ABSTRACT: The laser-engineered net shaping (LENS) process is a laser-assisted, direct metal manufacturing process under development at Sandia National Laboratories. The process incorporates features from stereolithography and laser surfacing, using computer-aided design file cross sections to control the forming process. Powder-metal particles (less than 150 µm) are delivered in a gas stream into the focus of a Nd:yttrium-aluminum-garnet laser to form a molten pool. The part is then driven on an x/y stage to generate a three-dimensional part by layer-wise, additive processing. In an effort to understand the thermal behavior of the LENS process, in-situ high-speed thermal imaging has been coupled with microstructural analysis and finite-element modeling. Cooling of the melt is accomplished primarily by conduction of heat through the part and substrate, and depending on the substrate temperature and laser-input energy, cooling rates can be varied from 102 K s–1 to 103 K s–1. This flexibility allows control of the microstructure and properties in the part. The experiments reported herein were conducted on 316 stainless steel, using two different particle-size distributions with two different average particle sizes. Thermal images of the molten pool were analyzed to determine temperature gradients and cooling rates in the vicinity of the molten pool, and this information was correlated to the microstructure and properties of the part. Some preliminary finite-element modeling of the LENS process is also presented.

Read Article

SOURCE: Hofmeister, W., M. Wert, J. Smugeresky, J. A. Philliber, M. Griffith and M. Ensz. “Investigating Solidification with the Laser-Engineered Net Shaping (LENSTM) Process”. TMS. July 1999.