Aluminium manual die casting technique....

[axis_control]

Hi,
here are some pics of aluminium casted in a PDC machine.

my querry is, can aluminium upto 60 grams be die casted using manual pressure ? remember the fine finish achived using centrifugal casting technique for jewellery making. I guess manual aluminium die casting should be as good.

may be a manual machine where once the laddle filled with molten metal is loaded into the shot, then a human plunges the shot piston using a lever system & the molten metal is transfered into the die to be casted. just like the industrial pdc machines , but on a very small level.

I am asking this because i want to cast aluminium pieaces of a scale model chopper bike & the parts have very fine details + the number of bikes is limited to 100 pieaces. getting them cast in a pdc machine would be an expensive affair & no one would agree to set up a die for 100 pieaces on their pdc machines.

Has anyone tried this before?.

[handlewanker]

Hi, die casting is usually for a hundred thousands parts, hence the expense of having a die made.
For a 100 parts I'd use lost wax casting.

This is in the region of DIY capability with a small electric or propane furnace for the melt, whereas the diecasting set-up is not user friendly due to the technique of getting the molten metal into the die etc.

There was a design in the Model Engineer magazine some years back where a guy made a small press like device for making small diesel engine pistons in aluminium alloy.

The device had a vertical plunger that was removed to pour the metal in and then the plunger was quickly reinserted and a lever used to force the metal to fill every detail in the cavity.

As the cavity was for pistons, the design was fairly simple, with machining to finish them off later.

If a complex shape was being considered, then it would need someone with an EDM set-up to spark out the design, or a pantograph machine.

If time is no problem then there is a small EDM design, that is also in the Model Engineer, and is capable of being made and used to do quite serious work by the average DIY'er with some electronic knowledge.
Ian.

[axis_control]

Originally Posted by handlewanker There was a design in the Model Engineer magazine some years back where a guy made a small press like device for making small diesel engine pistons in aluminium alloy. The device had a vertical plunger that was removed to pour the metal in and then the plunger was quickly reinserted and a lever used to force the metal to fill every detail in the cavity. As the cavity was for pistons, the design was fairly simple, with machining to finish them off later. If a complex shape was being considered, then it would need someone with an EDM set-up to spark out the design, or a pantograph machine. If time is no problem then there is a small EDM design, that is also in the Model Engineer, and is capable of being made and used to do quite serious work by the average DIY'er with some electronic knowledge. Ian.

Thank you for the reply...

The machine built by the guy must be a non ferrous metal forging machine. Even today almost all piston`s are made using the same process.

My parts are complex but can be done in a two part die (male-female). their thickness is from 1mm to 10 mm. If i get the die done & use the manual mold fill technique as discribed by me earlier, do u think i will achive a good finish on the aluminium?. I don,t think its necessary to use couple of 100 tons of pressure to achive that.

wow!..i have always wanted to build my own spark erossion machine.. please please tell me where can i find that design for the EDM.

[dang]

Hi,

Currently, I do Aluminum Gravity Die Castings in my backyard. Basically, I make a steel die on my mini mill. This die is built out of several different pieces of steel. After it's cut, I then polish the die to a mirror like shine and weld those pieces together.

When the die is finished, I melt the aluminum and simply pour it into the die. Gravity does the rest. The die is clamped together with simple screw clamps. I also use sand cores. The actual solidification of the Alum takes about a minute inside of the die. The surface detail is really good.

This is for larger parts.

Knowing what I know now, I'd do a few things differently.

1st I'd use Graphite for the actual mold structure. It's easy to cut. Waaay easier than steel is. I've seen people use a freakin Dremel to cut the stuff. It's permanent. It'll take the heat.

2nd, I'd cast using Zinc or Zamak instead of Aluminum. Especially for smaller parts which are mass produced. It has a lower melting point than Alum does, it requires about 2/3 of the energy expenditure to melt, and can deliver many of the same features. At least for non critical parts or those that don't require low weight and high strength. Oh, and if the mold is to be clamped shut, you'll find that the smaller die casting machines (200 ton and under), ONLY use Zinc. Aluminum is hotter and requires more force to keep the clamps shut tight. I believe that this high clamping pressure is so the machine can handle very large parts or molds. Also, repeatability and reliability is a big concern.

