Micro molding

Neilley, R., The Art of Fine-Tuning a Micro-Molding Business, Europe, Jan. 

When disposable filters are preferred (which may be the case for medical or microbiological analysis), it can be better to elaborate lower cost materials. A new and efficient way to prepare them is by deposition of polymers on patterned substrate structures (such as with phase separation micro-molding). 

Region-specific growth of CNTs has been achieved on a photolithographically patterned quartz surface or micro-molded surface with a micrometer resolution (Figure 13a). 

A third way to build up pFCs based on MEMS-polymers such as poly-dimethylsiloxane (PDMS) or polymethyl methacrylate (PMMA) or PCB-materials such as polyimid (PI) or FR4. These polymers can be micro-machined by molding or by laser ablation. Shah et al. [22,23] have developed a complete PEMFC system consisting of a PDMS substrate with micro-flow channels upon which the MEA was vertically stacked. PDMS micro-reactors were fabricated by employing micro-molding with a dry etched silicon master. The PDMS spin coated on micro-machined Si was then cured and peeled off from the master. The MEA employed consisted in a Nafion - 12 membrane where they have sputtered Pt through a Mylar mask. Despite an interesting method, this FC gave poor results, a power density of 0.8 mW cm was achieved. 

M. Heckele and W. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering, 14(2), 1-14, 2004. 

Drilling micro holes for effusion cooling, printed circuit boards, SEM aperture strips, inkjet nozzles, spray nozzles, satellite apertures, medical devices, and micro molds Automotive fuel injectors and nozzles Diamond nulled or turned micro grids, for optics, and also for functional surfaces Dental implants... 

Machining of micro molds and dies for a variety of applications including plastic parts mass manufacture... 

Zhao J, Mayes RH, Chen G, Xie H, Chan PS (2003) Effects of process parameters on the micro molding process. Poiym Eng Sci 43(9) 1542-1554... 

Klemic KG, Klemic JF, Reed MA, Sigworth FJ (2002) Micro-molded PDMS planar electrode allows patch clamp electrical recOTdings from cells. Biosensors and Bioelectronics 17 597-604... 

In either case, different tolerance, surface features, and accuracy may be required. Eor the micro injection molded parts themselves, the same rules apply (e.g., avoidance of sink points, etc.) as for normal plastic parts. Experience in micro-mold making and preliminary testing is mostly necessary. Here, the collaboration with the customer is a priority, much more so than in the area of standard shapes. 

Inclined surfaces and conical surfaces are often used in micro molds. In this principle, the mold halves are positioned to each other when closing the mold. The mold halves tense up to each other if the work was not done with absolute precision (which is not so easy with conical surfaces). When opening the mold, the tension releases, and there is a minimal lateral movement. This movement may be sufficient to damage the molded part or minimally deform it. This can have an impact not only on the dimensional stability but also on the process often the molded part can no longer be removed from the mold. 

Compared to conventional molds, the size of the inserts and injection molded parts are the real challenge for the designer in micro mold making. The durability of the insert in the injection molding compound after removal from the mold and the subsequent use must be taken into consideration. This can be achieved by constructive measures with special geometric shapes, but also by surface treatments of the inserts. 

---