Precision Investment Casting Research Articles

Effect of silica sol on performance and surface precision of alumina ceramic shell prepared by binder jetting

Using 3D printing technology to prepare ceramic shell used for precision investment casting can realize short process and efficient preparation of the ceramic shell, which has a great application potential in the casting field. However, the 3D printed ceramic shells often have the problems of low strength and accuracy. In this paper, a silica sol room temperature dip coating treatment combined with high temperature sintering method was proposed to improve the strength and surface precision of the ceramic shell prepared by the binder jetting. The effects of silica sol concentration and dip coating time on performance and surface precision of the alumina ceramic shell were studied. The mechanical properties and surface precision of the alumina ceramic shell prepared by the binder jetting were improved significantly with the increases of the sol concentration and dip coating time. With the dip coating time of 90 s and sol concentration of 30%, the maximum bending strength of the alumina ceramic reached 44.8 MPa, which was 18.9 times higher than that of the untreated alumina ceramic. The top surface roughness and side roughness of the alumina ceramic decreased from 6.87 μm to 5.70 μm and 7.55 μm–6.46 μm, respectively, compared to those of the untreated alumina ceramic.

Development of mullite-alumina ceramic shells for precision investment casting of single-crystal high-pressure turbine blades

Alumina-mullite ceramic shell moulds were developed to cast single-crystal hollow high-pressure turbine blades (SX-HPTB). Mullite and fine alumina powders were used as fillers. Two colloidal silica binders were used to bind the filler particles. One colloidal silica binder (binder A) had no polymer and the second colloidal silica binder (binder B) had 8 wt % polymer. Eight slurry compositions with fine alumina substitution (0, 10, 30 and 50 wt %) were prepared. Silica cores were used to achieve hollow castings. The effect of alumina substitution and binders on the slurry characteristics, flexural strength of green and fired samples, air permeability and self-load sag resistance was studied. It was observed that with an increase in alumina percentage, the test specimens showed increased viscosity, pick-up weight, density, green strength and fired residual strength. In addition, the slurries prepared from binder B possessed larger values of viscosity and pick-up weight compared to the slurries prepared from binder A. The residual strength of fired test specimens containing binder A was higher than those containing binder B. The test specimens with 30 wt % fine alumina substitution showed the highest self-load sag resistance w.r.t. each test temperature. Also, the air permeability of the fired samples was higher than the green (de-waxed) samples. The casting of hollow HPTB components was performed at two temperatures (1525 °C and 1550 °C) using nickel-based superalloy CMSX4. The HPTB components, cast at 1550 oC from ceramic shell mould having binder B and 30 wt % fine alumina substitution, resulted in an acceptable aerofoil profile and surface roughness.

Моделирование процесса виброударной обрубки точного литья по выплавляемым моделям

Моделирование процесса виброударной обрубки точного литья по выплавляемым моделям

Effect of Alloy Additions on the Structure and Mechanical Properties of the AlSi7Mg0.3 Alloy

Abstract The study presents the results of the investigations of the effect of Cu, Ni, Cr, V, Mo and W alloy additions on the microstructure and mechanical properties of the AlSi7Mg0.3 alloy. The examinations were performed within a project the aim of which is to elaborate an experimental and industrial technology of producing elements of machines and devices complex in their construction, made of aluminium alloys by the method of precision investment casting. It was demonstrated that a proper combination of alloy additions causes the crystallization of complex intermetallic phases in the silumin, shortens the SDAS and improves the strength properties: Rm, Rp0.2,HB hardness. Elevating these properties reduces At, which, in consequence, lowers the quality index Q of the alloy of the obtained casts. Experimental casts were made in ceramic moulds preliminarily heated to 160 °C, into which the AlSi7Mg0.3 alloy with the additions was cast, followed by its cooling at ambient temperature. With the purpose of increasing the value of the quality index Q, it is recommended that the process of alloy cooling in the ceramic mould be intensified and/or a thermal treatment of the casts be performed (ageing)(T6).

Modelling of dimensional accuracy in precision investment casting using Buckingham’s Pi approach

Precision investment casting (PIC) simulation software is being increasingly used to predict product quality. Input parameters; include factors such as mould temperature, melting temperature, casting material, number and location of feeding points, diameter and length of inflow channels, angle of channel with respect to the main sprue axis. The previous studies highlights that simulation results cannot help the engineer for workpiece other than the one simulated. In this paper a Buckingham Pi model (based upon Taguchi macro-model) for dimensional accuracy (Δd) is presented aiming at such generalisation. To achieve this, a number of experimental runs were conducted for a number of parts, with varying runner geometry and casting conditions. The parameters characterising part geometry have been chosen to be volume-to-area (V/A) ratio. The other input parameters are: slurry layer’s combination (LC) and molten metal pouring temperature. This study will provide main effects of these variables on Δd and will shed light on the Δd mechanism in PIC.

Comparison of Dental Prostheses Cast and Sintered by SLM from Co-Cr-Mo-W Alloy

Abstract The article presents the results of a comparative analysis of the metal substructure for dental prosthesis made from a Co-Cr-Mo-W alloy by two techniques, i.e. precision investment casting and selective laser melting (SLM). It was found that the roughness of the raw surface of the SLM sinter is higher than the roughness of the cast surface, which is compensated by the process of blast cleaning during metal preparation for the application of a layer of porcelain. Castings have a dendritic structure, while SLM sinters are characterized by a compact, fine-grain microstructure of the hardness higher by about 100 HV units. High performance and high costs of implementation the SLM technology are the cause to use it for the purpose of many dental manufacturers under outsourcing rules. The result is a reduction in manufacturing costs of the product associated with dental work time necessary to scan, designing and treatment of sinter compared with the time needed to develop a substructure in wax, absorption in the refractory mass, casting, sand blasting and finishing. As a result of market competition and low cost of materials, sinter costs decrease which brings the total costs related to the construction unit making using the traditional method of casting, at far less commitment of time and greater predictability and consistent sinter quality.

