17 July 2012

NerdKit: OMG CNC MACHINING

CNC: Computer Numerically Controlled.
Or, in layman's terms: Robotic. 

I've had the pleasure of using a CNC mill for the first time to make a new mold prototype for the NerdKit I am so diligently working on at my job this summer. And it's one of the coolest things I've ever used in my life. 



This prototype combines many aspects that are closer to the final product: a CNC milled mold, a caselike structure, an insert for compartments and such, a flush hinge, and better designed snapfit invagination/exphallation fasteners.


Also, I've figured out a trick in Solidworks to quickly "prototype" a mold without having to go through the Mold Tools. If you model a mold you can use the Shell feature on the part, which normally removed material from inside your part. If you choose "shell outward", you effectively form the part using a specified thickness material. Then you can "take it to a bandsaw" by cutting away excess "material" and...


...Voila! Much simpler than those gurshdurned mold tools. 

There's a handy Solidworks extension called HSMWorks Express which is the free 2.5-Dimensional cousin to the full 3-D CAM program HSMWorks. While machining in X and Y along a certain Z is all I need for this mold, 3D milling is nice for smooth curvatures and fillets. Unfortunately, I have to take into account the limitations of Express in my designs for CNC. 


But it doesn't come out so bad!

Someday I'll do some 5-axis CNC milling...


Engineer daydreams...



Here is some of that High Density Polyurethane I will be using as a stock material, mounted onto the Bridgeport EZ Track CNC mill.




Once I've localized the mill at the stock's origin, I'm ready to rip...







It even gives you an option to call for a tool change halfway through machining, so I can switch out the flat endmill for a ball endmill and touch it off before it cuts the hinge channel in the center. 



Can you see the resemblance?


And the next day it's off to the vacuum former! I drilled dozens of tiny holes along the hinge, edges, and invaginations to ensure the plastic truly takes the shape of the mold. 


I was sure to add plenty of this special non-stick spray to make the removal of the mold from our cheap plastic easier. 


Because of the small scale, I had issues with the material webbing along the hinge, but I managed to get one good part.


The insert my coworker made from a CNC mold fits perfectly.


The live hinge works pretty well, too! We'll have to test the design with the type of plastic we're using for the final product, however. 

Next, we make a full-scale prototype!

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