Edge - The filament we always wanted.

Posted On: 2016-05-13 17:38:50 ; Read: 18335 time(s)

 

Edge: The filament we always wanted.

Edge is a new material we’ve been working on and optimising for some time now. In summary, it combines the toughness and resilience of ABS, with ease of use that comes close to PLA, and adds a whole bunch of really superior processing properties that make printing the stuff a real dream.

The end result:

 

When we began printing parts at volume for BigBox we needed a material that could easily be printed reliably time and time again, still achieving the required mechanical and thermal properties for end-use parts.

PLA is certainly an easy material to print, but the low thermal performance and brittle mechanical nature wasn’t appealing for making printer parts from. ABS is much tougher than PLA and is more thermally resistant around hot parts of printers, however it can be a bit of a pain to print. Particularly large parts will often warp, the thermal contraction of the part can cause parts to split and crack along layers. We also didn’t want to deal with the fumes that would come with printing large volumes of ABS in a print farm.

We wanted a material that was easy and pleasant to print over and over again, producing accurate parts, but we wanted toughness and temperature stability that PLA couldn’t offer.

Conveniently there is a material, PET, which has a property window that lies between PLA and ABS, and PET has some additional very promising properties we’ll get into later.

Edge is based on PET, which means you can print it at temperatures that are very easy to achieve on most printers. Around 240C works well from our experience, with a bed temperature of around 80C.

Thermal Stability.

Edge is not a fussy material when it comes to temperatures and can be printed from 220-260C with great results. By using PET as the base material we get some really nice processing benefits. There’s a reason that PET is so widely recycled and PET bottles are one of the most valuable of the recycled material feedstocks, that’s because PET is quite resilient to degradation when being melted for processing. For 3D printing this means that we can hold Edge in the melt for a fairly long period of time before it starts to chemically degrade.

This is really important for situations like low layer heights with small nozzles where the flow rates are very low, and during dual extrusion printing when material is held at high temperatures in the hotend for extended periods which can cook more thermally vulnerable materials like PLA.

Generally it allows for a wide process window of times and temperatures while keeping the behaviour material consistent, and massively reducing the build up of carbonised residues inside your HotEnd.

Toughness and Strength.

When I got my first spool of PET material back in 2013 it was a brittle material and you could easily snap the filament like PLA. Because PET is so widely used in industry there is a wealth of additives and modifiers that can be used, we’ve heavily impact modified Edge to make it really very tough indeed. Edge has higher impact strength than most ABS materials even, but with better stiffness than ABS.

A final thing to note about Edge, which indeed applies to all PET/Polyester based materials is that moisture has more of an effect than you might expect. This took us by surprise, because on paper Edge has extremely low water absorption, less than ABS or PLA. You won’t see any bubbling or spitting like you would with a wet Nylon, in fact you would probably not notice a thing if you print with Edge that has absorbed moisture, the prints come out looking great. However prints from wet Edge will be notably more brittle, with reduced fracture toughness and tensile strength.

The left hand material test bar was printed with Edge fresh from the box, it took repeated back and forth impacts in order to get it to bend, neck, and ultimately break. The right hand material test bar was printed with intentionally wet material and clearly shows a classic brittle fracture.

What is happening here is an invisible chemical reaction called Hydrolysis. When polyester molecules are heated in the presence of water molecules the water molecule will bump into the long polyester chain somewhere along the length of the molecule, and the water reacts with the polyester, cutting the long polyester molecule into two shorter polyester molecules. These shorter chains result in a reduction in the bulk material properties. It’s worth noting that this happens with all PET/Copolyester based materials, and no manufacturer has mentioned this with some even stating that PET is immune to moisture and such things. It’s not a huge effect, but it’s noticeable and significant if you know about it, if you want to get the best toughness and strength from your Edge (or any PET/CoPolyester for that matter) then you should keep your material dry.

Adhesion.

Where things begin to get very interesting is when we look beyond the simple properties of the raw material as an injection moulding materials engineer might. If we consider the strength and resilience of a printed part we all know that the usual point of failure is between the layers of a part.

Often the actual properties of a material hardly come into play when looking at the strength of a printed part, if the layer bonding is poor the material never gets to do it’s job and the part simply fails at the bond.

The actual physics of what causes materials to bond from layer to layer is elusive, and I don’t think that anyone has done any serious research into what truly happens at the interface when you dump a hot molten plastic onto a cooler solid plastic. What I am certain of is that different materials behave very differently and bond in drastically different ways.

If you’ve printed a wide range of materials you’ve probably experienced how easy it can be to split ABS parts along the layers, and how nylon sticks to itself incredibly well with a bond that feels as strong between the layers as along the layers themselves. It seems that molecular deep magic is at play here, and polymers that have strong inter-molecular attraction form the strongest layer adhesion.

We’re by no means chemical engineers at E3D, but we’ve been doing our best to read up and theorise about what may be going on here. From the literature it seems like two materials stand out for having strong inter-molecular attraction, one is the Nylon family and another is the Polyester family. PET, upon which Edge is based, is a type of polyester and does exhibit strong inter-molecular attraction. If you’re interested in reading more in depth on the subject this is a fantastic resource. 

