Laser welding of metals

Precision laser welding of metals

Electrotechnical assemblies and products require ever greater functional scopes and power densities. Miniaturization is increasing. Joints, especially electrical connections, must be designed for ever higher temperatures.

Bonding and soldering are increasingly being replaced by welding. Often dissimilar metals such as copper have to be welded to iron. Wolf Produktionssysteme has developed a laser process that enables precise micro-welding.

Typical micro-welding tasks can be divided into butt joint welding and overlap welding. In electronic products, the workpiece at the top (wires, sheet metal strips or connecting legs) often has a much smaller cross-section than the one at the bottom. Therefore, three basic arrangements of the workpieces can be distinguished (see picture on the right).

The materials to be welded are often copper, brass (CuZn) or steel.

Principle

The material at the welding point is heated rapidly by the impact of the beam energy.

This creates a fusion zone with a width to depth ratio of approximately 1:1. This process is known as heat conduction welding.

Deep penetration welding is possible at higher energy densities. A vapour capillary, the so-called "keyhole", forms when laser radiation strikes.

This enables deep penetration welding in which the depth of the fusion zone is a multiple of the width.

Application

The following requirements must be taken into account for automatic microwelding with laser radiation:

When butt joint welding, the gap must be hit precisely
The gap dimension should not exceed 10% of the focal diameter, a zero gap is ideal
The absorption of the laser radiation varies greatly with the copper material depending on the condition of the surface
A defined diameter of the welding zone must be ensured. A sufficient welding depth must be ensured
The welding process should be monitored to ensure reproducibility and avoid errors

Process technology

In order to achieve a high and reproducible welding depth, not only a high pulse power but also a defined pulse duration is required. The fiber laser used has been designed for this purpose.

Despite these possibilities, the unfavorable absorption behavior of copper materials leads to unacceptable fluctuations in the welding depth. By varying the pulse power over the pulse duration, so-called plus shaping, a consistently high welding depth can also be achieved with copper.

The monitoring systems used for macro-welding cannot be used for micro-welding, so there is no real-time monitoring. An infrared camera allows important conclusions to be drawn about the welding process and quality. The local temperature profile and the temperature curve during cooling must be evaluated after welding.

Both spot and path welding are possible with the developed welding tool.

Modern fiber lasers with high beam quality and pulse energy are particularly suitable for this. We also offer solutions for contour welding on miniaturized components.

Whether laser marking or laser welding, demonstrations and tests for all laser processes can be carried out in the Wolf Technology Center.