Effect of composition on secondary dendrite arm spacing of Al-Si-Cu-Mg (Fe/Mn) alloys for a given cooling rate

Experiments were carried out to study the variation of secondary dendrite arm spacing (SDAS) of Al-Si-Cu-Mg-(Fe/Mn) alloys with the cooling rate and composition. Sand casting trials were carried out in Al-Si-Cu-Mg-(Fe/Mn) alloys with varying compositions of Si, Cu and Fe using an inverted mould. Alloys were prepared in an induction furnace at about 730ºC and triple-plate castings were cast using chills at the bottom of the plates for promoting directional solidification. Thermal information was acquired using pre-installed thermocouples through the mould wall. Optical microscopy studies were implemented to study the variation of secondary dendrite arm spacing (SDAS) as a function of chemical composition and cooling rate. The relationships between cooling rate and SDAS were plotted for the alloys and SDAS decreased with an increase in cooling rate and also with the increase in alloy composition

3D printing for rapid sand casting—A review

There are many 3D printing technologies available, and each technology has its strength and weakness. The 3D printing of sand moulds, by binder jetting technology for rapid casting, plays a vital role in providing a better value for the more than 5000 years old casting industry by producing quality and economic sand moulds. The parts of the mould assembly can be manufactured by precisely controlling the process parameters and the gas producible materials within the printed mould. A functional mould can be manufactured with the required gas permeability, strength, and heat absorption characteristics, and hence the process ensures a high success rate of quality castings with an optimised design for weight reduction. It overcomes many of the limitations in traditional mould design with a very limited number of parts in the mould assembly. A variety of powders, of different particle size or shape, and bonding materials can be used to change the thermal and physical properties of the mould and hence provide possibilities for casting a broad range of alloys. Limited studies have been carried out to understand the relationship between the characteristics of the printed mould, the materials used, and the processing parameters for making the mould. These deficiencies need to be addressed to support the numerical simulation of a designed part, to optimise the success rate and for economic as well as environmental reasons. Commonly used binders in this process, e.g. furan resins, are carcinogenic or hazardous, and hence there is a vital need for developing new or improved bonding materials

Characterisation of 3D printed sand moulds using micro-focus X-ray computed tomography

Purpose – Micro-focus X-ray computed tomography (CT) can be used to quantitatively evaluate the packing density, pore connectivity andvprovide the basis for specimen derived simulations of gas permeability of sand mould. This non-destructive experiment or following simulations can be done on any section of any size sand mould just before casting to validate the required properties. This paper aims to describe the challenges of this method and use it to simulate the gas permeability of 3D printed sand moulds for a range of controlling parameters. The permeability simulations are compared against experimental results using traditional measurement techniques. It suggests that a minimum volume of only 700 700 700 mm3 is required to obtain, a reliable and most representative than the value obtained by the traditional measurement technique, the simulated permeability of a specimen. Design/methodology/approach – X-ray tomography images were used to reconstruct 3D models to simulate them for gas permeability of the 3D printed sand mould specimens, and the results were compared with the experimental result of the same. Findings – The influence of printing parameters, especially the re-coater speed, on the pore connectivity of the 3D printed sand mould and related permeability has been identified. Characterisation of these sand moulds using X-ray CT and its suitability, compared to the traditional means, are also studied. While density and 3PB strength are a measure of the quality of the moulds, the pore connectivity from the tomographic images precisely relates to the permeability. The main conclusions of the present study are provided below. A minimum required sample size of 700 700 700 mm3 is required to provide representative permeability results. This was obtained from sand specimens with an average sand grain size of 140 mm, using the tomographic volume images to define a 3D mesh to run permeability calculations. Z-direction permeability is always lower than that in the X-/Ydirections due to the lower values of X-(120/140 mm) and Y-(101.6 mm) resolutions of the furan droplets. The anisotropic permeability of the 3D printed sand mould is mainly due to, the only adjustable, X-directional resolution of the furan droplets; the Y-directional resolution is a fixed distance, 102.6 mm, between the printhead nozzles and the Z-directional one is usually, 280 mm, twice the size of an average sand grain.A non-destructive and most representative permeability value can be obtained, using the computer simulation, on the reconstructed 3D X-ray tomography images obtained on a specific location of a 3D printed sand mould. This saves time and effort on printing a separate specimen for the traditional test which may not be the most representative to the printed mould. Originality/value – The experimental result is compared with the computer simulated results

Effect of process parameters on flexure strength and gas permeability of 3D printed sand molds

