The impact of manufacturing parameters on submicron particle emissions from a desktop 3D printer in the perspective of emission reduction

Abstract

Multiple studies have been dedicated to particle emissions from three dimensional printer (3D printer). They collectively have shown that 3D printers will emit significant ultrafine particles during their printing processes. An important step forward is to investigate the printing process in detail and help reducing emissions. This study investigates particle emissions from two filaments of acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) according to four steps (loading, heating, printing, and unloading) during the 3D printing process in constraint of product quality assessment. The results show that ABS filament triggers at least times higher particle emissions than PLA filament (ABS-printed product presents higher quality with higher nozzle temperature (240 °C); however, higher nozzle temperature triggers substantially higher particle emission. This study further identifies that the particle emissions are mostly triggered by the heating process rather than the printing process. It indicates that filament undergoes decomposition during the heating period after being loading into the extruder. As for product quality in terms of surface roughness and production deformation, ABS is not compatible to fast neither printing speed nor low nozzle temperature; the PLA filament exhibits significant tolerance to temperature and feed rate changes. An optimization, which is externally heating up both the extruder and platform before the filament is loaded, shows that pre-heating reduces particle emissions by 75% for ABS filament when compared with the conventional procedure.

Full text

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The impact of manufacturing parameters on submicron
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particle emissions from a desktop 3D printer in the
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perspective of emission reduction
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Yelin Deng1†, Shijie Cao2*†, Ailu Chen3, Yansong Guo4
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1: Department of Mechanical Engineering, University of Wisconsin-Milwaukee, WI, the United
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States, 53211
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2Department of Civil and Environmental Engineering, Soochow University, Suzhou, China, 215131
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†: The two authors declare equal contributions
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3SinBerBEST Program, Berkeley Education Alliance for Research in Singapore
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4Department of Mechanical Engineering, KU Leuven, Heverlee, Belgium, 3001.
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*: Correspondence author: shijie.cao@suda.edu.cn
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Tel: +86(0)512-67501742, Fax: +86(0)512-67601052
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Abstract
13
Multiple studies have been dedicated to particle emissions from three dimensional printer (3D
14
printer). They collectively have shown that 3D printers will emit significant ultrafine particles
15
during their printing processes. An important step forward is to investigate the printing process in
16
detail and help reducing emissions. This study investigates particle emissions from two filaments of
17
acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) according to four steps (loading,
18
heating, printing, and unloading) during the 3D printing process in constraint of product quality
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assessment. The results show that ABS filament triggers at least times higher particle emissions
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than PLA filament (ABS-printed product presents higher quality with higher nozzle temperature
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(240oC); however, higher nozzle temperature triggers substantially higher particle emission. This
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study further identifies that the particle emissions are mostly triggered by the heating process rather
23
than the printing process. It indicates that filament undergoes decomposition during the heating
24
period after being loading into the extruder. As for product quality in terms of surface roughness
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and production deformation, ABS is not compatible to fast neither printing speed nor low nozzle
26
temperature; the PLA filament exhibits significant tolerance to temperature and feed rate changes.
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An optimization, which is externally heating up both the extruder and platform before the filament
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is loaded, shows that pre-heating reduces particle emissions by 75% for ABS filament when
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compared with the conventional procedure.
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Keywords: 3D printer; particle emission; ABS; PLA; pre-heating; particle emission reduction
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Introduction
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Desktop three dimensional printers (in short for 3D printers thereafter) are increasingly gaining
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popularity [1]. From the perspective of manufacturing technology, 3D printing belongs to rapid
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prototype manufacturing process allowing producing objects without die as needed in traditional
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manufacturing process. Thus, desktop 3D printer can manufacture customized products at regular
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home or in office environment.
