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The objective of this paper is to demonstrate a method for producing embedded horizontal micro‐channels using a commercial line‐scan stereolithography (SL) system. To demonstrate that the method is repeatable, reproducible and capable of producing accurate horizontal micro‐channels, a statistical design of experiments was performed.

Demonstration of the technique was performed using a 3D Systems Viper si2^TM SL system and DSM Somos^® WaterShed^TM resin with polytetrafluoroethylene (PTFE)‐coated wire having diameters of 31.6 and 57.2 μm. By embedding the wire and building around the insert, the down‐facing surfaces were supported during fabrication enabling accurate fabrication of embedded micro‐channel geometries. The fabrication method involved first building an open micro‐channel, interrupting the SL process and inserting the wire, and then capping over the wire with multiple layers. After fabrication, the part with the inserted micro‐wire was post‐cured to harden any uncured resin around the wire. The micro‐channel was produced by simply pulling the wire out of the part. Scanning electron microscope images were used to examine and measure the geometries of the fabricated micro‐channels, and characterization through a statistical analysis was accomplished to show that the process was capable of producing accurate horizontal micro‐channels.

The measured data showed that the micro‐wires were successfully removed from the channels, leaving high quality micro‐channels, where the mean measured diameters for each wire were 2.65 and 2.18 μm smaller than the measured wire diameters (31.6 and 57.2 μm). Based on the statistical results, it is suggested that the method described in this work can rapidly produce repeatable and reproducible circular, embedded, and accurate micro‐channels.

The method developed in the current work was demonstrated on simple straight channels and a statistical study was used to show that the process is capable of repeatedly and reproducibly producing accurate micro‐channels with circular cross‐section; however, future studies are required to extend these procedures to more realistic and complicated geometries that may include non‐straight channel paths and non‐circular cross‐sectional geometries. The process can be used for micro‐channel fabrication with not only circular cross‐sectional geometries as shown here but potentially with a wide range of additional cross‐sectional geometries that can be fabricated into a PTFE‐coated micro‐wire.

This work demonstrates a process using commercial line‐scan SL and embedding a PTFE‐coated micro‐wire that is subsequently removed for producing repeatable and reproducible horizontal embedded micro‐channels of circular cross‐sectional geometries.

The present research investigates tailoring the physical properties of stereolithography (SL) epoxy‐based resins by dispersing controlled small amounts of multi‐walled carbon nanotubes (MWCNTs) directly in SL resins prior to layered manufacturing.

A modified 3D Systems 250/50 SL multi‐material machine was used where the machine was equipped with a solid‐state (355 nm) laser, unique ∼ 500 ml vat, overfill drain vat design that continuously flowed resin into the vat via a peristaltic pump, and 8.89 by 8.89 cm² platform. The vat did not include a recoating system. Pumping the composite resin assisted in maintaining the MWCNTs dispersed over long periods of time (with MWCNT settling times on the order of one week). The research approach required developing a method for dispersing the MWCNTs in SL resin, determining new SL build parameters for the modified resin and SL machine, and building and testing tensile specimens.

Mechanical mixing and ultrasonic dispersion provided simple means for dispersing MWCNTs in the SL resin. However, MWCNT agglomerates were observed in all the parts fabricated using the filled resins. Each concentration of MWCNTs resulted in a “new” resin requiring modifications to the SL build parameters, E_C and D_P. Once characterized, the modified resins performed similar to traditional resins in the SL process. Small dispersions of MWCNTs resulted in improvements in the tensile strength (TS) (or ultimate tensile stress) and fracture stress (FS) of tensile specimens as 0.025 percent (w/v) MWCNTs in DSM Somos^® WaterShed™ 11120 resin resulted in increases in TS and FS of 5.7 percent and 26 percent, respectively, when compared to unfilled resin. Increasing the concentration of MWCNTs to 0.10 percent (w/v) resulted in increases in TS and FS of 7.5 percent and 33 percent, respectively, over the unfilled resin. Transmission and scanning electron microscopy showed strong affinity between the epoxy resin and the MWCNTs.

Additional MWCNT type and concentrations in various SL resins should be investigated along with additional means for dispersion to provide sufficient information on developing new SL resins for unique functional applications.

It is anticipated that the methods described here will provide a basis for further development of advanced nanocomposite SL resins for end‐use applications.

This research successfully illustrated the dispersion and use of MWCNTs as a reinforcement material in a commercially available SL resin.