Effect of annealing and high-temperature heatings during soldering on structure and mechanical properties of alloy based on nickel aluminide

The article presents a study of the effect of various modes of annealing and process heatings on microstructure and properties of single-crystalline blanks of VKNA-1 intermetallic alloy on the basis of Ni3Al with crystallographic orientations of 〈001〉 and 〈111〉, obtained by the method of directional crystallization, and billets with polycrystalline structure from the VKNA-1VR alloy, made by the precision investment casting method.

Investigating the Effect of Shape Factor, Slurry Layers and Pouring Temperature in Precision Investment Casting

This paper aimed to investigate the effect of shape factor, slurry layers and pouring temperature in precision investment casting. Three controllable factors of the precision investment casting process (namely: shape factor, slurry layers (mold thickness) and pouring temperature) were studied at three levels each by Taguchis parametric approach and single-response optimization was conducted to identify the main factors controlling surface hardness, dimensional accuracy (Δd) and surface roughness (Ra). Castings were produced using aluminum (Al), mild steel (M.S.) and stainless steel (S.S) at recommended parameters through ceramic shell precision investment casting process. The micro structure analysis has been used to study the surface morphology. Analysis shows that for surface hardness, contribution of shape factor, slurry layers and pouring temperature is 0.07%, 0.70% and 99% respectively. As regards to surface roughness, contribution of shape factor, slurry layers and pouring temperature is 1.14%, 16.80% and 81.90% respectively. Further for Δd contribution of shape factor, slurry layers and pouring temperature is 1.53%, 22.47% and 72.88% respectively. Confirmation experiments were conducted at an optimal condition showed that the surface hardness, Δd and Ra of the precision investment casting were improved significantly.

The Deformation of Wax patterns and Castings in Investment Casting Technology

The dimensional accuracy of the final casting of Inconel alloy 738 LC is affected by many aspects. One of them is the choice of method and time of cooling wax model for precision investment casting. The main objective was to study the initial deformation of the complex shape of the casting of the rotor blades. Various approaches have been tested for cooling wax pattern. When wax models are cooling on the air, without clamping in jig for cooling, deviations from the ideal shape of the casting are very noticeable (up to 8 mm) and most are in extreme positions of the model. When blade is cooled in fixing jig in water environment, the resulting deviations compared with cooling in air are significantly larger, sometimes up to 10 mm. This itself does not mean that the final shape of the casting is dimensionally more accurate with usage of wax models, which have deviations from the ideal position smaller. Another deformation occurs when shell mould is produced around wax pattern and furthermore deformations emerge while casting of blade is cooling. This paper demonstrates first steps in describing complex process of deformations of Inconel alloy blades produced with investment casting technology by comparing results from thermal imagery, simulations in foundry simulation software ProCAST 2010 and measurements from CNC scanning system Carl Zeiss MC 850. Conclusions are so far not groundbreaking, but it seems deformations of wax pattern and deformations of castings do in some cases cancel each other by having opposite directions. Describing entirely whole process of deformations will help increase precision of blade castings so that models at the beginning and blades in the end are the same.

The scope of artificial neural network metamodels for precision casting process planning

Precision investment casting process planning has been tackled in the past according to experience. Recently, casting simulation software is being increasingly used to predict product quality by implementing ‘what-if’ scenarios. Input parameters include relatively simple factors such as mould temperature, melting temperature, casting material. They also include factors whose influence is more complex to quantify, such number and location of feeding points, diameter and length of inflow channels, angle of channel with respect to the main sprue axis. Simulation results cannot help the engineer for workpieces other than the one simulated. In this paper a series of feedforward artificial neural network (ANN) models is presented aiming at such generalisation. To achieve this, a large number of software simulation runs were conducted for a number of different small parts, with varying runner geometry and casting conditions. The parameters characterising part geometry have been chosen to be surface area and volume-to-area ratio. The different ANN models predictive capabilities are reflected to the respective training and generalisation errors. A user-friendly interface has been conducted for model execution in a complete application, whose main virtue is expandability.

Focus on Powder Injection Moulding

Metal injection moulding can offer designers flexibility in producing high volumes of complex shapes from a wide variety of materials, and also in many instances reduced cost. The main features of the process are compared with those of its main competitors, in particular precision investment casting, in an attempt to guide designers considering the use of this innovative PM technology.

Computer-aided development of an investment casting process

Using computer modeling and results visualization techniques, the gating design for a precision investment casting was improved, and the possibility for casting defects was detected. This approach resulted in a potential seven percent cost savings on the component alone and eliminated the expensive trial-and-error-process. With continuing improvements in computer workstations and modeling software, it should soon be possible to dramatically reduce the effort required to generate and analyze finite-element models.

Vacuum furnace techniques for metal injection moulded part debinding and sintering

A wide range of small intrically-shaped parts are being produced by injection moulding metal and ceramic powders. The process is cost effective, competing both with precision investment casting and conventional machining and sub-part assembly methods. Techniques employing modified vacuum furnaces and binder condensing systems have expanded the uses for the process to a wider range of parts by reducing the time required for binder removal. Conventional binder removal methods are compared with the vacuum process. Advantages of the vacuum furnace techniques are described. These include close carbon content control and high yields resulting from the uniform temperature. The results of binder removal studies and data on the successful scale-up from laboratory to two layer production size batch furnaces are presented.