Semi-automatic welding: in shielding gas, in carbon dioxide

Semi-automatic welding is mechanized arc welding with a metal consumable electrode (wire) in a shielding gas environment. The method is also known as MIG/MAG welding. Depending on the type of shielding gas used, a distinction is made between inert gas (MIG) and active gas (MAG) welding. Welding in a carbon dioxide environment is predominantly used as active gases. Unlike manual arc welding with coated electrodes, in mechanized welding, the electrode is supplied to the welding zone using mechanisms, and the welder moves the torch along the axis of the seam and performs oscillatory movements with the electrode as necessary.

Rice. 1. 1 – torch, 2 – nozzle, 3 – current-carrying tip, 4 – electrode wire, 5 – arc, 6 – seam, 7 – bath, 8 – base metal, 9 – drop of metal, 10 – gas protection.

Description and principle of operation of semi-automatic welding

Welding is carried out in an atmosphere of inert gases to avoid unwanted oxidation of the material of the joints and seams. The welding unit pumps gas (most often argon) to the welding site under slight excess pressure, thus displacing air oxygen from the working area. The electrode is a thin wire stored on a drum inside the welding machine. Both gas and wire are supplied to the working area by a special mechanism through reinforced tubes and then through the pistol grip of the welding torch.

The mass is supplied to the part using a clamp, as in conventional manual electrode welding. Plus is fed to the welding wire. The welder opens the gas supply valve and regulates the pressure, after which he turns on the feed mechanism at the speed specified by the technical conditions and touches the part with the tip of the electrode protruding from the torch. An electric arc occurs, the electrode melts and is used as solder. The edges of the parts to be joined are heated by an electric arc and welded together. The inert gas forms a protective atmosphere, preventing unwanted oxidation.

It is also possible to use a semi-automatic machine without gas for welding ordinary ferrous metal, for which specially designed grades of welding wire are used.

Features of wire welding

Features of welding with wire using semi-automatic equipment are as follows:

the filler material must correspond to the chemical composition of the product being welded;
the wire must meet government standards and be made from the correct components;
The terms and conditions for storing filler wire must be strictly observed.

A review of the features of work using filler wire should begin with welding basics. Most metals welded in production or at home are steel and manganese. Wire for connecting such products is the most in demand.

Welding of ferrous metals is usually carried out using the following types of filler material:

Wire Sv-08GS for joining low-carbon and alloy steels.
Wire Sv-08G2s for welding high-carbon steel.

Flux-cored wire is often used for welding ferrous metal products. This filler material allows welding to be carried out without additional gas supply to the welding zone.

Self-fluxing wire is a low-carbon steel tube with a powder core. When the metal melts, powder is released, forming a gaseous environment to protect the weld. As a rule, the fluxing powder contains rutile and metal dust.

Stainless steel is welded with wire grades Sv.-06Х19Н9Т, Sv.-04Х18Н9 or Sv.-01Х19Н9. This filler wire provides good mechanical and physical properties of the weld.

The connection of aluminum parts is carried out using SV-AK5 wire. A characteristic feature of this filler material is the unique color of the weld. Immediately before joining aluminum products, preparation should be carried out.

Semi-automatic welding using flux-cored wire.

This procedure is divided into steps:

Creating bevels or chamfers.
Mechanical cleaning of surfaces.
Washing with caustic substances to slow down the formation of a refractory oxide film on the surface of an aluminum product.
Preparation of a Teflon channel to reduce friction of the filler wire on the walls of a semi-automatic welding device.

Step-by-step instructions for using carbon dioxide welding for beginners include the following subparagraphs:

removing all foreign objects from the workplace;
turning on maximum lighting;
preparation of material and tools;
checking cable connections and functionality of extension cords.

After completing the above points, you should proceed to preparing the electric arc welding machine.

To do this you need:

unwind the welding sleeve;
connect the gas cylinder;
check the burner nozzle;
conveniently place all the parts to be connected and fasten them securely;
dress in welder's work clothes;
connect semi-automatic equipment to the network;
bring the torch to the intended connection site.

Upon completion of welding work using wire, you should:

remove your fingers from the wire feed buttons;
shut off the gas supply;
turn off the power to the equipment;
Allow the seam to cool for several minutes;
If defects are found, repeat welding.

The semi-automatic welding machine allows you to use all types of filler wire.

When performing work, it is important not to forget about protective equipment.

Semiautomatic welding machine with thyristor control.

The most complete welder equipment consists of:

Eye protection. The ideal equipment to protect a welder's vision is a mask, face shields and goggles.
Respiratory protection. Special filter masks will help the master to significantly reduce the impact of harmful fumes on internal organs.
Splash protection. Full body protection should include a flame retardant jacket and trousers. You can use overalls.

