The Influence of Extrusion Temperature on Layer Adhesion

Nozzle temperature is the first parameter that you usually set for a filament. Manufacturers often provide a range of temperatures in which the material can be printed. Some just select the middle of that range and print with it but I'm sure most of you have already printed one of the various temperature towers that are available. While printing them, you set different temperatures for each step, which can be, for example, done in PrusaSlicer by inserting the custom GCode M104 S and then the temperature. I usually start at the highest and work my way up to the lowest, because the chance that the print fails is usually higher at low temperatures. Once finished, you select a temperature at which the printing results look the best, with minimum stringing, nice overhangs and bridges and smooth surfaces. But that's just part of the story and before we continue I'd be interested in how you usually select your nozzle temperatures, so post a comment down below!

A typical Temperature Tower (by 3DMakerNoob)

Because I have already done some investigation in the past on the topic, I knew that usually, at higher temperatures layers fuse together better. What I tend to do on 3DMakerNoobs temperature test-tower, which is the one I usually use, is that I break the spikes with my fingers to get a feeling if some are harder to break than others. Besides that very rough method of testing, I wanted to properly find out if printing hotter always means better layer adhesion or if at some point we even run into material degeneration and therefore make the print weaker.

To test that, I printed quite a lot of my mini tensile test specimens in their standing orientation because that lets us later judge layer adhesion. I printed four samples for each temperature on my Prusa Mk3. To find out what really happens to the base polymer, I also printed lying specimens, where only the pure material strength is tested. This video covers PLA and PETG, both from dasFilament.

Mini Tensile Test Samples

We already know from another video that at lower temperatures, we often under-extrude, due to the backpressure in the nozzle. This caused samples at higher temperatures to be heavier than ones printed colder. More material usually means more strength. Even though I kind of compensate for that by measuring every test section of the samples before the test, this can also have other side-effects. So after printing the first set of samples, I printed a second batch with slightly adjusted flow settings so that all parts weight the same, +-1%. For PLA I tried extrusion temperatures from 190°C all the way up to 270°C in 20K increments and for PETG I went from 200°C to 260°C in 15K increments.

Initial and adjusted sample weights

Interestingly, the first set of PLA samples printed at 190°C were way under-extruded. Increasing flow only caused the extruder to jam, so we can see that we are already right at the lower temperature limit. With varying temperatures, we can already see significant differences in the looks of our prints, especially in the amount of stringing. The higher the temperature, usually the worse the quality. I also printed 3DBenchies at different temperatures and they show the same. Great looking prints at low temperatures. Some materials will even end up with a matt texture when you can print them cold and fast. The high-temperature parts, though, are quite stringy and even show voids and bubbles on the surface.

But let's start with the mechanical tests. The samples were loaded one after the other into my DIY universal test machine, to which plans I, by the way, linked down below. I then loaded the samples at a constant speed until they failed. The reference strength of a PLA sample printed lying is just around the 60 MPa mark. The more interesting results will now be the samples that I printed standing. The PLA samples printed at 190°C failed on average at 20 MPa but keep in mind that I had some issues with extrusion here. Next came the ones printed at 200°C. They were already significantly stronger and failed at 37 MPa. The 210°C parts failed at 39 MPa and the 230°C at 40 MPa. Now it became more interesting. The 250°C coupons showed a drop in strength and were only able to bear 37 MPa. The ones printed at the highest temperature of 270°C dropped even more off and failed at only 32 MPa. So, all in all, pretty interesting results.

Tensile Strength PLA

Let's see how PETG does! The reference strength of PETG when printed lying was 55 MPa, so a slight bit lower than PLA, but this material usually yields more and sometimes even doesn't break at all and is therefore tougher. My layer adhesion samples usually don't yield a lot before they break and the standing PETG samples printed at 200°C already broke at 18 MPa which is only 1/3 of the reference strength. The 215°C samples were stronger and failed at 22 MPa on average. The 230°C parts already showed 55% of the reference strength and failed at 30 MPa. The parts printed at 245°C, which is already a bit over the recommended range of my dasFilament PETG, were even a bit stronger and reached 60% of the reference strength so 32 MPa. The last dogbone samples manufactured at 260°C were once again weaker and failed at 24 MPa on average.

Tensile Strength PETG

So, all in all, a really nice strength VS printing temperature curve for both materials. We can clearly see that if we print too cold, layer adhesion is reduced because the new layer of material is too cold to properly fuse onto the existing material. Tough if we print too hot, this will degenerate layer adhesion as well. I'm not 100% sure why this is the case. Previously I thought that the material itself degenerates but I also tested just simple lying samples at various temperatures. There, changes in strength were not huge, so even those high temperatures don't seem to affect the material noticeably. I think moisture and therefore bubbles forming might affect the layer boundary, but maybe you have a better explanation for that phenomenon.

Influence on base polymer strength at different printing temperatures

Generally speaking, I think, we can summarize the results as follows. If you want to optimize your parts for the looks, rather go to the lower end of the recommended temperature scale. If you want to optimize your prints for strength, go to the upper limit and even a bit above. Keep in mind that emissions from the material also usually rise with higher temperatures, even up to the point that your material can decompose. Working with dry filament should always be a high priority because that can ensure consistent, well looking and also strong print results even at elevated temperatures. But how about you? How are you usually tuning in your temperatures for different applications? Let us know in the comments.

Layer Adhesion at different extrusion temperatures