Assessing Particulate and Chemical Emissions from Additive Manufacturing Processes
Abstract No:
1727
Abstract Type:
Student Poster
Authors:
N Gander1, T Reponen1, S Grinshpun1
Institutions:
1University of Cincinnati, Cincinnati, OH
Presenter:
Nathan Gander
University of Cincinnati
University of Cincinnati
Faculty Advisor(s):
Dr. Tiina Reponen, PhD
University of Cincinnati
University of Cincinnati
Dr. Sergey Grinshpun, PhD
University of Cincinnati
University of Cincinnati
Description:
The aim of this study was to assess the concentrations of airborne fine particles and volatile organic compounds (VOCs) emitted from the printing process at the Digital Fabrication Laboratory (DFL) in the College of Engineering and Applied Sciences of the University of Cincinnati. The study was limited to two locations within the building which included the teaching lab and plastic printing lab. One type of printer was used in the teaching lab and four types of printers were used in the plastic printing lab.
Situation/Problem:
Additive manufacturing (AM) is a rapidly emerging manufacturing technology. Rather than removing materials (in subtractive manufacturing (SM)), AM processes develop three-dimensional parts (both small and large) from Computer Aided Design (CAD) models. This process offers the beneficial ability to build parts with geometric and material complexities that could not be produced by alternative processes, such as SM (Guo & Leu, 2013).
AM technology is a subject of concern to occupational health researchers and industrial hygienists due to the potentially harmful gases and fumes that are emitted during the printing process. Thermal treatment and additive manufacturing of plastic materials are known to cause decomposition of the material, enabling the emissions VOCs and fine particles (Väisänen, 2019). Exposure to these agents may cause sensitization, irritation, and inflammatory effects on the skin, lungs, mucous membranes, and vital organs (Väisänen, 2019).
AM technology has made the process of machining small parts almost effortless in comparison to utilizing metal/plastic lathes. However, the introduction of new techniques often entails uncertainties regarding operator safety (Graff, 2016). The overwhelming amount of unknown health factors attributed to the AM process has led occupational health researchers to further analyze these potentially harmful exposures associated with this process.
There are no current health standards that apply to AM technology. However, it is feasible for one to compare the results obtained from the printing process to the background measurements taken prior to the start of printing. This shows how much the printing operation increases the level of air contaminants.
The lab director of the College of Engineering and Applied Sciences (CEAS) at the University of Cincinnati was concerned about the emissions from the various types of printers within the facility. The data collected from this study will not only provide further insight into what is being emitted into the air during the printing process but will also help in prioritizing the forthcoming control measures between the different printers.
AM technology is a subject of concern to occupational health researchers and industrial hygienists due to the potentially harmful gases and fumes that are emitted during the printing process. Thermal treatment and additive manufacturing of plastic materials are known to cause decomposition of the material, enabling the emissions VOCs and fine particles (Väisänen, 2019). Exposure to these agents may cause sensitization, irritation, and inflammatory effects on the skin, lungs, mucous membranes, and vital organs (Väisänen, 2019).
AM technology has made the process of machining small parts almost effortless in comparison to utilizing metal/plastic lathes. However, the introduction of new techniques often entails uncertainties regarding operator safety (Graff, 2016). The overwhelming amount of unknown health factors attributed to the AM process has led occupational health researchers to further analyze these potentially harmful exposures associated with this process.
There are no current health standards that apply to AM technology. However, it is feasible for one to compare the results obtained from the printing process to the background measurements taken prior to the start of printing. This shows how much the printing operation increases the level of air contaminants.
The lab director of the College of Engineering and Applied Sciences (CEAS) at the University of Cincinnati was concerned about the emissions from the various types of printers within the facility. The data collected from this study will not only provide further insight into what is being emitted into the air during the printing process but will also help in prioritizing the forthcoming control measures between the different printers.
