Selective Laser Sintering of Cu-Pb/Sn Solder Powders

Solid Freeform Fabrication (SFF) as an overall approach in the manufacturing field has been applied to very different areas and on different materials systems including polymers, ceramics, metals and vapor phase. Even though it is clear that polymers have enjoyed a rapid and successful advance in terms of applications, research in the other areas have shown potential applications as well. In this paper, Cu-Sn/Pb solder and Cu-Sn blends have been used as starting material for the Selective Laser Sintering (SLS) manufacture of SFF objects. The general properties of the objects thus produced are presented. In particular, density and microstructural characterizations results are discussed..Mechanical Engineerin

Selective Laser Sintering of Binary Metallic Powder

A selective laser sintering technique has been used to process metal powders and powder blends. Precursor powders include copper, tin, a 70Pb-30Sn solder and their blends. Excessive balling due to surface free energy effects occurred in single layer tests when the laser fluence was sufficient to cause melting of monolithic tin or solder. Improvements in single layer quality were obtained using copper-solder powder blends in a reducing atmosphere. The binary powder layers were characterized metallographically and the effect of processing parameters such as laser fluence and scan speed were assessed. Post-process annealing improved interparticle wetting and part strength. The influence of ZnCl2 flux was investigated when present as a coating in copper-solder blends. Multiple layer tests were performed on the most promising powder blends and the results are presented.Mechanical Engineerin

Solid Freeform Fabrication An Advanced Manufacturing Approach

Solid freeform fabrication (SFF) is the production of freeform solid objects directly from a computer model without part-specific tooling or human intervention. SFF has been realized in the last ten years through the merging of several previously distinct technologies: computer science, mechanical design, controls, high-energy beam technology and materials science and engineering. Their combination has produced over a relatively short time..frame numerous SFF methods. The value of SFF to the commercial sector is usually articulated in terms of reduced time to market (prototyping), low production "one-of-a-kind" parts and patterns for casting. The purpose of this introductory paper is to describe briefly some of the approaches to SFF as a background for the articles included in this proceedings.Mechanical Engineerin

Selective Laser Sintering to Produce NI-SN Intermetallics

A model system has been employed to investigate .the use of selective laser sintering (SLS) with a post-processing step to produce a compound having different properties than the precursor powders. The powder mixture examined consisted of95% (59% Ni and 41%8n) plus 5% ZnC12. This weight fraction of nickel and. tin produces. the intermetallic compound Ni3Sn upon equilibrium annealing. ZnCl2 was used as a wetting agent. Parts were fabricated using SLS and were then post-process annealed to create the intermetallic. Metallographic techniques and x-ray powder diffraction were used.to characterize the parts before and after annealing.Mechanical Engineerin

Laser Fusion Coatings of Functional Parts

Surface characteristics of functional parts made by Solid Freeform Fabrication techniques such as Selective Laser Sintering (SLS), Stereolitography Apparatus (SLA) or other fabrication techniques can be enhanced by the application of multi-element based laser fused coatings. Environmental protection and wear resistance, among other properties can be achieved by pre-depositing a slurry over the surface of the parts, followed by a high-speed scanning with a high power laser beam. Wetting of the part surface by the molten slurry is a main concern in this coating process. Wetting characteristics of molten slurry can be improved by the right combination of coating constituents, laser processing atmosphere, and laser processing parameters. Coating quality is also a critical issue to ensure good performance of the coatings especially for environmental protection. This paper presents results obtained for carbon-carbon composites coated with silicon-based slurries by laser fusion process. Criterion in selecting the coating constituents, laser process conditions, and oxidation test results are discussed.The authors gratefully acknowledge the support of the Ballistic Missile Defense Organization (BMDO) for this work. The research is being funded under the Small Business Innovative Research (SBIR) Program and managed by the Wright-Patterson Air Force Base, Dayton, Ohio.Mechanical Engineerin

Densification Behavior of SLS Processed Al2O3/Al Composite

Production of structurally sound parts by any rapid prototype technique is essential, because fully functional features are necessary where application testing is required. In the present work, a powder blend of A1203/AI (3:1 by weight) was mixed with ammonium dihydrogen phosphate and subjected to selective laser sintering (SLS) using a C02 laser. An attempt has been made to increase the powder bed density by introducing vibration to the part cylinder. These SLS processed preforms were then subj ected to a secondary heat treatment in a hydrogen atmosphere and to hot isostatic pressing. Densification behavior of these Al20 3/Al composite preforms is discussed.Mechanical Engineerin

