1. Investigating the Impact of Acetone Vapor
Smoothing on the Strength and Elongation of
Printed ABS Parts
Dorcas Kaweesa
1
Tuesday, August 09, 2016
Harry Gao1
Dr. Jacob P. Moore2
Dr. Nicholas A. Meisel1
1Penn State, University Park; 2 Penn State, Mont Alto
2. 2
Material extruded parts have rough surfaces due to their
layer by layer nature
Low cost AM systems are
prone to having rough
surface finishes
3. 3D printed parts are inherently anisotropic due to the
variations of material properties along the printed layers
3
Researchers show that different build orientation leads to variations
of material properties along or across the printed layers.
Ashtankar, et al 2013 The 0° samples were 31% and 15% stronger in tension
and compression respectively than the 90° samples
4. Hobbyists have looked into several post treatment
processes to mitigate surface roughness
4
Acetone vapor smoothing improves the
surface finish of ABS printed parts by
coherently diffusing the surface layers
Hot vapor treatment
Cold vapor treatment
5. Researchers have looked into the relationship between
treatment and the build orientation of the printed parts
5
• Surface quality depends on the
chemical reaction of acetone vapor
with the ABS material
Garg, et al. 2015
Chapman, et al. 2014
6. Surface roughness is also visible with sharp curves and
corners hence stress concentrations
6
• Stair stepping
increases with more
macro level stress
concentrations
• Can acetone vapor smoothing account for
the increased surface roughness caused
by macro level stress concentrations?
7. Research Question # 1
Considering build orientation and layer height, what
impact does acetone vapor have on the mechanical
properties of ABS printed parts?
7
Research Question #2
How can the use of acetone vapor address the issue
of stair stepping in highly curved regions with stress
concentrations?
8. A design of experiments approach was used to determine the
significance of specific parameters on strength and elongation
8
Orientations Layer Heights (mm) Treatment times (hrs)
XY 0.2 0
ZX 0.3 1
YZ 0.4 2
• Lulzbot TAZ 5 Printer• Specimen: ASTM D638-14 Type IV
9. 9
The significance of different build orientations was to
investigate the effect of pulling along layers as opposed to
across the print fibers
• Orientation
XY ZX YZ
• Layer heights were varied
to investigate the effects of
acetone vapor with
increasing layer heights
10. Cold acetone vapor treatment was used since it
provides more consistency and quality surface finish
10
Acetone vapor treatment times
were varied for 0 hours (no
exposure), 1 hour, and 2 hours
Specimens showing various treatment times and orientations: a) XY 0hr
and 1hr, b) ZX 0hr and 2hr, and c) YZ 1hr and 2hr.
(a) (b) (c)
11. All printed specimens were tested for mechanical
properties a minimum of 24 hours after the acetone
vapor treatment process
11
• Instron 5866 Machine
• Extensometer with a gauge
length of 25mm
• 5.08mm/min on a 1kN load
cell
12. The Kruskal-Wallis H test was utilized as a non-
parametric analysis of variance to determine significance
12
Parameter Strength p-value Elongation p-value
Orientation < 0.001 < 0.001
Treatment Time 0.092 0.183
Layer Height 0.717 0.454
• The test was used to determine if there was a statistically significant
difference in two or more groups of an independent variable on a
continuous dependent variable.
13. Tensile strength decreased in specimens printed in the
XY and YZ orientations as treatment time increased
13
14. The elongation at failure of the specimens in the XY
and YZ orientations shows a generally increasing trend
14
15. Preliminary testing investigated the effect of acetone
vapor in the presence of stress concentrations
15
Specimens used to investigate stress concentration showing various
acetone vapor treatment times: a) no exposure, b) 1hr, and c) 2hr.