The paper's aim is to explore a method using light absorption for improving manufacturing of complex, three‐dimensional (3D) micro‐parts with a previously developed dynamic mask projection microstereolithography (MSL) system. A common issue with stereolithography systems and especially important in MSL is uncontrolled penetration of the ultraviolet light source into the photocrosslinkable resin when fabricating down‐facing surfaces. To accurately fabricate complex 3D parts with down‐facing surfaces, a chemical light absorber, Tinuvin 327™ was mixed in different concentrations into an acrylate‐based photocurable resin, and the solutions were tested for cure depths and successful micro‐part fabrication.

Tinuvin 327 was selected as the light absorber based on its high absorption characteristics (∼0.4) at 365 nm (the filtered light wavelength used in the MSL system). Four concentrations of Tinuvin 327 in resin were used (0.00, 0.05, 0.10, and 0.15 percent (w/w)), and cure depth experiments were performed. To investigate the effects of different concentrations of Tinuvin 327 on complex 3D microstructure fabrication, several microstructures with overhanging features such as a fan and spring were fabricated.

Results showed that higher concentrations of Tinuvin 327 reduced penetration depths and thus cure depths. For the resin with 0.15 percent (w/w) of the Tinuvin 327, a cure depth of ∼30 μm was achieved as compared to ∼200 μm without the light absorber. The four resin solutions were used to fabricate complex 3D microstructures, and different concentrations of Tinuvin 327 at a given irradiance and exposure energy were required for successful fabrication depending on the geometry of the micro‐part (concentrations of 0.05 and 0.1 percent (w/w) provided the most accurate builds for the fan and spring, respectively).

Although two different concentrations of light absorber in solution were required to demonstrate successful fabrication for two different micro‐part geometries (a fan and spring), the experiments were performed using a single irradiance and exposure energy. A single solution with the light absorber could have possibly been used to fabricate these micro‐parts by varying irradiance and/or exposure energy, although the effects of varying these parameters on geometric accuracy, mechanical strength, overall manufacturing time, and other variables were not explored.

This work systematically investigated 3D microstructure fabrication using different concentrations of a light absorber in solution, and demonstrated that different light absorption characteristics were required for different down‐facing micro‐features.

In an effort to directly manufacture devices with embedded complex and three‐dimensional (3D) micro‐channels on the order of microns to millimeters, issues associated with micro‐fabrication using current commercially available line‐scan stereolithography (SL) technology were investigated.

Practical issues associated with the successful fabrication of embedded micro‐channels were divided into software part preparation, part manufacture, and post‐cleaning with emphasis on channel geometry, size, and orientation for successful micro‐fabrication. Accurate representation of intended geometries was investigated during conversion from CAD to STL and STL to machine build file, and fabricated vertical and horizontal micro‐channels were inspected. Additional build issues investigated included accurate spatial registration of the build platform, building without base support, and Z‐stage position accuracy during the build.

For successful fabrication of micro‐channels using current technology, it is imperative to inspect the conversion process from CAD to STL and STL to machine build file. Inaccuracies in micro‐channel representation can arise at different stages of part preparation, although newer software versions appear to improve representation of micro‐geometries. Square channel cross‐sections are most easily sliced and vertical channels are most easily stacked together for layered manufacturing. While building, a means should be developed for building without base and internal supports, providing feedback on Z‐stage position, and having the capability for cleaning the micro‐channels.

This research demonstrates that commercial SL technology is capable of accurately fabricating embedded vertical square cross‐section micro‐channels on the order of 100 μm (with reasonable advancements to smaller scales on the order of 10 μm achievable). Additional practical limitations exist on other channel geometries and orientations. The research used a single resin and additional material resins should be explored for improved micro‐fabrication characteristics.

Practical issues associated with micro‐fabrication of embedded channels with appropriate solutions using available SL technology were provided. It is expected that these solutions will enable unique applications of micro‐channel fabrication for micro‐fluidic and other devices.

This work represents an original investigation of the capabilities of current line‐scan SL technology for fabricating embedded micro‐channels, and the solutions provide the means for applying this technology in micro‐fabrication.

The purpose of this paper is to investigate the effects of aging, pre‐conditioning, and build orientation on the mechanical properties of test samples fabricated using stereolithography (SL) and a commercially available resin.

