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CRITICAL ASSEMBLY HINGE AND SNAP FITS ARE SUCCESSFULLY TESTED WITH DSM SOMOS® 8120 PROTOFUNCTIONAL® RAPID PROTOTYPING MATERIAL
The eight month project targeted lofty goals that included 50% cost reduction and six sigma quality standards. To achieve the cost savings and quality improvement, the IPPD team redesigned the product’s housing to include an assembly hinge and snap closure. These two critical elements of the design were evaluated using DSM Somos® 8120 resin. DSM Somos® 8120 is a high-speed liquid photopolymer that produces flexible, high-impact-strength, accurate parts using stereolithography machines. During the presentation of the final proposal, the IPPD team used the Somos® 8120 rapid prototypes to illustrate the practicality and functionality of the design. From this demonstration, Medtronic Xomed believes that IPPD’s modifications can increase their nerve stimulators’ profitability and strengthen long-term market leadership. Medtronic Xomed is a global leader in ear, nose and throat (ENT) appliances, and a leading provider of nerve monitors and stimulators. During a surgical procedure, relying on visual recognition of nerve structures can be difficult and may lead to irreparable damage. Nerve stimulators and monitors allow surgeons to locate nerves by inducing small electrical currents to excite and identify nerve locations. In September 2002, the IPPD team began the redesign project. Mike Maszy, manufacturing engineer for Medtronic Xomed, was the liaison engineer for the project. To begin the work, Maszy and his team stated loosely defined goals of cost reduction, design for manufacturability (DFM), quality improvement and styling enhancement. They also directed the team to design the product to fit with constant flow manufacturing processes. The IPPD team took on the challenge and further qualified the goals to be a 50% reduction in manufacturing cost, production of the product to six sigma standards and improvement of ergonomics and product appeal. Medtronic Xomed supported these project goals since they were aligned with the company’s journey into lean manufacturing and six sigma quality. An early focus of the IPPD team was on the assembly process of the nerve stimulator. The team believed that significant cost reductions could result from a simplification of the manufacturing process and a decrease in rework. The current assembly process requires seven steps. The molded cylindrical housing is loaded into a machine and dimpled for component placement. The internal components are loaded into the housing from the top of the tube and then sealed with a rolling operation. IPPD’s new concept incorporates a clamshell design – the cylindrical housing is split along its length - with an assembly hinge and snap fits. This one-piece housing increases visibility and control to simplify the installation of the internal components. Designed for manufacturability, the new housing reduces the number of assembly operations by nearly 75% and eliminates secondary work. This translates to savings in assembly time, labor and rework. Mike Maszy is impressed with IPPD’s design and the team’s fresh, new ideas. “The team has done an excellent job with the new housing design,” said Maszy. “I am equally impressed with the job they have done on DFM. We are confident that this work will deliver, if not exceed, the 50% cost reduction we are targeting.” During early design concepts, two rapid prototypes of the housing were constructed on a Viper si2™ SL system. While suitable for form and fit analysis, the prototypes were not capable of functional testing of both the assembly hinge and snap fits. This rigid SL material did not offer the required flexural properties. To overcome this limitation, small segments of the early design concept were machined in ABS for functional testing of the snap fits. As the project approached its completion date, the IPPD team needed functional analysis of the final design and a functional prototype that demonstrated the concept. Yet to be tested, assessing the functionality of the assembly hinge was vital. With no viable options, the IPPD researched the market and found DSM Somos® 8120, an SL material that blends flexibility, durability and accuracy. With its successful application to flexing component like hinges and snap fits, the team was confident that Somos® 8120 was the right solution. Michelle Wyatt, Account Manager for DSM Somos®, commented: “Somos® 8120 is ideally suited for this project because the material is especially useful in functional applications, such as medical products, where flexibility and impact strength are critical requirements.' Upon receiving Somos® 8120 prototypes of the housing, the IPPD team immediately noticed the difference from the previous SL prototypes. Color and surface finish were superior, but the most important aspect was the obvious difference in flexibility. David Rumsey, an IPPD team member, commented, “The Somos® 8120 prototypes were great. They were definitely more flexible than the previous prototypes, and the finish and color were much better.” The team now had a tool for functional evaluation of the hinge and snap fits. In the testing, the snap fits worked as intended, but the assembly hinge failed. Although the IPPD team was disappointed that the design required additional work, they learned, as all engineers do, that the benefit of a prototype is detecting problems. From the Somos® 8120 prototypes, the IPPD team determined that the assembly hinge required a redesign. With the project nearing its end, the IPPD team made its presentation of the final design proposal to Medtronic Xomed. Using the Somos® 8120 prototypes to show the design and manufacturing concepts, the IPPD team demonstrated the advantages of its DFM plan and innovative product features. Following the presentation, Mike Maszy stated, “I am very impressed with the design and look forward to beginning the commercialization process. This design will provide the impetus for DFM throughout the company.”
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