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New materials and processing = design success
April 23, 2001
5 Min Read
"It's absolutely axiomatic that materials are important to a project," says Martin L. Green, President of the Materials Research Society (Warrendale, PA).
Materials dictate a product's integrity, weight, function, and price. The right material can save a company thousands, while the wrong one can result in bulk, breakage, and lost sales.
For example, engineers in the automotive industry are using rare earth cobalt magnets, which offer a higher energy product than traditional permanent magnets made from alnico. With these new materials, automotive engineers can design smaller and more lightweight components, such as wiper motors and speedometer couplings, says Green.
Sometimes researchers spend years looking for just the right material. After working 20 years to find organic polymers that act as superconductors, scientists from Lucent Technologies (Murray Hill, NJ) recently created the world's first plastic material in which resistance to the flow of electricity vanishes below -455F, making it a superconductor. The plastic, a solution containing polythiophene, is an inexpensive material that could be widely used for applications such as quantum computing and superconducting electronics.
In the following examples, engineers also found that the right material and related processing technique resulted in substantial cost and time savings for their companies:
Thixomolding cuts parts
Don't write a check and expect to wait a day to put the money in the bank any more. With the new SourceNDP check sorter from Unisys (Plymouth, MI), banks can process checks within minutes rather than days.
As a check enters the shoebox-sized sorter, a magnetic ink character reader (MICR) reads the code imprinted at the bottom. A CCD camera captures an electronic image of the front of the check, and then the back. The whole sequence takes about 2 seconds per check, substantially cutting down on the time of each transaction.
Using a form of magnesium injection molding known as Thixomolding, designers at Unisys eliminated 55 parts from the original aluminum die cast design, surpassed their flatness requirement, and saved on manufacturing costs.
At the sorter's heart is the base plate, says Mike Saunders, mechanical engineer at Unisys. It's about 14 x 6 inches with 4 standoffs approximately 21/2 inches tall. "Everything in the machine mounts to the base," he says.
Originally, Saunders and associates planned on fabricating the base plate from die cast aluminum or zinc. Marketing wanted a metal base plate to give the look and feel of a stable, heavy-duty machine. Engineering needed a metal plate so the base would serve as a giant grounding plain for static electricity generated by the traveling paper checks. A metal plate would also act as an electromagnetic interference shield as well as a heat sink, says Saunders. But their biggest concern was the need for a tight flatness control-important to ensure that the checks traveled properly through the paper path.
"We wanted a flatness of 0.015 inch," says Saunders, "but die casting companies would only guarantee us a 0.035 inch."
Looking for an alternative, Saunders ran across an ad for Thixomolding(R) from Thixomat (Ann Arbor, MI). In this process, metallic feedstock, such as magnesium chips, is fed into a Thixomolding machine, where the chips are heated to a semi-solid state. Mechanical shearing of the semi-solid metal generates a thixotropic structure so that the semi- solid metal can be injected under pressure into a metal mold similar to plastic injection.
With this method, Phillips Plastics, a licensee of Thixomolding, guaranteed Unisys a flatness of 0.028 inch. "But the process worked so well, we ultimately got down to 0.015 inch," says Saunders.
In addition to achieving the desired flatness, Unisys also saved money. And by using the injection molding process instead of die casting, Saunders and associates replaced 55 parts of the base plate including such things as the sub plate, screws, threaded studs, and fan guard with one molded part, saving substantially on assembly and tooling.
Ink instead of copper
For those looking for an alternative to copper circuitry, GDSI (Amery, WI) may have the answer. Mark Ester, company president, says GDSI produces a double-sided polymer circuit made from one sheet of polyester. Instead of a copper-clad laminate that is etched to remove unwanted copper, GDSI additively applies conductive inks (typically silver, carbon or silver/carbon blends) directly onto polyester, PEN, or polyetherimide substrates. "We print the circuit image exactly where it is needed. Waste is almost eliminated with this additive process," says Ester. "And we can create double-sided circuitry with vias through the substrate, which reduces the need for a second substrate material"
By printing on both sides, GDSI's double-sided polymer circuitry offers the same packaging advantages of double sided copper circuitry at a fraction of the cost, the company says. Compared with copper circuitry, however, polymer circuitry is limited. Copper can carry up to 100 milliamps, while silver is limited to 50 milliamps or less. Polymer circuitry also has higher resistance.
Tooling for the body
Guidant Corporation's Ancure? Endograft(R) System treats abdominal aortic aneurysms, a potentially life-threatening bulge of the aorta, without surgical techniques. In this procedure, a surgeon uses a catheter to insert a sheath through the femoral artery in the leg, causing fewer traumas and resulting in a safe repair and recovery.
The company originally produced the Ancure delivery system with machined plastic components. Then Guidant approached Phillips Plastics about manufacturing the system with injection molded plastic parts. "We had to keep the function essentially the same as the machined product, but we worked toward making the products less expensive, more ergonomic, and easier for the surgeon to use," says Paul Bell, design engineer for Guidant.
Thanks to this new fabrication process and tooling method, Guidant saw substantial cost savings in several areas. "First, the market-entry tooling Phillips provides was less costly than the quote we got from traditional tool vendors," says John Ordway, purchasing manager for Guidant. In addition, the company saved time, as molded parts did not take as long to manufacture as machined ones.
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