Mask-Image-Projection-based Stereolithography Research Articles

An Investigation of Integrated Multiscale Three-Dimensional Printing for Hierarchical Structures Fabrication

Abstract Nature provides us with a large number of functional material systems consisting of hierarchical structures, where significant variations in dimensions are present. Such hierarchical structures are difficult to build by traditional manufacturing processes due to manufacturing limitations. Nowadays, three-dimensional (3D) objects with complex structures can be built by gradually accumulating in a layer-based additive manufacturing (AM); however, the hierarchical structure measured from macroscale to nanoscale sizes still raises significant challenges to the AM processes, whose manufacturing capability is intrinsically specified within a certain scope. It is desired to develop a multiscale AM process to narrow this gap between scales of feature in hierarchical structures. This research aims to investigate an integration approach to fabricating hierarchical objects that have macro-, micro-, and nano-scales features in an object. Firstly, the process setup and the integrated process of two-photon polymerization (TPP), immersed surface accumulation (ISA), and mask image projection-based stereolithography (MIP-SL) were introduced to address the multiscale fabrication challenge. Then, special hierarchical design and process planning toward integrating multiple printing processes are demonstrated. Lastly, we present two test cases built by our hierarchical printing method to validate the feasibility and efficiency of the proposed multiscale hierarchical printing approach. The results demonstrated the capability of the developed multiscale 3D printing process and showed its future potential in various novel applications, such as optics, microfluidics, cell culture, as well as interface technology.

Mask image grayscale regulation for projection stereolithography in tissue engineering

The mask-image-projection-based stereolithography (MIP-SL) is one of the most promising methods for preparing biological scaffolds. In this paper, a mask image planning method based on grayscale regulation is proposed based on the characteristics of the bio-scaffold structure. It is based on support vector machine method and iterative method to intelligently regulate mask pixel gray value, which can achieve low exposure error and accordingly better curing quality. Furthermore, in order to discuss the properties of grayscale regulation, single pixel light intensity function acquisition experiment and stereolithography simulation based on light intensity function and mask grayscale regulation experiment were carried out. Results show that the light intensity distribution function of single pixel follows Gaussian distribution, and the light intensity energy between adjacent pixels will affect each other. The grayscale regulation scheme can improve the degree of reduction of the cured shape of the resin and is beneficial to the curing accuracy.

3D-Printing Piezoelectric Composite with Honeycomb Structure for Ultrasonic Devices.

Piezoelectric composites are considered excellent core materials for fabricating various ultrasonic devices. For the traditional fabrication process, piezoelectric composite structures are mainly prepared by mold forming, mixing, and dicing-filing techniques. However, these techniques are limited on fabricating shapes with complex structures. With the rapid development of additive manufacturing (AM), many research fields have applied AM technology to produce functional materials with various geometric shapes. In this study, the Mask-Image-Projection-based Stereolithography (MIP-SL) process, one of the AM (3D-printing) methods, was used to build BaTiO3-based piezoelectric composite ceramics with honeycomb structure design. A sintered sample with denser body and higher density was achieved (i.e., density obtained 5.96 g/cm3), and the 3D-printed ceramic displayed the expected piezoelectric and ferroelectric properties using the complex structure (i.e., piezoelectric constant achieved 60 pC/N). After being integrated into an ultrasonic device, the 3D-printed component also presents promising material performance and output power properties for ultrasound sensing (i.e., output voltage reached 180 mVpp). Our study demonstrated the effectiveness of AM technology in fabricating piezoelectric composites with complex structures that cannot be fabricated by dicing-filling. The approach may bring more possibilities to the fabrication of micro-electromechanical system (MEMS)-based ultrasonic devices via 3D-printing methods in the future.

Mask Video Projection-Based Stereolithography With Continuous Resin Flow

The mask image projection-based stereolithography (MIP-SL) is a low-cost and high-resolution additive manufacturing (AM) process. However, the slow speed of part separation and resin refilling is the primary bottleneck that limits the fabrication speed of the MIP-SL process. In addition, the stair-stepping effect due to the layer-based fabrication process limits the surface quality of built parts. To address the critical issues in the MIP-SL process related to resin refilling and layer-based fabrication, we present a mask video projection-based stereolithography (MVP-SL) process with continuous resin flow and light exposure. The newly developed AM process enables the continuous fabrication of three-dimensional (3D) objects with ultra-high fabrication speed. In the paper, the system design to achieve mask video projection and the process settings to achieve ultrafast fabrication speed are presented. The relationship between process parameters and the surface quality of the built parts is discussed. Test results illustrate that the MVP-SL process with a continuous resin flow can build three-dimensional objects within minutes, and the surface quality of the fabricated objects is significantly improved.

Three-Dimensional Printed Piezoelectric Array for Improving Acoustic Field and Spatial Resolution in Medical Ultrasonic Imaging.

Piezoelectric arrays are widely used in non-destructive detecting, medical imaging and therapy. However, limited by traditional manufacturing methods, the array’s element is usually designed in simple geometry such as a cube or rectangle, restricting potential applications of the array. This work demonstrates an annular piezoelectric array consisting of different concentric elements printed by Mask-Image-Projection-based Stereolithography (MIP-SL) technology. The printed array displays stable piezoelectric and dielectric properties. Compared to a traditional single element transducer, the ultrasonic transducer with printed array successfully modifies the acoustic beam and significantly improves spatial resolution.

