Investment Casting Applications Research Articles

Experimental investigation on abrasive flow Machining (AFM) of FDM printed hollow truncated cone parts

Abrasive flow machining (AFM) process is mostly used to finish the complex-shaped products that are difficult to finish by the traditional finishing processes like grinding, lapping honing, etc. AFM process employed a viscoelastic polymer-based finishing media, which is the suspension of viscoelastic polymer, abrasive particles, liquid synthesizer, and additives to finish the complex parts. It is used in various engineering applications such as trim die, automotive, aerospace, bio-medical implants. The Fused deposition modeling (FDM) process is one of the commercial 3D printing processes used for manufacturing prototypes for investment casting applications and end-use products. The stair-stepping effect is the most common surface defect that occurs during the FDM printing process. AFM process is an excellent solution to improve the surface quality of FDM printed parts. In this paper, AFM finishing media was developed using a natural waste polymer as base materials which carry SiC powder as abrasive particles, waste vegetable oil as the liquid synthesizer, and glycerine as additives. The viscosity of AFM media optimized using Taguchi's orthogonal array L9 based experimental design. In the current study, the hollow truncated cone shape of ABS (acrylonitrile–butadienestyrene) material was fabricated by the FDM process and then finished using a one-way AFM process. This paper examined the parametric dependencies of AFM process parameters on the internal finishing of FDM truncated cone parts. The improved surface roughness of the FDM printed hollow truncated cone has been investigated relating to the AFM process parameters. The maximum surface roughness has been achieved by 94.26%. The process parameters, i.e., the percentage of abrasive concentration, abrasive mesh size, layer thickness, and finishing time, were identified for the improved surface quality of FDM printed hollow truncated cone parts.

3D printing ceramic cores for investment casting of turbine blades, using LCD screen printers: The mixture design and characterisation

The primary objective of this study is to demonstrate the possibility of developing silica, alumina, and zircon-based photocurable ceramic suspensions that can be used for visible light photopolymerization (> 450 nm) and to optimise the binder formulations for the purpose of LCD-based ceramic 3D printing applications. Reference ceramic components for this work are ceramic cores employed in the investment casting of high-pressure turbine blades and vanes. Arguably, one of the most critical steps in photoinduced ceramic 3D printing is developing suitable ceramic suspensions, having high ceramic loading, low viscosity, and short curing times. Ceramic suspensions with four different novel binder formulations and commercial ceramic powders used in core manufacturing (SiO2, Al2O3 and ZrSiO4) were investigated to achieve the best trade-off between: (1) their curing performance (cure depth and curing speed), (2) rheological properties of the binder mixtures at the solid loadings of 60 vol.% for SiO2, 55 vol.% for ZrSiO4, and 45 vol.% for Al2O3; and (3) the green body mechanical properties of the mixtures after printing. The effect of ceramic particles on the selected binders was examined individually, and the correlation between cure depth (Cd), volumetric loading, and curing speed are evaluated. The results show all binders designed in this study provide an adequate cure depth, even at high ceramic loadings. When the curing behaviour of all unloaded binder mixtures from the previous study [1] compared with the 10 vol.% SiO2 loaded mixtures, the cure depth of all formulated binder mixtures increased 50–55 % and the curing thickness of 60 vol.% SiO2 loaded suspensions were still slightly higher than their unloaded counterparts. The rheology outcomes indicate that lower viscosity binders always result in lower viscosity of the ceramic loaded inks, even without taking the effect of dispersants into account. Besides, the addition of N-Vinyl-2-Pyrrolidone (NVP) monofunctional monomer to the binder mixtures significantly reduces the viscosity and changes the normally linear relationship of the mix viscosity and its silica loading content. Among the binder formulations loaded with 60 vol.% of SiO2, the formulation providing the lowest viscosity and highest mechanical property consists of 5 wt.% of NVP, 45 wt.% of HDDA and 50 wt.% of Photocentric 34 resin. Although this binder mixture showed the highest green flexural strength when loaded by 55 vol.% ZrSiO4, all other mixtures loaded with zircon flour also demonstrated a near-fluid behaviour, below 200 s−1. In Al2O3 loaded mixtures, the HDDA di-functional binder formulations present lowest viscosity and the di- and multifunctional monomer blends (HDDA-Photocentric27) showed the highest mechanical properties when used in a 50/50 ratio. This work summarises the best binder choices for silica, alumina and zircon based ceramic suspensions used in core printing for investment casting applications through LCD screen printing.

