Machining a Living Hinge in Polypropylene
I have the need to prototype a product out of PP that contains several living hinges. Rapid injection molding this prototype is not a great option due to the large footprint of the part and therefore the large size of tooling it would require. I know PP is difficult to machine and I have read that creating living hinges this way is next to impossible to do. Can this be done? I’m interested to hear your insight on this!
To answer your question........it depends. What are the basic dimensions of your part, what are the dimensions of your living hinges. Please include the wall thickness of the main part and the hinges. How many parts are you looking for? Any grade of PP?
Outside of that woefully generic response, I'm curious and was interested in knowing what your hoping to learn from the machined part?
You can create a serviceable prototype integral hinge by coining (cold forming) the thin hinge feature. The process causes cold flow away from the forming tool and results in a degree of the desired molecular orientation across the hinge.
Machining the hinge is pretty much a lost cause I'd say. And however much you explain the difference between a prototype and reality, a broken model always makes a bad impression on somebody. Usually somebody influential.
Using properly molded hinge "inserts" is a nice idea although for this project there are 6+ hinges all at varying lengths. I guess one could do an injection run of shorter hinges and place them end to end to get all the desired lengths. Welding PP is not a process our shop is too familiar with either so that would be an added constraint, although it looks to be as simple as using a soldering iron and some filler material. I'll look into these options this week.