Browsing by Subject "LENS"
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Item Free Form Fabrication of Metallic Components Using Laser Engineered Net Shaping (Lens)(1996) Griffith, M. L.; Keicher, D. M.; Atwood, C. L.; Romero, J. A.; Smugeresky, J. E.; Harwell, L. D.; Greene, D. L.Solid free form fabrication is one ofthe fastest growing automated manufacturing technologies that has significantly impacted the length oftime between initial concept and actual part fabrication1 2. Starting with CAD renditions of new components, several techniques such as stereolithography3 and selective laser sintering4 are being used to fabricate highly accurate complex three-dimensional concept models using polymeric materials. Coupled with investment casting techniques, sacrificial polymeric objects are used to minimize costs and time to fabricate tooling used to make complex metal castings5 • This paper will describe recent developments in a new technology, known as LENSTM (Laser Engineered Net Shaping)6 7 8 9, to fabricate metal components directly from CAD solid models and thus further reduce the lead times for metal part fabrication. In a manner analogous to stereolithography or selective sintering, the LENSTM process builds metal parts line by line and layer by layer. Metal particles are injected into a laser beam, where they are melted and deposited onto a substrate as a miniature weld pool. The trace ofthe laser beam on the substrate is driven by the definition ofCAD models until the desired net-shaped densified metal component is produced.Item High Therma(University of Texas at Austin, 2009-09-15) España, Félix A.; Balla, Vamsi Krishna; Bose, Susmita; Bandyopadhyay, AmitSurface modification has been used to improve wear resistance, corrosion resistance and thermal barrier properties of metals. However, no significant attempts have been made to improve thermal conductivity by surface modification. In this work, we have examined the feasibility of enhancing thermal conductivity (TC) of stainless steel by depositing brass using Laser Engineered Net Shaping (LENS). The coating increased the TC of the substrate by 65% at 100 C°. Significantly low thermal contact resistance was observed between the coating and the substrate due to minimal dilution and defect free sound interface. Our results indicate that laser processing can be used on low coefficient of thermal expansion metal matrix composites to create feature based coatings to enhance their heat transfer capability.Item Microstructural and Mechanical Performance of Al2O3 Nanoparticle Reinforced 17-4 PH Stainless Steel Bulk Composite Parts Fabricated by Laser Engineered Net Shaping Process(University of Texas at Austin, 2016) Ning, Fuda; Hu, Yingbin; Liu, Zhichao; Wang, Hui; Cong, Weilong; Li, YuzhouAlloy 17-4 PH (AISI 630) is a precipitation-hardening martensitic stainless steel that has been extensively employed in the industries of aerospace, marine, and chemical. In this study, bulk parts of both 17-4 PH and Al2O3 reinforced 17-4 PH composites were fabricated on a steel substrate by laser engineered net shaping (LENS) process to investigate the effects of Al2O3 reinforcements on the part performance. The 17-4 PH powders were pre-mixed with Al2O3 nanoparticles by ball milling. The microstructures of both parts were observed using scanning electron microscopy and mechanical properties including microhardness and compressive properties were evaluated by means of a Vickers microhardness tester and a universal tester, respectively. The results indicate that Al2O3 reinforced 17-4 PH composite parts fabricated by LENS process exhibited superior microhardness and compressive properties as compared to pure 17-4 PH parts.Item Microstructure and Property Optimization of LENS Deposited H13 Tool Steel(1999) Brooks, J.; Robino, C.; Headley, T.; Goods, S.; Griffith, M.Direct laser metal deposition is a means of near net shape processing that offers a number of advantages including rapid prototyping and small lot production. With the LENS (Laser Engineered Net Shape) process [Ref 1], parts are fabricated by creating a laser melted pool into which particles are injected. Fabrication proceeds by moving the work piece, thereby building the structure line by line and layer by layer. In this manner a wide variety of geometries and structures can be fabricated. During fabrication, a complex thermal history is experienced in different regions of the build. These thermal histories include remelting and numerous lower temperature thermal cycles. Furthermore, the use of a finely focused laser to form the rapidly traversing pooL can result in relatively high solidification velocities and cooling rates. Previous work has developed LENS as an advanced manufacturing tool rather than exploiting its potentially unique attributes: real time control of microstructure, tailored material properties at different part locations, the production of graded structures, etc. Very often, however, material properties are not significantly