3D Printing Vs Traditional Tooling – Can 3D Printing Replace Traditional Methods?
By Andrew Hodson, Managing Director Verus Precision.
3D printed mould tools, are they real, do they actually exist and the simple answer is yes. To investigate further and to not be distracted by the smoke and mirrors 3D printing machine manufacturers put up, you need to look deeper into the technology and the process.
I have seen samples of chocolate moulds, pound coin moulds for trollies and ice cream sticks, but I have yet to see a successfully moulded complex technical moulding sample. If you’re answering a global crisis for trolley pound coins and have to deliver in 2 days then most likely a 3D printed mould will help all the lost shoppers from wondering aimlessly around the supermarket car park looking for a solution to the crisis. However to take the technology seriously, an in-depth investigation and serious R+D study needs to be conducted, documented and published.
At Verus we have conducted some trials with success and failure. Instead of the results being a firm Yes or No, it has raised more questions and revealed an information deficiency that needs to be fleshed out.
- Minimum drafts required
- Venting requirements
- Surface finish
- Ejection solutions
- Gating types
- Wall section limitations
- What will I actually learn from this process
The OEMs of the 3D printing Technologies have attempted to answer some of these questions. But they are far from definitive.
From our initial investigations we know that the printed cavities and inserts do require hand finishing and polishing before moulding. This can be in the form of draw polishing or possibly vapour polishing. This removes any surface imperfections from the mould face and eases ejection.
The biggest challenge in my opinion, ejection from the mould base. During our investigations we moulded polypropylene and ABS materials and both could be processed and injected successfully, the big issue is with ejecting the moulded component from the cavity.
Drafting and Polishing
Drafting and polishing is critical and this comes back to the question, “What am I going to get from the mould and what am I going to learn? If you have to change a design with 1 degree drafts applied, for standard tooling, to 6 or 7 degrees how is that going to affect the design and functionality of your moulded component and consequent assemblies?
It’s no coincidence that any samples that are seen from 3D printed moulds tend to be from shallow draw or half round components or very simple geometry with large drafting applied. In other words straight open and close moulds with large drafting.
I believe it is possible to mould more complex components but this would require extensive moulding time to discover the appropriate drafting and surface finish required to mould successfully.
This brings us to the next big question, Accuracy. The important thing to remember here is that you’re moulding a polymer with a polymer, all be it a photo polymer. The 3D printed cavities will have shrinkage, as the layers are put down the printed component heats up, this leads to differences in parallel and perpendicular shrinkage differences depending on the alignment of the print head.
Let’s say we can compensate for that in the cavity design similar to shrinkage allowance for a traditional steel mould. You then have to contend with the accuracy issues. 0.1 mm is stated but again this isn’t definitive. We have seen a range of 0.1 to 0.5 mm deviation from design to print. And that is a major limiting factor.
3D Printing Vs Traditional Tooling
I recently attended a seminar where a leading OEM presented an impressive sales pitch and casually announced that 3D printing will replace standard manufacturing techniques and has the potential to be massively disruptive to traditional tooling.
If I owned a mould tool shop I certainly wouldn’t be losing any sleep over 3D printing replacing traditional tooling any time soon.
At the same seminar I asked the question, “Considering the technologies and the materials 3D printing uses, just how accurate can it become and is there a limit.” Needless to say the question wasn’t answered.
So here is another question for you the reader to consider “Considering stereolithography has been around since the 1980s, has this technology already peaked and has it achieved its pinnacle of technological advancement?”
Pushing plastic into a mould hasn’t fundamentally changed in 50 years. Yes the machining techniques have become more accurate, but I certainly know tool making companies finishing cavities and inserts to one hundredth of a millimetre accuracies on 20 year old machines.
If you’re considering buying a 3D printing machine to produce injection moulds ensure you ask the questions and see through the smoke and mirrors. 3D printing in whatever form or technology has without question, allowed for the acceleration of the design development process, but it has its place and its uses.
Far from completely ruling out 3D printed mould cavities, we believe the questions raised need answering, so if nothing else we can define where and how this technology should be deployed. We plan on continuing our investigations into the technology and our next steps are to try and define drafts, surface finish and wall sections.