Thread forming screws/brass insert molding in polycarbonate (Lexan)

Question

Thread forming screws/brass insert molding in polycarbonate (Lexan)

RossH2 (Mechanical)

(OP)

21 Sep 18 21:22

Can anyone give me advise on designing screw bosses for injection molded Lexan? Should I avoid thread forming or self taping screws? Or is over molding brass inserts a better option? We could use heat staking but it significantly increases our product cost. Im shooting to use a M2 screw with a screw boss OD approximately 1.7-2.0 x the diameter of the screw or insert.

If we cant use Lexan does anyone have any recomendations of a resin that is optically clear that would accept thread froming screws or overmolded brass inserts?

Thanks for your time, I really appreciate any advice,

Ross

Pud (Mechanical) · Answer 1 · 2018-09-22 20:45:37

The best type of screws have modified thread angles to displace material to reduce burst stress.

Here is an example of a UK version [link https://www.pts-uk.com/products/screws-for-plastic...]PT screws[/link
A Google for 'screws for plastics' gives myriad hits for similar. All makers give boss details for various plastics.

www.tynevalleyplastics.co.uk

Politicians like to panic, they need activity. It is their substitute for achievement.

dgallup (Automotive) · Answer 2 · 2018-09-24 13:38:07

Over molding inserts is usually the best but most expensive option, heat staking should be cheaper. Self tapping plastic screws should only be used if they won't be taken in and out repeatedly. They are really intended for one use but you can usually get away with a couple of reuses. I've had good results with Acument Delta PT thread forming fasteners.

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Thread forming screws/brass insert molding in polycarbonate (Lexan)