Vacuum Casting Research Articles

Research on vacuum-electromagnetic casting of IN100 superalloy ingots

In order to improve the inner quality of superalloy master alloy ingots, the new technology of superalloy vacuum-electromagnetic casting, i.e. applying electromagnetic stirring (EMS) to the solidification process of superalloy vacuum casting was developed. The effect of EMS on the inner quality of IN100 superalloy ingots was studied with EPMA and optical microscope. The results show that while an EMS with 50 Hz frequency and 60 A current is imposed, the equiax crystals of IN100 superalloy ingots can be effectively refined and increased, and the central shrinkage porosity and the dendritic segregation of IN100 superalloy ingots are greatly reduced, so the inner quality of IN100 superalloy ingots is obviously improved.

Elastomeric inverse moulding and vacuum casting process characterization for the fabrication of arrays of concave refractive microlenses

We present a complete and precise quantitative characterization of the different process steps used in an elastomeric inverse moulding and vacuum casting technique. We use the latter replication technique to fabricate concave replicas from an array of convex thermal reflow microlenses. During the inverse elastomeric moulding we obtain a secondary silicone mould of the original silicone mould in which the master component is embedded. Using vacuum casting, we are then able to cast out of the second mould several optical transparent poly-urethane arrays of concave refractive microlenses. We select ten particular representative microlenses on the original, the silicone moulds and replica sample and quantitatively characterize and statistically compare them during the various fabrication steps. For this purpose, we use several state-of-the-art and ultra-precise characterization tools such as a stereo microscope, a stylus surface profilometer, a non-contact optical profilometer, a Mach–Zehnder interferometer, a Twyman–Green interferometer and an atomic force microscope to compare various microlens parameters such as the lens height, the diameter, the paraxial focal length, the radius of curvature, the Strehl ratio, the peak-to-valley and the root-mean-square wave aberrations and the surface roughness. When appropriate, the microlens parameter under test is measured with several different measuring tools to check for consistency in the measurement data. Although none of the lens samples shows diffraction-limited performance, we prove that the obtained replicated arrays of concave microlenses exhibit sufficiently low surface roughness and sufficiently high lens quality for various imaging applications.

Vacuum casting to manufacture a plastic biochip for highly parallel cell transfection

A novel polymer microarray fabrication technique is presented and applied to the realization of a biochip for highly parallelized cell transfection. The proposed microfabrication technique is derived from a macroscale rapid prototyping technique called vacuum casting. It was optimized to reduce production cost, in order to produce small series (100–10 000 chip series) of chips to meet demand in today's market of cellulomics. Microfabrication technologies and rapid prototyping technologies are combined to shape the master part, which can thus involve microsized features. The corresponding female structure is moulded in a flexible silicone material. The duplicated polymer chips are obtained by casting a thermosetting plastic under vacuum. The dimensional replication accuracy between the master part and the duplicated parts is uniform over the duplicated parts and better than 1%. Advantages of the proposed technique over existing plastic microfabrication techniques are discussed in the paper. Using this microfabrication technique, we produced a plastic biochip for highly parallelized transfection of arrays of living cells. The feasibility of parallel lipofection was demonstrated: two different plasmids encoding, respectively, eGFP and DsRED2 were inserted into HEK293T cells. The transfection was monitored through fluorescence observation after 72 h showing successful expression of both genes.

