously fed through the welding gun using a pulling mechanism. Simultaneously with the wire, a protective gas is supplied through the torch: inert (argon, nitrogen or helium), the function of which is to displace air, or active (carbon dioxide or oxygen), which is involved in the welding process. It is also possible to weld without using shielding gas, but this requires a special flux-cored (flux-cored) wire.
Advantages of semi-automatic welding:
- you can weld various types of materials (carbon and corrosion-resistant steels, aluminum and some alloys based on non-ferrous metals);
- the technology allows you to effectively weld parts of different thicknesses - from thin sheets to thick rolled metal;
- productivity is significantly higher than when using manual welding.
Flaws:
- equipment and consumables for semi-automatic MIG/MAG welding are more expensive than machines and electrodes for MMA;
- the need to use gas cylinders, which limit mobility and increase the cost of work.
There are other welding technologies: plasma, spot, laser, friction or explosion welding. But it is unlikely that their description would be appropriate in an article aimed at novice welders.
Note that many modern welding machines are universal equipment. For example, they can simultaneously have bayonet connections for the ground wires and electrode holder, which are necessary for manual MMA welding, and a connector for connecting a torch used for semi-automatic MIG/MAG welding. Such devices, which allow you to weld metal using several different methods, are suitable for welders who have to perform a wide range of tasks.
Maximum welding power
The maximum welding power, which must be indicated in the characteristics of the equipment, is one of the key parameters when choosing a welding machine. By increasing the power value, you can weld the metal deeper, make wider seams and use thicker electrodes.
When performing welding work, you need a power that will ensure reliable ignition of the electrode and its stable combustion, good heating of the metal and sufficient depth of the weld pool. For example:
- power 80 - 100 A - suitable for working with electrodes ∅ 2 mm, allows you to weld small shaped metal products with a thickness of about 2 mm;
- power 120 – 140 A - makes it possible to use ∅ 3 mm electrodes and weld metal structures from widely used angles and profile pipes;
- power 160 - 180 A - allows you to weld rolled metal with thick walls, such as channels, using electrodes ∅ 4 mm.
It should be borne in mind that when choosing a welding machine, you should always choose a device with a certain margin of maximum power (about 20% - 30%). Otherwise, the equipment will operate in critical load mode, and this has a bad effect on its reliability and durability.
The power adjustment range also has some significance. For example, to weld metal that is the thickness of a razor blade or the wall of a beer can, a very small power is required - about 5 A. It is unlikely that you will do this, but it will be nice if your machine allows you to reduce the value of the welding power to at least 30 - 40 A so as not to burn through the metal when working with thin sheet steel or small-caliber rolled metal.
Maximum size of electrode or wire
In the case of machines designed for manual arc welding, the maximum permissible electrode size is approximately proportional to the maximum power. But with semi-automatic devices the situation is different. Which wire can be used during operation is influenced not only by the power characteristics, but also by the design of the pulling mechanism. Its function is to ensure continuous smooth wire feeding at a given speed (without jerking or jamming).
The feed mechanism has rollers with grooves of a certain size, which have a U-shaped profile (for soft metal wire, such as aluminum) or a V-shaped profile (for steel wire). As a rule, the roller has two grooves of standard sizes (usually 0.6 and 0.8 mm, 0.8 and 1.0 mm, or 1.0 and 1.2 mm), but sometimes there are more. Therefore, it is the design of the broaching mechanism and the range of replaceable tips for the torch that come with the welding machine that determines what kind of wire a particular semi-automatic machine can work with.
Switching frequency
The switching frequency factor (PV) is a characteristic of welding equipment that describes its “endurance” and ability to work for a long time at maximum power without pauses. For example, a frequency of 70% means that a typical 10-minute operating cycle of the device includes up to 7 minutes of continuous operation, after which a 3-minute break is required to cool the “internals.”
When selecting a device according to this characteristic, you should take into account the intensity of the planned work and its nature. For example, for professional welding of large structures made of sheet steel, you need a machine that can be used to make long and thick continuous seams - for this it is better to take a model with a duty cycle > 70%. And for the manufacture of, say, forged fences, which are assembled from ready-made elements using “tack welds” (short or spot seams), it is quite possible to take a device with a PV of around 50%. Household tasks, which typically involve welding brackets to a fence post or hinges to garage doors, can easily be accomplished using a welding machine that has a duty cycle of ≤30%. Even such a small switching frequency (implying 3 minutes of welding and 7 minutes of rest) is quite enough for most craftsmen, because the welder in any case often has to pause and interrupt work in order to fit parts, change the electrode, remove scale from the seam and check its quality.
