What is Laser Welding?

The principle of laser welding

Laser welding is a kind of high precision welding method, which makes use of high energy density laser beam as a heat source. Laser welding is one of important aspects of laser material processing technology, which is mainly used for welding thin wall materials and welding at low speed in the 1970’s. The process of welding is heat conduction. Laser radiation heats the surface of workpiece. Then the heat on surface diffuses to the interior through heat conduction. Melt workpiece and form specific bath by controlling width, energy, peak power and repetition frequency of laser pulse. It has been successfully applied in precision welding of micro and small parts because of its unique advantages.

 

The advantages of laser welding

(1) Quantity of heat can be downed to the lowest requirement. Metallographic change in heat affected zone has small range;

(2) The welding parameters of 32 mm thickness of single pass welding is tested to be qualified, which can reduce the required time of thick plate welding and even can save filler metal;

(3) Electrodes are unnecessary. Laser welding has no concerns that electrodes are polluted or damaged. What is more, laser welding is not contact welding process. So, waste and deformation of machine tools can be reduced to the lowest level. 

(4) Laser beam is easy to focus, alignment, and be guided by optical instrument, which can be placed in the appropriate distance from the workpiece. And the laser can be guided again between machines tool surrounding workpiece and obstacle. Other types of welding cannot take their advantages for being limited by above space;

(5) Workpiece can be placed in closed space (Vacuum or internal gaseous environment is under control);

(6) A laser beam can be focused in a small area. It can weld small parts which are closed to each other;

(7) Laser welding can weld various materials. It can also connect various heterogeneous materials;

(8) It is easy to automatic high-speed welding. Laser welding can also be controlled by digit or computer;

(9) When welding thin materials or wire rod, melting back cannot occur easily just as electrical arc welding;

(10) It is not affected by magnetic field (while electrical arc welding and electron beam welding are easy). Laser can align weldments accurately;

(11) It can weld two kinds of metal having different physical properties, such as different resistances. 

(12) Vacuum is unnecessary, so as X-ray protection.

(13) If it is perforation type welding, the weld depth to width ratio is 10:1;

(14) It can switch device and transmit laser beam to a plurality of workstations.

 

The disadvantages of laser welding

(1) Position of weldments should be very accurate. It must be within the scope of the focus of laser beam.

(2) Weldments need clamp fixture. Ensure the final position of weldments align to welding spot impacted by laser beam;

(3) If the maximum thickness of welding limited by the penetration thickness is far more than 19 mm thickness of workpiece, the laser welding is not suitable for production line;

(4) For materials having high reflectivity and thermal conductivity such as aluminum, copper and their alloys,, welding will be affected by the change of laser.

(5)When carrying out laser welding from medium energy to high energy, use FPM plasma modul to drive ionized gas surrounding molten bath so that welding bead can appear again;

(6)The efficiency of energy conversion is too low, usually less than 10%;

(7)Welding bead solidifies quickly. It may have pores or embrittlement. 

(8) Expensive equipments.

 

In order to eliminate or reduce laser welding defects, better application of this excellent welding method, put forward some with other heat source and the process of making composite welding, maily laser and electric arc, laser and plasma, laser and induction heat compound welding, double laser beam welding, and multiple beam laser welding etc. In addition, all kinds of auxiliary process measures are put forward, such as laser welding with filler wire (can be divided into cold and hot wire welding wire welding),plus auxiliary magnetic field enhanced laser welding, protection gas control of weld pool depth of laser welding, laser assisted friction stir welding etc.