With that said, I'd skip the EDM machine all together. I'd build the molds on a small CNC mill that's enclosed to limit my exposure to nasty Graphite dust. That'd probably be best for a smaller operation.

I've also run across that homemade die casting machine article. It wasn't that impressive. Frankly, it looked a little dangerous to me. The molten material wasn't enclosed, that material was also manually fed, from a height, which is a dangerous lift all by itself. I wouldn't use it.

[axis_control]

Originally Posted by dang Hi, Currently, I do Aluminum Gravity Die Castings in my backyard. Basically, I make a steel die on my mini mill. This die is built out of several different pieces of steel. After it's cut, I then polish the die to a mirror like shine and weld those pieces together. When the die is finished, I melt the aluminum and simply pour it into the die. Gravity does the rest. The die is clamped together with simple screw clamps. I also use sand cores. The actual solidification of the Alum takes about a minute inside of the die. The surface detail is really good. This is for larger parts. Knowing what I know now, I'd do a few things differently. 1st I'd use Graphite for the actual mold structure. It's easy to cut. Waaay easier than steel is. I've seen people use a freakin Dremel to cut the stuff. It's permanent. It'll take the heat. 2nd, I'd cast using Zinc or Zamak instead of Aluminum. Especially for smaller parts which are mass produced. It has a lower melting point than Alum does, it requires about 2/3 of the energy expenditure to melt, and can deliver many of the same features. At least for non critical parts or those that don't require low weight and high strength. Oh, and if the mold is to be clamped shut, you'll find that the smaller die casting machines (200 ton and under), ONLY use Zinc. Aluminum is hotter and requires more force to keep the clamps shut tight. I believe that this high clamping pressure is so the machine can handle very large parts or molds. Also, repeatability and reliability is a big concern.

Sorry to reply late...was a bit busy

I loved reading your reply as its informative & also has arrowsed a few questions in my mind.

i really want to see some pics of the aluminium part surface that u casted in ur built die i have seen lot of pdc casted & centrifugal casted pieaces (lost wax) of aluminium , but never seen or handeled an aluminium pieace that was gravity casted that to in a metal die.

do u use this die for continious production or couple of pieaces ?.. also do u have a water cooling system in ur die?

About grafite ..I din know it can be used for molds & that to for casting of metal. I do know that it is used to make electrode for spark erossion die making process. now i will find out more info on the grafite mould technique, looks intresting & logical. I will also keep in mind about using zinc, but again my product is a scale model (show pieace) & demands excellent crome plating. I remember reading a table saying zinc has better plating properties than aluminium.

I will design a CAD model concept for the manual die casting machine & post the pic here soon (it might take couple of days) i would want to have sugestion on it.

Thanks for your reply !...cheers

[handlewanker]

Hi axis, you're right about the zinc taking chrome plating better than ally.

I used to work in the door furniture (locks,handles etc.) industry, and all of the components were made of zinc or brass.

The zinc stuff had the flash from the mold split removed, and the surface was then polished using various graded grit abrasive belts, and a final soft mop with a white waxy polishing compound to get the bright polish required for chrome plating.

If you're contemplating having the parts plated straight from the mold, it won't work.

The die casting, although giving a very smooth finish, still requires abrasive taping and bright polishing to get the finish for chrome plating, otherwise it has a dull fine pebbly finish.

A polished and chrome plated item has a MIRROR finish that will reflect clearly like a mirror.

We tried a vibro finishing process, where the parts are shaken up with abrasive pebbles, in a vibro finishing machine, especially formulated and shaped to get into the crevices, but they never came up to the finish of hand polishing.

You can cast anything by any method but the surface finish reflects the method used, and the pressure die cast method still isn't good enough to get highly finished items without further polishing, ask anyone in the tap ware industry.
Ian.

