Abstract
The formation of defects such as pores during deep-penetration laser welding processes is governed by the melt pool dynamics and the stability of the vapor capillary, also referred to as the keyhole. In order to gain an insight into the dynamics of the keyhole, the temperature in the transition region from the liquid to the gaseous phase, i.e., near the keyhole wall, is a physical value of fundamental importance. In this paper, a novel method is presented for directly measuring temperatures in the close vicinity of the keyhole front wall during deep-penetration laser welding. The weld samples consist of pure aluminum with a boiling point of 2743 K. The measurement is performed using high-speed pyrometry with a refractory tantalum probe capable of detecting temperatures that significantly exceed the boiling point of the sample material. Temperature curves are recorded from the beginning of the welding process until the moment the probe is finally destroyed through direct laser-tantalum interaction. With an effective spatial resolution up to 0.3 µm in the welding direction, a detailed investigation into the temperature ranging from the prerunning melt pool front to the keyhole center is possible, exhibiting temperatures of up to 3300 K in the vicinity of the keyhole front wall.
Highlights
Deep-penetration laser welding is a well-established yet still promising joining technology with a broad field of applications in the automotive, aerospace, and many other industries of great economic significance
The welding velocity was chosen to lie within the range of the Rosenthal regime so that the vapor capillary was expected to have circular cross-sections perpendicular to the laser beam axis with a homogeneous temperature distribution along its contour
This study presented an experimental setup that enables high-speed temperature measurements within the prerunning melt pool in the vicinity of the keyhole during deep-penetration laser welding
Summary
Deep-penetration laser welding is a well-established yet still promising joining technology with a broad field of applications in the automotive, aerospace, and many other industries of great economic significance. Allowing for high-aspect ratios, it has proven to be an ideal method for generating deep and narrow weld seams at comparatively low energy inputs [1]. High welding velocities and low thermal distortion of the joined parts qualify this technology for applications in manufacturing processes, e.g., for automated welding tasks or complex welding contours [2]. Thereby, a long and narrow vapor capillary, referred to as a keyhole, is formed in which the laser beam can propagate through multiple reflections so that the energy is absorbed along the complete depth of the capillary [4]. The keyhole diameter is approximately one to one and a half times the size of the beam diameter at the material surface [5] and is filled with metal vapor and shielding gas
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