Micro Molding


Gate location: It is critical to choose a gate location that will actually create uniform flow in a micro molded part. Without a uniform flow, the part may not fill the thin-walled cavities and do damage to the delicate pins and cavities. Thinking ahead as to how to remove this gate later on in the assembly process is important because if it has already been de-gated, the gate trim job may have left a divot or a proud protrusion that has to be rotated away from nesting, guide rails, or other parts. Gate vestige: Most micro molded parts are kept on an edge gate. If so, they need to be de-gated properly to avoid issues with small “picks” of material causing damage to an artery, or causing issues with automation and assembly. These small picks can be addressed in the mold design by placing a dimple in the wall thickness (if the walls are thick enough that is) so the vestige will “sit” below the surface of a guide or a mating component in the assembly. Surface finish: Often overlooked, the surface finish of a molded part is im- portant in “riding” or “guiding” features into other features. Some surface fin- ishes in assembly are best served with vapor honing or roughening the surface to provide improved surface area for bonding, for example. Smoother sur- faces in assembly can cause problems in ejection from the mold and a trade-off surface may be required in order to “steal from Peter to pay Paul.” Which one will be the lesser of the two evils is dependent on material selection. ME


Donna Bibber is President/CEO of Micro Engineering Solutions (www.microengineeringsolutions. com), a micro-focused design and manufacturing company providing micro machining, micro molding


(thermoplastic, silicone, pharma) and fast micro prototypes. Bibber has published hundreds of technical papers on micro manufacturing topics and was voted onto the List of 100 Notable People in Medical Devices.


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