flow rate, print speed, real printing time

[Food24 0]

Dear all,

recently i'm paying attention on the 3D Food Printing. Briefly, i printing edible objects by using innovative food formulation. I design my object by Tinkercad and i'm using CURA software to optimize printing conditions.

Of course, to print food is very differen than PLA filament. So, several traditional consideration about thickness of filament, temperature of nozzle, etc are not important in food Printing.

I use a WASP printer delta 2040 equipped with Clay extruder kit 2.00 .

I use print speed between 11 and 22 mm/s, a flow rate between 60 and 120%, a nozzle of 1.2 mm. The object is a pyramid of 29x29 mm for 22 mm height.

I measured the total printing time as a function of flow rate observing that it increases with flow rate. Below some results:

print speed(mm/s) flow rate (%) measured printing time (s)

11 70 140

11 70 139

11 70 140

11 127 198

11 127 198

11 127 198

Question n.1

Can you suggest me some hypothesis ? Maybe there are some limitation effect if the flow rate is too high producing a new equilibrium in the path planning of the printer ?

Question n.2

Also i measured the printing time as a function of print speed observing total time of 175 s, 195 s and 160 s for print speed of 11, 16 and 21 mm/s, respectively. It is a peak for 11 mm/s of print speed.

Anyone can help to to explain this observation ?.

Maybe when i change print speed the accelleration factor has different effect on the total printing time ? Also, it is possible that path planning of the printer changes with printing time ?

[gr5 2,173]

Does the WASP use Marlin?

I have spent many hours looking at the motion controller for Marlin and 3 other firmwares as well. They are surprisingly complicated. Since you only changed the flow (E=extruder axis) that simplifies what could have caused this. Some possibilities:

1) max acceleration for E axis

2) requested acceleration for E axis

3) max E velocity

4) E Jerk

5) retraction

Regarding #5: Do you have lots of retractions? If so try reducing the retraction distance in the slicer by the same amount you are increasing flow. So if you set flow to 200% you can cut retraction distance in half.

#3 I suppose is the easiest to check. photograph the extruder and look at it's speed during your print. Then try moving the E axis all by itself at top speed and see if it can go any faster. It could be your print is limited by E velocity.

Regarding #2 I don't have any ideas unless you also changed the flow between tests.

[Food24 0]

Dear gr5,

thanks for you suggestions. However I have some additional questions:

regarding n.5: Do you mean that the retraction distance can vary when flow (E-axis) increases? If so, when the flow is too high the motion controller increase the retraction distance to avoid problem in printing time but this effect create an increase in printing time ? Would be this a correct hypothesis ?

regarding n.3: May you explain better the effect of E-value limitation ? If understand that if E is too high the motion controller reduce the print speed.

Also, regarding the effect that i observed on printin time, a figure is attached were you can see my resutls

Thanks Food24

[gr5 2,173]

You didn't answer if you have many retractions. When you increase flow it increases the amount the extruder moves: FOR ALL MOVES. Including retractions. So if flow is 200% and retraction distance is 4mm then it will retract instead 8mm. Moving a further distance takes more time. The purpose of retraction is to keep the nozzle from leaking when it is moving but not printing.

I'd like to see what the part looks like. There is a feature in cura called "minimum layer time" I think. Typically I set it to 3 to 5 seconds. I think default is 10 seconds. If a layer takes less time than this then cura slows down the speed until it is > "minimum layer time". This code that slows the print down might not be smooth - it might have discrete speed changes. I don't know.

Your printer has many values built into the firmware (Marlin???). Here are some of them:

max velocity for X,Y,Z,E (4 settings)

max acceleration for X,Y,Z, E (4 settings)

max "jerk" (instant change in velocity at junctions) for X,Y,Z,E (4 settings)

So far that's 12 settings.

Also there is a default acceleration built into the firmware for X-Y-Z, E (2 settings) this can be changed with cura 2.X but cura 15.X and most slicers don't set this - it defaults to whatever marlin uses.

Also delta printers are complicated and need to convert long arcing movements into multiple sub-moves. This code needs to do trigonometry (e.g. sin, cos, tangent) and so uses up excessive cpu time such that if you print faster it splits a move into fewer sub-moves but then the "jerk" parameter takes over and can make the printer go slower potentially. I don't want to get into this but it can affect long moves the most.

Please explain how many retractions you have. Please explain more about your part geometry. Please say what firmware you use.

[Food24 0]

Dear gr5,

i'm using Marlin firmware. Retraction distance of 2 mm at rate of 20mm/s. Minimum layer time is 5 s. Nozzle size is 1.2 mm (with a clay extruder kit 2.0). Layer height is 1.1 mm (which allow to well fix well subsequent layers). Shell thickness of 1.2 mm. Infill of 25%. The 3D object is a pyramid with a size base of 29x29 mm and height of 22 mm. See below some cross sectional images of my object.

