What is fusion welding

Overview of the welding processes

As already mentioned in our previous article, there are innumerable welding processes, whereby a fundamental distinction must be made between fusion welding and pressure welding.

Table of Contents

Fusion welding process

In fusion welding, metals of the same type are usually connected to one another by melting and then flowing together the resulting molten mass. The joining of the parts to be joined takes place without any effort. The fusion welding processes include:

Fire welding

The metals to be joined are brought into a doughy state in the fire with the exclusion of air and then joined together with great pressure, for example with hammer blows.

Gas fusion welding

Colloquially also called oxy-fuel welding. The metal is heated by combustion gases. The temperature of the flame is around 3200 ° C. As a rule, a welding wire is used as the filler material.

Manual arc welding

This is one of the oldest electrical welding processes for metallic materials. An electric arc between an electrode and the workpiece is used as a heat source for welding. Due to the high temperature of the arc, the material is melted at the welding point.

Inert gas welding (SG)

Gas-shielded metal arc welding (MIG / MAG) is an arc welding process in which the consumable welding wire is continuously tracked by a motor at a variable speed.
Tungsten inert gas welding (TIG) can be carried out on any material suitable for fusion welding. With TIG welding, there are practically no weld spatter; the health exposure from welding fumes is relatively low. A particular advantage of TIG welding is that you do not work with a consumable electrode.
Orbital welding is a fully mechanical inert gas welding process TIG or MSG, in which the arc is mechanically guided 360 degrees around pipes or other round bodies without interruption. The orbital welding process is preferably used in pipeline construction, where consistently high seam quality must be achieved under controllable conditions.
At the Plasma welding a plasma jet serves as a heat source. Plasma is an electrically conductive gas that is highly heated by an arc. In the plasma torch, the plasma gas (argon) flowing through is ionized by high-frequency pulses and an auxiliary arc (pilot arc) is ignited.
Arcatom welding is a process invented in 1924 that uses the recombination energy of atomic hydrogen for welding.

Submerged arc welding

This is an arc welding process with a consumable wire or strip electrode, in which high deposition rates can be achieved. It is mainly used industrially for welding long seams and is not suitable for manual execution.

Laser welding

This process is mainly used for welding components that have to be joined at high welding speeds, with narrow and slender weld seams and with little thermal distortion. Laser welding or laser beam welding is usually carried out without the addition of a filler material. The laser radiation is focused using optics.

Electron beam welding

Here the required energy is brought into the process zone by electrons accelerated by high voltage (60–150 kV). The beam is formed in a high vacuum (<10−4 mbar) using a triode system consisting of a cathode, control electrode and anode. The welding process usually takes place in a vacuum.

Aluminothermic welding

This process is also known as thermite welding and is mainly used for welding railway tracks. A mixture of iron oxide powder and aluminum powder is ignited in a crucible with a hole on the underside, which stands on the connection point, from which liquid iron and aluminum oxide slag floating on it form at a temperature of around 2450 ° C.

Pressure welding process

In pressure welding, on the other hand, the connection is achieved by upsetting the heated surfaces under high pressure. The pressure welding processes include:

Resistance welding

This is a welding process for electrically conductive materials based on the Joule heat of an electrical current flowing through the connection point.
The connection partners are heated until the welding temperature is reached and welded at the point of contact under the effect of a force through solidification of the melt, through diffusion or in the solid phase.

Cold pressure welding

The connections are made under high pressure and below the recrystallization temperature of the individual parts. Here, the partners remain in a solid state, but plastic deformation with a strong approach of the contact surfaces is necessary. The extremely close contact between the two contact surfaces results in the destruction of interfering surface layers and a stable connection between the workpieces due to the interatomic bonding forces that now act.

Friction welding

Two parts are moved relative to one another under pressure, the parts touching one another at the contact surfaces. The resulting friction causes the material to heat up and plasticize.

Ultrasonic welding

This is a process for joining thermoplastics and metallic materials. The welding is achieved by a high-frequency mechanical vibration in the range between 20 and 35 kHz, which leads to heating between the components due to molecular and interface friction, and in the case of metals also to the interlocking and entanglement of the parts to be joined. Ultrasonic welding therefore belongs to the group of friction welding.
Explosion welding
This process enables two non-fusion-weldable materials to be permanently and firmly bonded to one another. With the aid of explosives, the two welding surfaces collide at at least 100 m / s at an angle of 2 ° to 30 °.

Electromagnetic pulse welding

Mixed materials, but also materials of the same type, can be connected to one another within about 25 μs without heat supply, in that one of the joining partners experiences a contactless impulse by means of a magnetic field and collides with the other partner.

Diffusion welding

Diffusion welding takes place at high pressure. The quality of the welded joints is extremely high and can be in the range of the material used.

MBP welding

This process (pressure welding with a magnetically moving arc) is an arc pressure welding process with which hollow profiles are butt-welded under protective gas. An arc is ignited between the surfaces to be joined and caused to move in a magnetic field along the edges of the joint. The edges heat up and melt. Subsequent upsetting leads to a pressure welded connection with a uniform upset bulge, which is usually not processed.

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