Introduction to welding – basic information to get you started

Welding began around 3000 years before Christ with the Sumerians Sumerians in southern Mesopotamia. Even then, people were welding similar base materials, in this case gold with gold. Later, the Egyptians used welding processes to build pipes from copper materials. However, ancient welding processes no longer have much to do with modern welding applications of the 21st century. Today, welding is one of the most important manufacturing processes when it comes to joining workpieces together. A wide variety of processes, such as metal active gas welding, electric welding or pressure joint welding, nowadays offer the possibility of joining steel and other materials together in different ways. When it comes to welding, the focus is on the workpiece when it comes to creating a joint between materials using fillet welds or butt welds.

Modern welding processes

Welding applications have become economically interesting since Oscar Kjellberg came up with the idea of providing a rod electrode with a coating in 1907. The elements contained in the coating serve to improve the properties of the arc and the weld seam, as well as to protect the weld pool from atmospheric oxygen and thus from unwanted oxidation.

There are now various welding processes, all of which have special areas of application as well as advantages and disadvantages. DIN EN ISO 4063 provides a list of welding processes, the most important of which are listed below:

• 111 Manual arc welding (manual metal arc welding)

• 121 Submerged arc welding with solid wire electrode (submerged arc welding)

• 131 Metal inert gas welding with solid wire electrode (MIG welding)

• 135 Metal active gas welding with solid wire electrode (MAG welding)

• 136 Metal active gas welding with welding powder-filled wire electrode (flux-cored wire welding)

• 141 Tungsten inert gas welding with solid wire or solid wire filler (TIG welding)

Distinction from soldering / welding

Soldering and welding are both processes for joining metals or other materials, but they differ in their processes and results.

In soldering, two metal parts are joined with a soft solder (e.g. a tin-lead alloy). In soldering, the solder is applied to the metal parts to be joined and melted by heating to a temperature above the melting point. The liquid solder flows into the gap between the metal parts and joins them together when it solidifies again as it cools.

Welding, on the other hand, is a process in which two metal parts are joined together by melting. During welding, the metal parts to be joined are heated to a high temperature until they melt or almost melt. The metal parts are then pressed together under pressure, creating a weld seam.

Compared to soldering, welding is generally a stronger connection, as the molten metal parts form a cohesive structure and are not separated by a soft solder. However, welding also requires higher temperatures and specialised equipment, whereas soldering can be carried out with simple tools such as a soldering iron.

Shielding gases

As metals tend to react with the environment at high temperatures (e.g. burning off of alloy components or oxidation of the workpieces), protective atmospheres are created during welding. The main aim is to protect the weld pool and the arc from the oxygen, nitrogen and other gases contained in the air. The shielding gas is supplied either directly to the welding torch through air nozzles or by other means, such as forming. The use of forming gases is preferably used for closed profile cross-sections such as pipes, but also with special devices when welding sheet metal. By closing the pipes with pipe plugs, trapped gas is held in the profile of the workpieces. The gas is channelled into the hollow cross-section through gas feedthroughs in the plug. This effectively protects the back of the weld pool against unwanted gases.

In welding processes such as manual metal arc welding, a small amount of shielding gas is formed by burning off the coating. A certain amount of shielding gas is also formed by the welding flux during submerged arc welding. A distinction is made between active, inert and mixed gases. A selection of shielding gases can be found in the standard sheet ISO 14175.

Rule of thumb for MIG and MAG welding: wire diameter * 10 = volume flow of shielding gas

Active gases

Active gases are often used in gas-shielded welding to protect the weld pool from the ambient air. Active gases are chemically reactive gases that can protect the weld pool from oxidation and other undesirable influences. Although they are labelled as active, their activity is generally low.

The most common active gas used in gas-shielded arc welding is pure carbon dioxide (CO2), which is obtained from industrial combustion processes such as burning lime or burning fossil fuels. Due to its low cost and high availability, carbon dioxide is often used for welding unalloyed structural steels where the burning off of alloy components is not a problem.

In addition to carbon dioxide, other gases such as nitrogen (N2) are also used in welding technology. Nitrogen is often used as a filler gas when using inert gases such as argon to protect the weld pool from contact with air and thus improve the welding quality.

