Spot welding

About: Spot welding is a research topic. Over the lifetime, 12491 publications have been published within this topic receiving 89845 citations. The topic is also known as: Spot_welding.

New technology for measuring dynamic resistance and estimating strength in resistance spot welding

Abstract: Because welded structures such as automotive bodies have become smaller and lighter, a strong emphasis is being placed on the quality of the welds. Over the years many quality estimation systems have been developed by several researchers in order to ensure that welds are of high quality. The dynamic resistance signal, which is closely related to the nugget formation of the weld, has been used very effectively for this purpose, together with the electrode displacement signal. However, in previous research, the dynamic resistance was calculated using process parameters that were measured in the secondary circuit of the welding machine, causing many in-process problems. In this study, the process variables, which were monitored in the primary circuit of the welding machine, are used to obtain the variation of the dynamic resistance across electrodes. This allows the dynamic resistance monitoring system to be applied to the in-process system without any extra monitoring devices in the secondary circuit. Also, in order to test the reliability of such a system, an artificial intelligence algorithm to estimate the weld quality using the primary dynamic resistance is proposed.

The effect of surface roughness, oxide film thickness and interfacial sliding on the electrical contact resistance of aluminium.

Abstract: Contact resistance measurements were made on aluminium alloy sheet with a configuration relevant to electrical resistance spot welding. Previous work has shown that a small amount of sliding is required at the interface to break down contact resistance when the material has a thin, insulating coating. Sliding on a macroscopic scale occurs at the electrode-sheet interface but not at the faying surface. For this reason, the contact resistance at the faying surface is high and its behaviour with applied force is observed to be anomalous. However, local sliding on a microscopic scale can occur at the faying surface, depending on the surface roughness. The effect of surface roughness and oxide film thickness was investigated in the present work. In addition, the degree of sliding required to break down contact resistance was quantified in experiments in which relative rotation was induced at the faying surface. It is estimated that a sliding displacement of only about 10 μm is required to produce a dramatic reduction in contact resistance. The results are interpreted in terms of Holm's constriction resistance theory of microscopic spots of metal-to-metal contact within a mechanical contact area largely insulated by the presence of the surface oxide films.

Melt pool dynamics during laser welding

Abstract: The dynamics of the melt pool and keyhole was investigated during CO2 laser welding using high-speed video photography and the laser reflectometer technique. A low-power argon laser beam, focused on the weld pool, provided illumination to obtain a direct image of the weld pool surface. The near-surface plasma emission background was decreased by using a narrow-bandwidth interference filter centred at the argon laser wavelength (514 nm). A variation in the shape of the keyhole opening with a characteristic frequency higher than 1 kHz was observed both during spot welding and during welding with a moving beam. For the case of spot welding with a 20 ms laser pulse, long-wavelength (about 1 mm) oscillations of the weld pool were observed with a frequency during the laser pulse and the first 5 ms after the laser pulse in the range 200-500 Hz. In the time interval starting at 25 ms and ending at approximately 40 ms from the beginning of the laser pulse, the long-wave oscillation frequency increased up to 1.3 kHz. The solidification time was determined to be approximately equal to the pulse duration for the spot welding. Surface deformation during cooling was also observed. This information is used to develop a model illustrating the dynamics of the post-pulse weld pool.

Coating material for protecting metals, especially steel, from corrosion and/or scaling, method for coating metals and metal element

Abstract: It was surprisingly found that when a suitable binder including a suitable filler is used during the high temperature treatment of a curing process, the coating materials of the invention change in such a manner that electrically conducting reactive layers are formed that allow welding and especially spot welding together with the metal substrate even after treatment at temperatures of more than 800 °C.