In the case of argon arc welding of aluminum, the arc is most stable when the electrode is in a vertical position and moving along the joint (during the welding of butt joints). An additive rod can be inserted from the front or back of the arc. However, in most cases the first method is used. Placement of the burner and rod for the additive in the process of welding straight-line joints can be as follows: butt-welding of the joint with an additive, flanged, with an overlap with a penetration.
Argon arc welding scheme.
In the case of welding of the flare connection, the arc should be of small length, but short circuits should be avoided. During the welding process, the electrode will be located below the top of the flanging. In the process of welding circular seams, the axis of the tungsten electrode is placed at an angle of 75-80 ° to the tangent with the base of the product at the weld, while the product will need to be rotated at the same speed. The circular seam ends with the overlap of the beginning of the seam on the section with a length of 18-20 mm. As a result, the arc should break. The rotation of the product must be sharply accelerated. If you make this technique correctly, then the final crater will be practically invisible on the circular seam.
Welding needs to be done at maximum speed, so correctly such a process can be performed only by a qualified welder. The motion of the burner should be straight-forward, without transverse oscillations. If you comply with these conditions, you can get a smooth and uniform along the entire length of the seam with a smooth, mirror-shiny base on top and a dense uniform fusion on the wrong side.
Scheme of jet protection during argon-arc welding.
Items that will be needed:
- thermally insulated casing;
- wire for additive;
- carbon rod;
- welding device.
Be sure to adjust the welding device.
How to prepare the surface for welding?
In most cases, the base of aluminum alloys is covered with a dense film of small thickness. Such a film has a high melting point and a large specific gravity. Such material complicates the ignition and maintenance of the arc during the welding process, and also prevents the connection of the edges of the main metal with the filler metal. Before making argon arc welding, a similar film will need to be removed from the base of the joined edges of aluminum alloys. The film can be removed mechanically or chemically. The first is used in the case of individual production. In the case of mass, it is advisable to use a chemical method of cleaning the base of aluminum alloys.
The mechanical method of cleaning the base of aluminum alloys involves removing a thin layer of metal with a steel brush or sandpaper of small thickness. The steel brush should be made of wire with a diameter of less than 0.15 mm.
Types of edge preparation for welding.
If you use a wire of large thickness, on the basis of aluminum there will be gross risks. In this case, the film layer will be removed unevenly, which may entail poor welding quality.
If you clean the aluminum base with a steel brush, you can get acceptable weld seams. Before cleaning, it will be necessary to degrease the surface, which can be done with solvents.
The base of aluminum alloys with zinc or magnesium is thoroughly cleaned. The easiest way to clean aluminum alloys with copper, iron or manganese is silicon.Back to table of contents
It should be noted that mechanical cleaning will not be able to ensure uniform removal of the film from the base of aluminum alloys. Using a brush is quite difficult to clean the edges that are joined. Therefore, in places where it is possible, it will be necessary to mechanically machine the joined edges on the machines. The effectiveness of the chemical cleaning method is established by measuring the contact resistance, which is proportional to the film thickness. In this case, it is recommended to use a microvoltmeter, which is graduated in micro-ohms.
The scheme of the seam when argon-arc welding.
For aluminum alloys in argon-arc welding, you can use the following chemical processing methods:
- Degreasing in alkaline solution and further clarification in a solution of phosphoric acid.
- Degreasing in alkaline solution with further clarification in a solution of nitric acid.
Edges of parts that are cleaned by one of the above methods can be easily welded. In this case, the seams will have a clean base. These cleaning methods are advantageous: on the basis of the treated edges, the film will have a slight thickness for 4-5 days.Back to table of contents
Existing connection types
In argon-arc welding of aluminum alloys, there is no flux, so in this case there are no restrictions on the choice of the type of joints. You can use the following compounds:
- butt joint
- with penetration lap;
- ordinary lap joint;
Types of welded joints.
Butt welding of aluminum sheets with a thickness of 0.8-3 mm should be done with small gaps. When welding aluminum with a thickness of 1.5-3 mm, the gap should be no more than 0.3 mm. Flare connection should be used for material with a thickness of 0.8-2 mm.
