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3D printing Guidelines: Basic process for selecting the optimum printing settings in your printer



The following instructions are ideal for selecting in just few steps the optimum printing settings in your SLA, DLP or LCD printer.

The following link compares the existing Stereolithography (SLA), Digital Light Processing (DLP) and LCD 3D printing technologies 

You should know that different printer units of the same printer model often require different printing settings (light exposure times) since their light power decays over their cumulative operating time.

SLA 3D printers use:

  • Laser beams with certain spot size (typically from 50 to 150 nm) and power (50 to 300 mW which moves from point to point tracing the geometry.

SLA DLP 3D printers use:

  • UV and Visible lamp or bulb digital projectors which last around 2000 hours or 
  • 365, 385 or 405 nm LED projectors which last over 20.000 hours
  • light power may vary from 0 to 40 mW/cm2 across the vat from (typically between 2-10 mW/cm2) for most printers of the same DLP technology

SLA DLP LCD 3D printers use:

  • Backlight LCD panels with 405 nm LED arrays, which transmit or block selectively the 405 nm backlight LED light for printing layer by layer 3D objects. There are two types of LCD screens or panels:
    • Standard multicolor RGB (Red Green Blue) LCDs which last around 400 hours
      • available light power for printing may vary from 0 to 1 mW/cm2 across the vat for most printers of the same LCD technology
    • Monochrome LCDs which last around 2000 hours
      • available light power for printing may vary from 1 to 2 mW/cm2 across the vat for most printers of the same LCD technology

The following graphs show a  typical light output decay vs cumulative operating time of multicolor RGB LCD panels, monochrome LCD panels, digital lamp projectors and LED projectors, all typically used in SLA, DLP & LCD 3D printers. 

Normal RGB LCD panels (backlight with LED at 405 nm) used in LCD 3D printers exhibit the fastest degradation (evidenced by a significant decay of the light transmittance through the vat after 300-400 hours cumulative operating times) since  are quite sensitive to uv degradation and to the heat generated during printing, especially at .long exposure times.

Monochrome LCD panels (backlight with LED at 405 nm) used in monochrome LCD 3D printers exhibit a similar decay to lamp projectors. Both exhibit a similar significant decay  through the vat after 1600-2000 hours cumulative operating times). They can exhibit shorter or longer lifetime depending on several variables such as: quality, thermal resistance, use, etc since por cooling and excessive heat released with long exposure times may decrease even further their lifespan.

The sort of LED projectors used in 3D printing work at 365, 385 and most of them at 405 nm. Their lifetime is over 15.000-20.000 hours and exhibit a constant light output for over 2000 hours cumulative operating times. 

Depending on the chosen 3D printer technology, its light power and the cumulative operating time, the light power available reaching the vat for printing may vary significantly even from printer to printer of the same  model depending on their cumulative operating time.

Note: Differences of exposure times of up to 10-15 seconds per layer have been observed for the same resin in two identical  LCD printer models with different cumulative operating times.

Since each 3D resin requires certain energy dosage (mJoule/cm2) for curing each layer, a decay of the light power (mW/cm2) needs to be balanced up with an increase of the exposure time (Energy dosage=Power x exposure time).       

The 3Dresyns team has designed the following instructions for helping you to optimise the printing settings of our 3D resins in your printer. They are ideal for monitoring and overcoming the natural decay of light power over time of your 3D printer.

Basic process for getting the optimum exposure times in your printer  

Step 1: Select your layer thickness, typically between 10-100 microns, for example, 50 microns as standard for your clear or colored 3D resin.

Step 2: Select your printing settings, supports density, tip size, power and exposure time if your printer permits it.

The following Curing Rate Table needs to filled up in just few minutes to find your optimum exposure time in your chosen printer since the exposure time needed to cure the resin depends on the light power crosdsing the vat:

Curing Rate Table, where the thickness of cured resin is measured at different exposure times:

Exposure time (seconds)  Thickness of cured resin (microns)
5 Example: 0 uncured
10 Example: 30 soft , poor adhesion. Requires more light to cure properly
15 Example: 60 cured, better adhesion
20 Example: 120, well cured, good adhesion
25

Example: 130,  well cured, good adhesion

30

Example: 140,  well cured, good adhesion

50

Example: 150,  well cured, very good adhesion. Ideal exposure time for printing the first 2 adhesion layers

75

Example: 170,  well cured, very good adhesion

 

Tuning steps:

