Semi-automatic welding of stainless steel: everything you need to know in one place

11/26/2020 Author: VT-METALL

Issues discussed in the material:

• The principle of semi-automatic argon welding
• Advantages and disadvantages of semi-automatic argon welding
• Important nuances of semi-automatic argon welding
• About using a semi-automatic machine when working with stainless steel
• About semi-automatic argon welding of cast iron
• Step-by-step semi-automatic welding process in argon
• About the choice of equipment for semi-automatic argon welding

Semi-automatic argon welding is the preferred metalworking method when it is necessary to obtain a high-quality weld. Welding parts in an inert gas environment guarantees the absence of corrosion and also allows you to speed up the work process without loss of quality.

Our material describes the basic principles of working with a semiautomatic device in a protective gas environment, provides recommendations for choosing equipment, and also describes the process itself. After studying the article, you will have a clear idea about this type of welding.

Content

• Is it possible to cook stainless steel with a semi-automatic machine and what is it?
• Advantages and disadvantages of semi-automatic welding
• Video about semi-automatic welding of stainless steel
• Features of welding stainless steel semi-automatically
• Use of Gas in Stainless Steel Welding
• Materials and equipment required for welding
• Welding wire selection
• Preliminary work before welding begins
• Semi-automatic welding of stainless steel with other types of metals
• Tables with semi-automatic welding settings
• Final work after welding

Is it possible to cook stainless steel with a semi-automatic machine and what is it?

Semi-automatic welding of stainless steel involves joining workpieces together in a protective gas environment. There are two technologies: MIG (metal inert gas welding) and MAG (active gas welding). To carry out this type of welding, shielding gas and welding wire are required, which is automatically continuously fed into the welding zone. Thus, the filler material melts together with the workpiece steel, forming a weld. The shielding gas coming from the cylinder is needed to prevent oxygen from penetrating into the welding zone and oxidizing the metal.

The principle of semi-automatic argon welding

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Semi-automatic argon arc welding is a mechanized process. In this case, the electrode wire is fed into the working area at a constant or variable speed, and in parallel with this, argon is supplied from the cylinder.

Abroad, the abbreviation MIG is often used to denote semi-automatic welding in argon. More precisely, this means any work in an environment of inactive gases.

If we compare argon welding with working in other gases, the first option has the best price-quality ratio.

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• Steel grades: classification and interpretation
• Aluminum grades and areas of their application
• Defects in metal products: causes and search methods

You need to understand that due to semi-automatic welding it is possible to cope with the problem of uneven heating of the workpiece and protect the welded joint. This effect is achieved due to the fact that the welding zone is protected by an inert gas, and the supply of filler wire is regulated in accordance with the automatic adjustment of the current strength. A broaching mechanism is responsible for feeding the wire, and with the help of a well-chosen ratio of feed speed and melting temperature, uniform filling of the seam is achieved.

Semi-automatic argon welding has the following features:

• Provides seam protection from oxidation.
• Argon is an inert gas, so it is not able to react with the metal of the workpiece.
• The gas displaces air from the welding zone, thus protecting the weld from oxidation. This function is most important for high-quality processing of non-ferrous metals.
• Provides increased connection strength.

Advantages and disadvantages of semi-automatic welding

Advantages:

• high productivity without loss of weld quality;
• absence of strong smoke, which makes welding indoors easier;
• a small amount of metal spatter (due to the gradual feeding of the welding wire);
• the ability to weld thin and thick workpieces;
• reduced amount of welding material consumption.

Flaws:

• the need to use a gas cylinder

This disadvantage lies in the difficulty of transporting the cylinder to the welding site. But if you take into account all the listed advantages, then you can easily turn a blind eye to this drawback.

The need for shielding gas in operation

Gas is often replaced with cored wire.

It consists of the following components:

• top metal layer;
• cores;
• flux.

The flux is located in the inner core. It is released when the top steel layer melts and provides the welding zone with protection from oxidation.

There are some drawbacks to using this element. The seams are not as reliable as when protecting the weld pool with gas.

Therefore, this technology is used only for soldering workpieces in hard-to-reach areas where it is impossible to deliver a gas cylinder with the smallest volume.

We recommend reading: How to weld stainless steel with electrodes

In all other situations, work is carried out only using gas and an electrode.

