Excess Nozzle Pressure Causing Feeder Problem

[michelide 4]

Hi All,

 

I recently had to diagnose a very complex problem that I was having with a new material and at this point have been able to mostly fix the problem but still do not know the root cause of the problem. Perhaps you could comment and help me out.

 

Excess nozzle pressure was causing the feeder to jam up to the point where it was digging into the filament and flexing it into an S.

 

After trial and error with cura and and ultimaker 2+ firmware settings I went through about 8 meters of material on the spool.

 

Cura settings that didn't seem to have any impact on this issue:

Printing the first layer thicker

Printing different layer thicknesses

Printing at different speeds

Printing at different temperatures in the material range

Printing more than one model concurrently on the build plate

Equalize filament flow (I still have it checked but checking it didn't fix this by itself)

Slower layers, slower layers did not help, I've set slower layers to 0.

 

Ultimaker 2+ firmware settings that didn't seem to have any impact on this issue

Printing with TPU 95 material setting (it printed the same as custom setting)

Print layers faster or slower

 

 

I then started adjusting the flow rate at different times during printing and this didn't completely fix the problem it only mostly fixed the problem.

 

I talked to form futura to get the recommended material settings for ultimaker 2+, I am working with an MD Flex Antimicrobial Nanocomposite material. Its a flexible 95A TPU. I was using recommended range of settings but still having issue. More temperature out of the material range would burn the material. No settings were clogging the material in the extruder. The flow out of the extruder was perfect when feeding without the build plate below it and very fast. The problem was only occurring when printing and only during 1 layer of printing. It didn't matter if a printed one or two models. I had the same problem on the same layer and every single time it caused the feeder to press too much pressure into the nozzle and caused damage to the material in the feeder.

 

During the final moments before the material in the feeder would become damaged I noticed that the nozzle started pressing way too much material out it was spewing a foamy or bubbly mess, it always started on layer 3 or layer 4. This happened on every printing every time because pressure was building up in the nozzle between the initial layer and the fourth layer to the point of damaging the material. This is when I started adjusting the filament flow manually on the printer while it was printing and checking nozzle pressure in the extruder by manually bobbing the bowden tube while it was printing to determine at what point pressure was building up in the extruder. After the first 2-3 layers went down perfect no matter what above listed settings I saw that the pressure started building up in the nozzle. This pressure happened quicker with 100% filament flow and less quickly with 40% filament flow. After two layers at 40% filament flow I had to reduce the filament flow to 10% before the pressure started building up for one layer. During this 10% layer the printer still extruded less foamy and bubbly material but it was not as bad. Directly after this excess material ejection I set the flow back to 100% with no more issues.

 

I've now printed 4 parts like with manually adjusting the flow settings with no feeder issues and I still have the problem on the 3rd or 4th layer where it seems something about either the GCode or the Printer firmware is trying to clear the nozzle during printing when it doesn't need to around the 3rd or 4th layer.

 

Any ideas on how to fix this so I do not need to watch the print between layer 0 and layer 4?