Investment Molds Research Articles

Role of silicon carbide in enhancing microwave hybrid heating and reducing dewaxing time in investment casting

Mould cracking is a common problem in investment casting (IC) that occurs during the dewaxing process, which is caused by the difference in thermal expansion between the wax pattern and the ceramic mould. Therefore, appropriate modifications to the mould, waxes and hybrid heating of the materials are proposed to address this problem. This study aims to investigate the effects of silicon carbide (SiC) addition on dewaxing time and mould structural defect in two different waxes (HYFILL B289 MOD S and SIVUCH L1203) under microwave hybrid heating. For the mould fabrication, stucco (Al2O3-SiO3) was added with various amounts of SiC to improve microwave heat absorption capabilities. The modified stucco was applied on layers 3–6 to ensure that the mould was more durable and suited for the casting process. The thermal expansion of the waxes and the ceramic mould was evaluated to determine its thermal expansion mismatch. The density, porosity, thermal conductivity, and dielectric properties were characterized to evaluate the properties of modified green mould. The results showed that SIVUCH L1203 wax outperformed HYFILL B289 MOD S wax, in obtaining a crack-free ceramic investment mould with a clean internal surface. This superiority is attributed to the exceptional thermal and absorption properties of the SIVUCH L1203 wax. Furthermore, the incorporation of SiC played a pivotal role in enhancing the hybrid heating process while maintaining the density and porosity of the green moulds. This was evident by the remarkable reduction of dewaxing time by 62% with 7.5% of SiC addition, which also contributed toward improving energy savings and sustainability.

Monitoring the effect of alloying elements segregation in Fe Mn Ni Al high Entropy alloy

Iron based high entropy alloy containing aluminum is facing a challenge in the liquid-solid transition regime due to its high affinity to segregation. In this research, the segregation of alloying elements in the designed high entropy alloy has been tracked after pouring in special investment mold that possesses different modulus with fluctuated solidification time. Different compositions of the targeted alloy were developed through melting of pure metals in induction furnace. X-ray Fluorescence (XRF), optical microscope, and SEM have been used for monitoring the chemical, and phase constituents among the different regions of solidification. In addition, the mechanical properties of the designed alloy have been determined using uni-axis tensile test, and impact toughness. It was well proved that the solidification time has a significant effect on promoting the characteristic properties of iron based high entropy alloy containing aluminum. Aluminum shows high percentage with increasing the solidification time. In addition, the mechanical observations proved that decreasing the solidification time enhance and improve the mechanical properties.

New process solutions in the manufacture of thermochemically resistant ceramic molds for casting titanium alloys

The paper provides the results of studies on interaction between titanium melts and silica-containing investment molds. Pure silicon, compounds of titanium oxides and silicides were detected by X-ray diffraction analysis in the contact zone. The problem of the negative impact exerted by the mold on the casting is solved by using thermally stable and chemically resistant monocorundum molds based on an alumina sol binder. A refractory suspension was developed for investment casting containing special additives to improve wax mold wetting with the suspension, and to increase the mold shell strength. The article studies sedimentation properties of suspension. A method was developed for accelerated curing of sequentially applied refractory suspension layers by vacuum drying and subsequent chemical curing with a gaseous reagent. The formation time is reduced from 3–5 h to 20–30 min per layer. Comparative studies of kinetics of alumina sol binder convective drying and vacuum dehydration were conducted. The process of moisture removal per unit surface of the applied refractory layer in a vacuum of 5–10 kPa increases by 2–6 times. X-ray phase analysis was used to study the alumina sol conversion during high-temperature heating. The solid gel of the α-Al2O3 stable phase is obtained in the alumina sol mold shell when the calcination temperature rises to 1300–1350 °C with a sufficient strength of 9–12 MPa provided by sintering additives added to the suspension. Recommendations are given for additional protection of refractory ceramic layers after vacuuming and drying: treatment of the last layer with gaseous curing agents and application of a polyvinylacetal solution with a density of 1100–1200 kg/m3. The process solutions proposed will make it possible to increase both the efficiency of titanium alloy forming and casting processes and the quality of castings.