Safety precautions when performing welding work include the following rules:

Carrying out work from wooden scaffolding. The use of metal protective masks and helmets is prohibited.
Providing light flux from a 12 volt power source.
Providing insurance for the welder using a string attached to the belt. The rope size must be at least 2 meters.
Providing the workplace with a special hood that ensures the removal of harmful fumes from the work area. In cases where it is impossible to provide exhaust, the welder must work in a hose gas mask or respirator.
Do not touch the workpiece to be welded with bare hands.
It is prohibited to carry out work in open areas during precipitation.

How to choose wire for a semi-automatic machine

To choose the right welding wire for semi-automatic machines, you need to take into account many important parameters:

The main material to be welded.
Material thickness.
Welding method (gas or not).
Welding machine power.

and some others.

So, for working with low-carbon steel, grades with low carbon and silicon content are suitable. They can be welded with copper-plated solid wire without the use of inert gas. This material is used for automatic and semi-automatic welding.

For alloyed, high-strength and stainless steels, materials with a similar content of alloying additives are selected, and the work is carried out in a gas atmosphere.

Gas welding process

Aluminum, due to its high chemical reactivity, should be welded in an argon atmosphere; the welding material should be of solid cross-section with a composition close to that of the specific alloy. To avoid the formation of an oxide film, aluminum wire should be stored in sealed packaging and unpacked immediately before loading into the machine and starting welding. Chemical or mechanical treatment of the welding area and welding material is often carried out.

Copper and its alloys are welded in an argon protective atmosphere

Copper and its alloys are also welded in an argon protective atmosphere. For copper, wire has the following subgroups:

pure and low-alloy products;
bronze;
castings and rolled products.

Ferrous metals, cast iron or nickel have high heat resistance and corrosion resistance. For them, flux-cored wire of the rutile group with a sufficient nickel content will be optimal.

Self shielding cored wire

Surfacing grades of welding materials are used for welding different metals

The wire diameter for semi-professional semi-automatic machines is most often 0.3-2 mm. If you have sufficient experience and skill, it is possible to use the same diameter for different operations, but for a novice master it is better to stick to the reference table included with the semi-automatic machine.

Rules for working with a semi-automatic machine

We list a number of requirements, or rather rules, that should not be neglected when using an automatic welding machine:

Before starting to operate the semi-automatic welding machine, you should carefully study the operating instructions;
when welding, you need to ensure strict polarity - “plus” should be on the torch, and “minus” should be on the part being welded;
To avoid unpleasant situations associated with human injury, when threading wire into the torch, you should not point the nozzle at yourself or other people. Here you need to be very careful, because the end of the wire can pierce your palm or other part of the body;
It is strictly forbidden to move the semiautomatic device during operation by pulling it by the burner or cable; there are handles for this;
in order not to damage the eyes and other parts of the face, you should work with a semi-automatic welding machine only in a special protective mask that has a light filter, the marking of which must correspond to the current range used in welding, and for additional protection you should use glasses with glass lenses, since glass does not transmit ultraviolet radiation;
for long and trouble-free operation of the device, it is necessary to clean all its insides from dirt and dust twice a year;
if, during an external inspection of the device, damage was discovered in the cable or burner sleeve, they must be immediately eliminated using insulating tape or heat-shrink tubing, and it is better to replace worn parts with new ones;
the shape of the groove must clearly correspond to the electrode material: V-shaped smooth is used for solid steel wire, V-shaped with notches for flux-cored wire, U-shaped for alloys and soft metals;
during operation, it is prohibited to touch the live parts of the semi-automatic welding machine, as well as to work with its covers removed;
the room in which welding is performed must be well ventilated, since aerosols released during work are extremely harmful;
Fire safety rules should be strictly observed;
We must not forget that during welding the welding seam heats up to very high temperatures, so it is strictly forbidden to touch these places;
It’s no secret that a semi-automatic machine, like any welding machine, is a source of electromagnetic radiation, which has an extremely harmful effect on human health. Not all people can work in such conditions, so you must first undergo a medical examination;
It is strictly forbidden to weld vessels and pipelines together with liquids, as well as vessels in which flammable and flammable liquids were previously stored;
do not overload the semi-automatic machine, work only under the conditions specified in the operating instructions, since this, firstly, is dangerous to the health of the operator, and, secondly, reduces the service life of the semi-automatic machine itself;
since a person is a carrier of static electricity, touching the elements of the electronic board is strictly prohibited, in this case they may breakdown;
The lid of the feed mechanism niche must be tightly and securely closed during operation so as not to become a source of injury to the operator;
welding should not be performed in a continuous mode, it should be alternated with regulated breaks, the duration of which and the intervals between them should be selected in accordance with the manufacturers' recommendations;
while operating the semi-automatic welding machine, it is strictly forbidden to switch the stages of the transformer installed on the welding power source;
all welding work should be performed only in clothing specially designed for this purpose, in addition, clothing must be completely dry in order to protect yourself from possible electric shock;
The flow rate of the shielding gas, which can be argon, helium, carbon dioxide or mixtures thereof, must be calculated optimally, since it forms a protective environment in the arc zone; in addition, the gas must be selected in accordance with the type of material being welded, as well as its thickness. The cylinder must be secured horizontally and securely enough.