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In compatible with the home and office conditions, materials required by these desktop 3D printers
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are generally thermoplastics, which can be processed at relatively moderate temperature and
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pressure [2]. A wide variety of materials can be used for filaments including acrylonitrile butadiene
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styrene (ABS), polylactic acid (PLA), polyvinyl alcohol (PVC), nylon, and other polymers. Among
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these thermoplastics, ABS and PLA are the most popular filament materials [3]. Since 3D printers
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are projected to enter people’s daily lives, environmental and health risks posed by these filaments
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during the printing process are now drawing attentions from researchers [3-7]. Researchers are
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currently interested to know whether the printing process, in particular, the fused deposition
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moulding (FDM), contributes to particle and organic carbon emissions. Several studies have been
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dedicated to this topic. The first study from Stephens et al. have shown that commercial 3D printers
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resulted in emissions of ultrafine particles (UFP) in the range of 11.5nm and 116nm and ABS
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filament triggered approximately 10 times higher emission rate than the PLA filament (~1.9 ×1011
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particles min-1 versus ~2.0 ×1010 particles min-1) [4]. Kim et al. found that ABS and PLA filaments
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emitted particles of 10-420 nm with most of the particles smaller than 100 nm. They also found that
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the ABS filament led to 33-38 times higher emission rate than the PLA filament [5]. The most
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recent study on this subject by Azimi et al. determined that total emissions of UFP (less than 100nm)
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were 108~1011 particles min-1 from various commercially available filaments (ABS, PLA, nylon,
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high impact polystyrene, laybrick, laywood, polycarbonate, transparent polyester resin filament and
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nylon-based plasticized copolyamide) [3]. These studies collectively agree on the presence of
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intense UFP emissions from the 3D printing process. UFP may pose significant health concern
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since they can easily accumulate in the pulmonary and alveolar regions of human lung [8], and may
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filtrate into the brain via olfactory nerve [9]. Multiple studies have shown that elevation of UFP
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concentration is associated with adverse health effects such as asthma symptoms [10,11].
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Prior studies have widely observed and characterized particle generation from 3D printers. Another
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important aspect is to identify solutions to reduce the particle emissions in terms of printer design
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and printing process. However, there still lacks studies revealing detailed mechanism of particle
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emissions. FDM is a commonly applied printing technology. The entire FDM based printing
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process can be decomposed into four steps. Firstly, the extruder is heated and filament is loaded into
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the extruder. Then, the extruder and bed platform are heated to the required nozzle and platform
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temperatures. Subsequently, the filament is extruded through the heated nozzle, melted and
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deposited at certain feed rate on the platform. When a product is finished, filament is unloaded from
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the extruder. Different filament materials require different processing windows of parameters
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(nozzle temperature, feed rate speed, plate temperature, and etc.) to obtain good quality products
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(e.g. surface roughness). On the other hand, these parameters may also exert substantial effects on
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the particle emissions.
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Therefore, this study aims to advance current knowledge by concentrating on correlations of
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particle emissions over the four stages of a 3D printing procedure. It investigates the mechanisms of
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particle generation and roles played by manufacturing parameters. It further proposes strategies to
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reduce particle emissions under the constraint of product quality. Findings of the current study
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would provide guidelines to optimize parameter settings achieving lower particle emissions without
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compromising product quality.
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Method
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The general methodology of this study is depicted in Figure 1. Firstly, it assesses impacts of
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different parameters combinations (nozzle temperature and feed rate) on particle emissions in a
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clean room with the same filament material.
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Figure 1 Methodology on particle emission and reduction for 3D printing process
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Secondly, the study decomposes the particle emissions according to each 3D manufacturing step.
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Thirdly, quality of the 3D printed products are evaluated and influences of printing parameters on
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particle emissions are revealed. Finally, based on the identified particle generation mechanism,
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solutions for particle emission reduction are proposed.
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Testing model and environment
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Measurements were conducted in an 8 m3 clean room (4m ×2m ×1m). The tested 3D printer was
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Product quality
assessment
Parameter influence
assessment and
optimization
Change in parameters
within suggestion range
Particle emission
decomposition
1
2
3
4

5
placed on a table in the clean room, 0.3 m above the floor (shown in Figure 2). For all tests, a so-
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called “make-robot” design, as shown in Figure 2a was used as the printed object. This design has a
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length of 29mm and a width of 26 mm. It is widely used in the 3D printing community as a
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standardized product design for performance comparison [5]. It has a range of features that are
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thought to potentially influence dynamic printer emissions such as solid volume, thin protrusions,
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overhang, and indentations. Figure 2b depicts the testing facility and environment. The testing
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facility contained two rooms: the clean room and monitor room, which were isolated by a separator.
