Dynamic Resolution Control in a Laser Projection Based Stereolithography System

In a typical Additive Manufacturing system, it is critical to make a trade-off between the resolution and build area for applications in which varied dimensional sizes, feature sizes, and accuracies are desired. The lack of the capability in adjusting resolution dynamically during building processes limits the use of AM in fabricating complex structures with big layer areas and small features. In this paper, a novel AM system with dynamic resolution control by integrating a laser projection in vat photopolymerization process is presented. Theoretical models and parameter characterizations are presented for the developed AM system. Accordingly, the process planning and mask image planning approaches for fabricating models with varied dimensional sizes and feature sizes have been developed. Multiple test cases based on various types of structures have been performed.Mechanical Engineerin

A Novel Projection Based Electro-Stereolithography (PES) Process for Composite Printing

Most current additive manufacturing processes can only process one material in one build. Few of them are able to fabricate multiple materials and composites, with limited choices of materials. In this research, we propose a novel Projection based Electro-Stereolithography (PES) process, which is able to fabricate composites with high resolution and fast speed, and a big range of material choices. The proposed novel additive manufacturing process integrates projection-based stereolithography and electrophotography approaches by using a photoconductive film and digital micro-mirror device (DMD). In PES, a photoconductive film is used to collect charged particles in the regions illuminated by light. More specifically, a laser beam is scanning on the film to create a latent image on the film and then a layer of charged particles is attracted to the illuminated area. A liquid bridge system and a stamping system have been developed to transfer particles from the film to liquid resin precisely. Furthermore, a digital mask is used to pattern the light irradiation of the DMD chip to selectively cure the photopolymer liquid resin and particles of that layer. By transferring particles with designed patterns to the resin in a projection based stereolithography system, we will be able to fabricate composites with various materials at microscopic resolutions very quickly. Challenges in this novel manufacturing process, including transferring of particles and curing control, have been discussed and addressed. The corresponding key parameters of the particles collecting, dropping and curing in the PES system have been identified. A proof-of-concept PES testbed has been developed and a couple of tests have been performed to validate the feasibility of the proposed additive manufacturing approach.Mechanical Engineerin

Fabrication of Smooth Surfaces Based on Mask Projection Stereolithography

The surface finish is critical for applications such as micro-fluid mixing and self-assembly that requires smooth fluidic flow and mechanical rotation respectively. However, in layer-based additive manufacturing processes, it is well known that the stair-stepping effect exists in the fabricated surfaces since a three-dimensional model is approximated by a set of two-dimensional layers. The fabricated surfaces are especially poor for the ones that are close to the horizontal plane. In this paper a novel approach for achieving improved surface finish has been presented for the mask-image-projection-based Stereolithography (MIP-SL) process. Theoretical models and parameter characterization are presented with experimental verification. The developed approaches have been incorporated in the process planning of the MIP-SL process. Multiple test cases based on various types of curved surfaces have been performed. A comparison of the built results based on the traditional and the newly developed approaches has been discussed to illustrate the effectiveness of our method.Mechanical Engineerin

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

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

Fast and Simple Fabrication of Multimaterial Hierarchical Surfaces Using Acoustic Assembly Photopolymerization (AAP)

Abstract Multimaterial surfaces with hierarchical features have many potential applications in self‐cleaning, droplet manipulation, microfluidics, and biomedicine, owing to their wide range of functionalities induced by structural and material contrasts. Here, a fast and sustainable manufacturing method, acoustic assembly photopolymerization (AAP), is presented for productions of such surfaces. In the novel AAP process, an external acoustic field is used to assemble microparticles to microsized patterns, while the photocuring is combined with the acoustic assembly to produce multilevel hierarchical features, such as cones and wrinkles ranging from nanometer to micrometer. The mechanism underlying the proposed multimaterial surface structuring technique is discussed, and the relationship between process parameters and surface structures is modeled. Effects of surface material composition patterns and surface topology on the hydrodynamic properties are studied. To demonstrate potential applications, three microreactors are designed and automated droplet manipulations are demonstrated. The application of the proposed surface manufacturing approach is further extended to fog harvesting. The AAP technology and the fabricated multimaterial hierarchically‐structured surfaces demonstrated in this study can be employed in many other advanced applications in microfluidics, tissue engineering, and also potentially many other fields such as mechanical systems and battery systems