Photocuring Temperature Study for Curl Distortion Control in Projection-Based Stereolithography

Polymerization shrinkage and thermal cooling effect have been identified as two major factors that lead to the curl distortion in the stereolithography apparatus (SLA) process. In this paper, the photocuring temperature during the building process of mask image projection-based stereolithography (MIP-SL) and how it affects parts' curl distortion are investigated using a high-resolution infrared (IR) camera. Test cases of photocuring layers with different shapes, sizes, and layer thicknesses have been designed and tested. The experimental results reveal that the temperature increase of a cured layer is mainly related to the layer thickness, while the layer shapes and sizes have little effect. The photocuring temperatures of built layers using different exposure strategies including varying exposure time, grayscale levels, and mask image patterns have been studied. The curl distortions of a test case based on various exposure strategies have been measured and analyzed. It is shown that, by decreasing the photocuring temperature of built layers, the exposure strategies using grayscale levels and mask image patterns can effectively reduce the curl distortion with the expense of increased building time. In addition to curl distortion control, the photocuring temperature study also provides a basis for the curl distortion simulation in the MIP-SL process.

3D printing of piezoelectric element for energy focusing and ultrasonic sensing

Piezoelectric ceramics are currently of considerable interest for their capabilities of converting compressive/tensile stresses to an electric charge, or vice versa. Because ceramics cannot be cast and machined easily, additive manufacturing (AM) processes (3D printing technology) open an effective pathway in geometrical flexibility. However, the piezoelectric properties limit the application of printed ceramics. This work demonstrates that a piezoelectric-composite slurry with BaTiO3 nanoparticles (100nm) can be 3D printed using Mask-Image-Projection-based Stereolithography (MIP-SL) technology. After a post-process, the density of 5.64g/cm3 was obtained, which corresponds to 93.7% of the density of bulk BaTiO3 (6.02g/cm3). The printed ceramic exhibits a piezoelectric constant and relative permittivity of 160pCN−1 and 1350 respectively. An ultrasonic transducer with printing focused piezoelectric element was fabricated to realize the energy focusing and ultrasonic sensing. A 6.28MHz ultrasonic scan was achieved by the transducer and successfully visualized the structure of a porcine eyeball.

Ceramic fabrication using Mask-Image-Projection-based Stereolithography integrated with tape-casting

Ceramic components with complex geometry are difficult to fabricate. Layer-based additive manufacturing processes such as ceramic-suspension-based stereolithography (SL) provide a direct way of fabricating ceramic components from computer-aided design (CAD) models. In such an SL process, fine ceramic powders are mixed with liquid photocurable resin into ceramic suspension. The suspension-based slurry is then used in the SL process to fabricate green parts with desired shapes. A sintering process is further required to convert the green parts into dense ceramic components. In this paper, several key challenges of the ceramic-suspension-based SL process are discussed including the recoating and curing ceramic suspension with high solid loading. A novel Mask-Image-Projection-based Stereolithography (MIP-SL) process by integrating ceramic tape-casting and bottom-up projection methods is presented for fabricating dense ceramic components from CAD models. Various approaches to increase the solid loading in green parts are discussed including suspension preparation, image projection, layer recoating and separation. A prototype system based on the presented ceramics fabrication process has been developed. Test cases of different types of ceramics are presented to demonstrate the effectiveness of the presented fabrication method. The post-processing of green parts to convert them into dense ceramic components is also discussed with some sintering results presented.

Digital material fabrication using mask‐image‐projection‐based stereolithography

PurposeThe purpose of this paper is to present a mask‐image‐projection‐based stereolithography (MIP‐SL) process that can combine two base materials with various concentrations and structures to produce a solid object with desired material characteristics. Stereolithography is an additive manufacturing process in which liquid photopolymer resin is cross‐linked and converted to solid. The fabrication of digital material requires frequent resin changes during the building process. The process presented in this paper attempts to address the related challenges in achieving such fabrication capability.Design/methodology/approachA two‐channel system design is presented for the multi‐material MIP‐SL process. In such a design, a coated thick film and linear motions in two axes are used to reduce the separation force of a cured layer. The material cleaning approach to thoroughly remove resin residue on built surfaces is presented for the developed process. Based on a developed testbed, experimental studies were conducted to verify the effectiveness of the presented process on digital material fabrication.FindingsThe proposed two‐channel system can reduce the separation force of a cured layer by an order of magnitude in the bottom‐up projection system. The developed two‐stage cleaning approach can effectively remove resin residue on built surfaces. Several multi‐material designs have been fabricated to highlight the capability of the developed MIP‐SL process.Research limitations/implicationsA proof‐of‐concept testbed has been developed. Its building speed and accuracy can be further improved. The tests were limited to the same type of liquid resins. In addition, the removal of trapped air is a challenge in the presented process.Originality/valueThis paper presents a novel and a pioneering approach towards digital material fabrication based on the stereolithography process. This research contributes to the additive manufacturing development by significantly expanding the selection of base materials in fabricating solid objects with desired material characteristics.

Smooth surface fabrication in mask projection based stereolithography

The surface finish is critical for applications such as optics, micro-fluid flow and mechanical assembly, in which optical lenses, fluidic channels and rotating components are all required to be smooth. However, the stair-stepping effect is well known in the layer-based additive manufacturing processes, in which a three-dimensional model is approximated by a set of two-dimensional layers. Consequently the fabricated surfaces have poor surface finishes especially those that are close to the horizontal plane. In this paper, a novel approach for achieving improved surface finish is presented for the mask-image-projection-based stereolithography (MIP-SL) process. Theoretical models and parameter characterization are presented for the developed methods. Accordingly, the process planning and calibration approaches for fabricating smooth up-facing surfaces in the MIP-SL process have been developed. Multiple test cases based on various types of curved surfaces have been performed. A comparison of the build results based on the traditional and the newly developed approaches illustrates the effectiveness of our method.

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.