Types of general purpose wire

Depending on the base material and type of coating, semi-automatic welding wire is divided into 4 main types:

Copper-bonded is the most popular and is used for welding low-alloy structural steels of general grades.

Copper-plated filler wire

Powder - does not require a protective atmosphere for use. The gas, which insulates the weld pool from air, is released during the evaporation of powdered additives.

Flux Cored Welding Wire

Stainless steel - a solid section, obtained by cold drawing from high-alloy alloys.

Wire for welding stainless steel

Non-ferrous – for welding non-ferrous metals such as aluminum or copper. Selected according to a composition close to the composition of the material being welded.

Colored Welding Wire

Other types of welding materials are also produced for semi-automatic machines, but they are used for highly specialized applications and are used relatively rarely.

What gas is used for semi-automatic welding - selection criteria

Let's talk about the criteria for choosing gas for semi-automatic welding in more detail. The choice of a particular gas is influenced by several parameters such as:

brand of product material;
connection responsibility;
economic indicators.

In most cases, the brand of the product determines the use of certain gases or their mixtures.

Inert gases are generally suitable for all types of steels, non-ferrous metals and their alloys. The use of inert gases for low-carbon and low-alloy steels is unjustified, since these gases are very expensive.

For carbon, low-carbon, structural steels, carbon dioxide (carbon dioxide) is used, as well as mixtures of CO2 with argon, CO2 + argon + helium.

When welding stainless steels (austenitic steels), for example, the well-known “medical” steel - 12Х18Н10Т and similar ones, are welded in a mixture of carbon dioxide and argon.

For welding non-ferrous metals such as aluminum, titanium, copper, argon is most often used, either in its pure form or a mixture with He. In its pure form, it is rarely used because it is very expensive.

Copper can be welded under nitrogen. For non-ferrous metals, mixtures containing CO2 and oxygen are not used.

Below we present a table where we clearly show the use of certain gases and their mixtures for various types of metal alloys.

Gas	Structural steels (low carbon)	Alloy steels (low, medium, high)	Titanium, aluminum and their alloys
Co2 (carbon dioxide)	Yes	Yes, with restrictions	No
Ar (Argon)	Yes (impractical)	Yes	Yes
Not (Helium)	Yes (impractical)	Yes	Yes
Ar + Co2	Yes	Yes	Yes
Ar+O2	Yes	Yes, with restrictions	No
Co2+O2	Yes	Yes, with restrictions	No
Ar+Co2+O2	Yes	Yes, with restrictions	No
Ar+He	Yes (impractical)	Yes	Yes

Copper-plated product

Copper-plated semi-automatic welding wire is excellent for working with low-carbon and low-alloy steels in an atmosphere of inert gases. It has high corrosion resistance and allows you to get a strong and durable seam. Copper-coated wire is also used for surfacing. It has an affordable price and a constant chemical composition.

Copper-plated wire for semi-automatic welding

The disadvantage of copper-plated wire is the evaporation of copper during the welding process, which significantly worsens working conditions and requires the use of insulating masks with a forced supply of clean breathing air.

Settings for work

This method of metalworking involves working with machines. We are talking about both the use of a source of electricity and the operation of a semi-automatic device. Usually the well-known outlet works, but only when the power supply is uninterrupted.

There is a need to work with a device that is responsible for supplying wires. Pay attention to the choice of replacement structures. Let's talk about these moments.

Powder electrode

The main reason for the popularity of powder-cored welding electrodes is the ability to weld without the use of shielding gas. The wire is a thin-walled metal tube filled with specially prepared powder. Several more tubes may be formed within the tube to provide sufficient rigidity. The thickness of flux-cored welding wire varies from 0.9 to 1.5 mm.

Depending on the composition of the powder, several subtypes are distinguished:

fluorite;
carbonate-fluorite;
rutile;
rutile-fluorite;
rutile-organic.

The principle of using such welding wire material is based on the evaporation of powder flux additives and the formation of protective gas bubbles from these vapors, protecting the weld pool from contact with atmospheric oxygen.

Flux-cored wire for semi-automatic welding

The main advantage of flux-cored wire is the ability to do without the supply of inert gas and work even in strong winds.

The disadvantages are the high price and increased fragility. If it breaks, the welding material has to be thrown away.

Features of semi-automatic welding in shielding gases

Well, we’ve come to the features of semi-automatic welding in shielding gases. First, let's finally define it... Semi-automatic welding is usually called PA or MIG. Such welding is an improved version, even a revolutionary solution. With its help, the quality of welds was improved in some cases. Moreover, work productivity has increased. Now, the same metal structures and products can be produced much faster, with the same quality of seams.

Also, among the features of semi-automatic welding in shielding gases, I would like to include the fact that there is no need to knock the slag off the seam. Which improves the aesthetics of the workplace. And also, during welding, much less combustion products are released. And this increases the health safety of the welder.

