Quality measures

[Shadow3]

How is print quality measured or judged? Are specifications set for print quality? What are typical and rare flaws that make a go/no go product, particularly in complex objects?

[Georgeh1ll]

The quality of 3D printers is mostly measured in the layer height/resolution. This is how thick or thin each layer in the process is. The thinner the layer the more detail there is but it also uses more material and takes longer to make. The thicker the layer the less detail there is but it also uses less material and takes a shorter amount of time to make. These layers are normally measured in millimeters or microns.

The standard resolution is around 0.2mm (or 200 microns) for most printers. However you can go as high as 0.4mm (400 microns) or down to 0.05mm (50 microns). Some printers even allow down to 20 microns or smaller but they are often very expensive to buy or print with. So basically lower number = better quality. Higher number = poorer quality but cheaper.

Flaws in FDM/FFF printers (the most common type) are overhangs. If there is a step overhang of around 65 degrees in your model it may need removable support material added to it, most hubs will do this for you. Also the product can’t be too small (less than 1cm^3) as it probably won’t print properly.

On the other hand resin printers can print small and complex but are expensive and require the product to be cleaned up. (I don’t know too much about this process sorry)

Hope this helps.

[Arnoldas]

Great summary George!

[Arnoldas]

Indeed, like George said, the most reliable measure of print quality is considered to be the layer height. It basically reduces the visibility of the fact that the object is 3D printed. Sometimes people appreciate the curves in the print as an artistic feature though.

However, the true difficulty in this layer by layer desktop manufacturing is when you have to lay the layer “in the air” , but the support structures seem to be solving that issue quite well.

What else would you like to know?

Cheers

[Stef_en_Paul]

I completely agree with the comments given by Arnoldas and georgh1ll, although I would like to add that your metric for print quality is also highly defined by what your goal is. If you want to make a model that looks good, layer height, bridging and material quality are important (like the others indicated). However if you are concerned about the mechanical qualities of your print this is different.

The variables that influence the mechanical properties of your print significantly are (in no particular order):

• print orientation
• material choice
• print temperature (influencing bonding between layers)
• color choice (e.g. blue is a more directional color than white, so blue will be stronger in one direction but weaker in another)
• print geometry (things like overall size, wall thickness, infill etc.)

You should note that the second point is not as straightforward as choosing the material with the greatest tensile strength. Although a product produced with injection moulding would be stronger made of ABS than PLA - with current printers PLA products are often stronger because this material is better suited for printing, resulting in a stronger bond between layers.

Analysing designs with FEM will only get you so far. Printed products behave like a composite material, not like injection molded products. What’s more, they are very ‘unreliable’ composite products since something small like opening a window during a print can already greatly influence your print’s mechanical qualities.

If you’re interested in this topic I highly recommend you read up on some of the research that has been done. I know there’s a handful of phd/master students working testing the mechanical qualities of 3D printed products - it is definitely an interesting topic to keep an eye out for!

Here’s an example of a good article comparing FDM to SLS printing:

FDM vs SLS 3D Printers: Which Tensile Properties?

^P

[Arnoldas]

Good one! completely agree!

[Georgeh1ll]

Lots of good points. Didn’t think about them. Nice one.

[Stef_en_Paul]

oh, I should add that I am talking mostly about consumer grade FDM, which is what I have experience with. Other technologies will probably have slightly different variables. I’m guessing for example laser sintered metal parts used for engine blocks etc. are heat treated after being shaped.