3D printed sand molds for the casting industry play a vital role in manufacturing intricate parts from a computer model. The possibility of producing fairly significant structural castings using a small job-box 3D sand mold printer is another advantage compared to the direct metal 3D printing processes. It is important to identify the relationship between the process parameters and the properties of the sand mold in order to produce a mold with the required strength, permeability and stiffness; to reduce gas emissions during casting and minimize the mass of combustible materials in the mold. Hence, it is possible to create an excellent casting by improving the design of such molds for liquid alloy filling and solidification. The relationship between the printing parameters and the properties of the mold can be a great tool for foundrymen, primarily to optimize the strength and permeability properties of these molds and therefore to provide exact boundary conditions for the solidification simulation prior to a casting trial. This paper reports on a study of a basic outline to quantify the role of the sand mold printing process parameters, particularly the recoater speed and print resolution, on the mold strength and permeability, and their impacts on the anisotropic behavior of the printed sand molds

Investigation of process parameter effect on anisotropic properties of 3D printed sand molds

The development of sand mold three-dimensional printing technologies enables the manufacturing of molds without the use of a physical model. However, the effects of the three-dimensional printing process parameters on the mold permeability and strength are not well known, leading the industries to keep old settings until castings have recurring defects. In the present work, the influence of these parameters was experimentally investigated to understand their effect on the mold strength and permeability. Cylindrical and barshaped test specimens were printed to perform, respectively, permeability and bending strength measurements. Experiments were designed to statistically quantify the individual and combined effect of these process parameters. While the binder quantity only affects the mold strength, increasing the recoater speed leads to both greater permeability and reduced strength due to the reduced sand compaction. Recommendations for optimizing some 3D printer settings are proposed to attain predefined mold properties and minimize the anisotropic behavior of the sand mold in regard to both the orientation and the position in the job box

Effect of Si content on the size of Fe-rich intermetallic particles in Al-xSi-0.8Fe alloys

Al-Si-Fe plates with Si contents of 4.5, 9 and 11 mass %, unmodified and Sr-modified, were quasi-directionally solidified in sand moulds with chills at one end. The size and nature of the Fe-rich intermetallics were determined along the plates. Two forms of the intermetallic were observed, α-Al8FeSi and β-Al5FeSi, in proportions and scale dependent on the cooling rate and the Si concentration. The size of the β-phase increased with the concentration of Si at low cooling rates. At high cooling rates the tendency to form α-Al8FeSi phase increased with increasing Si content reducing the size of the β-plates. Modification generally increased the size of the pre-eutectically formed plates while reducing the post eutectically formed ones

Effect of Si and Cu content on the size of intermetallic phase particles in Al-Si-Cu-Mg-Fe alloys

Al-Si-Fe plates with Si contents of 4.5, 9 and 11 mass %, unmodified and Sr-modified, were quasi-directionally solidified in sand moulds with chills at one end. The size and nature of the Fe-rich intermetallics were determined along the plates. Two forms of the intermetallic were observed, alpha-Al8FeSi and beta-Al5FeSi, in proportions and scale dependent on the cooling rate and the Si concentration. The size of the beta-phase increased with the concentration of Si at low cooling rates. At high cooling rates the tendency to form alpha-Al8FeSi phase increased with increasing Si content reducing the size of the beta-plates. Modification generally increased the size of the pre-eutectically formed plates while reducing the post eutectically formed ones

Reduced consumption of materials and hazardous chemicals for energy efficient production of metal parts through 3D printing of sand molds

Metals remain essential structural materials for many demanding engineering applications requiring high strength at elevated temperatures and good performance in environments subjected to high thermal fluctuations such as often encountered in the automotive, rail and aircraft industries. The sand-casting process is one of the most preferred methods of producing complex and intricate shaped components out of metals with good strength at elevated temperatures. Unfortunately, the sand casting process also leads to the direct and indirect production of carbon dioxide. Three-dimensional sand mold printing has been revolutionizing traditional production methods by reducing the unnecessary consumption of metal and chemicals when manufacturing a part through sand casting. This paper explores the opportunities that are emerging in the area of 3D printing of sand molds and the positive impact that these new technologies and practices are having on the environmental impact of current sand-casting processes. The paper demonstrates that 3D printing of sand molds enables new manufacturing strategies reducing the direct CO emissions and reducing the amount of metal required by enabling design optimization of both the component and mold/core assembly. Further benefits will be realized through the development of environmentally friendly binder systems