With the increasing usage of Al alloys in vehicle manufacture, it is necessary to join dissimilar Al alloys with lap joint. However, hot cracking is a challenging issue due to the chemical composition and thermal tension, which greatly determines the reliability of automobile operation. Among different Al alloys, the series 5000 (Al–Mg) and 6000 (Al–Mg–Si) are widely used. To better understand the hot cracking behavior, various stack ups of AA5754 and AA6013 were laser welded to investigate the effects of process parameters on hot cracking formation. The chemical composition, microstructure, fusion ratio, and fracture morphology of the weld joint were also examined. The results showed that the order of material stacking affected weld's susceptibility to hot cracking significantly, and the critical process parameters were obtained for tested conditions which could effectively reduce hot cracking. The findings from this work provide guidance for hot cracking prevention in laser welding of dissimilar Al alloys.

This study was to analyze the microstructure, microhardness, tensile and fatigue performance of the welded joints performed by a fiber laser on 22MnB5 and dual-phase steels (DP590, DP980) in similar and dissimilar combinations. The result shows that the weld zone (WZ) basically consisted of lath martensite. The HAZ in these steels can be divided into 3 parts: quenched, incomplete quenched, and tempered region. The WZ had the highest hardness, and a soft zone existed in the HAZ of all steels. Inside the WZ of the dissimilar welded joints, two hardness subregions were observed due to the difference in the alloying elements of these steels. Tensile specimens of the 22MnB5–22MnB5 and 22MnB5–DP980 welded joints were all broken in HAZ, while the 22MnB5–DP590 welded joints failed in the DP590 base metal (BM). The BM had a higher fatigue life than the welded joints, and the fatigue failure of the 22MnB5 similar and 22MnB5–DP980 dissimilar welded joints respectively occurred in the HAZ and DP980 BM. The fatigue fracture contained 3 parts: crack initiation, crack propagation, and the final fast fracture region.

For a better understanding of the physical phenomena associated with the appearance of defects in laser welding, a heat and fluid flow model is developed using Comsol Multiphysics®. This first step of the project is focused on the modeling of a static laser shot on a sample of steel. This 2D axially-symmetric configuration is used to study the main physical phenomena related to the creation of the keyhole. This model takes into account the three phases of the matter: the vaporized metal, the liquid phase and the solid base. To track the evolution of these three phases, coupled equations of energy and momentum are solved. The liquid/vapor interface is tracked using the Level-Set method. The calculated velocity and free surface deformation are analyzed. Melt pool shapes are compared with experimental macrographs and the influence of some parameters such as laser power is discussed.

The assembly of plastic microfluidic devices, MOEMS and microarrays requiring high positioning and welding accuracy in the micrometer range, has been successfully achieved using a new technology based on laser transmission welding combined with a photolithographic mask technique. This paper reviews a laser assembly platform for the joining of microfluidic plastic parts with its main related process characteristics and its potential for low-cost and high volume manufacturing. The system consists of a of diode laser with a mask and an automated alignment function to generate micro welding seams with freely definable geometries. A fully automated mask alignment system with a resolution of < 2 μm and a precise, non-contact energy input allows a fast welding of micro structured plastic parts with high reproducibility and excellent welding quality.

Robotic laser welding places extreme demands on the spatial accuracy with which the robot must position the focal point of the laser with respect to the joint to be welded. The required level of accuracy is difficult to achieve in a production environment without the use of end-point sensor based control of the robot. This requires that the end-point sensor frame and welding laser frame be accurately calibrated with respect to each other, as well as with respect to the robot wrist frame. This calibration can be difficult to perform since the sensor and laser frames are virtual in the sense that these are located in space with respect to the physical hardware, and the wrist frame of the robot is often not physically accessible. This paper presents the design of a calibration system with which these frames may be precisely defined with respect to each other.