Welding inverter - a device that allows you to connect the metal by welding. In comparison with a rectifier or transformer, inverter welding is easier, simpler and more affordable. How to learn to weld metal with an inverter?
Diagram of the elements of the inverter welding machine.
Inverter welding: sequence of operations
Welding technology consists of a series of sequential actions. Their correct performance provides a quality result - a solid connection between two metal surfaces. How to cook metal with an inverter, what to look for when learning to weld?Back to table of contents
Inverter welding machine power supply circuit.
- Preparation of the place for welding. The space within a meter radius is freed from wooden, paper, plastic objects. They may burn from a hot electrode or spark. The inverter is installed on the ground (concrete floor) and is connected to the electrical network. Two bars (wires with terminals "+" and "-") are strengthened as follows: the plus terminal is attached to one of the welded metal surfaces, an electrode is inserted into the minus terminal (this connection is called direct polarity, it is the most common). The body of the welder is closed with protective clothing (trousers, jacket, gloves), a face shield with a dark glass (light filter) is put on the face.
- We take in hand the terminal with the electrode. Turn on the inverter (toggle switch) - there is a small hum. Set the value of the welding current (control on the front panel). For a traditional electrode with a diameter of 3 mm, a welding current of 100 A is necessary. We drop the mask on the face (Fig. 1).
Ignition arc at the beginning of welding
Figure 1. The dependence of the diameter on the thickness of parts.
- We start welding. In the beginning it is necessary to ignite the arc. With experience this will be easy. For a novice welder, arc ignition is the first difficulty. Before starting the ignition, the electrode is tapped on the metal surface to remove the coating from its end. For the ignition of the cold metal arc (at the beginning of welding), the method of striking is used. It looks like the ignition of a match. The electrode is carried over the metal, slightly touching the surface of the welded part. In an inexperienced novice welder, the rod often sticks (glued to the metal). To detach it, you need to sharply tilt the terminal with the electrode in the other direction (break off the rod from the part). If not, turn off the power to the inverter. When the current is stopped, sticking will disappear.
- We strike sharply until an electric arc is formed. It is very bright, you can only look at it through a light filter.
- To maintain the arc fix the end of the electrode in 3-5 mm from the metal. At the beginning of training it will be difficult to maintain the necessary distance. If the electrode is brought too close, a short circuit will occur and it will stick to the part. If removed, the arc is lost, and it will be necessary to rekindle it again. During the welding process, the electrode is consumed, its coating burns out, and the base metal fills the seam between the surfaces being welded. Therefore, the hand with the terminal gradually goes down.
Weld Bath and Weld
Figure 2. The dependence of the diameter on the thickness of parts.
- When the arc is ignited, a liquid pool of molten metal is formed. This is a welded bath. To connect metal parts over the entire contact surface, the electrode slowly moves along the interface. Behind it moves the welded bath (liquid metal zone). The end of the rod oscillates (back and forth, left and right) relative to the seam between the two parts. This ensures the quality of the connection.
- If the arc was lost (the electrode was too far from welding), re-ignition is easier. To ignite the arc is enough to bring the end of the rod at a distance of several millimeters.
- A bright electric arc and a less bright welded bath are clearly visible in the welded shield. Contact surfaces being welded in the weld zone are less visible. However, it is impossible to remove the shield and pry on welding without a protective light filter. At best, the eyelids will scratch unpleasantly (feeling of sand in the eyes). At worst, you can lose your sight without the ability to restore it.
- When the rod is shortened to 5-6 cm, the welding is stopped, the inverter is turned off and the electrode is changed in the terminal.
- At the end of the welding, the solidified metal seam is tapped with a hammer to remove the slag layer. The seam cleared from slag has a brilliant surface.
Such is the technology of welding with an inverter as a whole. And now we will dwell in more detail on how to choose the right electrode and welding current.Back to table of contents
What electrodes to cook metal?
The electrode is a metal rod coated outside with a coating. The coating substance is a slag mixture, which, when welded, also melts, rises to the surface of the weld pool (it is lighter than metal) and protects the liquid metal from oxidation and saturation with nitrogen (Figure 2). In some cases, gas-forming additives are introduced into the coating, which ensure the evolution of gas during the melting of the electrode.
The composition of the inner core is determined by the type of metals being welded (low carbon and low alloy steels, brass and bronze, magnesium alloys, titanium alloys). In order to weld the metal of ordinary carbon steel, UONII electrodes are used. They are also used for corrosion-resistant steels. Welding of UONII is carried out only by direct current.
