Melt pool geometry in laser blank rim melting to generate continuous cylindrical preforms

摘要

When scaling the size of a body, size effects can occur. In micro range, the effects of surface tension dominate effects caused by gravitational force. This size effect is used within the laser blank rim melting process wherein the rim of a blank is locally melted by a laser beam. The melt pool forms cylindrical due to surface tension and thus locally increases the thickness of the blank, called cylindrical preform. In this paper process parameters are presented to generate cylindrical preforms with constant diameter at edges of blanks of 1.4301 (AISI 304). By observations with high speed camera and pyrometer it is found that, independent of the desired diameter of the cylindrical preform, the geometry of the melt pool needs to have a length-to-height-ratio of 3.0±0.4 to generate a continuous cylindrical preform. An analytical model is set up and presented supporting this finding. For larger values of the length-to-height-ratio, the melt pool separates and forms droplets while for smaller values formation of preform was not detected.