Evaporative Pattern Casting Process Research Articles

Investigation of ablation studies of EPS pattern produced by rapid prototyping

ABSTRACTExpanded Polystyrene (EPS) patterns are used in Evaporative Pattern Casting (EPC). The cost of EPS pattern-making through moulding cannot be justified for small batch production. As 3D printing or Additive Manufacturing (AM) is suitable for small volumes, several efforts have been made to develop these machines for EPS including Segmented Object Manufacturing (SOM) of the authors. EPS is typically processed through ablation or traditional machining, the former using hot tools in the form of profiled axisymmetric shapes, blades or wire. The efficacy of SOM machine relies on the performance of the individual sub-systems, so in the present work, the ablation studies of hot wire slicing of the machine is performed. The kerfwidth and surface roughness determine the quality of the pattern produced by ablation. The objective of the paper is to investigate the ablation process by introducing novel mathematical model to predict the kerfwidth for different power inputs and feedrates, which is further validated with experimental data. Subsequently, an empirical relationship is established to predict the surface roughness (Ra) of the sliced surface by performing regression analysis of collected experimental data. The different cutting zones have also been classified, which gives an overall understanding of slicing mechanism. The average error in surface roughness prediction is found to be around ±10%. With the help of these models, the SOM machine can produce better quality EPS patterns in terms of kerfwidth and Ra value, which finally depicts the quality of final casting produced by EPC process.

Effect of Coating Thickness on the Molten Metal Filling Rate of Cast Iron in the Evaporative Pattern Casting Process

Molten metal filling rate and polystyrene foam pattern decomposition were examined in order to clarify how to improve the metal flow length of cast iron in the evaporative pattern casting process. The molten metal filling rate and the decomposition rate of a polystyrene foam pattern were measured during a casting experiment. A copper alloy was also cast using the same method for the purpose of comparison. The molten metal filling rate of cast iron was lower than that of the copper alloy. The volume of the gas gap increased with increasing melt temperature and decreasing coating permeability. A large amount of liquefied resin was formed by thermal decomposition of the foam pattern. The molten metal filling rate increased with increasing coating permeability and increased further with increasing coating thickness in the final step of molten metal filling. Even with increasing permeability of the coating, there is an occurrence of misruns in the case of molten cast iron, while the use of a thicker coating increased the molten metal flow length.

Application of Taguchi’s approach for obtaining mechanical properties and microstructures of evaporative pattern castings

Taguchi’s approach to design of experiment was applied to determine the effect of some process parameters on the mechanical properties and microstructures of castings obtained by evaporative pattern casting process. Four process parameters with three levels were selected and used with Taguchi’s method to give nine experimental runs. Casting design system was employed to determine the gating parameters for each of the test castings in the study. The pattern material was polystyrene of density 2 g/cm3. The mechanical property tested where the ultimate tensile strength (UTS), percentage elongation and hardness value. It was observed that castings produced at pouring temperature of 650 °C had fine grains and the highest values of UTS and hardness values. There was a downward trend of these values as the pouring temperature increased from 650 to 700 °C and then to 750 °C. It was established that producing the Al alloy castings at pouring temperature close to 650 °C results in good mechanical properties and microstructures.

The Research of Properties of Experimental Ceramic Layers

Abstract In the evaporative pattern casting process, the surface of a polystyrene pattern (Styrofoam) is coated with a ceramic layer. This ceramic layer, which coats the evaporative pattern, should have specific physiochemical properties including: resistance to thermal, chemical, and erosive activity of molten metal and proper permeability for gases which are produced by the evaporative polystyrene pattern. The article presents the research results of properties of experimentally selected ceramic layers applied on a polystyrene pattern in the evaporative pattern casting process.

Density Optimization of Slurry of Coating Material Used in the EPC Process Through Taguchi's Parameter Design Approach

In the Evaporative Pattern Casting (EPC) process, the refractory coating plays an important role with the polystyrene pattern. It not only provides refractory protection to ensure no metal penetration and smooth surfaces, but it also acts as a membrane between the decomposing polystyrene pattern and the unbounded sand mass. In general zircon flour is used as a coating material in the EPC process but it is very costly. An attempt has been made to study the properties of the fly ash with the zircon flour and bentonite. The Taguchi design of experiments and analysis of variance (ANOVA) are employed to analyze the influence of the process parameters (Zircon flour, fly ash, and bentonite) on density of slurry of the coating material in the EPC process. In Taguchi method, a three-level orthogonal array has been used to determine the S/N ratio. The results reveal that the zircon flour, fly ash, and bentonite are the significant parameters. Zircon flour is the most significant factor influencing the response variable investigated. Rest of significant terms provides secondary contribution to density of coating material. The predicted optimal density of slurry of coating material is 1.44 gm/cm3.

