Aluminium manual die casting technique....

[Harryman]

You could centrifigually cast these parts in vulcanized rubber molds, it's reasonably inexpensive and works well for these applications. They can be cast in zinc, pewter or the bismuth based alloys mentioned above. You'd have a tough time getting the fins on a Harley motor to fill by gravity casting, I know, I've done it, PITA. I was in the business for 20 years and have cast, finished and plated plenty of model parts. There's several threads on the subject scattered around the forum. If you had the time and money to invest in the project, you can build the equipment yourself, and cast and finish the parts too. I'd suggest farming out the mold making and casting end of it though, just as a milling machine doesn't make you a machinist, a casting machine deosn't make you a caster.

I'd also step up above a die grinder for your polishing, get a bench mounted polishing lathe or bench grinder. It'll be way faster and you can get a better finish. You can get a mirror finish by tumbling, but it takes several steps and a bit of time, just like hand polishing. The most efficient way is a combo, go through 1 or 2 steps tumbling, a coarse and fine, a burnishing step to make it relatively shiney and a hand polish to give it a mirror finish prior to plating.

[axis_control]

That low temp alloy might work for you. It looks a bit on the expensive side though.

Axis, I'd definetly look into that Centrifugal Casting that Handlewanker mentioned. For parts that are as small and as detailed as yours need to be, it might just be the thing. If you look at the 1st link I provided, you'll see 3 different casting techniques documented on miniature engines built by Kawasaki. Engines with 1mm thick heatsinks. Some techniques don't do so well at the micro level.

definately the low temp metal alloy is on the expensive side when considering manufacturing. its ok for 1 or 2 pieaces but not for multiple parts.

I found that in spin cast technique though the whole process looks quite easy, it actually has a bit complicated procedure for maintaining the molten alloy temp.
i found this info on weikipedia
A melting furnace is necessary only when spin casting with metal. Understandably the metal must be in a molten state prior to introduction into the mold. However, it is necessary for a spin casting furnace to posses a temperature controller as there is an approximate range that works best for each metal. For example a particular zinc alloy is typically cast between 775-800 °F, whereas it actually melts much lower around 500 °F. If the metal is introduced to the mold at a higher temperature (in this case, above 800 °F), it will start to wear the silicone down prematurely, greatly shortening the mold life. If the metal is introduced at significantly lower temperatures (below 775 °F), its solidification time will similarly be shortened resulting in incomplete or low quality castings. Therefore, spin casting with metal requires not only a furnace with fine temperature control, but knowledge of what range to cast at.

If the rubber mould is distroyed while in production ..its gonna create problems to fulfill the orders on time. All depends on the furnace with temp control.

anyone herd of white metal here?...i have seen lot of intricate designs made in it.i am attaching a pic of figures made in white metal.

[axis_control]

You could centrifigually cast these parts in vulcanized rubber molds, it's reasonably inexpensive and works well for these applications. They can be cast in zinc, pewter or the bismuth based alloys mentioned above. You'd have a tough time getting the fins on a Harley motor to fill by gravity casting, I know, I've done it, PITA. I was in the business for 20 years and have cast, finished and plated plenty of model parts. There's several threads on the subject scattered around the forum. If you had the time and money to invest in the project, you can build the equipment yourself, and cast and finish the parts too. I'd suggest farming out the mold making and casting end of it though, just as a milling machine doesn't make you a machinist, a casting machine deosn't make you a caster.

I'd also step up above a die grinder for your polishing, get a bench mounted polishing lathe or bench grinder. It'll be way faster and you can get a better finish. You can get a mirror finish by tumbling, but it takes several steps and a bit of time, just like hand polishing. The most efficient way is a combo, go through 1 or 2 steps tumbling, a coarse and fine, a burnishing step to make it relatively shiney and a hand polish to give it a mirror finish prior to plating.

Thanks for replying Harryman,

I have been through couple of sites & all of them mention rubber moulds for casting low temp metal, but no one has mentioned the rubbers exact technical name (if it has a universal name) except where they r selling their own silicone compund with their own specific name.

wow!.20 yrs ..thts a lot of experience & that to in model making. I will find & read related threads.