[handlewanker]

BTW, graphite is worse than cast iron for mess and if you have to use the stuff, use a good respirator and a vacuum cleaner.

If you want to have the EDM plans for a small home built EDM then give me your email adress and I'll send the direct.
Ian.

[dang]

I'd have to agree about finishing being the most important step toward getting a good shine. Although it can take up alotta time, polishing before any sort of plating is extremely important.

On my steel molds, I used Diamond Polishing Paste that goes all the way up to .5 Microns. I still see inclusions in my castings from stray bits of the sand core as well as translation (mold to casting) scratches that I couldn't see even after I polished the mold interior.

For my part, I'm gonna be attempting to build a vibratory deburring machine in the near future. Like this one, http://www.cnczone.com/forums/showthread.php?t=14464
Hopefully it'll knock most of my casting's scratches and burrs.

For parts as defined and intricate as those being discussed here, I think some Diamond Paste like I used on the molds would work fine. It's available on Ebay.

And regarding that graphite mess, I'm totally gonna use a vacuum, maybe two, and an enclosure. The dust is really dangerous and shouldn't be underestimated.

[handlewanker]

Hi, no matter how good the mold is, the parts still require polishing to a mirror finish using Tripoli polishing compound on the mop if you want to have a mirror chrome finish.

If you cut down on the preperation wysiwyg for chrome finishing.

BTW, the best vibratory finishing cannot approach hand polishing unfortunately, and only gives you a dull sheen like the shine on alluminium foil, shiny but not mirror finish.
Ian.

[axis_control]

Originally Posted by handlewanker If you're contemplating having the parts plated straight from the mold, it won't work. The die casting, although giving a very smooth finish, still requires abrasive taping and bright polishing to get the finish for chrome plating, otherwise it has a dull fine pebbly finish. A polished and chrome plated item has a MIRROR finish that will reflect clearly like a mirror. You can cast anything by any method but the surface finish reflects the method used, and the pressure die cast method still isn't good enough to get highly finished items without further polishing, ask anyone in the tap ware industry. Ian.

Hi Ian ,
Thank you for your reply!.

I agree that the parts won’t get a mirror finish if I directly plate them after casting without any processing. I am thinking of using a die grinder & felt bobs.

What r ur views of building a small manual pressure die casting machine? The parts to be cast r not more than a volume of 25cc (may be I will try zinc) it might come upto 60 grms max. Here once when the metal is fed into the shot by a ladle , a person using a lever arrangement pushes the piston to force the metal into the die. The whole system works just like the industrial pdc machines, only that here the machine size is very small & hydraulics is replaced by human mussle. The machine would also be horizontal like the industrial pdc machines.

The tap ware industry is definitely the place where I can get exact knowledge about excellent finishes. Your replies reflect the same.

[axis_control]

Originally Posted by handlewanker BTW, graphite is worse than cast iron for mess and if you have to use the stuff, use a good respirator and a vacuum cleaner. If you want to have the EDM plans for a small home built EDM then give me your email adress and I'll send the direct. Ian.

I have never worked with graphite & have got more advice`s regarding the safety issue. I surely got to be careful if i am using it.

regarding the EDM plans , i have pm u my email id.
Thanks a lot!

[axis_control]

Originally Posted by dang For parts as defined and intricate as those being discussed here, I think some Diamond Paste like I used on the molds would work fine. It's available on Ebay.

if i have those casted in aluminium or zinc ...would only Diamond Paste polishing work?.. should i need to buff them before DP polishing ?

Here i have attached the pics of the part to be casted.Its an harley scale engine. The CAD modelling is not yet complete.
The engine would be casted in two parts split from the centre right upto the gear box. The fins on the engine block r 1mm in thickness & the groves r upto 2mm in depth. The engine is 60 mm high.
I visualize an excellent mirror finish on the finished product. now i wonder how much time will it take to polish a single pieace using a die grinder.