Printed injection mold with black resin - my experience


#1

I have printed a small injection mold to fit on my manual injection molding machine the IASCO 66M.

The print came out pretty good at 50 microns in black resin V1 and all needed details were very good visible. After the IPA bath I put the mold in an UV light for nail curing to eliminate the sticky touch. The mold is pretty tough now.

When I injected molten polypropylene at roughly 450 degrees Fahrenheit I neither notice any deformations on the mold nor loss of detail nor saw the mold melting but I found out that I did not align the sprue correctly with the injection nozzle so I could only injection 10% of the need material. As a consequence I will need to redesign the mold and make the design a bit bigger because I noticed some shrinkage but have not measured it exactly for now.

As mold release I used a normal silicon spray that after I sprayed it on the inside of the mold could completely dry off.

The good result and the strength of the Formlabs resin has motivated me to carry on with this project and see what I can get out of the combination Form 1+ / injection machine.

Please note that I am not an artist and I did not have any experience in using the Form 1+ or the 66M machine prior to this experiment. I just wanted to explore how far I could go for digital file to physical “product”.



DIY rapid injection molding
SLA Printed Molds for Casting Urethane Foam Parts
#2

I would love to try something like this.

Thanks for posting.


#3

Oh yeah that’d be awesome, hope to hear more about this!


#4

I was able to make a rubber mold directly from a part and even under 25 tons at 320°F for one hour the part held up but it did get extremely brittle. The mold cavity was nice and clean with crisp edges. I think in general if the plastic had just a little more elasticity to it the parts would be more functional


#5

I’ve also printed some molds to be used for injecting them with castable plastic. It works rather well, except sometimes it’s hard to remove the part from the mold. For simple stuff it works, however you can’t compare this to milling aluminum molds. Except that it costs a lot less of course and is much faster.


#6

Hi,

I have made a break through today and could properly inject Polypropylen in my mold and get a proper Playmobil sized sword.

Even though I did it at 550 Fahrenheit (290 Celsius) the mold withheld the heat and the inner structure/details are still sharp after 4 injections.

See the progress on plasticlabs.wordpress.com if you like. Please find the latest pictures attached as well.





#7

Hi Peter:

can you tell me a little more about your mold design? was it a whole block or was the mold hollow? also, I am not familiar with manual injection machines - do they heat the Polypropylene to a certain degrees before you inject? how did you find the optimal pressure to push? did you need to do any degassing step (like working with silicone?

thank you!
George


#8

Hi George,

the mold is made from a whole block of resin - this is necessary from my point of view to create a mold solid enough to be able to withstand

  • the clamp force (the pressure from outside that presses both mold halves tightly together to prevent leakage in the mold - thus allowing for the creation of sharp edges and details)

  • the injection pressure that ensures that the molten plastic can be squeezed into the very last corner of the mold

If the mold would be hollow it would break or deform pretty quickly.

The principle of injection molding machine as always the same - not matter whether it is a DIY and professional type of machine. The user fills small plastic pellets (in my case with a diameter of no more than 4mm) in a heated chamber that has a temperature well above 400 degrees Fahrenheit or 204 degrees Celsius.

In my machine the material must stay for 10 - 15 min in the heating chamber in order to melt completely and get the right consistency. As my melting chamber is vertical with a larger opening hole on the top end the material can degas while it melts.

I then inject it somehow constantly but quickly as the material cools while being pressured in the mold. If I inject to slowly it cools before it reaches the bottom/far end of the mold - resulting in the incomplete swords you can see above.

When the mold is filled the plastic flows over the top of the mold. Not very correct from an injection molding technique point of view but currently my own indicators that I can stop injecting. I want to switch to clear resin in order to be able to see how the mold is filled in the process.

There is no need to degas the plastic as it contains/produces no air as silicone. I release the air out of the mold with small air vents/channels. You can see the channel below the handle of the sword reaching out to the outside of the mold. This channels shall prevent that the plastic traps air in the mold that when compressed will burn the plastic and causes burns to the mold as well.

Before using the mold I spray it with silicon spray as mold release. After the injection I need to cool the mold for 2 - 3 minutes in order to help to plastic to get solid again. This will prevent the product from breaking or being torn apart while opening the mold.

