rapid process made sense. Plus, machining the sand mold allowed for certain design enhancements not possible or aff ordable with a traditional pattern. “When we use [the sup-
plier’s proprietary] process, we don’t need to put draft angle on the parts,” Lefebvre said. “So when we make large parts, it can be an advantage because the cast- ing will be lighter and less expensive than one casting with a pattern.” According to Poweleit, with sand
printing, as with most other RP methods, designs are not geometri- cally constrained. “We like to say that anything
you can imagine, you can cast, but sometimes making the tooling is a little bit more difficult,” Poweleit said. “The neat thing about these techniques is there’s the freedom from having to create the tooling to get to that geometry.” T e enhanced design freedom is
particularly important on one- or two- run orders when tooling for extended production will not be required.
Cost Factors When you are utilizing RP or rapid
manufacturing, you are eliminating the costs associated with building and de- signing permanent tooling for multiple design iterations, reducing your costs of production tooling for small quanti- ties, and in most cases reducing your time to market. But the faster methods come at a cost. According to Burrow, a signifi cant
portion of cost should go to solidifi ca- tion modeling. “Typically, because you only have
one part, you can’t aff ord to lose the one pattern or mold you’ve created, so solidifi cation software is important and adds a fair amount of cost,” he said. “With a complex part with a lot of cross sections, the solidifi cation modeling can end up being half the price of a permanent tool, but you can’t aff ord to lose the pattern, either.” Material costs associated with the RP method are also a factor when
the surface. T is can aff ect tolerances. As the step size between layers decreases, the need for secondary fi nishing decreases and dimensional accuracy improves.
Industries Served
Robotic sand machining technology can produce molds for large parts quickly and without investment in tooling.
Rapid prototyping has been widely used for years by the defense and aerospace industries, but other in- dustries are starting to take advantage, including the pump, medical and automo- tive aftermarket industries.
quoting a part. For instance, the SLA method is usually cost eff ective for parts produced within a 1-ft. cube, according to Poweleit. Beyond a 3-ft. cube, the method might not be cost eff ective because of the size and cost of the SLA material. However, some niche organizations can produce large parts using this method. Tooling-less processes can reduce the cost and time of making a pattern, but tooling isn’t always an expensive option. CNC cutting of tooling has improved in accuracy and speed. Ren board material (a polyurethane used for patternmaking) has become more economical. “I’ve quoted parts where I thought
rapid molding would be the way to go,” Burrow said. “But I found out that with CNC, we could build the pattern fast and deliver it in the same timeframe for less because the pattern is so easy to produce using the CNC process.” New methods continue to be
developed—for instance, a group at Iowa State Univ. is developing a rapid patternmaking machine that removes layers to build a pattern—but the traditional methods are improving, as well, Poweleit said. “[RP] is going bigger, faster,
cheaper,” Poweleit said. “When you are talking RP, taking minutes off is meaningful. Reducing material costs is another important improvement.” In additive manufacturing, the
“steps” between each layer, which are visible on the surface of a part or pattern, are narrowing. Usually, the steps between each layer require secondary fi nishing to blend them into
“T e defense industry uses it often when tooling is lost and two, four or six pieces are needed,” Burrow said. “T ey can provide a 2-D drawing, it can gen- erally be converted into a CAD model quickly and the additive manufacturing method is chosen which is best suited for that particular part. T at’s cost sav- ings for not having to buy tooling, plus it’s a fast turnaround.” T e pump market has utilized rapid
methods for similar reasons, par- ticularly to repair parts. T e medical industry often uses rapid methods for implants, such as knee and hip joints. In some cases, an individual’s original joint will be scanned to create a CAD model so the part is an exact fi t to the individual. Many experimental medi- cal equipment components also are prototyped to prove out a design. Baldor’s fi rst look at sand machined molds has convinced the company to consider rapid manufacturing for future power transmission projects. “If we have rush orders, it’s sure
we will consider [rapid sand mold machining] again, especially for the ‘one-shot deal,’” Lefebvre said. “We don’t use rapid casting on a regular basis, but it would be useful when a customer has an unpredictable request because of a breakdown.”
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Nov/Dec 2011 | METAL CASTING DESIGN & PURCHASING | 43
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