Material Testing Procedure for Pellet Extrusion

This article is divided into these main sections:

• Overview
• Choosing Gigabot X Materials
• Extrusion Testing
• Print Optimization Testing

For a video that summarizes this material testing procedure, see this recorded presentation given during the Open Hardware Summit 2022.

Overview

At re:3D, we frequently conduct material testing on a variety of materials to assess how well they print in our Gigabot X pellet 3D printer, as well as to establish print settings to ensure reliable prints. As a result of hundreds of hours of material testing, we developed a standardized material testing procedure for testing any material.

The procedure subjects a material to progressively stricter requirements for successful printing. This approach optimizes interdependent variables in a logical order, and identifies any roadblocks that prevent a material from printing successfully.

This material testing procedure does NOT guarantee that a material will print successfully, but it will offer relevant troubleshooting to get as close as possible to reliable printing.

Choosing Gigabot X Materials

Before conducting material testing, the material should be assessed for some general characteristics to make sure it's a good candidate for pellet 3D printing. Information on ideal Gigabot X materials can be found here: Choosing Gigabot X Printing Materials.

Materials that do not comply with the guidelines can still be tested, but may have resulting issues when trying to print.

Extrusion Testing

Extrusion testing determines whether the material can be extruded through the Gigabot X pellet extruder. This includes testing particle analysis, feeding, initial temperatures, maximum extrusion, and extrusion consistency.

The tests in this section include:

• Safety Precautions
• Dehydrating
• Particle Analysis with ImageJ
• Purging
• Establishing Temperatures
• Determining the Maximum Extrusion Rate
• Measuring Extrusion Consistency

Safety Precautions

When testing an unknown material, it is imperative to take the proper safety precautions. Before conducting any material testing with an unknown material, review the Material Testing Safety Precautions.

Dehydrating

Materials must be dried before running through a pellet extruder to extract any moisture from the material. For more information on drying materials, reference our Knowledge Base article Drying Filament, Flake, and Pellets. To dry a material for extrusion testing:

1. Check for any drying instructions in the material TDS. If the 
2. If no information is available, google if the material is hygroscopic. If yes, dehydrate for at least 12 hours at 100F in a food dehydrator, or 4 hours at 65C in the desiccant dryer. If not hygroscopic, only dry if the material is visibly wet.
3. Store the material in an airtight container and label the container with the manufacturer name, material name, drying conditions (hours, temperature, drying method), and date when dried.

After drying, moisture analysis can be conducted on the material to confirm if it's adequately dried.

Particle Analysis with ImageJ

Particle analysis is a useful tool to understand the particle size and quality of a material sample. Particle size can affect a material's ability to flow through the extruder. For information and instructions for conducting particle analysis with the free, open-source software ImageJ, refer to Particle Analysis with ImageJ.

Purging

The next step in extrusion testing is purging the extruder from its previous material to the material undergoing testing. Purging is essential to remove all of the previous material so it doesn't impact material testing results.

For instructions on how to switch materials in a Gigabot X, refer to Loading and Changing Gigabot X Material. For a more effective purge, use a purge material to help purge out the previous material (see Purge Materials for more information).

Establishing Temperatures

Next, establish initial extruder temperatures for extrusion. Note that some materials may extrude under a wide range of temperatures, and further temperature optimization may be conducted later in the material testing process.

To establish extrusion temperatures:

1. If using Simplify3D's Machine Control Panel, connect a computer with Simplify3D to the printer via USB.
2. Reference the material's TDS for extrusion temperatures, and set the heat zones to those temperatures.
   • If only a melting temperature is available in the TDS, set the bottom heat zone to the melting temperature, the middle heat zone to 10C cooler than the melting temperature, and the top heat zone to 30C cooler than the melting temperature.
   • If a TDS is not available, google the melting temperature of your material type and set the heat zones according to the previous step.
3. Wait for all heat zones to reach temperature.
4. Extrude for 20mm.
   • For Klipper, use the Extrude section on the Dashboard.
   • For Marlin, extrude either via the Viki (Prepare > Move Axis > Extruder0 > 10mm) or through Simplify3D's Machine Control Panel.
5. Adjust the temperatures until adequate extrusion is achieved (see troubleshooting tips below).

