Yayue Pan

A Fast Mask Projection Stereolithography Process for Fabricating Digital Models in Minutes

The purpose of this paper is to present a direct digital manufacturing (DDM) process that is an order of magnitude faster than other DDM processes that are currently available. The developed process is based on a mask-image-projection-based stereolithography (MIP-SL) process, in which a digital micromirror device (DMD) controls projection light to selectively cure liquid photopolymer resin. In order to achieve high-speed fabrication, we investigate the bottom-up projection system in the MIP-SL process. A two-way linear motion approach has been developed for the quick spreading of liquid resin into uniform thin layers. The system design and related settings for achieving a fabrication speed of a few seconds per layer are presented. Additionally, the hardware, software, and material setups for fabricating three-dimensional (3D) digital models are presented. Experimental studies using the developed testbed have been performed to verify the effectiveness and efficiency of the presented fast MIP-SL process. The test results illustrate that the newly developed process can build a moderately sized part within minutes instead of hours that are typically required.

Development of a Low-Cost Parallel Kinematic Machine for Multidirectional Additive Manufacturing

Most additive manufacturing (AM) processes are layer-based with three linear motions in the X, Y, and Z axes. However, there are drawbacks associated with such limited motions, e.g., nonconformal material properties, stair-stepping effect, and limitations on building-around-inserts. Such drawbacks will limit AM to be used in more general applications. To enable 6-axis motions between a tool and a work piece, we investigated a Stewart mechanism and the feasibility of developing a low-cost 3D printer for the multidirectional fused deposition modeling (FDM) process. The technical challenges in developing such an AM system are discussed including the hardware design, motion planning and modeling, platform constraint checking, tool motion simulation, and platform calibration. Several test cases are performed to illustrate the capability of the developed multidirectional AM system. A discussion of future development on multidirectional AM systems is also given. [DOI: 10.1115/1.4028897]

Multitool and Multi-Axis Computer Numerically Controlled Accumulation for Fabricating Conformal Features on Curved Surfaces

In engineering systems, features such as textures or patterns on curved surfaces are common. In addition, such features, in many cases, are required to have shapes that are conformal to the underlying surfaces. To address the fabrication challenge in building such conformal features on curved surfaces, a newly developed additive manufacturing (AM) process named computer numerically controlled (CNC) accumulation is investigated by integrating multiple tools and multiple axis motions. Based on a fiber optical cable and a light source, a CNC accumulation tool can have multi-axis motion, which is beneficial in building conformal features on curved surfaces. To address high resolution requirement, the use of multiple accumulation tools with different curing sizes, powers, and shapes is explored. The tool path planning methods for given cylindrical and spherical surfaces are discussed. Multiple test cases have been performed based on a developed prototype system. The experimental results illustrate the capability of the newly developed AM process and its potential use in fabricating conformal features on given curved surfaces. [DOI: 10.1115/1.4026898]

Rapid Manufacturing in Minutes: The Development of a Mask Projection Stereolithography Process for High-Speed Fabrication

The purpose of this paper is to present a direct digital manufacturing (DDM) process that is an order of magnitude faster than other DDM processes currently available. The developed process is based on a mask-image-projection-based Stereolithography process (MIP-SL), during which a Digital Micromirror Device (DMD) controlled projection light cures and cross-links liquid photopolymer resin. In order to achieve high-speed fabrication, we investigated the bottom-up projection system in the MIP-SL process. A set of techniques including film coating and the combination of two-way linear motions have been developed for the quick spreading of liquid resin into uniform thin layers. The process parameters and related settings to achieve the fabrication speed of a few seconds per layer are presented. Additionally, the hardware, software, and material setups developed for fabricating given three-dimensional (3D) digital models are presented. Experimental studies using the developed testbed have been performed to verify the effectiveness and efficiency of the presented fast MIP-SL process. The test results illustrate that the newly developed process can build a moderately sized part within minutes instead of hours that are typically required.Copyright

Fully Packaged Carbon Nanotube Supercapacitors by Direct Ink Writing on Flexible Substrates

The ability to print fully packaged integrated energy storage components (e.g., supercapacitors) is of critical importance for practical applications of printed electronics. Due to the limited variety of printable materials, most studies on printed supercapacitors focus on printing the electrode materials but rarely the full-packaged cell. This work presents for the first time the printing of a fully packaged single-wall carbon nanotube-based supercapacitor with direct ink writing (DIW) technology. Enabled by the developed ink formula, DIW setup, and cell architecture, the whole printing process is mask free, transfer free, and alignment free with precise and repeatable control on the spatial distribution of all constituent materials. Studies on cell design show that a wider electrode pattern and narrower gap distance between electrodes lead to higher specific capacitance. The as-printed fully packaged supercapacitors have energy and power performances that are among the best in recently reported planar carbon-based supercapacitors that are only partially printed or nonprinted.