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The 3D printer was connected to a condensed particle counter (CPC, Model 3776, TSI Incorporated,
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Shoreview, MN, U.S.A) outside of the clean room. Moreover, we fixed the sampling site at the
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source throughout the whole measuring process which was sufficient to reveal particle emissions of
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the printer. The CPC measured total number concentrations of particles in the size range of 2.5 nm-
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1 𝜇m. It had a reported maximum concentration of 3 x 106 particles cm-3 at a sample flow rate of 1.5
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L min-1. The CPC was placed inside the monitor room rather than the clean room. This could avoid
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particle emissions from human and minimize particle resuspension that may result in noises to
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particle concentrations inside the clean room. Meanwhile, the configuration was to reduce direct
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exposure to potential toxic emissions. The environment in the clean room was well regulated.
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Ambient temperature varied slightly between 26.5oC and 28oC. Relative humidity level in the clean
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room fluctuated a little more widely from 33%-40%. These ambient parameters generally presented
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good degree of uniformity during the period of measurements. The ventilation system in the clean
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room contained two fans: one located at top of the ceiling and the other fan located at back wall.
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When the fans were switched on, ventilation rate for this clean room was 60 h-1. When the
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ventilation system was off, the ventilation rate inside the cleanroom, which was approximately 0.1
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h−1, quantified by tracer gas decay method using carbon dioxide as the tracer gas.
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a. Printed object b. A simple diagram showing the air sampling set-up
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Figure 2 3D printing model and testing environment.
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Air sampling and analysis
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The CPC continuously monitored particle concentrations emitted by the 3D printer at time intervals
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of three seconds. Particle concentrations were measured during the entire printing process marked
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by key printing steps of filament loading, heating, printing, and filament unloading. The CPC was
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set at no dilution mode during the entire printing process. Sampling is directly fixed on top of the
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3D printer close to the extruder aiming to obtain the particle concentration immediately from the
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source. The measurements have been carefully monitored in response to the key steps during 3D
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printing:
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1. Measurement of background particle concentration in the clean room: Firstly, the ventilation
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system was operated for a time period to purge out background contaminants from the clean room.
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The purging would not terminate if the particle concentration was higher than a pre-determined
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level (<5 # cm-3). After the purging stopped, the CPC continued to monitor the background particle
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concentration for 10 mins and no increasing in particle concentration should be found.
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2. Monitoring of particle concentrations in the printing process: The whole printing process could
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be described with the successive steps of filament loading, heating, printing, and filament unloading.
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26mm
29mm
CPC
3D printer
Clean room Monitor room
Fan
Fan
Separator

7
The filament loading started with extruder heating until melting point of the filament was achieved
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(e.g., 220oC nozzle temperature and 110oC platform temperature for ABS filament). The filament
133
was then loaded into the extruder for subsequent printing. The heating process heated up
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temperatures of the extruder and platform according to the specific filament materials. Its duration
135
was mainly determined by the needed platform temperature. Once the temperature was achieved,
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printing was triggered according to the predefined feed rate. After finishing, the filament was
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removed through the unloading process.
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3. Removal of particles from the clean room: Researchers switched on the ventilation system to
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remove particles from the clean room when the printing process was completed. The 3D printer was
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set to be in off mode to restore nozzle temperature, platform temperature and clean room
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environment conditions before the next experiment.
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4. Evaluation of the printed objects by inspection of their quality: The quality check could identify
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defects on product surface, short shot, surface roughness, and deformation.
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Printer and filament
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The study was taken under one of the best-selling 3D printer model, FlashForge Creator dual
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extruder 3D printer. This 3D printer is compatible with ABS and PLA filaments (both were tested).
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All filaments were supplied in a diameter of 1.66mm. The filaments could be differentiated by
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color: red for ABS and black for PLA. Filament pools were mounted at back of the 3D printer
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machine and passing through a tube to guide filament feeding during printing. The ReplicatorG
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software (Sailfish, v2.0) was used to generate printing code for 3D printing operation [12]. The
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nozzle temperature and feed rate were changed according to the baseline setting specific to the
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filament material. For ABS materials, the baseline configuration was set at 220oC nozzle
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temperature and 60 mm s-1 feed rate according to the printing guideline [13]. The platform
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temperature was 110oC. It should be noted that for a specific filament, the platform temperature
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cannot be freely changed. It is determined according to shrinkage of the filament material. For
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material with higher level of shrinkage in cooling such as ABS (8 vol% shrinkage when cooling), a
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sufficient platform temperature is essential to avoid severe deformation [14,15]. In the study, the
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platform temperature was maintained at 110oC, which was a minimal platform temperature to
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ensure a successful printing while higher platform temperature was not attainable under the power
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of the 3D printer with current environmental setting. For the nozzle temperature, a recommended
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value was 220oC from the manufacture and possible processing variations were set for 200 and
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240oC. Subsequently, the influences of feed rate were studied by changing the baseline feed rate of
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60 mm s-1 to 30 mm s-1 and 90 mm s-1, respectively. Similar approach was also implemented on
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PLA material. The baseline setting of PLA was 200oC and 60 mm s-1, the platform temperature was
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60oC due to its much less shrinkage level. Variations on nozzle temperature include changing the
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baseline temperature to 180oC or 220oC, whereas alternative feed rates for PLA printing was set to
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be the same with the ABS printing process. The terminology for the experiment was set as tabulated
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in Table 1.
