Key things to know before calibrating resin 3D printer

Calibration of SLA 3D printer - AmeraLabs Town
Updated on March 16, 2018

In this AmeraLabs post we will dive into what is calibration of resin 3D printer and cover key things you need to know before running your calibration procedure.


Core settings

The goal of resin 3D printer calibration is to balance these three core settings:

Exposure time of a single layer

 

XY resolution

(i.e. which is pixel or laser spot size)

Layer height

(Z resolution)

 

Exposure time of a single layer.

The most important parameter is exposure time of a single layer. It defines light exposure duration for a single layer of an object that you are trying to print. This term applies to DLP and LED/LCD based 3D printers, because with such equipment entire layer is exposed whereas SLA printers’ laser “draws” each layer. For laser-based printers this notion of “exposure time” does not apply directly as in these printers you can adjust laser power and laser speed. You can increase 3D resin light exposure with laser either by increasing power or by slowing laser down.

Incorrect exposure is one of the major reasons why resin prints fail. Apart from such obvious reasons as loss of intricate details and dimensional accuracy, incorrect exposure settings will result in other distinct problems. Too long exposure settings will typically result in the following issues.

Bleeding of light

When light penetrates and cures material too deeply. It will result in loss of details and loss of dimensional accuracy in Z axis. Small features of your print will come out bigger than expected.

If you notice such effect shorten your exposure (cure time) settings. After printing another test print, evaluate the difference and adjust your settings again, if needed.

Scattering effect

When light’s straight trajectory deviates from intended one resulting in polymerization in undesired directions. Usually that happens due to the lack of light blocking pigment in 3D printing resin. Too long curing times may magnify this scattering effect. It will also result in loss of details and dimensional accuracy in Z as well as in XY axis.

You can start fixing this by reducing your exposure settings and/or adding more light blocking pigment. In most cases it is difficult to solve scattering effect issue without changing the 3D printing material type.

In regards to too short exposures you will end up having the following issues.

Under-cure effect

It will typically reveal itself as layer delamination in the middle of the part due to poor layer adhesion and will result in part or even full model stuck to the bottom of the resin tray. You can also observe serious loss of intricate details. They will come out smaller than expected, or absent at all.

Try to increase your exposure settings. After reprinting your test print, pay attention to the quality of small features.

Poor adhesion of the model to the build plate

Poor adhesion of the model to the build plate. It can even result in model falling down and damaging your resin tray. The most typical result is to see thick layer of 3D printing resin cured on the bottom of the resin tray and nothing on the build plate.

Increase exposure time of your first layer. Make it around 10 times longer than your normal layer cure time.

It is not possible to characterize exposure time parameter on its own. Exposure depends on and is a result of the rest of the factors. So let’s overview them one by one and see how they affect exposure time and at the end we will take a look at other causes that influence it, but are not that significant.

Resolution (X and Y axis)

XY resolution is the size of an individual pixel for LCD/LED and DLP systems and laser spot diameter for SLA laser systems. Generally, XY resolution is fixed for LCD/LED and SLA systems, so you do not have to worry about exposure changes due to XY resolution adjustments. If you own DLP projector with adjustable resolution, it can significantly affect your exposure times. When you move your projector up, you decrease your build area, which means that entire output of light source (in mW) is concentrated in smaller area (cm2), therefore, your mW/cm2 increases. Consequently, your 3D resin will get more light energy, which will result in shorter exposure times and faster chemical reaction. Opposite applies when you increase projector distance from the resin tray. When doing this entire output of light is concentrated in a bigger area, your mW/cm2 decreases and resin will get less energy per square unit. That will result in longer exposure times and slower chemical reaction.

Layer height (Z resolution)

Layer height determines the thickness of a single layer of an object that you are printing. It is so called Z resolution. You can choose from the most common layer heights which are 50μm and 100μm, but if you need extremely high quality and smooth surface, you can also aim for 25μm. Anything in between these numbers is also completely fine, but not very common. You should also keep in mind that practical difference between 50μm and 25μm with well mechanically tuned machine is negligible, whereas difference in 3D printing time is huge.

It is very difficult to come up with some sort of rule for exposure time changes regarding layer changes. Intensity of light passing through a media diminishes exponentially. That being said, absorption properties of 3D resin and its components determine the relation between exposure duration and layer thickness, which is not linear. However, here at AmeraLabs we use a rule of thumb that we will share with you and which you are welcome to use. If you go down below 75-100μm layer height and keep XY resolution constant, for a 50 % layer reduction you should lower exposure by 25%. This rule is a bit subjective and in some cases correct exposure can be even shorter, but it is a good starting point.


50% lower layer height = 25% lower exposure


How often should you calibrate your 3D printer?

Apart from calibration of 3D printer right after the purchase, there are quite a few occasions, when it is highly recommended to re-run calibration routines.

When changing 3D printing resin

If you change your 3D resin brand, it is also a good idea to re-run calibration procedures. Each brand of 3D resins is very different in terms of reactivity and pigment/dye concentration. With some 3D resin brands you should repeat calibration even after opening a new bottle, because you rarely know when it was manufactured and if well-established quality assurance procedures were used. At AmeraLabs each lot of our materials is run through enormous scientifically-proven testing procedures with various resin 3D printers in order to sustain identical performance each time.

Every 3–6 months

Light source of 3D printer is aging, no matter if it is a laser, DLP/UV projector or LED – its power decays as time goes by. To compensate that we recommend to periodically rerun calibration procedures. It is difficult to specify exact frequency, as it depends on how often you print and what type of light source you have. Thus, if you print for your own needs, it is fine to review your light source condition once in 3 to 6 months. If you see some visible changes in your printing quality (perhaps your light source is decaying faster than expected), you should rerun your calibration procedure. Of course, if you decide to completely change your light source, extensive calibration is a mandatory step to obtain decent printing results.

What’s next?

To ease the stress of calibration we have created AmeraLabs Town calibration part that is available for everybody here. It is also packed with an extensive guide on how to read and interpret its various features.

If you need more help or you have found mistakes in this post, drop us as an email and we will respond to you in 12 hours or faster.

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What tips do you have for calibrating 3D printers?