ИССЛЕДОВАНИЕ ЭФФЕКТИВНОСТИ РАБОТЫ КОНФОРМНЫХ КАНАЛОВ ОХЛАЖДЕНИЯ КОМПОЗИТНЫХ ПРЕСС-ФОРМ

The article deals with the issue of evaluating the performance of a composite metal-metal-polymer mold. The use of a composite mold, including a forming plate consisting of a metal, and a metal polymer introduced with a low cooling efficiency of such a mold. For this reason, it is important to develop technological solutions that ensure the efficient operation of the cooling system. The article provides mathematical calculations of the required amount of heat flow when molding thermoplastics into a mold. Further, based on the calculated data, a study is made using finite elements of the thermal conductivity of the metal-polymer part. The design of the composite forming plate of the mold described in the article involves the manufacture of a cooling channel profile as close as possible to the forming part of the mold and located in the metal-polymer part. Based on the analysis of the temperature viscosity of the metal-polymer part of the mold, conclusions and recommendations are given for the design of a curved investment mold. It allows designers to calculate the optimal geometric parameters of the cooling system. The design and manufacture of conformal cooling stages in the metal-polymer part is likely to be preferable for cooling the forming part of the mold by bringing the cooling reversal surface closer to the surface of the forming mold, resulting in increased durability and productivity of the composite mold.

On effect of friction between support filler and ceramic shell investment mould on its stress state during casting and cooling of steel casting

The results of a theoretical study of the regularities for change in the stress state of a cast multilayer shell investment mould during the cooling of a steel casting in it with a change in friction between the shell mould and the support filler, as well as friction between the layers in the shell mould itself.

Formation and Prevention of a Surface Defect on the Aerofoil of As‐Cast Nickel‐Based Single‐Crystal Turbine Blades

Surface scale is a common casting defect covering up to one‐third of the aerofoil on as‐cast single‐crystal turbine blades. To better understand and control this scale, the scaled and unscaled regions on the surface of a blade are observed. The surface of the unscaled region is covered with a relatively thick and uniform aluminum oxide layer. In comparison, the surface of the scaled region shows a different morphology, which is mainly composed of two different regions: one is a tessellated region with irregular polygons and the other with many irregular lines. The cross‐section and transmission electron microscopy samples of the scaled region clearly show that the surface is covered with double oxide layers of thickness 300–500 nm composed of several metallic oxides, which form after the normal microstructure of the base material during solidification. A specific region, which is in contact with the investment mold but remains in the scaled part, shows the possibility of this scale formation through the reaction of the initial aluminum oxide/mold wall material and the oxidation of the fresh surface of the base material. Based on these observations, the formation mechanism and the prevention of the surface scale are discussed.

Modeling and Simulation of Heat Transfer Phenomenon Related to Mold Heating during Investment Casting

Cast shape during investment casting process dictates properties and service life of the casting. These properties are the function of cast part parameters (both static and dynamic), part geometry and hence mold geometry, nature and type of metal being cast, properties (extrinsic and intrinsic) and processing parameters (rate of heating, rate of cooling, rate of pouring). Improper and inadequate manipulation and modification of mold properties degrade the properties and life of casting altogether. A mathematical model is developed using standard transport equations incorporating all heat transfer coefficients (HTCs) to determine the effect of external mold heating on the properties of the final casting and a simulation is performed in C++ to validate it against experimental results. Pure iron is casted in investment molds of silica sand with zircon coating. Airflow near the mold surfaces was partially restricted due to geometry of the molds and arrangement of the pieces around a tree. The variations in heat transfer coefficient contribute towards total heat transfer out of mold surface. External heating is found to be very effective for improved casting properties. The mold heat transfer profile is found to be in good agreement with experimental values validating the effectiveness of mold heating.

CAD-CAM assisted investment casting for preparation of dental crowns

This paper highlights detailed procedure for preparation of dental crowns (DC) by CAD-CAM assisted investment casting (IC) as a case study. Along with biocompatibility and bioactivity required for DC, it must possess good surface finish (required for aesthetic sense), acceptable dimensional accuracy (required for assembly purposes) and good surface hardness (required while chewing). In this paper efforts were made for improving surface hardness, finish, and dimensional accuracy of DC by controlling composition/proportion of Ni and Cr in IC process. Further in this case study stir casting (SC) assisted Ni and Cr based metal matrix composites (MMC) has been prepared in investment mould. The result of study reveals that different material composition influenced the microstructure and the hardness of the MMC prepared. Further with change in weight percentage of Ni and Cr, different microstructures with particle clustering was observed. The results are also supported with 3D rendered images.

