Abstract
The use of microfeature-enabled devices, such as microfluidic platforms and anti-fouling surfaces, has grown in both potential and application in recent years. Injection molding is an attractive method of manufacturing these devices due to its excellent process throughput and commodity-priced raw materials. Still, the manufacture of micro-structured tooling remains a slow and expensive endeavor. This work investigated the feasibility of utilizing additive manufacturing, specifically a Digital Light Processing (DLP)-based inverted stereolithography process, to produce thermoset polymer-based tooling for micro injection molding. Inserts were created with an array of 100-μm wide micro-features, having different heights and thus aspect ratios. These inserts were molded with high flow polypropylene to investigate print process resolution capabilities, channel replication abilities, and insert wear and longevity. Samples were characterized using contact profilometry as well as optical and scanning electron microscopies. Overall, the inserts exhibited a maximum lifetime of 78 molding cycles and failed by cracking of the entire insert. Damage was observed for the higher aspect ratio features but not the lower aspect ratio features. The effect of the tool material on mold temperature distribution was modeled to analyze the impact of processing and mold design.
Highlights
Micro-structured surfaces hold the potential to improve the inherent functionality of products ranging from consumer goods to medical devices to adhesive technology
Whether these systems work based on surface energy modification, light wave manipulation, or microfluidic transport, the inclusion of periodic or asymmetric positive and negative microscale features onto the surfaces of products can yield new properties which would not be intrinsic to an unstructured product
Issues have been a lack of standards for device testing and development [4], general market dynamics being unfavorable for investment [5], and practices which use processes and techniques for device creation which, at the laboratory scale, are simple and straightforward operations yet are not feasible to scale for mass manufacturing methods [6]
Summary
Micro-structured surfaces hold the potential to improve the inherent functionality of products ranging from consumer goods to medical devices to adhesive technology. When Vasco and Pouzada [29] utilized electron beam melting (EBM) to print an injection molding insert containing positive and negative micro walls (200 μm high by 100 μm wide) arrayed in pentagon and star patterns, they noted incomplete feature printing due to the minimum spot size of the laser This limitation is shared by all of the laser-based metal printing processes as they exhibit limited laser focus diameters of 50–300 μm [27]. Vasco and Pouzada [29] produced star and pentagon featured tooling through a laser-based SLA system, yielding a spot size of 75 μm; initial results were affected by early breakage of microfeatures during the injection cycle, tool duration was not reported and investigation of wear properties for the SLA tooling was abandoned Their channel designs had a higher high aspect ratio (AR = 2:1), which could have contributed to stress on the tooling. The mechanical propertiesEolofnHgTaMtio1n4a0tVB3resaukggested its%suitabil3i.t5y for withstanding the higher pressures and temperatures in theFmleixcruorainl jSetcrteinogntmh olding enMvPiraonme1n1t5
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