I agree about the bench mounted grinder as yesterday i tried polishing a hotwheels car base plate & found it time consuming using a die grinder. but here i had used a felt bob.
I have not done burnishing before. I don,t know how to burnish curved intricate parts as the burnishing tools r designed for straight plain surfaces.
Any tips on burnishing tools. Here is a pic for a curved handle burnished. I wonder what tool they used for burnishing. The second pic is a resin cup....may be that is flexible enough to reach the intricate parts.
..

ok ..seems like there is some problem uploading pics...i will upload these two pics later

[Harryman]

White metal is just a general term used to describe any of the low temp alloys previously mentioned.

You absolutely need a temperature controlled melting pot to get successful castings. To maintain the proper mold temp, you control the cycle time of the rubber mold in the casting machine. A shorter cycle time, the mold gets and stays hotter, etc.

Silicone molds can withstand the higher temps of zinc based alloys, but their life is not long compared to lower temp metals like tin (pewter). The key with zinc is to cast thinner, less massive parts so they cool quickly and don't cook the mold as badly. With pewter alloys, you can cast larger parts successfully and have a longer mold life, you can easily get thousands of parts out in pewter before remaking the mold. All molds do wear out however over time.

I have seen zinc successfully slush cast in steel molds, just poured in till it fills, and then dumped out, leaving a shell. No machine, just gravity. That'd be possible with some of your parts probably, but the fins on the motor would be tough. Rubber molds flex so you can get intricate parts out, steel ones don't.

[axis_control]

here r the 2 pics i was not able to upload. The first is a handle & the second probably is a flexible burnishing tool...(not sure if a flexible burnishing tool is available.)

U know how the handle must have been burnished? (was it done using a disk type flexible burnishing tool ? )

[Harryman]

The left handle shows the part after abrasive tumbling, you want the parts nice and smooth with a fine surface finish. You can also get to this point with a polishing wheel and a several abrasive cutting compounds.

The piece on the right is after tumbling with a burnishing media, most likely carbon or stainless steel shot or even ceramic balls.

You can if desired, tumble the piece in media like wood pegs or sawdust impregnated with polishing compound to get a mirror finish, but it takes a really long time.

The steps are really similar no matter doing it by hand or in a tumbler.

1: Cut down - removing any surface irregularities, flaws, orange peel etc.

2: Prepolish - refine the surface, removing any scratches from previous steps. You want a very fine matte finish.

3: Burnish - burnishing doesn't remove any significant amount of metal, it just pushes it down and around, erasing the tiny, tiny surface irregularities on the matte surface, creating the shine. Generally this step is only done by hand with a burnishing tool in areas where it's impractical to polish and in higher priced pieces like jewelry. In tumbling, this is commonly the final step. To get into nooks and crannies, you can use a magnetic pin tumbler, which uses tiny stainless needles, but just to make things more confusing, I like to use a pin tumbler early in the process, on raw castings or after cut down, not at the end.

4: Final polish - when polishing with a buffing wheel and compound, you're primarily smearing the surface of the metal around, not so much removing material. When done right, you can get a mirror finish, done wrong and you get streaks and waves in the metal.

The most efficent/cost effective way to get a bright, shiny finish on a large group of small parts is to tumble up to steel shot burnish, then hand polish.

[axis_control]

The most efficent/cost effective way to get a bright, shiny finish on a large group of small parts is to tumble up to steel shot burnish, then hand polish.

definately ur information is very valuable to me.

today I built a trial engine cylinder block & placed it into the chasis I have built for the chopper bike .....& learnt a lot of deal. I realised that no matter how perfectly the product is shaped, without that polished/plated mirror look it ein,t going anywhere. One would not even give a second look..actually not even a first.

I realise how important role polishing & plating play in this.

I will look out for those steel shots if they r available here...

[Harryman]

Small parts kind of puts you in the realm of jewelry finishing. Contact www.riogrande.com for a tool catalog, it's got plenty of info on equipment and processes.

definately ur information is very valuable to me.

today I built a trial engine cylinder block & placed it into the chasis I have built for the chopper bike .....& learnt a lot of deal. I realised that no matter how perfectly the product is shaped, without that polished/plated mirror look it ein,t going anywhere. One would not even give a second look..actually not even a first.