Fundamentals of Liquid Phase Sintering During Selective Laser Sintering

One of the advantages of the Selective Laser Sintering (SLS) process is that a variety of materials can be processed. However, the goal of being able to produce fully dense metal parts with no post processing has been elusive. Using Selective Laser Sintering to produce metal parts with full density without post processing poses a challenge since both the processing conditions and the metal system must be controlled. This article describes two metallurgical mechanisms by which loose metal powder beds could be sintered to nearly full density using a scanning laser beam. The mechanisms are particle rearrangement during liquid phase sintering (LPS) and in-situ infiltration. Some of the particles, when heated by the laser radiation, melt and form a liquid. Ifthis liquid has certain physical properties (e.g., low viscosity and high surface tension) and wets the other solid particles, then the SLS process can in theory produce dense layers by either mechanism. The purpose of this study is to determine the process and material selection parameters required to achieve fully dense parts during direct Selective Laser Sintering of metal.Mechanical Engineerin

Study on Selective Laser Sintering of Eucalyptus/PES Blend and Investment Casting Technology

AbstractThe paper studies the Selective Laser Sintering (SLS) of Eucalyptus/PES blend and the Investment Casting (IC) technology of the forming part. This blend is suitable for being the raw material of SLS, because not only it has low cost, but also it can be produced by SLS to form the parts with high molding precision and mechanical strength after post processing; also the prototype can be used as the investment pattern.Combining the Eucalyptus/PES blend (which is a kind of Wood Plastic Composite, WPC), SLS with IC can reduce the production cost, also shorten the product development and manufacture cycle. Meanwhile it realizes the application of low-cost WPC in precision casting production. Mould making in investment casting is an extremely important procedure, from analyzing and calculating the physical and chemical characters of the prototypes during melting. It is known that WPC parts can be burnt off by the process of low-temperature dewaxing and high-temperature roasting before investment casting. After blowing the ash off by high-pressure air, the precision of the cavity is similar to one using a wax pattern. So for single and batch production, the WPC can be used as the investment pattern of IC technology instead of wax or resin. This paper studies the investment casting technology which is suitable for patterns produced by Selective Laser Sintering of Eucalyptus/PES blend

Surface Roughness Enhancement of Indirect-SLS Metal Parts by Laser Surface Polishing

Laser polishing by means of shallow surface melting of indirect-SLS metal parts was achieved using high power CO2 and Nd:YAG lasers raster scanned at high speed. This was an effective technique for reducing surface roughness. The fast moving laser beam provides just enough heat energy to cause melting of the surface peaks. The molten mass then flows into the surface valleys by surface tension, gravity and laser pressure, thus diminishing the roughness. Surface roughness Ra data were obtained by profilometry measurements of the polished samples. An analytical model was developed based on the assumption that the surface of an SLS part consists of semi-spherical caps. The model was used to predict the Ra values as a function of laser power, scan speed and precursor powder particle size. The modeled results fit the empirical data within a 15% error.The Laboratory of Freeform Fabrication gratefully acknowledges the support of the Office of Naval Research for funding the project “Surface Engineering for SFF Processes”, Grant Nº: N00014-00-1-0334Mechanical Engineerin

Development ofDirect SLS Processing for Production ofCermet Composite Turbine Sealing Components - Part I

This paper presents the development to date of SLS (selective laser sintering) technologies for production of cermet composite turbine sealing components, the particular application being an abrasive blade tip. The component chosen for the application is an integral part of the low pressure turbine in a IHP'TET (Integrated High Performance Turbine Engine Technology) demonstrator engine. Both indirect and direct SLS techniques are being developed. Initial trials and process development involved the use of fugitive polymeric binders. Sequential refinements were performed to develop a binderless direct SLS process. Results from mechanical testing indicate that acceptable microstructure and properties are attainable by SLS with substantial cost savings as compared to the currently employed production method. This is the rust instance ofdirect SFF methods applied to a functional componentMechanical Engineerin