November 12, 2009
Originally Published MPMN November/December 2009
Molder Achieves Microminiature Features for Urological Catheter
Precise tooling and material selection enabled Miniature Tool & Die to mold a minimally invasive device with challenging design parameters
Using precise tooling, MTD micromolded tiny features for a urological catheter that other vendors deemed impossible.
Kidney stones are among the most-painful and, unfortunately, most-common afflictions of the urinary tract. In fact, more than 500,000 patients each year end up in the emergency room with kidney stone–related problems; almost 3 million see their healthcare provider with related concerns, according to the National Institutes of Health. To treat this distressing urological disorder, Boston Scientific (Natick, MA; www.bostonscientific.com) has developed a catheter with an articulating distal end. Inserted into the body through the urethra, the device is designed to navigate the narrow channels of the kidney and ureter, fracture the stone, and remove the debris through remote control of the articulating end of the catheter.
Yet despite the ambitious pursuits of the company, the extremely small requirements of the articulating components posed a distinct manufacturing challenge in terms of moldability. “It had to be very small and very strong,” recalls Isaac Ostrovsky, an engineer at Boston Scientific. Among the requirements were a wall thickness in some areas of 0.005 in., a 0.010-in. diameter, and 0.060-in.-long channels. “Vendors that I spoke with—there were at least three—tried to convince me that such a small thickness and small holes cannot be done, so I should change the design parameters. The truth is: If parameters were larger, the product is not needed.”
When Boston Scientific contacted Miniature Tool & Die (MTD; Charlton, MA; www.miniaturetool.com), however, the micromolder accepted the challenge. “There were some very thin sections with a fairly long flow length relative to their thickness, and what everyone told [Boston Scientific] was that it would not be possible to fill out those areas,” says Dennis Tully, president of MTD.
Although admittedly difficult, MTD decided that the project was feasible within its existing design parameters. The key to success for such minuscule features was proper tooling. “We spend a lot of time deciding how the best approach to the steel might be when we’re designing the tooling,” Tully says. This planning step is crucial because if a core pin is as little as 0.001 in. out of place, it could create an uneven flow that ultimately results in breakage of
The fragility of the core pins was also an issue in the ejection phase. Ejection of the final part from the mold after cooling is a precarious process when dealing with such microscale thicknesses and features. “There were four 0.009-in.-diam core pins that the part had to eject off of, and they really had no opportunity to be drafted due to the restrictions of the design of the application,” Tully says. “These are very dainty features, and if the part were to give any kind of a struggle during the ejection phase, you would probably break the cores.”
Taking this issue into consideration, MTD realized that material selection would be a determining factor in the success of this project. Furthermore, the material had to be able to withstand the intense pressure required to allow plastic to flow into such small areas. Weighing its options, MTD suggested using an acetal material, which offered the benefit of good fill coupled with easy release from the mold. The material offered the part the properties it required while making it moldable—a feat that other molders said was not possible.
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