Partially stabilized zirconia moulds fabricated by stereolithographic additive manufacturing via digital light processing

Partially stabilized zirconia (PSZ) moulds for aluminium casting were fabricated by stereolithographic additive manufacturing via digital light processing (DLP). Green parts were fabricated on DLP equipment using curable ceramic suspension. These suspensions were studied by performing photopolymerisable and rheological characterisations. Thermogravimetry (TGA) was used to analyse thermal stability of the suspension. Phase composition of sintered parts was determined by X-ray diffraction (XRD), while mechanical properties of green and sintered parts were studied by three-point bending testing. Flexural strength and Young's modulus of sintered parts were determined to be 803.7 ± 59 MPa and 203.4 ± 17 GPa, and these values decreased to 41.5 ± 3.9 MPa and 3.1 ± 0.3 GPa for green parts, respectively. Large pores were suggested to originate failure, with fracture mode being predominantly intergranular. Finally, sintered ceramic investment moulds were prepared by stereolithography and subsequently used for aluminium casting purposes. Dimensions of green parts before sintering were about 0.5% smaller than design values within the plane of layers, and approximately 0.5% larger than design values perpendicular to the layers. Sintering shrinkage was around 22% in both directions. Surface roughness of sintered moulds and aluminium casting materials were quantitatively determined by profilometry.

Manufacturing of Herringbone Gear Model by 3D Printing Assisted Investment Casting

3D printing technology and investment casting are used to manufacturing of a herringbone gear. Four kinds of gating system are designed and the numerical simulation of the four gating systems are executed. It is determined that the optimal casting mode of herringbone gears is the top casting system. Subsequently, the investment mold is made with PLA material by 3D printing technology and the mold shell is made of gypsum. Finally, experiment is performed to verify the validation of the top gating system. The results show that the combination of 3D printing technology and investment casting can effectively improve casting accuracy and production efficiency.

CAD-CAM Assisted Design and Preparation of Biocompatible Sensors and Transducers with Variable Microstructure

This paper highlights the detailed procedure for preparation of biocompatible sensors and transducers by CAD-CAM assisted investment casting (IC). Along with the properties such as biocompatibility and bioactivity, the presented materials possess good surface finish (required for aesthetic sense), acceptable dimensional accuracy (required for assembly purposes) and good surface hardness (required while chewing). In this paper efforts were made for improving surface hardness, finish, and dimensional accuracy of biocompatible materials by controlling composition/proportion of Ni and Cr in IC process. In this case study stir casting (SC) assisted Ni and Cr based metal matrix composites (MMC) has been prepared and composite prepared were poured in the investment mould. The result of study reveals that different material composition influenced the microstructure and the hardness of the MMC prepared. Further with change in weight percentage of Ni and Cr, different microstructures with particle clustering was observed. The employment of nickel and chromium composites for the fabrication of novel sensors and transducers is discussed.

Solution to Technological Problems of Raising the Reliability and Quality of Castings Based on Titanium Alloys

We consider the problems of the complex application of the aluminium-yttrium binder in the fabrication of high-temperature resistant melting crucibles and investment molds thermoschemically resistant to titanium melts. The results of the contact interaction investigations of a molten titanium alloy with a material of aluminum-yttrium ceramics are presented. The usage of ceramic products of α-Al2O3–Y3Al5O12∙α-Al2O3 composition under conditions of high-temperature melting and pouring under vacuum minimizes the physicochemical interaction and significantly reduces the alpha case layer on cast products, thereby improving their operational properties.

アコースティックエミッション解析によるチタンの変形・破壊機構に関する研究 : 第2報 シリカ-アルミナ-リン酸塩埋没材の鋳型に鋳造したチタン表層の多層構造組織の役割

アコースティックエミッション解析によるチタンの変形・破壊機構に関する研究 : 第2報 シリカ-アルミナ-リン酸塩埋没材の鋳型に鋳造したチタン表層の多層構造組織の役割

The development of an expansive type special cement bonded investment powder for castings of non ferrous metals and alloys

ABSTRACTAn attempt has been made to develop an investment powder which expands significantly in the setting period to meet the solidification shrinkage of most metals and alloys. Investment powders consisting of tricalcium aluminate, quartz, various sulphate bearing compounds and a small amounts of controlling agents (additives) were used in the preparation of the block investment molds. A413 Al-Si (Etial 140) alloy was melted and poured in these molds to cast a test specimen of a special geometry. The preliminary results show that it is possible to produce dimensionally accurate castings by using expansive type investment powders. Samples cast into block investment molds prepared from ordinary non-expansive investment powder were smaller than the pattern size, while those poured into molds produced from expansive type powders were the same size or greater than the pattern size.

Creep of the Investment Mold Material

The behavior of a shell mold for investment casting is analyzed in terms of the theory of creep of a ceramic material. Creep is considered as an integral characteristic of the behavior of a shell mold material, which depends on its heat resistance, cracking resistance, gas generation, and gas permeability. Practical recommendations are made to decrease the negative influence of material creep on the quality of a shell mold and, hence, the related ingot.

