Investment shell cracking

Shell cracking is the single greatest problem affecting investment casters. A clearer understanding of the factors affecting the melt profile of the wax can be gained using computational fluid dynamics (CFD) to model the interaction among 1) the thermal conductivity of the wax, 2) the thermal conductivity of the shell, and 3) the temperature of the autoclave during the autoclave de-waxing cycle. The most favorable melt profile results from a high autoclave temperature (438⁰K to 458⁰K) and saturated thermal conductivity of the shell (1.36 to 1.40 Wm⁻¹k⁻¹) in conjunction with a low wax thermal conductivity (0.33 Wm⁻¹k⁻¹). These parameters reduce the likelihood of shell cracking as a result of wax bulk expansion --Abstract, page iv

A Comparison of Binder Burnout and Mechanical Characteristics of Printed and Chemically Bonded Sand Molds

Various material systems have been created for Binder Jetting of sand molds; however, a formal analysis comparing the materials to commonly used foundry molding materials has not been conducted. In this paper the authors investigate potential differences in the material properties from four different commercially available binders systems for chemically bonded sand molds. Specifically, the authors compared the binder burnout characteristics and the tensile strength of sand created by 3D printing and conventional chemically bonded molding materials. Increased binder content can strengthen the mold but have adverse effect on part quality. Understanding the binder characteristics of printed molds are essential due to the potential defects from large amounts of gas generated from binder while pouring molten metal.Mechanical Engineerin

The Effects on 3D Printed Molds on Metal Castings

Additive manufacture of sand molds via binder jetting enables the casting of complex metal geometries. Various material systems have been created for 3D printing of sand molds; however, a formal study of the materials’ effects on cast products has not yet been conducted. In this paper the authors investigate potential differences in material properties (microstructure, porosity, mechanical strength) of A356 – T6 castings resulting from two different commercially available 3D printing media. In addition, the material properties of cast products from traditional “no-bake” silica sand is used as a basis for comparison of castings produced by the 3D printed molds.Mechanical Engineerin

Role of Stem Cells in Human Uterine Leiomyoma Growth

Uterine leiomyoma is the most common benign tumor in reproductive-age women. Each leiomyoma is thought to be a benign monoclonal tumor arising from a single transformed myometrial smooth muscle cell; however, it is not known what leiomyoma cell type is responsible for tumor growth. Thus, we tested the hypothesis that a distinct stem/reservoir cell-enriched population, designated as the leiomyoma-derived side population (LMSP), is responsible for cell proliferation and tumor growth.LMSP comprised approximately 1% of all leiomyoma and 2% of all myometrium-derived cells. All LMSP and leiomyoma-derived main population (LMMP) but none of the side or main population cells isolated from adjacent myometrium carried a mediator complex subunit 12 mutation, a genetic marker of neoplastic transformation. Messenger RNA levels for estrogen receptor-α, progesterone receptor and smooth muscle cell markers were barely detectable and significantly lower in the LMSP compared with the LMMP. LMSP alone did not attach or survive in monolayer culture in the presence or absence of estradiol and progestin, whereas LMMP readily grew under these conditions. LMSP did attach and survive when directly mixed with unsorted myometrial cells in monolayer culture. After resorting and reculturing, LMSP gained full potential of proliferation. Intriguingly, xenografts comprised of LMSP and unsorted myometrial smooth muscle cells grew into relatively large tumors (3.67 ± 1.07 mm(3)), whereas xenografts comprised of LMMP and unsorted myometrial smooth muscle cells produced smaller tumors (0.54 ± 0.20 mm(3), p<0.05, n = 10 paired patient samples). LMSP xenografts displayed significantly higher proliferative activity compared with LMMP xenografts (p<0.05).Our data suggest that LMSP, which have stem/reservoir cell characteristics, are necessary for in vivo growth of leiomyoma xenograft tumors. Lower estrogen and progesterone receptor levels in LMSP suggests an indirect paracrine effect of steroid hormones on stem cells via the mature neighboring cells

