MATERIALS • PROCESSES
To cast, or not to cast
Richard Phillips reveals the prime candidates for conversion of fabrications and assemblies to castings
T
he design and manufacture of a metal component involves a multitude of decision points and will be influenced by considerations such as structural performance, weight, lead time, cost and
aesthetics. Questions relating to precisely how that component is going to be manufactured are often left until the design is at a fairly advanced stage. This could be the case where there is pressure to get
a manufactured product to market quickly or where design engineers have already decided to fabricate an assembly or component due to familiarity with the process. The reality is that many of these fabrications – particularly components with complex geometries – could be cheaper, lighter and stronger if they were cast in one piece. A closer examination of the options available for component manufacture can often reveal considerable opportunities for improvements in manufacturing costs, lead times, performance and aesthetics. Clearly, casting will not always be an option, but there are certain component or manufacturing process characteristics that make some components particularly good candidates for conversion from fabrications to castings.
WHAT TO LOOK FOR A good starting point is to focus on assemblies with complex geometries that are difficult to fabricate. These could be machined or forged assemblies, particularly where several of these components are welded or bolted together. In addition to being time consuming and expensive, the welding process itself can also create stress and distortion. This is common when wrought sections are welded together. Casting components in one piece can deliver a homogenous microstructure so performance can be improved as weak points (welds) are eliminated. Weight reduction without loss of strength is often a
consideration for design engineers. Castings can allow material thickness to transition smoothly throughout a component. Metal can be placed only where it is needed, which can considerably reduce overall weight without compromising performance. Using just the
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quantity of metal required to achieve the desired performance also means that casting can use material more efficiently as there is less waste to start with and what there is can be recycled back into the production process.
Casting a complex assembly in one piece can deliver
tangible benefits where uniform directional strength is required. Wrought metal (rolled or forged) exhibits directionality (anisotropy) where a component has strength or ductility in one direction but its transverse properties are lower. Cast products are isotropic, which means that they deliver consistent strength and ductility in any direction. As castings are typically isotropic, uniformly heat-treated and more stress relieved than a
Industrial and agricultural machinery manufacture offers many conversion opportunities
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