Sumitomo (SHI) Demag demos medical micromolding application at NPE2015

When machine builders want to highlight the precision and repeatability of a micromolding system, they often turn to medical applications. The medical device industry is famously demanding of its suppliers in terms of meeting specifications and quality expectations. To borrow a phrase, if you can make it there, you can make it anywhere. Sumitomo (SHI) Demag (Strongsville, OH) carries on that tradition at booth W623 at NPE2015, where it will mold a miniature POM gear used in a novel cataract surgery device.

The 0.524-gram gear, measuring 0.775 mm in diameter and with just 85 microns of space between the teeth, will be molded on a SE30DUZ direct-drive all-electric machine. Sansyu FineTool (Takahama City, Japan) built the single-cavity cold-runner mold, which will be loaned to Sumitomo (SHI) Demag by micromolder Makuta Technics (Shelbyville, IN). A robot from Yushin America Inc. (NPE Booth W763) will remove the micro-sized part.

The gear rotates a surgical blade in the new I-core Capsulorrhexis instrument for cataract surgery developed by Eye Care and Cure (ECC; Tucson, AZ). The procedure involves creating a circular opening in the human eye’s capsular bag, which holds the lens that focuses light onto the retina.

When a cataract forms, it clouds the lens so that vision becomes impaired or even blocked. The surgical procedure that removes the clouded lens material requires a uniform opening in the capsular bag. Conventional devices often are difficult to use and slow, and laser systems, while effective, are expensive and bulky. By contrast, I-core is suited for use in small facilities and by healthcare providers in emerging economies. The single-use, presterilized, compact device performs a uniform circular opening in the capsule in a matter of seconds. The device fits through a micro incision and affords the surgeon better control than most conventional techniques.

“When you consider the micron-measured precision requirements of the gear teeth on this part and the importance of the function they perform, it’s hard to think of a better way to showcase the precision capabilities of our equipment,” says John F. Martich III, Vice President and Chief Operating Officer of Sumitomo (SHI) Demag’s U.S. operations.

“In a part weighing just a half gram, a stable process and shot-to-shot consistency are even more important than in typical molding applications,” adds Regional Sales Manager Tony Marchelletta. “The SL screw assembly, together with the Z-Molding capabilities of the SE-DUZ, meet all of the challenges this part presents."

The SL (Spiral Logic) screw assembly eliminates shear heating instability, which can cause fluctuations in molten resin density and other problems in traditional injection molding systems. With the SL screw assembly, the GS loading system matches the speed of the screw and can feed or meter the material, even at a pellet-by-pellet rate, according to the company. The screw is designed with no compression zone, eliminating melt stagnation or degradation in the barrel. Additionally, the GS valve, which replaces a check ring, is a positive-locking non-return valve that prevents backflow of material into the barrel. Resin pressure is stable the entire length of the screw, ensuring a highly stable process and shot-to-shot repeatability.

Meanwhile the Z-Molding Flow Front Control (FFC) system takes advantage of the energy in the flow front of the resin to complete filling in an even fashion rather than forcing material into open areas, and the Z-Molding Minimum Clamping Molding (MCM) system automatically defines the threshold where flash-free molding can occur and the point at which cavity venting is optimal.