Diffusion-Controlled Decohesion Using a Cu-Sn Alloy as a Model System

This research deals with a mode of brittle intergranular fracture in which a surface adsorbed embrittling element is driven into a grain boundary as a result of the application of a tensile stress across the boundary. A Cu-8%Sn alloy has been employed to explore this phenomenon, since tin is a surface-active element, and this alloy is known to suffer intergranular weakness at elevated temperatures. Intergranular cracking occurred by brittle, discontinuous crack advance at 265{degrees}C in vacuum with an average rate of 0.1{mu}m/sec. This behavior is analogous to sulfur-induced stress-relief cracking in steels and several cases of liquid-metal embrittlement, suggesting that this phenomenon has a generic nature

Mechanical and Material Properties of Castings Produced via 3D Printed Molds

Additive manufacture of sand molds via binder jetting enables the casting of complex metal geometries. Various material systems have been created for 3D printing of sand molds; however, a formal study of the materials’ effects on cast products has not yet been conducted. In this paper the authors investigate potential differences in material properties (microstructure, porosity, mechanical strength) of A356 – T6 castings resulting from two different commercially available 3D printing media. In addition, the material properties of cast products from traditional “no-bake” silica sand is used as a basis for comparison of castings produced by the 3D printed molds. It was determined that resultant castings yielded statistically equivalent results in four of the seven tests performed: dendrite arm spacing, porosity, surface roughness, and tensile strength and differed in sand tensile strength, hardness, and density

Lightweight Metal Cellular Structures via Indirect 3D Printing and Casting

Cellular materials offer high strength accompanied by low-density and can offer high stiffness, good impact-absorption, and thermal and acoustic insulation. In this paper, the authors describe their progress towards exploring the use of metal casting into 3D printed sand molds for creating cellular materials and sandwich panels. The use of 3D printing allows for the fabrication of sand molds without the need for a pattern, and thus enables the creation of cellular structures with designed mesostructure from a bevy of metal alloys. The quality-of-fill results for several cast aluminum cellular parts of varying geometry are presented in this paper, along with a discussion of overall truss diameter variation.Mechanical Engineerin

Fabrication of Cellular Cordierite Performs via Binder Jetting

Metal Matrix Composites (MMCs) combine two dissimilar materials – a metal as the matrix and a ceramic as the charge or insert to provide unique properties, e.g. low density, high specific strength, high specific modulus, and wear resistance. The ceramic inserts in these composite materials are limited to ceramic fibers and open cell stochastic ceramic foams due to geometric constraints imposed by traditional manufacturing processes. The geometric design freedom offered by Additive Manufacturing (AM) could enable a designer to realize ceramic preforms with complex cellular geometries that are designed to achieve multiple functions (e.g., low mass and increased stiffness). The goal of this work is to explore the use of Binder Jetting as a means of fabricating cordierite parts of designed mesostructure for use as ceramic preforms for MMCs. In this paper, the authors describe their exploration of the appropriate printing process parameters and post-process sintering parameters that enable successful fabrication of complex cordierite artifacts. Measurements of bulk density, linear shrinkage, porosity, and x-ray diffraction are conducted on pre- and post-sintered printed cordierite structures.Mechanical Engineerin

Design of Fiber-Reinforced Cellular Structures with Tensegrity Behavior Manufactured Using 3D Printed Sand Molds

Tensegrity structures provide a high stiffness to mass ratio since all the comprising elements are either in compression or tension. However, they have limited applications since fabrication of such structures is challenging due to their complexity and mainly requires manual assembly of components. The authors look to Additive Manufacturing (AM) as a means to introduce tensegrity behavior in cellular structures to enhance structural performance. Specifically, octet cellular structures are created by casting aluminum into 3D-printed sand molds embedded with continuous wires. In this paper, the authors describe design and analysis of octet cellular structures that feature high strength fibers held in continuous tension. Finite element analysis of 4- point bending test is used to evaluate the effectiveness of embedded fibers. Also, the presence of tensegrity behavior was evaluated using this analysis and testing. The structure with tensegrity behavior was found to be 30 % stronger. The simulation and experimental results were shown to match within 6 % error in the elastic region.Mechanical Engineerin