Characterization of the refractory coating material used in vacuum assisted evaporative pattern casting process

In the production of the casting using evaporative pattern of expandable polystyrene, the refractory coating applied to the pattern is an extremely critical factor. The coating is not required merely to prevent a direct contact with the sand and metal. But its main task is to support the sand during the brief interval between the gasification and replacement of pattern by the molten metal. In the present study, refractory filler material (flyash) has been used for coating the evaporative polystyrene patterns. Effect of temperature on the powder mixture containing zircon flour, filler material and binder was determined using Differentially Thermal Analysis (DTA) in the range from ambient temperature (20 °C) to 1000 °C. Powder particle morphology was analyzed by the scanning electronic microscope. X-ray diffraction analysis of the coating samples was carried out for 2 θ values from 10° to 80°. Prepared slurry was applied on the polystyrene pattern of 20 kg/m 3 density. Coating thickness was maintained between 0.15 and 0.20 mm. Al–7% Si alloy was poured at the pouring temperature (700 °C). Microstructure of the casting was investigated. The result reveals that the sample 4 has less material loss. It contains large and small particles and fine pores. Particles of different grain size contribute to better uniform, continuous coating on pattern due to cohesion between the particles. The phases (ZrSiO 4, TiO 2, Fe 2O 3, Al 2O 3 and SiO 2) make the stable compound which leads to high temperature refractoriness.

Optimization of tensile properties of evaporative pattern casting process through Taguchi's method

Evaporative pattern casting (EPC) process allows the production of complex parts and reduces machining of the part. To make a casting by EPC process, an expandable polystyrene pattern of the final part is made. In EPC process, all the limitations imposed by the binders and additives are absent as it is a binderless process. In this paper an attempt has been made to achieve a set of values of EPC process parameters that may yield optimum tensile properties to the Al–7% Si alloy castings. The effect of selected process parameters on the tensile properties of Al–7% Si alloy casting and subsequent optimal settings of the parameters have been obtained using Taguchi parametric design approach. The results indicate that the grain fineness number and the pouring temperature are the significant parameters in deciding the tensile strength and percent elongation after fracture of Al–7% Si alloy castings. Time of vibration and degree of vacuum are insignificant parameters. The predicted optimal value of tensile strength and percent elongation after fracture of Al–7% Si alloy castings produced by EPC process are 141.17 N/mm 2 and 2.713%, respectively, at 22 kg/m 3 density of expandable polystyrene pattern.

Effect of process parameters on impact strength of Al-7% Si alloy castings produced by VAEPC process

The castings produced by the evaporative pattern casting (EPC) process have blow holes. The blow holes in EPC castings are because of the non-escape of the gas produced as a result of burning of polystyrene pattern in the sand mold. To overcome the problem of blow holes, the EPC process is combined with the vacuum (V)- process. The vacuum applied to EPC mold draws the decomposed gases and improves the casting quality produced by the EPC process. The developed hybrid process has been termed as the vacuum assisted evaporative pattern casting (VAEPC) process. The objective of this paper to investigates the effect of process parameters, i.e, degree of vacuum, pouring temperature, grainfineness number, amplitude of vibration and time of vibration on the impact strength of Al-7% Si alloy castings in VAEPC process. In order to evaluate the effect of selected process parameters, the response surface methodology (RSM) is used to formulate a mathematical model which correlates the independent process parameters with the desired impact strength. The central composite rotatable design has been used to conduct the experiments. The results indicate that the impact strength decreases with increases in the grainfineness number and pouring temperature. Whereas, it has an inverse relationship with amplitude of vibration, time of vibration and degree of vacuum. The best value of impact strength (2.34 N/mm2) has been obtained at 400 mm Hg degree of vacuum imposed, 650°C as pouring temperature, 60 as sand grainfineness number, 460 μm as amplitude of vibration, and 70 s as time of vibration.

