End-users of large castings, such as this gear part, can obtain replacement parts quickly without replacing damaged or lost tooling.
arrive at additive manufacturing for a number of reasons and at different points of a product’s lifecycle, but the most obvious reasons are for samples and prototypes, he said. “They can try out a design and
actually have a casting, machine it and put it out there to see if it works,” Murray said. “They don’t have to build foundry tooling or wait weeks to get something cast.” So what makes for a good additive
manufacturing candidate? Grimm offered four elements: • Low volume. • High complexity. • Efficiency gains in the process. • Flexibility for design changes. “When a new part or a redesigned
part feels like a risk or could be problematic, that is your alarm bell,” he said. “When you are not sure about the design, trying something new or missed a date and in a time crunch, you could be a good candidate for additive manufacturing. In the design- er’s realm, it is an insurance policy.” Te additive manufacturing process
works similarly to that of an inkjet printer. Finely powdered sand and binder are repeatedly layered to build
a sand mold or core based on a CAD file. Production-wise, sand printed cores and molds are available in a variety of molding materials and bind- ers, including organic and inorganic, and can be used with most metals, including aluminum, magnesium, copper-base, iron and steel. Suppliers of sand printing technology continue to research new materials and binders to use. Build volumes range from 2.6 x 1.6 x 1.3 ft. to 13.1 x 3.3 x 2.3 ft.
Letting Imagination Loose What makes Murray giddy about
additive manufacturing goes beyond prototyping, into a Walt Disney, “If you can dream it, you can do it,” realm of manufacturing. Designers are not limited to working within the constraints of manufacturability. Because you are not removing cores from a corebox, certain conventional molding rules, such as draft, do not apply. Designing core assemblies as single cores removes the need for a fin where cores might have been glued together. In some instances, the core can be printed as part of the sand mold, providing closer tolerances because cores don’t have
to be set into the mold separately. For highly specialized, lower volume jobs, this design freedom is a strong case to utilize additive manufactur- ing for production runs. “Te young engineers are going to
start designing stuff that can only be made this way,” Murray said. “Before, an engineer would design a casting, and the foundry would have to tell him why it can’t be made and why it won’t work. Tat doesn’t fly anymore.” In markets such as military, aircraft and automotive, where designing weight out of a component is a huge driver, Murray sees additive manufac- turing playing the hero’s role. “If you can make a casting with-
out draft and take a pound out of an aircraft part, you are a god,” he said. Ingenuity abounds even in shipping.
Hoosier Pattern can ship cores printed within a thin-walled printed sand box that is then filled with loose sand. “You could print a box in a box in
a box, making it all at once,” Murray said. “You are limited only by your imagination.” In production scenarios, core
printing is emerging as a valuable tool for intricate parts requiring
December 2013 MODERN CASTING | 31
Photo courtesy ExOne.
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