How to increase throughput - Faster production rate

Increasing the extrusion production rate sounds as simple as increasing the screw speed, but understanding the limiting factors and following a step-by-step method is the best way to succeed.

1. Where to start ?

Before trying to increase the production rate of your process, we strongly recommend that you first focus on achieving flow stability. 

This process typically takes several hours, and mainly consists in adjusting the settings to troubleshoot various extrusion issues.

In this research phase, the screw speed is normally set to 3-7RPM.

In the next section, it is assumed that you are producing good quality filament without any extrusion problems. 

2. How much throughput can you expect ?

It depends on you quality criteria.

The rule of thumb is : the faster the production rate, the lower the quality. This does not apply 100% strictly, but summarizes the situation very well. 

Taking virgin (no fillers, not recycled) PLA as an example, you should be able to start around 350g/h, and go up from there.

600g/h is a reasonable goal for a material that is very-well suited for filament extrusion. While maintaining a good thickness tolerance close to +/-50microns.

In certain cases, you might be able to increase the throughput even more, closer to 800g/h, but filament quality (tolerance, roundness) will degrade.

3. The method

Summary :

Increasing the screw speed will increase the throughput.

The challenge lies in cooling down the output sufficiently before it passes in the puller.

Initial state :

  • Start a datalog with the DevoVision app.
  • Begin the experiment with settings which you know work very well for your material.
  • Place the output between the puller wheels but do not spool the filament
    • we recommend you place your Filament Maker close to the table's edge, so that the pulled filament can be collected on a box on the floor
  • Let the process stabilize. It is important to have an excellent baseline :
    • sufficient filament roundness
    • satisfactory thickness tolerance
    • pure output (in most cases, this means that all traces of Devoclean MidTemp EZ must be eliminated)
    • no extrusion incident for 20-30min

Adjustments until 100% fancooling :

  • Increase the screw speed by 0.2RPM
  • Wait 2min. This should give enough time for the system to adjust the pulling speed automatically
  • If the filament gets slightly squished by the puller, it means that the filament is too hot when reaching it
  • In that case, you should increase the fancooling until the filament becomes solid enough to keep its shape through the puller
  • Repeat all these steps

Adjustments at 100% fancooling :

At one point, you will need to apply 100% of fancooling. At that point, you will need to focus on the temperatures :

  • Increase the screw speed by 0.2RPM
  • Decrease the temperatures
    • you can first focus on H1 only, then the other temperatures. it is hard to define a pattern/rule
    • small adjustments of 2-3°C are wise
  • Wait 20-30min. The nozzle temperature depends on many factors (H1, but not only) and varies extremely slowly
  • Repeat

At one point, the extrusion flow will become too unstable. Below a certain temperature, unmelted particles will start coming out, and the nozzle will clog.

Additional notes :

  • The fancooling is a key parameter but depends highly on the room temperature and humidity. If your environment is not 100% controled, your results may vary
  • Major extrusion issues aside (unmelted particles, clogging,...), the tolerance might become too unstable. By keeping an eye on the product and the Filament Thickness graph in the datalog, you can decide when to stop increasing the screw speed
  • The automatic system which controls the pulling speed works optimally around 5RPM. Above 7RPM, Switching the puller speed from automatic to manual (in Main menu / Speed tuning) could help you achieve better results