Laser welding of copper is gaining more and more importance to create electrical contacts due to the high temperature resistance and high achievable mechanical loads. However, laser welding of copper in the past was always associated with low process stability. By using high brightness fiber laser sources, small laser spots can be generated which allows keyhole-based deep penetration welding even in copper with high quality. Unfortunately, a small spot size and keyhole welding lead to a small connection area between the two joining partners. To avoid this, spatial power modulation - a linear feed with superposed circular motion - has been introduced. By using an additional parameter, oscillation frequency, and amplitude, in conjunction with spatial power modulation, we can increase not only the connection area but also the stability of the laser welding process and quality characteristics of the welds. In addition to the conformity of the weld depth, the surface roughne ss of the weld is a measure of the quality. Especially in interconnection of lithium ion cells and high power electronics, the consistency of the weld depth influences the connection area, which is essential for the current-carrying capacity. The quantity of weld defects and irregularities has a direct impact on the surface roughness of the weld. This paper presents recent results on the influence of the spatial power modulation on quality characteristics during laser microwelding by analyzing the weld via three-dimensional longitudinal cross sections and via laser measuring of the weld surface. Experimental investigations are supplemented by finite element simulations which enable a detailed analysis of the influence of the laser scanning strategy on the geometry of the fusion zone

Laser transmission welding has become an established joining technique in series production of plastic components. Besides its unique process related properties, it also offers several monitoring methods to ensure a constant welding result. In most cases, pyrometry is the method of choice which contactless detects the heat emitted from the interface of the joining partners. Considering the transmission properties of polymers and the optical components between the workpiece and pyrometer, only a small fraction of the thermal process emission is able to penetrate to the detector of the pyrometer. Typically, in classic laser transmission welding, the thermal emission is measured in the spectral range 1.1–2.5 μm limited by the laser wavelength on the one side and the absorption capability of polymers/optical elements in the optical path on the other side. In absorber-free laser transmission welding, laser sources in the range of 1.6–2 μm are used in order to exploit the intrinsic absorption of thermoplastics. With the laser emitting in the sensitivity range of the pyrometer, optical filters have to be used to isolate the thermal radiation from the laser radiation which, however, attenuates the already weak thermal signature even further. An approach that does not require any optical filters is presented in this paper. The concept is operating the laser in a pulsed mode which enables detection of thermal emissions between two consecutive pulses without being overlaid by the laser radiation. Though laser radiation is not delivered continuously, the result demonstrates that it is still possible to obtain a nearly homogeneous seam when choosing an appropriate pulse regime. It is also shown how the detected signal can be utilized to adjust the focal position, which is an important but time-consuming aspect in absorber-free laser welding.

In this work, high-speed thermography is shown to effectively capture quasi-stationary temperature fields during the laser welding of steel plates. This capability is demonstrated for two cases, with one involving the addition of a ferritic-bainitic filler wire, and the other involving the addition of a low-transformation-temperature (LTT) filler wire. The same welding parameters are used in each case, but the temperature fields differ, with the spacing between isotherms being greater in the case where the low-transformation-temperature filler material is added. This observation is consistent with the differences in the extent of the heat-affected zone in each sample, and the shape of the weld pool ripples on the weld bead surfaces. The characterization of temperature fields in this way can greatly assist in the development of novel methods for reducing residual stresses, such as the application of low-transformation-temperature filler materials through partial-metallurgical injection (PMI). This technique reduces or eliminates tensile residual stresses by controlling the temperature fields so that phase transformations take place at the optimum times, and success can only be guaranteed through precise knowledge of the temperature fields in the vicinity of the welding heat source in real time.Keywords: Cooling rate / heat-affected zone (HAZ) / phase transformation / residual stress / temperature measurement / welding thermal cycle In dieser Arbeit wird Hochgeschwindigkeits-Thermographie zur effektiven Dokumentation quasi-stationä rer Temperaturfelder wä hrend des Laserstrahlschweißens von Stahl vorgestellt. Gezeigt wird dies am Beispiel von zwei reprä sentativen Schweißungen, wobei einerseits ein ferritsch-bainitischer Zusatzdraht und andererseits ein Low-Transformation-Temperature-(LTT) Zusatzdraht verwendet wird. In beiden Fä llen werden die gleichen Schweißparameter verwendet. Im Vergleich wird eine merkliche Abweichung der Temperaturfelder deutlich. Bei Low-Transformation-Temperature-Zusatzdraht vergrö ßern sich die Abstä nde zwischen den Iso-Corresponding author: S. Gach, Welding and Joining Institute (

The effect of spatial power modulation (SPM)—also known as wobble—for the welding of aluminum alloys has been investigated in laser beam microwelding. As the superposition of a high frequency circular oscillation movement and a global feed, two new parameters (A—amplitude and f—frequency) are added to the typical process parameters P—power and vw—welding feed rate. Microscopic and metallographic analyses have been used to determine crack appearance and position. With the choice of a sufficient ratio of A, f, and vw, the cooling behavior can be influenced. This also has an impact on the crack formation. Furthermore, the circular movement influences the local speed of the laser beam which in turn can affect the pore formation. The same effect appears on the depth stability as the keyhole formation strongly depends on the speed of the laser beam. The pore formation and weld depth stability have also been analyzed to determine the difference between conventional welding and welding with SPM.

A large-chamber scanning electron microscope (LC-SEM) provides an ideal platform for the installation of large-scale in situ experiments. Our LC-SEM has internal chamber dimensions of 1,2 × 1,3 × 1,4 m (W × H × D) (Fig.1) and makes it possible to incorporate novel in situ experimental devices, which are reported on here. The present manuscript describes in detail the development of in situ test equipment for the study of a broad range of processes in production engineering. Direct observation of the materials modification mechanisms provides fundamental insight into the underlying process characteristics. An in situ turning device was developed, tested and used to observe the chip formation on the microstructure scale of a 43CrMo4-sample. Laser beam micro welding was integrated into the LC-SEM to achieve in situ analysis of the welding process on stainless steel 1.4310. A heating module was employed for in situ wetting experiments to observe the formation and solidification of the melt of a tin-copper brazing filler on an aluminium cast alloy.