Magnetic-Field-Assisted Projection Stereolithography for Three-Dimensional Printing of Smart Structures

In this paper, an additive manufacturing (AM) process, magnetic field-assisted projection stereolithography (M-PSL), is developed for 3D printing of three-dimensional (3D) smart polymer composites. The 3D-printed magnetic field-responsive smart polymer composite creates a wide range of motions, opening up possibilities for various new applications, like sensing and actuation in soft robotics, biomedical devices, and autonomous systems. In the proposed M-PSL process, a certain amount of nanoor microsized ferromagnetic particles is deposited in liquid polymer by using a programmable microdeposition nozzle. An external magnetic field is applied to direct the magnetic particles to the desired position and to form the desired orientation and patterns. After that, a digital mask image is used to cure particles in photopolymer with desired distribution patterns. The magneticfield-assisted projection stereolithography (M-PSL) manufacturing process planning, testbed, and materials are discussed. Three test cases, an impeller, a two-wheel roller, and a flexible film, were performed to verify and validate the feasibility and effectiveness of the proposed process. They were successfully fabricated and remote controls of the printed samples were demonstrated, showing the capability of printed smart polymer composites on performing desired functions. [DOI: 10.1115/1.4035964]

Energy Consumption Modeling of Stereolithography-Based Additive Manufacturing Toward Environmental Sustainability

Summary Additive manufacturing (AM), also referred as three-dimensional printing or rapid prototyping, has been implemented in various areas as one of the most promising new manufacturing technologies in the past three decades. In addition to the growing public interest in developing AM into a potential mainstream manufacturing approach, increasing concerns on environmental sustainability, especially on energy consumption, have been presented. To date, research efforts have been dedicated to quantitatively measuring and analyzing the energy consumption of AM processes. Such efforts only covered partial types of AM processes and explored inadequate factors that might influence the energy consumption. In addition, energy consumption modeling for AM processes has not been comprehensively studied. To fill the research gap, this article presents a mathematical model for the energy consumption of stereolithography (SLA)-based processes. To validate the mathematical model, experiments are conducted to measure the real energy consumption from an SLA-based AM machine. The design of experiments method is adopted to examine the impacts of different parameters and their potential interactions on the overall energy consumption. For the purpose of minimization of the total energy consumption, a response optimization method is used to identify the optimal combination of parameters. The surface quality of the product built using a set of optimal parameters is obtained and compared with parts built with different parameter combinations. The comparison results show that the overall energy consumption from SLA-based AM processes can be significantly reduced through optimal parameter setting, without observable product quality decay.

Smooth Surface Fabrication Based on Controlled Meniscus and Cure Depth in Microstereolithography

In the layer-based additive manufacturing (AM) processes, a three-dimensional (3D) model is converted into a set of two-dimensional (2D) layers. Due to such conversion, one of the major problems in the layer-based AM processes is the poor surface finish associated with the layer-based stair-stepping effect. However, the surface finish is critical for various microscale applications such as micro-optics and microfluidics. The adoption of AM technologies as a means for fabricating end-use microcomponents and tooling has been limited by such poor surface finish. The aim of this research work is to apply the state-of-the-art meniscus approach and controlled cure depth planning in the mask image projection-based microstereolithography (MIP-lSL) process to address its surface finish challenge. Mathematical models of meniscus shapes and cure depths are developed for the MIP-lSL process. Related process parameters including the minimum meniscus points, sliced layer shapes for forming meniscus, grayscale image values, and Z offsetting values are optimized to achieve the minimum approximation errors between a built part and a given nominal geometric model. A set of test cases with various curved surfaces are designed to test the developed smooth surface fabrication method. The experimental results verify the effectiveness of the proposed methods for the MIP-lSL process. [DOI: 10.1115/1.4030661]

Study of separation force in constrained surface projection stereolithography

Purpose Recently, the constrained surface projection stereolithography (SL) technology is gaining wider attention and has been widely used in the 3D printing industry. In constrained surface projection SL systems, the separation of a newly cured layer from the constrained surface is a historical technical barrier. It greatly limits printable size, process reliability and print speed. Moreover, over-large separation force leads to adhesion failures in manufacturing processes, causing broken constrained surface and part defects. Against this background, this paper investigates the formation of separation forces and various factors that affect the separation process in constrained surface projection SL systems. Design/methodology/approach A bottom-up projection SL testbed, integrated with an in-situ separation force measurement unit, is developed for experimental study. Separation forces under various manufacturing process settings and constrained surface conditions are measured in situ. Additionally, physical models are constructed by considering the liquid resin filling process. Experiments are conducted to investigate influences of manufacturing process settings, constrained surface condition and print geometry on separation forces. Findings Separation forces increase linearly with the separation speed. The deformation and the oxygen inhibition layer near the constrained surface greatly reduce separation forces. The printing area, area/perimeter ratio and the degree of porousness of print geometries have a combined effect on determining separation forces. Originality/value This paper studied factors that influence separation force in constrained surface SL processes. Constrained surface conditions including oxygen inhibition layer thickness, deformation and oxygen permeation capability were investigated, and their influences on separation forces were revealed. Moreover, geometric factors of printing layers that are significant on determining separation forces have been identified and quantified. This study on separation forces provides a solid base for future work on adaptive control of constrained surface projection SL processes.

Fast Mask Image Projection-Based Micro-Stereolithography Process for Complex Geometry

In micro-stereolithograhy (lSL), high-speed fabrication is a critical challenge due to the long delay time for refreshing resin and retaining printed microfeatures. Thus, the mask-image-projectionbased micro-stereolithograhy (MIP-lSL) using the constrained surface technique is investigated in this paper for quickly recoating liquid resin. It was reported in the literature that severe damages frequently happen in the part separation process in the constrained-surface-based MIP-lSL system. To conquer this problem, a single-layer movement separation approach was adopted, and the minimum delay time for refreshing resin was experimentally characterized. The experimental results verify that, compared with the existing MIP-lSL processes, the MIP-lSL process with single-layer movement separation method developed in this paper can build microstructures with complex geometry, with a faster build speed. [DOI: 10.1115/1.4035388]