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View Full Version : Should I try to make my own injection mold?



jeremy13
11-09-2012, 10:03 PM
It will be a small mold 8X8 and have fore cavities. I have a CNC mill to make it and the CAD to draw it. The mill is a Haas TM1P it has a 6,000 rpm spindle. I know it is slow but it should work if I take my time. The mold will be what I think is a simple mold hallow cone mostly tapered. If Im figuring it right I can do 4 cones and have enough plastic for the runners and sprew. It is a 5oz machine and I will use polystyrene or ABS plastic.
Im thinking of going with this mold base.
http://www.ebay.com/itm/Aluminum-Prototype-Injection-Mold-Base-8x8-7075-Plastic-Moldmaking-/110880641876?pt=LH_DefaultDomain_0&hash=item19d1005354
We ran a test of the female cone and just filed it with plaster to get an idea of the shape. Came out amazingly smooth and no sanding on this mold.

http://i1224.photobucket.com/albums/ee374/Jeremy_Hanak/794A49E5-82B8-42F7-90DB-123FF86B2C95-1147-000001910742D4AC.jpg

davidh
11-09-2012, 11:48 PM
are you trying to avoid the $1000+ purchase ? if thats what your trying to do, i''d ask how expensive your time is to you ? it sounds like an interesting project. . . .

duckman
11-10-2012, 02:18 AM
Boy do I have ? , where are you filling from, tip of cone or parting line, where's the venting, how are you removing the molding from the core, what kind of machine is it going to run in, as I think of more ? I'll post them.

Tony Ennis
11-10-2012, 09:34 AM
How much pressure are we talking about here?

edit - which of our members does this for a living? I can't recall...

Grind Hard
11-10-2012, 10:17 AM
My brother "Liger Zero" does, I'll forward this to him.

jeremy13
11-10-2012, 12:00 PM
This will be a paying job sort of. The Explosives company I work for rather pay me to try and make the mold. This is still in the prototype phase. When all the kinks are worked out we will get a proper steel mold made. The price of the aluminum mold on e-bay is what I believe to be a fair price. By the time you add up aluminum stock, paying some to grind it flat and stress relive it. We have a 75 ton VanDorn toggle machine.
I was planning on filling from the base of the cone or the parting line. I was planning on a vent on the opposite side of the fill point. And if needed adding the machine able vents at the tip of each cone. Not shown but there will be a band on the base of the cone .25 high and .125 thick. The rest of the cone will be in the.050 thickness range. I was planning on putting the ejectors 3 or 4 around this band.
From what I have been reading I want to avoid having to do a core pulling mold or a stripper mold. But please tell me how to proceed. Or tell me to back off and call a pro.

Peter N
11-10-2012, 12:23 PM
It will be a small mold 8X8 and have fore cavities. I have a CNC mill to make it and the CAD to draw it. The mill is a Haas TM1P it has a 6,000 rpm spindle. I know it is slow but it should work if I take my time. The mold will be what I think is a simple mold hallow cone mostly tapered. If Im figuring it right I can do 4 cones and have enough plastic for the runners and sprew. It is a 5oz machine and I will use polystyrene or ABS plastic.

Well said Sir! I think you should have a go a making it -that's definitely the spirit of the 'Home Shop Machinist'
However, there are rather a lot of factors to consider when designing & making an Injection Mould, and they are very easy to get wrong, so please ask for information & explain a bit more about what you want to do and how you want to do it, and those of us who do this professionally should be glad to help.



How much pressure are we talking about here?

edit - which of our members does this for a living? I can't recall...

I do!
Design 'em, make 'em, mould 'em, sell 'em. One or two others here in the same line too, IIRC.

The first question I would probably ask is what is the size of the cone?
Also, if it is a prototype then you won't want to make 4 cavities in one hit. If you're developing it then you need room & space for changes. Lot easier to do that on 1 impression rather than 4....


Peter

jeremy13
11-10-2012, 12:39 PM
Hears is a cut away cone I made with my hand operated press I made for prototyping. The band at the base of the cone will get moved to the inside of the cone. Cone is 2” wide and 2.56” tall net weight is .42 oz
http://i1224.photobucket.com/albums/ee374/Jeremy_Hanak/pl2.jpg

Jaakko Fagerlund
11-11-2012, 02:54 AM
Do a one cavity mold only if you are prototyping, lot less headaches and room to improve. And steel mold bases are probably cheaper than the aluminum you showed.

What is the size of your cone?

Peter S
11-11-2012, 05:20 PM
One possibility is to look for a company which specialises in small run moulding. Sometimes we want say a few hundred - 2000 pieces with little chance of repeat, we go to a guy who has standard die sets already to go, he just makes a new cavity etc. and fits them to his existing tooling. In other words, he has a shelf-full of different cavities, forces, strippers etc that fit the same die set. Normally similar products like conveyor end caps and the like. It works well for us, quick and reasonable cost (Sorry can't recall figures, it's been a while)

jeremy13
11-11-2012, 09:23 PM
I guess prototype mold is a bad choice of words. As you can see we have a working prototype. We want to go in to limited production now and get some charges in the field to get some feedback. So a 4 cavity mold will do. This just kills me but the owner likes to just spend enough to make something work and make money. Then with that money go buy something a little better and get buy and so on. I hate doing things twice.

Peter are you talking about a MUD mold? Looked it to these to there is a companion to the cone, a cap to hold the DET cord in place. Got this prototyped to but I need to turn it inside out. I made it to fit on the inside of the charge and need to make it fit over the outside. It was kind of hard to get the cap out on the inside.
I think a steel MUD base would be perfect for both items. And use the aluminum molds for each item. We do plan on using two different plastics something like HDPE for the cap.
http://i1224.photobucket.com/albums/ee374/Jeremy_Hanak/pl4.jpg

Jimmer12
11-12-2012, 12:52 AM
That's not a very difficult part to mould, but designing a mould, making one and ending up with a useable part at the end will definitely have it's challenges. Aluminum moulds have their own set of challenges over steel moulds as well. I worked as a mould designer and mould maker, and have known poorly designed aluminum "prototype" moulds to be worn out in a few dozen shots, when the material ended up being far more abrasive than originally anticipated.

Have you considered looking into a moulding shop that is setup to do short run production jobs? One of my previous employers had a nice little setup where they had custom designed and built a couple of different sized mould bases, that could take interchangeable sets of core and cavities, without removing the mould from the press. They would then do short run production, as well as product verification moulding, before going ahead with a full production mould build. If that is something you are interested in, PM me and I will give you their contact info. If you have any specific questions about mould design, again feel free to PM me as I still occasionally do contract mould design work and don't mind sharing a bit of knowledge or assisting with some CAD work.