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The purpose of this paper is to review available technologies, analyse their features, propose a new approach of 3D sand mould printing based on line forming, introduce the manufacturing principle and show advantages of this approach, especially for larger parts with large Z steps in the build, such as 2 mm stepwise.

This paper introduces 3D sand mould printing, compares and analyses technological process and existing fabrication approaches among available technologies first. Then, a new approach of 3D sand mould printing is proposed to improve build speed. In addition, the proposed system will be analysed or benchmarked against existing systems.

A new approach based on line forming of sand mould printing is put forward by reviewing and analysing available technologies, to improve build speed from the aspect of basic moulding movement instead of optimization of moulding methods and process parameters. The theoretical calculation and analysis shows that build speed can be improved greatly, and it is more suitable for the manufacture of large-scale casting’s sand mould when considering dimensional accuracy and printing error, as well as uniformity of each layer.

The specific implement scheme of line forming and nozzle’s specific structure of this new approach need further study.

Much higher build speed of 3D sand mould printing with new approach brings evident implication for moulds companies and manufacturing industry, having a far-reaching influence on the development of national economy.

This paper reviews available technologies and presents a new approach of 3D sand mould printing for the first time. Analysis of the new approach shows that this new method of sand mould printing can boost build speed greatly. So, its application prospect is great.

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.

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.

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.

The experimental result is compared with the computer simulated results.

The purpose of this study is to analyse the problem of high binder content in sand mould and to solve it. Meanwhile, to increase build speed, especially for heavy casting’s sand mould with a high value in layer height, such as 2 mm in construction instead of the industry standard of 0.3 mm, line forming for three-dimensional (3D) sand mould printing is researched.

Brief introduction of 3D sand mould printing and key issues are given first. Then, this paper quantitatively analyses binder content in sand mould. Finally, to acquire sand mould with appropriate binder content and high build speed, line forming combining traditional furan no-bake sand manufacture technique is researched, as well as relevant feasible schemes and current progress.

The study shows that compared with traditional technique, binder content in sand mould produced by available 3D printing technique is too high, bad for sand mould’s properties and quality of castings, while line forming brings guaranteed binder content and improved build speed.

More experiments are needed to demonstrate quantitative analysis of binder content and to obtain flowability of moist sand, detailed structure design of nozzle and practical build speed, as well as methods of circulation of materials considering solidification time.

Line forming with higher build speed and suitable binder content means excellent properties of sand mould and castings as well, bringing obvious implication for moulds industries and manufacturing industry.

This new method could increase build speed and meanwhile guarantee binder content. Thus, its application prospect is promising.

With a growing list of available materials and processes, the inherent mechanical and thermophysical properties of three-dimensional (3D) prints are important design targets. This paper aims to study the functionality of binder jet 3D printed objects for thermally activated building construction elements and recyclable formwork for concrete structures.

Binder jet printed sand samples with various material and post-processing parameters (infiltration and baking) are prepared and studied. Using a statistical experiment design, the mechanical (flexural and compressive strength) and thermal (conductivity and specific capacity) characteristics are quantified.

Relative to the unprocessed “green” print samples, post-processing improved the flexural and compressive strength of the samples by factors of 6.9 and 21.6, respectively; the thermal conductivity and specific heat capacity were improved by factors of 7.7 and 1.2, respectively. For the investigated temperature range (20°C–200°C), the “green” prints showed excellent stability while the stability of post-processed samples depended on the infiltrate used. Microscopic images of the microstructures offered evidence to support improvement in the mechanical and thermo-physical characteristics of the 3D printed sand elements.

The literature review concluded that optimal printing parameters and infiltration under vacuum could further improve the mechanical and thermo-physical properties of the binder jet printed elements. However, both these factors were not explored in this research. The statistical experimental design approach provided more flexibility to choose the number of experiments for a fixed amount of time and resources. However, for future work, a more extensive number of experiments and reproducibility testing for each combination of binder-infiltrate is recommended.