Post-processing of ABS Replicas with Vapour Smoothing for Investment Casting Applications

The need of customized products with tight dimensional tolerances, lower production cost and shorter lead times led to the development of additive manufacturing techniques like fused deposition modelling (FDM). The digitally fabricated ABS patterns prepared on FDM needs to be processed by vapour smoothing (VS) in order to reduce the surface roughness. The post-processing of FDM-based patterns/replicas with VS increases their density, which increases heat input and complexities in ash removal during burnout stage from ceramic shell in investment casting (IC). This study highlights the step-by-step procedure for controlling the density of master patterns/replicas after processing with VS for IC applications.

High strength silica-based ceramics material for investment casting applications: Effects of adding nanosized alumina coatings

A nanosized alumina coating was synthesized on the surface of fused silica particles by electrostatic attraction. The effects of the coated fused silica particles on the cristobalite crystallization behavior, microstructure evolution, and flexural strength of silica-based ceramic cores were investigated. X-ray diffraction (XRD) was used to characterize phase transformations in the specimens, and the results indicated that the formed nanosized alumina coatings could retard cristobalite formation by inducing compressive stress on the fused silica particle surface. A mullite phase was also found due to the reaction of the nanosized alumina coating and the surface of the fused silica when the sintering temperature was increased to 1300 °C. Analysis using scanning electron microscopy equipped with energy dispersive spectrometry (SEM/EDS) suggested that alumina nanoparticles in the coated layer dispersed into a liquid phase and formed a barrier layer to impede the movement of the liquid phase, preventing the pore-filling process and increasing the open porosity of the ceramic specimens. Flexural strengths at room temperature were tested, indicating that increases in the sintering temperature of the specimens without coated fused silica powders had little effect on flexural strength. However, the flexural strength of the specimens with coated fused silica powders increased with increases in sintering temperature. The improvement in flexural strength was related to the reinforcement by sintering necks between particles and the improvement in the strength of the coated fused silica powder.

On Development of Functionally Graded Material Through Fused Deposition Modelling Assisted Investment Casting from Al2O3/SiC Reinforced Waste Low Density Polyethylene

The recycling of packaging materials such as low density polyethylene (LDPE) into useful product is one of the challenging tasks. Since waste LDPE has some issues like low mechanical strength and thermal degradation; some studies have been reported in recent past to improve these properties with ceramic/metallic reinforcements. In this work reusability of LDPE has been ascertained as functionally graded material (FGM) through aluminum (Al) matrix based investment casting (IC). This study highlights the use of SiC and Al2O3 as reinforcement in LDPE for IC applications as a novel method for development of FGM. The master patterns for IC were prepared from reinforced LDPE based feed stock filament (prepared on conventional screw extruder) on open source fused deposition modelling setup. The in-house prepared filament wire was subjected to mechanical and thermal testing to ensure recyclability and stability of the material. The photo micrographs and SEM images were collected to ensure the dispersion of SiC and Al2O3 reinforcements in Al based FGM.

Experimental investigations for dimensional accuracy and surface finish of polyurethane prototypes fabricated by indirect rapid tooling: a case study

In this research work, an effort has been made to study the influence of selected input parameters on the dimensional accuracy (linear as well as radial) and surface finish of polyurethane prototypes fabricated by vacuum casting (VC) process as a case study. The master pattern required for making a silicone mould has been fabricated by fused deposition modelling and its surface finish has been enhanced by chemical vapour smoothing process. Maximum shrinkage of 2.29 and 4.77% has been observed in the selected linear and radial dimension, respectively, after the VC process. Optimal parameter settings that were different for both the dimensions as well as surface finish have been obtained using Taguchi’s L18 orthogonal array. Finally, parameter setting that simultaneously minimizes the dimensional deviation and surface roughness has been found out using response optimization module of Minitab 17 software and the results obtained have been verified by performing the confirmation experiments. The tolerance grades for the selected dimension of the prototypes were found to be acceptable as per the ISO standard UNI EN 20286-I (1995) and DIN16901 for plastic materials. In addition, the C pk value greater than 1.3 indicated that the proposed process is highly capable. The surface finish and dimensional accuracy of prototypes are at par with the traditional moulding patterns, and hence, they can be used as end-products or plastic-based master patterns for investment casting applications.

