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Hobbyist Injection Moulding?

 
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LaughingCheese
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PostPosted: Sat Apr 24, 2010 11:38 am    Post subject: Hobbyist Injection Moulding? Reply with quote

I may have mentioned one of my goals is to build some RC aircraft.

I would like to make them out the same material these jets are made out of:

http://www.hobby-lobby.com/electric_jets.htm


At least for the A-10, it said it was "injection moulded foam." It didn't specify what kind of foam unfortunately. I don't think its depron, but I don't think its EPP either (that's the really durable stuff).



My question for now is how doable is hobbyist injection moulding? I never hear of it, there aren't any instructables projects to my knowledge.

Must be pretty difficult. Sad
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jegner
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PostPosted: Tue Apr 27, 2010 11:58 am    Post subject: Reply with quote

The Gingerly booklets have a how-to to make your own machine. Not too hard to do, but some work, like making your own vac-form machine. Several issues are not addressed, and that is how to get your plastic into the machine's heater [I'm thinking of my scrap HIPS left over from the vac forming process] and to make

Instructibles has a how-to guide using the guts from a hot glue gun. Again, getting hips into the heater.

You need to have a plan to create ingots, or bars, or rods for use in your machine, and recycling is they best way to go, but thats not worked out well, IMHO.

More work needs to be done, but this is a project I really want to get into.

JIm
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LaughingCheese
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PostPosted: Tue Apr 27, 2010 11:26 pm    Post subject: Reply with quote

jegner wrote:
The Gingerly booklets have a how-to to make your own machine. Not too hard to do, but some work, like making your own vac-form machine. Several issues are not addressed, and that is how to get your plastic into the machine's heater [I'm thinking of my scrap HIPS left over from the vac forming process] and to make

Instructibles has a how-to guide using the guts from a hot glue gun. Again, getting hips into the heater.

You need to have a plan to create ingots, or bars, or rods for use in your machine, and recycling is they best way to go, but thats not worked out well, IMHO.

More work needs to be done, but this is a project I really want to get into.

JIm


Thanks! Because of the lack of responses I was afraid I was being shunned or something. Very Happy


Do you need different types of injection machines for foam or plastic?

Or can one do both? That would be cool, but I'm more interested in the foam.


When you say ingets, are you talking about actual metal ingets/bars?

I guess that means I'd need a lost foam casting system or something too? Shocked


EDIT: Holy cow, you mean I would be ahead of YOU if I built one?!!?

Not that its a competition, just a scary thought...
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jegner
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PostPosted: Wed Apr 28, 2010 6:13 am    Post subject: Reply with quote

Sorry, ingots, I am referring to as simply the sheet plastic thats been chopped up and melted back down into a shallow mold that can easily be stored. Rods, or cubes would work too. I just don't have a term that fits any better than 'ingots'. Same way aluminum or brass is recycled back to a bulk state.

As for the foam, machine, thats a different material, and a different process, but my guess is, a hard plastic injection molding machine could be used to inject form foam plastics, but I'm not sure I understand what material you are referring to. Styrofoam, is, well, styrene and air, mixed [extruded] to make stuff.

EDIT: here is the link for the instructible: http://www.instructables.com/id/Home-Injection-Molding/
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LaughingCheese
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PostPosted: Wed Apr 28, 2010 1:14 pm    Post subject: Reply with quote

jegner wrote:
Sorry, ingots, I am referring to as simply the sheet plastic thats been chopped up and melted back down into a shallow mold that can easily be stored. Rods, or cubes would work too. I just don't have a term that fits any better than 'ingots'. Same way aluminum or brass is recycled back to a bulk state.

As for the foam, machine, thats a different material, and a different process, but my guess is, a hard plastic injection molding machine could be used to inject form foam plastics, but I'm not sure I understand what material you are referring to. Styrofoam, is, well, styrene and air, mixed [extruded] to make stuff.

EDIT: here is the link for the instructible: http://www.instructables.com/id/Home-Injection-Molding/


Oh, I was hoping to use EPP. Its a type of VERY tough foam, perfect for RC. Very Happy
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kruzer
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PostPosted: Sun May 02, 2010 8:55 pm    Post subject: EPP can be formed Reply with quote

I read somehere that EPP can be formed easy with a two piece mold. The material is available by the bags and heating it is no more than vac-forming. So, it's really not like a plasic injection mold where fairly complex issues at hand.

I thought about doing the same some years back but it's much easier to vac-form the wings and fuselage and glue it together form thin lexan sheets... or even cheap plastic sheets.
I fly RC when I have time and the real crash proof planes should be made from thin plastic and pump it up (inside) with air.

IE: take these ordinary water bottles. Empy it and try to crush it. Not possible. Add 1-3psi air and you can drive a car over it and won't break or even deform !!! Not mentioning it that it's MUCH LIGHTER than conventionnal construction.

I say that future of RC planes are really should go this route, rather than the same way as been done for the last 80 years. Exeriment with empty water bottle and see how cool is that. The trick is to get some sort of a valve like an innertube from a bike and then pressurise it. Even if you use a simple water bottle for the fuselage, the wings can be made the same way and attach it with rubber bands. You can dive the plane into the ground and all it will do is bounce.... minus the electric motor.

Am an expert on crashing RC's and don't have a single plane that's intact right now Smile
some of the planes (ZAGI) crashed nose first at least 40 times and still flew. Eventually all the innards dissetigrated and had to be put out of its missery.