More universal are the rods marking the ANO. They are suitable for both direct and reverse current of any polarity.
Electrodes differ not only in the composition of the coating and the rod, but also in diameter. The dimensions of the rod in the coating range from 1.6 mm to 5 mm in diameter. The thicker the parts to be welded, the larger the diameter of the electrode is necessary for their fusion. There are mathematical formulas for calculating the diameter for a given thickness of metal parts. Novice welder easier to use tables.
Secondary factors affecting the choice of electrode is the type of connection of parts (horizontal, vertical or overhanging welding, butt or fillet weld). From the data in the table it can be seen that the diameter of the electrode for the corner joint is slightly different from the diameter for butt welding of parts.
Electrode positions during welding.
At the same time, welding rods of large diameter are not used for welding overhanging surfaces. For the ceiling, their dimensions are limited to a diameter of 4 mm.
Variation of the diameter of the rod while maintaining all other parameters can increase or weaken the specific welding current (the current per unit cross section of the electrode). This will affect the depth of penetration and the thickness of the weld. If the electrode is thinner, the current strength is concentrated and melts deeper, the weld is narrow. If the electrode is thicker, the specific value of the current decreases, and the depth of penetration becomes smaller, and the width of the seam - greater.Back to table of contents
How to choose the value of welding current and its polarity?
The strength of the current determines the depth of penetration of the metal. The stronger the current, the more powerful the arc, the deeper the metal melts. The strength of the current is directly proportional to the diameter of the electrode and the thickness of the weld. It can be determined by formula calculations or use ready-made tables.
The strength of the current is affected by the location of the weld. The maximum current value is used to penetrate horizontal surfaces. In order to weld vertical seams, the current strength is 15% less, for overhanging (ceiling) connections - less than 20%.
A household inverter has a current scale of up to 200 A. In semi-professional models, the scale value is graded higher, up to 250 A.
Figure 3. Movement of the electrode during welding.
Polarity - the direction of movement of the current. The inverter allows you to change the direction of the current. How is this done and why is a polarity change necessary?
The flow of electrons (the current moves from minus to positive) in inverter welding moves from the “-” terminal to the “+” terminal. The terminal on which electrons come (“+”) warms up more strongly. This fact is used to ensure high-quality welding on various metals, with different thickness of elements. If the parts are massive, then the “+” terminal is attached to their metal surface (to one of the parts). Such a connection is called direct polarity, it is often used in welding.
If a thin sheet of steel or a high-alloyed alloy, which is prone to fading of alloying elements, is alloyed, then the “-” terminal is connected to them. The resulting polarity is called reverse. With such a current flow, the maximum heating occurs in the electrode, and the base metal heats up less.
Reverse polarity is characterized by greater arc stability, it is easier to ignite and support its burning.Back to table of contents
How to move the electrode while welding?
The electrode moves along the welding seam not straightforwardly, but along the return path (zigzag to the right-to-left, spiral, herringbone). This provides the highest quality penetration, lack of penetration and discontinuities in the seam. A diagram of the most traditional types of rod end movement during inverter welding is shown in Fig. 3
Control of the welding inverter.
The welding speed or the speed of movement of the electrode form the weld surface and its parameters: convexity, width and depth. The faster the welded bath moves, the smaller the depth of the seam and its bulge after solidification. The welded joint is narrow and even. Slow movement of the electrode increases the depth of the seam and gives its surface a more convex appearance, the welded joint is wide, with a significant bulge and surges.
At the end of welding, the terminal with the rod is delayed for several seconds in the zone of the end of the seam. This allows the molten metal to accumulate and prevent the formation of a crater.
The parameters of the weld affects the position of the electrode during welding. The angle of the electrode determines the position of the weld pool. The angle of the electrode to the metal surface should be close to 90º and may differ from it by 15-20º.
The indicators we considered (current magnitude, polarity, diameter, and type of electrode) are called welding characteristics. Their correct choice provides high-quality fusion of parts. For household welding with an inverter on the garden plot (greenhouse frame, staircase, grape arbor) or in individual construction (basement frame) electrodes with a diameter of 3 and 4 mm are most in demand, using a welding current of about 100 A, with direct polarity.
Inverter welding is an accessible learning process.
Inverters - a new generation of devices. They greatly facilitate the training of welding and have a number of additional functions to help the novice welder to become a professional.