Laser welding


Laser Welding is one of the newest methods of fusion welding. High speed and high precision are among the factors that have expanded the application of this welding process to various industries. With high-energy laser radiation to the desired level, the heat needed to create the molten pool and the process of bonding is provided. Laser beam welding is performed in three different ways based on a type of segmentation:

1. Conductive

This type of laser welding is performed at low energy density and produces a superficial weld effect.

The laser welding by conduction is divided into two groups:

Direct heating
Energy Transfer
Direct Heating:

Direct conduction welding can be used in a wide range of metals and alloys and in forms of thin-walled and thin sheets.

CO2, Nd: YAG and diode lasers with different energy levels, in the range of tens of watts, are used in this method.
Direct heating with a CO2 gas laser beam can be used for welding in butt joints in polymer sheets.

Energy Transfer :

In this method, an absorbing ink is placed in the joint edge of the binding. This ink absorbs laser beam energy and transmits it to a limited thickness of its surrounding material. This leads to the formation of a layer of melt coagulation that the freezing of this common area causes the connection to occur.

Transitional welding is a suitable method for connecting polymers. Composites can also be welded in this way, provided that the thermal properties of the phase phase and the reinforcing phase are similar. The thick sections of the fittings can be connected without melting the other external parts.

2. Conductive / Intrusive mode

This mode is done at an average energy density, and the depth is more effective than the previous one.

3. Intrusive mode (key hole)

The obvious feature of this method with which it is known is having a narrow and deep weld effect. In this method, laser light creates a string of evaporated material, known as the keyhole, inside the piece. This hole is a conductor for transferring the power of laser light to the material.

Basically, in high power densities, all materials can evaporate if they absorb energy. Therefore, in the welding process, a hole or boiling nebulizer is created by evaporation of the material. This hole is filled with materials that are melting from the walls.

Types of lasers
The laser beam is divided into two categories based on the type of source it produces:

1. Gas Laser

In this technique, the laser equipment is located inside a compartment. Put some CO2 and neutral gas in the chamber and create a potential difference in the gas mixture, so that the gas is emitted and emitting light. The light emitted is between two mirrors, and the intensity is so high that it passes through the second mirror and the laser is produced. After the second mirror, a lens is embedded in the system, which has the task of concentrating the production rays.

2. Solid state  laser

In this technique, instead of a gas mixture, a solid core is used. These cores are known as Nd: YAG laser.

Advantages and limitations of welding with laser
Advantages:

This method is applicable to different materials, because it does not have to be a conductor of electrical current.
In the production of electron beams, the tools should be non-magnetic, but there is no limitation in laser production.
The laser covers a wide range of energy levels, and therefore the energy is readily controllable and easy to use.
The thickness of the parts that can be welded with this method is very wide and includes a minimum thickness of 0.01 in.
The elegance of this process is very high, so it is used for small and fine fittings.
The heat input to the piece in this method is very close to the minimum heat required for the melting of metals. Therefore, the undesirable effects of excess heat in this method are not discussed.
The welding time is very short in this method and there is no filler.
Compared to arc welding, there is no need for an electrode. Therefore, the contamination caused by the electrode is eliminated.
Laser beams with optical equipment have the ability to focus, divert, and orient. Therefore, the possibility of welding of inaccessible places is provided.
Different materials, especially non-diffusers, are capable of welding with this method.
This method can be easily mechanized.
Magnetic fields affect electric arc and electron beam. But they do not work on the laser.
Non-matched materials with different shapes can be welded in this way.
The laser beam can be moved to other places for welding.
Limitations:

The precise control of the position of the piece relative to the laser beam is necessary because its width is very narrow.
The welding of some metals with high reflectivity is difficult with this method.
Quick freezing in this way may result in cracking or cracking of the porous structure.
If the energy produced is high, there is the possibility of plasma formation. Therefore, plasma protection is also required. To solve this problem, one should either use low power to produce the laser, or use neutral helium gas in the laser method.