Remember through this calibration testing process that the objective is to find the best printing settings of your 3D resin in your printer to meet your overall specifications, to say printing speed, or resolution, or biocompatibility.
All prints (3DTest 1 and 2) require no extra supports – position them straight on the build plate. Please read this document to help you understand the objectives of the calibration test prints.
Most 3D printed materials benefit from a gentile post cure exposure to UV/Visible light, which significantly improves the degree of cure of the printed resins and consequently their safety and biocompatibility. Most of our resins may be used directly as printed but will exhibit even better properties after post curing for around 5-60 minutes in any conventional commercial light box. Excessive light power, time, and temperature during post curing above 60ºC can cause yellowing to some materials.
Our resins are designed to cure with UV/Visible light from 250 to 420 nm and different light powers, from the very low power typical of LCD printers, to the high power of the new generation of SLA lasers and DLP projectors. Asiga printers permit choosing your light power for each sold wavelength 385 and 405 nm.
The calibration process for Asiga starts with selecting the optimum light power and printing temperature. The higher the temperature, the lower the viscosity, the adhesion and peeling force needed to separate the printed layers from the vat. Viscous resins are normally more biocompatible and tougher than lower viscosity ones and can really benefit from printing them at 30-35ºC to increase their flow and reduce their stickiness or adhesion on the vat.
On the other hand, the higher the power the faster the printing speed but the lower the resolution. After choosing the optimum power for your printer specifications, it is necessary to undertake the spot timer test with the following times, to say, for example, 2, 5, 10, 15, 20, 25, 30, 50, 75, and 100 seconds. After measuring the thickness of the drops or spots with a calliper, a curing rate table needs to be drawn including exposure times in seconds, energy dosage in mJoule per cm2, and spot thickness in mm for each exposure time.
Then, select the z layer thickness for printing: typically, 0.05-0.1 mm, which usually give good print resolution. Now, select as exposure time, the time needed to cure in between one and two layers. Use as burn in exposure time 4 times the time needed to get very good adhesion and cure on the glass slide, usually, between 70 and 80 seconds for most 3D resins. Normally 2 layers are enough as burn in layers.
In the Composer, use any INI file as reference. Then in the build wizard, specify your chosen power, exposure time, burn in exposure time, etc. It is suggested to leave at zero the XY and Z compensation values and use the maximum speed values. Other complex values can be ignored or used at their medium point of the interval.
3DTest1: the wedge!
This first print is used to check that the printability of a high surface print, such as a wedge, which has a size of 156 x 46 x 9 mm thick. Its size can be increased to cover most of the vat or decreased to speed up the calibration. It should be printed at e.g. 0.05 mm or higher Z layer thickness with a start exposure time of the seconds needed to cure 1.5 Z layers. In you are in a hurry it is not needed to finish the print if the first 15-20 layers printed successfully. Alternatively, instead of the wedge, you may print 3Dtest1 the flat coin without any supports, in case you are interested in printing small parts at high resolution.
In case you face up failure to print the wedge or the flat coin, then you need to identify the reason for failure. Print failure can be due to under curing or over curing:
- Under curing is due to insufficient exposure time to cure each layer and adhere it on the previously printed layers. Adhesion on one side of the print but insufficient on another side is usually due to poor Z calibration, or levelling of the build platform, or to non-uniform light power distribution across the vat. If this is the case, double check these settings. If lack of adhesion persists, increase the exposure time several seconds until full adhesion is obtained across the whole wedge.
- Over curing is due to excessive exposure time (or light power, or the combination of both) to cure each layer and adhere it to the previously printed layers. Too high power, or too long exposure time, or the combination of both, provoke yellowing, shrinkage, and brittleness or fragility of prints which can break during printing
3DTest2: the flat coin with supports
This print is the most important; it helps setup and refines the most things as quickly as possible. It will permit us to identify the accuracy of the printed resin in the chosen printer settings. Excessive thickness in xyz planes is normally caused by light bleed. Print failure, can be easily overcome by adjusting the exposure time.
Please remember that all printer types will have available certain UV or visible light power at the build surface to cure the resin. This power is measured in mW/cm2. Dependent on the printer design this power can vary greatly and can even vary from one point of the build area to another (non-uniform light power distribution).
This power can be measured using a radiometer that has a sensor in wavelength range of the light source.
In terms of the best print orientation for high quality printing, this flat print or coin orientation is not ideal, the printing plane orientation (parallel to the build plate) is the worst possible scenario – it is likely to trap liquid resin, which will be overexposed to light and will tend to cure causing bleeding in the z direction, appearing the back of the coin thicker than the theoretical 2.0 mm of the original STL file. Additionally, the tips of the supports are deliberately tiny to simulate print zones with nearly no supports.
All these features are deliberate; they make the print difficult to print. If these test pieces print well then 99.9% of all prints with that resin in the future will be a success. As mentioned before, a good starting point would be to set the exposure times per layer between 1 and 2 layers, to say, the time needed to print 0.075 mm (for printing Z layers of 0.05 mm) in the spot timer test.
Possible printing problems and solutions with 3DTest2 print:
Note: during the following stages do not alter the base or burn in layer exposure time – just the build layer times. You established the base exposure time with the first test print (3DTest1).
Base and first part of supports print but the coin is found separated in the resin vat.
This is caused by possibly one of two reasons; the material is too reactive and brittle, and the supports have snapped off where they join the coin. Or the material is not reactive enough and is curing too soft and the coin has separated.
Use your fingers or a needle and try to press it into the top of the cone or support attached to the base plate. Is the material at the top of the printed cone relatively too soft, or tender, or too hard, or brittle?
- If it is too soft, or tender, repeat the print after increasing the exposure time and use the time needed to print 2 z layers, or 0.1 mm (100 microns) in the spot timer test, for printing z layers of 0.05 mm (50 microns), and repeat the print
- If it is too hard/brittle repeat the print after decreasing the exposure time and use the time needed to print between 75 microns in the spot timer test and repeat the print
Continue this process until the print works (it may take several prints).
The coin has printed but the thickness of the coin is much thicker than 2.0 mm
This is caused by light bleeding in the z direction due to excessive light penetration, normally caused by excessive light power or exposure time.
Our 3Dresyns are delivered ready to print with good resolution in a wide range of light powers. In case you want to print at a very high speed at very high power of e.g. 20 mW/cm2, you may end up needing to use our resolution adjuster or resolutioner Fine Tuner LB1 Bio. First, you will need to repeat the calibration after adding Fine Tuner LB1 Bio in steps of 1% (remember to shake it well or warm it up to approximately 70ºC until crystals dissolve completely) until the support legs and the back of the coin are printed correctly with good definition and with the original thickness of 2.0 mm of the coin. Make sure that no light bleed is spoiling the printed circles down to your goal resolution down up to 2 mm, the smallest concentric circle.
It can take time to do these tests, but the result is worth it. You will have the very best physical material properties, accuracy, and printability for a particular resin type on your specific printer settings specifications.
Photo polymeric resins are not like clothes and “One size fits all” does not yield the best results for a range of printers. When you have found the optimum for your type of printer – record your printing settings. In the future you can print using the build wizard or create your own INI file.
Enjoy the results of the hard work!!
The 3Dresyns team