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Mechanical Engineer Review: Functional Rapid Prototype Enclosures

On a current project, we designed a modified COTS 7″ ruggedized tablet based on our Hydra-F6. The project required expanded battery life and customized sealed connectors. In order to meet the requirements, we had to build a completely new enclosure. Prototype parts in this size and quantity (

We considered various prototype processes including stereolithography (relatively inexpensive but too brittle), CNC machined plastic (high per piece cost but good mechanical performance), and pseudo-mold processes (high set up cost but most similar to production parts). After reviewing the options, we decided on a 3-D print using black ABS-M30 material and also a slightly cheaper selective laser sintering (SLS) process with black nylon 12 glass-filled material. Both processes and materials were chosen for the balance of cost versus mechanical strength.

As you see in the attached pictures and video (below), the parts perform very well; both parts handled the installation of press fit brass inserts without issue. The design also called for the circuit boards to be held down with self-threading screws, which both enclosures accepted (even with multiple insertions) without problem. While these prototype tablets are not built to withstand full MIL-STD-810 shock, vibration and drop tests, they are able to handle an accidental drop or two during regular use, which is also a plus.

However, though the final tablets were designed to be IP67 compliant, neither prototype material holds up well against water. The 3-D printing process leaves a relatively porous surface, which water drips through after a matter of seconds. The SLS material holds up a little better, but tends to absorb the water which may compromise its structural integrity. Devices using these materials should make minimal contact with liquids.

In terms of aesthetics, the 3-D printed part (based on the resolution we chose) clearly exhibits (pictured) the layer by layer gradients along all curved surfaces. Since these units are not production products, this may not be a critical factor, but the relatively smooth curves on the SLS model yield a more polished device. The glass-filled nylon has a nice matte finish, but the surface does exhibit patches of discoloration, possibly due to moisture absorption or production finishing processes.

Overall, we are very pleased with the performance of these prototypes. Even though enclosures of this size and complexity will cost several hundred dollars per set, it is well worth the expense at an early stage to avoid tooling costs and maintain design flexibility. These prototypes permit the device to withstand typical wear and tear and even some limited stress testing. In conclusion, we found that for aesthetics, the SLS process produces the best results, while the material properties of the 3-D printed ABS creates a product that is more durable under mechanical stresses.





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