Engineering Insight

Stent Guide Maker Uses Electric Moulding Machines to Achieve High Precision

Posted by emdtadmin on September 1, 2009
Initial outlay pays off handsomely in part quality, reduction in cycle time and extension of tooling life span, says contract moulder


Miniature guides are used by surgeons to accurately place stents within arteries. Moulding these tiny parts to tight tolerances in a repeatable manner requires a different set of skills from a surgeon, but both operations require exacting precision. BCR Plastics AG (Vallorbe, Switzerland;, which designs and manufactures tooling and provides contract moulding services, set out to assemble the expertise necessary to manufacture precision guide elements in 2005 by bringing mouldmaker Beco and injection moulders Cebo and Rolla into its orbit. With a little help from a battery of electric moulding machines, the manufacturer now routinely fabricates stent guidance components that weigh as little as 0.0012 g and measure 2.5 mm in length with an external diameter of 1.8 mm. Permissible tolerances are in the range of ±2%.

In order to meet the unique challenges of precision micromoulding, BCR has installed all-electric Roboshot moulding machines from Fanuc (Stuttgart, Germany) in its shop. The machines boast clamping forces between 30 and 50 t and are equipped with 16-, 22- and 28-mm standard screws. It is also worth noting that the electric machines allow plastification to continue during mould open times, says Rolf Bucher, BCR Sales and Marketing Director. In addition, a range of injection moulding operations including part ejection, part blow down and cooling can be done simultaneously. One of the primary benefits of electric machines compared with their hydraulic counterparts, however, is a 30% reduction in cycle time, adds Bucher. And then there is the matter of precision.

“Electric machines are more precise—by a factor of 10, at least—than hydraulic machines,” Bucher says. “In particular, mould closing is smoother and more precise in electric machines, which can increase the life span of the mould significantly,” he explains. “Even after six months of around-the-clock production of several million parts, no wear can be detected on the mould.”

While these features come at a cost, the return on investment must be measured against the losses incurred as a result of downtime when conventional equipment is used, according to Cor Smit, CEO of BCR Plastics. The company runs approximately 25 injection moulding machines from other manufacturers at its facility, which allows it to make sound comparisons.

“If I could produce microparts on a standard machine at half the investment cost with a reasonable return, I would do it,” says Smit. “But that equation does not work. Initially, we had serious discussions about the cost of the machines. Eventually, we calculated empirically that the one-third reduction in cycle times and low part reject rate [made possible by the electric equipment] was the way to go,” explains Smit. Electric moulding machines, on average, are amortised 40% faster than hydraulic machines after five years (or 30,000 operating hours), according to Smit.

With the stent guidance system, BCR has ventured into a growing market, strengthening its position as a supplier to the med-tech industry. The manufacturer also produces parts for medical endoscopes in large quantities and lends its expertise to the moulding of a measuring lens for use in visual diagnostics. Poised for further growth, the Swiss company has completed its expansion and consolidation phase, which also included the establishment of a German subsidiary in Stuttgart, BCR Deutschland, to better serve the European market and interact more effectively with customers.

Copyright ©2009 European Medical Device Manufacturer

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