ite iron through rapid prototyped moulds using the EOS S700 SLS machine proved that the cylinder heads were similar in all aspects to traditional prototypes, but reduced manufactur- ing lead times from 4-6 months to 2-4 weeks.6
surfaces of the sand particles due to the presence of inclusions such as Al2
guchi experimental evaluation8
and are indicative of the relatively easy melting of O3
, forming a salt-like eutectic with the SiO2 . Ta- of the influence of process pa-
rameters on significant properties such as strength and perme- ability of LASER-CORN resin-coated quartz sand particles processed on an EOSINT S700RO SLS machine revealed that the compressive strengths were equal to or better than those of traditional moulds, and that the permeability was considerably higher than referenced industry standards for synthetic sands.
The other RP process that allows direct production of pat- ternless moulds from CAD models is 3D printing by Z Cor- poration and notably, the potential application of 3D print- ing for the direct production of ceramic shells as patternless moulds for metalcasting was identified very early by Sachs et al.,9
Curodeau et al.,10
while investigating the Direct Shell Production Method. used 3D printing to produce ceramic shells
within hours, without the use of any pattern and used the alu- mina ceramic shells to cast orthopaedic prostheses with CoCr. A comparison between 3D printing and SLS reveals that the SLS technology is expensive, requires long processing times and high power usage. Since Z Corporation offers a ceramic mould material suitable for casting nonferrous metals and al- loys, 3D printing finds renewed interest as a means of rapidly producing patternless moulds. Kochan11
took an early look at
the 3D printing process and elaborated on the effectiveness of the process particularly in terms of the build size and the processing time. The ability to cast nonferrous metals into moulds produced directly from CAD files meant considerable time savings, rapid casting of prototypes (using realistic ma- terials), and economical and rapid production of small pro- duction runs (10-20 parts). Bak12
ferences between the two sand systems, thermo-mechanical effects and distortions in overall dimensions were higher in the sand produced by the PUCB process.
Investigations
led to an understanding of the bonding mechanism of sintered moulds7
Once the effectiveness of 3D printing in producing quick castings of nonferrous metals and alloys was established, further research was undertaken to establish the mould and casting characteristics obtained using the rapid casting methods. Bassoli et al.15
while comparing the relative mer-
its of producing an automotive part, by direct casting into printed moulds and indirectly through the use of a printed starch pattern for investment casting, reported an average surface roughness of 10 µm for the castings made from print- ed moulds. A benchmark model was used to assess accuracy indicators such as: surface profile, circularity, concentricity, and angular tolerance of parts produced from materials like starch (ZP14) and plaster (ZP100) on a Z400 3D printer, Dimitrov et al.16
showed that material type, build direction,
and magnitude of measurement contribute to deviations in measured accuracies. Plaster-based powders were found to yield higher accuracy, possibly due to finer grain size, while both materials yielded parts that were slightly larger than the original CAD models, though an intelligent selection of the scaling factor could easily resolve this issue. Comparative assessment of the surface quality of castings produced from moulds made by traditional means and printed using ZCAST 501 showed that the surface roughness is slightly higher in the case of RP moulds resulting in a Ra (Ra = arithmetical mean roughness of a surface) value of 14.9 mm compared to 13.6 mm obtained in traditional moulds, possibly due to the stair-step effect of the layered manufacturing technique.17
notes that 3D printing is far
superior in terms of production capability, compared to SLS and the capability to produce local tooling to facilitate short production runs. Considering the production of 50 dispensing manifolds, it was observed that 3D printing was an effective and economical solution, with tolerances around ±0.38 mm and surface roughness of 200-300 µm.
Lyons13 compared the green strength and the response of
moulds produced by 3D printing to conventional coatings (i.e., paste wax and polyvinyl alcohol) and found that printed moulds can be made to reasonable tolerances. Thermal dis- tortion testing by Rebros et al.,14
of printed sand moulds us-
ing silica sand and a furan binder printed on a ProMetal S15 rapid casting machine in comparison with chemically bond- ed sand using Phenolic-Urethane Cold Box (PUCB) showed thermal cracking in both samples at elevated pressures and temperatures leading to distortions in specimen shapes. While testing after 90 seconds did not show significant dif-
26
It is apparent that most research in rapid casting methods thus far, is limited to either establishing the effectiveness of a par- ticular technique in the rapid production of functional cast- ings or the evaluation of the surface roughness or dimensional stability of the castings in a few cases. Clearly, the advantage of rapid casting in small run production systems is obvious; these methods are gaining popularity and most likely will become important production techniques suited to specific manufacturing tasks. While traditional casting methods offer a vast amount of data on the mould and casting characteristics, influences of process parameters on key responses and opti- mum conditions in various situations researched over the past decades, these new mould materials and the rapid casting pro- cess lack sufficient information for the foundry practitioners to appropriately choose process conditions. Research into the mould materials characteristics using ZCAST501 conducted by the current authors18,19
allowed the evaluation of optimum
baking time and temperature for the material ZCAST501, suggested by Z Corporation for moulding purposes. While permeability was a bit low, compressive strengths obtained at approximately 1 MPa were acceptable and the optimum bak- ing time and temperature were found to be 227C (440.6F) for 6.2 hours and 173C (343.4F) for 5.5 hours for the best perme- ability and compressive strength.
International Journal of Metalcasting/Summer 2011
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