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Table 1. Summary of the experimental conditions and labels.
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Material
platform
temperature (oC)
Travel rate
(mm/s)*
Nozzle
temperature (oC)
Feed rate
(mm/s)
Label
ABS
110
80
200
60
ABST200FR60
ABS
220
60
ABST220FR60
ABS
240
60
ABST240FR60
ABS
220
30
ABST220FR30
ABS
220
60
ABST220FR60
ABS
220
90
ABST220FR90
PLA
60
120
180
60
PLAT180FR60
PLA
200
60
PLAT200FR60
PLA
220
60
PLAT220FR60
PLA
200
30
PLAT200FR30
PLA
200
60
PLAT200FR60
PLA
200
90
PLAT200FR60
Notes: T and FR respectively corresponds to temperature and feeding rate, e.g.,” ABST200FR60” : printing with ABS
171
materials under baseline temperature of 200 oC and feeding rate of 60 mm s-1;*
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Results
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ABS particle emissions
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Figure 3 presents time-resolved particle emissions from the 3D printer when nozzle temperatures
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and feed rates varied. For the purpose of providing a high resolution on each printing step, we do
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not depict the entire long period of background measurement. Figure 3a shows particle emissions
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when the nozzle temperature had different setting with constant feed rate while Figure 3b depicts
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particle emissions when feed rates were changed at a fixed nozzle temperature of 220oC. The first
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dotted line at the beginning indicates the background particle concentration measurements. Firstly, a
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small particle peak present in in each graph panel during the filament loading process. The printer
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was repositioned to printing preparation and started heating after finishing filament loading. As
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temperature approaching the predetermined value, particle concentration was increasing up to a
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level of ~105 # cm-3 when nozzle temperature was set at 240oC (Figure 3a). When the required
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temperatures were achieved, printing started and concentration started to fall. For example, the
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emission decreased from 20000 # cm-3 to 10000 # cm-3 in the case of 240oC nozzle temperature.
186
After finishing, unloading would generate emission peaks. Figure 3a clearly demonstrates the
187
significant impact of nozzle temperature on particle generation. The concentration in order of 103 #
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cm-3, recorded for 200oC nozzle temperature dramatically increased to 104 # cm-3 at 240oC.
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a, Influences of nozzle temperature on ABS particle emissions
b. Influence of feed rate on ABS particle emissions
Figure 3. Influence of manufacturing parameters on ABS particle emissions of 3d printer
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The influence due to the feed rate, shown in Figure 3b, presents similar pattern as Figure 3a. For
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instance, emission concentrations started falling when printing was initiated. However, the middle
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level feed rate of 60 mm s-1 contributed the most significant level of particle emission while the
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30mm s-1, the slow mode printing process and the high speed 90 mm s-1 feed rate, marked the lower
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particle emission concentration.
195
PLA particle emissions
196
Figure 4 presents particle emissions from PLA. The results are subsequently compared with
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particles emitted from ABS (Figure 5). Similarly, the influences of nozzle temperature on particle
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emission based on the PLA filament were investigated by fixing the feed rate at 60 mm s-1.
199
However, for the case of PLA filament, due to significantly low setting of the platform temperature,
200
there was no visible heating process. In other words, printing would start immediately after filament
201
loading. Meanwhile, PLA filament did not induce recognizable peaks at filament loading and
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unloading as in the case of ABS filament loading. The influences from nozzle temperature present a
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similar pattern as in Figure 3. When the printing temperature was below 200oC, particle emission
204
from PLA filament printing process was very limited (<5000 # cm-3). However, when nozzle
205
temperature was set above 200oC, significant particle emission was triggered. In this case,
206
emissions were recorded as high as 20000-40000 # cm-3. In addition, significant fluctuation was
207
recorded during the printing process.
