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.
So join us and don’t miss out.
Insight: Elastomeric Manufacturing
Hello and welcome to this week’s Insight.
Now, unless you’re well-versed in material science, there’s a fair chance you’re not aware of the term elastomeric manufacturing. Well, perhaps the best way to provide a quick explanation is by giving an example of an elastomer you probably know very well – one that’s durable, flexible, temperature resistant, biocompatible in many cases, and suitable for lots of different manufacturing processes.
Specifically we’re talking about silicone rubber here, which is a typical example of an elastomer. Elastomers are strong, usually flexible, and are able to offer up a whole load of enhanced mechanical, chemical, and optical properties, depending on what you need.
But don’t worry. This isn’t just going to be a lecture about the theory behind elastomers. Instead we’re going to do what we do best and take a quick scan through the options you have for producing elastomeric components.
First of all, your supplier should have a range of liquid silicone rubber, known as LSR, which is ideal for injection moulding. This process uses equipment that is both similar to, and is completely opposite to, plastic injection moulding. Let me explain that a little.
The injection moulding process for LSR is this: equal parts of a chemical catalyst and the liquid silicone rubber are forced together into a chilled mixing chamber. From here we inject it into the mould cavity, which in the case of LSR is heated to speed the vulcanisation process. Once everything is cooled we have a finished, rubbery part that’s ready to use.
One of the great things about LSR moulding is that the design rules around it are really quite forgiving. Worries over wall thickness, draft angles, undercuts, and corner radii can largely be tossed out the window – which is rather comforting if you’ve been fretting over them when using other methods. That’s because LSR has the consistency of water as it enters the mould—there are no problems with sink, knit lines, and voids at sharp corners or around deep ribs.
Nor is part ejection a problem—LSR parts generally remain flexible enough to pull from even the most straight-walled of moulds. About the only thing designers need to be concerned with is flash, because LSR has such low viscosity. This means that clean and consistent parting lines should be used wherever possible.
There are two distinct types of LSR available, one of which is opaque and another that’s see-through. This optical-grade LSR is second only to glass when it comes to transparency, and suitable for use in the food industry.
The next materials we’re going to look at are a family known as TPE or TPV. The full name for these is – and you may want to get a pencil ready because it’s a mouthful - thermoplastic vulcanizate and thermoplastic elastomer. These are great materials that really come into their own when we use an overmoulding process.
We’ve already spoken about overmoulding in its own video so we won’t go into too much detail here, but if you need a quick catch-up it’s essentially adding another layer of material to an existing moulded part – if you’re looking for an example, it’s commonly used to add grippy handles to tools.
In any case, there’s a huge number of materials in this little family, and I won’t list them all here!
But, there are a handful of options you might want to know about. Santoprene 111-45 TPV, for example, has excellent resistance to fatigue, while Versaflex OM 1040X-1 has a soft feel, excellent aesthetic appearance and bonds well to polycarbonate or ABS, making it a great choice for gripping surfaces on medical devices.
Finally, there’s Hytrel 3078, which is just an incredible example of the durability of elastomers, thanks to its ability to flex, bend, and pull far longer than standard rubber material.
The design guidelines for all of these materials is a little bit up in the air. Technically it falls somewhere between the “almost anything goes” of LSR and those associated with traditional thermoplastics. When in doubt, upload your CAD model to your manufacturer and they should be able to help you out.
Right that’s it for this week. I look forward to seeing you again next Friday.
With special thanks to Natalie Constable.