There are some videos on Youtube where you can see DIY injection molding processes.

Hope I could answer your questions.


#9

Hello Peter

Did you still making injection molds in your Formlab printer? Did you use other materials for the mold base and also inject other plastics resins?

Best regards,

Luís


#10

Hi,
i did not use any other resin so far, but I assume that the clear resin could be better suited for mold making due to its better strength.

I habe tried ABS so far but me machine is not really suitable for this plastic to inject - cannot get enough pressure and I can barely reach the right melting point. Additionally ABS emits toxic fumes when melted.

I found out that my sprue is too narrow for ABS so the mold would need to be redesigned with a 4mm wide sprue.

Nest material I want to try is Polypropylene (PP) as it has lower melting point than ABS and better material flow but mold would need a 4mm sprue AS well.

Potentially I would go for a mold made out of grey resin this time to increase strength and try how many shots I get before the cavity starts to degrade/deform.

So currently only a lot oft thought but no actual progress.


#12

[quote=“katie87, post:11, topic:2769”]
I also didn’t use any product with the help of resin… Moreover I can say that if anyone’s have mind to mould the product with another idea expect black resin… They can try art injection moulding which are semi or fully automated with pick and place robots… This is also the good or suited idea way for mould making to enhance products strenght


#13

Was wondering if anyone has tried this with the tough resin?


#14

Hi everyone - this is definitely an application we’re interested in and it’s definitely possible to some extent with our current standard resins. For a nice example, check out this great video about Stickybones who are already successfully printing injection molds in our Black resin. Stickybones Video

@CaitlinAshford I haven’t seen anyone molding with Tough as it has a much lower HDT than our Standard Resins so I think it would be more prone to warping. Tough Data Sheet , Clear Data Sheet


#15

I have one guess of what he did to his hand. :smile:


#16

Hi There,

I’ve printed a small (quarter size) object with the Tough resin, and must say that I’m a little disappointed in the qualities. I was expecting a hard, strong print much like a molded ABS part, but the tough resin is a bit too rubbery and feel that it won’t allow for very good snap together parts. Does anyone else have any suggestions? I rinsed the usual amount of time in the IPA baths for 10 minutes each then placed it in a UV chamber that I built for about 1 hour. Does it need more UV time? Or maybe adding some heat to the chamber?

Any help would be appreciated.
Ken


#17

Hi Ken,

Tough prints typically need to be post cured for at least 2 hours under a 30 - 40W light. If the parts still seem rubbery, they likely just need to be under the UV light a bit longer.

Best,

Kara


#18

Thanks Kara, will try longer.

On the subject of making molds, I’ve made some injection molds using aluminum filled epoxy poured into an aluminum frame and worked quite well, so in order to save a bit of resin, what about making the “resin” part of the mold as a thin shell, then pouring the epoxy as a backing?


#19

We’ve been working on this application a little bit internally and are happy to share our results in the latest whitepaper which you can access here.

We printed the molds in Formlabs Clear resin and used a desktop injection molder from Galomb Inc. We shot around 25 parts of LDPE and used aluminium frames to encase the mold halves.

Happy to answer any questions about injection molding if this is an application you’re interested in or experimenting with!


#20

I just wanted to add a little to this based on my experiences.

The aluminum frames are pretty much a must have. They do two things.

As the white paper says they keep the part from warping during molding. My experience is that higher pressure molds will not work at all without being fully enclosed. When I tried parts that were not enclosed I couldn’t put enough pressure into the cavity without lifting the parting line or completely shattering the mold from the closing force.

The other thing that the aluminum cavity does that’s not in the white paper is heatsink the injector. This helps keep the print from failing at the injection area as seen in the early posts.

Tip, if the molds are pushing past the parting line you’ll need to bump up the closing force slightly. Just shim the printed part of the mold to close a little further. I use aluminum foil layers in the bottom of the aluminum cavity to tune this. Just don’t go too far because the extra clamping can deform the cavity enough to change the part shape.

You can mold with ABS with this method on a larger machine. Glass filled material will work for a few shots if needed.


#21

Thanks for sharing - we’ve been trying to push the example on more industrial equipment and have seen results which support both your findings - about helping with heat dissipation and also shimming the printed mold to help it close further.