Rapid Casting of Light MetaLs:
an expeRiMentaL investigation Using tagUChi Methods S. Singamneni, O. Diegel, D. Singh and N. McKenna
School of Engineering, AUT University (Auckland University of Technology), Auckland, New Zealand Copyright © 2011 American Foundry Society
abstract
The phrase ‘rapid casting’ is being increasingly used to represent specific casting processes designed to reduce the total manufacturing lead time, by expediting selected critical steps. Rapid Prototyping (RP) is the means through which this is achieved, either directly or indirectly. There have been sporadic reports on this topic in the recent literature, but since the approach has the potential for considerable savings in production time, it offers opportunities for more design freedom in terms of patternless moulding, a scientific understanding of the process needs to be developed. This paper is an attempt in this direction, considering the rapid casting achieved by direct printing of sand moulds from Computer Aided Design (CAD) models, using 3D printing. The mould performance when used to cast light metals such
introduction
Rapid casting is one possible route to rapid manufacturing, the potential revolution in manufacturing processes in the near future, due to the brisk developments occurring in ad- ditive manufacturing processes. Additive manufacturing or layer manufacturing techniques have the unique capability to produce very complex shapes with low melting materials such as polymers and wax or powdered metals, such as tita- nium or steel. Common additive manufacturing techniques were able to produce complex shapes with relatively easy melting materials which led to the production of sacrificial patterns for investment casting and the replacement of time consuming manual patternmaking with Laminated Object Manufacturing (LOM). Direct production of sacrificial moulds followed next with processes such as Selective Laser Sintering (SLS) and 3D printing for the patternless produc- tion of complex sand moulds directly from CAD files. This paper focuses on the latter process and attempts to estab- lish the effectiveness of casting light metals (i.e., aluminium and magnesium) through experimental evaluation of casting characteristics using a multi-factorial approach.
The initial application of Stereolithography (SLA) for the production of a sacrificial pattern with a non-engineering plastic1
using other RP techniques2
and the subsequent extension of the same approach have produced promising results
International Journal of Metalcasting/Summer 2011
as aluminium and magnesium under varying conditions is studied in terms of mechanical characteristics and surface quality of the castings. Taguchi L9 experimental design is used to consider the total number of factors and the size of the resulting experimental designs. The results indicate the suitability of patternless moulds for casting aluminium and magnesium alloys without any loss of essential characteristics, but the process variables have a complex influence on the overall outcome in each case and the best results can only be obtained by the optimum combination of factors in each alloy system.
Keywords: rapid prototyping, casting, manufacturing, 3D printing
in terms of dimensional accuracy and surface finish, apart from significant time savings gained. Shell cracking result- ing from the thermal expansion of patterns during burn- out3
(acrylonitrile butadiene styrene) RP patterns from corro- sive degradation4
tions being investigated subsequently. While the residual ash content (2.218%) was typical of the Fused Deposition Modelling (FDM) pattern, compared to traditional foundry wax (0.04%), higher burnout temperatures were expected to lower the residual ash content.4
and the chemical attack of the ceramic shell by ABS were some of the other intriguing ques-
Overall, elimination of hard
tooling, leading to significant time and cost savings, without any appreciable loss in the dimensional quality was reported for small run production.
Though direct production of sand moulds or shells was at- tempted by using SLS and 3D printing, early research at- tention was focused on the SLS process, targeting renewed design freedom, reduced lead times, and costs.1
While the
initial trials assured sufficient dimensional accuracy and re- peatability, the surface quality was adversely affected due to the stair-step effect resulting from the mould walls. Intake manifold moulds for a KTM 525-cc single cylinder engine were produced using an EOSINT S700 SLS machine us- ing silica Croning sand resulting in an adequate casting and moulds with good gas permeability.5
Production of V6 cylin- der blocks using aluminium, grey iron and compacted graph- 25
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