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In electric welding, an electric arc is used to heat the metal. It occurs between the part and the electrode – a rod made of conductive metal (sometimes non-metal). The temperature of the arc melts the metal. The fusion zone at the junction of parts is called a weld (weld) seam. For different metals and different types of compounds, the welding technique, the position of the electrode, the speed of its movement, and the amplitude can change. How to properly weld a seam so that the connection is not only reliable, but also beautiful, let’s talk further.
Types of welds and joints
Seams have a fairly extensive classification. First of all, they are divided according to the type of connection of doers. Depending on the requirements for reliability, the seam can be applied on one or both sides. With double-sided welding, the structure is more reliable and holds its shape better. If there is only one seam, it often turns out that the product is warped: the seam “pulls”. If there are two of them, these forces are compensated.
It is impassable to note that in order to obtain a high-quality weld, the metal should not be rusty. Therefore, the welding spots are pre-sanded or treated with a file – until the rust disappears completely. Further, depending on the requirements, grind or not the edge.
Butt joint (butt seam)
A butt seam in welding is used when joining sheet metal or pipe ends. The parts are laid so that there is a gap of 1-2 mm between them, if possible, they are rigidly fixed with clamps. During the welding process, the gap is filled with molten metal.
Thin sheet metal – up to 4 mm thick – is welded without prior preparation (rust removal does not count, it is required). In this case, cook only on one side. With a thickness of parts from 4 mm, the seam it can be single or double, but edge sealing is required in one of the ways shown in the photo.
- With a part thickness from 4 mm to 12 mm, the seam can be single. Then the edges are cleaned in any of the ways. It is more convenient to do one-sided preparation with a thickness of up to 10 mm, and thicker parts are cleaned more often in the form of the letter V. U-shaped cleaning is more difficult to perform, therefore it is used less often. If the requirements for welding quality are increased, with a thickness of more than 6 mm, stripping is required on both sides and a double seam on one side and the other.
- When welding metal with a thickness of 12 mm or more butt, a double seam is definitely needed, it is impossible to heat such a layer on one side. Edge trimming is double-sided, in the shape of the letter X. It is unprofitable to use V or U shaped edge trimming with such a thickness: several times more metal is required to fill them. Because of this, the consumption of electrodes increases and the welding speed is significantly reduced.
If, nevertheless, it is decided to weld metal of great thickness with one-sided cutting, it will be necessary to fill the seam in several passes. Such seams are called multilayer. How to weld a seam in this case is shown in the figure below (numbers indicate the order of laying metal layers during welding).
Read about welding thin metal with an inverter welding machine here.
Lap joint
This type of connection is used when welding sheet metal up to 8 mm thick. It is boiled on both sides so that moisture does not get between the sheets and there is no corrosion.
When performing a seam with an overlap, it is necessary to correctly select the angle of the electrode. It should be around 15-45°. Then a reliable connection is obtained. With a deviation in one direction or another, the bulk of the molten metal is not at the junction, but to the side, the strength of the connection is significantly reduced or the parts remain not connected at all.
Tee and corner connection
The tee joint in welding is the letter “T”, the angular – the letter “G”. A tee joint can be with one seam or two. Edges can also be cut or not. The need for edge cutting depends on the thickness of the parts to be welded and the number of seams:
- metal thickness up to 4 mm, single seam – without edge processing;
- thickness from 4 mm to 8 mm – without edging double seam;
- from 4 mm to 12 mm – single seam with cutting on one side;
- from 12 mm, the edge is cut off on both sides, and two seams are also made.
The fillet weld can be considered as part of the tee. The recommendations here are exactly the same: thin metal can be welded without cutting edges, for greater thickness, you have to remove the part from one or two sides.
Corner and tee joints sometimes have to be welded on both sides (two seams). To properly weld such a seam, the parts are rotated so that the metal planes are at the same angle. In the photo, this method is signed “in the boat.” This makes it easier to calculate the movement of the electrode, especially for a beginner with welding.