Input voltage and power consumption
Characteristics such as input voltage and power consumption are very important criteria when choosing equipment for an area with a problematic power supply or a mobile workshop that requires power from a generator (note that there are special welding generators that combine the functions of a welding machine and a mini-power station) . For example, the most powerful welding machines create such a large load on the network that it is hardly reasonable to use them in a home workshop, and they often require a direct connection to the panel, bypassing the automation. It should also be remembered that only 230 V devices can operate from a regular household electrical network, and in workshops of factories and factories connected to three-phase power, 400 V models are more in demand.
Auxiliary functions and protective systems
With the transition to inverter circuits and the gradual reduction in cost of electronic components, manufacturers of welding equipment began to improve their products, adding new features and functions that make the welder’s work easier and more convenient and safe.
- Hot Start - when the electrode touches the workpiece, the welding machine emits a pulse of increased power. Thanks to a short-term significant increase in power, the electrode instantly heats up to a high temperature, easily and confidently lighting the arc.
- Arc Force - the welding machine automatically produces “surges” of power in the process of transferring drops of molten metal through the arc gap from the electrode to the workpiece. Short-term, clearly controlled “jumps” in power strength allow you to increase the melting rate of the electrode, increase the depth of the weld pool and avoid “sticking” (welding the electrode to the workpiece).
- Protection against sticking(Anti-Stick) - if sticking cannot be avoided, the automation instantly resets the power to a minimum value or turns off the welding machine altogether. With this function, the “stuck” electrode is easily separated from the workpiece without damaging the coating (coating made of powdered materials) and therefore remains suitable for further use.
- Open Circuit Voltage Reduction(VRD) is a user safety feature. Its essence lies in the fact that at moments when the device is turned on, but welding is not carried out (for example, when preparing for work or while checking the quality of the seam), the electrodes are not supplied with operating voltage, but reduced to a safe value (usually within 10 – 20 V). Thus, closing the circuit when accidentally touching the electrode with a hand or other parts of the body does not lead to electric shock to the welder. Note that in many countries, workers on construction sites and in workshops of enterprises are required to use welding machines with the VRD function enabled under the terms of life insurance.
A device equipped with all the listed “tricks” will not turn you, with the wave of a magic wand, into a highly qualified specialist in manual arc welding. But if you are a beginner learning the basics of welding, or do not have much experience, then the above-mentioned auxiliary functions will greatly facilitate your first steps and help you make fewer mistakes. Therefore, when choosing your first welding machine, it makes sense to look closely at those models that have Hot Start, Arc Force and Anti-Stick.
Modern semi-automatic welding machines also have some functions that are useful both for beginners (help at the initial stage of learning electric welding) and for professionals (allowing them to work faster and make better quality seams).
- Pulse welding is a mode of operation of a semi-automatic inverter, in which the main welding power is supplemented by high-power pulses (usually 5 to 10 times stronger than the background power), following with a frequency of several tens to several hundred hertz. Current pulsation improves the processes of droplet transfer and metal mixing in the weld pool, reduces the number of pores and defects, improves the quality of the weld and the strength of the joint.
- Synergic control is an “intelligent” function that facilitates the process of setting up equipment. The firmware of the electronic unit that controls the operation of the welding machine contains an extensive library of standard programs. The catalog of ready-made settings includes programs for welding various types of steels, non-ferrous metals and alloys. The welder is required to indicate the input data (type of metal, thickness of the workpiece, wire size, composition of the shielding gas, etc.), and the electronics itself will select a package of optimal operating parameters (power strength and output voltage, wire feed speed, frequency and duration of pulses, etc.). P.). If during work the welder manually changes one of the parameters, then the rest are adjusted automatically. Thanks to the selection of optimal modes and electronic control of the welding process, machines with synergetic control improve the quality of work and reduce the likelihood of errors.
- 2/4-stroke mode is a method of controlling equipment that allows you to change the “behavior” of a semi-automatic device. In 2-stroke mode, the welding machine operates when the torch button is pressed and turns off when it is released. When working in 4-stroke mode, the equipment does not respond to releasing the button, but turns on and off only when the button is pressed - this makes it more convenient to work with long seams.
Brief conclusions
When choosing a welding machine for a garage or home workshop, you should ask yourself a number of questions and answer them honestly:
- What are we going to cook? — it is better to initially select equipment for more or less specific tasks, taking into account the type of metal and its thickness;
- what is your experience? — for beginners, a device with electronic “assistants” that help avoid mistakes is definitely better suited;
- How often will we do welding? — equipment for occasional and continuous use can vary greatly in price and reliability;
- what kind of work will we do? — when choosing a machine, you should take into account the following factors: work outdoors or indoors, welding with short or long seams, the ability to connect gas cylinders, etc.
Note that in welding it is not the brand of equipment that matters, and certainly not its cost. The main thing is experience and skills honed in practice. Even the best welding machine with the most advanced technologies and functions will not do the work for you and will not turn a beginner into a highly skilled welder. Therefore, it makes sense to look for your first welding machine among inexpensive models and mid-price class equipment, focusing on the characteristics and reviews.
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