Printing with Light Weight PLA

When I saw the vid of the EDF Seagull being flown, 2 of them actually, one did, one didn't, I knew I had to have one.
Light Weight PLA, (LW-PLA) is a newish filament that has a foaming agent in it. The foaming occurs when extruded at higher temperatures (typically 250 - 260^oC). Since my sister was in the UK recently I got her to bring a roll back with her. The colour selected was natural since then I wouldn't have to add much weight in the way of paint.
These instructions on how to use came from the Colorfab web site.
"
1 PRINT CUBES (Download here: Test Cube) AT A SET SPEED IN TEMPERATURES VARYING FROM 200°C UP TO 280°C
2 MEASURE PERIMETER THICKNESS OF EACH CUBE, NOTE TEMPERATURE WITH HIGHEST EXPANSION.
3 PRINT CUBES WITH DECREASING STEPS OF FLOW, USING TEMPERATURE FOUND IN STEP 2.
4 FIND THE CUBE AT WHICH PERIMETER THICKNESS EQUALS NOZZLE SIZE.
"
My first problem was the test cube wouldn't download, it's item 271736 on Thingyverse, once I had the cube, how hard could it be?

Klippy
If your printer has a PTFE feed tube to the nozzle (most do) then even 250C is close to its limit for protracted use.
It is this fact that is holding me back more than the cost of the LW-PLA

First to Simons' concern
I have installed a Titan Hot end, these are the parts

if the tube is PTFE (probably) it's never given any trouble.

Considerable steps are taken to keep the heat away from the tube

There's a 40mm fan on the other side of those fins
The feeder tube comes in at the top of the carriage

and goes up to the extruder stepper that's mounted remotely to keep the weight off the carriage.

That is interesting but it does rather show how important it is to get the heat away from a PTFE feed tube.

To carry on, I followed the instructions for calibrating the LW-PLA

You can see the discolouration as the temperature goes up, the expansion was the same at 250^oC and 260^oC so I decided the temperature to use was 250^oC
The wall at 200^oC was 1.16mm, and at 250^oC was 1.51mm

Having tried, and failed to get the wall thickness down to 0.4mm, note the poor infill of the 30% flow rate floor.

I then realised that I was mis-reading the instructions, I should be reducing the flow rate until the wall thickness was the same as the 200^oC wall
63% was the number!
What was interesting to me was the weight, the 200^oC cube weighed in at 25grains, the 250^oC cube with the 1.16mm wall was 15.2grains

Right, so lets print something.

As you can see that didn't go well!
Going back to the Plane print web site I noticed they quoted a setting I didn't seem to have. What I didn't know up to then was that your profile panel can show different settings according to whether you selected Basic, Advanced, Expert or All.
I didn't realise Cura was so powerful. Some 180 different settings have to be fine tuned according to a closely printed crib sheet! After I'd input all the setting changes using the 'All' profile the very next print gave me this

The first, closest to the camera, fell over 10minutes short of a 6hour print! I changed the base to Brim and the second attempt, perfect.

Klippy
Having achieved a pretty significant weight saving of 25 to 15 I suppose the next is to try to quantify their relative strength and stiffness.
After all the important advance is to save weight but with less than a corresponding reduction is strength and stiffness.

Is the finished foamed surface significantly different to that of a non foam filament?

As filament PLA is much stiffer and shinier than LW-PLA. The surface of LW-PLA more 'satin', I've found that LW-PLA is quite happy to extrude at much lower temperatures than PLA but is not easy to use. During my learning curve I've had to strip the extruder parts (both ends) 4 or 5 times). LW-PLA will stick in the nozzle if you even glare at it!
Once the LW-PLA has foamed it doesn't extrude easily. With PLA you can print a component, take it off the Bed, and start printing another component, try this with LW and you're in trouble.

This chamfer is one of the problems.

What is that curved artefact that you have printed?

Hi Jon, that's the tail of the Plane print Seagull I'm printing.
The finished item is very flexible but very strong in certain directions

this incomplete skin is quite flexible

then I can squeeze the fins together

by comparison the rudder hinging point (the whole thing moves for control)

is very strong and in-compressible.
This is a surface finish comparison

The layer height is 0.25mm but the cube is 0.15mm so not really comparing apples with apples.

In the light of the caveat from Plane print that nozzle temperature should not be more than 240^oC I decided to print these test pieces

On the left at 250^oC, the foil surface is 0.75 and weighing 52.1grains.
On the right at 240^oC, the foil surface is 0.85 and weighing 53.4grains.
13% thicker (stronger?) but only 2.5% heavier, I think I'll be printing at 240^o.

I've checked the above figures twice now and even re-generated the code, changing only the temperatures. What you see is what you get!
Our current load shedding means I only have 4 uninterrupted hours of print time, the prints waiting to be done are all in excess of 8 hours. These parts, a cover and the thrust tube have to be done in PLA

The thrust tube is 40mm in diameter and 0.5mm thick weighing 68gns, I was quite impressed with it.

Using LW-PLA is a pain, but rewarding when you get it right.
If you have a power cut

You get this, without the cooling fan the filament heated in the feeder tube, and expanded in the tube, original filament at the top, hot end at the bottom. This took several hours to get out!
Once the filament has foamed it will not extrude so you must include an extruder filament retract in the post processing, I use 100mm. The retract gives you a spoiled end

You must pull out the filament and cut this off.
Failure to do this will result in zero extrusion with the next print. Obviously as the next print starts you must remember to advance the filament 100mm if you are using anything other that LW-PLA.

Klippy
This all very useful stuff. Many thanks.
It would seem you have more problem than most of us, power cuts and 3D printing do not mix!
I would imagine such a situation is even worse when using LW-PLA!

LW-PLA sticks to the bed very easily which can lead to other problems, Having a Skirt means that the extrusion process has stabilised but doesn't work with tall objects.

All tall objects need a Brim, otherwise they fall over!
Failure to set the Flow rate (63% for me)

On the right is 100%, left is 63% The internal fill is visible but can't be felt. What is of concern is the obvious movement towards the end of the 180mm print
At this stage I do have a number of parts that are usable.

Top right is a wing tip, sands quite easily but does get grubby. The outer ailerons look ok but the inners, 2 required, definitely need a re-think.

After the deformation the part returned to the original shape.
Then I tried the thumb test

I'm putting about 10lbs/inch²
Anything that I printed at 260^oC is definitely not fit for purpose, the part crushes or breaks quite easily.