Casting using HDPE

I am interested in using recycled HDPE in order to cast some small parts for my ASHPD that I am working on. I have watched a lot of videos and have an infinite amount of bottles to use. I have the basics down on using the medium. I would like to make a mold to cast the parts in. My question is what would be good to use for a mold material? I know when using HDPE, it requires pressure during the cooling to keep warping down. This can be accomplished with a simple clamp until it cools. I don't care about making one at a time, thats ok, in fact preferred so I can make any adjustments if need be and don't have to fix several cavities.

Would silicone work for this with wood backing support? I have seen videos of people making blocks with it, but at that point I could just buy the are material and make a bunch of one offs, which is partly what I am looking to avoid. I don't mind making a master and then molding it in order to use the mold.

Thanks in advance

What videos did you watch? Sounds like you are wanting to injection mold which there is a discussion about how expensive tooling (molds and the heater/screw set up) are.

Why do you need HDPE? Is is just because you have an infinite amount of bottles to use? Is there a recycling facility nearby? How do you plan on melting the HDPE bottles?

TazMan2000

cavx said:

What videos did you watch? Sounds like you are wanting to injection mold which there is a discussion about how expensive tooling (molds and the heater/screw set up) are.

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They were basics on using HDPE for projects. Softening and such for use or such. I was just in that thread. It's more of a push in and then use another piece of wood to keep pressure on it.

TazMan2000 said:

Why do you need HDPE? Is is just because you have an infinite amount of bottles to use? Is there a recycling facility nearby? How do you plan on melting the HDPE bottles?

TazMan2000

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it doesn't need to be, it seems easy enough to use and I work at a car dealer that has these bottles going into the trash. They're black saving me a little extra work. I have an old crock pot I'm going to try. It's all preliminary at this point.

What are you trying to cast? Anything with detail is probably not going to work with silicone, even with Mold Max 60. You could try making a plaster mold and your master out of clay.

Sounds interesting. I casually looked into that sort of thing when I noticed how many interesting colors bottles come in for things like shampoo. Some kind of neo-mod jewelry would be fun.

As long as you're using plastic in the final color the object will be it should work out fine. HDPE is a biotch to paint for sure.

I would think for mold material, anything rated for white metal casting would certainly hold up.

-Rog

Stivie said:

What are you trying to cast? Anything with detail is probably not going to work with silicone, even with Mold Max 60. You could try making a plaster mold and your master out of clay.

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I need to make these parts for the arms. I know they're not super simple, but it would give me all the same dimensions for each part and save me from having to make all them from scratch. I thought about plaster then thought it would too brittle for holding pressure. The HDPE shrinks as it cools but it will warp too so keeping pressure on it is key. I realize this is all theory and conjecture but I'm willing to give it a shot if I can work out the mold details. I can start with the flatter parts and work up to the more complex items.

Rogviler said:

Sounds interesting. I casually looked into that sort of thing when I noticed how many interesting colors bottles come in for things like shampoo. Some kind of neo-mod jewelry would be fun.

As long as you're using plastic in the final color the object will be it should work out fine. HDPE is a biotch to paint for sure.

I would think for mold material, anything rated for white metal casting would certainly hold up.

-Rog

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Never thought to look into metal casting materials. If I could heat the mold too, that would give me more working time. From what I've seen most people stick to making ingots of sorts and then using it as a raw material. One guy made blocks for testing his CNC machine and just clamped it from all sides in a wood form. Made soap looking stuff. Another made longer rectangular forms again in wood with a pivoting closure that he clamped. He would cutni to length then turn it on his lathe. I'm looking to go one step further and dump the heated material into the plates and clamp them. If all I have to do is clean some flash up and maybe a little filing and sanding that would be ideal.

Gixxerfool said:

They were basics on using HDPE for projects. Softening and such for use or such. I was just in that thread. It's more of a push in and then use another piece of wood to keep pressure on it.


it doesn't need to be, it seems easy enough to use and I work at a car dealer that has these bottles going into the trash. They're black saving me a little extra work. I have an old crock pot I'm going to try. It's all preliminary at this point.

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You can thermoform HDPE with good results. Depending on how you make the tools, you could even call it injection.

If you are not melting the plastic to a liquid, you can make your tools from MDF. Cheap and easy to work.

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cavx said:

You can thermoform HDPE with good results. Depending on how you make the tools, you could even call it injection.

If you are not melting the plastic to a liquid, you can make your tools from MDF. Cheap and easy to work.

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Great suggestion. I've seen people use canola oil as a release, would you suggest something different or none at all?

You should not need a release agent. You are pushing the heated plastic into the tool. This is sort of like female tooled vacuum forming except that there is no vacuum.
What is interesting in both methods is that as the plastic cools, it shrinks slightly and pulls away from the tool. Once cooled, you should be able to lift the part out of the tool with little effort.

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cavx said:

You should not need a release agent. You are pushing the heated plastic into the tool. This is sort of like female tooled vacuum forming except that there is no vacuum.
What is interesting in both methods is that as the plastic cools, it shrinks slightly and pulls away from the tool. Once cooled, you should be able to lift the part out of the tool with little effort.

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That makes sense. Thanks so much for your help. On to shop for supplies.

Gixxerfool said:

That makes sense. Thanks so much for your help. On to shop for supplies.

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One of the best plans of attack might be to make a plunger system. It is double the work, because you have to make both male and female tools, but as I said, MDF is cheap and great for this kind of work. Basically you push the heated plastic into in shape. It has no choice but to follow the shape of the tooling.

The very first time I did this was late 1980's when I needed a spare plastic sharpening stone holder for a camping knife. The only thing I did wrong was not round the corners of the male tool and it gave the final parts points on the tips on the closed end. Other than that, it looked like a bought part. It was made from 3mm Polyethylene that I heated with a blow torch. My tools were all MDF.