What are ways to avoid heat creep?

Question

Printer configuration and many settings affect heat creep. Heat creep stopping extrusion doesn't necessarily involve melting the filament too high above the nozzle. All it takes is making the filament too soft. The filament may bend and wad up (the importance to avoid gaps in the hot end allowing this). On direct drives (not Bowden tubes) the filament can get soft so that the teeth on the direct drive cuts a notch in the filament instead of pushing it through the nozzle.

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Fig. 1: Some typical signs of heat creep on the filament of a direct drive. 1) notch in filament where gear spins in soft filament. 2) normal teeth marks in filament. 3) soft filament bending. 4) soft filament bunches in open area. With a Bowden tube, the filament widens at the end.

Fig. 2.: Another example of heat creep with a direct drive extruder.

Note: Setting the retraction too high can cause the extruder to jam, but this is not heat creep. Although, the symptom could be mistaken for heat creep.

Also note: Printing materials like PETG too fast can clog the nozzle because the filament doesn't have time to melt. This is the opposite cause from heat creep. On some direct drive extruders you can tell the difference in the appearance of the jammed filament moving too fast versus heat creep because the filament is rigid when moving too fast and tends to jam in the nozzle giving a similar appearance to heat creep in Bowden tubes extruders. When PETG jams in a direct drive as shown in Figure 3, both raising the temperature of the extruder (more heat to melt the filament) and improving the cooling of the heat sink (drive teeth digging into stiffer filament) also helps.

Fig. 3.: Filament with end expanded in nozzle showing jam from filament moving too fast and not heating enough.

A defect in the filament can jam in the tube to the hot end, as well as the filament hanging up on the spool or in the path to the hot end. This can also stop extrusion.

Of course different materials change the characteristics of heat creep, but what are other things affecting heat creep?

This is expanded from How is heat creep characterized?

Answer 1

Things to consider (This is expanded from How is heat creep characterized?):

1. The air volume of the cooling fan on the hotend heat sink affects the temperature gradient across the heat sink. Usually the size/geometry of the fan depends on the printer design, so the main parameter of a fan that controls air volume is the rpm. I've noticed fans fitting hotends from 6,000 to 10,000 rpm. The higher rpm the better as far as preventing heat creep. Of course, make sure the fan is spinning properly.

2. The raising the temperature of the extruder increases the chance of heat creep.

• A high resistive connection to the sensor will cause a lower that actual temperature reading. Thus, the controller will raise the hotend to a higher temperature than set, which can cause het creep.

3. Razing the temperature of the heated bed, especially when the printer is in an enclosure, increases the chance of heat creep because this raises the temperature of the air the fan blows across the heatsink.

• What can be useful is using higher extrusion and bed temperatures for the first layer, then set lower temperatures on subsequent layers to reduce the chances of heat creep.

4. The slower the print speed the higher the chance of heat creep. That's because a slower print speed gives the filament more time to heat up in the extruder. Many slicers have a setting that slows down the print speed if a layer will finish below a given time. If this slowed down time causes heat creep, the extrusion will stop when the printer reaches these smaller area layers.

• Too much travel of the extruder without extruding has a similar effect because the filament isn't moving. I verified that connecting isolated structures on a design with heat creep can eliminate it. Using a little more material for thin walls is better than scraping prints.

Example: This is easy to demonstrate with PETG. Design a table printed top down 100 mm square with four legs 5 mm square and 100 mm long. Set the parameters so that you start to get heat creep when printing the legs. Now put four 1 mm thick walls between the legs to get the heat creep to go away.

• Sometimes if you start a second print without letting the extruder cool down from the first print, heat creep will cause the extruder to jam.

5. The heater block might be too close to the heatsink so that they bypass the heat breaks reduction in conducting heat.

6. Hotends for temperatures 245 °C and below can use such things as Teflon tubing in the heat break to isolate the filament from the metal. But, +250 °C nozzle temperatures need all metal hotends.

7. The PID settings in the firmware might be letting the hotend temperature overshoot too high.