Also filament diameter is set as default value of 1.75 mm although i'm using a plastic tip of 1.2 mm.

My general idea is that by using a clay extruder with a plastic tip of 1.2 mm I have a completely different behaviour that the expected ones by CURA.

For instance, it is possible that I see a printing time lower than the estimated time by CURA when i printing a low print speed of 11 mm/s. It is possible that control motion allows faster movements than the predicted value?[/media]

However, back in the effect of flow (E-axis) on printing time i measured greater printing time as flow increase as follow: 69, 98 and 127%. On the basis of your explanation it is possible that my printer is limited by some velocity values in X,Y,Z axes. By changing flow at 69, 98 and 127% I increase all axes movement. Since the movement of delta printer are very complicated i reach some velocity limits both at 98% (for istance in x axis) and at 127% (probably in x and y axes) observing a progressive increases in printing time. Could be a behaviour like this ?

[gr5 2,173]

Flow should only affect the E axes. But if you are at the speed limit of the E axis (I think you are - this is VERY fast flow rate because your layers are so thick - 1.1mm) then increasing flow means you have to slow down the x,y,z axes. The E axis can't go any faster so instead the other 3 axes slow down.

You might be able to increase the maximum E velocity and still print just fine. Usually when people tune the axes on a delta they pay more attention to the x,y,z axes and less attention to the extruder.

In Marlin - in the menu system - under "motion" maybe? You should be able to set "emax" which is maximum E velocity. if you go too fast the extruder will make a funnty noise and not extrude at all. It's not bad for the printer but of course the part won't print so well. I would play with that. I would set emax to 10X your current velocity and play with flow rate until the extruder fails.

[Food24 0]

Dear gr5,

just a couple of questions on the basis of you explanation:

if the first your response you told me: 'When you increase flow it increases the amount the extruder moves: FOR ALL MOVES'.

Then, in your second comment, you stated that 'Flow should only affect the E axes'.

I'm confused about it.

When I increase print speed (feed rate) i increase both X,Y,Z rate and E axis rate because it is necessary more material vs time.

Similarly, when i increase flow rate (E-axis) i also incrase the X,Y,Z rate to make possible a good deposition.

But are these two case the same?

Let me assume that i increase the speed rate from 10 mm/s to 20 mm/2 (twice) and that the E-axis increase also of two time. If so, the new equilibrium should allow to mantain the deposition rate (amount of material extruded for second) constant because all axes incrased in twice.

Contrarly, if i increase the flow of 200% i should see an increase of print speed in X,Y,Z axis from 10mm/s to 20 mm/s.

Going to my question:

If i increase speed of X;Y,Z axes of 100% (or 50%) i should be see an increase of E-axis of the same amount (100% or 50%)? and similar result should be obtained if i increase the flow of 50% or 100% (obtaining an increase in X,Y,Z axes of 50% or 100%).

 

Thanks

Food24

[gr5 2,173]

Dear gr5,

you told me: 'When you increase flow it increases the amount the extruder moves: FOR ALL MOVES'.

When you increase the flow it increases the extruder only. Not x,y,z. So if the move was from x,y,z,e (0,0,0,0) to (10,0,0,10) and flow is 200% then the x axis moves 10mm and the E axis moves 20mm.

But when I capitalized "FOR ALL MOVES" that was because if you are doing a retraction it also doubles the distance of the retraction. Retractions tend to be slow. So making retractions twice as slow is very noticable on your total print time. Especially if you have many of them.

When you increase the feedrate or speed it takes the requested speed in the gcodes and increases that value. So if the feedrate in the gcodes was 50mm/sec and feedrate is 200% then the new REQUESTED feedrate is now 100mm/sec. The feedrate is the speed of all the axes combined. So if only X is moving then that's the speed of X axis. If only E is moving then that's the speed of E axis. If many axes are moving it's the overall combined 4 dimensional speed (square each axis, add it up, take square root - also known as pythagoris theorem).

However in addition to requested speed Marlin also has a MAX speed for each axis. You are printing VERY fast in the E axis so if you happen to be close to the max speed for E and then you request 200% flow that also implies the E axis needs to go twice as fast. But if E axis is already at max speed then the printer will then slow down the other 3 axes to produce twice as much flow on as with 100% flow.

In other words if your normal print at 100% flow happens to have the E axis moving at 10mm/sec and 10mm/sec happens to be the limit of the E axis (max speed in marlin) then if you increase the flow to 200% the other 3 axis will have to slow down because the E axis is already at it's limit.

I could be wrong about your E axis already at the limiting speed.