3D printing has been identified as a promising opportunity to reduce material usage and improve construction efficiency in the field of architecture and building engineering. The emerging fabrication technologies are further expected to significantly reduce the operational energy of buildings through performance integration, i.e. multi-functional building elements with integrated heat- and mass-transfer capabilities to replace conventional systems.

This study has quantified the impact of infiltration on the mechanical and thermo-physical characteristics of sand-printed elements and, as such, reports reproducible functional performance maps for sand-print applications. The research demonstrates a way to achieve the desired functional characteristics of 3D prints through combinations of material selection and process/post-processing parameters.

The major concern technologies during the processing through three-dimensional printing (3DP) are the mechanical and boundary properties of sand models. The parameters such as activator content, resolution X, layer thickness and re-coater speed play a vital role in 3DP sand components. The purpose of this paper is to recommend the optimal process parameters for the best sand mold properties.

In this paper, taking the parameters of the activator content, resolution X, layer thickness and re-coater speed as the influence factors, an orthogonal test of L16(44) was designed to discuss the influences of those parameters on the mechanical and boundary properties. Three-point bending (3PB) test was used to characterize the actual bending strength, and the boundary accuracy was assessed by the deviation of the three-point bending samples compared with its design scale.

The experimental results showed that the resolution X and layer thickness are the main parameters affecting sand mold properties. The strength will attain its maximum when the resolution X and layer thickness are the minimum. The optimal parameters were screened and verified by the confirmation test. The optimal process parameters for best strength and less gas evolution are the activator of 0.19%, resolution X of 0.1 mm, layer thickness of 0.28 mm and re-coater speed of 210 mm/s.

The novelty of this paper is the select of significant parameters on 3D-printed sand model properties. A mathematical model was built to analyze the effect of these parameters. The optimal process parameters for the best properties were got.

Metal casting industry is in recovery phase after the crisis in 2008; customer demand continues to increase, with 98.6 million metric tons cast in 2011. Traditional ferrous and non-ferrous casting techniques require one shot or permanent moulds which require tooling to produce. Tooling particularly for developmental projects can be costly and take valuable time to produce. Additive manufacturing (AM) has been used to manufacture sand patterns for metal sand casting using laser sintering and sand bonding. This research aims to focus on characterising the sand-bonded process developed by ExOne GmbhH Germany.

The approach taken in this research is to evaluate characteristics of parts built in the build volume for dimensional accuracy, tensile and compressive crush strength, density, impact strength and high temperature resistance. These properties are required to compare the 3D sand printing (3DSP) process to direct laser sand sintering (DLSS) and traditional Furan-based casting sand mixtures. The samples were taken from a production machine over a period of 30 days to ensure consistency.

The 3DSP process has the capability to manufacture sand patterns to an accuracy of ±0.5 mm or error less than 0.3 per cent; it has also demonstrated the best build position to achieve accurate parts. The research has demonstrated the 3DSP patterns are comparable to traditional methods for important casting material characteristics such as tensile, compression and impact strength. It has been shown that the 3DSP process is capable manufacturing significantly larger parts, with build production rates up to 30 times higher compared to similar parts manufactured via the DLSS process.

As they has been very few 3DSP machines sold in Europe and particular UK, they has been little research into this new technique, and, therefore, they is a reliance on machine manufactures data for assessment. This research into 3DSP has increased the knowledge of this process significantly.

This research would be of interest to designers and manufacturing engineers wishing to take advantage of the implications of having new design freedom, tool less manufacturing with short lead times in a wide range of materials using fundamentally tried and tested century’s old casting techniques.

The research for this paper revealed very little published academic research in this area; therefore, this work will increase the body of knowledge for this niche AM process.

The purpose of this paper is to analyze the current state of the art manufacturing techniques using sand molds for the casting industry by the means of additive manufacturing (AM). In particular, this review will cover two families of 3D printing in regards to sand mold fabrication.