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a. Influence of nozzle temperature on PLA particle emission
b. Influence of feed rate on PLA particle emission
Figure 4. Influences of manufacturing parameters on PLA particle emissions
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13
Figure 4b exhibits experimental results regarding the impacts of feed rate of PLA on particle
210
emissions. In general, all feed rate settings lead to similar particle concentration of around 3000-
211
5000 # cm-3. Moreover, at 220oC nozzle temperature, particle concentration was around 35000 #
212
cm-3. For the influences from feed rate as in the PLA filament printing, the pattern in Figure 3b
213
repeats again in the case of PLA filament printing. The high feed rate level of printing process led
214
to the lower emission concentration during printing. The highest emission concentration was
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recorded when using the middle feed rate. Replicated tests for entire measuring procedure were also
216
conducted (data not shown) with both filaments of ABS and PLA, which revealed the same order of
217
magnitude of particle concentration, and the same level influences of manufacturing parameters on
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particle generation (see Supporting Information).
219
Figure 5 combines the particles emissions from ABS and PLA filaments for comparison. At the
220
same feed rate of 60 mm s-1 , Figure 5 (a) shows filaments present comparable particle emissions
221
around 5000 # cm-3 under 200oC nozzle temperature, though some significant emission peaks (~104
222
# cm-3) In case that nozzle temperature reached 220oC (Figure 6(b)), ABS filament exhibited
223
substantially higher particle emissions than PLA filament caused by ABS filament heating.
224
225
(a) 200oC nozzle temperature (b) 220oC nozzle temperature
226
Figure 5 Emissions comparison between ABS and PLA filament
227
Product Quality Assessment
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Being a manufacturing process, the most important goal of 3D printing is to generate product with
229
good quality. Essentially, the quality will be evaluated according to the intended function of the
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product. Since currently application of low cost desktop 3D printers is expected to be mainly in
231
recreational purpose, product surface quality and structure deformation are the main indicators. The
232
evaluation was implemented via visual inspection.
233
ABS product: for the ABS product, we can clearly identify that 90 mm s-1 feed rate would lead to
234
significant deformation and short shot during printing due to the excessive printing speed. As
235
shown in Figure 6a, defects and deformation were presented on the back side of the materials. On
236
the other hand, lower nozzle temperature (200oC and 220oC) was not beneficial for ABS filament
237
printing as well. Figure 6b and Figure 6d show products from 220oC and 200oC at 60 mm s-1. Both
238
cases lead to considerable deformation and coarse surface due to viscous ABS flow. However, a
239
slower speed (30 mm s-1) seems to improve the quality of the product (Figure 6c). The best quality
240
product was achieved at 240oC nozzle temperature and 60 mm s-1 as represented by Figure 6e.
241
242
Figure 6 ABS 3D printed product quality assessment
243
PLA product: Figure 7 presents product quality assessment with the PLA filament. Since PLA has
244
high lower melting point and elevated flow ability, PLA filament is much easier to be manufactured
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via the FDM process. Initial visual check concludes that these products were printed with similar
246
quality in terms of deformation and surface roughness.
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248
Figure 7 PLA 3D printed product quality assessment
249
Discussion
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The discussion section will provide further in-depth analysis on particle emissions in the course of
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3D printing process in correlation to the following factors: nozzle temperature, feed rate, and
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filament materials. Suggestions are highlighted for future design of the 3D printing process
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provided that the product quality is met.
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ABS filament printing
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Influence of nozzle temperature: For both filament materials (see Figure 3 and Figure 4), the
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nozzle temperature is found to be a critical factor on particle emission. In a decomposed analysis on
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the ABS printing process, the first small peak in particle emission related to filament loading can be
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ascribed to extrusion. For conventional plastic manufacturing process, extrusion or injection may
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cause certain degree of plastic fraction, which will result in particle emissions. The long waiting
260
period between filament loading and inception of 3d printing is because that platform temperature is
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relatively difficult to lift. The 3D printer, among many other low cost desktop 3D printers, does not
262
have a cover, which may provide insulation for platform heating. Such design causes a prolonged
263
heating time. The nozzle temperature for the loaded extruder is maintained by air cooling control.