Features of welding stainless steel semi-automatically

Like any other method, semi-automatic welding has its own characteristics. Let's look at the most important

of them:

• The gas mixture for welding should include 70% carbon dioxide and 30% argon
• The welding angle should be from 5 to 10 degrees relative to the part for better weld penetration. This is especially true for welding thick parts
• reverse polarity
• The visible length of the filler material should be between 6 and 12 mm. When forming a seam, the distance from the nozzle to the metal should be minimal

There are usually 3 methods of joining workpieces using semi-automatic welding:

1. Jet transfer

It is used when it is necessary to weld thick-walled parts together. For this purpose, flux-cored wire and special heads are used.

2. Short arc

weld thin stainless steel to prevent metal burning

3. In a protective gas environment

The most traditional welding method, where argon, carbon dioxide or a mixture of both is used as a shielding gas. We'll talk about this in more detail below.

Aluminum Welding Wire

For welding aluminum, aluminum wire, produced on spools, or aluminum rods, sold in packages, can be used. Filler wire, as well as rods, are rarely made of pure aluminum; they are mainly an alloy of aluminum with silicon and magnesium.

This alloy is universal for welding products containing aluminum in its composition. The percentage of the alloying element in the wire and rods is not too high (for example, silicon can be contained from 0.5% to 5%), so the physical characteristics of the weld change slightly, to a greater extent this affects the resistance to oxidation and the prevention of the formation of microcracks.

Use of Gas in Stainless Steel Welding

When we use a semi-automatic machine for welding stainless steel, the following question arises: “What gas to use?”

There are 3 gas options that can be used:

Argon

Semi-automatic welding of stainless steel in an argon environment is widely used due to the aesthetics of the resulting seams, but has disadvantages such as an abundance of spatter, arc instability and high cost.

Carbon dioxide

Semi-automatic welding of stainless steel in a carbon dioxide environment is the cheapest option, but due to even more splashes than with argon, the seams turn out to be very rough.

A mixture of argon and carbon dioxide

Basically, these mixtures contain 98% argon and 2% carbon dioxide, or 95% and 5%, respectively. This is the best option, because... it combines both affordable cost and good seam quality. If there are no high requirements for the type of seam, the percentage of carbon dioxide can be increased to 30.

But is shielding gas always necessary?

The answer is no. A protective environment can be achieved without the use of gas. In this case, an analogue of solid wire is used - flux-cored wire. It is a thin-walled tube, which is filled with flux and gas inside. The top is covered with a metal protective layer, which, when melted, releases flux, which in turn blocks the access of oxygen to the welding site.

At the same time, flux-cored wire is not used so often due to the inability to provide the necessary protection for the welding zone. This, in turn, reduces the quality of the seam - it becomes less durable and strong.

What properties of aluminum should be taken into account when welding it?

Understanding the nuances of the processes occurring in the structure of aluminum when performing welding work with it is especially important for novice welders. To understand this well, you need to become familiar with the chemical properties of this metal, which is characterized by its low specific gravity, high strength and exceptional chemical reactivity.

The most significant characteristic of aluminum, which not only experienced but also novice welders should know about, is its ability to quickly react with oxygen, which leads to the formation of a refractory oxide film on the surface of the metal. Typically, aluminum itself can melt at a temperature of 650 degrees, and to melt the oxide film covering its surface, a heating temperature exceeding 2000 degrees is required. When welding with direct current, the unmelted oxide film can be immersed in the molten metal, thereby deteriorating its internal structure.

Argon arc welding diagram

Another feature that should be taken into account when welding this metal is that it does not change its color when heated. Because of this, it is quite difficult to visually determine the degree of heating of the parts being joined, which often leads to burn-throughs and leakage of molten metal during welding.

A property of aluminum that should be taken into account if you are planning to weld parts from this metal is a significant coefficient of its volumetric shrinkage, which often leads to the occurrence of stresses and deformations inside the formed weld and, as a result, to the formation of cracks in it. To avoid such unpleasant consequences, it is necessary to modify the weld or compensate for metal shrinkage by using more welding wire.

Any instruction for welding aluminum, as well as alloys based on it, requires that the specialist performing it is aware of the characteristics of this metal, which include:

• high chemical activity;
• low melting point of the metal itself;
• significant volumetric shrinkage.

