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Metal Casting Technologies : March 2008
www.metals.rala.com.au 32 TECHNOLOGY FEATURE models, set up and run simulations, and evaluate simulation results. Until recently there was no simulation software tool that could assist the operator in developing the initial set-up. And, once a simulation was completed, if a defect was discovered, there was no advice given in how to improve the situation. All these decisions were in the hands of the software user, and results depended heavily on their individual expertise. New software tools have attempted to address this issue, by using simulation results to help the user design a rigging system that will provide liquid metal into the mould in such a way that a quality casting will result. This process actually reduces overall operator effort, while simultaneously improving results. Analysis by Jeff Meredith of these tools shows that improvements of well over 15 per cent are achievable, and in some cases energy savings of more than $100,000 per year were possible on the production of a single part. BRINGING TECHNOLOGY TO INDUSTRY To assist the SMEs involved in metal casting to meet the challenges of competing in a global market, there are numerous programs operating in Australia. One such program is run by the CAST Cooperative Research Centre (CAST CRC) which aims specifically to assist Australian metal manufacturers to stay competitive and increase their market share. Some SMEs have benefited from CAST CRC's Best Practice program, which was recently awarded for excellence by the CRC Association Committee. In the 2005/2006 financial year, 16 companies undertook 19 projects, producing major savings through manufacturing process improvements and product development. A few examples where adoption of individual Best Practice project outcomes had considerable impact for the participating SMEs include: ■ $40,000 per annum savings identified in an Energy Audit at Melbourne Gravity ■ 25 per cent cycle time reduction for aluminium wheels and hubs for New Castalloy, increasing capacity and reducing operating and maintenance costs ■ improved product quality and reduction in time-to-market through a die design project with Merne Products ■ $140,000 per annum savings achieved in a cycle time reduction project for Nissan Casting Australia Another example is Rogers Industries, which supplies Bocar Automotive Products with cast products (e.g. bumper bar components) for the assembly and manufacture of accessories (e.g. bumper bars) for companies such as Toyota, Holden, Nissan and Ford. Fig. 1 As an example of how 3D modelling can create the adequate design and position of risers for feeding a casting, consider the casting model shown in Figure 1. Designing the risering for this casting begins with selecting the casting alloy and mould material, which in this case are AISI 1030 carbon steel and green sand. A Finite Difference mesh is generated, and a simulation is run with no risers attached. The result of this simulation is shown in Figure 2 as a plot of critical fraction solid time throughout the casting. By applying the formulas and algorithms, the suggested risers were added to the casting model and a verification simulation was run. This is an important step, as it must be realised that the riser size calculations are approximations and cannot take into account all of the complex thermal interactions which occur in a fully-rigged casting. The risered casting and the simulation results, appear as shown in Figure 3. The macro porosity prediction (the dark area in the image on the right) shows clearly that the volume provided by the risers was sufficient to feed the casting without formation of internal shrinkage porosity in the casting. Fig. 2 Fig.3