2501: Intra-Fraction Patient Displacement During Image-Guided Stereotactic Body Radiation Therapy (IGSBRT) for Lung Treatment

To evaluate the intra-fraction displacement in image-guided stereotactic body radiation therapy (IGSBRT) for the treatment of lung lesions. An IGSBRT program for the treatment of lung lesions has been implemented at the University of Florida. A total dose of 48 Gy is given in 4 fraction treatments (i.e., 12 Gy/fx). For immobilization, patients are first fit into a Medical Intelligence BlueBAGTM vacuum mold with negative pressure of approximately 700 psi. A plastic sheet is draped over the patient and sealed to the Blue Bag, and negative pressure of about 70 psi is continuously applied to suppress patient motion during the treatment procedure. Finally, a fabric band (about 15 cm wide) is wrapped around the patient’s abdomen; the bladder of blood pressure cuff is placed underneath the band at the level of the epigastrium. The bladder is filled to approximately 40 psi pressure for patient discomfort to further minimize breathing motion. Treatment planning is made based on the internal target volume (ITV) obtained from a 4D computed tomography (CT) simulation. For image-guided initial patient setup, an on-board KV image system of Elekta Synergy® S linear accelerator is used. Once the patient is manually aligned, a volumetric cone-beam CT image (ini-CT) is acquired and registered to the reference CT image based on bony anatomy (typically the vertebral body closest to the target) to obtain the amount of adjustment needed. A precise translational adjustment is made using Medical Intelligent HexaPOD™ 6D Robotic Treatment CouchTOP. Another volumetric cone-beam CT image set is obtained at the end of treatment (end-CT). Intra-fractional patient displacement from the initial treatment setup was evaluated by analyzing end-CT image data. For the first 8 cases, mean lateral, longitudinal, vertical, and overall displacements between ini-CT and end-CT were 0.5±0.6, 0.8±0.8, 0.7±0.7, and 1.5±0.9 mm, respectively. Mean treatment time as measured from ini-CT to end-CT was 22±9 min. Considering setup and walk-in/out time, an hour treatment slot is assigned for this procedure. The immobilization technique that is used at the University of Florida for lung IGSBRT is effective in minimizing patient intra-fraction displacement.

Dimensional accuracy analysis of implant framework castings from 2 casting systems

<h3>Purpose</h3> To compare the dimensional accuracy of implant framework castings from an argon vacuum casting machine with those from a centrifugal casting machine. <h3>Materials and Methods</h3> Three 4 × 10-mm external hex-type implants (3i/Implant Innovations) were embedded in an acrylic resin block 7 mm apart, with a 2 mm offset of the middle implant. Eight reference points were marked on the implant collars. Twenty implant bar frameworks were waxed with UCLA abutments, invested with a ringless system, and subjected to the same thermal cycle. Ten wax patterns were cast in gold alloy using an oxygen-propane torch and centrifugal casting system; 10 were cast using an argon vacuum casting machine (KDF; Denken). The White 1-screw technique was applied after sequentially tightening the mesial and distal abutment screws to 10 Ncm. Fit of the implant framework castings was evaluated by measuring the marginal opening between the casting and implant at the reference points. These measurements were averaged and statistically compared for differences. <h3>Results</h3> The mean marginal openings at the most distant measuring locations from the tightened retaining screw at location 1 was between 44 and 48 μm for the centrifugal system compared to between 28 and 32 mm for KDF (<i>P</i><.01). For screws tightened at location 3, the mean marginal openings at the most distant measuring locations were between 40 and 51 mm for the centrifugal system compared to between 27 and 29 μm for KDF (<i>P</i><.01). <h3>Discussion</h3> In comparison with the centrifugal casting and oxygen-propane system, the argon vacuum system was more accurate and user friendly and less technique-sensitive. <h3>Conclusion</h3> The argon vacuum casting machine tested produced more accurate, better-fitting implant-supported prosthesis frameworks than a conventional centrifugal casting system. The "1-screw" method of evaluating casting fit was most effective when either of the prostheses' end screws were tightened.—<i>Reprinted with permission of Quintessence Publishing.</i>

Synthesis and Rietveld Analysis of Zn4‐xCdxSb3 Bulk Crystals in the Zn‐Rich Region.