264
During the preparation, the level of particle emissions, as measured by the particle concentration at
265
the source point, gradually creeping north and reaching the highest level in the course of the whole
266
printing trial. Though the nozzle temperature settings, 200~240oC for ABS, is safely below the
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material decomposition temperature (270oC), filament material, which is statically situated in the
268
small extruder, may not be evenly heated. In practice, nozzle temperature is difficult to be precisely
269
controlled. It is likely that nozzle temperature might shortly exceed the defined level before air
270
cooling was activated and brought the temperature down. Thus, thermal decomposition may occur
271
induced by inhomogeneous heating, and triggers several high emission peaks during the heating
272
period. Particle emissions are found to be very sensitive to nozzle temperature settings. Orders of
273
magnitude differences in particle concentration were recorded for both types of filaments when
274
nozzle temperature increased from the lower to upper end.
275
An interesting finding for ABS printing is that particle concentration gradually decreased when the
276
printing process is initiated. During the printing process, a steady material flow will be generated
277
passing through the extruder and deposited onto the platform. The dynamic printing process may
278
explain why particle emissions were reduced because heat could be disseminated out of nozzle due
279
to material flow. Thus, a subsequent implication is that particle emission may mainly be triggered
280
by thermal decomposition due to heating in the preparation period than the printing.
281
Influence of feed rate: Figure 3b shows that feed rate can impose impact on particle emission as
282
well but the particle emissions by different feed rates are less sensitive to the feed rate as to nozzle
283
temperature. This finding fits previous postulation indicating that particle emission is mainly
284
activated by inhomogeneous heating of nozzle. This may also explain why lowest particle emission
285
during printing process is identified at high feed rate of 90 mm s-1. Though higher feed rate may
286
elevate material fraction, high speed printing largely facilitates heat dissipation, and thus limits the
287
thermal decomposition. Initially, particle emissions at 30 mm s-1 and 60 mm s-1 feed rate levels are
288
the higher than that in 90 mm s-1. During the printing process, nozzle temperature can be easily
289
disseminated, and thus thermal decomposition can be reduced leading to particle emissions from all
290
feed rates converged.
291
292
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PLA filament printing
294
Influence of nozzle temperature: Understanding of emission pattern of PLA filament printing
295
process (Figure 4) is best illustrated by comparing its particle emission profile with those in ABS
296
filament printing (Figure 5). As shown in Table 1, the bed platform of PLA filament printing
297
requires much lower temperature. As such, heat preparations in the case of PLA filament printing
298
were very fast, and thus, no visible interval can be identified in Figure 4a and Figure 5. This
299
difference lays down the major reason why printing with the PLA filament did not result in as
300
significant particle emission as ABS filament. Printing processes were immediately activated after
301
filament loading, and hence, the heating period, which triggers significant particle emission in ABS
302
filament printing, were largely eliminated. Therefore, though nozzle temperature was set at 180oC-
303
200oC, close to 220oC decomposition temperature of PLA [16] (nozzle temperature at ABS was set
304
in range of 200-240oC in reference to its 270oC decomposition temperature [17]), particle emissions
305
were orders of magnitude lower than the situation in ABS filament printing. When nozzle
306
temperature was further promoted to 220oC, bordering its decomposition temperature, particle
307
emissions from PLA decomposition were significantly triggered. The particle concentration, in this
308
case 35000 # cm-3, is comparable to the level recorded in ABS filament printing. Figure 5 also
309
clearly demonstrates the influence of the heating process. In Figure 5(b), even though significant
310
higher particle emissions were generated at 220oC nozzle temperature for ABS filament, at end of
311
the printing process, particle concentration of ABS filament decreased to 20000-30000 # cm-3,
312
which is comparable to that of PLA filament.
313
Influence of feed rate: Figure 4b demonstrates particle emissions with different feed rate in PLA
314
filament printing. We could still identify that the middle range feed rate (60 mm s-1) is found to be
315
moderately higher than the end range (30mm s-1 and 90 mm s-1) as in the case of the ABS printing.
316
This can be explained by two mechanisms controlling particle emission during the printing process:
317
1) decomposition from the nozzle, 2) material fraction during extrusion. The middle range feed rate
318
is then associated with relatively more intense material fraction compared to lower end feed rate,
319

18
while relatively less capable of disseminating heat from nozzle as in the higher end feed rate. The
320
combined effect is believed to be the drive pushing the 60 mm s-1 feed rate exporting slight higher
321
particle emission than feed rates at ends.
