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 from non-metal). The temperature of the arc melts the metal. The zone of fusion at the junction of the parts is called the weld (welding) seam. For different metals and different types of joints, the welding technique, the position of the electrode, the speed of its movement, the amplitude can change. How to properly weld the seam, so that the connection turned out not only reliable, but also beautiful, let's talk further.
- 1 Types of welds and joints
- 2 How to boil a seam
- 3 Cleaning of welds
- 4 Weld seams defects
Types of welds and joints
Seams have a fairly extensive classification. First of all, they are divided by the type of connection of workers. Depending on the requirements for reliability, the seam can be superimposed on one or both sides. With two-sided welding, the design is more reliable and holds the shape better. If the seam is one, it often turns out that the product is warped: the seam "pulls". If there are two, these forces are compensated.
It is impassable to note that in order to obtain a high-quality welded seam, the metal must not be rusty. Therefore, the welding places are pre-sanded or treated with a file - until the rust disappears completely. Further, depending on the requirements, the edge is sewn or not.
Butt joint (butt weld)
Butt weld in welding is used when joining sheet metal or pipe ends. The details are laid in such a way that there is a gap of 1-2 mm between them, if possible, fixed firmly with clamps. During welding, the gap is filled with molten metal.
Thin sheet metal - up to 4 mm in thickness - is welded without preliminary preparation (rust removal does not count, it is mandatory). In this case, cook only on one side. With a thickness of parts from 4 mm, a seam can be single or double, but edge sealing is required in one of the ways presented in the photo.
- With a workpiece thickness of 4 mm to 12 mm, the seam can be single. Then the edges are cleaned by any of the methods. It is more convenient to do one-sided preparation at a thickness of up to 10 mm, and thicker parts are cleaned more often in the form of a letter V. U-shaped trimming is more difficult to perform, therefore it is used less often. If the requirements for welding quality are increased, at a thickness of more than 6 mm, stripping is necessary on both sides and a double seam is required on one side and on the other.
- When welding metal with a thickness of 12 mm butt, as if a double seam is required, it is impossible to heat such a layer from one side. Trim edges are double-sided, in the form of the letter X. Use at this thickness V or U shaped edge stripping is unprofitable: to fill them, several times more metal is required. Because of what the expense of electrodes increases and speed of welding considerably decreases.
If the metal of a large thickness is cooked with a one-sided cutting, it is necessary to fill the seam in several passes. Such seams are called multilayered. As in this case, weld the seam is shown in the figure below (the digits indicate the order of laying the metal layers during welding).
On welding of thin metal inverter welding machine read here.
This type of connection is used when welding sheet metal up to 8 mm thick. Cook it from two sides, so that moisture does not get between the sheets and there is no corrosion.
When making a seam, overlap, it is necessary to choose the correct angle of the electrode. It should be of the order of 15-45 °. Then a reliable connection is obtained. When you deviate in this or that direction, the bulk of the molten metal is not at the joint, but in the side, the strength of the connection is significantly reduced or the parts remain completely unconnected.
T-joint and corner connection
The T-joint in welding is represented by the letter "T", the angular - in the letter "G". The T-joint can be with one seam or two. The edges can also be cut or not. The need for cutting the edge depends on the thickness of the welded parts and the number of seams:
- thickness of metal up to 4 mm, single seam - without edge treatment;
- thickness from 4 mm to 8 mm - without processing the edges seam double;
- from 4 mm to 12 mm - single seam with cutting from one side;
- from 12 mm the edge is cut from two sides, and the seam is made also two.
The corner seam can be considered as part of the T-joint. Recommendations here are exactly the same: a thin metal can be welded without cutting edges, for a greater thickness, you have to remove a part from one or two sides.
Angle and T-joints sometimes have to be cooked on both sides (two seams). To properly weld such a seam, the parts are turned so that the metal planes are at the same angle. In the photo, this method was signed "in a boat". So it's easier to calculate the movements of the electrode, especially the beginner with welding.