Attention! An important topic is safety precautions when performing welding work. Compliance with which is mandatory for everyone!

I would like to draw your attention to a few more features.

The copper current-carrying tip is selected depending on the diameter of the wire used.
The wire feed speed depends on the set current and per revolution.
The operating gas pressure should be carefully adjusted so as not to overdo it. If a lot of gas is exposed, the welding will feel much harsher, and the seam will not be as beautiful and high-quality.
When performing work outdoors, take into account the presence and strength of wind. If wind is present, add operating gas pressure. Or cover the welding area with a screen. Otherwise, the wind will blow the gas away. As a result, the weld pool will remain unprotected. And these are pores and other defects in the weld.
Don't forget to clean the nozzle and tip of any dirt. Otherwise, problems with the quality of the seam will arise.
The semi-automatic machine really does not like welding on painted surfaces, as well as rusty and dirty ones.

Conclusion

Semi-automatic gas shielded welding is an excellent solution for stationary work in a workshop. Provides high productivity and seam quality. If you have decent skills, there is no need for additional seam stripping.

The ease of mastering semi-automatic welding arouses the interest of amateurs. And it’s not in vain. After all, PA is perfect for garage and household work.

Don't forget to rate the article, repost and, if necessary, leave comments! Thank you for your attention and understanding!

Stainless flexible electrode

Flexible electrodes for welding stainless steel are produced by cold drawing from high-alloy steel alloys.

They have the following positive qualities:

refractory;
corrosion resistant;
resistant to aggressive environments;
long shelf life;
provide excellent seam quality.

Stainless flexible electrode

A noticeable disadvantage is the high cost of such welding material. This hinders its widespread use.

Non-ferrous metals

It is not so easy to qualitatively weld non-ferrous metals or their alloys. It is necessary to carefully comply with the requirements of technical specifications and the correct selection of consumables and equipment.

Copper and its alloys

The welding process is strongly influenced by the following high properties of copper itself and its alloys - bronze and brass:

thermal conductivity;
reactivity with hydrogen;
coefficient of thermal expansion.

These properties can lead to insufficient strength near the seam area and the seam itself, increased metal fluidity and the appearance of hot cracks. Therefore, when working on copper and its alloys, wires with a high tungsten content give the best results. This allows you to reduce the evaporation of zinc and tin and preserve the chemical composition and physical properties of the material.

Aluminum and magnesium alloys

The surface of parts and workpieces made of such alloys is constantly covered with a layer of refractory oxides, which prevent the melt from the weld pool from fusing with the base metal of the parts. The remains of this difficult-to-remove layer in the form of slag inclusions can get into the weld material, significantly deteriorating its quality.

When operating with reverse polarity current in the electric arc zone, cathodic cleaning of parts is carried out. But this technique allows you to remove only a thin layer of oxides. Therefore, before welding, the oxide layer should be removed by acid treatment or cleaning. It is also important to remember to remove the oxide layer from the surface of the welding wire.

Argon welding of aluminum

Alloys AB, AK6, AKV are especially susceptible to hot cracks during welding, so it is recommended to use wire containing about 5% silicon for them.

Welding is carried out in an atmosphere of pure argon, or in its mixture with helium.

Semi-automatic welding: possible adjustments during the process

In order for the seam to turn out smooth and beautiful, you need to feel the semi-automatic machine and be able to adjust it correctly. It is necessary to set the necessary parameters according to the setting tables that are attached to the technical documentation for the device of a particular type. You cannot cook at a low operating current: this will affect the quality of the seam, and in some cases it will not even be possible to connect the parts together. The following principle is observed: the thicker the metal, the higher the operating current or voltage (depending on the operating principle of the semiautomatic device).

How to cook semi-automatic video lessons:

WELDING OF ALUMINUM SEMI-AUTOMATIC

A semi-automatic machine can be used to weld various metals, and aluminum is no exception. But there are special rules, since this metal has some special features. On its surface there is a thin layer of amalgam, whose melting point is much higher than that of aluminum (more than 2000 degrees, while the base metal melts at 650 degrees). In this case, argon is used as an inert gas. Since aluminum quickly melts and begins to flow, a substrate is used to work on a semi-automatic welding machine.

The welding process itself occurs with consumable electrodes under the influence of direct current of reverse polarity - this is when a negative charge is attached to the part, and a positive charge to the torch. Such welding techniques contribute to high-quality melting of the workpiece and rapid destruction of the top layer. Although for such a connection you can use another trick - pre-clean the product to remove the oxide film. You can read more about the features of working with aluminum here.

The joining technique can be performed in different spatial positions using different types of seams.

Activated wire

This welding material is close in composition to flux-cored wire, but special additives are added to it, optimizing parameters in the weld pool area and preventing metal destruction during and after welding. Structurally activated wire is designed differently than flux-cored wire. The percentage of additives is significantly less and does not exceed 6-8% of the total linear weight. In this case, additives are not poured into the cavity, but are built into the body of the wire in the form of thin channels, and the material combines the advantages of solid wire and flux-cored wire. Due to the small proportion of additives, welding with such wire can only be carried out in an inert gas atmosphere.

