As technology becomes thinner and lighter, so do the parts that make devices function. For this reason, today’s most cutting edge tech companies are so fascinated with ultra-thin walled micro molding advances. But ultra-thin walled micro molding isn’t just about mold or cavity size. It’s just as much an art, as it is science and engineering.
First of all, what does ultra-thin walled micro molding look like? In an internal test, Accumold achieved a 42:1 aspect ratio, with a wall thickness, of 0.003 in. or 0.076 mm. While those numbers are truly impressive, the mold success wasn’t determined by heat, pressure and mold cavity size alone.
In our testing to determine how far we could push a diverse selection of resins, the mold was not modified between runs in any way, including the gate or runner system. We used standard processing windows as specified for each resin as the only variable to give each process a chance to fill the part on its own. The one critical dimension targeted was to maintain the .003” thickness.
In order to give the mold the best chance of filling, it was built with a thick to thin transition to create an optimal opportunity. This is not always possible when designing custom parts, but it gives micro mold engineers a great comparison to objectively determine what resins might give the best possible chance for success in various medical device, wearable or electronic projects.
To determine what might ensure success ultra-thin walled micro molding, our engineers asked numerous resin suppliers for their opinion on the moldability of our thin wall part. We also asked what thermoplastic would be most likely to fill the entire mold cavity. In all cases, our resin suppliers communicated strong doubt the part was even moldable. Most suggested we make the part thicker. We didn’t.
Ultra-Thin Walled Micro Molding Results
Our results showed that of the materials we tested, Polyethylene, Polypropylene, Polyoxymethylene, and Liquid Crystal Polymer achieve our 42:1 wall aspect ratio with only the Liquid Crystal Polymer, Polyethylene, and Polyoxymethylene filled completely, although, with a few minor mold adjustments, some of the other resins would have filled completely as well. This completely defied our predictions, software analysis from applications like Moldflow and even our own resin supplier opinions.
We were able to prove that resin data sheets can lead to inconclusive expectations when applied to the micro-mold area. The data is often calculated using much larger sample bars and their stated parameters may not apply. Most recommended gate sizes, for example, are larger than many of the micro-molded parts we produce.
Ultra-thin walled micro molding is not just science, it’s an art form and it’s not always possible to know what will fill. That’s why it’s always important to speak with a DFM engineer, like those at Accumold. If you have a project in mind, please reach out right now. Let’s take a peek.
This article is a short summary to our full white paper: Whitepaper: Material Selection / Thin-Wall Study
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