Machine Learning for Modeling of Printing Speed in Continuous Projection Stereolithography

Continuous projection stereolithography technologies, also known as the Continuous Liquid Interface Production (CLIP), can achieve build speeds an order of magnitude faster than conventional layer-by-layer stereolithography process. However, identification of the proper continuous printing speed remains a grand challenge in the process planning. To successfully print a part continuously, the printing speed needs to be carefully adjusted and calibrated for the given geometry. In this paper, we investigate machine learning techniques for modeling and predicting the proper printing speed in the continuous projection stereolithography process. The synthetic dataset is generated by physics-based simulations. Experimental dataset is constructed for training the machine learning models to find the appropriate speed range and the optimum speed. Conventional machine learning techniques including Decision Tree, Naïve Bayes, Nearest Neighbors, and Support Vector Machine (SVM), ensemble methods including Random Forest, Gradient Boosting, and Adaboosting, and the deep learning approach Siamese Network are tested and compared. Experimental results validate the effectiveness of these machine learning models and show that the Siamese Network model gives the highest accuracy.Mechanical Engineerin

Fast Recoating Methods for the Projection-based Stereolithography Process in Micro- and Macro-Scales

The purpose of this paper is to present a recoating method for the development of a direct digital manufacturing (DDM) process that can be an order of magnitude faster than other currently available DDM processes. In the mask-image-projection-based Stereolithography (MIP-SL) process, projection light controlled by a Digital Micromirror Device (DMD) can quickly cure liquid photopolymer resin in a whole area; a fast recoating method is required for achieving truly high-speed fabrication. We investigate the bottom-up projection system in the MIP-SL process. For the macro-scale MIP-SL process, a two-way linear motion approach has been developed for the quick spreading of liquid resin into uniform thin layers. In comparison, a direct pull-up motion can be used in the micro-scale MIP-SL process. 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.Mechanical Engineerin

Development of a Low-Cost Parallel Kinematic Machine for Multi-Directional 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. non-conformal material properties, stair-stepping effect, and limitations on building-around-inserts. Such drawbacks will limit additive manufacturing to be used in more general applications. To enable 6-axis motions between a tool and a work piece, we investigate a Stewart mechanism and developed a low-cost prototype system for multi-directional additive manufacturing processes such as the Fused Deposition Modeling (FDM) and CNC Accumulation. 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 multi-directional additive manufacturing system.Mechanical Engineerin

Effect of Constrained Surface Texturing on Separation Force in Projection Stereolithography

In projection stereolithography (SL) processes, the separation of a newly cured layer from the constrained surface is a historical technical barrier and still greatly limits its printable size, process reliability and print speed. This paper presents an approach to reduce the separation force in projection stereolithography (SL) processes by texturing the constrained surface with radial microgroove patterns. Separation forces with conventional smooth constrained surface and textured surface are both modeled. The analytical model suggests that a proper design of micro patterns of the constrained surface is capable of reducing separation forces greatly. Furthermore, a projection SL testbed with online separation force monitoring unit is developed for experimental study. Experimental results verified the effectiveness of micro surface textures in reducing separation forces. Test cases also show that with the help of the proposed textured constrained surface, parts with wide solid cross sections that could not be printed using conventional methods were manufactured successfully. The influence of the textured constrained surface on the printed parts’ surface roughness is studied, a grey scale projection approach is proposed to eliminate the influence and improve the surface quality of printed parts. Hence, the presented methods can help to improve the manufacturing capability of Projection SL processes.Mechanical Engineerin