Introduction
Despite the fast and ongoing advances of Additive Manufacturing processes (AM), parts printed by Binder Jetting (BJ) technology present high brittleness, specially in ceramic materials. Thus it is a challenge to reduce it through post-processing (PP) to create competitive mechanical and thermal strengths. One of the most widely used PP is the infiltration, which is a way to achieve high density parts without the large shrinkage to full density [1]. Infiltration occurs when the liquid is drawn into the open pores of the printed part through capillary action and solidifies. In this sense, this work proposes two objectives: 1. Characterize the 3D printer powder base material, - grain size distribution
and chemical composition - and print moulds directly for rapid casting applications, and examining their dimensional changes and friability;
2. Analyse the main influential parameters of infiltration on the flexural and tensile properties of 3DP parts, infiltrated with common materials.
of α
Parti cle 1 Parti cle 2
Particle 1
Particle 2
a)
b)
INFILTRATION FOR IMPROVEMENT OF THE MECHANICAL AND THERMAL PROPERTIES OF 3D PRINTED PARTS
WITH PLASTER POWDER MATERIAL
Edwin Ocaña-Garzón1,2, Jorge Lino Alves2, Leonardo Santana3
1Departmento de Ciencias de la Energía y Mecánica (DECEM), Universidad de las Fuerzas Armadas–ESPE, Sangolquí, Ecuador; 2INEGI, Faculty of Engineering University of Porto, Portugal; 3International
CNPq fellow, Faculty of Engineering University of Porto.
Materials and Methods
The 3D printing material VisiJet® PXL Core with water based binder VisiJet® PXL were printed in a 3D printer Projet 660 Pro (3D Systems, USA). The infiltrating materials are Ethy Silicate (ES), Levasil (L), Ludos SK (LSK), Aeordisp (AD),Ticoat-N (TN) and Zirconium Acetate (ZA).
Results and Discussions
For powder characterization, two types of representative particles were identified, (spot 1 and 2), with their chemical composition (Fig. 2). Particle 1 has a similar composition of CaSO4.0.5H2O, and particle 2, contains calcium
sulphate and additives with a high carbon presence such as polyacrylonitrile ─(C3H3N)n─ [4].
Fig. 2. a) SEM analysis of 3DP powder particles, and
b) crystals of α-CaSO4·0.5H2O (adapted from [3])
Conclusions
• The 3DP powder material can be considered multimodal powder, whose
main constituent is
CaSO4.0.5H2O with (C3H3N)n, among others.• All infiltrated moulds reached a suitable thermal resistance to withstand the casting, since none of them presented the visual sign of burnout.
• The moulds mechanically were not strong enough, especially those with thin walls. However, best results were achieved with Ludox SK.
• Large increase in flexural strength was obtained, 447%, 338% and
150% for epoxy resin, cyanoacrylate and water, respectively, which suggests the importance of the PP in this technology.
Fig.3. PSD of 3DP powder, in volume density (%)
CAD Dim.
Av. size by wall thickness Av. Dev.
VisiJet® PXL Core powder was characterized in order to determine
the chemical composition and
particle size distribution (PSD), in a
First study: a simple geometry for
moulds with 4 different wall
thicknesses was printed, whose internal dimensions were controlled prior to infiltration (total immersion at different times, see Table 1 and 2) with binders recommended for investment casting.
Table 1. Internal average dimensions of green mould samples (mm)
Heat Code Wall thickness Spec.(mm)
Table 2. PP moulds samples condition and results
Moulds were cured at RT with forced air for 2 hours, and later post-cured at 3 different thermal cycles (Fig. 1). After that, Al alloy AlSi9Cu3 was casted on them at 700 ºC and finally, their toughness was evaluated.
Second study: Epoxy Resin (E), Cyanoacrylate (CY), magnesium sulphate (MS), and drinking water (W), were used as infiltrated materials in accordance with the methods recommended by the provider [2]. One batch was not infiltrated (referential green specimens). Three-point bending and tensile tests were conducted according to ASTM D790 and ASTM D638 respectively, to obtain the maximum flexural “
s
fM” and tensile strengths “s
tM”.Fig. 1. post-curing heating cycles of moulds samples.
* Hydrolyzed (with 50% isopropyl alcohol)
SEM (Phenom ProXL USA) with EDS.
Regarding infiltration, for up to 120 s. of immersion times (not all the infiltrates allowed to work), provided greater penetration into the mould, but greater times, caused surface softening. After infiltration and full cure, the aluminium was casted (Fig. 4), and after cooling its friability was evaluated.
Table 2 indicates a friability property that uses an arbitrary scale, with values from 1 to 8, where 1 was assigned to the
specimen with better
consistency and 8 to the
worst.
Fig. 5 shows the average size of the 3DP specimens before
and after impregnation,
relative to the second heating
cycle, where most of the
infiltrates were used. The
dimensional stability of sample 1T30 in all sides was the best one. Specimen 7T3.5 (Nº7 and wall thickness 3.5mm,
immersed in AERODISP®)
experienced mould shrinkage, and specimen 3T2.5 exhibited some growth.
In the second study for flexural strength, it can be concluded
that even for samples
infiltrated with E (16.45 MPa)
and CY (14.68 MPa), their
standard deviation does not intersect each other (Fig. 5). In the case of infiltration with MS, the values obtained were too low, 0.66 MPa, and the green
part is 3.01 MPa, which
indicates a good repeatability of the 3D printer.
Figure 4. Moulds submitted to heat treating a) cycle 1, b) cycle 2 and c) cycle 3, after casting.
Fig. 5. Variation of the internal dimensions in specimens after impregnation (heating cycle 2).
Keywords: Infiltration; 3D printing; powder characterization; mechanical strength; plaster moulds; rapid casting.
Acknowledgements
Authors gratefully acknowledge funding of Project to Universidad de las Fuerzas Armadas, ESPE, and Project
NORTE-01-0145-FEDER-000022 - SciTech - Science and Technology for Competitive and Sustainable Industries, cofinanced by Programa Operacional Regional do Norte (NORTE2020), through Fundo Europeu de
Desenvolvimento Regional (FEDER).
The overlay curves of PSD of powder, in % volume density, are shown in Fig. 3. It can be seen that in % of equivalent volume: up to 10% have <7.12µm; up to 50% have a <36.1µm; and up to 90% have < 77.3µm.
a) b)
Fig. 5. Maximum a) flexural strength, and b) tensile strength of infiltrated specimens compared with manufacturing data.
Tensile tests showed that the infiltrate E is slightly less resistant of these two infiltrates.
References
[1] Feenstra, F.K., Method for making a dental element. 2005, US Patents: USA; [2] 3D Systems, I. StrengthMax User Guide. 2013 [cited 2016 apr. 29]; Available from: https://3dscentral.3dsystems.com/attachments/.pdf; [3]
