Best practice with ABS: no delamination, no cracking, no warping.

[abuharsky]

Hello All.
I spent a couple of weeks, even months in a vain attempt to print anything bigger than 40mm cube from ABS plastic.
There are no problems with printing small models, but with large models having constant problems: you just can not print any big vase without cracks and delaminations!

First, I tried few experiments with slicer(KISSlicer) settings for better adhesion between layers (slightly more flow rate, slightly more hotend temp - 240C, 250C instead of 230C, very low speed - 20-30 mm/s).

Second, I tried to make simple enclosure for printer using cardboard.



Third, I tried to print model inside thin wall to make thermos effect to get uniform cooling of the plastic.



although it did not work out all the details of cracked :X



I wanted to understand why this is happening.


At high temperatures, the plastic expands when low narrows, it creates internal tension. It is necessary to calculate or determine experimentally the value of narrowing:

1) look for the coefficient of thermal expansion ABS: 73.8 * 10 ^ -6 ° C-1 ( http://temperatures.ru/pages/tempera...o_rasshireniya )
2) remember physics 6th grade ( http://goo.gl/fP6CPU )
3) calculate how much less will be the length of the extruded rod 100mm at the bed temperature of 100C and 230C of the nozzle
ΔL = a * L * Δt = 73.8 * 10 ^ -6 * 100mm * (230C - 100C) = 0,96mm - which is almost 1% of the original length.

Upon reaching room temperature, 25 ° C - it is 1,5% (ΔL = a * L * Δt = 73.8 * 10 ^ -6 * 100mm * (230C - 25C) = 1,51mm)


1% - It is very small.

--------------

Accordingly, with this small change in length of the plastic (1%) occurs corresponding to the internal pressure value of which is not too high.


The fact is, if the bonding strength is higher than the internal stresses - problem solved.


Then I tested the strength of bonding layers.
Testing methodology is simple: on the printed cylinder with 2 perimeters I evenly apply pressure with finger on the wall as long as it is not cracked between layers. By the depth pressing I detected the magnitude of the applied strength.


== Print speed affects the adhesion, but not much: I got about the same results for speeds 30-50mm/s;
== Much greater affect temperature of the extrusion: at 220C-260С I got the same bad result (plastic cracked from the slightest finger pressure), but the situation changed dramatically at temperature 270C-280C.
(Also, I have 2 different ABS filaments from different manufacturers, for the second filament I determined the optimal temperature in 260C.)


Finally, a few rules for successful work with ABS:
1) maximum heat for your particular filament (note that not all filaments are the same, they have different properties: viscosity, shrinkage, bonding and etc.)
2) the average print speed (I recommend 30-60mm/s)
3) calibrated heated bed and ABS juice for good adhesion of the first layer; ( http://www.makerbot.com/blog/2011/06...g-and-curling/ )
4) a bit of luck!


UPDATE #1
Most often china thermistors can't show you real temp of your nozzle, when you think its 250C, in real it may only be 220C(or 280C). Don't forget to fine tune your temp sensors.

[abuharsky]

At this moment I have few succeeded prints (big models up to 150mm in diameter and up to 180mm in height) at 280C without any enclosure and for some models with enabled extrusion cooling fan(!!!):


1) single perimeter, 30mm/s, 0.4 nozzle, 280C, extrusion cooling fan OFF
(top no cracks, it is because of the fact that one of the perimeter for this detail is not enough or need support)





2) 2 perimeters, 70mm/s, 0.4 nozzle, 280C, extrusion cooling fan ON (full speed)

[abuharsky]

3) Vase 185mm height, 1 perimeter, spiral mode, flow 200%, 280C, 60mm/s speed


4) Vase ~150mm x 100mm, 3 perimeters, 280C, 80mm/s, gray low cost ABS.

[AbuMaia]

Very nice results! I currently print at 240, but I'll try increasing it some more. Thanks for the helpful post.

[abuharsky]

I have successfully tested ABS from 3 different manufacturers at 280C - same result.

[gmay3]

Really cool info! I'm likely going to increase my extrusion as well. I've been printing at 225 all this time but might try 230 or 235 as a default.

[pichuete]

thanks for the info! ill try bumping up my extruder temp . in addition im having very good bed adhesion with an PEI sheet over my glass . it sticks so well that you can not even take off the printed part until it cools below 60c . and the best part is you dont need to add anything . no spray , slurry or tape .

[usarmyaircav]

thanks for the info! ill try bumping up my extruder temp . in addition im having very good bed adhesion with an PEI sheet over my glass . it sticks so well that you can not even take off the printed part until it cools below 60c . and the best part is you dont need to add anything . no spray , slurry or tape .

Pichuete, how did you attach the PEI sheet to your glass?

[pichuete]

i used 3m adhesive transfer tape 468m , its as thing as a sheet of paper and transfer heat well . they sell it in different sizes in my case i used the 0.5 in and apply but if ill do it again i would buy 1 in . to cover the glass . they also sell a 12x12 sheet of this tape but i think it will be harder to work with this thing is very sticky

[usarmyaircav]

That tape can be spendy, I will probaboy go with a 12x12 sheet and cut it down to 10x10 as that seems to be decent route with the cost being about $12 on Amazon.