Am planning to make these (air filled) planes eventually when I have the time an the vac-form machine done. I still favor using a water bottle for fuselage and just make the wings and tail.

cheers
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Culvan
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PostPosted: Mon May 03, 2010 3:49 pm    Post subject: Re: EPP can be formed Reply with quote

kruzer wrote:
I thought about doing the same some years back but it's much easier to vac-form the wings and fuselage and glue it together form thin lexan sheets... or even cheap plastic sheets.
I fly RC when I have time and the real crash proof planes should be made from thin plastic and pump it up (inside) with air.

IE: take these ordinary water bottles. Empy it and try to crush it. Not possible. Add 1-3psi air and you can drive a car over it and won't break or even deform !!! Not mentioning it that it's MUCH LIGHTER than conventionnal construction.

I say that future of RC planes are really should go this route, rather than the same way as been done for the last 80 years. Exeriment with empty water bottle and see how cool is that. The trick is to get some sort of a valve like an innertube from a bike and then pressurise it. Even if you use a simple water bottle for the fuselage, the wings can be made the same way and attach it with rubber bands. You can dive the plane into the ground and all it will do is bounce.... minus the electric motor.


Part of the strength of the inflated water bottle design is the round shape. If you had something rectangular and tried that it would start to bulge (and try to become water bottle shaped). Of course there will be a pressure where there's no significant change in geometry and a benefit to the strength. I guess the question is how much benefit can you get from that point? You could probably improve the pressure tolerance the same way new air matresses work (with struts inside to absorb some of the force.)

Back to the original post

I'm not really an expert on injection molding, but I thought I'd toss this out. my understanding of injection molding is that it's expensive to make the tooling required to do it, but once you have it you can make lots of the parts you tooled for for a low cost. From what I've read in your other posts, I don't think you are looking for a high up front cost to get low unit costs for huge part runs. I could be wrong about that. If you are interested in selling high volumes of a limited range of parts then it may be the way to go. I think the research you've already done has shown you that it is not a common hobbist undertaking. I think that's because for most hobbists there are easier ways to accomplish what injection molding does. There are more traditional ways of making foam molds.

Just to point you in the direction I'm looking, here's a few products for making foam objects http://www.smooth-on.com/Rigid-and-Flexible/c10/index.html

Andy
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LaughingCheese
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PostPosted: Mon May 03, 2010 4:54 pm    Post subject: Re: EPP can be formed Reply with quote

[quote="Culvan"]
kruzer wrote:
I thought about doing the same some years back but it's much easier to vac-form the wings and fuselage and glue it together form thin lexan sheets... or even cheap plastic sheets.
I fly RC when I have time and the real crash proof planes should be made from thin plastic and pump it up (inside) with air.


Part of the strength of the inflated water bottle design is the round shape. If you had something rectangular and tried that it would start to bulge (and try to become water bottle shaped). Of course there will be a pressure where there's no significant change in geometry and a benefit to the strength. I guess the question is how much benefit can you get from that point? You could probably improve the pressure tolerance the same way new air matresses work (with struts inside to absorb some of the force.)



Yeah, I'm guessing that method won't work for some of my designs.

Its also highly experimental. :\


Quote:

Back to the original post

I'm not really an expert on injection molding, but I thought I'd toss this out. my understanding of injection molding is that it's expensive to make the tooling required to do it, but once you have it you can make lots of the parts you tooled for for a low cost. From what I've read in your other posts, I don't think you are looking for a high up front cost to get low unit costs for huge part runs. I could be wrong about that. If you are interested in selling high volumes of a limited range of parts then it may be the way to go. I think the research you've already done has shown you that it is not a common hobbist undertaking. I think that's because for most hobbists there are easier ways to accomplish what injection molding does. There are more traditional ways of making foam molds.

Just to point you in the direction I'm looking, here's a few products for making foam objects http://www.smooth-on.com/Rigid-and-Flexible/c10/index.html

Andy



Well I'm looking at injection moulding with EPP, and I'm not sure that stuff would be as strong as EPP.


Also, could I use a CNC to make the ingot molds or do they need to be metal?
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kruzer
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PostPosted: Mon May 03, 2010 10:39 pm    Post subject: Made many injection molds... Reply with quote

I made many injection molds I was in that business some years ago and it's not a simple matter.
Unless you have 20-50K sitting in your pocket to make even a simple mold, forget it.
China may make it cheaper but they want money up-front.
Anyway, for hobby stuff injection molds are not practical at all.

BTW, I flew a 'water bottle plane' and it flies well and crashed it many times and nothing happened to it. The bottle is natural fuselage. The wings were made the same way but flat and just enough pressure inside to hold the shape.
No need to make it as a mattress with compartments.... a few ribs in the design made it quite rigid.

I really should dig out my test model and post a picture and video.
It's somewhere in the attic and who knows in which box !
As I said it was a test model and now I know for a fact that it will work and I was going to refine the design with two-half pieces glued together. The best way to make it is with blow molding but then it's a HUGE cost to do so.

As soon as I have my vac-form machine operational I'll give this project a shot.... as soon as I have time.

Am thinking of buying something already made vac-form macine because I just don't have the time to build it.
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kruzer
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PostPosted: Mon May 03, 2010 10:44 pm    Post subject: EPP Reply with quote

BTW, I went through the same kind of idea of injection molding epp about 14 years ago. In Los Angeles there are many of these companies but the tooling killed the project.

EPP is verystrong and stands up to lots of abuse in RC flying.
Maybe there are some other ways to do nowdays?
Am not familiar with anything new to this process.

I even had a Chinese company lined up to make them (EPP) but didn't worked out in the end.
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