Investigation of solidification cracking susceptibility during laser beam welding using an in-situ observation technique

Abstract

In recent years, laser beam welding has found wide applications in many industrial fields. Solidification cracks are one of the most frequently encountered welding defects that hinder obtaining a safe weld joint. Decades of research have shown that one of the main causes of such cracks are the strain and the strain rate. Obtaining meaningful measurements of these strains has always been a major challenge for scientists, because of the specific environment of the measurement range and the many obstacles, as well as the high temperature and the plasma plume. In this study, a special experimental setup with a high-speed camera was employed to measure the strain during the welding process. The hot cracking susceptibility was investigated for 1.4301 stainless steel, and the critical strain required for solidification crack formation was locally and globally determined.

Solidification Crack Evolution in High-Strength Steel Welding Using the Extended Finite Element Method

“…Similar observations can be found in[30]. Bigger initial current cracks and more concentrated weakening of cross-sectional current areas result in higher susceptibility of the current section to solidification cracking, as reported in[39,40].…”

Finite element analysis of in-situ distortion and bulging for an arbitrarily curved additive manufacturing directed energy deposition geometry

“…10 additional layers were deposited on top, while measuring in-situ displacements with the commercial 3D-Digital Image Correlation system GOM Aramis 4m at 5 Hz image acquisition frequency and 1 ms exposure time (Figure 1c). As described by Bakir [17] in investigations of hot-cracking and Agarwal [18] for laser welding in-situ measurements, overexposure of the sensors due to the bright process light could be avoided by using narrow bandpass optical filters, transmitting only wavelengths in the range of 810 nm ± 22.5 nm. To generate enough background light for the optical measurement, a defocused, monochromatic laser illuminated the sample with 808 nm light.…”

“…In a recent publication by Biegler et al [16], a new measurement method was established to determine in-situ distortions directly on a DED wall sample during build-up. 3D-Digital Image Correlation (DIC) was utilized, extending previous works by Bakir et al [17] for in-situ crack observation and by Agarwal et al [18] for in-situ strain investigation during laser welding onto additive manufacturing DED. During deposition, the DIC system takes pictures of a stochastic speckle pattern on the sample and tracks changes in the pattern resulting from straining and distortion of the underlying sample from two angles [19].…”

In Situ Monitoring of Additive Manufacturing Using Digital Image Correlation: A Review

“…In order to have sufficient light for the optical measurements, an 808 nm defocused monochromatic laser beam from a DILAS compact diode laser was used. This DIC-based set-up was also used by the research group in other studies [ 74 , 75 , 82 ]. Xie et al [ 76 , 78 ] successfully obtained full-field strain measurements on a manufactured thin-wall during the LENS AM process using 2D DIC.…”