# Zamak casting in permanent molds



## forhire (Jan 1, 2019)

This semester I decided to take a page out of Lyle Peterson's (Tubalcain,mrpete222) play book and rather than turning flywheels I would attempt to cast them. But unlike Lyle's lead flywheels I had to be lead free. I also wanted to try casting the flywheels directly to the shaft forgoing the need for set screws. So I thought I'd try Zamak 3 which melts at 728F. Normally for gravity permanent molds Zamak 12 is preferred but my pot tops out at 750F which is too low for Zamak 12. I was concerned with the molds sticking so I opted for boron nitride lubricant/wash which has worked treat. The wash lasts a long time on the ladle. It generally has to be reapplied every 5 to 10 parts depending on wear.

The process is simple. The students turn a shaft to length and file a flat on one end. It works without the flat but it may turn during machining. They then insert the shaft into the warm mold and pour in the zinc (Zamak). Let it cool a minute, pop it out of the mold, and it's ready for the next pour. The students then cut off the sprue, paint it, and then turn it to final dimension.






Also just prior to the holiday break we milled a very simple mold of a snowflake design. By the end of the day we could do about one a minute. The electric melting pot worked great and acted as a holding furnace. I can't imagine trying to hold/control the temperature in the gas furnace all day. The students were amazed they could complete the ornament in about 5 minutes which included casting, fettling, drilling a hole, and bending the hanger. Good intro to simple wire forming jigs. 





For those of you that haven't seen Lyle's video here is a link:


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## vtcnc (Jan 2, 2019)

Wow. This is really great! I’d like to learn more about the mold material, how they were made and the boron/nitride wash. Is there anything more you can share on that front?


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## CarlosA (Jan 2, 2019)

What he said ^ plus ... source of the Zamak. This could be great for hobby machinist type work especially if the molds are easy to make with normal home shop equipment.


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## forhire (Jan 2, 2019)

vtcnc said:


> Wow. This is really great! I’d like to learn more about the mold material, how they were made and the boron/nitride wash. Is there anything more you can share on that front?



I used ZYP Coatings BN Aerosol Lubricoat. I bought this off Amazon but McMaster has another brand for less but haven't tried it.
https://www.zypcoatings.com/top-selling-boron-nitride-coatings/bn-aerosol-lubricoat/
https://www.mcmaster.com/10515k35

The molds were milled A36 plate steel I had on hand. I wasn't willing to put too much into the molds if the zinc wasn't going to work, I was worried about the zinc "galvanizing" the steel but it wasn't an issue at all. I believe the aluminum in the zamak creates a barrier. I did have some of the dross stick to the galvanized sheet metal I dumped it onto. I also cast into an aluminum mold I had on hand (for plastic injection molding) and the BN coating protected it. I'll upload a photo of that cast tomorrow.



CarlosA said:


> What he said ^ plus ... source of the Zamak. This could be great for hobby machinist type work especially if the molds are easy to make with normal home shop equipment.



The Zamak was from Roto Metals. It comes in 4lb ingots for about $15 each.  I'm sure I could have found it cheaper but I only bought 40 lbs and they shipped quick. I figured my pot would hold about 30 lbs and I wanted some extra for make up. Even running all day over a couple days I had very little dross. I was happy with the quality.
https://www.rotometals.com/zamak-3-ingot-aluminum-4-zinc-96/


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## forhire (Jan 2, 2019)

Here are a couple more photos. Back side of an ornament headed for remelt. A test cast in a mold that was designed for plastic injection molding. This mold is aluminum with the BN wash. It took a couple tries to get this one and it didn't fill out the center handle making it worthless as a top. But it is certainly promising and aluminum molds are easy to make.


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## derf (Jan 2, 2019)

This came at a good time...I've been researching zinc die casting for the last few days.
Did you pre-heat the steel mold before you poured? If so, what temperature for zamak 3?


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## ttabbal (Jan 2, 2019)

Nice! I've been tossing around trying out casting, but the setup with sand and such always seemed a bit fiddly. How did you make the molds? CNC?