Another significant factor in overall part strength is the density to which you can pack those extruded tracks together to form dense areas for structurally significant parts of a print like walls. Edge packs like no other material I have ever seen, and seems to form almost fully dense structures. To the microscope!

Here’s some printed ABS, broken so that you can see the internal structure of the part. Pretty much as expected you can clearly see each extruded track, with the standard gaps between each extruded track.

In stark contrast here is a similar break in an Edge part. It’s almost fully dense! You can’t even see where the original tracks were, they’ve seemingly been agglomerated into a single solid structure that has far fewer voids and much more uniform strength in all directions (isotropy).

The combination of intermolecular forces creating excellent bonds, and the ability to create parts with higher density and fewer voids certainly seems to translate into a real boost in strength, and Edge forms superb bonds between layers that easily exceed ABS and come close to even rivalling Nylon in producing parts that are strong in all three directions.

A really critical feature of Edge is that we’ve worked hard with adhesion modifiers etc to get it to stick brilliantly to itself, the bed, and Scaffold - our soluble support material. It’s nearly at the point where you can just use clean glass, but for proper adhesion the easiest and most reliable solution is UHU Stic. We’ve tried every commercial print sticker, spray, brush on gloop, plenty of household stuff like tapes and hairspray. We always come back to the glue stick. Conveniently the glue stick and Scaffold are pretty similar on the adhesion chemistry front, which means that we get both excellent bed-adhesion, and best-in-class adhesion to the Scaffold support material. We’ve got more to come soon on the subject of Scaffold, but to say we’re excited about it is an understatement.

There are two aspects of Edge that one should be aware of when printing it. The first is a side effect of Edge being such a strongly adhesive material, it does really like to stick! This means that with some of the more aggressive bed adhesive sprays Edge can stick so well that it will actually pull off flakes of glass from beds, easily avoided, just use glue stick instead. Edge also likes to stick to nozzles a bit more than ABS or PLA, and you can get some build-up on the nozzle, this doesn’t really cause much of a problem but it’s something to be aware of. We’ve got a pretty neat solution for stopping material building up on nozzles that we’ll be releasing shortly which stops gunk building up and makes printing nicer with any material. More on that soon.

Bridging and overhangs.

There are a bunch of other important, yet almost intangible and not well understood properties of polymers that make them “nice to print”. ABS has a fantastic ability to be extruded into place and stay put, this gives great ability to form nice overhangs in situations where PLA would curl up or droop down. This seems deeply related to the viscosity and fluid behaviour of the materials in free space. Edge manages to distinctly exceed PLA in this regard, with great overhangs and accurate formation of small features.

It’s hard to pin this down to a single measurable number, but current PET materials seem to be lacking when it comes to being extruded into place, and staying where you put it. Standard PET materials out there seem a bit "watery" and often want to slump, droop and string to a degree that causes issues. Edge has a great balance of flow through the nozzle, but also enough ‘body’ to hold its shape and form accurate predictable parts.

The largest benefit here is getting really cracking overhangs that form predictably and reliably. The highly adhesive nature of Edge comes into play here too, because the extruded filament will grab immediately to the material beside it preventing it falling free.

Another really important factor is something called melt-strength which is the ability of the molten polymer to resist being stretched, this is absolutely crucial in 3D printing as when we form bridges, or transition from sparse infill to top solid layers we rely on melt strength to stop the liquid melt just sagging down. Conveniently it just so happens that Polyesters like Edge can be made to have great melt strength and form some really fantastic, tight bridges. The moisture thing comes into play here again too, moisture means shorter chains, shorter chains mean lower melt strength, and lower melt strength means worse bridging. So keep your filament dry!

Appearance.

Because the base-resin for Edge is clear, this gives us a fantastic blank canvas upon which to create fantastic true vibrant colours. Whereas PLA and ABS are the colour of gone off milk when not pigmented Edge being totally clear allows for a nearly unrestricted range of colours. Edge is inherently a very glossy shiny material, and really shows details well.

We decided to make up some more unique colours, of which a firm favourite is Limey. We can also do cool things like include metallic flecks that are visible within the material, which we’ve exploited to create a British Racing Green type colour - Green46. We’re excited to see what we can do in the future with new colours and types of visual effect that go beyond simple colouration.

We also get a lot of feedback from people who want a range of more sedate monotone colours. These are apparently very useful for creative types who print parts for models, architecture or parts that need to be painted. The engineers at E3D did not realise that there were so many shades of the colour grey, “Surely there could not be more than two types of grey?”. However the more creative people in marketing assured them that there could indeed be many shades of the colour grey, and that people might like that. So there are 4 whole invigorating greys, we’re excited to see what you do with them.

Edge: just make things.

We really think that the material properties - strong, stiff, and tough combined with the process improvements in areas like layer adhesion, bridging and melt stability make Edge a real candidate for replacing both ABS and PLA. Certainly here at E3D it’s now our primary material we reach for when we want to ‘just make a thing’.


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