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International audience; 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.

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 CO2 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.

3D sand mould printing using binder jet technology can enable many technical improvements in casting practice, including part consolidation, design of parts to optimise the consumption of materials and hazardous chemicals, and on-demand and flexible size part manufacturing near the customer. Incorporating artificial intelligence in optimising the design of moulds, printing process parameters, and solidification processes may help automate a production facility and reduce labour time. Elimination of hazardous chemicals from industrial use may be a challenge. Therefore, an alternative technology to fuse the sand particles during printing or an environmentally friendlier alternative option for the binders and other consumables should be utilised with the 3D sand printing process. Properties of parts produced using 3D printed sand moulds have the potential to be better than the properties of parts produced using traditional casting due to this technology's benefits. This technology is an enabling technology for traditional casting processes rather than a competing technology. It is causing a paradigm shift in casting design because of the mould geometries achievable by using additive manufacturing to produce the sand mould. This paper reviews the first twenty years of research and challenges in developing 3D sand printing processes as an innovation for sustainable manufacturing.

COVID-19 has caused a global pandemic since December 2019. It has impacted not only the wellbeing of human society but also has been damaging to the global economy. This has imposed severe threats and challenges on businesses. The British government has launched aid schemes to combat the new scenarios developed as a result of the pandemic. This paper aims to assess the impact of COVID-19 on foundries in the UK. Recorded responses from a detailed survey of the British foundries were analysed and short- and long-term action plans for the foundries are suggested. The current status, challenges, and future direction of the UK foundries are discussed. An opinion for the use of additive technologies with business model innovation for the de-centralised foundries is presented.

Purpose Micro-focus X-ray computed tomography (CT) can be used to quantitatively evaluate the packing density, pore connectivity and provide 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 µm3 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 µm3 is required to provide representative permeability results. This was obtained from sand specimens with an average sand grain size of 140 µm, 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-/Y-directions due to the lower values of X-(120/140 µm) and Y-(101.6 µm) 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 µm, between the printhead nozzles and the Z-directional one is usually, 280 µm, 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.

Several detailed studies have comprehensively investigated the benefits and limitations of laser-assisted machining (LAM) of titanium alloys. These studies have highlighted the positive impact of the application of laser preheating on reducing cutting forces and improving productivity but have also identified the detrimental effect of LAM on tool life. This paper seeks to evaluate a series of the most common cutting tools with different coating types used in the machining of titanium alloys to identify whether coating type has a dramatic effect on the dominant tool wear mechanisms active during the process. The findings provide a clear illustration that the challenges facing the application of LAM are associated with the development of new types of cutting tools which are not subjected to the diffusion-controlled wear processes that dominate the performance of current cutting tools.

International audience; The development of sand mold three-dimensionalprinting technologies enables the manufacturing of moldswithout the use of a physical model. However, the effects ofthe three-dimensional printing process parameters on the moldpermeability and strength are not well known, leading theindustries to keep old settings until castings have recurringdefects. In the present work, the influence of these parameterswas experimentally investigated to understand their effect onthe mold strength and permeability. Cylindrical and barshapedtest specimens were printed to perform, respectively,permeability and bending strength measurements.Experiments were designed to statistically quantify the individualand combined effect of these process parameters.While the binder quantity only affects the mold strength, increasingthe recoater speed leads to both greater permeabilityand reduced strength due to the reduced sand compaction.Recommendations for optimizing some 3D printer settingsare proposed to attain predefined mold properties and minimizethe anisotropic behavior of the sand mold in regard toboth the orientation and the position in the job box.