Perforated overlap arc welding is used for material with a thickness of less than 2 mm. When joining this type of edge should be pressed to the lining. This is necessary in order to ensure a tight fit of the elements to each other. The amount of overlap is determined based on whether you plan to melt the edges of the overlap through or not. In the first case, the edge of the bottom sheet should be located at the end of the forming groove so that this edge is used to form the bottom side of the seam. The amount of overlap is equal to the width of the groove. If it is good to drive off the edges, then you can make a corner joint on a material up to 2 mm thick without using a filler material.
High-quality execution of the connection implies an accurate fit of the edges. You should know that the gaps can cause enhanced oxidation of the edges, which will lead to porosity and the appearance of zones of fusion, which are located on the plane of contact of the edges with the installed additive.Back to table of contents
Nuances to know
Aluminum alloys have a high thermal conductivity, so in the place of welding the thickness of the joined blanks should be the same. If it is necessary to join the workpieces with walls of different thickness, the thicker edge should be cut at the welding site to a thickness that is equal to the thickness of the other edge.
In places where the design allows, it is recommended to use liners to facilitate the process of welding aluminum with argon and to make large tolerances on the fit of the joint. Lining should be made of stainless metal. A groove should be provided in the lining under the seam.
Butt bezkosnye connections are used for aluminum alloys with a thickness of less than 3 mm. If the workpiece is thicker, the edges to be welded will need to be mown.
Constructions with a wall thickness of 1-3 mm are connected by a single-layer seam. If the wall thickness is more than 3 mm, butt joint welding with bevel edges should be performed in several layers. The first layer is to melt the edges without filler material, another layer needs to be applied with the material for the additive on the completed first layer. Before you put the second layer, the first layer must be cleaned by mechanical or chemical method. When it is possible to weld from both sides, the workpieces are welded without bevel edges 6.5 mm thick.
Scheme of the welding machine.
In the case of welding of aluminum with a thickness of more than 1.6 mm, you will need to use wire for the additive, since the molten bath tends to form a concave base. Therefore, it will not be possible to use automatic welding of aluminum alloys if there is no device for mechanical wire feed for the additive. Be sure to be configured for this design.
Overlap joints and steamers are welded to the wire for additive. Such a wire can not be used, but in this case, the upper edge should be melted in order to be able to replace the wire for the additive.Back to table of contents
Aluminum welding technology
It is quite difficult to ignite an alternating current arc by touching a tungsten base made of aluminum with an electrode. To ignite the arc, at the beginning of the weld seam you need to lay a carbon rod, on which the arc will be ignited. After the tungsten electrode is heated, the arc can be easily excited on the main metal. To ignite the arc on the rod of coal is quite simple. Coal has a low thermal conductivity, and therefore in the process of a short circuit will quickly heat the material and the end of the tungsten electrode. Coal and tungsten can be characterized by a powerful thermionic emission from their base, due to which a stable arc will be excited in the process of removing the tungsten electrode. The heated end of the tungsten electrode will emit a powerful stream of electrons that support the burning of the arc in the process of transferring it to the metal.
Aluminum is characterized by fluidity, because it is recommended to weld in the down position.
If necessary, arc welding on a vertical base is performed from top to bottom for a metal thickness of less than 5 mm and from bottom to top for a workpiece thickness of more than 5 mm.
In some cases, cracks may form at the beginning of the seam. To avoid this, you will need to preheat the joint in the initial part of the seam. To do this, on the length of 35-45 mm the arc needs to heat up the joint several times, while the arc must burn in an inert gas. After that, arc welding is performed at maximum speed.
The choice of welding mode is influenced by the geometric shape and dimensions of the parts. With the help of arc welding in an inert gas environment, aluminum casting can be performed. To prevent the appearance of cracks, castings before welding will need to be preheated to 400 ° C. The welding is performed using a metal for the additive, the composition of which corresponds to the composition of the metal casting. Places that are subject to welding, will need to be pre-cleaned by mechanical means. After the brewing is done, the casting should be placed in a heat-insulated casing, and then slowly cooled.
In the case of a mechanized aluminum welding process, you will need to sustain a specific wire feed speed for the additive. If arc welding is performed at minimum speed, it is important to prevent overheating and oxidation of the wire for the additive.
Such a wire can be fed in any way that will ensure a uniform feed rate and its change. Mechanized argon arc welding is performed on the lining. The use of gas protection from the inside of the seam will not give positive results.
Argon arc welding of aluminum is a complex process, so you need to know the connection technology.