Trumpf has developed a pulsed, green laser for efficient welding of copper, the TruDisk 421 pulse. This new disk laser, in pulsed mode, operates at a mean power of 400W, generating laser light at 515nm. Light in the green spectrum solves the problems previously experienced when using infrared lasers to weld copper.
Copper is an excellent conductor of both heat and current, making it a suitable metal for many applications in a variety of industries and sectors. In addition to medical technology and the automotive, chemical and foods industries, copper is indispensable to electronics and electrical technology.
Due to ever more compact housings and the higher performance capacities of electronic components, demands on the production and joining technologies for copper components are also rising.
When using the laser to weld copper, beam sources with an infrared wavelength are commonly used. The two greatest challenges here are good reproducibility and low spattering. At a wavelength of 1,000nm (IR), copper is highly reflective. Uniform welding seams – which will depend on the surface properties – can be guaranteed only to a certain degree, a degree that is often not sufficient for industry.
Spattering is a problem during deep welding. The spatter can damage the component and, in the worst case, cause short circuits on the board. Both can be countered by properly matching the laser parameters – such as the distribution of power density, the pulse width and the shape of the vapour channel. But despite this, the results are often still less than ideal.
What cannot be influenced are the surface tension and viscosity of copper. Both properties are lower, when compared with steel and they lead to a less stable weld pool. This is aggravated by increased energy loss due to the high thermal conductivity of copper. The pulsed green laser from Trumpf leads to a considerable improvement in the process.
To generate the green wavelength in the TruDisk 421 pulse, the frequency of the laser beam is doubled inside the laser resonator. Copper absorbs the green light far better than the infrared, which means that the material reaches its melting temperature faster, the welding process starts quicker, and less laser power is required.
While the infrared laser works with 2.6kW of peak pulse power, the green laser requires only 1.4kW for the same welded seam. The process is more energy-efficient with less spatter. The green laser also improves the reproducibility of the results. Regardless of whether the surface is oxidised, ground, sandblasted, rough or polished to a high gloss, with green laser beams the copper welding seams can always be made at uniform quality.
Among the reasons for this is that absorption at room temperature is independent of the surface properties. The use of shielding gases like argon and nitrogen will result in a welded seam of even higher quality. These shielding gases can be used efficiently and sensibly only when welding with the green laser. When using the inferior infrared alternative, the surface of the weld pool reflects more strongly because of the gas. This means that greater laser power is necessary for welding.