Laser welding

Today there are numerous welding techniques other than gas welding and arc welding for every special field, because different materials call for different techniques. There are numerous techniques just for welding metals. Laser welding is the future for welding metal.

Other conventional welding techniques like, for example, TIG(tungsten inert gas welding), MAG(metal active gas welding), or plasma welding do not reach the energy densities needed for a deep welding effect.

The principle of laser welding is to create laser radiation and with it the energy, that is necessary for the welding process. This energy is lead by a deflection mirror and a focusing device, e.g. focusing mirror, to where it should have it’s effect, to the joint of the work pieces.

The work pieces themselves are positioned and fixed in such a way in the work piece seat, that the focused laser beam can be diverted exactly on the additional seam. The laser welding head moves along the joint over the work piece. The enormous energy density of the laser beam in focus makes the material melt and vaporize

The pressure of dissipating metal vapor can become so high, that a vapor channel forms in the material – the so-called “ keyhole”. This “keyhole” penetrates a few millimeters deep into the material.

When the laser welding head moves over the work piece, the keyhole moves with it under the laser welding head. The two casts flow into one another behind it. The joined and mixed material cools off and the cast solidifies to a narrow welding seam.

The welding seam is usually protected from reaction with the air by a shield gas during the machining. Other gases, the work gases, can aid and control welding process. When welding with a laser, two different welding techniques are used: heat conduction welding and deep welding. When using heat conduction welding, the material is melted only on the surface. In this way, welding seams a few tenths of a millimeter deep are formed. This welding technique is useful with pulsed laser, which is used for welding components for the electronic industry or for medical small parts. When producing, for example, gear parts, profiles or thick walled tubes, very deep and narrow welding seams are required. In these cases, deep welding is done with the CO₂ laser.

In industrial practice laser welding is used mainly for joining coated materials, sheet stacks and components of different sizes where distortion at risk.

With steels, the weldability of the workpiece depends in the first place on the amount of carbon in it. Chrome nickel steels are generally easy to weld and permit high welding speeds because of their low heat conductivity. Non – ferrous metals are generally poorer to weld as steel. The reason for this is that these alloys have a lower degree of absorption for the laser radiation than in the case with steels.

Titanium and titanium alloys are easy to weld with the laser. A feature, though, make the welding process difficult – they react heavily to principle components in the air: oxygen and nitrogen. Here both by welding and by cooling down, the welding seam must be selectively work on with shield gas or even in a shield gas atmosphere.

If you compare laser welding with tungsten inert gas welding, metal active gas welding or plasma welding, the great advantage of laser welding can be seen in the possibility of deep welding. With other techniques, it is not possible to achieve the required energy density for a deep welding effect.

Exercises

1. Learn the following words and word combinations:

conventional -традиційний

density -густина

deflection -відхилення

to divert -відхиляти

seam -стик

to vaporize -випаровуватися

to dissipate -розсіюватися

vapor channel -паровий канал

to penetrate -проникати

shield -щит

TIG -зварювання вольфрамовим електродом

в інертному газі

MAG -зварювання металевим електродом

в середовищі захисного газу

heat conduction welding -теплопровідне зварювання

deep welding -глибоке зварювання

Дата добавления: 2015-11-16