Considering all of the above, it can be argued that it is thanks to welding aluminum with argon that high-quality, beautiful and reliable connections of parts are obtained. And if you use semi-automatic equipment to perform such welding, you can effectively solve two problems at once: protect the welding zone from harmful environmental influences, and also compensate for significant metal shrinkage due to the constantly supplied welding wire.

Of course, in addition to this technology, there are other methods of joining aluminum parts using welding, the specifics of which every specialist should know about.

Modes of argon arc welding of aluminum and its alloys

Materials and equipment required for welding

1. Semi-automatic welding machine as a power source
2. Gearbox

Necessary for semi-automatic welding to regulate the gas pressure coming from the cylinder. Each type of gas has its own reducer.

3. Solid or cored wire (material identical to the parts being welded to improve the quality of the seam)
4. Shielding gas cylinder

To exclude point 4, it is necessary to choose a flux-cored wire, and it is necessary to remember about the reduction in the quality of the seam.

5. Means of protection:

• A welding mask is a mandatory means of protecting the eyes and face during welding work.

Welding helmets are produced in several types: with a small area covering the face and head, with a large protective covering including the neck and hair, and also with a rising light filter.

• Gaiters are a necessary attribute to protect the welder’s hands

They are made from split wood or canvas. In addition, they differ in the number of finger compartments.

Welding process

The following steps must be followed:

1. The burner and ground cable are installed.
2. A reducer is installed on the argon cylinder . You need to check the gas pressure, it should be higher than the residual pressure.
3. A hose is installed on the outlet fitting of the cylinder and clamped with a clamp . Its second end is connected to the welding machine.
4. According to the instructions for the welder, set the value on the flow reducer to the value recommended by the manufacturer. To do this, you need to open the control valve.
5. Clean the burner wire channel if there is any wire left there from previous work.
6. Install the reel onto the unwinding rod . Check that the positions of the pins and mounting holes match.
7. The wire is passed through a rolling roller.
8. Reinstall the pressure roller.
9. Using the adjusting screw, set the clamping force so that the wire does not slip in the groove.
10. The wire is pulled into the burner cord channel with the conductive tip removed.
11. Screw a tip of a suitable diameter onto the burner and install the nozzle in place.
12. Connect the device to the network.
13. Prepare parts to be welded . The entire width of the edge is cleaned to a metallic shine.
14. Edge cutting and chamfer preparation are not required for metal surfaces up to 2.5 mm thick . Aluminum is further cleaned with acetone.
15. After preparing the parts and checking the equipment, connect the power supply terminals . With direct current, reverse polarity is applied. “+” is connected to the torch with wire, and “-” to the product.
16. Turn the switch that feeds the wire into the working position.
17. The electric arc ignites . It is enough to touch the metal in the presence of a melting wire.
18. It is recommended to check the accuracy of the settings on non-working metal (sample) . And if necessary, adjust.
19. Welding is in progress . The movement of the burner nozzle should be in one direction only, without lateral movements. On a vertical part, the nozzle moves from top to bottom.
20. If the metal thickness is large, heating to a temperature of 150-3000C is required.
21. Parts are welded at high speed with a single-layer seam.
22. You need to finish welding by gradually reducing the arc temperature (decreasing the current). Before doing this, remove (stop feeding) the filler wire.

Welding wire selection

Solid wire

It gives good seam quality, despite the fact that it has a low cost.

Cored wire

It produces a lower quality seam, but allows welding work to be carried out without the use of gas cylinders.

Copper-plated

It is mainly used for welding in carbon dioxide and its mixtures. The use of this type of wire leads to an increase in arc stability.

Filler wire is produced from 0.13 to 6 mm in diameter.

How to configure the equipment correctly

The complexity of welding aluminum is due not only to the chemical properties of this metal, but also to the need to strictly adhere to the optimal modes for performing this technological operation. In order to thoroughly understand the rules for performing such a complex process, it is not enough to simply watch a training video; it is important to understand the nuances of this operation.

The features of the process under consideration, which the training video will not tell you about, include the following.