I realise how important role polishing & plating play in this.

I will look out for those steel shots if they r available here...

[axis_control]

Yes ...exactly Harry.....i did picture the jewellery look in my mind for the chopper & thts what i am looking forward to achieve. After all the look is the most important aspect in scale modelling.

Thanks for the link i am checking it out..

[jeb]

Once the CAD model is done, you could use a rapid prototype to make and RTV mold. A friend of mine got a few things from www.printapart.com and the detail was really fine. The models can be fragile, so you might need to make a mold of the printed prototype, cast some urethane resin or something reasonably durable that you can sand, and then use that as your master to make another RTV mold for casting low melting point metals.
cheers,
JEB

[OCELOTL]

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.

Can someone please point me in the direction of where I can find both of these (the die casting and EDM) plans. Thanks for your help.

Gabe

[handlewanker]

Hi Gabe, and also for anyone else who wants to dabble with an EDM setup, here's a few drawings and an explanation on building one using generally available materials.

In case they don't come up big enough to read properly, just send me your email adress and I'll send them direct to you.
Ian.

[heenaveer]

Thank you so much for sharing this post....really useful

[tinalulu]

I am really lucky to come here. First allow me to introduce myself, I am Tina ,live in Ningbo China, Ningbo, which is a modernization, industrialization, commercialization coastal city, and also is a "die casting mould town".
I worked in one of the professional die casting mould manufacturing company in China. and act as an professional english translater, help foreign customers communicate fluently with our mould design engineers.
I hope to study here, and recognize more of the world casting peer. Also anyone who want to realize China die casting, can communicate with me.

[ihavenofish]

.

[Calico]

Hi guys,
After reading this old thread, I have a similar project.
Casting small alumunium car engine model.
I'm thinking milling the graphite for mold.
And spinning the mold like jewelry lost wax ?

Anyone has done this ? Please let me know if any success ??

Thank you

[awerby]

Why not just mill it in wax and use the regular lost wax process? Machining graphite takes special tooling, and the dust is not only abrasive, which will get into the moving parts of your machine and ruin them, but conductive, so it will get into your electronics and ruin them too.

Graphite also is very conductive of heat, so you have to heat it up or the metal will freeze as soon as it hits it. If you want to make a lot of these little engine blocks, just mill one in wax, make a silicone rubber mold of it, and cast as many waxes as you need.

[Calico]

well lost wax is expensive, I have so invest the heater also to heat the lost wax.
I dont mind milling the graphite once.
the powder also costly here.

I need to make maximum 20 pieces of part.
I just wondering if spinning using graphite mold is working, but anybody tried before ?
for me milling graphite is easier and cheaper.

[handlewanker]

Hi, just my opinion, but making the mould to make the part is back to front for low volume........I think it would be much easier to make the part in wax....whatever.... then make the silicon mould from it to make the wax ones you coat with ceramic slurry to cast in..

You'll need a furnace to melt the metal for the casting so heat is going to be available anyway for the ceramic mould baking and the wax removal.

You could also make the pattern with a 3 D printer if not the actual part itself.
Ian.

[ihavenofish]

well lost wax is expensive, I have so invest the heater also to heat the lost wax.
I dont mind milling the graphite once.
the powder also costly here.

I need to make maximum 20 pieces of part.
I just wondering if spinning using graphite mold is working, but anybody tried before ?
for me milling graphite is easier and cheaper.

graphite is a bad choice for your mould. its very expensive, not at all durable, and requires and expensive specialised dust collection system and machine preparation to mill.

graphite is used for crucibles, because its mostly inert to a high temperature. its also used for electrodes for EDM to MAKE steel moulds. but its never used as a working mould on its own. (except in special cases for glass forming).

if youre doing 20 pieces, lost wax is the cheapest solution. make a rubber mould of the part, pour waxes (can do it by hand on the stove if youre careful), then plaster to make the mould. melt out the wax in an oven or with a steamer, and then pour your molten aluminium via gravity.

or make the waxes and farm out the casting.