Plates of Al-(a)Si-(b)Cu-Mg-(c)Fe alloys with varying content of (mass pct) Si (a = 3, 4.5, 7.5, 9, 10, or 11), Cu (b = 0, 1, or 4), and Fe (c = 0.2, 0.5 or 0.8) were cast in sand molds with a heavy chill at one end to ensure quasi-directional solidification over a wide range of Secondary Dendrite Arm Spacing (SDAS). Statistical analysis on the size of the β-Al5FeSi, α-Al8Fe2Si, or Al2Cu intermetallics on Backscattered Electron images showed that a high Si content reduced the size of the β platelets in alloys with up to 0.5 Fe content regardless of the SDAS, whereas at small SDAS the refining effect extended up to 0.8 Fe, and involved α-phase intermetallics which replaced the beta platelets at those concentrations. At low Si contents, a high Cu level appeared to have similar refining effects as increased Si, through the formation of α-phase particles in the post-eutectic stage which agglomerated with the Al2Cu intermetallics. A high content of Si appears to make the overall refining process less critical in terms of SDAS/cooling rate.

The intermetallic microstructure in two representative regions of the cross section, the corner and the core, of a cast-to-shape tensile specimen was studied. Available 3D data of the intermetallic, obtained with focused dual ion beam tomography, were incorporated into a finite element code to simulate the deformation behavior. The modeling reveals a high structural compliance at both the corner and the core, akin to the bending-dominated behavior of cellular foams. The high compliance suggests that the percolating microstructure should keep most of its structural integrity, reinforcing the alloy without compromising the ductility, for strains above 1%. Scanning electron microscope observations of the damage by cracking of the intermetallic along the gauge of a tensile specimen deformed to fracture supported this prediction.

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.

Six Al-Si-Cu-Mg-(Fe/Mn) alloys with two levels of each of Cu, Si, and Fe/Mn were cast in the form of quasi-directionally solidified plates. The secondary dendrite arm spacing (SDAS) was measured as a function of the distance from the chill end for each composition and related to the local cooling rate as determined by thermocouples embedded in one of the cast plates. For a given cooling rate, Si has a strong, consistently refining effect on the SDAS per unit of solute content. Cu showed its strongest refining effect at low-Si and high-Fe contents. It is argued that the scale of the SDAS is determined by a combination of five main factors: constitutional undercooling; the fraction of Al-Si eutectic; and the amount, morphology, and distribution of the various intermetallic phases. The first two factors affect the early stages of the dendrite structure and SDAS formation, whereas the ones involving intermetallics affect the dendrite-coarsening mechanisms in the post-eutectic stage. The latter ones are more sensitive to cooling rate than the ones involving solute in solution. The scales of both, SDAS and intermetallics, can be predetermined to a measurable extent through the solute content to best suit particular casting conditions.