When connecting a thin and thick metal, the angle of inclination of the electrode should be different - about 60 ° to a thicker part. In this situation, most of the heating will be on it, the thin metal does not burn out, which can happen if the angle of inclination is 45 °.
Welding of fillet welds
When welding fillet welds, it is necessary to monitor the position and movement of the electrode. You should get a seam with a uniform filling. It is easier to implement this if you put parts for welding "into the boat", but this does not always happen.
If the lower plane is horizontal, it often turns out that there is little on the vertical plane, and also in the corner of the metal: it stacks down. This happens if at the top of the corner the electrode is less than near its lateral surfaces. The movement of the electrode tip should be uniform. The second reason is the too large diameter of the electrode, which does not allow to fall below and warm up the joint normally.
To avoid the appearance of this defect, the arc is ignited on a horizontal surface (at point "A"), moving the electrode to a vertical surface, then in a circular motion, return it to its place. When the electrode is above the joint, it has a slope of 45 °, as it moves up the angle decreases slightly (the figure in the picture on the left), when the transition to a horizontal surface, the angle increases. With this technique, the seam will be filled evenly.
When welding the corner joints, also make sure that the time for finding the electrode at all three points (on the sides and in the center) is the same.
On the choice of electrodes for inverter welding machines, read here.
Position in space
In addition to different types of joints, seams can be arranged in different ways in space. There are they in the bottom position. For the welder this is the most comfortable. So the easiest way to control the welded bath. All other provisions - horizontal, vertical and overhead seam - require a certain knowledge of welding techniques (see how to make such seams read below).
How to boil a seam
When welding in the lower position, there is no difficulty even for a novice welder. But all other provisions require knowledge of technology. There are recommendations for each provision. The technique for performing welds of each type is discussed below.
Welding of vertical seams
When welding parts in the vertical position, the molten metal slides down under the action of gravity. To prevent the drops from falling off, use a shorter arc (the tip of the electrode is closer to the welded bath). Some masters, if the electrodes allow (do not stick), they are generally supported by a part.
Preparation of metal (cutting edges) is carried out in accordance with the type of connection and the thickness of the parts to be welded. Then they fix in the given position, connect with a step of several centimeters short short cross seams - "tack". These seams prevent parts from moving.
The vertical seam can be cooked from the top to the bottom or from the bottom to the top. It is more convenient to work from below-up: so the arc pushes the welded bath up, preventing it from sinking down. So it's easier to make a quality seam.
This video shows how to properly weld a vertical weld with electric welding with electrode movement from bottom to top without detachment. The technique of a short roller is also demonstrated. In this case, the electrode moves only up and down, without horizontal displacement, the seam is almost flat.
To connect the parts in a vertical position can be with the separation of the arc. For novice welders, this can be more convenient: during the breakaway the metal has time to cool down. With this method, it is even possible to support the electrode on the shelf of a welded crater. It's easier. The scheme of movements is almost the same as without detachment: from side to side, with loops or a "short roller" - up and down.
How to cook a vertical seam with a detachment, see the next video. In the same video lesson, the effect of the current on the shape of the seam is shown. In general, the current must be 5-10 A less than the recommended electrode for this type and the thickness of the metal. But, as shown in the video, this is not always true and is determined experimentally.
Sometimes a vertical seam is brewed from the top to the bottom. In this case, when igniting the arc, keep the electrode perpendicular to the surfaces to be welded. After ignition in this position, heat the metal, then lower the electrode and cook already in this position. Welding a vertical seam from top to bottom is not very convenient, it requires good control of the welded bath, but in this way you can achieve good results.
How to cook a horizontal seam
The horizontal seam on the vertical plane can be kept from right to left, or from left to right. There is no difference, to whom, as it is more convenient, he so cooks. As when welding a vertical seam, the bath will tend to go down. Because the angle of the electrode is quite large. It is selected depending on the speed of movement and current parameters. The main thing is to keep the bath in place.