• Before starting welding, it is important to correctly select and set the operating modes of the semi-automatic machine (voltage, current, welding wire feed speed, polarity).
• In order for the resulting weld to have the required quality and reliability, it is necessary to select the right consumables.
• If you watch a video demonstrating semi-automatic welding of aluminum, you will notice that this process is accompanied by the formation of a large amount of soot. This should also be taken into account when performing such a technological operation.

Like any complex technological process, welding aluminum parts using a semi-automatic machine requires careful preparation, which includes the following activities:

• tips for welding equipment are selected that are optimally suited for filler wire of a certain diameter;
• the surfaces of the parts that need to be cooked are thoroughly cleaned;
• semi-automatic welding modes are selected, which depend on several parameters: the thickness of the parts to be joined, the type of connection, etc. (to make it easier for you to select welding modes, you can use special tables or parameters that are specified by the requirements of the relevant GOSTs);
• When welding aluminum semi-automatically, the tip of the device is positioned at the required angle to the surface of the parts being joined.

Scheme of welding when welding aluminum

When welding aluminum, which has high thermal conductivity, it is very important to control the degree of heating of the workpieces being joined in order to prevent them from overheating and, as a result, deformation.

Preliminary work before welding begins

Immediately before starting the welding process, the following steps must be performed:

1. Clean the surface on which welding will take place until it shines with an abrasive material.
2. Remove chamfers if the wall thickness of the workpieces being welded is more than 4 mm
3. Degrease the surface with alcohol, acetone, gasoline or solvent
4. Remove moisture by heating the edges with a burner to 100⁰C
5. To eliminate internal stress, the metal is heated to 200⁰ before welding.

Preliminary work before welding begins

Regardless of the type of gas providing the protective environment (argon or carbon dioxide), the rules for semi-automatic welding are the same:

1. The current must be of reverse polarity
2. The burner must be tilted in such a way as to ensure sufficient penetration depth and the correct seam width
3. It is enough to make the wire overhang up to 12 mm
4. Gas flow can be adjusted from 6 to 12 mᶾ/hour
5. The shielding gas is passed through a drying agent (usually copper sulfate) to remove moisture. Before use, it must be calcined at 200 ⁰C for about 20 minutes.
6. To protect against hot splashes, surfaces adjacent to the joint must be treated with chalk dissolved in water
7. To avoid the formation of hydrogen cracks, welding should be started approximately 5 mm from the edge of the workpiece
8. Welding must be performed with a smooth movement of a semi-automatic torch along the seam. If you make transverse movements, the molten metal may go beyond the protective environment

Oscillator for aluminum welding

The main purpose of the oscillator is to create a large potential difference on oppositely polar elements. Due to this, at the moment when we bring the electrode to the metal being welded, the arc is ignited in a non-contact manner, already at a sufficient distance. This prevents the electrode from touching the part being welded.

If you imagine an expanded diagram of alternating current in the form of a sinusoidal type graph, then when the polarity changes, the graph crosses zero values. At current values ​​close to zero, aluminum welding cannot occur. The oscillator is used to provide an additional high-voltage pulse of a given amplitude at these moments, thereby compensating for low current values. The welding process remains stable. The pulse generation process is synchronized with the main sine wave. Modern oscillators are capable of generating high-frequency pulses of 500 kHz.

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Semi-automatic welding of stainless steel with other types of metals

Today's semi-automatic welding technologies make it possible to join stainless metal with aluminum, high and low alloy metals, as well as other alloys.

Distinctive features of semi-automatic welding of stainless steel with other metals:

• When welding ferrous metal with stainless steel, the yield strength of the metal decreases, protecting the surface from the effects of the environment
• when we weld St40 to stainless steel, we use 08G2S wire, which helps to avoid rupture of the seam at the junction of two types of metal after cooling
• to weld stainless steel with copper it is necessary to use low-melting solders and flux
• The pulse mode is used for welding stainless steel with aluminum and other metals, resulting in increased resistance to corrosion and improved quality of penetration.
• Argon is used for welding aluminum to stainless steel using the pulse mode. Copper cored wire is recommended.

Semi-automatic argon welding of cast iron

There is an opinion that argon is only suitable for working with non-ferrous metals, but this is not true, because quite often it is used for welding cast iron and steel.