Active gases are therefore mainly used in gas-shielded welding to protect the weld pool from oxidation and other undesirable influences. Although they are labelled as active, their activity is generally low and their use depends on the specific requirements of the welding process and the materials to be welded.

Inert gases

If a reaction of the weld pool or the arc with the environment is to be almost completely prevented, inert gases are used. Argon (Ar) and helium (He) are frequently used. These are noble gases from the eighth main group of the periodic table. Noble gases are inert, as atoms have a fully occupied (or empty) electron shell (see also Wikipedia: Noble gas configuration). This fully occupied shell prevents chemical compounds from being formed with other atoms or molecules in an undesirable way. These would need free electron pairs.

In most cases, argon is used for intergas welding. If a base material has a high thermal conductivity (copper, aluminium), a mixed gas containing helium is used. Pure helium, on the other hand, is only used in special applications and is also very expensive.

Mixed gases

Mixed gases are a popular choice for shielded arc welding as they can utilise the synergy of the properties of different gases to improve the welding quality. Compared to pure gases, mixed gases offer a higher welding speed, better welding quality and reduce the risk of welding defects such as porosity.

Typical mixed gases for gas-shielded welding often contain a high proportion of carbon dioxide (CO2). This gas ensures a stable arc, increases the welding speed and helps to reduce spatter. In addition, argon is often added to improve the welding quality and protect the weld pool from oxidation.

Depending on the application and material, other gases such as oxygen (O2), helium (He) and nitrogen (N2) can also be added. Oxygen increases the welding speed and helps to reduce welding defects such as porosity. Helium increases thermal conductivity and reduces susceptibility to welding defects such as cracks. Nitrogen is often used as a cost-effective alternative to argon and improves the welding quality.

The choice of mixed gases is usually based on the specific welding process and the requirements of the material. Factors such as the welding position, the weld seam preparation and the size of the welding wire must be taken into account.

Overall, mixed gases offer a flexible and effective solution for improving welding quality and productivity in gas-shielded welding.

Selection of gases according to ISO 14175

Designation ISO 14175	Composition	Composition Function
I1	100% Ar	Inert
I2	100% He	Inert
I3	0.5 – 95 % Ar, rest He	Inert
M21	15-25% CO2, rest Ar	weakly oxidising
C1	100% CO2	oxidising
N1	100% N2	inert
O1	100% O2	strongly oxidising
Z	gases not included	–

Welding consumables for welding

Welding consum ables are an important component of many welding processes and are used to specifically influence the weld metal and improve the quality of the welded joint. Depending on the requirements and intended use, welding consumables are available in different forms and designs.

An important aspect when selecting the right filler metal is the type of base material. Only materials of the same type can be welded together. Welding steel, for example, requires the use of steel filler materials, while welding aluminium requires the use of aluminium filler materials. The specific requirements of the welding process, e.g. the welding position, welding current or welding speed, must also be taken into account when selecting the correct filler material.

In addition to the type of base material and the process-specific requirements, the mechanical properties of the filler metal also play an important role. In particular, the strength, toughness and corrosion resistance of the material should be mentioned here. In order to guarantee the quality of the welded joint, these properties must be harmonised with those of the base material.

The type of filler metal varies depending on the welding process and material. In manual welding processes such as TIG welding or gas welding, the filler material is fed manually, whereas in automated processes such as MIG/MAG welding or submerged arc welding, a conveyor system integrated into the welding machine feeds the filler material.

In general, filler materials are an indispensable part of welding technology and contribute significantly to the quality and durability of welded joints.

Manual arc welding

Welding using an arc and stick electrode is called manual arc welding (process number ISO 4063: 111). Common abbreviations are manual metal arc welding, MMA or MMAW (Manual Metal Arc Welding).

The stick electrodes used are usually provided with a coating. This makes it possible to weld without protective gas measures. It is therefore also possible to weld outdoors or even under water.

Most ferrous materials, nickel materials and other non-ferrous metals can be welded. Welding aluminium materials is hardly used any more and is no longer covered by standards.

