How to bring a 3D printed 2-cavity injection mold to life – Part 2

Making the most inexpensive injection mold

As we have first made ourselves familiar with the molds sprue, runner, gate systems and its cavities we were then able to design it properly.

Now lets take a look at 3D printing, actual costs and see how ABS shots look like.

3D printing

In order to get a good quality mold while printing in your home try to get an SLA or DLP printer that is working with UV sensitive resin. With a resolution of 50 microns (0,05mm) you will get fine surface that should be good enough for the first test and even for near commercial products.

However you will still see some very fine printing lines which looks even bigger on my detail photos. With the finest resolution of 0.025mm these lines should virtually disappear but printing times will increase by the same factor.

The cured (hardened) resin will also make sure that the mold will survive the heat of the injected molten ABS of 220-285 degress Celsius for a couple of times. Please do not consider an FDM printer for this exercise as the results will be frustating.

Even tough initial set-up costs for such a printer are high you will get the quickest turn around time. I can do the complete 2-cavity mold (both sides) in one print that will take around 7 hours. Start it when you go to bed and wake up with the job finished. Some post-processing with isopropanol alcohol and some Dremel action take an additional 1,5 hours.

preform-2-cavity-uzi-4

preform-2-cavity-uzi-3

Professional 3D printing services will make you wait for at least 3 days – by this time you could have printed your 3rd iteration of the complete mold 🙂

Costs of the mold

The 2-cavity mold will consume 94,60 ml of Formlabs resin including support structure. Not taken into consideration the costs oft he Form 1+ , power, the resin vat, isopropanol alcohol and normal costs of usage for my printer the resin costs for the complete 2-cavity mold is around 15,20 Euro in total (given that 1 liter costs 160,65 Euro).

Printing the same mold in „Polyjet white“ from Sculpteo will cost you

5 days turn around time à 245,76 Euro

Maybe the comparison is not exactly correct my point is that once you own an SLA/DLP printer you are more likely to print more molds because you can get nearly 10 molds out of 1 liter resin that you will shell out 2457,60 Euro for 10 Sculpteo molds.

I have not tried it but my guess would be that the Sculpteo molds degrade the same way as my molds does in the sprue area and parting line.

Injection molding parts

As you can see from the pictures the actual injection molded products come out quite nice – given the absolute low cost approach.

imag2620

But due to the high melting point of ABS and the direct contact of the mold with the hot nozzle of the injection molding machine my molds had two issues:

  • burn marks on the top of the mold
  • build up of a gap ath the top of the mold

The gap builds up due to the hot nozzle, the injection pressure and finally the shrinkage of the Formlabs material because the heat deflection temperature is only around 70-75 degrees Celsius.

3d printed injection mold top view

DIY ABS injection molded toy UZI

The result is that you will have more and more flash in the top section of the mold that in the end makes your parts unusable.

To prevent this one could use an aluminum frame around the 3d printed mold to prevent the direct contact between hot nozzle and mold and to provide more overall strength to the mold itself.

Nevertheless the cavities will stay clean and sharp during the injection trial, meaning no details get lost.

3D printed 2-cavity injection moldWith proper handling (cooling of the mold, adequate injection pressure, other material than ABS, etc) and the aluminum frame in might be possible to get 50 good shots out of the mold before it generally deforms at the parting line.

For a 2-cavity mold this would mean 100 parts in total. From my perspective a really good result for a 3d printed DIY injection mold.

ABS plastic and other materials

When using ABS plastic please keep in mind th
at heated ABS is emitting some toxic fumes – so make sure you only use this material in a very good ventilated area and wear a professional breathing mask.

The flow rate of ABS is not good meaning you need to bring in a lot of muscle/lever to squizze the hot material through the nozzle and into the last corner of your mold.

But ABS creates very strong and lasting parts as leading toy manufacturers show us everyday.
If you want to use a material with lower melting point and better flow rate that have at LDPE or PP/PE.

These materials are not as strong as ABS but should give instantly better results and your mold should benefit from it with a longer life

Safety equipment

To protect myself I am wearing this safety equipment while injection molding

  • thicker leather gloves to prevent burning your hands
  • cleaner visor to protect my face in case the mold explodes
  • professional breathing mask against ABS fumes

 

Have fun with the my results and give it a try yourself 🙂

 

Lots of shots

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