Effect of evaporative pattern casting process parameters on the surface roughness of Al–7% Si alloy castings

Evaporative pattern casting (EPC) process has drawn great attention from both academia and industry in recent years. The expandable polystyrene (EPS) pattern is a key feature of EPC process which is buried in unbonded sand and replaced by molten metal. This paper investigates the effect of process parameters like degree of vacuum, pouring temperature, grainfiness number, amplitude of vibration and time of vibration on the surface roughness of Al–7% Si alloy castings in EPC process. In order to evaluate the effect of selected process parameters, the response surface methodology (RSM) is used to formulate a mathematical model which correlates the independent process parameters with the desired surface roughness. The central composite rotatable design has been used to conduct the experiments. The analysis of results indicates that the surface roughness increases with increase in degree of vacuum, pouring temperature. Whereas, it has an inverse relationship with grainfiness number, amplitude of vibration and time of vibration.

Parametric optimization of surface roughness castings produced by Evaporative Pattern Casting process

In the present paper Taguchi's approach has been applied to the Evaporative Pattern Casting (EPC) process of Al–7%Si alloy to determine the most influential control factors which will provide better and consistent surface roughness to the castings regardless of the noise factors present. In order to evaluate the effect of process parameters such as grain fineness number, time of vibration, degree of vacuum and pouring temperature on surface roughness of EPC process castings, the Taguchi parameter design and optimization approach is used. Through the Taguchi's parameter design approach, optimal levels of process parameters have been determined. The results indicated that the grain fineness number, time of vibration, degree of vacuum were the significant parameters in deciding the surface roughness of Al–7%Si alloy castings. Pouring temperature was the insignificant parameter. The predicted optimal value of surface roughness of Al–7%Si alloy castings produced by EPC process was 2.31 μm. The results were confirmed by further experiments.

Effects of Reduced Pressure and Coat Permeability on Casting Characteristics of Magnesium Alloy in Evaporative Pattern Casting Process

A magnesium alloy was adopted to an evaporative pattern casting (EPC) process to combine advantages of each. In the present study, foam patterns were cast at a top gating system under atmospheric and reduced pressure to evaluate casting characteristics of AZ91D to develop a complete EPC process for high productivity of magnesium alloy castings. Filling time and temperature of molten metal were measured during mold filling. It was recognized that the average filling velocity was affected by the difference of the coating material and the degree of reduced pressure. The grain size of the magnesium alloy was slightly dependent on the degree of reduced pressure. It was considered that the application of the high reduced pressure, which changed the shape of melt surface from convex to concave, was related to the occurrence of internal defects such as cold shut laps or folds in the casting.

Thermal Decomposition Behavior of Expandable Pattern Including Blended Metal or Metal Oxide Powder in Evaporative Pattern Casting of Al-Si System Alloy

We investigated thermal decomposition behavior of expanded patterns including thermal decomposition accelerators such as Ni, NiO, CuO and Cu 2 O (hereinafter referred to as powder-blended expanded patterns) in an aluminum alloy evaporative pattern casting process; the following results were obtained. When these metal or metal oxide powders were blended in EPS (expandable polystyrene) patterns, an exothermic reaction occurred between metal or metal oxide powder and aluminum alloy melt. This reaction prevented, temperature drop at the top of the melt flow. In addition, these kinds of powder accelerated pattern thermal decomposition. As a result, the pattern thermal decomposition gas volume increased and aluminum alloy melt filling decreased.

Analysis of vibrations during sand casting in the evaporative pattern casting process

The paper describes research conducted to evaluate the influence of horizontal and vertical vibration on the movement of dry, unbonded silica sand in the evaporative pattern casting (EPC) process. Mathematical equations were developed for the alternative vibration options and incorporated in computer models that were subsequently validated experimentally by using accelerometers that were strategically placed in the moulding box and sand. The mathematical models showed good correlation with the experimentally derived results. The practical significance of the results is that the mathematical model can be used in the design of vibratory tables. Further, the results will enable the practitioner to predict the position of dead zones within the moulding box where sand will not flow and, consequently, patterns cannot be completely invested with sand. Thus the practitioner can reduce the likelihood of producing defective castings.