Name: indirect fabrication of lattice metals with thin sections using centrifugal casting
Uploaded: 2016-05-14T14:00:00
Description: Watch this Scientific Journal Video about Indirect Fabrication of Lattice Metals with Thin Sections Using Centrifugal Casting at JoVE.com

This study received support from the Research Initiation Grant (RIG) of the Vice President for Research and Economic Development at the University of North Texas (UNT). The authors also thank KCIS Co. Ltd for partially supporting this study. The support from PACCAR Technology Institute at UNT to the success of this publication is greatly appreciated.

1. Planning of Experiment
<ol>
	<li>Draw a sacrificial pattern (an octet truss structure with a sprue system) using computer aided design (CAD) software as shown in Figure 1 and save the CAD model as an STL file format. 
	Note: The sacrificial pattern is an integrated pattern of the octet truss structure with a sprue system that will be eventually melted for casting. Because the sacrificial pattern includes both the octet truss structure and the sprue system, it does not exactly represent the octe...

<ol>
	<li>Gibson, L. J., Ashby, M. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Cellular Solids-Structure and properties. , (1997).</li><li>Schaedler, T. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultralight+Metallic+Microlattices.">Ultralight Metallic Microlattices.</a> J. Science. 334 (6058), 962-965 (2011).</li><li>Zheng, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrastiff+Mechanical+Metamaterials.">Ultrastiff Mechanical Metamaterials.</a> J. Science. 334 (6190), 1373-1377 (2014).</li><li>Ju, J., Summers, J. D., Ziegert, J., Fadel, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+of+Honeycombs+for+Modulus+and+Yield+Strain+in+Shear.">Design of Honeycombs for Modulus and Yield Strain in Shear.</a> J. Eng. Mater. &amp; Technol. 134 (1), 11-22 (2012).</li><li>Lee, J., Kim, K., Ju, J., Kim, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compliant+Cellular+Materials+with+Elliptical+Holes:+Materials+Design+with+Mechanisms.">Compliant Cellular Materials with Elliptical Holes: Materials Design with Mechanisms.</a> Transactions of the ASME: Eng. Maters. &amp; Technol. 131 (1), 1-14 (2015).</li><li>Tan, H., Qu, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chap+6:+Impact+of+Cellular+Materials.">Chap 6: Impact of Cellular Materials.</a> Cellular and Porous Materials in Structures and Processes. , (2010).</li><li>Phani, A. S., Woodhouse, J., Fleck, N. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wave+Propagation+in+Two-Dimensional+Periodic+Lattices.">Wave Propagation in Two-Dimensional Periodic Lattices.</a> Acoust. Soc. A. 119 (4), 1995-2005 (2006).</li><li>Kumar, R. S., McDowell, D. 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P. 12, 683-690 (2011).</li><li>Song, B., Dong, S., Liu, Q., Liao, H., Coddet, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vacuum+Heat+Treatment+of+Iron+Parts+Produced+by+Selective+Laser+Melting:+Microstructure,+Residual+Stress,+and+Tensile+Behavior.">Vacuum Heat Treatment of Iron Parts Produced by Selective Laser Melting: Microstructure, Residual Stress, and Tensile Behavior.</a> Mater. Design. 54, 727-733 (2014).</li><li>Yadroitsev, I., Smurov, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+Morphology+in+Selective+Laser+Melting+of+Metal+Powders.">Surface Morphology in Selective Laser Melting of Metal Powders.</a> Ph. P. 12, 264-270 (2011).</li><li>Antonysamy, A. A., Meyer, J., Prangnell, P. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+Build+Geometry+on+the+&#946;-grain+Structure+and+Texture+in+Additive+Manufacture+of+Ti-6Al-4V+by+Selective+Election+Beam+Melting.">Effect of Build Geometry on the &#946;-grain Structure and Texture in Additive Manufacture of Ti-6Al-4V by Selective Election Beam Melting.</a> J. of Mat. Charact. 84, 153-168 (2013).</li><li>Ladani, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Local+and+Global+Mechanical+Behavior+and+Microstructure+of+Ti6Al4V+Parts+Built+Using+Electron+Beam+Melting+Technology.">Local and Global Mechanical Behavior and Microstructure of Ti6Al4V Parts Built Using Electron Beam Melting Technology.</a> J. of Metalllur. &amp; Mater. Trans. 46, (2015).</li><li>Chiras, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Structural+Performance+of+Near-Optimized+Truss+Core+Panels.">The Structural Performance of Near-Optimized Truss Core Panels.</a> Solids Struct. 39, 4093-4115 (2002).</li><li>Meisel, N. A., Williams, C. B., Druschitz, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lightweight+Metal+Celluar+Structures+via+in+Direct+3D+Printing+and+Casting.">Lightweight Metal Celluar Structures via in Direct 3D Printing and Casting.</a> Proceedings of the 24th Solid Freeform Fabrication Symposium. , (2013).</li><li>Mun, J., Ju, J., Yun, B. -. G., Chang, B. -. M., Kim, D. -. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Numerical+Study+of+Molten+Aluminum+for+Investment+Casting+of+3D+Cellular+Metals.">A Numerical Study of Molten Aluminum for Investment Casting of 3D Cellular Metals.</a> Proceedings of the ASME International Mechanical Engineering Congress and Exposition. , (2013).</li><li>Mun, J., Yun, B. -. G., Ju, J., Chang, B. -. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Indirect+Additive+Manufacturing+Based+Casting+of+a+Periodic+3D+Cellular+Metal+-+Flow+Simulation+of+Molten+Aluminum+Alloy.">Indirect Additive Manufacturing Based Casting of a Periodic 3D Cellular Metal - Flow Simulation of Molten Aluminum Alloy.</a> Manufact. Process. 17, 28-40 (2015).</li><li>Challapalli, A., Ju, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuum+Model+for+Effective+Properties+of+Orthotropic+Octet-Truss+Lattice+Materials.">Continuum Model for Effective Properties of Orthotropic Octet-Truss Lattice Materials.</a> Proceedings of the ASME International Mechanical Engineering Congress and Exposition. , (2014).</li><li>Taylor, H. F., Flemings, M. C., Wulff, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Foundry Engineering. , (1959).</li><li>Mun, J., Ju, J., Thurman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Indirect+Additive+Manufacturing+Based+Casting+(I+AM+Casting)+of+a+Lattice+Structure.">Indirect Additive Manufacturing Based Casting (I AM Casting) of a Lattice Structure.</a> Proceedings of the ASME International Mechanical Engineering Congress and Exposition. , (2014).</li><li>Mun, J., Ju, J., Thurman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Indirect+Additive+Manufacturing+of+a+Copper+Alloy+Cubic+Lattice+Structure.">Indirect Additive Manufacturing of a Copper Alloy Cubic Lattice Structure.</a> Proceedings of the 25th Annual International Solid Freeform Fabrication Symposium. , (2014).</li><li>. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Volume+2+Properties+and+Selection:+Nonferrous+Alloys+and+Pure+Metals.">Volume 2 Properties and Selection: Nonferrous Alloys and Pure Metals.</a> Metals Handbook Ninth Edition. , (1979).</li><li>Romano, J., Ladani, L., Razmi, J., Sadowski, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temperature+Distribution+and+Melt+Geometry+in+Laser+and+Electron-beam+Melting+Processes+-+A+Comparison+Among+Common+Materials.">Temperature Distribution and Melt Geometry in Laser and Electron-beam Melting Processes - A Comparison Among Common Materials.</a> J. of Additive Manuf. 8, 1-11 (2015).</li></ol>

