APP – Fixing obvious extrusion issues

Once your material starts coming out of the nozzle for the first time, the settings adjustment process begins.

The first step is to fix the “obvious” extrusion issues.

At this stage, it is important to not spool the filament, just pull it.

1. What are “obvious” extrusion issues ?

The obvious issues are the ones you can see with the naked eye. In general, they are easy to notice, understand, and fix.

The most common extrusion issue (thickness deviation) is not in this list. It has to do with the flow stability, which is a lot more difficult to manage and time-consuming. This will be the focus of the next finetuning step.

Fixing the first extrusion issues will result in a homogeneous, smooth output that comes out continuously and allows you to focus on the tolerance.

2. Troubleshooting each issue

Most extrusion issues can be fixed by tweaking the experimental process. But sometimes, when the material is really incompatible with the filament making process, only changing the material can solve the issues.

Important note : When you adjust the settings during this step, we recommend you to apply the same changes to all heaters, whenever possible. Because this step is not the final finetuning step, it is easier to work with rough baselines rather than specifics.

Bad additive dispersion (when working with additives)

This only occurs when extruding a composite material which has not been pre-compounded into pellets beforehand. The additive might segregate and form tiny solid plugs visible in the filament, or even one big obstacle that clogs the barrel completely. The following changes might increase the homogeneity of the mix:

  • if the additive is a powder or short fibers, then a polymer in powder form will work better than pellets
  • start by mastering the base polymer first, without the additive. Then start with a small amount of additive (max 5% weight).
  • use a difference size of additive (below 100 microns if possible)

Incomplete fusion (big punctual bumps in the filament)

This is usually a problem occuring in the first zones (H4, H3). It is good to experiment with all the heaters, and also focus on H4 and/or H3 separately.

  • Increasing the temperatures (steps of 5°C)
  • Decreasing the temperatures (steps of 5°C)

Note: increasing the temperatures does not necessarily mean that the material will melt more. Sometimes it is better to increase the friction, by decreasing them.

Weak flow (almost no material comes out)

This can happen when:

  • The material melts in the feed zone. Then you can decrease H4.
  • Ratholing or bridging is happening in the hopper. Then you can use the Feeder.
  • The material is too viscous. Then you can increase the temperatures.
  • The material is not viscous enough. This can happen with injection grades for example, or when the temperatures are too high, or when the material degrades (hydrolysis or another form of degradation)
  • There is not enough pressure to push the material. You can try to decrease H4 and H3 while increasing H1.
  • The barrel is partially or totally clogged. Purging the machine with Devoclean MidTemp (if the processing temperatures are below 300°C) or Devoclean HighTemp (above 300°C) might unclog it.

Bubbles

  • Lower the temperatures (small steps of 5°C)
  • Make sure the material has been properly dried, if it is hygroscopic.

Solidification/build-up at the tip of the nozzle

Certain polymers, especially the most crystalline ones, can solidify very fas upon exiting the nozzle, and stick to its tip. This issue becomes more likely when the temperature in the room is cold.

  • Make sure the magnetic plate is well-positioned on the hole around the nozzle
  • Angle the fans so that they blow as downward as possible (not horizontally nor straight toward the nozzle)
  • Increase the temperatures (especially H1)
  • Lower the fancooling percentage

Streaks on the surface

This refers to continuous streaks, or lines, carved into the surface of the filament.

Note: fibers can make the surface rough with lots of lines, so can bubbles, but those lines are not continuous.

  • A build-up of solid material at the tip of nozzle may cause this issue.
  • If the nozzle is damaged, then it should be changed.

Filament falling “like a snake”, not vertically down through the sensor

This can cause zeros in the reading, because the filament leave the reading angle of the sensor.

  • Decrease the fancooling
  • When this happens, it is often easier to decrease the fancooling by a lot, or completely, and manually re-position the filament in the puller again, nice and straight

Filament sticking to the puller wheel

  • Increase the fancooling
  • Decrease the screw speed
  • Decrease the temperatures (especially H1)

Filament ovality

There are 2 types/causes of ovality:

  • Ovality due to asymmetric shrinkage. The filament becomes oval before reaching the puller. This mainly happens with highly crystalline plastics such as HDPE and PP. In that case you can:
    • lower the temperatures (especially H1)
    • use a circular cooling device.
  • Ovality due to the compression by the puller. The filament is round when going down through the sensor, but gets flattened/crushed by the wheels. There are several solutions:
    • Increase the fancooling
    • Decrease the temperatures (especially H1)
    • Decrease the screw speed

Sensor reading zeros

If the filament sometimes moves out of the sensor’s reach, then this is normal (see “Filament falling “like a snake” ” above).

If not, it means the sensor reads zeros when it should not:

  • The sensor must be cleaned.
  • Light from the room is interefering with the optical sensor. Try to cover the opening of the sensor with a piece of tape.

3. Example

Let’s take the standard PLA from 3devo.
PLA was inside the machine from the start. We just fed more PLA at 200°C, 5RPM, 50% fancooling.

Here are the problems we can face, and their solutions:

  • The output is full of bubbles. PLA degraded inside the barrel since last time, which explains the generation of bubbles, but only for a few minutes.
  • The filament sticks to the puller wheel.
    • All temperatures down to 180°C (steps of 5°C)
    • Fancooling up to 100%.
  • Filament ovality, due to the filament being squished between the wheels. This issue is just one level below the previous, but the core problem is the same.
    • Screw speed down to 3.5RPM

At this point the filament was smooth, quite round, and coming out continuously without any other visible problem.