Rapid Steel Tooling Via Solid Freeform Fabrication

With increasing part complexity and requirements for long production runs, tooling has become an expensive process that requires long lead times to manufacture. This lengthens the amount oftime from "art to part". Rapid tooling via stereolithography (SLA), filled epoxies, etc. have been stopgap measures to produce limited prototyping runs from (10 to 500 parts). This gives poor dimensional analysis and does not allow for limited production runs of 1000+ parts. The method ofproducing prototype tooling with a powdered metal process has been developed that produces tooling with a hardness greater than 35 HRC and total shrinkage less than 0.5%. This tooling process manufactures production ready tooling that will perform extended cycle runs (100,000+). Manufacturing ofthis tooling takes 1 to 2 weeks and will compare favorably with production grade steel tooling. Originals drawn in 3D CAD can be used to prototype the master that will allow for the production ofthe rapid metal tool set. process starts with a rapid prototyped model made by whatever process is desired or a machined master. For this paper a Sander's Model Maker II® rapid prototyping machine was used to fabricate the model. After the model ofthe tool set is made, a silicone rubber negative is cast around that model. After the silicone rubber model is made, a heated slurry ofmetal powders and polymers is poured into the mold to create the green tool set. The tool set is left to cool, and then removed from the silicone rubber mold. The tool set is then debound and sintered to produce a final tool set with properties approaching hardened tool steel.Mechanical Engineerin

Quark mass correction to the string potential

A consistent method for calculating the interquark potential generated by the relativistic string with massive ends is proposed. In this approach the interquark potential in the model of the Nambu--Goto string with point--like masses at its ends is calculated. At first the calculation is done in the one--loop approximation and then the variational estimation is performed. The quark mass correction results in decreasing the critical distance (deconfinement radius). When quark mass decreases the critical distance also decreases. For obtaining a finite result under summation over eigenfrequencies of the Nambu--Goto string with massive ends a suitable mode--by--mode subtraction is proposed. This renormalization procedure proves to be completely unique. In the framework of the developed approach the one--loop interquark potential in the model of the relativistic string with rigidity is also calculated.Comment: 34 pages, LATE

Electronic Structure and Magnetic Exchange Coupling in Ferromagnetic Full Heusler Alloys

Density-functional studies of the electronic structures and exchange interaction parameters have been performed for a series of ferromagnetic full Heusler alloys of general formula Co$_2$MnZ (Z = Ga, Si, Ge, Sn), Rh$_2$MnZ (Z = Ge, Sn, Pb), Ni$_2$MnSn, Cu$_2$MnSn and Pd$_2$MnSn, and the connection between the electronic spectra and the magnetic interactions have been studied. Different mechanisms contributing to the exchange coupling are revealed. The band dependence of the exchange parameters, their dependence on volume and valence electron concentration have been thoroughly analyzed within the Green function technique.Comment: 9 figures, 6 table

Fabricación y caracterización de aleaciones porosas de Ti y Ti6Al4V producidas mediante sinterización con espaciador