For conventional metal casting, it is important to keep the molten metal&#39;s flow smooth and streamlined in &#39;laminar&#39; in the mold cavity and rather avoid irregular and agitated flow generally observed in turbulent flow27. Accordingly, it is important to properly design the inlet of the sprue system associated with the rotating speed of a centrifugal arm to maintain the flow of molten metal inside the lattice mold cavity &#39;laminar&#39;.
In this study, the critical steps ...

Cellular metals are the metals made up of an interconnected network of solid struts or plates and have complex micro-architectures with voids1. Examples include both i) randomly structured stochastic foams and ii) periodically ordered two-dimensional (2D) honeycombs and three-dimensional (3D) lattice truss structures. They have received attention due to their high specific stiffness and strength1-3and high specific resilience4-5, excellent energy absorption for impact loading6, acoustic insulation7, possible design of heat dissipaters and heat exchangers8. Especially, periodically ordered lattice structures have the potential to engineer the properties superior with a capability to control the internal porous network geometry.
Due to their complex internal porous network geometry, it is difficult to manufacture cellular metals using the conventional subtractive machining. As such, researchers have started looking for alternative methods to fabricate cellular metals: forming gas in liquid metal or mixing metal powder with blowing agents were explored for manufacturing stochastic metal forms9. Due to the lack of control over cell topology, it is hard to tailor mechanical properties. Alternatively, manufacturing methods for periodically ordered cellular metals were explored: stamping thin sheets of metal into a corrugated shape followed by joining them to create periodic structures10, bonding slotted metal sheets11, extrusion12, weaving and blazing metal filaments to fabricate textiles13. Even though these manufacturing methods offer repeatable patterns, the patterns are still limited in the planar direction. In an effort to generate 3D pattern repetition, researchers started using additive manufacturing (AM); e.g., Selective Laser Melting (SLM)14, Electron Beam Melting (EBM)15, and Direct-Metal Laser Sintering (DMLS)16. Despite their capability to fabricate 3D ordered complex lattice geometries, there still exist some limitations: difficulty using metals with high thermal conductivity and high optical reflectivity17, high thermal residual stress18, poor surface finish with the &#39;balling&#39; phenomenon during laser or electron melting 19, anisotropic properties20-21 of parts caused by a combined effect of the layered manufacturing, anisotropic formation of grains, powder size, power and scanning speed of laser or electron beam15, high energy consumption, etc.
Combining polymer based AM with metal casting may provide an alternative method to manufacture lattice metals. One may call this &#34;indirect AM&#34;. Indirect AM may provide a solution to overcome the technical problems of direct AM of metals mentioned above. Several efforts have been made to manufacture lattice metals using indirect AM combining 3D printing of polymers with gravity based casting22-25; e.g., an investment casting combined with fused deposition modeling (FDM) to fabricate a lattice alloy22-25 or sand casting combined with a sand powder based AM23. The gravity based casting appears to remain a technical challenge to overcome - misrun and porosity caused by sudden solidification of molten metals when they meet network structures with sharp corners of lattice structural molds25-26. Relatively large surface area of lattice structural molds also appears to contribute to sudden cooling, resulting in premature solidification25-26.
In this study, we propose an alternative indirect AM that may overcome the misrun during manufacturing of lattice metals - centrifugal casting to a lattice mold cavity made by a 3D printed lattice sacrificial polymer pattern. We use a digital light processing (DLP) based 3D printing method to build a lattice structural sacrificial pattern followed by centrifugal casting of Al and Cu alloys. The objective of this study is to provide a detailed protocol on fabrication of 3D lattice metals having a complex shape and a thin wall thickness. The main contribution of this process is to provide an opportunity to extend the selection of materials with low manufacturing cost for manufacturing lattice metals.