  • Remove the build platform from the printer.
  • Apply a drop of the liquid resin on a glass slide (or FEP film) and position it on the vat or resin tank in the printer at your chosen (if variable in case your printer has a light power controller) or standard light power and cure it for example for 5 seconds.
  • Then, remove gently with tissue paper the unreacted liquid resin from the glass slide or FEP film (always cleaning its surface gently with isopropanol) and measure with precision the thickness of the cured resin (if any in too short exposure times) with a caliper or micrometer.
  • Repeat the cure test again with a drop of fresh resin but with a longer exposure time, for example, 10 seconds, then remove the unreacted liquid resin with a paper, clean and measure again the thickness of the cured resin.
  • Repeat this process with longer exposure times, for example 15, 20, 25, 30, 50, 75 and 100 seconds.

 

    The Curing Rate Table can be filled up even faster if just a light spot of eg 3-5 mm diameter is used to cure the resin in the centre of the resin tank. The glass slide or FEP film covered with resin can be slided sidewards to make a row of spots cured at different exposure times. A basic stl file of a cylinder of eg 3-5 mm diameter, without the build platform, can be used for undertaking the cure test in one go at different exposure times.

    As mentioned the Curing Rate Table can be easily filled up representing exposure times, for example for 5, 10, 15, 20, 25, 30, 50, 75 and 100 seconds in DLP and LCD printers (these times can be varied if needed to adapt to different print speeds and resin systems), versus thickness of the cured resin at each exposure time.

    If your printer is an open mode laser based SLA printer adapt the laser exposure settings accordingly. If your printer is a closed mode printer, which does not allow any exposure time changes, then use our Fine Tuner FT1 to adjust the print speed of the resin and secondly use of  Fine Tuner LB1 Bio to maximise resolution.

    If your printer supplier provided the light power across your resin tank, in mWatt per cm2, then, by multiplying power by exposure time, the energy dosage  in mJoule per cm2 can be calculated for your different exposure times. This is ideal for undertaking scientific and professional 3D printing. 

    Alternatively an external radiometer, measuring light in the wavelength range of your printer, commonly 385  or 405 nm, can be used for measuring the light power of your DLP and LCD printer across the resin tank. The use of an external radiometer is highly recommended for monitoring the natural light power decay of DLP projectors and LCD panels. Professional 3D printing requires the use of an external radiometer for quality control and for monitoring the lifetime of your DLP projector and/or LCD panel.

    Note: considering that a z layer thickness of 50 microns has been chosen for printing, the exposure time needed to cure the resin and have succesful prints, will be the exposure time required to cure at least one layer of 50 microns. This obvious asumption is commonly ignored by beginners.

    Normally the optimum exposure time is the time needed to cure in between one and two layers,in this example, the time to cure between 50 and 100 microns, which is approximately around 14 and 18 seconds. In order to increase accuracy is recommended to repeat the cure test table with exposure times closer to our print specifications, for example 10, 12, 14, 16 and 18 seconds.

    It is recommended to initially start printing with the  exposure time needed to cure 1.5 layers. Depending on results, the exposure time can be reduced by using the time required to cure between 1.1 and 1.2 layers with the goal of increasing print speed and resolution.

    In order to have good adhesion of the resin on the build platform is important to print at least 2 adhesive  layers at long  exposure times to ensure optimum adhesion and good printability.

    As rule of thumb, use for curing the adhesive layers 4 times the standard exposure time. Alternatively, more scientifically, use a exposure time at which the resin showed optimum adhesion and cured well on the glass slide or FEP film. In this example, in 50 seconds the resin cured well and had very good adhesion on the glass slide (see example on the Curing Rate Table above), so this time can be chosen for curing the first 2 adhesive layers. Once the exposure times have been chosen, then the next step is:

    Step 3: Start printing using 2 adhesive layers (use the exposure times as already explained) and for standard layers use initially the exposure time needed to cure 1.5 layers. 

    IMPORTANT NOTE: Several calibration stl files can be sent upon request for fine tuning our resins in your printer. Request them by email to: info@3dresyns.com

    Step 4: Evaluate the quality of your print.

    Option 1: If you are fully satisfied with the quality of your print, then it is not necessary to fine tune our 3Dresyns further.

    Option 2: If you are not fully satisfied with the quality or detail of your print it is necessary to fine tune the 3D resin and/or adjust your printing settings.

    Depending on the origin of the print quality problem, different solutions are available. Click on this link to find more detailed information about common printing problems and solutions

     For printing support please contact us at: info@3Dresyns.com