Where does most of the $ go in mold making? If someone were to make a 3D print to be molded for example. I have no clue what the process is like.
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The gist of it is you have a 3d model that you want to mold, then you make a negative of that in a block, then have to create channels for liquid plastic to flow into the negative space. The 3d model has to be specifically designed to be molded though because if you just throw any model in there without a draft on the faces then it is going to basically impossible to de-mold. In this specific instance once you have the mold designed in CAD you throw it on a resin printer with the correct type of resin and boom you have something you can use for a relatively low quantity of parts. Most molds however are CNC’ed out of various types of metal depending on how long you want the mold to last you.
I have very surface level knowledge on this though as I have only looked into it and not designed parts that have been molded. @Venom121212 can probably provide some more clarity.
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What would happen if you made a mold out some type of CNCed plastic that has melting point higher than the plastic you are trying to mold. I think the general concept of making a mold suitable for a few hundred parts would be a good idea. Just need to figure out how to do it and keep the investment relatively reasonable.
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The mold blocks are large metal cost. They’re absolutely massive and require engine hoists to move around. These are usually hardened, high grade steel since they are injected with tons of pressure and need to maintain that pressure. Aluminum molds are a cheaper option but will die out faster. This is honestly an ideal application for esk8 scale manufacturing. The mold in the pictures above has been running for 30+ years and just now needed to be pulled because the surface plates have worn down ~0.001" on both halves. This introduced a bit of a parting line on the part but again, lasted so long that it was worth it for them. We’ve run hundreds of thousands of these parts.
The next big cost is the tool maker. It takes a lot of intelligent planning to figure out ideal gate/sprue sizes and location to minimize burns, splay, voids, etc, vacuum systems needed, venting, and a ton of other things. Lots of times, we get parts and simply can not mold them due to design constraints so we offer advice on how to design for ease of molding and best looking parts. Good engineers already know how to do this but not always!
Then you have to actually cut this hardened metal to insanely precise levels. This is usually done on a cnc/mill commonly referred to as bridgeport.
Tldr, lots of metal, lots of precision
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The injection pressure required to move molten plastics at the appropriate speed would obliterate a hard plastic mold. We’re talking tons of pressure into a sealed cavity.
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I assume it’s not a simple answer but in rough terms/orders of magnitude; what’s the cost and lifetime of a cheaper aluminium mold vs a big boy hardened steel one?
As an example if that makes it less vague: an aluminium mold for a part like a 40-50T pulley (60-80mm square, 30-50mm thick). Would that produce like 10x fewer parts or 1,000x fewer, and cost 2x or 500x less to machine in the first place? Feel free to ignore question if it’s too much like extra hours at work xx
Also if that mold pictured above is for a packing tape or date label gun, I think I’ve used slightly too many of them over the last few years
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Steel tooling has an average life span of 50,000-100,000 parts
Aluminum tooling has an average life of 10,000-25,000 parts and is roughly a third of the price.
This is highly influenced by factors such as amount of glass fiber infill used. That shit wrecks aluminum molds and is generally never used in them except in very low percentages.
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Beautiful, thank you!
Yeah my main (read: 99%) source for this is AvE on youtube and he often talks about GF chewing through a mold. I do love this guy’s videos, though they often have the effect of making me think I can do things that are completely implausible. Access to a CNC that can get through at least aluminium seems outside my pay grade but maybe some of the other folks here want to give this a go. Machining an injection mold for acrylic lenses - YouTube.
The 3-4 digit prices of “desktop injection molding” machines also looks dangerous, given the existence of stuff like PCBway CNC services and similar. Even a lower estimate of 10k parts sounds very encouraging for our projects, if someone got the stars to align on cheap off-hours machining or something
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For most ESK8 applications 10-25k parts per mold should be more than sufficient.
For a few hundred parts, or you take the vaccuum casting route or 3D printed SLS/MJF (for small parts, price/part can get really low, MJF is more cost effective for higher runs), Injection molding is not cost effective under a few thousands of parts unless you really need some specific material, don’t forget a mold has to be designed and machined by experts that also have a high hourly rate.
You can even buy yourself a used vaccuum casting machine for the price of a mold 
(maybe not with a nylon module tho)
It’s a real struggle I’ve also been fighting with at work, when you’re at the limit you chose the one that’ll set you back the least if it fails…
One could try to get in contact with dragonfly engineering (on YT), he seems to do low volume molding
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PEEK is not really a material we need 
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“Strong enough” Is not really whats the right word here. I think what you are looking for is “right material properties” 60/40 abs is plenty strong enough, but nylon is just harder wearing.
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Dont you guys mill a copper positive that then gets “sparked” In the steel mould base?
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I dont know the english term for this. In dutch its “Vonk verspanen”
I imagine this process is costly too. I learned that when designing for injection moulding to always keep a . 2mm fillet on all edges due to this process.
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Electroerosion
That’s only needed for some complex parts as I recall (deep thin pockets were you can’t get with an end mill)
We’re I worked at a mouldmaker they also used graphite for it, but they made like up to 128 cavities with really tight tolerances, no real use for it for esk8 parts I’d say
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You mean EDM Sinker ?
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Yes, I’ve heard both terms but EDM is much more common
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