Gallery, Projects and General > How do I??
Injection molded fan
Joules:
John, all those blade roots want to have a radius. Sharp edges in plastic moulds are stress risers and will cause issues with plastic flow and blades shearing off in use. You need to also think about how you're going to get plastic into pockets without air locks leaving voids in your moulding.
10mm to 1.5mm will also be problematic. Try to maintain an even thickness or progressive changes. The thin blades will be drawn back into the thicker section as the plastic cools.
Depending on your surface finish, you might get away with no draft angle on the blades, but it's not good practice. Even a degree or two helps, the plastic will key into any imperfections in the mould making release difficult.
Joules:
The easiest way to add draft to your mould is to shim one side of the rotary table and cut the blade slots. Move the shim to the other side and do a second pass, you now have draft on both blade sides. I normally hand finish areas with a flex drive tool (Dremel etc) and burr to blend corners and edges.
John Rudd:
--- Quote from: Joules on April 07, 2017, 08:04:43 AM ---John, all those blade roots want to have a radius. Sharp edges in plastic moulds are stress risers and will cause issues with plastic flow and blades shearing off in use.
ok, so I need to put a small radius on the corners?
You need to also think about how you're going to get plastic into pockets without air locks leaving voids in your moulding.
any suggestions?
10mm to 1.5mm will also be problematic. Try to maintain an even thickness or progressive changes. The thin blades will be drawn back into the thicker section as the plastic cools.
hummm...not sure what that means?
Depending on your surface finish, you might get away with no draft angle on the blades, but it's not good practice. Even a degree or two helps, the plastic will key into any imperfections in the mould making release difficult.
oh....looks like I need a rethink....
--- End quote ---
:doh:
I thought about using fibreglass/resin and pressing it into the mold under pressure as an alternative method of manufacture....
Joules:
Yep radius all your edges.
If you think about injection moulded parts they have sprues, a tapered hole in the corner of each blade allows plastic to flow and a place for air to be compressed. The sprue is trimmed off afterwards, hairline grooves are added to moulds to allow air to bleed away, but not let plastic flow.
:lol: 10mm to 1.5mm, I think I just misunderstood your dimensions. If the fan backing is kept pretty close to the blade thickness you get less distortion than going from thick to thin sections within a mould.
Alternatively make the whole fan out of G10 board and epoxy it together. Then balance the fan.
Casting is way easier than injection moulding, and possibly spin casting would give you hours of entertainment.
Joules:
http://www.likecool.com/Rotational_Moulding_DIY--Tools--Gear.html
Like the above.
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