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Close Packing in Crystals of Cyanophenylene/Thienylene Derivatives

A new molecule, designed as a potential active material in field effect transistor (FET) devices and constituted by p-cyanophenylene and -thienylene residues, has been synthesized and characterized by electrochemical, photophysical, and structural points of view. Its crystal structure, derived from powder XRD data, displays higher close packing as compared with molecular crystals constituted by similar residues. The crystallization aptness has been demonstrated by growing solid films, from 15 nm to 2 μm thick, using high vacuum depositions, casting, and spin coating techniques. AFM investigation shows well formed needles, univocally oriented with respect to the substrate. The HOMO/LUMO levels, matching the electrode working function, the film orientation, and the close packing, suggest its promising use as an active layer in FET devices.

Institute of Iron and Steel Technology at the TU Bergakademie Freiberg

The Institute of Iron and Steel Technology was founded more than 130 years ago. In the 90s and in the last years the institute was equipped with modern devices for vacuum melting, casting and heat treatment, the slag laboratory was enlarged, the analytic laboratory completed and the material development and metallography were strengthened with new instruments. The large range of research fields allows to meet industrial needs from process metallurgy over casting and solidification to control of microstructure and resulting material properties. Besides research with industrial partners the basic research is a strong motor for future practice.

Vacuum casting, a new answer for manufacturing biomicrosystems

In this work, the vacuum-casting process is pushed to its dimensional limits thanks to microfabricated original parts. The successful replication of those parts with a slightly adapted vacuum-casting process demonstrates that this technique is suitable for biomicrosystem manufacturing and development.

Microstructural Investigation of Hard Phases in As-Cast Ni-Ti Memory Alloy

Abstract Ti4Ni2O, Ti4Ni2N, TiC and Ti2Ni are brittle compounds usually formed during production and processing of the Ti-Ni SMA alloys. These compounds adversely affect on workability and shape memory properties of the alloy. This paper presents most recent findings related to the morphologies of various inclusions and Ti-Ni phases formed during and after vacuum induction melting and casting of Ti-45wt.% Ni material. Cast samples were mechanically and/or electrolytically polished and etched. Extensive optical and scanning electron microscopic studies were carried out to characterize the composition and microstructure of the as cast Ti-Ni alloys. Results indicated that mechanical polishing followed by etching was not proficient to reveal sufficient data on physical specifications and morphological changes of the born brittle oxide and nitride and carbide phases. An innovative set of electropolishing/etching conditions was, therefore, prescribed to yield detailed information on morphologies of the brittle phases. Experimental conditions were devised for characterization of the Ti2Ni precipitates, as well.

Synthesis and Rietveld analysis of Zn 4 − xCd xSb 3 bulk crystals in the Zn-rich region

A series of nine bulk crystals of the Zn 4 − x Cd x Sb 3 compounds ( x = 0–2.00 with 0.25 step) has been successfully synthesized and the detailed crystal structure has been refined by powder XRD study using the Rietveld method including the quantitative analysis. The substitution limit of the Cd atoms for the Zn 4 − x Cd x Sb 3 system has been extended to x = 2.00 by employing the vacuum casting method without annealing. The purities and densities of the bulk crystals exceeded approximately 96 mass% and 95% of XRD density, respectively. The lattice parameters of the a and c-axes in the system increase linearly with increasing Cd content x with obeying the Vegard law.

EBSD and XRM of Phases in Vacuum Cast Composite Alloys

Introduction There have been a number of new processes developed that allow the joining of very dissimilar materials such as titanium alloys, wear resistant white irons, cast irons and ceramic materials to ferrous (mild steel) and non-ferrous (aluminium) alloys. These new processes have allowed the development of more complex composite shapes to be produced. However, with any new process development, an understanding of the mechanism of bonding is required. Through the use of x-ray mapping (XRM), chemical phase imaging as well as electron back scattered diffraction (EBSD) analysis, very useful information on the mass transport across the interface as well as phase segregation, texture variations and phase distribution within the bond interface can be obtained. Results from this investigation on a number of bonded materials are presented and the importance of XRM and EBSD in providing a better understanding of the physical and chemical processes involved in metallurgical bonding/welding of dissimilar materials discussed.