<table>
	<tbody>
		<tr>
			<td>Motorized centrifugal casting machine</td>
			<td>Rey Motorized Centrifugal Casting Machine, Rey Industries Inc.</td>
			<td></td>
			<td>Made in U.S.A. by Rey industries, Inc. Dallas, TX 75220</td>
		</tr>
		<tr>
			<td>Gypsum powder</td>
			<td>Satin Cast 20, FindingKing Kerr</td>
			<td>7960</td>
			<td>Gypsum powder is used to make the investment mixture</td>
		</tr>
		<tr>
			<td>Ployjet 3D printer</td>
			<td>Projet HD3500 Plus, 3D Systems</td>
			<td></td>
			<td>This polymer based 3D printer to print out sacrificial pattern for casting.</td>
		</tr>
		<tr>
			<td>Cartridge materials - UV curable and castable acrylic plastic</td>
			<td>VisiJet Procast, 3D Systems</td>
			<td></td>
			<td>This is castable material that is going to be burn out before casting</td>
		</tr>
		<tr>
			<td>Cartridge materials- support material</td>
			<td>VijiJet S300, 3D Systems</td>
			<td></td>
			<td>This is support material that is going to be removed before pattern assemble</td>
		</tr>
		<tr>
			<td>Ancient Bronze Casting Grain</td>
			<td>Rio Grande</td>
			<td>706051</td>
			<td>This true bronze grain contains no zinc. Highly fluid, it melts quickly, casts cleanly and provides a good balance between strength and durability. The warm, deep-bronze color has rich red undertones, and the alloy takes a good patina. 
			Composition is 90% copper with an amount of tin; fits into the CDA#90700 category. This grain is sold in 1-lb. packages.</td>
		</tr>
		<tr>
			<td>Aluminum Round Wire, 1/8&#34;, 1-Lb. Spool, Dead Soft</td>
			<td>Rio Grande</td>
			<td>134700</td>
			<td>Lightweight and strong, aluminum wire is an economical and versatile choice. Not as bright-white as silver, aluminum offers a warmer tone much like that of platinum. Solder ONLY with low-temp solders such as Stay-Brite; suitable for both pulse-arc and laser welding. This quality aluminum wire is packaged on 1-lb. spools.</td>
		</tr>
		<tr>
			<td>Computer aided design software (Pro-e)</td>
			<td></td>
			<td></td>
			<td>This software can be replaced with the others such as Auto CAD, Catia, and so on.</td>
		</tr>
		<tr>
			<td>ProJet Finisher 1-A</td>
			<td>3D Systems</td>
			<td></td>
			<td>This machine is used to melt the support material.</td>
		</tr>
		<tr>
			<td>160 Watt 2.5 Liters Digital Ultrasonic Cleaner with Timer Heater Rings Tools</td>
			<td>Chicago, Electric, Power Tools</td>
			<td></td>
			<td>85 oz. capacity, Five cleaning cycles: 90, 180, 280, 380 and 480 seconds, Clean with or without heat, Easy-to-read LED digital timer, Clear-view window</td>
		</tr>
		<tr>
			<td>Fan&#160;</td>
			<td>Honeywell Inc.&#160;</td>
			<td>HT-800</td>
			<td>120V A.C., 60Hz., 0.85A. TP</td>
		</tr>
		<tr>
			<td>Paraffin wax for wax sheet - Modeler&#39;s Pink Wax Sheet, 3&#34; by 6&#34;, 24-Ga.</td>
			<td>Rio Grande</td>
			<td>700075</td>
			<td>Sheet wax is flexible and can be cut or formed into any shape. It&#8217;s ideal for designing since you can draw or trace directly onto the sheet; choose green or pink depending on which will best show your designs. High manufacturing standards ensure exceptional consistency and significant price savings. Value is enhanced by larger package quantities at the same price as the smaller packages available elsewhere. Each 8-oz. package contains approximately 30 sheets.</td>
		</tr>
		<tr>
			<td>Paraffin wax for wax stick - Modeler&#39;s Medium Red Sprue Wax, 8-Ga</td>
			<td>Rio Grande</td>
			<td>700741</td>
			<td>A pliable, softer sprue wax than the firm blue. Good for forming gates and sprues and burns out cleanly with no residue.</td>
		</tr>
		<tr>
			<td>Alcohol Lamp</td>
			<td>Rio Grande</td>
			<td>700008</td>