Earlier research carried out on the ductility of Al-Si-Cu-Mg alloys have showed that thenductility of Al-Si-Cu-Mg alloys with high levels of Fe (0.5 wt. %) and Cu (4.0 wt. %) isnincreased at high (7~9%) concentrations of Si. Quantitative metallographic analysisnperformed on these alloys suggested that the refinement of both Fe-rich b-Al5FeSi and Curichnt-Al2Cu intermetallics, arose from the shorter solidification path accounting for thenincreased ductility. More recent studies on the effect of Si concentration on the size and shape of iron-rich (Al5FeSi) intermetallic phase of ternary Al-Si-0.8Fe alloys showed thatnthe size of b-Al5FeSi plates increased with increasing silicon content. It was then proposednthat the presence of Cu was adamant to the refining effect of Si, presumably through thenintroduction of low melting point pools of Cu-Al eutectic. It was proposed that Fe remainednin solution in the Cu-rich liquid, whereas the liquid pools were dispersed by the highnvolume fraction of Al-Si eutectic, thus resulting in a finely dispersed and highly refinedndistribution of Fe- and Cu- rich intermetallics.Hence, this project has conducted a systematic study across a range of Al-Si-Cu-Mg alloysnto elucidate the mechanisms by which increased Si refines and disperses the Fe- and Curichnphases, increasing the materialrs ductility. Limits to the effect have been determined,nand the optimum content of the alloy components have been identified. This isnsupplemented by an optimisation of composition, providing the basis for improvednproperty-processing alloy selection.nThermal information of various Al-Si-Cu-Mg-Fe alloys were obtained during solidification,nusing computer controlled data acquisition device and the LabView-Signal Expressrnsoftware, and the corresponding SDAS were also measured on optical microscope imagesnfollowed by intermetallic particle size distributions that were measured using imagenanalysis software, Image-Prornsoftware, on the BSE SEM images in order to compare thensize refining effect of Si and Cu content on the Fe-rich and Cu-rich intermetallic phasenparticles for different SDAS, i.e. different cooling rate. EBSD and EDS mapping and pointnanalysis were used to identify the Fe-containing intermetallic phases. Sample preparednusing FIB was also used to further confirm elements, by EDS in TEM, on the script-like Fecontainingnintermetallic phase.Si and/or Cu content showed a considerable decrease in the size of SDAS for a constantnaverage solidification rate which should only be calculated between the liquidus and nsolidus temperatures; not between the liquidus and eutectic temperatures, especially whennhaving many solute elements, for the range of experimental Al-Si-Cu-Mg- Fe) alloys nstudied here. The relationship between cooling rate and the SDAS for the alloys wasndetermined in the form of l2 = a Rnmn where a and n are composition- nependent fittingnparameters, that also depend on the cooling rate calculation method. The combinednpresence of high levels of Cu, Si and Fe which produces intermetallics nthroughout thenentire solidification period, but particularly in the latter stages, hinders the SDASncoarsening, refining the SDAS for given cooling rate. nFe intermetallics exist as two different phases depending on the SDAS and Sinconcentration: (1) script-like a-Al8Fe2Si; (2) plate-like b-Al5FeSi. A preferential formation of na-phase particles is observed at high cooling rates, leading to an overall decrease in thensize of the intermetallics. Modification with Sr increases the size of pre-eutectically (Al-Si) nformed b- l5FeSi intermetallic plates whereas it reduces the co-eutectic and post eutecticnb-Al5FeSi plates (observed as curved-shape), especially at low cooling rates. i.e. there arentwo different distributions of Fe-bearing intermetallics that form in Sr-modified Al-Si-Fenalloys.nHigh levels of Si and/or Cu decreased the amount and size of the b-Al5FeSi nplatelets innAl-Si-Cu-Mg-Fe casting alloys, especially at small SDAS if the Fe level is below the Sindependent critical level for the formation of the pre-eutectic platelets (for the Fe-bearing nphases precipitation in the post eutectic stage). At small SDAS, in the low Si (4.5%) alloys,nCu leads to decreased size of the intermetallics whereas in the Cu-free, high-Si alloy, the nplates are replaced by a mixture of the irregular alpha-Al8Fe2Si and b-Al5FeSi platelets, i.e.nin the Cu containing alloys, plates are nformed even at small SDAS.nHigh levels of Si decrease the size of the Fe-bearing intermetallics in Al-Si-Fe alloys at 0.2 nand 0.5 Fe level. This effect is accompanied by the formation of script-like phases, npossibly a-Al8Fe2Si or branched b-Al5FeSi plates, isolated or clustered together. Thescript-like Fe-intermetallics are formed, in high Si nalloys, at low and high solidification ratesnfor the 0.2 and 0.5 Fe alloys. In the low Si alloys, this only occurs at high solidification rates. The number density of script-like particles is higher in the high Si and low Fe alloys, nsuggesting that the eutectic Si provides additional nucleation sites. A high level of Cunrefines the intermetallic particles in nthe low Si alloys, but it may have the opposite effectnwhen the Si level is high. The optimal composition for a strong and ductile casting usingnsecondary Al-Si-Cu alloys nappears to be 9Si and 1 Cu, for the alloys Fel0.5, and for thenalloy with Fe g0.5 a high Si (g9 mass %) with a maximum SDAS of 30 mm. The SDAS nshould not exceed 30 nmm for Cu g1%, for both low and high Si, in order to obtain a wellrefined population of intermetallic particles.