Microstructures and mechanical properties of Fe 3Al-based Fe–Al–C alloys

In this paper results on the microstructures and mechanical properties of Fe 3Al-based Fe–Al–C alloys with strengthening precipitates of the perovskite-type κ-phase Fe 3AlC x are presented. The alloys are prepared by vacuum induction melting and cast into Cu-moulds. The composition of the Fe 3Al matrix of the investigated Fe–Al–C alloys varies between 23 and 29 at.% Al. The ternary C-additions range from 1 to 3 at.%. The microstructures of the alloys are characterised by means of light optical microscopy (LOM). Phase identification is performed by means of X-ray diffraction (XRD). The strength of the alloys as a function of temperature is determined through compression tests. The room-temperature ductility is evaluated by tensile tests. The fracture surfaces of the tensile specimens are analysed using scanning electron microscopy (SEM).

A laboratory scale moulding technique to fabricate high precision 2D columnar and honeycomb structures

Two-dimensional columnar structures as well as honeycomb hole structures for electromagnetic bandgap (EBG) applications in the microwave range are generated by vacuum moulding of a specially designed wax feedstock of high alumina loadings into a polyethylene wax mould. Its counterpart, honeycomb hole structures, are produced by usage of silicone rubber moulds. The structured ceramic parts with an aspect ratio of about 4 show an Archimedes-type density of about 97.0%. Damages on the sample's structures that could occur during demoulding/debinding were minimized by the adjustment of the mould material to the feedstock system, the implementation of a suitable moulding technique and an optimisation of the thermal wax burnout process. The processing technique describes a route to obtain ceramic structures of high precision with a minimum of technical requirements.

Effect of casting technique on surface roughness and consequent mass loss after polishing of NiCr and CoCr base metal alloys: a comparative study with titanium

Statement of problem Surface roughness of cast metal frameworks may lead to difficulties in finishing or polishing procedures and weaken the framework. Purpose The aim of this study was to assess the surface roughness of 2 base metal alloys, submitted to different casting techniques, to determine the influence of surface roughness on loss of mass after polishing compared to commercially pure titanium castings. Material and methods Forty disk-shaped wax patterns (8 × 2 mm) were randomly assigned to 5 groups (n=8): (1) CoCr alloy (Wironit), acetylene-oxygen flame casting (WFC), (2) NiCr alloy (Verabond II), acetylene-oxygen flame casting (VFC), (3) CoCr alloy, vacuum casting (WVC), (4) NiCr alloy, vacuum casting (VVC), and (5) commercially pure Ti alloy (Ti) melted by electric arc in argon gas atmosphere. WFC and VFC served as controls. Both NiCr and CoCr alloys were invested in phosphate-bonded investment (Termocast). Ti was invested in ammonium dihydrogen phosphate (Rematitam Plus). The wax patterns and casting techniques were standardized. All specimens were cleaned with airborne-particle abrasion (aluminum oxide). Surface roughness (Ra) was assessed using a surface-test analyzer at 3 different sites. To evaluate the loss of mass, the specimens were weighed on a precision balance, then polished with 150-600 grain sandpaper until clinically acceptable (minimum roughness of 0.09 μm). The specimens were then reweighed. A 1-way analysis of variance (ANOVA) and Tukey HSD test (α=.05) were performed. Results Statistical analysis showed that VVC and WVC had significantly ( P=.0050; P=.0057) smoother surfaces (2.43 ± 0.53 and 2.23 ± 0.49, respectively) than VFC and WFC (2.99 ± 0.44 and 2.83 ± 0.61, respectively), but were not significantly different from Ti (2.49 ± 0.62). The loss of mass (in %) was not significantly different for any group (3.18 ± 0.72, 3.14 ± 0.93, 3.36 ± 1.05%, and 4.14 ± 1.28% for VVC, WVC, VFC, and WFC, respectively). The mass loss of Ti was 4.32 ± 1.16. Conclusion Within the limitations of this study, the base metal alloys submitted to vacuum casting showed decreased surface roughness, similar to that of titanium, compared to base metal alloys submitted to acetylene-oxygen flame casting. There were no significant differences in loss of mass after polishing for all tested specimens.

