Lost wax casting

[Keith_W]

I came across this post in another forum. I thought that it would be of interest to MSW'ers, so I am reposting part of his post here: 

 

 

"These logos were custom designed by myself. They were made by shapeways in Solid silver (yep, silver). Cost around $70 each. Shapeways use lost form casting to produce these. They print the design in wax. Form a mould around the wax (probably plaster of paris or something). Then the molton silver is poured onto the wax. The wax dissappears and what you see is left. They even cast with platinum (dont ask what the price for platinum is)."

 

(That's AUD$70, i.e. about USD$50). 

 

The company he refers to is this one: http://www.shapeways.com/

 

This process might be useful to make plaques for our models, and maybe castings for bow and stern decorations. I haven't checked yet, but they may be able to use a cheaper metal if it's "only" for castings. Given that I will be spending 3 years of my life on my current model, I think that about $100 for a nice silver plaque would be worth it! 

[jbshan]

It's an ancient technique.  You might inquire if another metal is possible since silver needs polishing.  Nickle and chrome stay clear, gold can be put onto a base metal in micron thicknesses so not probably as expensive as you might think.  Because the wax and plaster goes away, there's no problem doing 3D objects, just doing more than one.  A new wax I think needs to be made for each casting.

[Keith_W]

Yes, I know that the technique has been around for a while. That's how Rodin made his bronze busts. But what is new about this is the use of 3D printing and the ability to send CAD files through the net, and receive the finished casting in the mail. In the past you would have to make the casting yourself, make the mold, melt your own metal ... that's just a bit too much work for me  

[grsjax]

For simple shapes using a low melting point alloy like brittania metal it is very doable at home.  The one thing to remember it to incorporate as many vent holes as you can into the casting to ensure a complete fill out.  Using plaster to make the molds is probably the easiest way.  After the mold is dry use low heat to melt the wax and let it run out of the vents.  Keep the heat on for a while to ensure all the wax is out.  Heat the mold, melt the alloy and pour.  As was said above the disadvantage is one casting per mold but for one offs it is hard to beat.

 

One more thought.  For series production you can make a split mold to turn out wax masters.  Only works with symmetrical shapes like cannon.

Edited August 8, 2015 by grsjax

[jbshan]

Actually, I was thinking of these little guys.  Hard to make an interim mold to make pairs of them, whereas a wax would do it nicely for a one-off.

 

[JPZ66]

Hi,

 

There are a couple of ways to go about this process...I won't go into that except for this much ....

 

You can create a master...from nearly any material, mold it in a type of heat resistant silicone, and make injected waxes for the investment casting process, or you can create wax masters for either 'one off' ( risky ) or to use for other forms of molding, and again making additional wax copies for the investment process.

 

The "Investment" is a type of refractory grade material, similar in appearance to plaster, but capable of allowing very high temperature materials to be poured or cast into it. Brass, silver, gold, platinum, etc.

 

No matter which way you tackle the front end work, once you create a 'tree' of wax masters and set up, pour and create the investment mold, the mold is then cured and baked in a high temp oven for very specific cycle of temps and time to both cure the investment AND melt out the wax masters....leaving behind the exact cavity of the master which then gets filled with your casting Metal. - The 'Flask' ( the part that is the investment mold in a metal cylinder ) will be taken from the oven or kiln, and either gravity or vacuum cast with the metal that is ready and waiting. The flask needs to be at a quite high temp when this is done. Again, a separate topic all its' own....for another thread maybe one day.

 

Throughout the process, there is a small percentage of shrinkage produced at the different stages, and knowing both the molding materials and the final casting materials will be a part of the initial design...i.e; the original master is often created at anywhere from 1-3% oversize to account for this. For very small parts this process shrinkage may not be noticeable, but if the parts have a bit more size or mass, and are requird to fit as a part of an assembly.....well, you get the idea.

 

The good thing about creating a silicone mold for wax injecting, is that if you decide you want more of the castings, you simply make more of them and repeat the investment process for more metal castings.

 

BTW - there are quite a few silicone mold materials to choose from and the type of investment will depend on the desired finish, type and temp of the metal to be cast....none of these parts of the process are " one size fits all ".

 

I hope I have not added any confusion here....hopefully it sheds a little light on the process. There are a few decent videos on the internet out there, but most that I have seen are less han satisfactory for really explaining things well.

 

- Joe

Edited September 29, 2015 by JPZ66

[JPZ66]

I should also like to mention, that when multiple waxes are created, they will each need to be imspected, cleaned up (of parting lines, etc) and assembled into a 'tree'...looks a lot like a Christmas tree when done, and then is ready to be made into the investment mold stage....the great part about investment molded metal castings, is that they have no parting lines...only the attachment point of gates and vents, which are easily trimmed and cleaned.

 

It is certainly possible to create low temp metal castings at home, but there are a number of downsides. Foremost of them is that the low temp metals available typically do not have much strength and many will 'rot' over time. Some contain lead. For low temp metal castings, you can simply mold your master in a high temp resistant silicone and won't need to worry about any plaster molds or the like. If you are a DIY'er...Please follow the directions of any casting kit you buy and be very carefull with even the low temp metals...they most certainly can cause serious injury to you and your household equipment if not handled properly.

 

When you move up a step to actual shop castings, one must consider there are a number of different formulas even for brass. Not very home casting friendly due to the required temperatures, proper crucibles and so on.

 

I was supposed to have my shop up and running by now, but got sidetracked with a different venture......at any rate, I will be setting up my casting operation in the coming months, and will once again be able to cast large or small quantities in everything from resin to lead free pewter / brittania, brass, silver and gold ( forget about platinum ! )

 

Anyone desiring more information about molding, casting in resin or metal, feel free to shoot me an email with your questions. I'm happy to assist if I can.

 

- Joe

[JPZ66]

Found this very brief video on YouTube....a quick overview of the process, but gives you the idea....