I used to be Gleason expert trained at Gleason Works in Rochester NY on spiral bevel gears that were cut! Gleason had absolutely ultimate precision and expertise in machines and – even then meeting the required AGMA class was difficult after heat treatment-quenching press etc.
Imagine getting perfect rolling contact with contact remaining on the flank without riding hard line on edge and root of gear pair, trick to good gear performance is achieving constant velocity of rotation without pulsation, knocking. Anybody who claims to have made spiral gears, please ask for rolling accuracy chart!!
Now these gears share a common trait with TIR lenses for LED- automotive headlamps, LED-Streetlamps etc- being ultra precision in molded part along with thick thin sections making it impossible. Even long cycle times will cause geometry variation and compensating profile is only way out, unless you do two shot molding- first shot does the bulk of molding with zoned cooling so part has uniform average temperature in thick and thin wall, overmold with a uniform layer in second shot and that can help improve geometry. Here you could add lubricity in top layer having core of tough material that may be cheaper.
Focus should be on geometry driven molding issues- everyone can machine a CAD with ultra precision in steel, but part will always deviate due to thick-thin section of a spiral gear tooth geometry. We just filed a patent on improving bond with reduced stress on the interface of two shots with ultra fast cycle times and dis-similar materials – if you ever get to that issue.