			<td>Use this lamp to heat wax-working tools or as a flame polisher. The heavy glass reservoir has faceted sides to allow it to be tipped for angling the flame. A screw adjustment for the 7&#34; x 3/16&#34; wick controls the height of the flame. A safety cap snuffs the flame and prevents fuel evaporation. For the best flame, use methyl alcohol fuel. Replacement wicks available. Reservoir holds 5 oz. (150ml) of fuel.</td>
		</tr>
		<tr>
			<td>Wax carving tool set - Soft Grip Wax Carvers, Set of 10</td>
			<td>Rio Grande</td>
			<td>700329</td>
			<td>This boxed set offers the best in cutting and shaping technology. Each of these ten high-quality steel wax-carving tools features a 5/16&#34; PVC covered handle that ensures a sure, comfortable grip through hours of work and all have sharp edges for shaping and fine detailing. Sharpen or custom-shape each tool to fit your needs. These tools provide exceptional tool strength and deliver excellent results. This set comes in a hinged, foam-lined wood box.</td>
		</tr>
		<tr>
			<td>Rubber Mixing Bowl, 1-1/2 Qt.</td>
			<td>Rio Grande</td>
			<td>702131</td>
			<td>This highly-flexible vulcanized rubber bowl is easy to grip, will not be marred by a spatula and cleans with ease.</td>
		</tr>
		<tr>
			<td>Pyrex Beaker, 1,000ml</td>
			<td>Rio Grande</td>
			<td>335040</td>
			<td>Ideal for holding and heating bath plating solutions, this genuine Pyrex glass beaker is sturdy and durable.</td>
		</tr>
		<tr>
			<td>Rio Premium Stainless Steel Flask, 2-1/2&#34; dia.</td>
			<td>Rio Grande</td>
			<td>70201514</td>
			<td>This solid, #304-quality stainless steel flask is corrosion-resistant, durable for a long service life and performs under extreme temperature without distortion.</td>
		</tr>
		<tr>
			<td>CAST/T Ceramic Casting Crucible, 450g</td>
			<td>Rio Grande</td>
			<td>705047</td>
			<td>Made exclusively for the CAST/T centrifugal casting machine, this crucible is designed with an angled base that slides into the hinged bracket on top of the casting machine. This brings the crucible into perfect alignment with the center of the flask ring to ensure an error-free pour.</td>
		</tr>
		<tr>
			<td>MyWeigh iBalance 300 Digital Scale</td>
			<td>Rio Grande</td>
			<td>116850</td>
			<td>This scale is used to measure the weight of the sacrificial and sprue system for metal which is going to be used for centrifugal casting.</td>
		</tr>
		<tr>
			<td>Rubber bottom - CAST/T Flask Ring Base</td>
			<td>Rio Grande</td>
			<td>705025</td>
			<td>Specially made for the CAST/T centrifugal casting machine, this rubber base accommodates all Table King flask ring styles, creating a secure, airtight seal throughout the investment process. The center post fits either of the wax disc styles for complete versatility.</td>
		</tr>
		<tr>
			<td>Scotch&#174; Colored Duct Tape, 1 7/8&#34; x 20 Yd., Blue</td>
			<td>OfficeMax&#160;</td>
			<td>22353766</td>
			<td>This scotch tape is used to make sure that the gypsum-water mixture fully covers the assembled sacrificial pattern inside the flask by allowing for extra material above the flask height</td>
		</tr>
		<tr>
			<td>Vacuum casting machine - V.I.C. 12 Tabletop Solid- and Perforated-Flask Casting Machine with The Rio Assistant, 110-Volt</td>
			<td>Rio Grande</td>
			<td>70511814</td>
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			<td>Quality, German-made frames are our most popular saw frames, and this frame includes a sampler pack of Rio German saw blades! The adjustable saw frame allows you to achieve the blade tension you want. Throat depth is 102mm (4&#34;). Saw blades have rounded backs that make cutting curves and corners easy and are made from hardened, tempered steel.</td>
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</table>

