3D Printing with PETG - How does the printing temperature affect strength? || Setup & Tips

In a previous video I printed and tested dozens of PLA specimens to find out if the printing temperature changes the strength of your parts. I got a couple of requests to do the same investigation with another commonly used printing material – PETG. And that’s exactly what I did. Stay tuned, guten Tag and welcome to CNC kitchen. So if you print functional parts you are usually trying to make them as strong as possible that they do not fail during usage. As I found out in one of my previous videos it makes quite a difference if you print your PLA at 180 or 240°C. By using higher print temperatures, the layers seemed to fuse together way better so that the adhesion between the layers more than doubled. Obviously, there is a limit when higher hotend temperatures start degenerating the plastic leading to worse print quality and also strength of your parts. So around two years ago I purchased my first roll of PETG filament which claimed to unite the good printability of PLA with the heat resistance of ABS. Unfortunately, I wasn’t really happy with the material at that time. It often did not stick to the bed properly then the prints were bubbly and tuning in the setting was a nightmare. Sometime later I bought another roll of a different manufacturer which already worked better but still was far away from the ease of printing with PLA. After my last PLA test video I thought that I should give it another try and if I’m already tuning in the settings for the material I can take a look at the influence of different printing temperatures. When I get a new material I usually tune it in the following way. I search the internet or look on the filament itself to find the first recommendations for the temperatures. I insert the filament into the printer at the recommended temperature and perform a calibration of the extruder. So the slicing software later relies on the fact that, if it wants to push 10mm of filament into the hotend, really 10mm are fed into it. This means that the control board of your printer needs to know by how many degrees, or actually how many steps your extruder motor needs to turn to extrude the given amount of material. So, the factor “steps/mm filament” needs to be calibrated. You can roughly calculate this value if you know how many steps your motor needs for one rotation of your extruder gear and if you know the radius of this extruder gear. But everyone who has already worked with different material groups knows that for example PLA and PETG behave differently. PLA is stiffer, so it does not get pushed into the teeth profile of the gear as far as PETG. This means that the effective radius is bigger and therefore you need less steps per mm as with PETG. There usually is quite a good value for the calibration factor in your firmware, but I highly recommend to tune it for each material group separately. This is done quite simple. I mark a given length, for example 60mm on my filament, then I use any interface software like OctoPrint of Pronterface to extrude a slightly smaller amount of filament, here 50mm. Make sure that the extrusion speed is not too high, because this could screw up your results. After the extrusion is finished measure by what amount your filament was moved. By dividing the desired extrusion by the real extrusion, you will get your extrusion multiplier. This is the value which you put into your slicer together with the measured diameter of your filament. If you don’t have a very exotic 3D printer there should be plenty of profiles on the internet, or even provided for your printer and your material type. I used the Prusa PETG profile in Slic3r and only edited extrusion multiplier, filament diameter and the temperatures. I printed the first parts with theses settings and finetuned the extrusion multiplier to end up with really nice print results! From my experience PETG likes to be underextruded just a tiny bit. The only real quality difference to PLA is the slight stringiness, which could be further optimized and the worse performance in overhangs. So now to the temperature test. As a start, I wanted to find out what the temperature range of my PETG was, so I printed out one of these temperature towers with values from 205°C to 280°C. So we can see that the print did not fail at any of these temperatures. Still the quality really starts to degenerating at higher temperatures. The results seem to be okay up until 250°C at which point you see quite a lot of bubbles forming in the print. Also the stringiness increases constantly. Overhangs printed very well all the way up to 280°C. Bridging became really bad from temperatures higher that 250°C. The fine details seem to be printing well up to 235°C and then gradually become more and more squished out. So from these results I would say that the printing temperature should be set between 205°C and 235°C but how does the strength change with the temperatures? In order to investigate this, I printed out a couple of tensile tests specimens from temperatures between 205°C and 265°C. Half of the specimens were printed lying on the printbed to test the strength of the filaments strands itself and the other ones were printed upright to test how the layers adhere to each other. I fired up my DIY tensile testing machine and destroyed them one by one, measuring the force at which they broke. So let’s take a look at the results. The blue bars show the average Ultimate Tensile Strength of the lying specimens, the orange bar the average values of the standing ones which represent the layer adhesion. As expected and similarly to PLA, the strength of the lying specimens is not significantly affected by the print temperature. The layer strength on the other side has its maximum at temperatures of 220°C and then gradually falls off, which is different to the PLA results. So this means, that this time we really have a sweetspot of strength and quality because also the printing results were very good at 220°C. I have printed all of the specimens with the partcooling fan running at 50%. I turned it off for one set of specimens which resulted in more than 25% better layer adhesion. You might be thinking “hey, why do we use it at all?”. But if you print a detailed part without the fan on, you will notice, that the print results get way worse at some details and the stringiness increases. This might be a good tradeoff for some parts, but generally I think you should have it turned on for the sake of print quality. I have also noticed during my tests and this is also my general experience with PETG that it is sometimes just inconsistent to use. I printed one batch of specimens at a very dry and one at a humid day. The ones printed on the humid day had significantly less strength than the ones from the dry day. This shows that this material is susceptible to moisture which is a downside from that material group. One thing which still confuses me is the fact that the material is very ductile if you slowly load it in direction of the filament strands. I was not really able to break one of the specimens because they just strained and strained! Also, if you bend a specimen by hand it will only deform but not break. Everyone who has already worked with PETG will know that it usually behaves quite brittle, actually even more than PLA! I am no polymer expert, so I don’t know if that has something to do with viscoplasticity, but if I load a part by an impact force, like with a hammer, it will shatter into small pieces without any sign of plastic straining. If anyone can explained that behavior to me, I would be really happy to know! I am thinking about building an impact testing machine. Maybe then I can also compare this parameter. One last thing to say: The tests that I perform will probably not be applicable to any brand of PETG, since every manufacturer has their own recipe for the material. Still I hope you learned something. If you have suggestions for other tests, then please let me know. If you liked the video, please give it a thumbs up. Consider subscribing if you don’t want to miss more of these videos. Check out my other technical content on the channel. Thanks for watching, auf wiedersehen and I’ll see you next time!

Channel: CNC Kitchen

Views: 534,649

Keywords: 3d printing, petg, pla, strength test, prusa i3 mk2, i3 mk2, printing temperature, setup, printing tips, petg tips, print temperature, 3d druck, pla alternative, diy, tensile test, ultimate tensile strength, uts, brittle, das filament, das filament petg, filament review, multec, extrudr, cnc kitchen, 3d printer, how strong is petg, zugtest, festigkeit, how strong are 3d prints, guide, review, data, analysis, prusa i3, printing, 3d, tips

Id: qif070PErNU

Length: 8min 26sec (506 seconds)

Published: Mon Jun 05 2017