Additives are easily ionized compounds of light metals and slag-forming components that improve the stability of the operating parameters of the weld pool. They increase the stability of the electric arc.

The following advantages of activated wire can be formulated:

Wide range of compatible equipment. Wire, unlike flux-cored wire, allows bending and does not require specialized feeding devices.
High quality of the seam due to lower surface tension of the workpieces being joined and low hydrogen saturation.
Reduces current consumption by protecting the welding area from excessive heat loss.

Welding wire

The main disadvantage of activated wire is the need to use gas. This increases the complexity and cost of the operation.

Operating principle of semi-automatic machine

Semi-automatic welding machines are mostly simple equipment. Its main parts are an adjustable direct current source, which supplies the welding voltage, as well as a special mechanism designed to feed the welding wire into the welding arc zone, and the feed is performed at an adjustable speed.

The arc has reliable protection thanks to the gas flow created by the burner, where it enters from a cylinder with the same gas. The electrode feed speed and welding voltage are adjusted simultaneously.

As already mentioned, the welding wire must be fed into the arc zone at a strictly defined speed. Only in this case will the welding process proceed stably. Otherwise, at the slightest break in the wire feed, the arc breaks, and this leads not only to a decrease in the quality of the weld, but also to other more serious consequences, which include, first of all, burn-through of the seam, melting of the electrode tip and other failures and defects.

For high-quality feeding, it is necessary to check the drive rollers before work. It is necessary that the feed roller has a V-shaped groove, the size of which must match the size of the wire, and that this groove is in good condition, that is, not worn out.

Often when people experience poor feed, they will increase the clamping force on the drive rolls, which can only make the feed worse as the wire can become deformed. In addition, the burner guide channel can be damaged for the same reason.

During operation, the welding wire passes through the torch through a guide channel, which over time tends to become dirty and wear out. As a result, the resistance of the electrode feed increases, until the wire stops completely.

This should not be allowed; it is better to notice these changes in time and replace the guide channel with a new one, installing which you need to be very careful, since if its length, external and internal diameters do not match, serious feeding problems may arise. In other words, the whole point of replacement is lost and normal welding is still not possible.

In order to reduce wire contamination, as well as premature wear of the guide channel, it is better to choose a semi-automatic machine with a closed feed mechanism. This approach to wire feeding significantly better protects it from dust, moisture, oxidation, etc.

Now a few words about the contact tip of the torch, through which the actual welding current is supplied to the electrode (welding wire). It is clear that for high-quality welding, the wire must have high-quality and reliable contact with this tip. It is necessary to monitor the degree of wear of this part of the semi-automatic welding machine in order to replace it in a timely manner.

All these seemingly little things are of great importance for high-quality welding performed using a semi-automatic machine. Good condition of equipment is the key to success, and poor care of it is the first and surest step to the occurrence of all kinds of malfunctions.

Best Solid Welding Wire

Solid wire is used when working with high-carbon and low-alloy structural steels. Available in two versions

Copper plated.
Not copper-plated.

Copper-clad wire for welding

Copper plating significantly improves the corrosion resistance of the seam, but during welding it saturates the air with copper vapors that are harmful to health. In order to protect labor and create favorable working conditions, non-copper-bonded wire equipped with anti-corrosion coatings is increasingly being used.

Aluminum welding wire

Non-copper-clad solid wire is also divided according to purpose for:

high-carbon and low-alloy steel grades;
high-alloy and refractory steel;
stainless steel;
alloys of copper and aluminum.

Types and markings of welding wire

Russian Federation standards describe about 80 different grades of welded wire. However, in practice, no more than a dozen are widely used.

Welding wire marking

The remaining grades are highly specialized materials for special and rather rare applications, such as:

manufacturing of nuclear reactors, internals and nuclear power components;
aerospace industry;
specialty shipbuilding, including submarine hulls and armor;
equipment for production, transportation and processing of oil and gas;
housings and equipment for chemical reactors;
other high technology industries.

The wire designation consists of several groups of numbers and symbols:

diameter in millimeters;
destinations:
for surfacing - “Np”.
carbon content in hundredths of a percent;

Symbols of alloying elements

content of alloying additives as a percentage; if the content is less than 1%, then it is not indicated:

X-chrome.

N-nickel.

M – molybdenum.
C – silicon.
N – nickel.
X – chrome.
C – zirconium.
G – manganese.
A - nitrogen.
B - tungsten.
T - titanium.
Yu - aluminum.
F - vanadium.
B - niobium.
D - copper.
C - silicon.

Requirements for material purity.
AA - special purity.
Smelting method.

VI - vacuum induction.
VD - vacuum-arc. Sh. - electroslag.

