Signal analysis of voltage noise in welding arcs

Gas tungsten arc welds were made on low alloy steel plates to which intentional defects (discontinuities) were imposed. Disruption of shielding gas, welding over surface films, and tack welds produce changes in what is otherwise a relatively uniform voltage signal. The arc voltage was 15 volts + or - 2 volts with 300 mV ripple noise from the power supply. Changes in this steady noise voltage varied from 50 mV to less than one millivolt depending on the severity and the type of change experienced. In some instances the changes were easily detected by analysis of the signal in real time, while in other cases the signal had to transformed to the frequency domain in order to detect the changes. Discontinuities as small as 1.5 mm in length were detected. The ultimate sensitivity and reproducibility of the technique is still being investigated

Transient Liquid-Phase Bonding Using Coated Metal Powders Ni-20Cr and 304L stainless steel powders coated with a melting point depressant, Ni-10P, were used as the interlayers to produce large root opening 304 stainless steel joints

ABSTRACT. Powder particles coated with a small amount of melting point depressant (MPD) reveal different sintering behavior in comparison to an uncoated powder mixture of the same composition. Interlayers consisting of the coated powder particles were used in the transient liquid-phase (TLP) bonding process. The coating material and the thickness of the deposit are important parameters that influence shrinkage. The amount of MPD was controlled such that the volume fraction of the liquid was very small but existed at all contacts, thus improving densification of the interlayer. Ni-20Cr and 304L stainless steel powders coated with Ni-10P were applied to join 304 stainless steels. Fully dense joints with mechanical properties comparable to those of the base metals were obtained with Ni-20Cr powder interlayers, whereas joints with 304L stainless steel powder interlayers showed inferior mechanical properties due to residual porosity in the joints

Penetration and Defect Formation in High-Current Arc Welding At high currents, the weld pool turns into a thin liquid film, causing humping, undercutting, and fingerlike penetration

ABSTRACT. An explanation for penetration and defect generation in the weld pool at high currents is proposed. In this regime, the arc pressure pushes the molten metal to the rear of the weld pool, creating a thin layer of liquid metal under the arc. Premature solidification of this thin layer initiates humping, split bead, parallel humping, tunnel porosity, and undercutting. The thin nature of the liquid layer is the cause of increased penetration at high currents. We propose a simple model to predict the onset and type of humping defect

Penetration and Defect Formation in High Current Arc Welding: Final Report

The work performed during the three previous years can be roughly divided into two main categories: (1) development of advanced modeling techniques; and (2) modeling of arc welding process. The work in the first category comprised the development of the Order of Magnitude Scaling (OMS) technique, which is complementary to numerical modeling techniques such as finite elements, but it provides approximate formulas instead of just numerical results. Borrowing concepts from OMS, another modeling technique based on empirical data was also developed. During this stage special software was also developed. The second category comprised the application of OMS to the three main subsystems of arc welding: the weld pool, the arc, and the electrode. For each of these subsystems they found scaling laws and regimes. With this knowledge, they analyzed the generation of weld pool defects during high current arc welding, proposed a mechanistic description of the process, and possible solutions