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deisel
26-01-2013, 12:49 PM
Morning

I figure theres a few on here that make ali and steel moulds for injection purposes im looking for tips advice do's and dont's on polishing the cavity materials/tools used.
And also adding a visable texture to the mould sand blasting or acid?

BedlamRik
26-01-2013, 04:58 PM
Hi Diesel, I don't do metal moulds (yet)
but i do do Resin and Silicone.
I'll wager that its a piece of string question, and dependant on a lot of factors. I.E. what size mould cavity etc.
I'll put money on using toothpaste,auto sol. or other metal buffing compound with a cloth or polishing mop. rather than an acid though.
I'd be tempted with a "dremel" type tool (without going into the bearing debate lol.)

deisel
26-01-2013, 06:18 PM
hello martin
were talking small stuff here a couple of inches square tops but as there mechanical parts to be made ,need retain size or as close as possible.
while searching i keep coming across ceramic fibre sticks in sets of various grades that can be shaped to suit,seem bloody expensive for what they are but may be just what i should be looking at,

regarding texturing i cant find much info on it other than the usual sales patter,id like to do it myself, it seems ideal for hiding machining marks and looks great.
theres sandblasting which ive never done,but will shell out for if need be,but id like to try out filling the mold with an acid and leaving it for the required time.ta

r0bsk1
26-01-2013, 07:38 PM
Hi deisel, be careful creating a texture in a mould. It can cause the resin to lock in to the mould. On release you'd either leave bits of resin behind or possibly damage the mould.

I work with composites and a shiney mould is what you're looking to acheive for best release to maintain the mould lifetime. Refinishing the mould after a lock-in would of course make the mould slightly larger.

As for finishing the mould I use wet and dry paper through the grades to about 2000 grit. Then machine polish with mops for a mirror finish. You can then use a scotch pad to take away the shine from the moulded part. Depends on what kind of texture you're looking for i suppose.

Jonathan
26-01-2013, 08:14 PM
I get the impression these are injection moulds for plastics, not resin. It's going to depend on the detail required for the parts in question - if its artistic parts that's quite different to general widgets with more flat surfaces than curved profiles.

r0bsk1
26-01-2013, 08:22 PM
I get the impression these are injection moulds for plastics, not resin.

Plastic is a resin in its liquid state.

Jonathan
26-01-2013, 08:35 PM
Plastic is a resin in its liquid state.

Actually it's the other way round - some resins are called plastics in their solid state. Plastics belong to the set of materials called resins, hence I specified plastics to narrow down the discussion since I suspect these moulds are for thermoplastics, so stating plastics is equally, if not more, accurate. The reason for this supposition is the user's previous posts regarding an injection moulding machine.

Anyway, what material are the moulds going to be made from? If aluminium then this article (http://www.moldmakingtechnology.com/articles/optimizing-aluminum-tools) suggests they should be plated with nickel.

r0bsk1
26-01-2013, 09:16 PM
Actually it's the other way round - some resins are called plastics in their solid state. Plastics belong to the set of materials called resins, hence I specified plastics to narrow down the discussion since I suspect these moulds are for thermoplastics, so stating plastics is equally, if not more, accurate. The reason for this supposition is the user's previous posts regarding an injection moulding machine.


Therefor they will be injecting plastic in the form of a resin.

oscar
26-01-2013, 09:38 PM
We use an ultra sonic polisher and then mops in a dremel type tool for very fine and mirror finishes. Anything that needs a textured surface is done on the spark eroder.

deisel
26-01-2013, 09:43 PM
Hi deisel, be careful creating a texture in a mould. It can cause the resin to lock in to the mould. On release you'd either leave bits of resin behind or possibly damage the mould.


Thanks for the info r0b,probably saved me a few quid right there!
The texture i was thinking of is the grippy eggshell like texture found on phones,remotes ect so nothing heavy , i will have to do a sacraficial mould maybe with the parts shrinkage when cooled i might get away with it.


Yes for injection molding jonathan,there sometimes referred to as resin pellets used,

Robin Hewitt
26-01-2013, 10:01 PM
I am planning to make some moulds using Alumec 89, it's like that 7075 T6 the Yanks rave about but takes a deeper temper, or so I am told.

Right now I am all theory and no experience. I thought about bead blasting to get that sparked look. I think sand blasting is a no-no on iron because it is the perfect key for rust unless you bead blast afterwards, I find sand blasted iron is rusty before I get it home even on a hot sunny day. I presume you could protect your shut-offs while blasting and cut the gates after maybe?

OTOH Alumec lasts longer if you anodise which includes a dunk in dilute nitric to remove any extant oxidation before it goes in the sulphuric. Anodising could negate any previous texture. I actually have hopes it might smooth the surface somewhat in those hard to reach spots. Bit worried about whether the ejector pin sleeves are going to fit if I can't block their holes off while it's in the tanks, shellac?

Regarding someone's earlier comment, I believe the draft angle is supposed to protect the finish on ejection.

I did buy a die grinding pencil. They are air driven at enormous rpm and come with a 3mm collet. Haven't played with it yet, not really sure what goes in it, the bottle of oil seems to have emptied itself and the instructions have dire warnings about what happens without.
Whatever, a sparked finish is now passe, the Law of Bling says polish the crap out of it :beer:

Jonathan
26-01-2013, 10:49 PM
Anodising could negate any previous texture. I actually have hopes it might smooth the surface somewhat in those hard to reach spots. Bit worried about whether the ejector pin sleeves are going to fit if I can't block their holes off while it's in the tanks, shellac?

From the anodising I've done I can confirm that you get the same finish after anodising as before. The parts are always slightly smaller - it's hard to say how much but bearings wont have the proper fit after anodising. That's easily solved by pressing some nylon into the bores and the same tactic works well for protecting threads. People block areas of a part off so they can anodise them a different colour to the rest, so it can't be that hard. Probably just need something resistant to sulphuric acid and sodium hydroxide.

Robin Hewitt
24-01-2014, 11:02 PM
I am told you can recreate a spark eroded texture by sand blasting.


Now some speculation... a steel cavity might need glass bead blasting as well or rust is instantaneous and you want the cavity side to separate when the mould opens not when the ejectors hit, so don't over key the surface. An Alumec cavity might benefit from anodising if you want it to last but I don't know what that would do to a surface texture. You can frost glass using a mist of hydrofluoric acid, wonder if you could frost an Alumec mould using a spray of caustic soda or frost an anodised mould using a spray of nitric?

Of course you need a good draft angle to avoid smearing the sides when you open the mould. Minimum of 1.5 degrees for ABS :rugby:

deisel
26-01-2014, 10:06 AM
[QUOTE=Robin Hewitt;53917]I am told you can recreate a spark eroded texture by sand blasting.
QUOTE]
yep theres an injection moulder i spoke to down south who commercially makes angling products rod rests etc and uses this method.
with the part i had in mind to do, the software i use predicted it would be full of errors as i wanted to use delrin,im told in its usable state it has the consistancy of play doe.
im working on a drawing for a smaller less demanding part that consists of two parts again delrin i will attempt this regardless of what software says and see what happens plan is to use an airbrush sized kit to lightly texture the mould.