Coatings are used to protect the weld metal from atmospheric oxygen. During combustion, these form a flue gas that surrounds the weld. Slag formers are also present, which form a solid, glass-like and gas-tight layer over the weld seam. This can be removed after the welding curtain by lightly tapping with a welding hammer. Typical types of coating are

• Basic coatings (made of fluorspar and calcite)

• Acidic coatings (made of magnetite)

• Cellulose coatings (made of cellulose, also known colloquially as “paper electrodes”)

• Rutile coating (made from rutile TiO2)

Advantages and disadvantages of manual metal arc welding

Advantages:

• As no welding gas is required, the process can be used anywhere. This means that welding technology is often used on construction sites

• Cost-effective devices. In contrast to large MIG/MAG systems, systems for manual metal arc welding have a simpler design and are therefore often cheaper.

• Due to the flat sloping characteristic curve of the welding machines, they are also often suitable for TIG welding. In some cases, the necessary devices are already included in the welding power source (device for gas supply, etc.).

• Welding with alternating and direct current possible (depending on the rod electrode, purely basic electrodes are normally welded with direct current at the positive pole. Others with alternating current or with direct current on the negative pole. Please refer to the manufacturer’s information)

• Quickly changeable electrode diameter. This allows quick adaptation to the welding task. Diameter standardised in DIN EN 759.

• High availability of stick electrodes. Suitable electrodes are commercially available for many applications.

• Can be used in all welding positions.

Disadvantages:

• Low deposition rate. This makes the process slow and time-consuming.

• Partly toxic and even carcinogenic substances in the welding fumes. PPE required!

• High heat input.

• High demands on the welder’s manual dexterity.

• Possible problems with hydrogen. Re-drying of electrodes often necessary.

• Weld seam quality is highly dependent on the care and experience of the welder. Improper workmanship can lead to cracks and irregularities in the weld seam.

• A high weld seam quality requires good pre-treatment of the workpiece, i.e. thorough cleaning and, if necessary, preparation by grinding or milling.

• The welding current is more difficult to control with MMA welding than with other welding processes. An uneven power supply can lead to irregular melting performance.

• A possible danger with manual metal arc welding is the formation of cracks due to stresses in the material. These can be avoided by slowly cooling the workpiece after welding.

• The material of the electrodes is also an important factor in manual metal arc welding. Different electrodes are suitable for different materials and applications. It is important to choose the right electrode to achieve optimum weld seam quality.

• During manual metal arc welding, spatter can occur, which can be deposited on the surface of the workpiece and contaminate it. To avoid this, the weld seam should be protected with a welding shield cover.

• MMA welding is comparatively slow compared to other welding processes and therefore may not be the most efficient option for large projects. However, it is ideal for smaller projects and repairs.

MIG/MAG (MSG) welding

The most common process used in trade workshops is metal active gas or metal inert gas welding. MIG refers to the process of arc welding with a consumable wire electrode using an inert gas. MAG is welded with an active gas. GMAW (gas metal arc welding) is the generic term for both processes.

The process number for MIG welding is 131 according to ISO 4063 and 135 for MAG welding. This welding process is usually used to weld steels, aluminium and nickel materials and their alloys.

Filler metal

Wire electrodes for gas-shielded arc welding are usually wound onto spools. Common diameters are 0.6, 0.8, 1.0, 1.2 and 1.6 mm. Wire diameters of 0.9mm are also often used in the automotive industry. Powder-filled wires are sold in diameters from 1.6 to 3.2 mm and are usually used for build-up welding.Solid wire electrodes are usually plus-poled, flux-cored wire electrodes are minus-poled.

The categorisation of different filler metals is explained using the following example:

ISO 14341-A-G 46 5 M21 3Si1

• ISO 14341-A: Standard of the filler metal

• G: Wire electrode

• 46: Elongation at break

• 5: Impact energy

• M21: Shielding gas

• 3Si1: Composition of the filler metal

Arc types in MSG welding

The material transfer from the welding torch to the component is realised by the arc. The most important lever here is the pinch force, an electromagnetic force that acts on every current-carrying conductor. The pinch force increases with increasing amperage and is only sufficient for a very coarse material transfer at low ampere settings on the welding power source. As the amperage increases, the electromagnetic forces cause the arc to constrict, resulting in a fine droplet transfer and even a spray arc.

