MDDI_Medical Device & Diagnostic Industry

MDDI, June 2014

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MD + DI MEDICAL DEVICE AND DIAGNOSTIC INDUSTRY JUNE 2014 | 39 Molding PUTTING THE CONTRACT MANUFACTURING PUZZLE TOGETHER FROM MEDICAL SUBASSEMBLIES TO FINISHED DEVICES Phone 763.972.9206 FAX 763.972.2096 ISO 9001:2008 ISO 13485:2003 •Product design to commercialization •Medical Subassemblies to Finished Devices •Project planning to meet your needs and execution time line •In-house modular automation. Automation without all the capital investment •Silicone molding and Extrusion, Thermoplastic molding •Overmolding, insert molding •Class 10,000 Cleanroom manufacturing •In-house tooling be acceptable in the final product or be re- moved through secondary processing. This, of course, adds cost. The location of the gate can also result in localized effects that can change the part's physical properties. For example, the pressure required to cause the material to flow into the mold cavity through the restricted gate can result in concentrated stress, increasing the shear in the gate area and producing a potentially defective part. Design engineers must also ask how the part will be ejected from the mold. In an ini- tial design review, a part may have reasonable wall thickness and features, but the geometry may not allow ejector pins to remove the part from the mold. Thus, engineers must take this factor into consideration as well. Rapid Prototyping vs. Micromolding One of the dilemmas associated with rapid prototyping is that it does not have the same restrictions as molding. Rapid pro- totyping can create features with opposing undercuts or details that are not within the normal opening and closing direction of the mold. And because parts with such features would not release normally from the mold, a secondary side action—of a mechanical, hydraulic, or pneumatic nature—could be necessary. Alternatively, the mold could re- quire some type of lifter—an ejector pin or feature inserted into the mold at an angle so that it moves away from the part as the part is ejected. But if the part's features are undercut, face each other, and are too close together, there is no chance for the mold components to move to clear the undercut without hitting the opposing mold components, which are also trying to move out of their undercuts. Sometimes it is necessary to be creative in the tooling approach to work around such restrictions, making it incumbent on the design engineer to be cognizant of the challenges before getting too locked into a design. Know Your Design As soon as a part design is completed—or even conceived—it should immediately be reviewed to determine whether it can with- stand all the manufacturability challenges it will face. Design engineers should review the material selection, part geometry, ability to fill the cavity with material, ability of the mold to eject the part from the cavity, and ability of all the mold components to sustain proper thermal control to achieve optimal cooling or heating of the cavity. One of the tools that can be employed during such reviews is software simulation, a method by which it is possible to test—from a theoretical or from a simulation stand- point—different gate locations, mold and melt temperatures, and material processing parameters. This method allows engineers to simulate the cavity-filling process, part warping as a result of residual stresses, cool- ing times, pack times, and pressures. Much work has been performed to correlate simu- lations with actual product results, thus al- lowing engineers to reasonably predict the robustness of the molding process. Jeff Randall is vice president of en- gineering at MRPC. Reach him at 2 ES450990_MD1406_039.pgs 06.03.2014 02:41 UBM black yellow magenta cyan

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