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Putting Theory into Practice

July 9, 2010
As rapid prototyping gets more sophisticated and rapid manufacturing techniques are developed, business models emerge for metalcasters wishing to adopt faster or more customer-focused processes.
Graphicast designers work with customers to develop cost-effective castings, including solutions for the radii, cast surfaces, and near-net-shape geometry, to optimize production and to reduce machining.
A foam pattern that Aesir Metals produced for a bevel gear. “Within 10 days of the PO being cut,” details Aesir Metals operations manager Mark DeBruin, “the customer had castings.”

Earlier this year, a new foundry started up in eastern Ohio, near Youngstown. Apart from the audacity of starting such a business in the teeth of such a challenging economy, partners Mark DeBruin and Jeff Rocco appeared to have a fairly recognizable plan to produce ductile and gray iron castings. Their production equipment includes two coreless induction furnaces, a tundish ladle, a custom-designed compaction table, and a 36X48 in. flask, though larger molds can be accommodated, too.

But, what appears to be typical foundry is something much more, and Aesir Metals LLC in Struthers, OH, is developing a model — or prototype — for other metalcasters to improve their competitive prospects. Aesir’s strategy involves prototyping, in particular rapid prototyping.

Rapid prototyping is a manufacturing concept, not necessarily a metalcasting process — though, not necessarily not a metalcasting process either. Rapid prototyping involves developing physical prototypes of finished products before starting series production.

Prototyping presents a range of possibilities for metalcasting operations, both theoretical (e.g., product and/or process design) and practical (i.e., time-saving production of patterns and cores.)

Product designers have been working with rapid prototyping technologies for more than two decades, sometimes in parallel or as an extension of computer-aided design (CAD) software. These technologies, like stereolithography and fused deposition modeling, are additive processes in which a prototype structure is built layer by layer in a foam or other lightweight material that can hold the desired shape. Such processes have been a boon to patternmakers and the foundries that they supply. The patternmaking sector now includes numerous suppliers of foundry-ready patterns manufactured with rapid prototyping technology and machinery.

The technology also has given rise to “contract casting,” a term applied to firms that offer design services and rapid prototyping to engineering and/or manufacturing organizations, to help them convert their concepts into actual products. Such outfits make it possible for entrepreneurs or even large organizations to compress product development time and cost, reducing the time needed to produce a casting, finish and assemble it, and bring it to market.

Under contract
An example of such a company is Graphicast Inc., which emphasizes that designing a product to take advantage of rapid prototyping capabilities means that manufacturing capabilities (and limitations) can be addressed from the beginning of a project, so design flexibility is maintained. Graphicast makes design specialists available to customers, working with them to develop cost-effective casting solutions for a cast product. These solutions include the draft, radii, cast surfaces, and near-net-shape geometry, all in order to optimize the casting process and to reduce rework or machining.

A close view of a steel casting Aesir Metals produced using the lost foam process in under 10 days from receipt of the order.

Following the design stage, Graphicast produces graphite tooling and molds for the net-shape castings. Because graphite molds can be machined easily, manufacturers can modify their designs without much difficulty, even after production has begun. The final products are cast in a zinc-aluminum alloy, and then machined and finished. The company indicates that the typical turnaround time, from finished CAD design to production sample, is four to six weeks.

Graphicast’s customers have included manufacturers of communications devices, sensor housings; computer and office systems; electronic and electrical cases; industrial machinery and packaging; instruments and controls; and scientific equipment.

One of its customers is Isotech Inc., a Pennsylvania distributor of OEM products that plans to supply aluminum parts to industrial, commercial, and analytical and medical lab markets. “Our partnership with Graphicast is a great fit and allows us to bring dynamic manufacturing capabilities to our customers,” Isotech president Joe Casillo said recently.

Casillo explained that the Graphicast mold can be produced faster than a diecasting mold and at an average of 20% of the cost, and can be stored indefinitely and reused for future production orders.

Isotech also likes the zinc-aluminum alloy, which has a density approximately equal to cast iron, but capable of more design flexibility and high-quality surface finishes than can be achieved with other casting processes.

“The graphite casting process is a good fit for OEMs needing to produce quantities of 200 to 20,000,” said Casillo. “The reduced costs allow for rapid prototyping, short-run production, and product testing.”

Stereolithography on the factory floor
Graphicast works as a contractor to designers and manufacturers, but foundries hoping to adopt rapid prototyping techniques to their operations have some options. Stereolithography has advanced beyond patternmaking to cover mold and core production, thus bringing the processes out of offices or labs and into the foundry operation.

An as-cast exhaust connector unit for a racing vehicle, cast in Ni-hard D5-S ductile iron by Aesir Metals using the lost-foam process in a quick turnaround cycle.

The most notable name in this effort is ExOne Co.’s Prometal RCT business, which builds machines that use stereolithography to produce sand molds and cores directly from CAD models. The latest version of the technology is its S-Max machine, now available.

Like the previous ProMetal RCTTM systems, the S-Max converts a CAD model into a pattern by dispensing “micro droplets” of a sand-and-resin media into thin layers that ultimately form the final product — a core or mold. Finished products can be sized up to 1,8001,000700 mm.

The S-Max system creates complex shapes without any of the customary machinery needed for core or moldmaking, saving time in the overall production process. Compressing the time for design and production also adds to the foundry’s ability to modify and customize molds according to changes in product design or production requirements.

Lost foam as RP
Whereas many applications of rapid prototyping in metalcasting rely on new technology, Aesir Metals is using established processes and deploying them with more insight to customers needs. The startup operation in Struthers, OH, is a lost foam foundry making itself available to supply large steel and iron castings with very short turnaround times.

Aesir Metals’ operations manager Mark DeBruin explains that his experience and metallurgical understanding of both iron and steel is important, because it allows Aesir to work an understanding of the capabilities and potential for casting both metals.

The new S-Max from ExOne Co.’s Prometal RCT business is a plant-floor machine that used stereolithography to produce sand molds and cores directly from CAD models by dispensing “micro droplets” of a sand-and-resin media into thin layers that ultimately form finished products up to 1800 x 1000 x 700 mm.

Lost foam casting uses foam patterns, and according to DeBruin the time it takes to produce the foam pattern is the only restriction on Aesir’s ability to deliver castings with short lead times. Aesir’s patterns are produced in various ways, including CNC machining foam blocks into patterns for large castings. Recently, DeBruin reports, the company cast and delivered a large casting of a steel bumper for a military vehicle, with as-cast holes, and accomplished the turnaround just 10 days.

Similarly, Aesir has cast large-scale rolling mill gears weighing up to 800 lb. The gear business is a market that has shown particular promise for the new company, and while Aesir is emphasizing its prototyping capability it is the capability for low-volume production of such products where it intends to establish its niche.

At a Society of Manufacturing Engineers (SME) conference in May, DeBruin demonstrated to designers and manufacturing engineers how lost foam casting accomplishes more than other prototyping technologies by quickly producing parts that are close to final, for aerospace, commercial vehicles, and other markets where design specification and low-volume production capability are critical. He recalls that many listeners were in disbelief, because of their perception that lost foam casting is suitable for large-volume orders. By changing those perceptions, Aesir Metals intends to establish lost foam casting as a rapid prototyping process.