When connecting thin and thick metal, the angle of inclination of the electrode should be different – about 60 ° to the thicker part. In this position, most of the heating will fall on it, thin metal does not burn through, which can happen if the angle of inclination is 45 °.
Fillet Welding
When welding fillet welds, the position and movement of the electrode must be monitored. You should get a seam with uniform filling. It is easier to implement this if you put the parts for welding “into the boat”, but this does not always work out.
If the lower plane is located horizontally, it often turns out that there is little metal on the vertical plane, as well as in the very corner: it stacks down. This happens if the electrode is at the top of the corner for less time than near its side surfaces. The movement of the electrode tip must be uniform. The second reason is that the electrode diameter is too large, which does not allow you to go lower and warm up the junction normally.
To avoid the occurrence of this defect, the arc is ignited on a horizontal surface (at point “A”), moving the electrode to the vertical surface, then return it to its place in a circular motion. When the electrode is above the joint, it has a slope of 45°, as it moves up, the angle slightly decreases (the figure in the picture on the left), when moving to a horizontal surface, the angle increases. With this technique, the seam will be filled evenly.
When welding corner joints, also make sure that the time spent by the electrode at all three points (on the sides and in the center) is the same.
Read about the choice of electrodes for inverter welding machines.
Position in space
In addition to different types of joints, seams can be located in space in different ways. They are in the down position. For the welder, this is the most comfortable. This is the easiest way to control the weld pool. All other positions – horizontal, vertical and ceiling seam – require certain knowledge of welding techniques (read below how to weld such seams).
How to weld a seam
When welding in the lower position, no difficulties arise even for a novice welder. But all other provisions require knowledge of technology. Each position has its own recommendations. The technique for making welds of each type is discussed below.
Welding vertical seams
During welding of parts in a vertical position, the molten metal slides down under the action of gravity. To prevent droplets from coming off, a shorter arc is used (the tip of the electrode is closer to the weld pool). Some craftsmen, if the electrodes allow (do not stick), generally lean them on the part.
Metal preparation (grooving) is carried out in accordance with the type of joint and the thickness of the parts to be welded. Then they are fixed in a predetermined position, connected with a step of several centimeters with short transverse seams – “tacks”. These seams do not allow the parts to move.
A vertical seam can be welded from top to bottom or from bottom to top. It is more convenient to work from the bottom up: this is how the arc pushes the weld pool up, preventing it from lowering down. This makes it easier to make a quality seam.
This video shows how to properly weld a vertical seam by electric welding with the movement of the electrode from bottom to top without separation. The short roll technique is also demonstrated. In this case, the electrode movements occur only up and down, without horizontal displacement, the seam is almost flat.
It is possible to connect parts in a vertical position with an arc separation. For novice welders, this may be more convenient: during the time of separation, the metal has time to cool. With this method, you can even rest the electrode on the shelf of the welded crater. It’s easier. The pattern of movements is almost the same as without a break: from side to side, loops or a “short roller” – up and down.
How to cook a vertical seam with a gap, see the next video. The same video tutorial shows the effect of current strength on the shape of the seam. In general, the current should be 5-10 A less than recommended for a given type of electrode and metal thickness. But, as shown in the video, this is not always true and is determined experimentally.
Sometimes a vertical seam is welded from top to bottom. In this case, when starting the arc, hold the electrode perpendicular to the surfaces to be welded. After ignition in this position, heat the metal, then lower the electrode and cook in this position. Welding a vertical seam from top to bottom is not very convenient, it requires good control of the weld pool, but in this way you can achieve good results.
How to weld a horizontal seam
A horizontal seam on a vertical plane can be carried out both from right to left and from left to right. There is no difference, to whom it is more convenient, he cooks like that. As when welding a vertical seam, the bath will tend to go down. Therefore, the angle of inclination of the electrode is quite large. It is selected depending on the speed of movement and current parameters. The main thing is that the bath stays in place.