If the metal flows down, increase the speed of the movement, less heating the metal. Another way is to do arc breaks. During these short intervals, the metal cools slightly and does not drain. You can also reduce the current slightly. Only apply all these measures in stages, but not all at once.
The video below shows how to properly weld the metal in a horizontal position. The second part of the video about vertical seams.
This type of welded joint is the most complicated. Requires high skill and good control of the welded bath. To perform this seam electrode keep at right angles to the ceiling. The arc is short, the speed of movement is constant. They perform mainly circular movements that extend the seam.
Cleaning of welds
After welding on the surface of the metal remain scraped with scale, a drop of metal and slag. The seam itself is usually convex, protruding above the surface. All these shortcomings can be eliminated: clean.
The cleaning of the seams after welding is done step by step. At the first stage, using 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 Bulgarian, equipped with a grinding disc for metal. Depending on how smooth the surface should be, use a different grain of abrasive.
Sometimes, when welding plastic metals, requires tinning - coating the weld with a thin layer of molten tin.
Weld seams defects
Beginners often encounter errors when making seams, which lead to defects. Some of them are critical, some are not. In any case, it is important to be able to determine the error, then to correct it. The most common defects among novices are the uneven width of the seam and its uneven filling. This is due to uneven movements of the tip of the electrode, a change in the speed and amplitude of the movements. As experience accumulates, these shortcomings become less noticeable, after a while they disappear altogether.
Other errors - when choosing the current strength and the magnitude of the arc - can be determined by the shape of the seam. In words it is difficult to describe them, it's easier to portray them. The photo below shows the main defects of the form - undercuts and uneven filling, the reasons that caused them are spelled out.
This defect consists in incomplete filling of the joint of parts. This drawback needs to be corrected, since it affects the strength of the joint. Main reasons:
- insufficient welding current;
- high speed of movement;
- insufficient preparation of edges (for welding of thick metals).
Eliminated by correcting the current and reducing the length of the arc. Having selected correctly all the parameters, they get rid of this phenomenon.
On the choice of inverter welding machine for home and dacha read here.
This defect is a groove along the seam on the metal. Usually occur when the arc is too long. The seam becomes wide, the arc temperature is not enough for warming up. The metal along the edges quickly solidifies, forming these grooves. "It is treated" with a short arc or a correction of the current strength in a larger direction.
With a corner or T-joint, the undercut is formed due to the fact that the electrode is directed more towards the vertical plane. Then the metal flows down, the groove is again formed, but for a different reason: too much heating of the vertical part of the seam. Eliminated by lowering the amperage and / or shortening the arc.
This is a through hole in the weld seam. Main reasons:
- excessively high welding current;
- insufficient speed of movement;
- Too much clearance between the edges.
The methods of correction are clear - we try to choose the optimal weld regime and the speed of the electrode movement.
Pores and sagging
Pores look like small holes that can be grouped together in a chain or scattered over the entire surface of the seam. They are an impermissible defect, since they significantly reduce the strength of the connection.
- when the welded bath is insufficiently protected, excessive amounts of protective gases (poor quality electrodes);
- draft in the welding zone, which deflects protective gases and oxygen gets to the molten metal;
- if there are contaminants and rust on the metal;
- insufficient cutting of edges.
The influx occurs when welding with filler wires with improperly selected modes and welding parameters. They represent a sluggish metal that does not connect to the main part.
Cold and hot cracks
Hot cracks appear during the cooling of the metal. Can be directed along or across the seam. Cold appears already on the cold seam in cases where the loads for this type of seam are too large. Cold cracks lead to the destruction of the welded joint. These disadvantages are treated only by re-welding. If there are too many drawbacks, the stitch is cut and re-applied.
The welding technique of an inverter is described here.