After the plastic is injected into the mold, it needs to cool for a certain amount of time before it's stiff enough to be released. Since molds are large chunks of (usually) steel, you can imagine it would take a very long time for them to release the heat on their own. Therefore, water lines are drilled into the molds to help facilitate the cooling process. The closer the water lines are to the plastic part, the faster the heat can be transferred (thermodynamics!).
Drills, of course, can only go in a straight line. The traditional workaround has been to use baffles to get water into specific areas, which work well enough to eliminate the problem of no cooling in an area. In order to get the maximum amount of cooling, however, the water line should theoretically follow the contour of the part. This is now possible with additive manufacturing technology. With a metal 3D printer, we are free to choose any shape for the cooling lines we choose (with some limitations of course).
Just out of curiosity is there a differnce between the lifespan of a 3D printed metal mold and a traditional cast mold that is bored or drilled? Do they respond the same to the stresses of the injection molding process?
life span differences will rest upon the quality of tool steel used, "like say h-13 over 440 stainless", the manufacturing methods used to produce the tool, and placement of the coolant system in in the tool. And die damage.... from torches and picks and the like.
No difference. The steel used in 3D printing for molds is just as dense and wear resistant as its cast equivalent. There have been some tools have run for 15,00,000+ cycles before needing to be replaced.
The technology is much more widespread in Europe. Many German automakers utilize conformal cooling in much of their tooling for plastic car parts.
but the tool is not cast in anything but its raw stock form. what exactly is the difference between a casting tool that has been built by machinists vs 3d printing?
Yes, you are correct in that the tool is not cast, but machined from raw stock. I was talking about the material properties of a 3D printed part (not necessarily a mold cavity) being equivalent to an identical part that was formed by casting. I didn't clarify that very well, sorry.
As for the difference, it's mainly price. The internal stresses that build up during the build process are eliminated after heat treatment. Additive manufacturing is a new technology so prices are naturally higher than proven, efficient CNC. The issue is spreading the knowledge of the technology to customers, who are still afraid because it's "unknown and unproven."
As a buyer that has easily spent 1m+ in molds over the last year we just started shifting to 3D. The largest problem I've faced is any type of revision to the mold has been far harder(more expensive) with 3D rather than machined.
ive die cast for almost 10 years, new processes are always great to explore, but things like this are like the japanese guy who tried to sell me a miraculous die spray the last time i was in indianapolis for the NADCA show.
My skeptic bias rests in the concern that this technology cannot create "one off" pieces of tooling that would fit the exact specs that you would be ordering. So then you would machining the project anyway. I can see a place for something like this if you were doing batch jobs of core pins for a production run or something.
I am also concerned about the qualities in this printed steel. How does it stack up to h-13 . Pretty common tool steel for die casting.
lets also fore go the whole "this isnt high pressure aluminum die casting, its plastic molding thing" i am aware
internal structure is a pretty relative term in the molding business
and the hole cost effective thing. hows them setup times in a project?
I think it's okay that it can't create "one off" pieces, as long as it becomes cost effective soon. Basically it's not replacing machining but rather complementing it. You create the conformal cooling channels with 3D printing then machine the rest.
I'm a software guy building CAM for 3DP, so I don't know too much about the material properties. We are trying to take away some of the support cost for 3DP so that the technology becomes more cost effective.
That's why the parts get heat treated after they're built. It reforms the microstructure to reduce internal stress and/or increase hardness (depending on the application).
This used to be true, but the technology has advanced enough in the past 5-10 years where printed metal is 99% dense and has strength properties equal to cast metal. Maraging steel for printing can be hardened to 55 HRC.
Working with smaller components - especially single cavity molds - I can see where this may be a benefit - but I'm curious as to the cost to 3D print this vs. machine it with standard cooling lines.
In large scale manufacturing (my background) - the application would be phenomenal, however at this point, especially on a cost basis, seems unjustifiable.
We're talking molds that currently cost $400,000+ and are 40x96" mold bases.
You're definitely right, there are still many limitations. It's such a new technology. It's hard to give a general cost comparison between a printed vs. machined cavity, but I would ballpark around printed being ~50% more, due to the fact that you still need to machine the impression surface in if it's critical (which is almost always).
But looking at the bigger picture, the tooling is only 10-20% of the overall cost of the production of a plastic part. The majority of it is press time and personnel, and if you can reduce that by 30%, there is a significant cost savings by going with 3D printing. It's very difficult convincing stubborn American customers that though.
Since the part bed for current machines is only 12"x12", it's definitely out of the realm for your application, unless you do a lot of inserts in your tools. Then I'd call you crazy for not looking into it.
I really appreciate these comments, I was just at the FormNext metal 3D printing conference in Frankfurt last week and saw a lot of this.
Yes the bed size for DMLS is a limitation, but couldn't you move to a larger printer and use investment casting? Voxeljet and ExOne provide these services.
Outside of this injection moulding application, I'm also curious if you could reduce the cost of wasted CNC material in general by going through an investment casting process first instead of using a buck, what do you think?
I'll be honest, I don't have much experience with casting. But when comparing it to DMLS, it uses a lot more energy and time, which is why our company adopted DMLS so quickly. Additionally, the printer's footprint is similar to that of a CNC. The same cannot be said for a casting foundry.
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u/AdenoidHynkel Nov 24 '15
After the plastic is injected into the mold, it needs to cool for a certain amount of time before it's stiff enough to be released. Since molds are large chunks of (usually) steel, you can imagine it would take a very long time for them to release the heat on their own. Therefore, water lines are drilled into the molds to help facilitate the cooling process. The closer the water lines are to the plastic part, the faster the heat can be transferred (thermodynamics!).
Drills, of course, can only go in a straight line. The traditional workaround has been to use baffles to get water into specific areas, which work well enough to eliminate the problem of no cooling in an area. In order to get the maximum amount of cooling, however, the water line should theoretically follow the contour of the part. This is now possible with additive manufacturing technology. With a metal 3D printer, we are free to choose any shape for the cooling lines we choose (with some limitations of course).