Author Topic: Plastic injection molding ( moulding?)  (Read 372 times)

Offline John Rudd

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Plastic injection molding ( moulding?)
« on: July 29, 2020, 08:07:47 AM »
I'm thinking of building a small injection machine to make some plastic fans that I need.

One fundamental question is how large a heater do I need?
The temperature will be controlled at around 230 C so any excess heat capability of the heater is really redundant...if you get what I mean?
I was thinking 2 x 150 Watt heater bands around an extruding chamber 45 mm diameter with an internal bore and lentgh yet to be determined...

If anyone has experience in this field, feel free to educate me....
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Offline charadam

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Re: Plastic injection molding ( moulding?)
« Reply #1 on: July 29, 2020, 10:50:04 AM »
John,

Wouldn't 3D printing be a better method?

Offline Lew_Merrick_PE

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Re: Plastic injection molding ( moulding?)
« Reply #2 on: July 29, 2020, 11:01:50 AM »
Hi John  --  My approach is (admittedly) somewhat weird in that my set-up allows me to Die Cast as well as injection moldI use a pair of 1000W heaters along with a "bang-bang thermocouple temperature controller to manage my molding temperature (a friend of mine made one for me for about USD5.00 back in 2002).  --  Lew

Offline John Rudd

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Re: Plastic injection molding ( moulding?)
« Reply #3 on: July 29, 2020, 11:41:51 AM »
@ charadam,
Firstly I dont have a 3d printer.... :Doh:, 2nd, I dont have access to a 3d scanner or other means of providing an stl (?) file for printing one, 3rd, I dont know anyone with a printer... :scratch: and 4th, not sure if a printed fan would endure the motor speeds....in excess of 4000 rpm... :scratch:
The fan(s) is (are) for a vintage electric drill that I'm refurbishing, the fan once removed cannot be replaced as it is destroyed in order to remove it...,( crap design I know... :doh:) but there you have it...
Also the plastic fan has a metal centre boss where it fits onto the motor shaft....

I've molded some fans in resin using a silicone mold, but havent tried them to see if they stand up to the speed....but the original fans are probably molded in the first place..,

Lew, thanks for your approach, sounds like there's an excess of available heat at 2kw..... :zap:,
I'm going to use a PID temp controller to control the heaters....

I'll post up a picture of the type of fan I'm on about....
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Offline ddmckee54

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Re: Plastic injection molding ( moulding?)
« Reply #4 on: July 30, 2020, 01:06:03 PM »
I've got my doubts that that a silicon mold would stand up to the pressure of injection molding.  As far as a 3D printed fan surviving the motor speed, there are versions of 3D printed model airplanes with 3D printed props and 3D printed fans for a ducted fan.  Both of these would be running at higher RPM's than a drill motor runs at.

You don't need a 3D scanner to create the STL file, you use a 3D CAD package to design the 3D model and then export the model to an STL format.  You DO still need a 3D printer though, know anybody that's got one?  There's a lot of us on here that have one, and a fan for a drill wouldn't take that long to print - probably only an hour or two.  The other thing is that because you are molding the part at an elevated temperature, you need to allow for shrinkage if you need a dimensionally accurate part.  Since this is supposed to fit on a shaft dimensionally accurate is probably a good idea.

Don
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Offline John Rudd

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Re: Plastic injection molding ( moulding?)
« Reply #5 on: July 30, 2020, 01:35:02 PM »
Don,
Thanks for sharing your thoughts on this....I didnt know that 3d printers are used for df fans.... :scratch:
The silicone mold was used to create a resin cast fan...
As for accuracy of fit, the centre of the molded fan has a metal bush insert, that takes care of shaft fit....
So, I would need to have a CAD program, learn to use it, need a 3d printer and learn to use that....thats a lot of learning....
An imm seems a better idea.... :scratch:
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Offline Joules

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Re: Plastic injection molding ( moulding?)
« Reply #6 on: July 30, 2020, 01:57:56 PM »
LOL, just solder a fan up from tinplate (biscuit tin)  You can use your prop balancer for, well balancing it.
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Offline John Rudd

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Re: Plastic injection molding ( moulding?)
« Reply #7 on: July 30, 2020, 02:11:14 PM »
I think I might be making this too complicated.....

I need a fan....whether plastic or metal....

I could just take some al sheet, cut a circle, make some saw cuts and fold the blades up...
The centre could be re-inforced with the bushes I have recovered from the original plastic fans...so that takes care of it....
Or go to the expense of making an imm....hmmmm  :coffee:
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Offline Joules

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Re: Plastic injection molding ( moulding?)
« Reply #8 on: July 30, 2020, 02:15:26 PM »
By any chance, would you need the drill to make the moulder   :wack:

Fans ???   Does this drill have previous form.
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Offline John Rudd

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Re: Plastic injection molding ( moulding?)
« Reply #9 on: July 30, 2020, 03:18:49 PM »
Joules,
I've probably mentioned before on these pages about Stanley Bridges drills, that I've collected and refurbished over the years...
As part of the process, the cooling fan removal is part of it and they are usually destroyed in the process...
I attempted to make ine out of aluminium bar, but it was too labour/machine intensive....cost me at least two 2mm milling cutters...for one!
So I went to cold molding, a silicone mold cast from an original, to cast, in resin, new fans.I made several but never used them after deciding the hardened resin eas too brittle/fragile...
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Offline charadam

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Re: Plastic injection molding ( moulding?)
« Reply #10 on: July 30, 2020, 03:34:04 PM »
John,

I will happily print any fan .stl file you provide.

There are some on thingiverse that are scaleable.




Offline John Rudd

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Re: Plastic injection molding ( moulding?)
« Reply #11 on: July 30, 2020, 04:39:34 PM »
Charadam,
 
Thanks for the offer....unfortunately I cant do stl files, dont have cad....

Looks like I'm going to do some metal bashing...with some al sheet.
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Offline WeldingRod

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Re: Plastic injection molding ( moulding?)
« Reply #12 on: July 30, 2020, 07:07:12 PM »
Can you take a picture of these fans?

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Offline John Rudd

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Re: Plastic injection molding ( moulding?)
« Reply #13 on: July 31, 2020, 04:38:03 AM »
As requested....
So the first is the silicone mold used to mold the new resin fan, next is the steel bush insert, this sits in the centre of the mold and has the resin cast around it, it then strengthens the centre of the fan.
Next is an aluminium fan machined from solid....finally, two fans, the one on the left is the cast version, the right one is an original
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Offline Sea.dog

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Offline awemawson

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Re: Plastic injection molding ( moulding?)
« Reply #15 on: July 31, 2020, 08:50:00 AM »
 :clap: :clap: :clap: :clap:

Two countries divided by a common language !
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Offline WeldingRod

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Re: Plastic injection molding ( moulding?)
« Reply #16 on: July 31, 2020, 01:46:53 PM »
I would take your master part, smooth some wax into all the blade base corners to get a radius in there, and re-do the mould.  Then cut some small pieces of paper and fold them so that the go to the end of each blade and turn the corner into the disc.  Lay down a fiberglass doughnut and your core.  Pour in low viscosity resin!

Or, with slow resin, dip each paper bit before slotting it in.

The various fiber bits will provide a lot of reinforcement.

You might balance and spin test them in a steel pipe before final installation.

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