If the metal flows down, increase the speed of movement, warming up the metal less. Another way is to make arc breaks. During these short intervals, the metal cools down a little and does not drain. You can also reduce the current a little. Only all these measures are applied in stages, and not all at once.
The video below shows how to properly weld metal in a vertical position with a horizontal seam.
Ceiling seam
This type of welded joint is the most difficult. Requires high skill and good control of the weld pool. To perform this seam, the electrode is held at right angles to the ceiling. The arc is short, the speed of movement is constant. Perform mainly circular movements that expand the seam.
Weld cleaning
After welding, scale splashes, drops of metal and slag remain on the metal surface. The suture itself is usually convex, protrudes above the surface. All these shortcomings can be eliminated: clean up.
Cleaning the seams after welding is done in stages. At the first stage, with the help of a chisel and a hammer, scale and slag are knocked off the surface. On the second, if necessary, compare the seam. Here you need a tool: a grinder equipped with a grinding disc for metal. Depending on how smooth the surface should be, different abrasive grits are used.
Weld defects
Beginning welders often make mistakes when making seams that lead to defects. Some of them are critical, some are not. In any case, it is important to be able to identify the error in order to correct it later. The most common defects among beginners are the unequal width of the seam and its uneven filling. This happens due to uneven movements of the electrode tip, changes in the speed and amplitude of movements. With the accumulation of experience, these shortcomings become less and less noticeable, after a while they disappear altogether.
Other errors – when choosing the current strength and the size of the arc – can be determined by the shape of the seam. It is difficult to describe them in words, it is easier to depict them. The photo below shows the main shape defects – undercuts and uneven filling, the reasons that caused them are spelled out.
Lack of penetration
This defect consists in incomplete filling of the joint of parts. This disadvantage must be corrected, as it affects the strength of the connection. Main reasons:
- insufficient welding current;
- high speed of movement;
- insufficient edge preparation (when welding thick metals).
It is eliminated by correcting the current and reducing the length of the arc. Having chosen correctly all the parameters, they get rid of such a phenomenon.
Read about choosing an inverter welding machine for home and garden.
undercut
This defect is a groove along the seam in the metal. Usually occurs when the arc is too long. The seam becomes wide, the temperature of the arc for heating is not enough. The metal around the edges quickly solidifies, forming these grooves. “Treated” by a shorter arc or by adjusting the current strength upwards.
With a corner or tee connection, the undercut is formed due to the fact that the electrode is more directed to the vertical plane. Then the metal flows down, a groove forms again, but for a different reason: too much heating of the vertical part of the seam. Eliminated by reducing the current and / or shortening the arc.
Projog
This is a through hole in the weld. Main reasons:
- too high welding current;
- insufficient speed of movement;
- too much gap between the edges.
The correction methods are clear – we are trying to choose the optimal welding mode and the speed of the electrode.
Pores and bulges
The pores look like small holes that can be grouped in a chain or scattered over the entire surface of the seam. They are an unacceptable defect, as they significantly reduce the strength of the connection.
Pores appear:
- in case of insufficient protection of the weld pool, an excessive amount of protective gases (poor quality electrodes);
- draft in the welding zone, which deflects protective gases and oxygen enters the molten metal;
- in the presence of dirt and rust on the metal;
- inadequate edge preparation.
The sags appear when welding with filler wires with incorrectly selected welding modes and parameters. Represent a numb metal that has not connected to the main part.
Cold and hot cracks
Hot cracks appear as the metal cools. Can be directed along or across the seam. Cold ones appear already on a cold seam in cases where the loads for this type of seam are too high. Cold cracks lead to the destruction of the welded joint. These shortcomings are treated only by repeated welding. If there are too many flaws, the seam is cut off and re-applied.
The inverter welding technique is described here.