Methods:
Air monitoring was conducted in two separate locations in the CEAS at the University of Cincinnati. The first location was the teaching lab, which functioned as a space for students to operate the 22 desktop extruders under the supervision of the course instructor. The second location was the plastic printing lab, which functioned as a space for the lab director and student workers to print various types of plastic objects/figures for academic purposes. In the plastic printing lab, two printers (Polyjet and Projet) were studied with and without their respective controls. Monitoring consisted of two phases: in the first phase, air monitoring was conducted WITHOUT the control, whereas in the second phase, air monitoring was conducted WITH the control. The controls in this study were limited to two HEPA air cleaners and individualized sources of local exhaust ventilation. The type of control was dependent on the location.
For each phase, air monitoring at each location took approximately three hours to complete. There was a 30-minute background monitoring, a 2-hour monitoring while printing, and a 30-minute post-monitoring. Stationary monitoring was conducted using a P-Trak and PPBRae, which were placed side-by-side on a rolling cart. The cart was placed as close as possible to the printer operator. Throughout the process, there was a mobile P-Trak that was used to obtain the spatial distribution of particles throughout the printing process. It was relocated every five minutes to allow for a more representative sample to be taken of the entire room.
The face velocity of each laboratory hood was measured with a thermoanemometer. Ventilation measurements were performed for each of the return and supply air vents by using a ventilation hood. Prior to measuring the air flow with the ventilation hood, a smoke tube was utilized to determine whether each room was under positive or negative pressure.
The data were analyzed using Microsoft Excel. The following comparisons were included: background vs. printing process without control, background vs. printing process with the control, and printing process without the control vs. with the control. The results from this analysis had determined whether there were significant increases in concentrations for fine particles and VOCs.
For each phase, air monitoring at each location took approximately three hours to complete. There was a 30-minute background monitoring, a 2-hour monitoring while printing, and a 30-minute post-monitoring. Stationary monitoring was conducted using a P-Trak and PPBRae, which were placed side-by-side on a rolling cart. The cart was placed as close as possible to the printer operator. Throughout the process, there was a mobile P-Trak that was used to obtain the spatial distribution of particles throughout the printing process. It was relocated every five minutes to allow for a more representative sample to be taken of the entire room.
The face velocity of each laboratory hood was measured with a thermoanemometer. Ventilation measurements were performed for each of the return and supply air vents by using a ventilation hood. Prior to measuring the air flow with the ventilation hood, a smoke tube was utilized to determine whether each room was under positive or negative pressure.
The data were analyzed using Microsoft Excel. The following comparisons were included: background vs. printing process without control, background vs. printing process with the control, and printing process without the control vs. with the control. The results from this analysis had determined whether there were significant increases in concentrations for fine particles and VOCs.
Results / Conclusions:
The preliminary results show that VOC concentrations in the teaching lab, including background, printing, and post-printing, were as follows (average ± standard deviation): 802 ± 386 ppb for HEPA air cleaners OFF, 404 ± 60 ppb for HEPA air cleaners ON at 50 CFM, and 318 ± 46 ppb for HEPA air cleaners ON at 700 CFM. The respective range of VOC concentrations was from 0 to 2,649 ppb when the HEPA air cleaners were off. The concentrations ranged from 266 to 496 ppb when the HEPA air cleaners were on the LOW setting (50 CFM) and from 252 to 416 ppb when the HEPA air cleaners were on the HIGH setting (700 CFM). The VOC concentrations were 2.3 times higher during printing compared to background when the HEPA air cleaners were off. During printing, VOC concentrations decreased to almost half with the implementation of the HEPA air cleaners (on the LOW setting) compared to the experiment without the HEPA air cleaners. At the HIGH setting, these concentrations decreased even further, being close to the background levels. The maximum VOC concentration was 2,649 ppb when the HEPA air cleaners were turned off. This peak occurred 25 minutes after the printing had started.
The fine particle concentrations spiked approximately 47 minutes after the printing had started. These peaks reached as high as 5,680 particles/cc.
In the plastic printing lab, the average ± standard deviation of VOC concentrations was as follows: 779 ± 420 ppb for Polyjet with NO control, 707 ± 460 ppb for Polyjet WITH control, 881 ± 532 ppb for Projet with NO control, and 1,222 ± 819 ppb for Projet WITH control. The average VOC concentrations from the Polyjet were slightly lower with the control (707 ppb) in comparison to without the control (779 ppb). From the Projet, the VOC concentrations were slightly higher with the control (1,222 ppb) in comparison to without the control (881 ppb). The most discernible peak from the Polyjet occurred approximately 2 hours and 15 minutes into printing when the VOC concentrations reached approximately 2,500 ppb. The highest peak from the Projet was seen 3 hours into the printing process, with a value of approximately 4,500 ppb. Furthermore, the VOC concentrations were quite high when all the printers were running simultaneously in comparison to the other tests.