Troubleshooting Tips:

• E0 and E1 temperatures must be at least the material’s melting point. The E2 temperature must be below the material’s melting point.
• Indications that E0 and E1 temperatures are too high include:
  • Plastic melts into a puddle on the bed
  • Smoking or vapor release
  • Low viscosity and/or oozing
• Indications that E0 and E1 temperatures are too low include:
  • Motor skipping
  • Cloudy or matte color
  • High viscosity
• Indications that E2 temperature is too high include:
  • Extrusion looks great, then gradually decreases and significantly underextrudes
• For more extrusion troubleshooting, refer to the Inconsistent Extrusion section of the Gigabot X Extrusion Issues article

Determining the Maximum Extrusion Rate

1. Set up a way to quickly pass commands to the printer. 
   • For Marlin: Connect the printer to a computer with Simplify3D via USB cable
   • For Klipper: Use the Klipper interface, either on the touchscreen or via Wifi
2. Heat up the extruder to the optimal temperatures determined in the previous step.
   • If using Simplify3D: Use the Active Toolhead dropdown and the On/Set buttons to set the heat zone temperatures.
3. Set the extruder speed to 5mm/s.
4. If using Simplify3D, jog in the Z axis by 0.1mm.
   • This is to circumvent a bug. Whenever the printer is connected to Simplify3D, the first jog command sent to it will cause it to move very slowly during the duration of the jogging movement. Any subsequent jog commands work fine. Jogging a small distance in the Z direction for the first command allows the bugged command to execute quickly.
5. Extrude for 1mm, then 10mm to confirm that the material can extrude at that speed. If yes, extrude for 200mm. Record the settings, as well as any evidence of motor skipping.

   • If using Simplify3D: Make sure Tool 0 is selected before any extrusion commands. If it is not selected, the extruder motor may turn in reverse.

     

6. If there is no motor skipping, increase the extruder speed in 1 mm/s increments and repeat the previous step until the motor begins skipping.
7. Once the motor starts skipping or extrusion is interrupted in some way, further optimize the maximum extrusion rate by adjusting the extruder motor speed using the bisection method.
8. Once the final max extrusion speed is determined, record it. This value will be later used to calculate the maximum extrusion rate.

Measuring Extrusion Consistency

This test will establish the extrusion consistency given the temperature and speed settings established in previous tests. It will also collect data on the amount of material extruded, which can be used to calculate maximum extrusion rate.

To quantify the extrusion consistency of a material:

1. Set the extruder speed to the maximum extrusion speed determined in the previous section.
2. Clear away any previously extruded material from below the nozzle.
3. Extrude for 200mm
   • If the motor skips during the 200mm purge, decrease the extrusion speed and return to the previous step to determine the maximum extrusion speed.
4. Mass the extrudate and record it.
   • If the mass is less than 5g, repeat the extrusion step for a longer length than 200mm to extrude enough material.
5. Repeat 4 more times, massing and recording the amount of extrudate for each extrusion trial.
6. Calculate the standard deviation across the 5 trials to quantify extrusion consistency.

To troubleshoot inconsistent extrusion, refer to the Inconsistent Extrusion section of the Gigabot X Extrusion Issues article.

To calculate maximum extrusion rate:

1. Calculate the average mass of the 5 trials.
2. Determine the extrusion time for each trial in seconds by dividing the millimeters extruded by the extruder speed in mm/s.
3. Calculate the maximum extrusion rate in kg/hr by dividing the average extruded mass by the extrusion time, and multiplying the result by 3.6 to convert all the units.

Note: the above calculation will not be accurate if the material showcased extrusion inconsistency.

Print Optimization Testing

Print optimization testing establishes what print geometries a material can achieve, and the resulting print settings. This procedure attempts to use the material to print increasingly complex geometries to optimize extrusion calibration, extruder and bed temperatures, bed adhesion, ooze settings, and other print settings.

The tests in this section include:

1. Purging
2. Printing a Calibration Cylinder
3. Printing a NIST Test Artifact

Purging

If needed, purge the extruder from its previous material to the material undergoing testing. Purging is essential to remove all of the previous material so it doesn't impact material testing results.

For instructions on how to switch materials in a Gigabot X, refer to Loading and Changing Gigabot X Material. For a more effective purge, use a purge material to help purge out the previous material (see Purge Materials for more information).

Printing a Calibration Cylinder

The first test print is a calibration cylinder, which is a simple cylinder model sliced with the following settings:

• 2 Solid Bottom Layers
• 0 Solid Top Layers
• 1 Perimeter
• 0% infill

This creates a hollow cylinder with two bottom layers and a single perimeter wall. The cylinder is used to optimize:

• Bed adhesion
• Extruder temperatures
• Extrusion rate calibration

To troubleshoot bed adhesion, refer to Bed Adhesion Issues.

To calibration extrusion rate, refer to Calibrating the Gigabot X Extrusion Rate.

Printing a NIST Test Artifact

The NIST Test Artifact is a standard geometry that acts as a torture test for complex geometry and small features, and it is ideal for use with 0.8mm or smaller nozzles. It can be downloaded for free from the NIST website here. The NIST Test Artifact tests:

• Bridging
• Stringing
• Stair-stepping
• Small holes
• Small pegs

Questions or concerns? Reach out to our support team at support@re:3D.org or open a support ticket.