Weak PETG

[gwatson1990 1]

I've recently made the transition to PETG from PLA on my Ender 3. I've been printing with eSun PETG at 240c nozzle, 80c bed, 40mm speed, 20mm initial layer and around .95-.97 extrusion multiplier. My prints have been looking good however, long story short if I do a drop test on a project of mine, the PETG breaks before the PLA everytime. I've been printing anywhere between 230c - 245c range but the results have been the same. Isnt PETG supposed to be stronger and less brittle? I'm always reading about how tough it is so I'm assuming there must be some user error somewhere, but I'm out of ideas at this point. The PETG has been breaking across the grain and delaminating before the PLA even with a 6 layer wall and bottom thickness as opposed to the PLA at 2 layers. Any thoughts would be greatly appreciated!

[geert_2 557]

I also have noticed that PET and NGEN (which seems to be similar to PET, from colorFabb) are not stronger than PLA. Although for snap-fit lockings, carabiner hooks, and similar things that need some flexibility, PET is much better than PLA, because PLA will crack over time.

 

Also, PET can withstand the heat of the sun, and can be used in a car. PLA can not: it deforms even in mild sunny spring or autumn weather.

 

But for pure strength where flexibility and temperature resistance are not required, PLA can often withstand more than PET.

 

In my PET-models the fracture lines go diagonal through the material, and follow the stress concentrations. They do *not* follow the layer lines. So it has to do with material strength itself, not with layer bonding.

 

However, if in your model the cracks would follow layer lines (=delaminate), there is a bonding problem. This could be due to printing too fast, or using too much cooling fan. So the next layer does not heat up the previous layer well enough, and it does not fuse together. Try turning off the fan, or reduce it to the absolute minimum required for your model. Also, try printing a bit slower: 25...30mm/s.

 

At 20mm/s I can succesfully print PET at 2015°C (recommended range 215...250°C, brand = ICE, from company Trideus in Belgium).

 

[gwatson1990 1]

Thank you! I will trying lowering it to 20mm/s. So is PLA+ a good alternative to PETG? I'm looking for something that has good impact resistance without having to upgrade my hot-end to all metal (I realize that might be a unicorn though). Originally I wanted to try ABS, but I kept on reading about the fumes which deterred me more than the printability... are they that bad?

[gr5 2,167]

PLA is the easiest material to print and it's strong.  PETG is slightly harder.  ABS, nylon, most other materials are even harder.  This is because of the temperature they need to be when you bond one layer down onto the layer below.

 

You can either enclose your printer to get the air up to 35-40C or you can lower the fan speed to the minimum where it still turns.  This is a different value for every printer.  Or both.  If you turn the fan off you will get great layer bonding but overhangs and bridging won't be so good - the part will look kind of melty.  So you want just a little fan.

[gwatson1990 1]

So raise I need to try and raise the ambient air temp for better adhesion on PETG? I have a heat lamp that I can clamp on out of the way that might help some. 

[gwatson1990 1]

I slowed the print speed on my test cube that's printing right now from 40mm/s to 20mm/s as suggested and I already see a difference in the way my layers. Thanks for the input!