This paper will discuss the sand casting manufacturing processes of AM by binder jetting (3D printing) and selective laser sintering. Scientific articles, patents and case studies are analyzed. Topics ranging from the technology types to the economic implications are covered.

The review investigates new factors and methods for mold design, looking at mechanical properties and cost analysis as influenced by material selection, thermal characteristics, topological optimization and manufacturing procedure. Findings in this study suggest that this topic lacks vigorous scientific research and that the case studies by manufacturers thus far are not useful.

As demonstrated by the limited data from previous published studies, a more comprehensive and conclusive analysis is needed due to the lack of interest and resources regarding the AM of sand molds.

This study is a useful tool for any researchers with an interest in the field of AM of sand molds.

Key perspectives are proposed.

This review highlights current gaps in this field. The review goes beyond the scientific articles by curating patents and professional case studies.

In this paper, the effects of the adhesive and curing agent contents on the tensile strength, bending strength, gas evolution and gas permeability of three-dimensional printed sand molds are studied. A strength model of the three-dimensional printed sand molds is proposed. The multi-material composite sand mold forming test is carried out. In addition, the mesostructure of the sand mold is studied.

The performances of three-dimensional printed sand mold such as tensile strength, bending strength, gas evolution and gas permeability are studied using the standard test methods. The mesostructure of the sand mold is studied by digital core technology.

A sand mold strength model based on the resin adhesive content, curing agent content and sand mold compactness are obtained. Two types of multi-material composite three-dimensional printed sand molds are proposed. An increase in the curing agent content in the sand mold widens the mesoscopic characteristic size distribution of the sand mold, and large-sized mesostructures appear, resulting in a decrease in the sand mold bearing capacity.

Process parameters that affect the performance of three-dimensional printed sand mold are revealed. The sand mold bearing curve provides a reference for the ultimate design of three-dimensional printed sand mold.

The paper deals with experimental work on the performance and mesostructure of multi-material composite three-dimensional printed sand mold with different contents of adhesive and curing agent. That gives a perspective on future designs of sand mold based on these principles.

This paper aims to determine how the viscosity and curing agent content affect the flowability of moist silica sand granules. In addition, a coating device was designed according to the flow properties of silica sand granules.

The flowability of silica sand granules premixed with two curing agents of different viscosities is studied using a Jenike shear apparatus. An open-ended device was used in discharge testing of sand granules with a design based on the variable dip angle of the two plates and variable outlet size.

The test results show that increasing the curing agent content would significantly decrease the flowability of silica sand granules, and a curing agent of higher viscosity has a greater effect on the flowability of silica sand. The presence of a curing agent strengthens the cohesion among sand granules, lubricates them and restrains their deformation. The shape function of the coating device was obtained by theoretical derivation.

The flow properties provide a valuable theoretical guidance for the design of coating device for sand mold printing.

This paper deals with experimental work on flow properties of silica sand granules with different viscosities and curing agent content. The shape function of a wedge-shaped coating device is obtained based on experimental data.

Three-dimensional (3D) printing technology allows geometric complexity and customization with a significant reduction in the structural environmental impact. Nevertheless, it poses a serious threat to the environment when organic binders are used. Binder jet printing of alkali-activated geopolymer precursor can represent a successful and environmental-friendly alternative.

The present work reports about the successful 3D printing of metakaolin-based alkali-activated concrete, with dimensional integrity and valuable mechanical behavior.

The geometric behavior was studied as a function of alkali activator flow rate, and the minimum geometric deviation with complete saturation was recorded at 103 mg/s. The printed specimen is characterized by a modulus of rupture as high as 4.4 MPa at 135 mg/s.

The 3D printed geopolymer-based concrete can be potentially used in a wide range of structural applications from construction to thermal insulation elements.

The analysis of the 3D geopolymer-based concrete printing system and material conducted in this paper is original.