Cast iron is an alloy based on iron and carbon. This metal is difficult to weld, as cracks and pores often appear at the seams. In addition, cast iron rapidly oxidizes. For this reason, its welding is usually carried out using flux-cored wire or argon, because the latter allows the formation of seams without slag. This is important, because welding cast iron is still relevant when repairing older cars.

To connect cast iron parts, tungsten-based wire is chosen. In most cases, general or local heating of the metal is used, although the cold method can also be used. The master can also choose between direct and alternating current, the strength of which depends on the thickness of the metal of the product and the diameter of the wire. You need to understand that normally there should be 50–90 A of current per 1 mm of wire. For such work, graphite, cast iron wire, as well as those made on the basis of copper, iron, and nickel are suitable.

Tables with semi-automatic welding settings

Butt bottom position

Vertical spatial position

Corner connection lower position

Tig welding modes

The argon welding mode consists of a number of parameters that must be set correctly. The main parameters of this welding mode are the following:

• type and polarity of current;
• current strength;
• arc voltage drop;
• speed of electrode movement;
• gas consumption;
• distance between the burner nozzle and the additive.

Argon welding is usually carried out with a current of straight polarity. Most types of metal are welded using direct current. Due to their physical and chemical characteristics, magnesium, aluminum and beryllium are boiled using alternating current. The amount of welding current is strictly dependent on the diameter of the electrode, metal, type and polarity of the current. The current value is set by technologists in the form of tables.

For an ideal weld, the voltage drop across the arc should be in the range of 11 - 14 volts. To maintain such a voltage drop, it is necessary to maintain a distance between the electrode and the metal from 1.5 to 3 mm. The choice of torch speed is at the discretion of the welder. Only he can select the correct speed, based on the complexity of the welding trajectory and his level of skill.

The consumption of protective gas is calculated by technologists based on many factors influencing the process. There is no point in describing them; for non-specialists it is difficult and therefore uninteresting. However, in fairness, it should be noted that an experienced welder can adjust gas consumption based on the appearance of the seam.

The type of weld joint dictates the required distance between the filler material and the torch nozzle. For butt joints, a distance of 3-5mm is recommended. For T-bars and corners, a little more - 5-8mm.

Final work after welding

1. Mechanical processing - removing bubbles by tapping them with a heavy object through a smoothing iron and splashes resulting from melting the metal
2. Pickling - removing scale that causes corrosion from seams with a special compound
3. Passivation is the application of agents to the weld to form a chromium oxide film on it, which protects against corrosion.

Useful tips

At the end of the article I would like to share a few useful tips for welding stainless steel that will help improve the quality of the final weld:

• during welding in a protective atmosphere (a mixture of argon and carbon dioxide), reverse polarity is established, and when using flux - direct polarity
• for the distance between the wire and the joint, it is recommended to take a value not exceeding 12 mm
• you need to move the burner from left to right with an inclination away from you so that it does not cover the seam from us
• the connection of thick-walled parts is performed at an angle of 5 - 10⁰ to ensure deep penetration, as well as a strong and reliable seam
• when welding thin stainless steel, the torch is tilted forward, thus reducing the depth of penetration and minimizing the risk of burn-through

Welder tasks when working with aluminum

Taking into account the peculiarities of the behavior of aluminum alloys during welding, you must solve the main tasks during the work: get rid of the oxide film, ensure a stable arc during welding and timely supply of welding wire so that the aluminum welding process is continuous, otherwise it will have to start again.
The welder must:

• get rid of the oxide film at the seam: pierce it with an electrical impulse or mechanically clean the surface using a metal brush or by chemical etching. To pierce the film, a special pulse operating mode of the equipment is used;
• when choosing a welding mode, avoid burning through the metal due to the increased thermal conductivity and low melting threshold of aluminum, leading to a rapid loss of strength when heated. To do this, he must ensure the required process temperature and an arc of 12 to 15 mm in length, select the correct electrodes and filler wire size suitable for the thickness of the aluminum parts being connected and the torch nozzle;
• take into account the tendency of aluminum to significant linear shrinkage (almost twice as much as steel) upon rapid cooling after heating, since this leads to the creation of internal stress with the formation of deformation cracks or craters in the weld area. To prevent this, you need to start the welding process with a high welding current in order to break through the oxide film, and finish it by gradually reducing it towards the end of the process, this will soften the sudden change in temperature and prevent the formation of a crater.