322
Product Quality
323
In this study, the product quality was only evaluated based on aesthetic aspects: surface roughness
324
and production deformation. The two indicators were selected because current desktop 3D printed
325
products are mainly for recreational and occasional use. Further development may allow 3D printed
326
product enter daily application such as wrench, cup, or chair. In this case, quality assessment should
327
expand to mechanical and physical performance of the product. The two filaments present
328
completely different associations between printing parameters and product quality. For ABS
329
filament, strong linkage can be observed between the investigated parameters and quality of the
330
final product. The conclusion is that ABS is not compatible to fast printing speed nor low nozzle
331
temperature. On the other hand, the PLA filament exhibits significant tolerance to temperature and
332
feed rate changes. The different pattern is determined by their different properties in melt viscosity
333
and temperature. ABS polymer is an amorphous polymer without a specific melting point
334
temperature. Normally, ABS needs to achieve above 200oC to allow a sufficiently smooth flow and
335
printing temperature above 230oC for ABS is widely used. On the other hand, the PLA has a
336
melting temperature around 150 - 160oC. The melting viscosity of ABS (155 - 1550 Pa s) [18] is
337
significantly higher than PLA (14 - 900 Pa s) [19].
338
Results implication and suggestions for future desktop 3D printer design
339
The fine particle emissions from 3D printers are reported by several independent studies in the
340
literature. The most recent study from Azimi et al. concluded that particle emissions are sensitive to
341
the type of the filament materials and to the platform temperature [3]. The authors also noted that
342
when platform temperature is low, increasing nozzle temperature from 185oC to 230oC results in
343
little change in overall emissions. Findings of the current study can nicely explain the mechanisms
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behind the phenomenon. In the current study, we have found that compared to actual printing
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process the heating process is the main contributor of particle emissions related to the nozzle
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temperature. In a general type of setting, a higher platform temperature is expected to be correlated
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with a prolonged heating duration, and thus, a higher emission rate will be triggered for this type of
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filament. Meanwhile, when platform temperature is low (45oC noted in [3]), the step-by-step
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emission analysis indicates that printing will be ignited immediately. Thus, particle emission in this
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situation will exhibit dissociated correlation with the nozzle temperature. Meanwhile, this study also
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shows that both types of filament tend to have the same level of the emission rate when
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decomposition happens. Thus, from this point of view, material type is not the intrinsic reason
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leading to different emission intensities between ABS and PLA.
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To further reveal the importance of the heating process on ABS filament printing, we designed
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another experiment to provide the product with ABS at the same temperature (240oC) and feed rate
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(60 mm s-1). However, platform and extruder were preheated before ABS filament is loaded into the
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extruder (ABST240FR60(N)). Before printing, platform was washed with acetone and isopropanol
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and extruder was significantly unloaded. Figure 8 shows that moderate particle emission can still
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be recorded during the heating process, which may be ascribed as small fraction of filament
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material residual in extruder. After platform temperature reached 110oC, the ABS filament was
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loaded into the extruder. In this case, printing was immediately activated. The emissions were
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recorded during unloading. By changing the conventional 3D printing procedure to eliminate
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filament heating, result shows that particle emission is substantially reduced.
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Figure 8 Optimization of ABS filament printing in terms of particle emission
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With this finding, some suggestions can be drawn with the product quality as the restriction
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requirement. For ABS filament, it is not possible to lower the nozzle temperature from the quality
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concern. Thus, printing with ABS requires a good indoor ventilation. For PLA filament, a direct
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suggestion is try to limit its nozzle temperature. A lower touch temperature at 180oC is preferable.
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From the feeding rate perspective, a fast feed rate (90 mm s-1) is suggested for PLA filament, which
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lowering exposure duration.
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For future design of the desktop 3D printer machine, an important direction is to target the heat
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dissipation within the nozzle. Thus, the cooling system must be carefully designed to ensure that
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thermal decomposition can be contained. The 3D printer we are using adopted an air cooling, future
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research on other cooling method in relation to particle emission is recommended.
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Acknowledgements
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The authors would like to acknowledge the financial support from both Natural Science Foundation
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for youth of Jiangsu Province and China (Grant No. BK20150328 and 51508362).
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