different than those of wrought materials. The. goal of this program is to exploit the unusual thermal environment experienced during fabrication, and the ability to design and vary alloy composition. In this paper we describe this approach using H13 tool steel in which only the thennal fields are varied through changing process parameters to achieve desired properties.Item Process Maps for Laser Deposition of Thin-Walled Structures(1999) Vasinonta, Aditad; Beuth, Jack; Griffith, MichelleIn solid freeform fabrication (SFF) processes involving thermal deposition, thermal control of the process is critical for obtaining consistent deposition conditions and in limiting residual stress-induced warping of parts. In this research, nondimensionalized plots (termed process maps) are developedJrom numerical models of laser-based material deposition of thin-walled structures that.map out the effects of changes in laser power, deposition speed and part preheating on process parameters. The principal application of this work is to the Laser Engineered Net Shaping (LENS) process under development at Sandia Laboratories; however, the approach taken is applicable to any solid freeform fabrication process involving. a moving heat source. Similarly, although thinwalled structures treated in the current work, the same approach could be applied to other commonly fabricated geometries. A process map for predicting and controlling melt pool size is presented .and numerically determined results are compared against experimentally measured melt poollengthsfor stainless steel deposition in the LENS process.Item Process-Specific Microstructure-Sensitive Modeling of Fatigue in Additively Manufactured Ti-6Al-4V Alloys(2022) Lado, Lionardo; Ataollahi, Saeed; Yadollahi, Aref; Mahtabi, Mohammad J.Thanks to its high strength-to-weight ratio and corrosion resistance, Ti-6Al-4V has gained a lot of attention in additive manufacturing (AM) of complex parts with aerospace and medical applications. The realistic loading condition in these applications is mostly cyclic, thus fatigue failure is the main mode of failure. On the other hand, due to presence of local defects in the current state of AM materials, the main challenge with AM of metallic parts is their fatigue resistance and durability, being much lower than the conventional counterparts. In this study, a simplified microstructure-sensitive fatigue (MSF) approach was developed to model the fatigue life of AM Ti-6Al-4V specimens by incorporating microstructural features and defect properties, such as grain size, pore size and pores nearest neighbors. The studied AM methods include Laser Engineered Net Shaping (LENS), Electron Beam Melting (EBM), and Selective Laser Melting (SLM). Each of these processes use different approaches in constructing the three-dimensional object, yielding in different microstructure of the final part. For this work, microstructural data were collected from previous experimental studies. Scanning Electron Microscopy (SEM) images were used to examine the fracture surfaces of the AM specimens and determine the defects responsible for fatigue failure. With an emphasis on the microstructurally small crack growth, model parameters were calibrated for fatigue data for different AM processes, while keeping process-independent parameters as constant. The results showed that a simplified MSD fatigue model with limited number of process-dependent governing parameters can be calibrated for each set of data.Item Process-specific Microstructure-sensitive Modeling of Fatigue in Additively Manufactured Ti-6Al-4V Alloys(2022) Lado, Lionardo; Ataollahi, Saeed; Yadollah, Aref; Mahtabi, Mohammad J.Thanks to its high strength-to-weight ratio and corrosion resistance, Ti-6Al-4V has gained a lot of attention in additive manufacturing (AM) of complex parts with aerospace and medical applications. The realistic loading condition in these applications is mostly cyclic, thus fatigue failure is the main mode of failure. On the other hand, due to presence of local defects in the current state of AM materials, the main challenge with AM of metallic parts is their fatigue resistance and durability, being much lower than the conventional counterparts. In this study, a simplified microstructure-sensitive fatigue (MSF) approach was developed to model the fatigue life of AM Ti-6Al-4V specimens by incorporating microstructural features and defect properties, such as grain size, pore size and pores nearest neighbors. The studied AM methods include Laser Engineered Net Shaping (LENS), Electron Beam Melting (EBM), and Selective Laser Melting (SLM). Each of these processes use different approaches in constructing the three-dimensional object, yielding in different microstructure of the final part. For this work, microstructural data were collected from previous experimental studies. Scanning Electron Microscopy (SEM) images were used to examine the fracture surfaces of the AM specimens and determine the defects responsible for