The fine particle concentrations varied between approximately 500 and 6,000 particles/cc. The most notable peak was seen approximately 27 minutes after all four types of printers had started.
In conclusion, the HEPA air cleaners in the teaching lab proved to be effective in reducing the overall concentrations of VOCs. The experiments in the plastic printing lab showed increased VOC concentrations with the controls than without them. Therefore, the local exhaust ventilation in the plastic printing lab requires further evaluation before improvements can be recommended to improve its efficiency.
The fine particle concentrations spiked approximately 47 minutes after the printing had started. These peaks reached as high as 5,680 particles/cc.
In the plastic printing lab, the average ± standard deviation of VOC concentrations was as follows: 779 ± 420 ppb for Polyjet with NO control, 707 ± 460 ppb for Polyjet WITH control, 881 ± 532 ppb for Projet with NO control, and 1,222 ± 819 ppb for Projet WITH control. The average VOC concentrations from the Polyjet were slightly lower with the control (707 ppb) in comparison to without the control (779 ppb). From the Projet, the VOC concentrations were slightly higher with the control (1,222 ppb) in comparison to without the control (881 ppb). The most discernible peak from the Polyjet occurred approximately 2 hours and 15 minutes into printing when the VOC concentrations reached approximately 2,500 ppb. The highest peak from the Projet was seen 3 hours into the printing process, with a value of approximately 4,500 ppb. Furthermore, the VOC concentrations were quite high when all the printers were running simultaneously in comparison to the other tests.
The fine particle concentrations varied between approximately 500 and 6,000 particles/cc. The most notable peak was seen approximately 27 minutes after all four types of printers had started.
In conclusion, the HEPA air cleaners in the teaching lab proved to be effective in reducing the overall concentrations of VOCs. The experiments in the plastic printing lab showed increased VOC concentrations with the controls than without them. Therefore, the local exhaust ventilation in the plastic printing lab requires further evaluation before improvements can be recommended to improve its efficiency.
Primary Topic:
Engineering Controls and Ventilation
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Acknowledgements and References
List any additional people who worked on the project or provided guidance and support along with details on the role they played in the research. (Please include first name, last name, organization, city, state and country).
Graff, P., Ståhlbom, B., Nordenberg, E., Graichen, A., Johansson, P. & Karlsson, H. “Evaluating Measuring Techniques for Occupational Exposure during Additive Manufacturing of Metals: A Pilot Study.” Journal of Industrial Ecology, vol. 21, no. S1, 2016, doi:10.1111/jiec.12498.
Guo, N. & Leu, M.C. “Additive Manufacturing: Technology, Applications and Research Needs.” Frontiers of Mechanical Engineering, vol. 8, no. 3, 23 Jan. 2013, pp. 215–243., doi:10.1007/s11465-013-0248-8.
Väisänen, A.J.K., Hyttinen, M., Ylönen, S. & Alonen, L. “Occupational Exposure to Gaseous and Particulate Contaminants Originating from Additive Manufacturing of Liquid, Powdered, and Filament Plastic Materials and Related Post-Processes.” Journal of Occupational and Environmental Hygiene, vol. 16, no. 3, 21 Mar. 2019, pp. 258–271., doi:10.1080/15459624.2018.1557784.
Practical Application
How will this help advance the science of IH/OH?
Furthermore, the proposed study will help identify critical knowledge gaps (regarding uncertainties in assessing printer operator exposures) that exist among the printing machines within the confines of the CEAS campus at the University of Cincinnati. This is expected to benefit the DFL team as they can use the study findings to promote engineering and administrative controls in this environment. Successful completion of this study will also provide general recommendations that will allow professionals to further combat the potentially harmful exposures associated with the AM processes throughout a variety of applicable settings.