(a) (b) (c)
16. The tensile strength was affected by the delamination
between the layers
16
0
2
4
6
8
10
12
14
0 0.5 1 1.5 2 2.5
Strength(MPa)
Smoothing time (hr)
Stress Concentration
No Stress Concentration
Delamination of layers
largely effect the specimen’s
ultimate tensile strength
17. The behavior of the specimens in relation to elongation
at failure is driven by delamination between the layers
17
0
0.5
1
1.5
2
2.5
0 0.5 1 1.5 2 2.5
Elongation(%)
Smoothing time (hr)
Stress Concentration
No Stress Concentration
Macro- scale stress
concentrations due to the
geometry affected the
specimens’ elongation at failure
18. By treating with acetone vapor and performing
tensile tests, we can conclude that:
• Layer thickness does not have any statistical
significance on the mechanical properties
for both treated and non-treated specimens
• Mechanical properties are significantly
affected in the XY and YZ orientations by the
duration of acetone vapor treatment
• There is no impact of acetone vapor for
specimens in the ZX orientation due to
delamination between the layers
18
19. Investigating the Impact of Acetone Vapor
Smoothing on the Strength and Elongation of
Printed ABS Parts
Dorcas Kaweesa
19
Tuesday, August 09, 2016
dvk5404@psu.edu
503-927-2612
Thank you!
Questions?
Editor's Notes
Talk about how parts printed off of low cost machines are prone to having rough surface finishes
Since the low cost machines produce 3D printed parts with rough surfaces, the parts also exhibit large amounts of material anisotropy.
Existing research has explored the effects of material anisotropy and build orientations on the mechanical properties of AM processes. This research in particular (referring to Ashtankar) studied the tensile and compressive strengths of ABS material extrusion parts with different print angles. 0 deg for XY orientation and 90 deg for ZX orientation. They found out that the 0 deg samples were 31% stronger in tension and 15% stronger in compression. This matches our intuition that for parts printed in the XY orientation, the load applied pulls across the fibers (parallel to the print layers) to overcome the strength of the material itself. We also know by intuition, that for the parts printed in the ZX orientation, the load applied pulls along the layers (perpendicular to the print layers) to overcome the bonds between the layers.
Having different build strategies or build parts in different orientations can result in different material and mechanical property variations depending on the individual part layers printed
One way to address the surface roughness inherent in material extrusion systems is using post treatment processes like acetone vapor smoothing
Acetone vapor smoothing offers potential solutions to the problems we face with surface roughness on 3D printed parts. Generally, there is a hot vapor treatment version where by (describe the process) and there is cold vapor treatment version where by (describe the process).
Hot vapor treatment
-Involves heating the jar so that the acetone evaporates
Researchers have also looked into different forms of acetone vapor treatment in relation to the orientation of 3D printed parts specifically with ABS material.
This research in particular (referring to Chapman) compared hot vapor treated and non-treated printed ABS parts and found that the hot vapor treated parts had a slight reduction in the tensile strength but an improved strain and toughness due to elongation.
Garg’s study describes the difference between hot and cold vapor treatments as well as the method of dipping the part in a lukewarm acetone solution.
Both studies noted that the hot vapor treatment was difficult to control in terms of acetone concentration. For the second research, dipping the part in lukewarm acetone solution could easily damage the part, giving an unevenly smoothed surface. Treatment time was mentioned as especially important for the best results for surface finishes.
Surface roughness is visible in regions of sharp corners hence stress concentrations (Which are also highly dependent on build parameters especially orientation and layer height)
Macro level stress concentrations – are stress concentrations caused by the part’s geometry (notches)
Micro level stress concentrations – are stress concentrations caused by the layers
Bigger gap between the layers (macro curves) hence a bigger stress concentrations
Stair stepping increases with more macro level stress concentrations. With that, acetone vapor may be able to address some the additional stair stepping that comes as a result of the stress concentrations
A valid question to ask then is that (We are trying to see, “can acetone vapor smoothing account for the increased surface roughness caused by macro level stress concentrations?”
1. What is the impact of acetone vapor smoothing on the mechanical properties considering orientation and layer height(thickness)?
2. How can acetone vapor smoothing address stair stepping in highly curved regions with stress concentrations?
Taguchi methods- DoE
A model of the specimen was designed and printed according to ASTM standard for tensile testing after post treatment processing. Specimens were printed on the Lulzbot TAZ 5 with 100% infill to maximize part strength and match the bulk properties of ABS material.