[ES] El titanio es un material biocompatible que, además de presentar buenas propiedades a la corrosión, posee una elevada resistencia mecánica teniendo en cuenta su baja densidad. En el campo de la pulvimetalurgia, entre otras aplicaciones, este material se usa con objeto de obtener materiales porosos para aplicaciones biomédicas. Recientemente se ha investigado la aplicación de los materiales porosos en la fabricación de implantes de cadera. La razón principal está basada en la reducción de la rigidez de los implantes, lo cual minimiza los efectos del ¿apantallamiento de tensiones¿, al aproximarse su módulo elástico al del hueso. El propósito del presente trabajo, es producir materiales porosos mediante la técnica de sinterización con espaciador, usando el bicarbonato de amonio como propulsor de la formación de poros. Para la obtención de los mismos, se ha utilizado polvo de titanio de diferentes tamaños de partícula, usando diversas presiones de compactación. Antes de realizar la sinterización, se han evaluado las propiedades mecánicas de las muestras en verde, de modo que se permita su manipulación. Tras realizar la sinterización, se ha evaluado la densidad y porosidad. Igualmente, se ha valorado el efecto de estas variables en las propiedades mecánicas y el módulo elástico, obtenidos mediante el ensayo de flexión a tres puntos. La caracterización microestructural se ha realizado mediante microscopía óptica y electrónica.[EN] Titanium is well-known to be a biocompatible material with good corrosion properties and good strength, taking into account their low specific weight. In powder metallurgy field, titanium has been used in order to obtain porosity materials for biomedical applications. Recently, porous materials have been investigated for their use like hips implants. The principal reason is based on a reduction of stiffness implants, minimizing effects of stress shielding. The purpose of the present work is produced porous materials by space holder technique using ammonium bicarbonate like spacer. Scaffolds of titanium have been fabricated by powders of titanium with different grades of particle size and compacting pressure. Before sintering, stability of green parts has been studied by mechanical test. After sintering, porosity has been evaluated besides mechanical properties and elastic modulus by three points bending test. The microstructural characterisation is performed by optical and electron microscopy.Tojal Domenech, C.; Amigó Borrás, V.; J.A. Calero (2013). Fabricación y caracterización de aleaciones porosas de Ti y Ti6Al4V producidas mediante sinterización con espaciador. Revista de Metalurgia. 49(1):20-30. doi:10.3989/revmetalm.1206S2030491Montealegre-Melendez, I., Neubauer, E., & Danninger, H. (2009). Effect of starting powder grade on sintering and properties of PM titanium metal matrix composites. Powder Metallurgy, 52(4), 322-328. doi:10.1179/174329009x457117Eriksson, M., Andersson, M., Adolfsson, E., & Carlström, E. (2006). Titanium–hydroxyapatite composite biomaterial for dental implants. Powder Metallurgy, 49(1), 70-77. doi:10.1179/174329006x94591Schiefer, H., Bram, M., Buchkremer, H. P., & Stöver, D. (2009). Mechanical examinations on dental implants with porous titanium coating. Journal of Materials Science: Materials in Medicine, 20(8), 1763-1770. doi:10.1007/s10856-009-3733-1Amigó, V., Salvador, M. D., Romero, F., Solves, C., & Moreno, J. F. (2003). Microstructural evolution of Ti–6Al–4V during the sintering of microspheres of Ti for orthopedic implants. Journal of Materials Processing Technology, 141(1), 117-122. doi:10.1016/s0924-0136(03)00243-7[6] H.D. Kunze, Metal Powder Report 50 (1995) 36.Esen, Z., & Bor, Ş. (2007). Processing of titanium foams using magnesium spacer particles. Scripta Materialia, 56(5), 341-344. doi:10.1016/j.scriptamat.2006.11.010Robertson, I. M., & Schaffer, G. B. (2010). Swelling during sintering of titanium alloys based on titanium hydride powder. Powder Metallurgy, 53(1), 27-33. doi:10.1179/003258909x12502872942534Li, C. F., Zhu, Z. G., & Liu, T. (2005). Microhardness of pore walls in porous titanium prepared with novel powder metallurgy. Powder Metallurgy, 48(3), 237-240. doi:10.1179/174329005x64162Euh, K., Lee, J., Lee, S., Koo, Y., & Kim, N. J. (2001). Microstructural modification and hardness improvement in boride/Ti–6Al–4V surface-alloyed materials fabricated by high-energy electron beam irradiation. Scripta Materialia, 45(1), 1-6. doi:10.1016/s1359-6462(01)00981-2De Oliveira, M. V., Moreira, A. C., Appoloni, C. R., Lopes, R. T., Pereira, L. C., & Cairo, C. A. A. (2006). Porosity Study of Sintered Titanium Foams. Materials Science Forum, 530-531, 22-28. doi:10.4028/www.scientific.net/msf.530-531.22Azevedo, C. R. F., Rodrigues, D., & Beneduce Neto, F. (2003). Ti–Al–V powder metallurgy (PM) via the hydrogenation–dehydrogenation (HDH) process. Journal of Alloys and Compounds, 353(1-2), 217-227. doi:10.1016/s0925-8388(02)01297-5Esteban, P. G., Bolzoni, L., Ruiz-Navas, E. M., & Gordo, E. (2011). Introducción al procesado pulvimetalúrgico del titanio. Revista de Metalurgia, 47(2), 169-187. doi:10.3989/revmetalmadrid.0943Amigó, V., Reig, L., Busquets, D. J., Ortiz, J. L., & Calero, J. A. (2011). Analysis of bending strength of porous titanium processed by space holder method. Powder Metallurgy, 54(1), 67-70. doi:10.1179/174329009x409697Reig, L., Amigó, V., Busquets, D., & Calero, J. A. (2011). Stiffness variation of porous titanium developed using space holder method. Powder Metallurgy, 54(3), 389-392. doi:10.1179/003258910x12707304455068Bram, M., Schiefer, H., Bogdanski, D., Köller, M., Buchkremer, H., & Stöver, D. (2006). Implant surgery: How bone bonds to PM titanium. Metal Powder Report, 61(2), 26-31. doi:10.1016/s0026-0657(06)70603-8[20] R.M. German, Powder Metallurgy and Particulate Materials Processing, Metal Powder Industries Federation, New Jersey, USA, 2005, pp.121-260.[22] L.J. Gibson y M.F. Ashby, Cellular Solids: Structure and Properties, 2nd ed., Cambridge University Press, Cambridge, UK, 1997, pp. 175-231.[23] R.M. German, Powder Metallurgy Science, 2nd ed., Metal Powder Industries Federation, New Jersey, USA, 1994, pp.241-299.[24] R.M. German, G.L. Messing y R. G. Cornwall, Sintering Technology, Marcel Dekker inc., New York, USA, 1996, pp. 349-430.[2] E. Benavente-Martínez, F. Devesa y V. Amigó, Rev. Metal. Madrid 46 (Nº extra) (2010) 19-25.[7] G. Ryan, A. Pandit y D.P. Apatsidis, Biomaterials 27 (2006) 2.651-2.670.[9] C. Aparicio, F. J. Gil, A. Padrós, C. Peraire y J. A. Planell, Rev. Metal. Madrid 34 (Nº. extra) (1998) 184-189.[19] X. Zhao, H. Sun, L. Lan, J. Huang, H. Zhang y Y. Wang, Mater. Lett. 63 (2009) 2.402–2.404.[21] C. Tojal, J. Devaud, V. Amigó y J.A. Calero, Rev. Metal. Madrid 46 (Nº extra) (2010) 26-32.[25] C. Leyens y M. Peters, Titanium and Titanium Alloys. Fundamentals and Applications, ed.Wiley VchGmbh&Co., Weinheim, Alemania, 2003, pp. 423-424

