Laser Beam Brazing Research Articles

Laser beam brazing of aluminum alloys in XHV-adequate atmosphere with surface deoxidation by ns-pulsed laser radiation

Laser beam brazing is an established manufacturing process due to its low heat input and esthetically appealing seams. However, brazing of materials with high oxygen affinity, such as aluminum alloys, requires the removal of surface oxides prior to the brazing process, commonly through the application of chemical fluxes that may be harmful to the environment and to health. The approach presented here dispenses with the use of fluxes and involves oxide layer removal by means of ns-pulsed laser radiation within an atmosphere that is adequate to an extreme high vacuum (XHV) in regard to the oxygen content. By doping the process gas with monosilane (SiH4), an oxygen content equivalent to an extreme high vacuum with an oxygen partial pressure below 10−20 mbar is realized. Hence, a subsequent reoxidation is actively prevented so that wetting of the base material by the filler material and consequent diffusion processes are enabled. The wetting angle between filler material and material is used to evaluate the effectiveness of laser-based deoxidation under an XHV-adequate atmosphere.

Influence of an oxygen-free atmosphere on laser beam brazing of aluminium with prior surface deoxidation by pulsed laser radiation

Aluminium alloys, like AlMgSi1 and AlMg3, cannot be joined in industrial processes by laser beam brazing without the use of fluxes due to their resistant oxide layer. The aim of this study is to dispense with the use of flux. For the investigations, an oxygen-free atmosphere was created by using the highly reactive gas monosilane and thus achieving O2 partial pressures of 10−18 mbar. After removal of the oxides by a laser source with 1064 nm wavelength, pulse energies of max. 0.3 µJ and pulse durations of 45 ns, reoxidation is prevented by the oxygen-free atmosphere, so that brazing is carried out on an oxide-free material surface. The bead on plate seams show a materially bonded brazed joint in cross-section. Reference experiments without monosilane either show no wetting or an increased melting of base material. The influence of laser beam power for brazing, pulse energy for deoxidation and wire feed was investigated.

Influence of the brazing speed on the seam characteristics in laser beam brazing of zinc coated steel

In car body manufacturing, the joints in the outer skin exterior shell are especially challenging. They have to fulfill very high surface quality requirements. Laser beam brazing of electrogalvanized steel is a well established process for these joints in the direct view of the customer. However, the quality of the brazed seam is very sensitive to changes in the process parameters or in the environmental conditions. Currently, the process speed is limited due to quality requirements of the brazed seam. In this paper, the authors describe the influence of the brazing speed on the resulting braze seam. By the use of high-speed videography, the authors study the process and analyze the occurring macroscopic effects. The two main effects that can be observed with high-speed videography are surface instabilities and an inhomogeneous movement of the melt pool front. Moreover, the authors could detect a correlation between the movement of the melt pool front and the formation of notches.

Fully Integrated Process Control

AbstractLaser beam brazing and welding are well established joining techniques in the automotive industry; in particular for the body in white production. These processes are mainly used to join two‐piece trunk lids as well as to connect the roof and sidewall with a visible seam or to weld doors in steel or aluminum. Hence, the requirements upon the optical appearance of the brazed seams are very high and quality monitoring is essential. In cooperation of Scansonic MI GmbH and Fraunhofer ILT, a first prototype of a fully integrated on‐line process control system has been developed — SCeye.

Development of low‐melting‐point filler materials for laser beam brazing of aluminum alloys

In order to develop low‐melting‐point filler materials for laser beam brazing of aluminum alloys, Al–Si–Cu based alloys and Al–Si–Zn based alloys were produced via spray forming and associated deformation processes. The selected alloys were spray formed in the form of billet with a diameter around 160 mm and hot extruded into wire rods with a diameter of 8 mm. The extrusions were further cold worked into thin wires with a diameter of 1.2 mm via rotary swaging. Finally, the filler wires were applied in the laser beam brazing of AA6082 structures. It showed that the newly developed filler materials could meet the requirements of the laser beam brazing of aluminum alloys. Particularly, the laser beam brazing process using the spray‐formed filler materials required a significantly lower energy input and allowed for higher brazing speed as compared to the conventional AlSi12 filler material.

Laser Brazing with Beam Scanning: Experimental and Simulative Analysis

Laser beam brazing with copper based filler wire is a widely established technology for joining zinc-coated steel plates in the body-shop. Successful applications are the divided tailgate or the zero-gap joint, which represents the joint between the side panel and the roof-top of the body-in-white. These joints are in direct view to the customer, and therefore have to fulfil highest optical quality requirements. For this reason a stable and efficient laser brazing process is essential. In this paper the current results on quality improvement due to one dimensional laser beam deflections in feed direction are presented. Additionally to the experimental results a transient three-dimensional simulation model for the laser beam brazing process is taken into account. With this model the influence of scanning parameters on filler wire temperature and melt pool characteristics is analyzed. The theoretical predictions are in good accordance with the experimental results. They show that the beam scanning approach is a very promising method to increase process stability and seam quality.

The Role of Zinc Layer During Wetting of Aluminium on Zinc-coated Steel in Laser Brazing and Welding

Abstract The zinc layer of zinc-coated steel is known to be a crucial factor for the spreading of liquid aluminium on the coated surface. For industrial brazing and welding processes these zinc-coatings enable a fluxless joining between aluminium and steel in many cases. Yet, the reason for the beneficial effect of the zinc to the wetting process is not completely understood. Fundamental investigations on the wetting behaviour of single aluminium droplets on different zinc-coated steel surfaces have revealed a distinct difference between coated surfaces at room temperature and at elevated temperature regarding the influence of different coating thicknesses. In this paper the case of continuous laser brazing and welding processes of aluminium and commercial galvanized zinc-coated steel sheets are presented. It is shown that in the case of bead-on-plate laser beam brazing, the coating thickness has a measureable effect on the resulting wetting angle and length but does not have a significant impact in case of overlap laser beam welding. This might be linked to different heat transfer conditions. The results also strongly indicate that proper initialbreakup of oxide layers is still required to accomplish good wetting on zinc-coated surfaces.

Laser Tools in the Manufacturing Process

AbstractAdvanced joining technologies are the key to efficient lightweight design. Of course, this also includes the use of highly advanced laser technologies. Laser beam brazing and remote laser welding represent significant innovations in body manufacturing at Audi. These innovative developments combined with intelligent monitoring systems and process modeling computations are paving the way for comprehensively optimized production. They fulfill the most stringent quality requirements for automotive products.

Influence of the brazing process parameters on the microstructural characteristics of copper alloy jointsPaper Presented at the 4th National Welding Day, Workshop: “Brazing” Genova, 25–26 October 2007.

This paper reports the results of microstructural characterization studies conducted on copper alloy joints obtained by different brazing processes. In particular, tests have been conducted on Cu–Ni–Zn ternary alloys (nickel silvers), traditionally used in the spectacle industry, in order to highlight the merits and any metallurgical and functional defects in samples obtained using two different heat input methods: induction and LASER beam welding. Along with the metallographic analysis of joints made using the traditional induction brazing technique, the joints obtained by LASER brazing have been investigated. In particular, it has been evaluated as to how altering the process parameters pertaining to both the LASER beam (power and impact time) and base metal surface conditions (presence or absence of surface oxides) can significantly influence the formation of macroscopic defects in the joints or on deformation of the components themselves. Hence, the main scope of the paper has been an attempt to identify the optimal process parameters for LASER beam brazing, so that the joints thus obtained have acceptable mechanical properties, while maintaining good aesthetic appearance, a decidedly essential requirement in components for spectacles.