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

Abstract

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.

Study of the evolution of transport properties induced by additive processing sand mold using X-ray computed tomography

“…(Kadauw, 2014) characterized the local density of sand mold using industrial computed tomography, and found good agreement with the experimental density of sand mold. Some typical results were reported recently by (Sivarupan et al, 2018) for the use of X-ray µ-CT to characterize the additively processed porous structure like 3DP sand mold. (Anbar et al, 2019) used LBM to predict permeability from a computer-generated sphere packing, and to study the impact of sand compaction from the simulations.…”

“…An average pore connectivity value of Z ≈ 3 is obtained. In this regard, (Sivarupan et al, 2018) showed in a previous work that the speed at which the recoater spreads the sand particles on the job box platform affects the poreconnectivity, hence affecting the permeability. It can be deduced from the results displayed in Table 2 that the size of the grain does not affect pore connectivity, in contrast to the case of recoating speed.…”

Investigation of selected parameters effect on 3D printed sand mold properties through Taguchi method

“…Microfocus X-ray computed tomography can be used to quantitatively evaluate the packing density, pore connectivity and provide the basis for specimen-derived simulations of gas permeability of sand mold. Sivarupan et al (2019) simulated the gas permeability of 3D printed sand molds with this method.…”

Challenges and opportunities to integrate the oldest and newest manufacturing processes: metal casting and additive manufacturing

“…Similar to all AM processes, 3DSP requires a three-dimensional digital model of the desired part, which may be created directly with a computer-aided drafting software package and/or reverse-engineered from a three-dimensional point cloud of the desired final part geometry (Campbell et al , 2011). Simultaneously, this three-dimensional model can be used in simulation analysis for examination of metal flow and solidification rates for a range of casting and mold designs across different alloy systems (Sivarupan et al , 2019; Sama et al , 2018). Once this model is exported as a stereolithography file, process planning for every slice across the part in a layer-by-layer technique can be completed (Campbell et al , 2011; Druschitz et al , 2016).…”

“…Unlike traditional sand or high-pressure die casting, 3DSP castings and mold design are not limited by the need for draft angles, minimum wall thickness (based on 3DSP capabilities), aspect ratio, rounding of angular features and parting lines with their associated flashing (Sivarupan et al , 2019; Sama et al , 2018). Complex internal features (e.g.…”