Contact-less measurements of Shubnikov-de Haas oscillations in the magnetically ordered state of CeAgSb2_2 and SmAgSb2_2 single crystals

Shubnikov - de Haas oscillations were measured in single crystals of highly metallic antiferromagnetic SmAgSb$_{2}$ and ferromagnetic CeAgSb$_{2}$ using a tunnel diode resonator. Resistivity oscillations as a function of applied magnetic field were observed via measurements of skin depth variation. The effective resolution of $\Delta\rho\simeq20$ p$\Omega$ allows a detailed study of the SdH spectra as a function of temperature. The effects of the Sm long - range magnetic ordering as well as its electronic structure ($4f$-electrons) on the Fermi surface topology is discussed

Separation of suspended particles in microfluidic systems by directional-locking in periodic fields

We investigate the transport and separation of overdamped particles under the action of a uniform external force in a two-dimensional periodic energy landscape. Exact results are obtained for the deterministic transport in a square lattice of parabolic, repulsive centers that correspond to a piecewise-continuous linear-force model. The trajectories are periodic and commensurate with the obstacle lattice and exhibit phase-locking behavior in that the particle moves at the same average migration angle for a range of orientation of the external force. The migration angle as a function of the orientation of the external force has a Devil's staircase structure. The first transition in the migration angle was analyzed in terms of a Poincare map, showing that it corresponds to a tangent bifurcation. Numerical results show that the limiting behavior for impenetrable obstacles is equivalent to the high Peclet number limit in the case of transport of particles in a periodic pattern of solid obstacles. Finally, we show how separation occurs in these systems depending on the properties of the particles

Decay of the turbulent cascade of capillary waves on the charged surface of liquid hyrdrogen.

We study the free decay of capillary turbulence on the charged surface of liquid hydrogen. We find that the decay begins from the high frequency spectral domains of the surface oscillations and is of a quasi-adiabatic character. The characteristic relaxation time of the whole turbulent cascade is close to the viscous damping time for capillary waves of frequency equal to the driving frequency

Analysis of cosmic ray variations observed by the CARPET in association with solar flares in 2011-2012

The CARPET cosmic ray detector was installed on April 2006 at CASLEO (Complejo Astronmico El Leoncito) at the Argentinean Andes (31.8S, 69.3W, 2550 m, Rc=9.65 GV). This instrument was developed within an international cooperation between the Lebedev Physical Institute RAS (LPI; Russia), the Centro de Radio Astronomia e Astrofsica Mackenzie (CRAAM; Brazil) and the Complejo Astronmico el Leoncito (CASLEO; Argentina). In this paper we present results of analysis of cosmic ray variations recorded by the CARPET during increased solar flare activity in 2011-2012. Available solar and interplanetary medium observational data obtained onboard GOES, FERMI, ISS, as well as cosmic ray measurements by ground-based neutron monitor network were also used in the present analysis.Fil: Makhmutov, V.. Lebedev Physical Institute; Rusia. Universidade Presbiteriana Mackenzie; BrasilFil: Raulin, J. P.. Universidade Presbiteriana Mackenzie; BrasilFil: De Mendonca, R. R. S.. National Institute for Space Research; BrasilFil: Bazilevskaya, G. A.. Lebedev Physical Institute; RusiaFil: Correia, E.. Universidade Presbiteriana Mackenzie; Brasil. National Institute for Space Research; BrasilFil: Kaufmann, Pierre. Universidade Presbiteriana Mackenzie; BrasilFil: Marun, Adolfo Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Fernandez, German Enzo Leonel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Complejo Astronómico "El Leoncito". Universidad Nacional de Córdoba. Complejo Astronómico "El Leoncito". Universidad Nacional de la Plata. Complejo Astronómico "El Leoncito". Universidad Nacional de San Juan. Complejo Astronómico "El Leoncito"; ArgentinaFil: Echer, E.. National Institute for Space Research; Brasi

New pathomorphological classification of subdural hematomas

Objective to develop a pathomorphological classification of subdural hematomas, which reflects the aspects of their pathogenesis and time of occurrence that are important for forensic analysis. Materials and methods.The study is based on a prospective pathomorphological analysis of the qualitative evolution of 200 of subdural hematomas in closed and open non-penetrating craniocerebral trauma. Results.The new pathomorphological classification of subdural hematomas is developed. It takes into account a hierarchical sequence of hematoma characteristics: the presence and severity of organization; the genesis of encapsulation and resorption, and the mechanism of organization. Conclusion.The developed pathomorphological classification is recommended for use in the course of forensic or medical expert analysis of subdural hematomas