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Metal Casting Technologies : March 2008
www.metals.rala.com.au 30 Even smaller companies like APCO Engineering, based in Tasmania, have been able to provide custom manufacturing, pattern making, casting and machining at world standard due to solid modelling technology. The company currently supplies componentry to Incat, maker of high-speed catamarans. There are a number of issues in confluence today which make the use of the latest software critical for a foundry to consider, said Meredith. "First is the requirement by customers for shorter lead times as well as pressure to reduce cost and casting prices. Second is the wide availability today of 3D CAD models for most new castings." Thirdly, Meredith explained that many experienced foundry engineers nearing retirement age are being replaced by younger people without the years of experience needed to develop a "feel" for the casting design process. He said providing an automation tool to these younger engineers can dramatically increase their productivity in designing casting processes. Again, one of the major barriers to broader implementation of simulation technology throughout the industry has been the amount of operator effort and expertise required to create TECHNOLOGY FEATURE the idea that the modulus approach is essentially an attempt to estimate the solidification times of various parts of the casting prior to attaching the rigging. However, using modern casting simulation software, the solidification time of every point within a casting can be calculated very quickly, and does not need to be estimated. It is often the case that, having downloaded a 3D CAD model by email, it is possible to run a simulation of the casting within just a few minutes, using the Finite Difference Method, to obtain solidification time information throughout the casting. The next question was how to relate this information to potential risers of various sizes which might be attached to the casting. At this point, having simulated only the casting with no risers, we cannot directly compare the solidification time of any arbitrary riser with the casting. The answer to this question was the development of a calculation which could convert the solidification times in the casting to equivalent modulus values. This would allow the user to directly compare a riser with the casting, since a modulus value for a riser can generally be calculated easily. Another question to be answered was whether, given an array of modulus values within the casting, a system could be devised which would recognise separate feeding areas within the casting and thus give advice as to how many risers would be required, and where they should be located. This has been accomplished by development of pattern-recognition software which is able to locate isolated areas of high modulus values, which are essentially "hot spots" in the casting which need to be fed. In some more rangy castings, there may be many such areas; therefore the system must be able to discriminate between very small areas which don't need feeding, and larger areas which do. The level of discrimination can be set by the user, by adjusting a "slider bar" from a "Less Sensitive" position to a "More Sensitive" position. Once the individual feed areas are identified, an appropriate riser can be sized for each of these. Since the maximum modulus value and the volume of each feeding area is known, it is relatively simple to apply known rules (as discussed above) to calculate the correct size riser for each area. Also, by plotting the location of the maximum modulus values within each feeding area, we can pinpoint the required attachment point for each riser. Of course, the actual attachment point is subject to considerations such as parting line location, ease of removal, machine locating points and other practical issues. Process improvements identified via CAST CRC's Best Practice program have resulted in one Queensland casting company saving $75,000 per annum. These savings coupled with a new business plan are set to improve the long term competitiveness of Investment Castings Qld -- a privately owned family company currently manufacturing high quality, low volume castings in a wide range of materials to diverse markets. This is a range of castings from the foundry using lost wax and hard sand moulding processes.