Structured oxide ceramics by a sodium chloride moulding technique

Moulding is becoming a powerful technique for the fabrication of structured ceramic microcomponents. The aspect ratio of the structures to be produced has always been a limiting factor for the applicability of moulding techniques. A vacuum moulding process was developed to supply high aspect ratio ceramic structures. Special designed paraffin wax feedstocks based on alumina and sodium chloride moulds were used for the patterning of periodic columnar structures of some centimeter extension with columns of some millimeter height and an aspect ratio of more than 11. It is shown that the processing technique described features a route to obtain ceramic structures of high precision with a minimum of technical requirements.

Elemental development of beryllide electrode for pebble production by rotating electrode method

Beryllide (Be 12Ti) is being considered one of the promising candidates for advanced neutron multipliers. In order to realize the pebble production, a vacuum casting process has to be applied. In the present study, an elemental technology to fabricate beryllide rods by a vacuum casting was developed. There were two major technical subjects to realize this process. The first was to identify a furnace material that shows minimum chemical reaction with beryllide. Another was to develop a procedure to cast durable ingot without any shrinkages and cracks. Reactivity between Be 12Ti melt and refractory materials such as CaO, MgO and BeO was tested. It was clarified that the BeO crucible had less reactivity with melt and no contamination. Casting tests with a MgO cylindrical mold in a vacuum chamber revealed that the mold dimension was critical to minimize shrinkages and cracks. From this study, elemental technologies to be developed were made clear.

Rapid Prototyping models for surgical planning with hard and soft tissue representation

This paper presents a new approach to build medical models for surgical planning with realistic haptic and optical representation of different types of tissue. This new kind of combined anatomical models is realized by applying different Rapid Prototyping (RP) techniques. Based on medical datasets, preferably computer tomography (CT) scans of the affected region, both soft and hard tissue structures are reconstructed. A stereolithography apparatus builds the hard tissue models and the vacuum casting technique allows to manufacture realistic representations of soft tissues.

Composite rapid prototyping: overcoming the drawback of poor mechanical properties

Stereolithography and vacuum casting are two well-established techniques for producing complex parts for rapid prototyping purposes. Although they have been used across a wide range of industrial sectors, parts fabricated by those techniques exhibit weak mechanical properties hindering thus their further application as functional prototypes under loading conditions. This paper investigates the effects of the addition of nonwoven glass fibre mats, and of various thicknesses, on the mechanical properties of laser solidified and vacuum moulded specimens. The test specimens were fabricated using an epoxy-based photopolymer for the stereolithography and a polyurethane resin for the vacuum casting process, correspondingly. Embedment/bonding issues of the reinforcing mats are discussed, while comparisons of the mechanical properties between nonreinforced and their fibre mat reinforced counterparts are also presented. Experimental results show that fibre mat addition yields higher measured tensile properties, with the most pronounced improvements obtained for the reinforced polyurethane specimens.

Filling system for investment cast Ni-base turbine blades

In investment foundries, it is usual to pay relatively little attention to the design of the filling system of a casting. Vacuum-cast turbine blades represent a typical case, where the mould filling process is poorly controlled, the mould cavities themselves often being top-filled. The consequential surface turbulence causes the entrapment of oxide film on the liquid surface, despite the use of vacuum melting and pouring. In this work, bottom filling principles were used to minimize turbulence. X-ray radiographic video was used to observe and compare the filling of both bottom- and top-filled moulds. Ni-based alloy investment-cast blades melted and cast in vacuum clearly validated the bottom filling design. Compared to conventional top filling in vacuum, dye penetrant indications were reduced by approximately a factor of 10, and hot cracking appeared to be eliminated.