Any experience / advice on small scale injection moulding (ABS etc)?

GunnerBill

Active Member
In concurrence with some other projects I'm considering making some parts using injection moulding.

Various sizes, perhaps up to the size of a rifle stock as per my Plasma rifle threads elsewhere.

Any advice very welcome.
 
I used to set up molds and run injection molding machines at a factory. The equipment used for this is seriously heavy duty. 50 plus pound steel molds, compound that needs to be heated to at least 400 degrees and a ton of toxic fumes. And the machines themselves are very expensive. Really a nasty job. Couldn't imagine doing this at home.
Not to burst your bubble, or maybe I misunderstood.
 
I used to do rubber injection molding in a factory as well. Agreed with jake88 this isn't something I would think would be easily replicated at home. Our presses were hot water heated barrels and even the smallest machine was 100k tons per square inch under lock. Maybe some molding would suit your needs better.
 
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The closet thing you'll get, and even these are not priced for the average hobby Joe, is a Morgan Press. I'm running these in my shop.
 
Agreed with the comments above; very expensive (steel/alu molds) and machine/press would cost an arm, leg, kidney + fumes!
As for a "small mold" I don't see much the use of such technique; too expensive, unless you want to make oodles of pieces and even then, the mold has to be cleaned up regularly and has a "shelf life" also (that means paying for a brand new mold).
 
Maybe I'm not even thinking about the same thing - pouring resin/liquid plastic into a mould and waiting for it to set?

I'm showing my ignorance here aren't I <meh!>

I saw a youtube of someone doing this with hot glue describing it as injection moulding, obviously hobbyist but even so...
 
Injection mlding really only makes sense for high volume sales for offsetting the tooling and production costs (set up, overheads, schedualing, engineering required).

3D printing and resin casting falls into the low-volume realm.
 
Maybe I'm not even thinking about the same thing - pouring resin/liquid plastic into a mould and waiting for it to set?

I'm showing my ignorance here aren't I <meh!>

I saw a youtube of someone doing this with hot glue describing it as injection moulding, obviously hobbyist but even so...

Resin casting is what you're talking about. But the process of using a hot glue gun to inject molten material into a casting could be considered injection moulding, however, I don't think you'll find too many here who use hot glue singularly as a building medium.

If you want to cast a rifle stock, you will either need a very large RTV mould, or have a reinforced mould made.

TazMan2000

TazMan2000
 
OK thanks guys for clearing this up for me.

My main objective was to iron out the inconsistencies in making the stock. Not so much the shape (which is the beauty of the thing and the "art") but the point at which it fixes to the support structure for the barrel.

I guess I'm gonna have to get better at the engineering side of woodworking!
 
OK thanks guys for clearing this up for me.

My main objective was to iron out the inconsistencies in making the stock. Not so much the shape (which is the beauty of the thing and the "art") but the point at which it fixes to the support structure for the barrel.

I guess I'm gonna have to get better at the engineering side of woodworking!

How many stocks are you wanting to make? I see a heap of posts about wanting to mold and cast a part as a 1 off and I have to question the logic for the following -

1. First up, before you even consider molding casting, you NEED a master part to make a mold of. So many people I talk to seem to have missed that part.
Your master part can be pretty made from anything, but if you are only making 1, then your master is your part. End of story.

2. There is a cost to molding and casting materials that many I speak to people I speak to have not a clue about. They think molding silicone is the same as caulking silicone. Not it is not and whilst caulking silicone can work, it can be hit and miss so far as picking up all the details.

3. The volume of the mold is something people don't consider. Not sure what you guys pay for molding silicon in the US, but here in Australia, we are looking about $65.00/KG. To reduce the mount you need, a jacketed mold might be more suited. This is especially useful for larger parts.

4. Resins vary in both cost and performance. Cheap resin is, well cheap resin and may or may not give you the results you are chasing. Good quality polyurethane does cost more and you will get a better result, but the success comes down to you, how you work it and pour it.

There are plungers that sort of INJECT resins into large molds. Maybe that is what your thinking about?
 
There is the Benchtop Injection Molder but it costs $3500 for only the base machine and casts are max 3.3×2×2 inches. (moulds are always bigger than casts)
Then the big costs are of for accessories, moulds etc.

Consider also that because it does not have any built-in cooling elements, push-pins etc. there is a bit of manual work and time involved.
I would wager than there could be a 3D printer for home use that would be faster than this machine.
 
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If you have a TechShop close by they all have the hobby injection molders. Most have resin mold frames that allow you to make the mold out of heavy resin that can be removed from the frame after use and stored. The resin will hold up for about 20 castings.
If it is a one off you can make the mold out of plaster or Durhams Water Putty. Plaster will give you 1 maybe 2 castings, water putty will last for about 5. the thing to remember is the hobby machines don't hold a lot of the plastic pellets so large thick items are a no go.
 
You mention specfically ABS in your title. If you're looking to do thermoplastic injection molding, that would be very, very expensive.

You can make a mold and inject A/B resin, but for something like a stock I can't really imagine it being necessary. You typically only inject when your part doesn't have space for a proper pour spout, or when your spout is lower than the highest point of the mold.






How many stocks are you wanting to make? I see a heap of posts about wanting to mold and cast a part as a 1 off and I have to question the logic for the following -

1. First up, before you even consider molding casting, you NEED a master part to make a mold of. So many people I talk to seem to have missed that part.
Your master part can be pretty made from anything, but if you are only making 1, then your master is your part. End of story.

That is a weird and short sighted statement to make. A master is generally a step in a larger process. Whether you're making a one off or ten makes no difference to the process -- what is important is the finished piece. If his master is wood, and he wants one plastic part, he would take that master, mold it and cast the plastic part.
 
That is a weird and short sighted statement to make. A master is generally a step in a larger process. Whether you're making a one off or ten makes no difference to the process -- what is important is the finished piece. If his master is wood, and he wants one plastic part, he would take that master, mold it and cast the plastic part.

Generally it is. But you also need to factor in time and money. Is he wanting to do a run (sell parts to re-coupe the costs of molding/casting materials) or just make something cool for himself? It might seem short sighted and even limited thinking but if you were to make a one off and wanted plastic, wouldn't you just use plastic?

The claw (pictured) is made from 20mm Perspex and sanded to 800 grit. It is a one off and I had no intention of molding and casting translucent claws, so I just went right to a medium that I wanted the final part to be made from - hard, clear plastic. It was a smallish scrap with not much other use. The shape if not quite right, but it took 4 hours to make and cost nothing. And it was fun to do for the afternoon. If I was to mold and cast, I'd be looking at $200 (assuming I have to buy all my materials from scratch) to make the one translucent claw and that does not take into consideration specialized equipment like a vacuum chamber/pump to get it bubble free, which this is.
 

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