How to get the best effect of different materials in laser precision welding

At present, laser precision welding is mainly used in electronic products, such as shell, shield, USB connector, conductive patch, etc. it has the advantages of small thermal deformation, precise controllable action area and position, high welding quality, heterogeneous material welding, easy to realize automation, etc. But when welding different materials, we need to use different welding methods.

Kunshan jour laser welding engineer based on many experimental results, summed up in the production and manufacturing process of consumer electronics, high reflection materials, metal sheet, dissimilar materials and other different materials should use which way of laser precision spot welding, in order to get the best welding effect.

1. Laser precision spot welding of high reflection materials

When welding aluminum, copper and other high reflection materials, different welding waveforms have great influence on the welding quality. The high reflectivity barrier can be broken through by using the laser waveform with pre peak. The instantaneous peak power can quickly change the metal surface state and make its temperature rise to the melting point, so as to reduce the reflectivity of the metal surface and improve the utilization rate of energy. In addition, due to the fast heat conduction speed of copper, aluminum and other materials, the appearance of solder joints can be optimized by using slow drop waveform.

On the other hand, the absorptivity of gold, silver, copper and steel decreases with the increase of laser wavelength. For copper, the absorptivity of copper is close to 40% when the laser wavelength is 532nm. In addition, by using infrared laser and green laser respectively for pulse spot welding of red copper, it can be found that the size of infrared laser spot welding is inconsistent (Fig. 1), while the size of green laser spot welding is more uniform, the depth is consistent, and the surface is smooth (Fig. 2). Therefore, the welding effect of green laser is more stable, and the required peak power will be more than half lower than that of infrared laser.

Peak wave

The welding effect of 1064nm wavelength

The welding effect of 532nm wavelength

2. Laser precision spot welding of sheet metal

The results show that the material is easy to be broken down and the welding spot is large when the pulse laser is used to weld the metal sheet; Because of its instability and low absorptivity of laser in solid state, high reflection materials often have the phenomenon of burst point and false welding. In order to solve the welding difficulties of thin plate and high anti metal, the QCW / CW mode of fiber laser is modulated by analog quantity and digital quantity respectively. N pulses can be output at one trigger, and single point multi pulse welding can be realized with low power.

Modulation mode

High frequency pulse spot welding surface forming

Weld section

3. Laser precision spot welding of dissimilar materials

When laser welding dissimilar materials, it is easy to appear the problems of false welding, crack and low connection strength. This is due to the large difference of physical properties between the two, low mutual solubility, and easy to generate brittle compounds, which greatly reduce the mechanical properties of welded joints. Using high beam quality nanosecond laser, through high-speed scanning mode, accurately control the heat input, inhibit the formation of intermetallic compounds, realize the overlapping of dissimilar metal sheets, and improve the weld forming and mechanical properties.

Because of the advantages of high beam quality, high peak power, adjustable and controllable, quasi continuous fiber laser and MOPA pulse width adjustable fiber laser have become ideal light sources for laser precision spot welding.

4. Laser used

A 150W / 1500W quasi CW fiber laser

The product has various compatibility and control modes, can switch pulse and continuous mode, and can handle the processing tasks of two previous lasers at the same time. The pulse width waveform is flexible and adjustable, air cooling and heat dissipation, and the electro-optic conversion rate is more than 30%. It is another choice for long pulse width and high peak power applications.

A 120W MOPA pulse width tunable fiber laser

The two-stage amplification of pulse width tunable fiber laser is constructed by MOPA, and the pulse width and frequency can be adjusted independently, which makes more laser applications possible. The pulse width is adjustable from 60 to 350 ns, the peak power is up to 10 kW, and the repetition rate is up to 1000 kHz. Equipped with self-developed on-line isolator, it is an ideal laser source for laser fine processing.