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## forhire (Jan 2, 2019)

derf said:


> This came at a good time...I've been researching zinc die casting for the last few days.
> Did you pre-heat the steel mold before you poured? If so, what temperature for zamak 3?



I'm glad others are finding the information of value. I didn't really find a whole lot of information when I was researching. I took the dive fairly blind. It worked wonderfully. I am also looking into spin casting using vulcanized rubber molds that look promising. I'd like students to be able to go from a 3D print to metal fairly quickly. I am setup to sand cast but it can take weeks to get a whole class through the process.

My pot is rated at 750F. I put a piece of k-wool on the top to help keep the heat in so I'm not sure of the actual temperature. I'll bring my pyrometer in later this week and see what it's actually running. I put the molds on the top rim of the pot under the k-wool to warm them up. After a few parts you actually need to let molds cool a little between parts. You do need to keep the ladle warm also as the zamak cools pretty fast. I used a small bottom pour ladle. Not sure if bottom pour was needed as the material is very clean.

I've been trying to think up a design for parallel opening tongs so I can run the molds faster.


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## forhire (Jan 2, 2019)

ttabbal said:


> Nice! I've been tossing around trying out casting, but the setup with sand and such always seemed a bit fiddly. How did you make the molds? CNC?



Designed the parts in Fusion 360. Did a combine cut to make the negative from the mold halves. CNC milled from mild A36 plate steel. Used a 3 degree end mill for the relief draft. This is the screen shot with the shaft that is over molded. I initially used dowel pins but the heat combined with the wash caused one to stick so hard we had to drill it out, despite having a nice sliding fit to start. Next time I'll locate using balls. For this run we are squaring the halves when clamping.


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## vtcnc (Jan 2, 2019)

forhire said:


> Designed the parts in Fusion 360. Did a combine cut to make the negative from the mold halves. CNC milled from mild A36 plate steel. Used a 3 degree end mill for the relief draft. This is the screen shot with the shaft that is over molded. I initially used dowel pins but the heat combined with the wash caused one to stick so hard we had to drill it out, despite having a nice sliding fit to start. Next time I'll locate using balls. For this run we are squaring the halves when clamping.
> View attachment 283888



You are referring to alignment pins, correct? If I’m interpreting this correctly, wouldn’t a taper pin be helpful in preventing any binding?


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## forhire (Jan 2, 2019)

vtcnc said:


> You are referring to alignment pins, correct? If I’m interpreting this correctly, wouldn’t a taper pin be helpful in preventing any binding?



Yes. The pins I used had a sliding fit at the start tapered pins would have been better. I used what I had on hand. In the end they weren't really needed.


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## forhire (Jan 8, 2019)

This morning I took the die grinder to the mold. I'm still trying to get the feed just right. Later my students cast a bunch of flywheels to the shafts. Most turned out very well with only a small number that will be remelted. The sprue still needs a smart whack to release but then the wheel and shaft both release cleanly.


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## forhire (Dec 20, 2019)

For a second year we did ornaments using a gravity permanent mold. I've been super busy and the time almost escaped me. Somehow I knocked this mold out in about an hour or so. I even forgot to order more lubricoat so we ran bare molds. The A36 mild steel molds held up great. We did about 150 ornaments this year. Basically the same mold as last year except I used a circular sprue that was like a funnel. This really cut down on failed pours even with various students casting throughout the day. If I wouldn't have milled the year into the mold half using a straight endmill the parts likely would have simply fallen out of the mold when seperated. Without draft the part had to be knocked out with a brass hammer. Maybe next year I'll plan ahead instead of waiting until the day before Christmas break. Of course everyone had a great time making something to take home for the holidays.


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## RJSakowski (Dec 21, 2019)

forhire said:


> I've been trying to think up a design for parallel opening tongs so I can run the molds faster.








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## forhire (Jan 1, 2020)

A little late for this year but I have flash copper plating sorted which allows the zinc parts to be nickel plated. These test parts are straight out of the mold without any fettling, sanding, or polishing.


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