Neutron radiography and tomography investigations on the porosity of the as-cast titanium femoral stem

Gating system design in the centrifugal casting is one of the factors that influence the porosity of the femoral stem. The objective of this research is to analysis the porosity in the as-cast titanium femoral stem by neutron radiography and tomography. Three gating system designs which in three-ingates, four-ingates, and four-ingates by inversed position of the femoral stem were casted by a vertical centrifugal casting in investment mold. The porosity distribution in the titanium femoral stem was investigated by the neutron radiography film and followed by neutron tomography. The results indicate that there are large internal porosity in the subsurface region on both of the four-ingates designs but only small internal porosity on the three-ingates design. The large porosity also takes place in largest part of the femoral stem at all of the gating system designs. The product may be rejected due to the sub-surface porosity. The three-ingates design has the smallest risk on the reject product.

Investigation of Al/Steel Bimetal Composite Fabrication by Vacuum Assisted Solid Mould Investment Casting

Bimetal composites are a group of promising engineering materials with high developing and service potential.Especially in many elds they can be a powerful low cost alternative to metalceramic composites. The mostcommonly encountered type of these composites is steel reinforced aluminium matrix composites which stand outwith high wear and abrasion resistance. Signi cant fabrication processes of metal/metal composites are based onliquid metal techniques. In this study, Al/steel composite specimens were produced by using acuumv assisted solidmould investment casting technique. A7075 wrought aluminium alloy were in ltrated into steel preforms, whichwere produced with 304 stainless steel and H13 hot-work tool steel turnings, in the plaster based solid investmentcasting moulds. Microstructure observations, HV microhardness measurements, scanning electron microscopy andenergy dispersive X-ray spectroscopy analysis were carried out for characterization.DOI:10.12693/APhysPolA.126.1327ACS:P 81.30.Fb, 81.30.t, 81.20.n

Multi-Piece Post-Crown for Multi-Rooted Teeth with Non-Parallel Canals: A Direct Pattern Technique

Problems associated with custom cast posts for multi-rooted teeth with nonparallel canals following the traditional direct pattern technique result from using different metals in fabricating post core systems include failures due to electrolytic action of dissimilar metals and unfavorable effect upon the physical properties of wrought metal posts. The preheating temperature of the investment mold may lead to recrystalization of the wrought metal post. This article describes a technique, for constructing customcast post-core system for the multirooted teeth with nonparallel canals, to address these problems. The technique is simple, accurate, reproducible, and eliminates the drawbacks of the traditional direct post-core pattern for multirooted teeth with nonparallel canals.

The Research of Gypsum Investment Mould Used as Forming Micro-Castings

By applying ultrasonic solidification, gypsum based micro casting mold with different chemical compositions were sintered at different temperatures. The influence of processing parameters and sintering temperature on the microstructure and surface roughness were investigated. Meanwhile, the effect of sintering temperature on the bending strength was studied. The result showed that the nucleation rate of gypsum can be significantly improved under high temperature and pressure, which was caused by the effect of ultrasonic cavitation. Under the frequency of 100 KHz and the power of 200 W, 20 min, the morphology of gypsum transfers from flake and needle into near spherical after 20 min, and the grain size can be refined to around 500 nm. The value node of surface roughness occurs at the sintering temperature of 600 °C. The surface roughness is the lowest when the gypsum content is 60% and under the sintering temperature of 600 °C, which can reach Ra ~ 0.22 um. The bending strength of mold roughly increased with the increase of content of gypsum. There is no obvious rule for the mold strength with the change of sintering temperature. The mold strength reaches the highest value when the sintering temperature is 600°C.

Alpha-Case Reduction Mechanism of Titanium Powder-Added Investment Molds for Titanium Casting

The surface alpha-case reaction of Ti casting using Ti powder-added investment molds was investigated. During the curing procedure, Ti powders (0, 10, and 50 mass%) were mixed with three types of investment mold materials (Al2O3, ZrSiO4, and ZrO2) to form an interstitial TiO2 phase, which is an alpha-case reaction compound. The microstructure and surface hardness profiles of Ti castings with Ti powder-added investment molds indicated that the alpha-case thickness was significantly reduced from approximately 350 to 50-100 μm, and a remarkable reduction in the maximum micro-Vickers hardness value of the Ti casting surface was also achieved. As observed from the experimental results, the alpha-case reduction mechanism suggested that the phase transformation from TiO2 to TiO not only acts as an effective barrier to O diffusion, but also reduces Al, Si, and Zr concentrations at the casting surface. This reduction might be caused by contact area reduction between the Ti powder-added investment molds and the Ti melts.