Table:- This is overview of the parameters used to answer the research questions
***With the different orientations, we are specifically looking at the ZX orientation to investigate the effect of pulling across the printed layers as opposed to pulling along the part fibers (X and Y orientations)
***With the different layer heights, we are trying to see whether the faster prints with the larger layer heights and rougher surfaces can be fixed by smoothing
Larger (rougher) layers (0.4mm)- faster print
Smaller layers (0.2mm) – slower print
Flat block covered with aluminum foil supported the specimens being treated
Acetone-soaked paper towels helped trap acetone vapor in the container
A p-value of 0.05 or lower implied statistical significance thus the Kruskal Wallis H test showed that there was a statistically significant difference in the tensile strength and elongation at failure in the different orientations (highlight red).
Tensile strength shows a statistically significant difference for treatment time at a p-value of 0.1 (highlight orange)
There was no statistically significant difference in the tensile strength and elongation at failure between the different layer heights (no highlight)
From the Kruskal Wallis H test, since we found out the layer height was not statistically significant, the layer height was held constant at 0.4mm for another set of experimentation and the results were analyzed for further investigation.
This graph shows that as the treatment time increases, when the fibers of the printed specimens are being pulled in the XY and YZ orientations, they weaken.
That is why the tensile strength decreases almost similarly for the specimens printed in the XY and YZ orientations.
Another aspect we were trying to investigate was that by pulling the layers apart as in the ZX orientation, is there an increase in the cohesion between the layers due to acetone vapor smoothing? We found out that the tensile strength almost stays the same (constant) and acetone vapor smoothing does not really play a role in increasing cohesion between the layers.
The key trends regarding the elongation at failure, there is minimal change for layers being pulled across in the ZX orientations where as with pulling across the fibers for the XY and YZ orientations, there is a drastic change; an increase in the elongation.
****For some reason, there is an uncertainty in the downward trend and a large standard deviation in the XY orientation after 1 hour of acetone vapor treatment.
Earlier on, I mentioned the idea of surface roughness and that when we have parts with curved surfaces, we observe increased stair stepping and stress concentrations. With that in mind, we wanted to investigate and analyze the effect that acetone vapor treatment would have on the behavior of this highly curved geometries.
For this investigation, a new tensile specimen, which we referred to as the stress concentration specimen was designed in the ZX orientation with a curved notch and a constant layer height of 0.4 mm as shown. This was to show a significant amount of surface roughness that would develop upon printing.
All procedures for acetone vapor treatment and tensile testing stayed the same and the results for these new stress concentrations specimens were compared with the previous non-stress concentrations specimens
This graph represents the tensile strength of the specimens at different smoothing times. It clearly shows by the line highlighted in red that with the curved geometry, there is minimal effect of the acetone vapor on to the tensile strength.
After 2 hours of acetone vapor treatment, there was an indiscernible difference in the tensile strength due to the delamination of the layers
The elongation at failure show statistical significance but the difference is less than half a percent between the parts with curved geometry and the non-curved geometry so the magnitude is basically the same.
There is a slight increase in the elongation but only to a minimal degree. It seems like the acetone vapor does not fully permeate through the layers causing delamination
The macro level stress concentrations caused by the part’s geometry and the curved notches were in part responsible for the elongation
Micro level stress concentrations – are stress concentrations caused by the layers
I would like to remind you that at the beginning, the main goal for this research was to investigate what impact acetone vapor has the mechanical and material properties of printed parts. Based on our findings, we can point out that
Layer thickness has no statistical significance on the specimen’s mechanical properties
Mechanical properties of specimens highly rely and are affected by the length of acetone vapor treatment
Since the acetone vapor does not fully permeate far enough, the material properties are not change and acetone vapor has no effect for the ZX orientated specimens. This also applies to the stress concentration specimens whereby as long as there is no process that allows for full permeation of acetone into the layers, the ZX orientation will not be affected by acetone vapor.
