Injection molded fan

[John Rudd]

Prompted by another member, Joules....I have given thought to making a new fan for my drill refurb project....
As I need a few of these, milling from a blank seemed tedious....

[John Rudd]

Simple enough to make or so it seems, although the added complication is that there is a centre boss with a steel insert....

[John Rudd]

Fortunately, I have the steel inserts from the fans that were destroyed during their removal...
So now onto making the mold....
Starting with an alloy blank disc, I machined the slots that would form the 'blades'....sadly I got part way thru when the motor on my mill gave up!

[John Rudd]

Now the centre of the disc has been bored to take the metal insert and there will be a locating pin on the main mold so that the insert is centralised when all is assembled ready for plastic injection...

[John Rudd]

So once this part is completed, I need to think about plastic/inj mold machine and anything I might have forgotten....
So if anyone has any tips or advice or suggest if I've gone about this the wrong way, do let me know....
I do need advice in what type of plastic....any ideas...?

Btw, the fan is around 50mm dia and around 10 mm thick at the thickest part...motor speed is around 5-6000rpm...

[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]

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....

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.

  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.

[AdeV]

http://www.likecool.com/

Bugger, there went the rest of the day then!

Superb website, thanks for the link!

[Joules]

These are a very useful set of videos to get an introduction to injection moulding.

[John Rudd]

Had some success with molding!
Made a silicone mold from the original fan then cast a fan in the mold.....
Looks good, just need to machine the fan to size and balance it....

[Joules]

Now that, does look like it turned out well.  No problems with air trapped in the blade areas ?

[John Rudd]

Joules,
No issues at all with any aspect.....In fact, the mold was so good at replicating the original fan, I could actually see the the part number....TPD6.....in both mold and new fan.....

I've since cleaned up the new casting and fitted it to the drill motor and it works a treat....

[awemawson]

That's come out really nicely John 

In my youth (*), when money was even tighter than it is now, I took a mould impression off a plastic handled Stanley screwdriver using Vynamould and cast some home brew mix of polyester resin, chopped strands of fibreglass, and paint as a dye, into file handles, putting the tang of the file into the unset resin. The Stanley name was nice and clear in the finished product. I noticed the other day that I still have a rat tailed file equipped with one of those handles !



(* I was probably 16 at the time, and that's 52 years ago  )

[vtsteam]

Had some success with molding!
Made a silicone mold from the original fan then cast a fan in the mold.....
Looks good, just need to machine the fan to size and balance it....

Wow, looks fantastic, John!