The fatigue properties of welded components can be improved by means of post-weld treatments, like TIG dressing or hammering. This article describes the results obtained in the research project “DURIMPROVE”, in which the effects of post-weld treatments on welds in high strength steel were investigated.
Due to the growing environmental concern and the increasing demand for more ecological methods of transportation, composite materials that combine low weight and high resistance have raised the interest of several industrial sectors. Among these materials, the metal-plastic composites (MPCs) can be highlighted, who combine a low weight and a relatively high mechanical resistance. Such materials are used in advertising signs, building panels, motor shielding, etc. Mechanical joining of MPC materials is to be avoided when protrusions are not allowed or because of aesthetical reasons. Welding is therefore considered as an interesting alternative. However, qualitative joining using welding of the MPC materials to other MPC materials or to metallic plates is a real challenge. Due to their special features (layer structure, material mix, etc.), conventional manufacturing processes are therefore only of limited or no use at all. In particular, the polymer core layer is a barrier for the use of conventional joining methods. This contribution presents a novel joining approach for MPCs. The basic approach is the local melting of the polymer layer by ultrasonic waves and displacement of the molten plastic material by pressure on the cover sheets. This work proposes the investigation of the use of non-conventional solid-state welding processes, such as ultrasonic welding (USW) and refill friction stir spot welding (RFSSW), for joining MPCs with aluminium sheets. Prior to the application of the joining processes, the intermediate plastic core of the MPC materials is displaced using ultrasonic vibrations, so that the materials can be joined as monolithical materials. These joining concepts are validated experimentally. The obtained weld quality is assessed based on destructive and non-destructive testing methods.
Metal–plastic composites (MPCs) are gaining importance mainly due to high strength to weight ratio. They consist of three layers, two outer metallic cover sheets, and a plastic core. The presence of that inner plastic layer makes them rather unsuitable for joining by means of any conventional welding processes, which significantly reduces the application range of MPC. In this work, three various resistance spot welding (RSW)-based concepts were developed to overcome that limitation and join Litecor to DP600 steel. In all cases, a dedicated initial stage was implemented to RSW, which was aimed at removing the non-conductive polymer layer from the welding zone and creating the proper electrical contact for the resistance welding. These were, namely: (i) shunt current-assisted RSW; (ii) induction heating-assisted RSW; and (iii) ultrasonic-assisted RSW. The development of each concept was supported by finite element modeling, which was focused on setting the proper process parameters for polymer layer removal. Finally, the macro- and microstructure of exemplary RSW joints are shown and the most common spot weld features as well as the further development possibilities are discussed.
There are several reasons why automation of welding production is gaining more and more importance. For example, skilled welders are nowadays scarce. Besides that, the weld quality obtained when using automatic welding processes has shown to significantly reduce the need for rework.
The present publication proposes an empirical evaluation of real-time quality monitoring of MIG/MAG welding of dissimilar high strength steels DP800 and DP1000 in T-joints based on the measurement of the processes parameters. A new strategy is proposed to evaluate the quality of the welds of HSS materials using the ISO 5817 standard. From the obtained results, a correlation between the process parameters and the quality of the weld was established. An operational comparison between cobot and manual welding was performed based on their repeatability. The results confirm the higher repeatability of the mechanised cobot process and the feasibility of using process parameters as an in-situ NDT technique for production control.
Driven by the demand for increased manufacturing efficiency of engineering structures, WAAM which is also known as directed energy deposition-arc (DED-arc), can basically be seen as the integration of an “additive” principle in the wire-arc welding process.