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Materials Photo courtesy Cordis Neurovascular ceramic: As people were taking steps, their joints were literally squeaking—loudly!—and these are permanent implants, so there’s no easy way to minimize the sound. The other challenge with ceramics is that they’re comparatively brittle—if they receive the wrong impact, they break, creating a problem much worse than noisy joints.” While the squeaking is a quality of life problem, it is not much of a wear problem. Ceramics are essentially selflubricating. But there are also serious machining issues with ceramics. They are extremely hard, so shaping them is a problem—especially when you need such a perfect fit. Nitinol: Thanks for the Memory A material that is growing in popularity for certain applications is the titanium/nickel alloy nitinol, which has shapememory capabilities that make it exceptional, MacNeal says, and there are players in the industry that specialize in making devices that take advantage of that ability. “A common example would be nitinol stents,” she notes, “which can be manufactured in a shape needed to rebuild a blood vessel, then collapsed to a much narrower diameter for easier insertion into the vessel, and finally allowed to resume its ‘remembered’ original shape as a scaffold to support the blood vessel.” Cordis Enterprise stent, a self-expanding shape-memory nitinol microstent. Shape-memory nitinol is also used for filters deployed in the aorta—if a blood clot gets through the aorta into the heart, it can mean instant death for the patient. MacNeal is impressed with the nitinol-based solution. “These filters are amazing—shape memory allows them to be inserted in a compact form, but when they deploy, they look like fishing lures, with tiny prickers or barbs that extend out to catch clots before they can enter the heart.” Nitinol is also a metal popular in angioplasty applications: “The cardiac sector of the medical device industry is huge— Putting MIM in Gear at Parmatech ATW about an articulation gear part in an instrument subsidiary Parmatech Corp. (Petaluma, CA) was approached by a medical instrument manufacturer primarily used for minimally invasive surgical operations. The component was designed to be polymer injection molded, but during trials and development, the articulation gear would strip due to the forces involved. Since it was already in late-stage development trials, the OEM had temporarily switched to an aluminum machined part to be able to continue production without delay. The machined part was then insert molded with plastic. Machined aluminum was sufficiently strong to prevent stripping of the gear teeth, but the subsequent cost to machine was a significant departure from planned costs. The OEM launched the product with the more expensive machined component, and then sought to convert the machined component to a MIM part. The part is insert molded, a process in which tolerances are typically accurate to within 0.0005" (0.0127 mm). Historically, plastic molders have been hesitant to use MIM parts for insert molding, because the tolerances are so tight that if the MIM part’s dimensions miss any tolerance, the insert molder’s tools could be destroyed. One of the most commonly used alloys, MIM-stainless steel 17-4, was chosen due its low material cost, robust operating parameters, and extensive operational history in terms of as-sintered tolerance capability. Parmatech made the 17-4 stainless steel articulation gear part with its proprietary MIM process, and then sent the part to the insert molding company, which put the part into the mold, sealed it and injected the insert molding. The two pieces, now joined together, were sent to the ultimate customer for assembly into the instrument. MIM process variation can induce a ±0.003" (0.076-mm) tolerance on a 1" (25.4-mm) dimension, so planning to put a MIM part into a hard tool steel mold, and have it properly shut off to prevent flash or tool damage, is a challenging exercise. Parmatech worked closely with the insert mold tool builder to determine precisely how much room we had and tolerances required. The critical portion of Parmatech’s sintering is to make sure the part’s feet have a certain pocket or envelope that must fit exactly: missing just one part risked crashing the insert molder’s tool. At the end of the day, the customer received an insert-molded MIM part that met their functional and cost requirements. The success of the project demonstrates how MIM can be used to increase part strength without the high cost of machining, even when insert molding operations are involved. Cost savings were substantial over the machined part, with no individual part handling occurring after the initial stack at molding. In addition, there is a much higher production rate capability with injection molding compared to machining. MIM material strength meets application requirements, and MIM material surface finish on the gear teeth was superior to that of machining. There was very little material waste in fabricating the parts versus machining and no secondary operations involved with burr removal like those needed in machining. 82 ManufacturingEngineeringMedia.com | May 2013
Materials second in size only to orthopedics. Cardiac applications call for companies that are good with wires; pulling wires and forming wires ... nitinol use is at the forefront of much of that.” Photo courtesy Symmetry Medical Hip implants made from Ti-64. Competing in the Disposables Sector Plastics are playing an important role in the disposables market. For hospitals, one-use products such as syringes and IV bags are easier to deal with, in terms of quality and sterilization concerns, said MacNeal. “If it’s a single-use throwaway, you know that unless there was a problem at the manufacturer’s sterilization facility, the product can be trusted. On the other hand, disposables are costly. And in particular, how are you going to enter the emerging markets where a lot of industry growth is happening, when these products are so expensive While a single disposable product itself may be cheap, the number needed can make them an expensive choice. “Some hospitals are looking at reclaim and reuse, and considering investing in metal versions of the products and sterilization processes and reuse instead of disposables. “The cardiac sector of the medical device industry is huge—second in size only to orthopedics.” Our company is working with an OEM to develop a disposable metal suturing device. In this case metal is desirable for its strength. There’s a cantilevering action involved for which plastic just isn’t strong enough in the size the company is looking at. But machining the piece from metal would be prohibitively expensive, so they’re looking at manufacturing the device through the use of metal injection molding—MIM, one of our company’s primary technologies. MIM: Sinter of Excellence “With MIM, you start with powdered metal with a consistency similar to flour, and mix it with a binder—usually a polymer—and heat it so that the binder can flow but the metal 84 ManufacturingEngineeringMedia.com | May 2013
Page 1 and 2: Photo courtesy Seco Tools Materials
Page 3: Materials “Those higher levels we
Page 7: Materials Photo courtesy ATW Compan

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