However, in addition to the set amperage, the welding gas is also a prerequisite for a spray arc. A gas with low thermal conductivity is required here.

Long arc

The long arc in MAG welding is a special type of arc that occurs in CO2-rich gases with a CO2 content of at least 25 %. Compared to the normal arc, the long arc is longer and remains stable for longer. However, violent short circuits are rather rare with the long arc, but when they do occur, they are particularly intense. This is due to the fact that the long arc generates very high short-circuit currents, which leads to a higher deposition rate and thus to larger quantities of coating.

The long arc is particularly suitable for welding thick sheets or for bridging larger gaps between the parts to be welded.

Short arc

The short arc is a welding arc that burns with constant short circuits. In contrast to the long arc, the short-circuit current is lower. During welding, the material transition takes place during the short circuit. This means that the arc is always extinguished during the welding process. The reason for this is that the current flow is briefly interrupted when the welding electrode comes into contact with the workpiece. However, the arc is re-ignited by increasing currents during immersion in the weld pool. This process is repeated continuously during the welding process and results in a uniform weld seam.

Short arcs are mainly used when welding thin materials, as they have a lower heat input than long arcs and therefore deform the material less.

Spray arc

The spray arc in MAG welding usually occurs at higher amperages and is a great advantage for many welders. Compared to a normal arc, it burns almost without short-circuiting and therefore offers high stability and even power development. Another important characteristic of the spray arc is its good directional stability, which ensures a more precise weld seam.

In addition, the spray arc is characterised by a high penetration depth, which makes it particularly suitable for welding thick-walled workpieces. Due to its low energy loss, it also consumes less power and therefore enables greater energy efficiency. The lower burn-off losses also make the spray arc an economical alternative to the normal arc.

Another advantage of the spray arc is its tendency towards penetration notches, which is significantly lower than with a normal arc. As a result, weld seams can be produced without disturbing notches. The tendency to spatter and porosity is also significantly lower with the spray arc, which results in a higher quality weld seam.

Overall, the spray arc offers a number of advantages in MAG welding that make it an attractive option for many welding applications.

Special status of pulsed arc

A pulsed arc can be produced using an internal circuit in the welding power source. The main advantages are less heat exposure, as the arc does not burn continuously. However, there is also better penetration, as higher peak currents can be set.

Advantages and disadvantages of MIG/MAG welding

Advantages

• Many areas of application. Applications exist for almost all common materials

• Good seam quality

• Quick to learn manual skills

• All positions possible

• Small and high thicknesses can be welded

• High availability of welding consumables

Disadvantages

• Can only be used in a protected environment Shielding gas can be blown away in windy conditions

• Higher acquisition costs

• Seam defects are almost unavoidable in some cases

TIG welding

Tungsten inert gas welding (TIG) is a welding process that is categorised as tungsten inert gas welding in accordance with EN 14640. Designations such as TIG (tungsten inter gas welding) or GTA (gas tugsten welding) are commonly used in other language areas. Process numbers according to ISO 4063 are:

• 141: TIG welding with solid wire electrode

• 142: TIG welding without filler metal

• 143: TIG welding with filler wire

In the TIG process, the arc burns between the workpiece and a tungsten electrode that does not burn off. Tungsten is chosen as the electrode material here because a very high melting point is guaranteed. This prevents the electrode from melting during welding. The welding filler material is fed by hand or by machine. The wire is fed cold or hot by means of resistance heating using an additional device. The welding process is used to realise joint welds and build-up welds. Inert gases such as argon or helium are preferably used. In some cases, a small amount of hydrogen is added.

The special feature of this process is the ability to produce precise and high-quality seams. The main disadvantage is the low melting rate. An application must be carefully considered.

As with manual metal arc welding, welding current sources with a falling characteristic curve are used. This has the advantage that a constant current can be maintained with variable arc lengths. In contrast to MIG welding, where the arc length remains constant due to the automatically guided wire, in TIG welding every movement means a change in arc length.