For the production of electrodes - letter E.
Copper plated - letter O.
Link to GOST.

So, for example, from the designation you can find out that the Sv-08G2S brand contains 0.08% carbon, 2% manganese and less than 1% silicon. This filler wire is suitable for gas welding of alloy steel.

Marking of the brand Sv-08G2S

The world's leading welding wire manufacturers - ESAB, Autrod and others - use their own designation systems that comply with American or European standards. Dealers of these companies always have at the ready tables of correspondence between their brands and the brands provided for by GOST.

Welding wire diameters

General purpose welding wire is available in diameters from 0.3 to 12 mm. The most widely used diameters are from 0.8 to 2 mm.

For example, a 2 mm wire allows you to weld metal from 3 to 5 mm thick. Another parameter to choose is the welding mode, primarily the current strength. There are special tables for selecting the thickness of welding wire.

Basic welding parameters

It is important to remember that if your power supply network has low or unstable voltage, then it is better to reduce the diameter of the welding wire to avoid under-welding.

Welding wire consumption control

In order to manage the cost of welding work, it is necessary to control wire consumption.

The key factors determining consumption are:

chemical composition of the metal;
wire diameter and quality;
characteristics of the welding unit;
use of shielding gas.

A widely used standard for the consumption of welding material, depending on the length of the seams and the complexity of the product, is considered to be 1-2% of its total mass. To this amount add 6% for waste and wire loss

Semi-automatic gas welding

A semi-automatic welding machine for working in a protective gas environment is considered a new type of welding, which is just beginning to gain popularity today. However, over the past 20 years he has earned the trust of experts. The method allows for two types of work:

MIG (Metal Insert Gas), where the connection of metal elements is carried out under the influence of an inert gas. The latter can be argon or other gas mixtures.
MAG (Metal Active Gas) involves welding using an active gas such as carbon dioxide.

Due to the large and heavy gas cylinders, this technology cannot be used in all conditions; the equipment lacks mobility. Whereas for stationary work this type of welding is indispensable.

The composition of the electrode wire used includes silicon and manganese. By feeding the wire into the welding zone along with carbon dioxide, an environment is formed that protects the electrode and welding surface from environmental influences.

What is the main advantage of this type of semi-automatic welding? This method of joining metal makes it possible to better monitor the process. In addition, the use of a gas environment allows you to complete the job faster, since gasless welding requires changing electrodes and removing slag from weld seams.

In a protective gas environment, a weld is obtained that is significantly superior in quality to the result of gasless welding. True, there are some subtleties here. Thus, the choice of gas mixture plays a key role. If active CO2 gas is used, the seam will be scaly, with burrs, that is, with the effect of stuck balls. Whereas, due to a mixture of 80% argon and 20% carbon dioxide, a smooth and even seam is formed that does not require additional processing.

Serious disadvantages of the technology are the need to provide protection when working in open areas and additional costs associated with the supply of gases.

Modern mechanisms and welding wire feed speed

Modern semi-automatic units are divided according to the type of welding:

in inert gases;
using cored wire;
submerged;
universal.

Units for working with inert gas are equipped with an automatic valve that cuts off the gas supply when welding is stopped. Units for working under submerged arcs are equipped with a burner with a funnel. They use thicker wire, so they have a stronger feed mechanism.

Depending on productivity, duration of continuous operation and resource, units are divided into:

Household.
Semi-professional.
Professional.

According to the degree of their mobility, semi-automatic welding machines are divided into portable, mobile and stationary.

Industrial units are equipped with three-phase power supply. They can work around the clock without shutting down for cooling and allow you to weld high-quality, durable and even seams.

Units for working with flux-cored wire are equipped with an improved feed mechanism that prevents deformation and creases of fragile wire. Universal semi-automatic machines have additional equipment:

welding torches;
special nozzles;
improved feed rollers.

which allows them to be used in many operating modes

Feeding mechanism (broaching) of semi-automatic welding machine

The wire feed system includes:

Electric motor.
Transmission.
Reinforced tube.
Feed rollers.

In relation to the burner, the supply system can be pull, push or pull-push. In a push system, rollers are placed near the inlet of the torch hose and push the wire into the torch channel. With a pull feed system, the rollers are placed directly in the burner. This makes the torch heavier, but increases the stability of the wire feed and reduces the likelihood of deformation and creases. Pull-push feed is used for long lengths of reinforced hose in professional distributed welding stations.

There are two ways to adjust the feed speed. The first uses a three-phase asynchronous electric motor, and the speed is adjusted in steps by changing gears in a gearbox reminiscent of a car. The second option is used in cases where it is important to provide very fine adjustment of the feed speed, for example, when welding thin sheets of metal. The electric motor operates on direct current, and its rotation speed is controlled by an electronic circuit with an accuracy of several revolutions per minute.

Types of welds in semi-automatic welding

Semi-automatic welding technology allows you to obtain different types of seams, depending on the equipment settings.