indirect fabrication of lattice metals with thin sections using centrifugal casting

One of the typical methods to manufacture 3D lattice metals is the direct-metal additive manufacturing (AM) process such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM). In spite of its potential processing capability, the direct AM method has several disadvantages such as high cost, poor surface finish of final products, limitation in material selection, high thermal stress, and anisotropic properties of parts. We propose a cost-effective method to manufacture 3D lattice metals. The objective of this study is to provide a detailed protocol on fabrication of 3D lattice metals having a complex shape and a thin wall thickness; e.g., octet truss made of Al and Cu alloys having a unit cell length of 5 mm and a cell wall thickness of 0.5 mm. An overall experimental procedure is divided into eight sections: (a) 3D printing of sacrificial patterns (b) melt-out of support materials (c) removal of residue of support materials (d) pattern assembly (e) investment (f) burn-out of sacrificial patterns (g) centrifugal casting (h) post-processing for final products. The suggested indirect AM technique provides the potential to manufacture ultra-lightweight lattice metals; e.g., lattice structures with Al alloys. It appears that the process parameters should be properly controlled depending on materials and lattice geometry, observing the final products of octet truss metals by the indirect AM technique.

Using the indirect additive manufacturing described in the protocol section, Al and Cu alloys were used for manufacturing octet truss metals, as shown in Figure 1. The whole casting procedure is summarized in Figure 2. The procedure consists of eight sections: (a) sacrificial pattern printing (b) melting-out of support material (c) removal of residue of support material (d) pattern assembly (e) investment (f) burn-out of sacrificial patterns (g) centrifug...

Watch this Scientific Journal Video about Indirect Fabrication of Lattice Metals with Thin Sections Using Centrifugal Casting at JoVE.com

Indirect Fabrication of Lattice Metals with Thin Sections Using Centrifugal Casting

An indirect additive manufacturing method combining a 3D printing of polymers with a centrifugal casting is outlined for manufacturing 3D octet truss metals (Al and Cu alloys) having a unit cell length of 5 mm with a wall thickness of 0.5 mm.

One of the typical methods to manufacture 3D lattice metals is the direct-metal additive manufacturing (AM) process such as Selective Laser Melting (SLM) ...