American Society for Testing and Materials (ASTM) Standard D638 Type I specimens were manufactured in a Viper si2 SL system using WaterShed™ 11120 resin. The specimens were manufactured in two different build setups, designed to fit batches of 18 or 24 specimens with different build orientations. The specimens were randomly tested in tension, and a design of experiments (DOE) was used to determine the effect of aging (4, 30 or 120 days), pre‐conditioning (ambient, desiccant, or ASTM recommended conditioning), and build orientation (flat, on an edge, or vertical) on the ultimate tensile stress (UTS) and elastic modulus (E) of SL fabricated samples. Additionally, the fractured samples were imaged using scanning electron microscopy (SEM) to characterize the fractured surfaces.

Results showed that aging, pre‐conditioning, and build orientation each had an effect on the mechanical properties of the SL samples. In general, the samples aged at the shortest time frame (4 days) and the samples preconditioned according to ASTM recommendations had the lowest values of UTS. Regarding the effect of build orientation, the specimens built flat (with layers oriented along the thickness of the sample) had the lowest UTS and E values and the mechanical properties were statistically different from those built vertically or on an edge. The specimens built in the vertical orientation (with layers oriented along the length of the sample) had the highest values of UTS and E, yet the mechanical properties of the samples built on an edge (with layers oriented along the width of the sample) were not statistically different from the samples built vertically. SEM images of the fractured specimens showed fracture surfaces typical of polymers with a mirror zone and changes in surface texture from smooth to coarse.

The research was limited to a single commercially available resin. Through a statistical DOE approach, statistically significant differences in mechanical properties of SL fabricated samples were found as functions of aging, pre‐conditioning, and build orientation. These results can assist the ASTM F42 Committee with developing test standards specific to SL and the additive manufacturing community.

The statistical analyses presented here can help identify and classify the effects of fabrication, storage, and conditioning parameters on mechanical properties for SL fabricated parts. Understanding how the mechanical properties of SL resins are affected by different parameters can help improve the use of SL for a variety of applications including direct manufacturing of end‐use products.

The purpose of this paper is to present a hybrid manufacturing system that integrates stereolithography (SL) and direct print (DP) technologies to fabricate three‐dimensional (3D) structures with embedded electronic circuits. A detailed process was developed that enables fabrication of monolithic 3D packages with electronics without removal from the hybrid SL/DP machine during the process. Successful devices are demonstrated consisting of simple 555 timer circuits designed and fabricated in 2D (single layer of routing) and 3D (multiple layers of routing and component placement).

A hybrid SL/DP system was designed and developed using a 3D Systems SL 250/50 machine and an nScrypt micro‐dispensing pump integrated within the SL machine through orthogonally‐aligned linear translation stages. A corresponding manufacturing process was also developed using this system to fabricate 2D and 3D monolithic structures with embedded electronic circuits. The process involved part design, process planning, integrated manufacturing (including multiple starts and stops of both SL and DP and multiple intermediate processes), and post‐processing. SL provided substrate/mechanical structure manufacturing while interconnections were achieved using DP of conductive inks. Simple functional demonstrations involving 2D and 3D circuit designs were accomplished.

The 3D micro‐dispensing DP system provided control over conductive trace deposition and combined with the manufacturing flexibility of the SL machine enabled the fabrication of monolithic 3D electronic structures. To fabricate a 3D electronic device within the hybrid SL/DP machine, a process was developed that required multiple starts and stops of the SL process, removal of uncured resin from the SL substrate, insertion of active and passive electronic components, and DP and laser curing of the conductive traces. Using this process, the hybrid SL/DP technology was capable of successfully fabricating, without removal from the machine during fabrication, functional 2D and 3D 555 timer circuits packaged within SL substrates.

Results indicated that fabrication of 3D embedded electronic systems is possible using the hybrid SL/DP machine. A complete manufacturing process was developed to fabricate complex, monolithic 3D structures with electronics in a single set‐up, advancing the capabilities of additive manufacturing (AM) technologies. Although the process does not require removal of the structure from the machine during fabrication, many of the current sub‐processes are manual. As a result, further research and development on automation and optimization of many of the sub‐processes are required to enhance the overall manufacturing process.

A new methodology is presented for manufacturing non‐traditional electronic systems in arbitrary form, while achieving miniaturization and enabling rugged structure. Advanced applications are demonstrated using a semi‐automated approach to SL/DP integration. Opportunities exist to fully automate the hybrid SL/DP machine and optimize the manufacturing process for enhancing the commercial appeal for fabricating complex systems.