HF ignition devices are preferably used. This has the advantage that the arc can be ignited without contact. As a result, contamination of the weld pool by tungsten can be avoided. Furthermore, the tungsten electrode also remains free of contamination from the base material and requires less reworking.

Tungsten electrodes

A tungsten electrode has a relatively high melting point. Approx. 3400°C and therefore wears away only slightly at moderate amperage. The arc is also only ignited in the shielding gas, so that oxidation on the electrode hardly occurs. TIG electrodes are standardised in ISO 6848 and the properties can be influenced by adding various oxide additives:

Material of the electrode	Symbol	Characteristic colour
Pure tungsten	WP	green
Tungsten with thorium oxide	WT10 WT20 WT30	yellow red violet
Tungsten with zirconium oxide	WZr3 WZr8	brown white
Tungsten with lanthanum oxide	WLa10 WLa20 WLa30	black gold blue
Tungsten with cerium oxide	WCe20	grasu

Attention: Tungsten electrodes with thorium oxide are radioactive and should no longer be used!

Quality assurance during welding

DIN EN ISO 9000 ff. forms the basis for many quality management systems. However, this standard requires special approaches for “special processes”. DIN EN ISO 3834 can provide a remedy here. This offers a QM system for welding technology. It is based on “quality levels” for various welding requirements. Many execution standards (e.g. DIN EN 1090) refer to adapted levels of DIN EN ISO 3834levels of DIN EN ISO 3834.

Training as a welder

The training of welders in Europe is in fact not an independent profession, but often part of other metalworking professions. The qualification of welders is determined by an examination in accordance with DIN EN ISO 9606, which can be carried out by any professionally qualified company or a professionally qualified person. Training is not mandatory, but is often recommended before the test.

In the unregulated sector, there is no legal requirement for welders to take a welder’s test. However, it is strongly recommended that examinations are taken at a testing organisation in order to be able to provide evidence of care in the event of damage.

If welders are tested within a company, this should be carried out by a welding coordinator in accordance with DIN EN 14731. Welding specialists, welding technicians and welding engineers have the necessary background knowledge to carry out such a test. In this case, however, the burden of proof of correct qualification lies with the company.

The ISO 9606 standard contains requirements for the testing of welders in various welding processes and material groups. Among other things, it specifies the scope of the test, the test procedure and the test criteria. The examination consists of practical welding tests and theoretical knowledge tests. In order to maintain the validity of the welder’s examination, welders must regularly demonstrate their skills in practical welding tests.

Overall, the training of welders in Europe is regulated by the ISO 9606 standard and it is recommended that examinations are taken at a testing organisation in order to be able to provide evidence of care in the event of damage.

Dangers during welding

Welding applications are also associated with considerable hazards. When workpieces are welded, there is a risk of electric shock due to high currents and voltages. On the other hand, high radiation exposure due to UV light and the development of smoke must be dealt with.

The training standard for welders, DIN EN ISO 6906, always takes these dangers into account. Welding work should only be carried out by qualified personnel. Employers are also obliged to create a suitable working environment. Suitable high-quality personal protective equipment (PPE) and systems for disposing of welding fumes are mandatory. It may also be advisable to use a breathing mask (especially when welding on materials containing chromium (!!!)).

1. Fire hazard: Welding can produce sparks that can ignite flammable materials. Welders must therefore ensure that the work area is free of flammable materials. It must also be ensured that all welding equipment is working properly and has no leaks.

2. Noise: Welding can be very loud and can damage the welder’s hearing. Hearing protection is therefore essential.

3. Gas hazard: Welding can release gases that can be toxic or explosive. Welders must ensure that there is adequate ventilation in the work area to prevent the build-up of dangerous gases.

4. Eye damage: Welding can cause eye damage as the bright UV light from the welding arc can damage the retina of the eye. Welders must therefore wear suitable safety goggles or welding helmets equipped with an automatic darkening system.

5. Skin damage: The UV radiation released during welding can also damage the welder’s skin. Protective clothing, including long sleeves and trousers, gloves and welding creams, are essential to prevent skin damage.