The new compound has a hardness of about 46 gigapascals, the equivalent of 6.67 million pounds per square inch, slightly harder than CBN's hardness of 6.53 million psi. Diamond's hardness is between 10.15 million and 14.5 million psi. Alan Russell, associate scientist at Ames and professor of materials and engineering at Iowa State University, said the lab is tweaking the alloy's composition to see if it can be made even harder.

The new alloy also may be the least expensive—estimated at $700 per pound—of a very pricey group of materials. Cubic nitride-boron has a price tag of $7,000 per pound, and diamonds cost around $2,000 per pound. If commercial-grade (95 percent pure) boron, the main ingredient, is used to make the alloy instead of ultrapure boron, the cost could be even lower, perhaps $200 per pound, said Russell, who cautioned that his estimates were very rough and still preliminary. If initial estimates are close, the development could mean big savings to manufacturers that use these materials in abrasives and cutting tools for grinding and machining.

Diamond is not an option for cutting and grinding steel, because it degrades into graphite when it contacts iron at high temperatures. CBN, now the material of choice, is extremely expensive.

In tests, the new silicon-magnesium-aluminum-boron alloy has not reacted with iron the way diamond does. A Michigan company that supplies tools, dies, and molds to the automotive industry has tested the alloy with good results—especially that the material didn't fracture. However, Russell said, other attributes—such as lubricity and thermal conductivity—still need to be looked at to judge the material's suitability for metal cutting. For example, the alloy wears faster than CBN.

The alloy also has conductive properties that are unusual for an ultrahard material, noted Russell. Electrical conductivity is on the order of a semiconductor, such as doped silicon, he said. Potential applications—purely speculative at this point—are welding operations for microprocessor chips, as well as uses that have sliding wear, such as electric motor commutators.

Another interesting attribute of the alloy is that it can be melted into a liquid, opening up the possibility that it can be thermally sprayed in coating operations. The material is also being investigated for pulsed-laser deposition.

GW Plastics engineers examine a critical ABS part injection molded of PPS resin with a hot-runner valve-gate system in a 16-cavity mold.

The part was to be molded of Ryton BR111 polyphenylene sulfide, or PPS resin, supplied by the Phillips Chemical Co. of Bartlesville, Okla. Ryton BR111 PPS exhibits superior thermal and chemical resistance as well as high flexural modulus, according to Phillips. The high modulus provides good torque retention even after thermal cycling, a desired performance goal.

The small part includes a groove of about 0.25 inch from the top to receive a rubber O-ring. Any weld line mismatch or flash would hinder the function of the piston. "Even a sliver of material from the flash could rub against the ring, causing wear and even a cut, breaking the seal the ring should provide," said Timothy D. Holmes, GW's director of engineering. In this case, the customer mandated absolutely no flash, and the cost per piece did not allow for secondary trimming operations to remove excess plastic.

Chris Scherf, GW's tooling engineer for the project, explained that the part design specification required the outside diameter and O-ring groove diameter to be within 0.001 inch, and the parting line mismatch had to be held to the same specification.

A hot-runner valve-gate system was chosen to minimize gate vestige, according to Holmes. "We also knew that it was best to fill the part from the top," he added.

The gate vestige could not extend above the top surface, because a specific volume of hydraulic fluid has to be maintained within the ABS cylinder, and this is partly controlled by the height of the piston. A vestige of plastic standing above the piston could change that dimension, and could also chip off and contaminate the hydraulic fluid, Holmes noted.

GW Plastics, which was involved with the project from the prototype stage, molded parts and did capability studies that helped it design and build the production tool. "Ryton PPS proved to be very stable and had no shrinkage," said Holmes, who worked with Phillips engineers to optimize the process. Once the basic design was approved and the vestige problem solved, GW established a production process capable of hitting the targeted nominal part dimensions.

Until recently, producing living hinge prototypes by stereolithography was not possible. Instead, Tyco relied on using a computer numerical control machining process, which was time-consuming and expensive, according to Bob Zubrickie, a manufacturing engineer at the company's Harrisburg, Pa., plant. In one case, for example, CNC machining to create living hinges took longer than 50 hours to complete 10 parts, at a cost of $2,800, he said.

Tyco overcame that hurdle with the use of Somos 8110 epoxy-based photopolymer, supplied by DSM of New Castle, Del., which has a combination of flexibility and rigidity that makes it possible to create living hinges by stereolithography. The resin has an elongation at break of 27 percent and Izod impact value of 1.63 pounds per square inch. Somos 8110 mimics the mechanical properties of thermoplastic living hinges in production parts, according to Zubrickie.

The top housing is made from a flexible thermoplastic; above is its prototype made from DSM Somos 8110 epoxy-based photopolymer.

Tyco used Somos 8110 to make prototypes of connector housings, which protect fragile electrical components such as wires and connectors. A connector housing is initially in the "open" form to allow the components to be arranged in the housing correctly. Once the components are in place, the connector housing may be folded by hand along the living hinge to its closed position, and then installed in the electrical device.

"Somos 8110 significantly reduced production times and costs for prototypes of connector housings," Zubrickie said. He believes new material developments need to play a key role in stereolithography prototyping advancements.

Using stereolithography with Somos 8110, 12 parts were produced in less than five hours, at a cost of $260. It also gives a realistic feel of the plastic, mimicking the production material, he added, noting that this reduced the number of design iterations.

Upon experimentation, Zubrickie found that orientation was critical in the prototype hinge. Building the living hinge in the z-axis improves the strength of that area, because it ensures that the hinge will contain many build layers. By contrast, he found that building the hinges in either the x or y direction creates a score line leading to premature fracture. "When building the hinge in the x or y direction, I can't even get 15 degrees movement before breakage, he said. Implementing the z orientation allows me to obtain 90-degree movement—and in one case, I was able to cycle the hinge 12 times," he said.

Stereolithography saves time and money in the early product concept stage, Zubrickie noted. Stereolithography can work hand in hand with other prototyping methods such as CNC machining to make living hinges. Designs can first be made in stereolithography, before bringing the part to CNC machining and finally into production.

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