The overall goal of this video is to demonstrate the process of filling a cellular microcavity with molten metal for the fabrication of lattice metals by centrifugal casting. This message can help answer key questions such as, how the process parameters, material properties of molten metal, and geometry of lattice mold cavity are correlated with the flow and solidification in rapid microcasting. This technique supplements direct 3D printing massive of metals, in manufacturing lattice metals, and expands the material selection in the design space of lattice metals.Today, I will be demonstrating the procedure with doctoral student Jiwon Mun. In preparation, draw a sacrificial pattern of an octet truss structure with a sprue system using computer-aided design software. This integrated pattern of an octet truss structure with a sprue system gets melted during casting.Using the CAD software, record the volume of the sacrificial pattern to calculate the required metal mass. After printing the acrylic model, proceed with the casting process, which is detailed in the text protocol. The next step is the melting out of the support material.Following this, the residue of support material is further removed. Then, the pattern is assembled. Following its assembly, an investment mixing process is performed.Be sure to remove all lumps in the investment water mixture. Next, is the burnout process. To begin, set the time on the furnace according to the heating and cooling schedule.For a flask of this size, the burnout will take six hours. Now, turn on the furnace and start the burnout schedule. During the burnout, the sacrificial pattern melts and dissociates into a gas.Now, continue with the casting process described in the next two sections. Before beginning, ensure that the centrifugal casting machine's arm spins with an angular velocity of 425 RPM. Find the setting needed for this speed using a tachometer.Select a ceramic crucible to melt each alloy. Using a metal cutter, chop the alloys into 10 millimeter to 20 millimeter pieces. Chop up around 150 grams of each alloy, which in this case are aluminum and copper.Now, weigh out the precise mass of each alloy needed for the lattice design. The pattern cavity must be filled precisely to capacity with molten alloy. Now, get a bucket of water at room temperature ready.30 liters is sufficient. Next, put on flame retardant clothes and put on gloves and goggles. Now, take the plaster mold temporarily out from the furnace.Place it into the flask cradle of the centrifugal casting machine, and balance the arm of the centrifuge. Then, return the plaster mold back into the furnace, and start heating the machine to 482 degrees Celsius. Meanwhile, place the crucible in the crucible holder, and load the chopped alloy into the crucible.Next, set up the acetylene torch. Open the valve of the connected oxygen tank, and maintain the gas pressure near 96.5 kilopascals or 14 PSI. Then, carefully ignite the torch and control the intensity of the flame with the gas pressure.Be very careful. The flame gets up to 1, 200 degrees Celsius. Now, carefully melt the chopped alloy in the crucible until it is completely liquified.Use a carbon rod to stir the alloy and melt it with the neutral part of the torch's flame. The proper melting of the metal is critical, because if the metal is too cool, it will not fill the entire form. But, if it's too hot, the increasing porosity will cause structural issues.Now, take the preheated plaster mold from the furnace, and load it into the flask cradle holding arm next to the crucible with the molten alloy. Close the cover of the machine and let the arm spin for at least three minutes. The machine starts spinning automatically when the cover is closed.About 420 RPM's creates an inlet velocity at the mold cavity of 8.03 meters per second, as calculated by the macroscopic particle dynamics and the angular velocity. After three minutes, cut the power to the centrifugal casting machine. Then, open the cover, and using tongs, remove the plaster mold from the flask cradle.Let the mold cool at room temperature for 15 to 20 minutes, until the color of the alloy returns to that of its solid phase. Then, using tongs, quench the plaster mold in the water bucket for about five minutes. When the mold is near room temperature, it is completely quenched.Now, to obtain the lattice metal inside the mold, just dissolve the mold in water. The Jibsen mold will easily dissolve within two minutes. Post-processing is now possible, such as cleaning by sandblasting, which is described in the text protocol.Be sure to use the described sandblasting pressure as the molds are somewhat fragile, especially the aluminum octet truss which has thin walls. Using the indirect additive manufacturing described in the protocol section, aluminum and copper alloys were used to manufacture octet truss metals. The burnout process was carried out for six hours to melt out the sacrificial pattern.After the centrifugal casting process, the final products were octet truss metals made with aluminum and copper alloys. The molten aluminum alloy fully filled the entire lattice mold cavity without a misrun. On the other hand, the molten copper alloy appeared to have a casting defect caused by premature solidification at the early stage of injection of molten metal at the inlet.After watching this video, you should have a good understanding of the effect of process parameters on filling of molten metal into cellular microcavity, doing indirect fabrication of lattice metals using centrifugal casting. After its development, this technique paved the way for researchers in the field of lattice metals to explore indirect fabrication, by combining 3D printing of polymers with centrifugal casting.

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