When selecting laser welding light source, factors such as welding material, joint geometry, speed and so on should be fully considered.
With the wide application of laser welding in the manufacturing industry, how to correctly select laser source is a practical problem that manufacturers need to face.
At present, the laser sources available in the market include optical fiber, pulsed Nd: YAG, diode, disc and CO2 laser source (CW Nd: YAG laser source has basically been replaced by optical fiber and disc laser, so it is not mentioned in this paper).
The selection of laser source should fully consider various factors, such as welding material, joint geometry, welding speed, geometric tolerance, system integration requirements, etc. of course, the budget should also be considered.
Each laser source has its own characteristics, which can meet different welding requirements.
Of course, it can also be replaced in some cases.
CO2 laser, with a wavelength of 10604nm and power of 1 ~ 20kW, is a very mature laser, and has been the main laser source for high-power processing since the 1980s.
This efficient diode-pumped laser is actually a small core-diameter silicon-based fiber.
The laser source appears in the optical fiber, so it does not need to be corrected, and when the small core diameter optical fiber is mapped to the focusing lens, the minimum focus size can reach 10 microns.
The compact laser usually the first mock exam in two configurations: low power welding (less than 300W).
And multi-mode for high-power welding.
The improvement of the power of diode laser single light-emitting surface devices, the emergence of new cooling channel technology, and the development of micro optical element technology that can focus the beam into optical fibers with a diameter of less than 1000 microns have promoted the emergence of diodes as welding lasers.
The flat YD: YAG crystal thin disk of the disc laser is placed in the center of the CW laser – the disc laser is designed to avoid the inherent problems of the rod laser.
A 0.01in thick disk is used, and the other side is supported by a cooling device.
With this design for cooling, the laser power can reach 10kW and the beam quality can be guaranteed.
Pulsed Nd: YAG laser
This laser uses a single Nd: YAG laser rod to generate high peak and low average power for welding through flash lamp excitation.
For example, a relatively low power, 35W average power, can produce 6kW peak power.
The combination of peak power and narrow pulse width not only ensures the quality of material welding, but also provides effective control for energy input.
Select laser according to penetration size
The selection of laser can be divided into less than 0.01in, 0.01 ~ 0.03in and more than 0.03in according to the penetration.
Generally speaking, multiple laser sources can be selected to complete welding, but for performance and budget considerations, only one or two light sources can be selected.
Of course, the final decision may also be affected by many other factors, such as sample quality, geographical factors, after-sales service, preferences of system integrators, etc. of course, it may also be affected by popularity.
Weld penetration less than 0.01in
Pulsed Nd: YAG laser is mainly used, followed by fiber laser.
Considering component assembly, joint shape, material and coating, the whole welding process needs to be better controlled, and pulsed Nd: YAG laser is the best choice.
The use of peak power can produce a welding beam with a spot size greater than 1000 microns, which has great flexibility in selecting the spot size, so as to maximize the process window of the welding itself and ensure the necessary tolerance in the production environment.
Fiber laser is the only continuous-wave laser in this category, because fiber laser can make the spot size after beam focusing less than 25 microns, so as to obtain the high power density required for welding.
In order to ensure price competitiveness in the field of micromachining, the power of fiber laser generally does not exceed 200W, which limits its maximum spot size and cannot provide sufficient power density.
Generally, the size of the solder joint does not exceed 75 microns.
This is one of the biggest limitations of fiber lasers.
In actual production, when adjusting joints/components according to fit tolerance and superposition tolerance, it is often impossible to ensure an error range of ± 15mm.
Fiber laser is mainly used in lap welding of thin materials with high requirements for welding joints in order to ensure stability.
The fiber laser uses a lens with a focal length of 150 mm, which can produce light spots with a diameter of less than 25 microns, which brings enough operation space to the processing.
By using lap welding, fiber laser can obtain weld with penetration of 0.01 in or even higher than 0.01 in at a high speed;
The penetration depth of 0.004in can be obtained by 200W single-mode fiber laser at the speed of up to 50In / s.
In contrast, pulsed Nd: YAG laser can meet all applications except thin foil welding.
The spot size, pulse width and peak power range of the laser are large, so it can almost meet various welding requirements after adjustment and optimization.
0.01 ~ 0.03in (0.254-0.762mm) weld penetration
The above application classification of pulsed Nd: YAG laser and fiber laser is still valid here, but the range is narrow.
Pulsed Nd: YAG laser is used in most spot welding, while fiber laser with about 500W power and spot diameter of 0.01 μm can be used in butt welding and fillet welding with low tolerance.
Pulsed Nd: YAG laser has relatively high-cost performance.
500W and 25W lasers can bring different weld penetration at different welding speeds;
The peak power can ensure penetration performance, while the average power can ensure the welding speed of seam welding.
Diode lasers with power between 500 ~ 800W can weld components with large tolerance, and the speed is generally slower than that of optical fiber and disc lasers, but a large tolerance can make up for this deficiency.
Weld penetration greater than 0.03in (0.762mm)
All lasers are suitable for this range.
The penetration depth of pulsed Nd: YAG laser is about 0.05 in (1.27 mm), while other types of lasers can reach 0.25 in (6.35 mm), and some even exceed 0.5 in (12.5 mm).
Generally speaking, the welding parts suitable for pulsed Nd: YAG laser in this range are relatively small, such as pressure sensors with seam welding.
In addition, in terms of speed and penetration, the automotive industry basically covers almost all applications, and optical fiber, CO2, disc and diode lasers can be used.
The main differences between these laser sources are beam quality, brightness and wavelength.
Beam quality refers to the focusing ability of laser, and brightness refers to the power density in the focused beam.
For example, the beam quality of CO2 laser and fiber laser is similar, so that if other parameters are the same, they can focus into light spots with the same diameter.
The wavelength of the optical fiber laser source is one-tenth of that of the CO2 light source, so the spot diameter that the optical fiber laser source can produce is one-tenth of that of the CO2 light source;
The beam quality and brightness of the fiber laser source are better.
In laser welding, the penetration depth and speed are directly proportional to the beam quality and brightness, but the welding stability and tolerance are not so directly related to the beam quality and brightness.
Therefore, a balance must be found between welding performance and quality and the width of the process window.
It should be noted that in order to meet the actual needs, the beam quality can be reduced, but the poor beam cannot be improved.
At 0.25in penetration, the welding speeds of the above lasers are very close;
Optical fibers and discs are faster than CO2, while diodes are slower than CO2.
Welding with higher-power lasers usually requires two shifts, which means that the choice of which laser is also related to the cost of purchasing lasers.
Although CO2 laser has a large number of users and they are very familiar with this technology, the single welding cost of CO2 laser is much higher than that of fiber, disc and diode laser.
Compared with plasma and arc welding, laser welding has more advantages in welding applications with penetration requirements of more than 0.25in, and can greatly reduce thermal deformation.
The reduction of thermal deformation can maintain the geometric shape of the part, so that it is no longer necessary to reprocess the geometric shape of the part.
The matching of parts may cause problems under this thickness.
The process flow of wire filling or the combination of laser welding, plasma welding and arc welding can be adopted.
There are many kinds of laser sources for laser welding, each of which has its own characteristics and is suitable for different needs.
It is very important for users to fully understand which laser source can best meet their welding needs.
If you need a welding system, the best way is to work with the system supplier, who can decide the best laser.
In addition, you can contact different laser manufacturers and send welding samples to them to determine the best solution.
When choosing a laser, remember that welding needs to be balanced in terms of penetration, speed, stability, production part accommodation and tolerance.