Laser Engineered Net Shaping Research Articles

Optimization of the LENS Rapid Fabrication Process for In-Flight Melting of Feed Powder

A model for in-flight melting of feed-powder particles propelled through a laser beam in the Laser-Engineered Net Shaping (LENS) process has been developed. The model is next incorporated in an optimization analysis to determine optimum LENS process parameters (laser power, particle velocity, and the angle between the laser-beam axis and particle trajectory), which maximize the probability for in-flight particle melting while ensuring the absence of melting of the surface of the substrate. A simple model, based on solution of the thermal energy conservation equation, is also developed to determine the laser-power threshold for melting of the substrate surface. The optimization analysis is then applied to Inconel 625 Ni-Cr-Mo superalloy. The results show that by maximizing the laser power and the residence time of the particles in the laser beam (increases with reductions in particle velocity and particle trajectory angle), the probability for in-flight particle melting can be greatly increased, i.e. relatively coarse (−30/+40 mesh size) particles can be melted by propelling them through the laser beam.

A Process Map for Consistent Build Conditions in the Solid Freeform Fabrication of Thin-Walled Structures

In solid freeform fabrication (SFF) processes involving thermal deposition, thermal control of the process is critical for obtaining consistent build conditions and in limiting residual stress-induced warping of parts. In this research, a nondimensionalized plot (termed a process map) is developed from numerical models of laser-based material deposition of thin-walled structures. This process map quantifies the effects of changes in wall height, laser power, deposition speed and part preheating on melt pool length, which is an essential process parameter to control in order to obtain consistent build conditions. The principal application of this work is to the Laser Engineered Net Shaping (LENS) process under development at Sandia Laboratories; however, the general approach and a subset of the presented results are applicable to any SFF process involving a moving heat source. Procedures are detailed for using the process map to predict melt pool length and predictions are compared against experimentally measured melt pool lengths for stainless steel deposition in the LENS process.

Understanding the Microstructure and Properties of Components Fabricated by Laser Engineered Net Shaping (LENS)

AbstractLaser Engineered Net Shaping (LENS) is a novel manufacturing process for fabricating metal 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 similar to 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.

Characterization of Laser Deposited Niobium and Molybdenum Silicides

AbstractRecent advances in laser deposition technology have made the production of advanced composite materials more technically feasible. By utilizing the unique characteristics of the laser deposition process, materials can be made that are difficult to produce by conventional methods. Structural silicide materials hold promise for high temperature applications, unfortunately, their low toughness has prevented their practical use [1-4]. The introduction of a second phase can greatly increase their low temperature mechanical properties. Laser direct deposition can be used to deposit these materials near net shape and produce an in-situ alloy that has the desired structure for improving properties. In-situ alloying was accomplished by using an Optomec LENS™ (Laser Engineered Net Shaping) machine to deposit elemental niobium-silicon and molybdenum-silicon-boron powder blends. The resultant microstructures showed a homogeneous structure with a primary silicide phase surrounded by a continuous eutectic phase. These deposits were characterized using scanning and transmission electron microscopy, x-ray diffraction, and by energy dispersive spectroscopy.

Taking a Powder

This article focuses on the use of laser in conjunction with metal powder. The use of the laser in conjunction with metal powder could be regarded as an extension of rapid prototyping, which has involved plastic parts almost exclusively. However, terms such as ‘direct metal fabrication’ and ‘rapid manufacturing’ suggest that developers have much more ambitious goals in mind for powder metals. Lockheed Martin Tactical Aircraft Systems in Fort Worth, Texas, is operating a research facility based on the laser engineered net shaping (LENS) process on the same factory floor where the F-16 fighter is assembled for the US Air Force. Optomec Design Co. in Albuquerque builds machines for use with the LENS process. Tests of Sandia National Laboratories' laser engineered net shaping process take place in a tank at Lockheed Martin Tactical Aircraft Systems. Much can be done in direct metal fabrication to improve the thermal conductivity of tooling for injection molding and die casting. The result can be increases in cycle times of as much as 80 percent.

Understanding thermal behavior in the LENS process

In direct laser metal deposition technologies, such as the laser engineered net shaping (LENS) process, it is important to understand and control the thermal behavior during fabrication. With this control, components can be reliably fabricated with desired material properties. This paper will describe the use of contact and imaging techniques to monitor the thermal signature during LENS processing. Development of an understanding of solidification behavior, residual stress, and microstructural evolution with respect to thermal behavior will be discussed.

Characterization of Laser-Deposited TiAl Alloys

ABSTRACTMicrostructure of TiAl produced by Laser Engineered Net Shaping (LENS) has been characterized using optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has been shown that the substrate has a significant effect on the microstructure deposited. Depending on operational parameters, either equiaxed γ-TiAl/α2 -Ti3AI or single phase α 2 microstructure can be obtained. In-situ heating experiments reveal that nucleation of lamellae often starts at grain boundaries in this retained α 2grains. By careful control of post heat treatment, an ultra fine lamellar microstructure may be obtained, which may significantly improve tensile property in these alloys [3].