This work broadly demonstrates what can be achieved by integrating multiple AM technologies together for fabricating unique devices and more specifically demonstrates a hybrid SL/DP machine that can produce 3D monolithic structures with embedded electronics and printed interconnects.

Many psychologists posit that intrinsic motivation generated by personal interest and spontaneous satisfactions is qualitatively different from extrinsic motivation generated by external rewards. However, the contemporary neural understanding of human motivation has been developed almost exclusively based on the neural mechanisms of extrinsic motivation. In neuroscience studies on extrinsic motivation, striatum activity has been consistently observed as the core neural system related to human motivation. Recently, a few studies have started examining the neural system behind intrinsic motivation. Though these studies have found that striatum activity is crucial for the generation of intrinsic motivation, the unique neural basis of intrinsic motivation has not yet been fully identified. I suggest that insular cortex activity, known to be related to intrinsic enjoyment and satisfaction, is a unique neural component of intrinsic motivation. In this chapter, I addressed the theoretical background to and empirical evidence for this postulation.

Although many researchers have widely studied additive manufacturing (AM) as one of the most important industrial revolutions, few have presented a bibliometric analysis of the published studies in this area. This paper aims to evaluate AM research trends based on 4607 publications most cited from year 2010 to 2020.

The research methodology is bibliometric indicators and network analysis, including analysis based on keywords, citation analysis, productive journal, related published papers and authors indicators. Two free available software were employed VOSviewer and Bibexcel.

Keywords analysis results indicate that among the AM processes, Selective Laser Melting and Fused Deposition Modeling techniques, are the two processes ranked on top of the techniques employed and studied with 35.76% and 20.09% respectively. The citation analysis by VOSviewer software, reveals that the medical applications field and the fabrication of metal parts are the areas that interest researchers greatly. Different new research niches, as pharmaceutical industry, digital construction and food fabrication are growing topics in AM scientific works. This study reveals that journals “Materials & design”, “Advanced materials”, “Acs applied materials & interfaces”, “Additive manufacturing”, “Advanced functional materials” and “Biofabrication” are the most productive and influential in AM scientific research.

The results and conclusions of this work can be used as indicators of trends in AM research and/or as prospects for future studies in this area.

The purpose of this paper is to investigate a build process variation for fused deposition modeling (FDM) in which contours and rasters (also referred to as internal fill patterns) are built using different layer thicknesses and road widths. In particular, the paper examines the effect of the build process variation on surface roughness, production times and mechanical properties. Additionally, a unique FDM process was developed that enabled the deposition of discrete multiple materials at different layers and regions within layers.

A multi-material, multi-technology FDM system was developed and constructed to enable the production of parts using either discrete multi-materials or the build process variation (variable layer thickness and road width). Two legacy FDM machines were modified and installed onto a single manufacturing system to allow the strategic, spatially controlled thermoplastic deposition with multiple extrusion nozzles of multiple materials during the same build. This automated process was enabled by the use of a build platform attached to a pneumatic slide that moved the platform between the two FDM systems, an overall control system, a central PC and a custom-made program (FDMotion) and graphic user interface. The term multi-technology FDM system used here implies the two FDM systems and the integration of these systems into a single manufacturing environment using the movable platform and associated hardware and software. Future work will integrate additional technologies within this system. Parts produced using the build process variation utilized internal roads with 1,524 μm road width and 508 μm layer height, while the contours used 254 μm road width and 127 μm layer height. Measurements were performed and compared to standard FDM parts that included surface roughness of planes at different inclinations, tensile testing and fabrication times.

Results showed that when compared to the standard FDM process, the parts produced using the build process variation exhibited the same tensile properties as determined by a student's t-test (p-values > 0.05, μ1-μ2 = 0, n = 5). Surface roughness measurements revealed that the process variation resulted in surface roughness (R_a) improvements of 55, 43, 44 and 38 per cent for respective planes inclined at 10, 15, 30 and 45° from vertical. In addition, for a 50.8 × 50.8 mm square section (25.4 mm tall), the build process variation required a minimum of 2.8 hours to build, while the standard FDM process required 6.0 hours constituting a 53 per cent reduction in build time. Finally, several manufacturing demonstrations were performed including the fabrication of a discrete PC-ABS sandwich structure containing tetragonal truss core elements.

This paper demonstrates a build strategy that varies contour and raster widths and layer thicknesses for FDM that can be used to improve surface roughness – a characteristic that has historically been in need of improvement – and reduce fabrication time while retaining mechanical properties.