Medical Manufacturing
• Pharmaceutical induced stents, anchors, needles, and sheaths
• Pharmaceutical powder inhalers • Diabetic pump with onboard valves • Hydrogel, and collagen implants • Micro aspirators • Biopsy forceps, sensors, and gears • Neurosurgical coil assemblies • Transdermal patches with injection-molded polymer needles
• Intraocular and ophthalmic implants • Hearing aids • Cranium reconstruction implants and tissue reconstruction matrixes
• Microfluidic point of care devices • Tiny endoscopes • Smart cancer therapies • Micro-guided surgery
A few planets need to be aligned in order for thin-walled
micro molding to be possible: a generous melt flow polymer (generally speaking >10-g/10-min melt flow); an extremely accurate core-to-cavity alignment (generally speaking <25% of tolerance); and highly balanced flow path (by mold design, part design, venting, etc.). Most thin-walled micro molding applications exhibit a
level of extreme manufacturing challenge. It is rare that they are manufacturable as initially designed or napkin-sketched, but oſten they are scaled down versions of something similar on the market, just several magnitudes smaller or requiring an experimental material due to a drug-releasing agent or characteristic.
A Solid Process Plan Tese devices may require pharmaceutical drugs directly
compounded with or added to polymers, metals, membranes, and have working gears, levers, and drive mechanisms to make the device function repeatedly and with robust longevi- ty. With these functions in mind, and the fact that these devic- es are so thin-walled, it is important that they are developed in such a way that it is expedient, robust, and tested to form, fit, and function to be able to work in extreme environments such as the human body or at exposed temperatures and pressures. As a result, thin-walled micro molded components require a solid process plan for success. Tis thin-walled micro molding plan may include some or
all of the following critical considerations: Proper material selection: low viscosity, low molecular weight
polymers; drying; moisture testing; material characterization. Micro computational analysis: thermal analysis; mold flow,
fill, deflection analysis; computational fluid dynamics. Ultra-precision tooling: robust mold design to last full de- preciation; core to cavity alignment; pre-validated spares.
36 Medical Manufacturing 2014
Elastomeric catheter tip overmolded onto a nylon tube.
A process plan for thin-walled micro molded device or
assembly must first consider if the thin walls will fill with a certain material, melt flow, and tooling strategy. A solid model is used to perform computational analysis to theoretically esti- mate these conditions and their design. Because micro molds and initial parts can be costly in their development cycle, micro mold flow analysis provides an insurance policy that a particular design will fill with a particular material. Micro molded components can be as small as dust specks or have features that are that small.
Flow Analysis and Modeling Methods An assumption made all too often when comparing
parts made by conventional molding methods to micro molding methods is that parts can be filled with the same software and same modeling methods. Flow analysis and modeling parts flowing through a 0.02" (500-µm) gate is
Properly sized and selected micro molding machine: shot
size appropriate; screw design fitting shear and heat profile of material; adequate injection pressures (30,000–50,000 psi; 207–345 MPa). Solid molding process plan: DOE; specialty nozzles; extreme
temperature, humidity; injection position control. Surface finish/coating: surface area for tiny geometry adhe-
sion; coating/plating/surface treatment for bonding micro assemblies; static-resistant surfaces; cleanliness. Handling: Te less handling the better; delicate tooling to
move, bond; extreme registration of part in several planes. Metrology: critical inspection criteria to microns; gage
R&R plan. Packaging: blister packaging; static-free bags; nitrogen- sealed foil bags; glass or plastic vials.
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