According to the type of connection, seams produced by semi-automatic machines are divided into:

butt;
T-bars;
overlap;
corner.

Features of semi-automatic welding.
According to their spatial position, welds are usually divided into:

horizontal;
vertical;
ceiling;
lower ones.

Popular ceiling seams are usually made in two stages:

Welding the root seam. The preparatory seam is usually performed with three-millimeter electrodes with low current.
Full completion of the seam.

The second welding stage of the ceiling seam can be performed in two ways:

Welding using short, jerky seams or spot welding. This welding method prevents drops of molten metal from falling on the operator. When performing such a procedure, additional welding may be required at the beginning and end of the seam.
Cooking with the shortest possible arc. This approach will allow the metal to quickly harden, immediately after the electric flame is removed.

Bottom connections, made using semi-automatic or manual arc welding, are often used in factories and industries. Such welds provide high mechanical characteristics due to the uniform distribution of molten metal.

Semi-automatic welding modes when making corner joints can be different.

Table of characteristics of semi-automatic welding machine.

Semi-automatic gas welding of corner metal structures can be performed:

With a perpendicular arrangement of two workpieces. This technique allows you to weld only the internal joint. Cooking perpendicularly located tubes should include making a concentric weld around the circumference.
With an angle of less than 60 degrees between the parts being welded. The best option for performing a fillet weld. In this case, the workpieces are completely boiled.

The butt weld is the most popular method of joining pipelines or steel sheets.

This type of welding is divided into:

one-sided welding;
one-sided welding and processing;
double-sided welding.

One-sided welding in shielding gases is used for product thicknesses of no more than 4 millimeters. If the parts have a thickness of more than 8 millimeters, it is necessary to perform double-sided welding.

The best method for ensuring high strength of a thick product when welding one side is to groove the edges. The cutting is carried out using a grinder or a file. During the processing of the joined ends, a bevel of 45 degrees is formed.

An overlap joint is usually performed to ensure high tensile strength of the product. The seam should be made on both sides of the contacting surfaces to avoid moisture accumulation.

A T-joint is in most cases used to secure the base of a metal structure. When the metal thickness is more than 4 millimeters, it is recommended to use a double-sided weld.

Vertical

The technology of semi-automatic welding of a vertical seam has several important principles:

Molten drops of metal should solidify faster than with conventional welding. This condition is necessary due to the gradual flow of molten metal downward under the influence of universal gravity. The required droplet size can be ensured only by reducing the size of the welding arc.
Vertical welding is done from bottom to top. The welding method ensures the absence of sagging and unevenness when making a vertical seam.

There are several rules that can be followed to guarantee a high-quality vertical connection when welding from top to bottom:

use of a short arc;
perpendicular position of the electrode at the beginning of welding;
the location of the electrode at an acute angle relative to the weld seam.

Welding wire feeder.
Although such steps make it possible to obtain a vertical seam by welding semi-automatically from top to bottom, as the lessons learned by experienced welders show, such joints have much more meager characteristics.

There are three technologies for welding vertical seams using semi-automatic machines:

Triangle. It is used when connecting parts with a thickness of less than 2 millimeters. The essence of the method is as follows: during the operation of the welding arc, liquid metal flows from bottom to top onto the already solidified metal. In this case, the flowing slag moves at a certain angle, depicting a triangle.
Herringbone. Method used to join 2-3mm gaps. Welding begins from the plane of one of the edges. Then, using an electrode, the metal is melted throughout the entire thickness of the workpiece, after which the arc is drawn to the very depth of the gap.
Ladder. The best option for eliminating large gaps between parts. The method involves performing welding work using a zigzag movement of electrodes from edge to edge.

Horizontal

Semi-automatic welding allows you to perform high-quality horizontal seams. Performing such operations is not much different from creating vertical connections. The welding process can be performed both from right to left and from left to right.

You can get a high-quality horizontal seam by taking into account these subtleties:

the arc burning force must be equal to the gravity force of the metal drops;
the speed of movement of the electrode must be selected separately for a horizontal seam;
Welding work should be carried out continuously in order to keep the melt under control.

Arc welding sometimes makes it impossible to complete a seam in one go. In this case, you can use the welding technique with periodic arc extinguishing. When metal thickness is up to 4 millimeters, the use of various welding patterns is allowed.

Otherwise, the quality of making a horizontal connection using semi-automatic or manual equipment completely depends on the skill of the welder.

Semi-automatic welding machine.

The process of creating a horizontal welding seam can be divided into four stages:

Creating a root roll. The root weld bead is made with a short electric arc. The angle of inclination of the electrode to the surface should be about 80 degrees. The primary roller, as a rule, is created with the maximum current allowed for the equipment.
Formation of the secondary roller. The process begins with setting the average current strength. The secondary roller is made in one pass, in which it is advisable to use an electrode with a large diameter. The second welding bead should be formed using the forward angle technology.
Getting the third roller. The tertiary bead can be created in two ways, depending on the success of the previous stage. If the secondary roller has a large area, then the third should lie exactly in the center. If the second roller turned out to be standard, then the third stage is performed in two approaches.
Final welding of parts.

