Our Insight video series will help you master digital manufacturing.
Every Friday we’ll post a new video – each one giving you a deeper Insight into how to design better parts. We’ll cover specific topics such as choosing the right 3D printing material, optimising your design for CNC machining, surface finishes for moulded parts, and much more besides.
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Hello and welcome to this week’s Insight.
Today I’m going to focus on a quite remarkable 3D printing technology called Polyjet. It offers great accuracy but even better than that it allows you to alter the part’s material properties in different places on the build.
Let’s just stop and think about that. You can have different colours and hardness levels in each layer, and each layer is just 30 microns thick – or put another way about a quarter of the thickness of a sheet of printer paper.
Now I know that 3D printing is the ultimate flexible technology allowing you to design and produce virtually any shape or geometry that you want, but Polyjet takes flexible manufacturing even further.
For the right part or prototype it’s a great option, but you do need to understand both its capabilities and its limitations before you get too carried away. And there are some design considerations that you need to take account of when considering Polyjet but I’ll come onto that towards the end of this video.
Let’s start with the technology. You all know how an inkjet printer works, well a polyjet printer is a bit like that but instead of jetting drops of ink, it jets drops of photopolymer that solidify when exposed to UV light. The key is that the technology can mix multiple materials together that range from rigid to rubber-like. A part is built up one layer at a time, cured and then another layer is added.
There is a small disadvantage to the process in that each part is completely coated in a support material that needs removing by hand using a pressurised water stream and a chemical solution bath.
Having said that, what you end up with is something rather special. The highly accurate part has one of the best surface finishes of any additive process. It’s ideal for producing complex parts and geometries with multiple materials and colours, all from the same build process.
This makes such parts great for simulating elastomers and flexible parts and also prototyping designs for overmoulding and liquid silicone rubber moulding.
We’ve found that it is a popular processing choice across industries. The automotive industry uses it for things such as rubber seals and semi rigid gaskets, the medical industry for prototyping orthopaedic implants and dental prostheses for fit testing and in sport it’s great for producing flexible straps and covers for equipment.
Now I mentioned that there are some design considerations with Polyjet that you need to know about. Let’s quickly go through them now.
So, point one. While you can design unsupported walls and features as small as 0.8mm, if you want to use them for load bearing or another function then they need to be at least one millimetre across. You also need to think about their height, which will depend on the material that you use and the part’s geometry. As a general rule you are better to avoid very tall freestanding walls and bosses as they can get damaged when your supplier removes the support using the pressurised water stream that I mentioned earlier.
And talking about removing the support material, it is hard to remove it from holes, slots and channels that are smaller than 0.75mm across. In fact, you are better avoiding them at this size as anything this narrow may not form properly anyway.
Next on my list, if you need weep holes and landlocked shapes then you need to make them large enough to allow the rinsing of the support material. In fact, unless you have a very good reason, I would suggest that you leave them closed. Don’t worry, you won’t notice the trapped support material.
Now as I have said this process is great for prototypes of over moulded parts or for those with integral gasket material, but you should design them with zero clearance to 0.05 millimetre interference fit. If you leave any sort of gap, then the components could end up coming apart in your hands.
But let’s finish off with a couple of real positives. The digital photopolymers used have a lovely soft feel and flexible features, they also have really good grip, impact resistance and of course using the process you can achieve a really nice multi toned coloured look.
Okay so you need to bear these design considerations in mind, but let’s not forget what this amazing process can offer you. It will produce parts and prototypes with properties that are simply not possible using other technologies. It’s certainly something to think about.
That’s it for this week. I look forward to seeing you again next Friday.
With special thanks to Natalie Constable.