Fused deposition modelling based rapid patterns for investment casting applications: a review

Purpose – This paper aims to review the industrial and biomedical applications of state-of-the-art fused deposition modelling (FDM)-assisted investment casting (FDMAIC). Brief literature survey of methodologies, ideas, techniques and approaches used by various researchers is highlighted and use of hybrid feedstock filament-based pattern to produce metal matrix composite is duly discussed. Design/methodology/approach – Pattern replica required for investment casting (IC) of biomedical implant, machine parts, dentistry and other industrial components can be directly produced by using FDM process is presented. Relevant studies and examples explaining the suitability of FDMAIC for various applications are also presented. Findings – Researches to optimize the conventional IC with FDM solutions and develop new hybrid feedstock filament of FDM done by researchers worldwide are also discussed. The review highlights the benefit of FDMAIC to surgeons, engineers and manufacturing organizations. Research limitations/implications – The research related to this survey is limited to the suitability and applicability of FDMAIC. Originality/value – This review presents the information regarding potential IC application, which facilitates the society, engineers and manufacturing organizations by providing variety of components for assisting FDM. The information reported in this paper will serve doctors, researchers, organizations and academicians to explore the new options in the field of FDMAIC.

Experimental Investigations for Use of ABS Replicas in Investment Casting Applications

In the present research work effort has been made to study the use of acrylonitrile butadiene styrene (ABS) replicas in investment casting (IC) applications. The study starts with selection of the component for industrial application with an idea of improvement in dimensional accuracy (Δd) of the component. The input parameters are part orientation in fused deposition modeling (FDM), number of layers, layer combination and type of materials in IC. The study highlights the percentage contribution of different input parameters on Δd for ABS replicas in IC.

English

The purpose of this paper is to examine the suitability of fused deposition modelling (FDM), for the production of a pattern that can be used in direct manufacturing applications. In this work, the benchmark was identified and its best part orientation in a FDM machine was located through experimentation. Control charts and process capability histogram were drawn to assess the process capability of the FDM process. The micro hardness of the prepared sample was measured to check the suitability of the process for investment casting applications. Further dimensional accuracy of patterns was established by IT grades as per the ISO standard UNI EN 20286-I (1995). It was observed that the performance indices for all the dimensions in the present study are greater than 1. The study of photo micrographs using SEM gave an insight into the properties of the component (produced by FDM). This study highlights that the tolerance grades for ABS plastics are consistent with the permissible range of tolerance grades as per the ISO standard UNI EN 20286-I (1995) and DIN16901 standard.

Recycling of alpha-titanium technological scrap for exhaust system parts manufacturing

Abstract In this paper, five different titanium alpha alloys obtained by investment casting, and recycled titanium scrap which originated from other technological operations have been studied in order to investigate their basic properties and to determine the industrial feasibility of the manufacturing of recycled titanium exhaust system parts on an industrial scale. Chemical analysis after a first and a second melting step, a complete mechanical characterization and oxidation resistance test at different temperatures have been performed. The direct influence of the alloying elements, like Si and Al, on the oxidation resistance of titanium at high temperature has been studied, in order to identify the best blended alloy for investment casting applications. An important aspect which has also been evaluated is the increase of oxygen content after remelting of the blend alloys and its impact on the mechanical properties. Results show that it is possible to use the identified blend alloys to obtain cast components suitable for applications requiring exposure at a temperature up to 700 °C, and for the Si-richer blends, up to 800 °C.

Mathematical modeling for surface hardness in investment casting applications

Investment casting (IC) has many potential engineering applications. Not much work hitherto has been reported for modeling the surface hardness (SH) in IC of industrial components. In the present study, outcome of Taguchi based macro-model has been used for developing a mathematical model for SH; using Buckingham’s π-theorem. Three input parameters namely volume/surface-area (V/A) ratio of cast components, slurry layer’s combination (LC) and molten metal pouring temperature were selected to give output in form of SH. This study will provide main effects of these variables on SH and will shed light on the SH mechanism in IC. The comparison with experimental results will also serve as further validation of model.

Mathematical modelling of dimensional accuracy in vacuum assisted casting

Vacuum assisted casting (VAC) is one of the prototype making processes used to generate replicas of plastic components (PC) for batch production activities (like: investment casting applications). In the present study, the outcome of the Taguchi model has been used for developing a mathematical model for dimensional accuracy (DA) using Buckingham's π-theorem for VAC of PC. Four input parameters, namely material type, mixing ratio (hardener: softener), de-mould time and de-mould temperature, were selected to give output in the form of DA. This study will provide the main effects of these variables on DA and will shed light on the mechanism of DA in VAC for replicas of PC. The comparison with experimental results will also serve as further validation of the model.

Investment casting

This article considers some of the more recent developments in investment casting. A description of the process is given, together with a discussion of the process capabilities. Some design pointers are noted and the range of alloys currently available in the investment-cast form are summarised. Recent metallurgical and process developments which are discussed are Hitchiner's CLA and CLV processes, Directional Solidification and Hot Isostatic Pressing, as applied to investment casting. The final section of the paper reviews the production of investment castings on a global basis and notes some areas which represent potential growth in terms of investment casting applications.