During the work process, you should carefully monitor the upper part of the seam being formed, since it is in this area that various welding defects appear.

Advantages and disadvantages

The main advantage of welding wire is the high quality of the resulting weld by a welder of average or even initial qualifications with little experience. To achieve comparable quality with traditional stick electrodes, a highly qualified welder with extensive welding experience is required.

The second indisputable advantage is the possibility of long-term work without interruptions to change the electrode, which ensures welding of long seams in one step and improves both the technical quality and the aesthetic impression of the seam.

Another important advantage is the simplicity and convenience of working in an atmosphere of protective gases. When welding with conventional electrodes, it would be necessary to place the product and the welder in an insulating gas mask in a sealed chamber, greatly increasing the labor intensity of the work and gas consumption.

The disadvantage of the method is the high cost of materials and equipment, however, taking into account the lower required qualifications of the welder and the lower labor intensity, the cost per linear meter of welding is lower.

BASIC RULES FOR WELDING WORK

To become a real professional, you need to know everything about semi-automatic welding, and safety is one of the important aspects. It is necessary to study and every time comply with all the norms and standards prescribed in GOST. Safety precautions must not be neglected when working with fire and gas cylinders. It is also important to protect yourself by wearing a uniform and a mask that will protect your eyes from UV burn.

Not only beginners, but also experienced craftsmen are recommended to initially try the seam on a rough part or on an inconspicuous area to make sure that the settings on the semi-automatic welding machine are correct. Before using the unit, you must read the instructions and follow them during operation. And yet, the device cannot work continuously. That is, you need to pause periodically; this is written in the instructions for them.

Automatic and semi-automatic welding requires a long training process, which includes theoretical and practical knowledge. Training to become a welder is a long and responsible job, although once you understand everything, you can understand that it is not difficult if you follow all the recommendations.

And in the end, I would like to answer one of the most frequently asked questions, what is the difference between automatic welding and semi-automatic welding:

automatic welding is a process in which the movement of the arc and the supply of the electrode are mechanized;
semi-automatic welding is a type of welding in which the wire is fed mechanically and the arc is moved manually.

How to cook semi-automatically video:

Stainless steel welding

It is carried out in a protective atmosphere of argon due to the increased chemical activity of stainless steel in a heated and molten state.

In addition, large casting shrinkage, as well as reduced electrical and thermal conductivity of stainless steel, leads to the need to select special welding modes.

Wire for welding stainless steel

For welding stainless steel, full-section wire made of high-alloy steels is used, selected according to the similarity of the composition to the material being welded. For especially critical products, tungsten wire is used.

Wire for welding stainless steel

Flux-cored wire is also used for welding stainless steels without supplying shielding gas from a cylinder.

Gas selection

Either argon or carbon dioxide is used as a protective atmosphere.

Sometimes, to reduce the cost of the operation, acetylene is chosen as a gas, but it is explosive and requires a lot of experience from the welder.

The use of flux-cored wire allows you to do without gas, but this mode also requires high qualifications and is not recommended for particularly critical products.

Stainless steel welding technology in a carbon dioxide environment

When welding stainless steels, the following conditions must be met:

Use reverse polarity mode.
Do not allow the wire to fly out more than a centimeter.
Monitor gas consumption, it should be from 6 to 12 m3 per minute.
Use a desiccant - copper sulfate.
Use chalk solution as splash protection.
Operate the burner smoothly, without jerking.
Move at least 5 cm from the edge of the part.

Metal preparation

It is necessary to clean the welded edges and the surrounding area from contamination with a steel brush.
Degrease surfaces with white spirit or a special solvent.
Treat the surface with a special anti-metal splash agent. This will help reduce post-op stripping to a minimum.
Achieve a welding gap sufficient to compensate for shrinkage.

Welding technical diagram

Due to the low thermal conductivity of stainless steel, in order to avoid overheating of the welding zone, operating current values are used that are 15-20% lower than when welding conventional structural steels.

Welding technical diagram

In addition, it is necessary to ensure a minimum welding gap sufficient to compensate for casting shrinkage

Semi-automatic welding

Metalworking in protective gases is possible under the control of a semi-automatic mechanism. The latter is considered a separate apparatus and at the same time a whole complex of mechanisms. We are talking about gas cylinders.

Work usually takes place either at a post, on a machine, or without a post. A typical semi-automatic machine for working in a protective nitrogen environment looks like this: a design consisting of an electricity source, a device for supplying wire, a light, a cable, a cooling apparatus, a gas supply system and other structures.

The purpose of the welding machine differs depending on the type of working gas. MAG welding uses active nitrogen, while MIG welding uses passive nitrogen. The first type of welding cannot use the second type of gas, and vice versa.

To avoid thinking, buy a universal device that can work with two types of gas. You will increase your welding capabilities.