No abstract

Laser-engineered net shaping (LENS) is a rapid direct manufacturing process. The LENS process can be analyzed as a sequence of discrete events, given that it is a layer-by-layer process. The thermal history associated with the LENS process involves numerous reheating cycles. In this article, the thermal behavior during laser deposition with LENS is simulated numerically by using the alternate-direction explicit (ADE) finite difference method (FDM). The simulation results showed that deposited material experiences a significant rapid quenching effect during the initial stages of deposition and can attain a very high cooling rate. With an increase in deposit thickness, the rapid quenching effect decreases and eventually disappears. The effects of the processing parameters on the thermal behavior of deposited materials were also simulated and analyzed. The objective of this study is to provide insight into the thermal history during the LENS process, where the ability to correlate process parameters to microstructural evolution is a motivating force.

The thermal behavior during laser-engineered net shaping (LENS) processing was numerically simulated using the alternate direction explicit finite difference method in Part I of this work. In this article, Part II, the numerical simulation results were compared to experimental results obtained with LENS-deposited 316L stainless steel. In particular, the cooling rate that is present during LENS deposition was established on the basis of dendrite arm spacing (DAS) measurements with and without a melt pool sensor (MPS) and a Z-height control (ZHC) subsystem. The microstructure of the deposited materials was characterized and analyzed, and the corresponding microhardness was measured as a function of distance from the substrate. The influence of thermal history on microstructure evolution was analyzed and discussed based on both modeling and experimental results. The results discussed in this article suggest relatively good agreement between experiments and modeling.

Laser Engineered Net Shaping (LENS) is a novel manufacturing process for fabricating metaI parts directly from Computer Aided Design (CAD) solid models. The process is similar to rapid prototyping technologies in its approach to fabricate a solid component by layer additive methods. However, the LENS technology is unique in that fully dense metal components with material properties that are similar to that of wrought materials can be fabricated. The LENS process has the potential to dramatically reduce the time and cost required realizing functional metal parts. In addition, the process can fabricate complex internal features not possible using existing manufacturing processes. The real promise of the technology is the potential to manipulate the material fabrication and properties through precision deposition of the material, which includes thermal behavior control, layered or graded deposition of multi-materials, and process parameter selection.

For many years, Sandia National Laboratories has been involved in the development and application of rapid prototyping and direct fabrication technologies to build prototype parts and patterns for investment casting. Sandia is currently developing a process called Laser Engineered Net Shaping (L,ENS.M> to fabricate hlly dense metal parts directly fkom computer-aided design (CAD) solid models. The process is similar to traditional laser-initiated rapid prototyping technologies such as stereolithography and selective laser sintering in that layer additive techniques are used to fabricate physical parts directly from CAD data. By using the coordinated delivery of metal particles into a focused laser beam, a part is generated. The laser beam creates a molten pool of metal on asubstrate into which powder is injected. Concurrently, the substrate on which the deposition is occurring is moved under the beadpowder interaction zone to fabricate the desired cross-sectignal geometry. Consecutive layers are additively deposited, thereby producing a three-dimensional part. This process exhibits enormous potential to revolutionize the way in which metal parts, such as complex prototypes, tooling, and small-lot production parts, are produced. The result is a complex, fblly dense, near-net-shape part. Parts have been fabricated fiom 316 stainless steel, nickel-based alloys, H13 tool steel, and titanium. This talk will provide a general overview of the LENSTM process, discuss potential applications, and display as-processed examples of parts. Background Sandia National Laboratories is a multi-program laboratory operated by the Lockheed Martin Corporation for the U.S. Department of Energy. As an engineering laboratory responsible for the design and. manufacture of a variety of prototype electrical and electromechanical devices, a need continually exists for producing complex parts in a timely and more efficient manner. Over the years, Sandia's manufacturing processes have evolved fiom labor-intensive, manually operated machine tools to computer-aided machining centers and wire-feed electrical discharge machines. Despite advances in computer numerically controlled (CNC) machining, many components at Sandia still required extensive, time-consuming fabrication and assembly. Sandia is not alone in *This work was supported by the United States Department of Energy under contract DE-ACO4-94AL85000 DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the