Mark T. Ensz

Laser engineered net shaping (LENS™): A tool for direct fabrication of metal parts

For many years, Sandia National Laboratories has been involved in the development and application of rapid prototyping and dmect fabrication technologies to build prototype parts and patterns for investment casting. Sandia is currently developing a process called Laser Engineered Net Shaping (LENS~) to fabricate filly dense metal parts dwectly from 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 apart is generated. The laser beam creates a molten pool of metal on a substrate into which powder is injected. Concurrently, the substrate on which the deposition is occurring is moved under the beam/powder interaction zone to fabricate the desired cross-sectiwal geometry. Consecutive layers are additively deposited, thereby producing a three-dmensional 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 comple~ filly dense, near-net-shape part. Parts have been fabricated from 316 stainless steel, nickel-based alloys, H13 tool steel, and titanium. This talk will provide a general overview of the LENS~ process, discuss potential applications, and display as-processed examples of parts.

Object reconstruction from layered data using implicit solid modeling

Abstract This paper presents an automated technique for constructing 3-D implicit solids from moderately to very dense cross-sectional (layered) data sets. A collection of 2-D cross sections is generated from the layered data by merging circular primitives using implicit solid modeling (ISM) techniques. The geometry of the circles comprising each layer is determined through a nonlinear optimization process using a cost function that measures discrepancies in the distance from data points to the boundary of the reconstructed cross section. The starting configuration of the optimization (that is, the initial size and location of the primitives) is developed from information provided by a 2-D Delaunay triangulation of each layer of the data set. After optimization, the individual 2-D cross sections are joined into a 3-D solid by performing a blend, or “morph,” between the separate layers. By utilizing weighted information from multiple layers, local curvature information is included in the blend object, resulting in a smooth transition between cross sections. The effectiveness of the algorithm is demonstrated through the reconstruction of several representative examples.

Implicit Methods for Geometry Creation

In this paper, we briefly review the existing direct implicit geometry generation methods, which include creation of blending surfaces, a limited family of sweeps, and reconstruction of solid geometry from a sample set of surface data points. A broader approach is presented, utilizing the properties of the graph of the implicit defining function, to systematically construct swept solids and perform morphing between sections by implicit methods.

Femtosecond laser machining of steel.

Femtosecond laser processing is a promising new technology for the fabrication of micro-scale components from engineering materials, such as metals. In the femtosecond time regime, the ablation process is nearly a solid to vapor transition, thereby providing access to cut smaller features. Sandia National Laboratories has constructed a femtosecond laser microfabrication system to study the ability to produce microscale components in metals and glasses. In this paper, we will report on our initial studies to understand the metal ablation process with respect to manufacturing process parameters. With this understanding, we will show that femtosecond laser processing can fabricate complex components with fine feature detail and clean surfaces. A key finding in this work is the substantial effect of layer decrement on resulting recast material deposition when processing in air.

Algebraic computer aided-design with Maple V2

This paper describes implicit_solids which implements implicit solid modeling (ISM) using MapleV2. Implicit solid modeling refers to the method that uses an implicit function to define a composite object. Various primitives are pre-defined and joined using Boolean operations to form the resulting implicit function [Storti et al. 1992].

Materials Issues for Micromachines Development - ASCI Program Plan

This report summarizes materials issues associated with advanced micromachines development at Sandia. The intent of this report is to provide a perspective on the scope of the issues and suggest future technical directions, with a focus on computational materials science. Materials issues in surface micromachining (SMM), Lithographic-Galvanoformung-Abformung (LIGA: lithography, electrodeposition, and molding), and meso-machining technologies were identified. Each individual issue was assessed in four categories: degree of basic understanding; amount of existing experimental data capability of existing models; and, based on the perspective of component developers, the importance of the issue to be resolved. Three broad requirements for micromachines emerged from this process. They are: (1) tribological behavior, including stiction, friction, wear, and the use of surface treatments to control these, (2) mechanical behavior at microscale, including elasticity, plasticity, and the effect of microstructural features on mechanical strength, and (3) degradation of tribological and mechanical properties in normal (including aging), abnormal and hostile environments. Resolving all the identified critical issues requires a significant cooperative and complementary effort between computational and experimental programs. The breadth of this work is greater than any single program is likely to support. This report should serve as a guide to plan micromachines development at Sandia.

Laser Wire Deposition (WireFeed) for Fully Dense Shapes LDRD

Direct metal deposition technologies produce complex, near net shape components from Computer Aided Design (CAD) solid models. Most of these techniques fabricate a component by melting powder in a laser weld pool, rastering the weld bead to form a layer, and additively constructing subsequent layers. This report will describe anew direct metal deposition process, known as WireFeed, whereby a small diameter wire is used instead of powder as the feed material to fabricate components. Currently, parts are being fabricated from stainless steel alloys. Microscopy studies show the WireFeed parts to be filly dense with fine microstructural features. Mechanical tests show stainless steel parts to have high strength values with retained ductility. A model was developed to simulate the microstructural evolution and coarsening during the WireFeed process. Simulations demonstrate the importance of knowing the temperature distribution during fabrication of a WireFeed part. The temperature distribution influences microstructural evolution and, therefore, must be controlled to tailor the microstructure for optimal performance.