When Coastcast was approached by Canada’s World Heart Corporation (WorldHeart) about producing prototype titanium castings for a ventricular assist device (VAD) it quickly decided that rapid prototyping was the only way it could produce high quality patterns in time to meet WorldHeart’s deadline.

A ventricular assist device is an auxiliary pump designed to provide long-term support for people suffering form heart failure.  In the past, VADs have been bulky units that have required patients to be hooked up to external pumps or power supplies. WorldHeart Corporation, based in Ottawa, Ontario, Canada, is developing the first fully implantable VAD and needed titanium castings for laboratory testing. 

According to WorldHeart, the new HeartSaver VADTM  will offer lifesaving benefits to thousands of cardiac patients whose only previous hope might have been heart transplants.  Similar in size to a natural heart and weighing approximately 500 grams, the HeartSaver VAD^TM  is designed to be implanted in the chest cavity to assist a damaged or poorly functioning heart.  Power to the device is transferred through the patient’s skin and tissue so that no permanent body openings are required, and a custom-designed microchip allows the device to be remotely monitored or even controlled through a telephone line.

WorldHeart came to Coastcast, a public company with two foundries in the United States and six in Mexico, because of Coastcast’s titanium investment-casting expertise.  Coastcast is one of the world’s largest manufacturers of titanium golf clubs.  In addition, the company makes a variety of cast orthopedic implants and surgical tools.  According to Coastcast’s medical sales manager, Dennis Brookings, making  hard-tooling to produce wax patterns for WorldHeart’s complex castings would have taken at least 18 weeks and cost more than $50,000.  And because WorldHeart’s design was still in development, subsequent design changes would have required expensive reworking of the tools.

So Brookings contacted Sigma Time Compression Technologies in Newport Beach, California.  Sigma suggested using WorldHeart’s CAD model to build casting patterns directly out of a proprietary material with physical characteristics similar to those of conventional investment-casting wax.  Coastcast knew that the patterns could be used without any alteration of the company’s casting methods. 

Sigma’s director of engineering, James Klohr, says it took about 90 hours to build each of the investment-casting patterns.  They measured approximately six inches long, five inches wide, and two inches tall. Klohr says it is capable of delivering superior feature definition and accuracy.  Klohr says Sigma built the parts using a 0.0002-inch layer thickness and did no finishing on the parts before delivering them to Coastcast.

Coastcast’s product engineer, Roy Redfern, says the foundry was able to successfully cast all ten of the patterns it received from Sigma.  After casting, he says, the titanium parts were put through a hot-isostatic-pressing (HIP) process to remove any gas inclusions and a chemical-milling (chem-mill) operation to create a super-smooth surface finish.  When titanium is cast, it develops a very hard surface that is almost impossible to finish.  Chemical milling uses acid to remove this hard shell. 

Coastcast was able to deliver the first finished casting to WorldHeart within approximately seven weeks of receiving the CAD file.  Over the next four months, it sent WorldHeart an additional nine castings, which WorldHeart used for testing. 

As a result of its evaluation of the prototype parts, Corson says, “WorldHeart decided to modify the HeartSaver’s design, both to reduce weight and improve manufacturability.  If hard tooling instead of rapid prototyping had been used to create the casting patterns, these design changes would have been much more time-consuming and expensive.”

Currently, Coastcast is in the process of creating hard tooling for preproduction HeartSaver VAD^TM   castings.  In the meantime, it also has asked Sigma to make patterns of WorldHeart’s final design.  Thus, weeks before WorldHeart will receive its first castings from the hard tool, Coastcast will be able to deliver production-grade castings of the new HeartSaver VAD^TM   design for further evaluation. 

(Taken in part from Incast Magazine, originally from Rapid prototyping report: Editor Geoff Smith-Moritz)