fatigue failure. With an emphasis on the microstructurally small crack growth, model parameters were calibrated for fatigue data for different AM processes, while keeping process-independent parameters as constant. The results showed that a simplified MSD fatigue model with limited number of process-dependent governing parameters can be calibrated for each set of data.Item Sacrificial Materials for the Fabrication of Complex Geometries with LENS(1998) Schlienger, E; Griffith, M.; Oliver, M.; Romero, J.A.; Smugeresky, J.Item Software Development for Laser Engineered Net Shaping(1998) Ensz, M. T.; Griffith, M. L.; Harrwell, L. D.Laser Engineered Net Shaping, also known as LENSTM, is an advanced manufacturing technique used to fabricate near-net shaped, fully dense metal components directly from computer solid models without the use oftraditional machining processes. The LENSTM process uses a high powered laser to create a molten pool into which powdered metal is injected and solidified. Like many SFF techniques, LENSTM parts are made through a layer additive process. In the current system, for any given layer, the laser is held stationary, while the part and its associated substrate is moved, allowing for the each layer's geometry to be formed. Individual layers are generated by tracing out the desired border, followed by filling in the remaining volume. Recent research into LENSTM has highlighted the sensitivity ofthe processes to multiple software controllable parameters such as substrate travel velocity, border representation, and fill patterns. This research is aimed at determining optimal border outlines and fill patterns for LENSTM and at developing the associated software necessary for automating the creation ofthe desired motion control.Item Thermal Behavior in the Lens Process(1998) Griffith, M.; Schlienger, M. E.; Harwell, L. D.; Oliver, M. S.; Baldwin, M. D.; Ensz, M. T.; Smugeresky, J. E.; Essien, M.; Brooks, J.; Robino, C. V.; Hofineister, W. H.; Wert, M. J.; Nelson, D. V.Direct laser metal deposition processing is a promising manufacturing technology which could significantly impact the length oftime between initial concept and finished part. For adoption ofthis technology in the manufacturing environment, further understanding is required to ensure robust components with appropriate properties are routinelyfabricated. This requires a complete understanding ofthe thermal history.during part fabrication and control ofthis behavior. This paper will describe our research to understand the thermal behavior for the Laser Engineered Net Shaping (LENS) process!, where a component is fabricated by focusing a laser beam onto a substrate to create a molten pool in which powder particles are simultaneously injected to build each layer. The substrate is moved beneath the l~ser beam to deposit a thin cross section, thereby creating the desired geometry for each layer. After deposition of each layer, the powder delivery nozzle and focusing lens assembly is incremented in the positive Z-direction, thereby building a three dimensional component layer additively. It is important to control the thermal behavior to reproducibly fabricate parts. The ultimate intent is to monitor the thermal signatures and to incorporate sensors and feedback algorithms to control part fabrication. With appropriate control, the geometric properties (accuracy, surface finish, low warpage) as well as the materials' properties (e.g. strength, ductility) of a component can be dialed into the part through the fabrication parameters. Thermal monitoring techniques will be described, and their particular benefits highlighted. Preliminary details in correlating thermal behavior with processing results will be discussed.Item Thermal characterization of direct metal deposition(2014-05) Knapp, Cameron Myron; Kovar, Desiderio; Landsberger, SheldonThe temperature distribution in the vicinity of the laser used in direct metal deposition (DMD) plays a critical role in determining the final microstructure and properties of the deposit and the heat-affected zone within the substrate. A system of deposition samples were studied consisting of AISI 1018 steel powder deposited onto an AISI 1018 steel substrate as a single pass or as overwritten multiple passes. The laser power and speed were varied to influence the heat input and the rate of cooling. The use of idealized one dimensional lines allowed for the solution of a quasi-steady state analytical temperature distribution. Numerical predictions were made using the commercial software SysWeld™ for single pass depositions. Peak temperatures and cooling rates were determined at selected locations experimentally using micro-hardness measurements which were supplemented by obtaining thermocouple data taken during deposition. The analytical model, numerical predictions, and experimental results are compared for single pass depositions to determine the extent to which existing commercial codes can accurately model the thermal environment for DMD.