Stereolithography Additive Manufacturing Research Articles

Terahertz optical properties of polymethacrylates after thermal annealing

Polymer-based stereolithographic additive manufacturing has been established for the rapid and low-cost fabrication of terahertz (THz) optical components due to its ability to construct complex 3D geometries with high resolution. For polymer-based or integrated optics, thermal annealing processes are often used to optimize material properties. However, despite the growing interest in THz optics fabricated using stereolithography, the effects of thermal annealing on the THz dielectric properties of polymethacrylates compatible with stereolithography have not yet been studied. In this paper, the authors report on the THz ellipsometric response of thermally annealed polymethacrylates prepared using UV polymerization. The findings indicate that the investigated polymethacrylates maintain a stable optical response in the THz spectral range from 650 to 950 GHz after thermal annealing at temperatures up to 70°C for several hours.

Fabrication of Nasoalveolar Molding Devices for the Treatment of Cleft Lip and Palate, Using Stereolithography Additive Manufacturing Processes and Computer-Aided Design Manipulation Software.

Nasoalveolar molding (NAM) is a presurgical orthopedic treatment modality that attempts to reorient misaligned bony and soft tissue structures in patients with clefting of the lip and palate. The NAM devices are implemented prior to surgical intervention in order to minimize the gap across the cleft and thereby reduce tension across the eventual repair. Currently, NAM devices are fabricated in a laboratory and then refined chairside by the provider. The present article describes the potential of three-dimensional (3D) printing and computer-aided design (CAD) software for the fabrication of NAM devices. A workflow was developed to demonstrate the use of 3D printing and CAD software to design NAM devices. This workflow encompasses scanning an impression into CAD software, performing a series of manipulations, and then printing the digital model. To test the workflow, a cleft palate plaster model was scanned into CAD software. Through a series of linear and angular freeform manipulations of the body, the model was modified to display a cleft with a reduced alveolar gap. Sequential molding devices were produced which would gradually apply pressure to targeted areas of hard and soft tissue until the cleft is minimized. The resulting devices are printed using a stereolithography printer. The use of 3D printing and CAD software shows promise in improving the accuracy, speed, and cost-effectiveness of designing NAM devices. The accuracy and flexibility from digitally visualizing the manipulations made to an appliance before its creation can result in a more personalized device for the patient.

Partially stabilized zirconia moulds fabricated by stereolithographic additive manufacturing via digital light processing

Partially stabilized zirconia (PSZ) moulds for aluminium casting were fabricated by stereolithographic additive manufacturing via digital light processing (DLP). Green parts were fabricated on DLP equipment using curable ceramic suspension. These suspensions were studied by performing photopolymerisable and rheological characterisations. Thermogravimetry (TGA) was used to analyse thermal stability of the suspension. Phase composition of sintered parts was determined by X-ray diffraction (XRD), while mechanical properties of green and sintered parts were studied by three-point bending testing. Flexural strength and Young's modulus of sintered parts were determined to be 803.7 ± 59 MPa and 203.4 ± 17 GPa, and these values decreased to 41.5 ± 3.9 MPa and 3.1 ± 0.3 GPa for green parts, respectively. Large pores were suggested to originate failure, with fracture mode being predominantly intergranular. Finally, sintered ceramic investment moulds were prepared by stereolithography and subsequently used for aluminium casting purposes. Dimensions of green parts before sintering were about 0.5% smaller than design values within the plane of layers, and approximately 0.5% larger than design values perpendicular to the layers. Sintering shrinkage was around 22% in both directions. Surface roughness of sintered moulds and aluminium casting materials were quantitatively determined by profilometry.

Stereolithographic Additive Manufacturing of Ceramic Components with Micropatterns for Electromagnetic Wave Control

Stereolithographic Additive Manufacturing of Ceramic Components with Micropatterns for Electromagnetic Wave Control

Evaluation of MRI-compatible pneumatic muscle stepper motors

Abstract The automation of instruments and tools (e.g. bone drill) or robotic devices (e.g. needle positioning robot for prostate surgery) for use in interventional MRI (iMRI) is still challenging due to a lack of accurate, affordable and completely metal-free actuators and motors. Inspired by biological muscles, a bionic equivalent known as the fluid muscle actuator (which can be operated pneumatically or hydraulically) is well-known in the mechanical engineering industry. Fluid muscle actuators have multiple beneficial characteristics: they are simple, self-returning, low-friction and can produce relatively high actuation forces at low diameters and pressures. We present two novel designs for metal-free, pneumatic stepper motors for potential application in iMRI. Our stepper motors are powered by simple pneumatic muscles, which are assembled from low-cost off-the-shelf components. Besides, the components of the stepper motor demonstrators were 3Dprinted using a stereolithographic additive manufacturing process (SLA printing). We evaluate the effect of pneumatic muscle length on contractile force and length. Our results demonstrated the functional feasibility of the pneumatic muscle-powered and fully MRI-compatible stepper motor designs. In a next step, we will optimize the motor´s design, characterize their performance and reliability, and use the stepper motors to power a micropositioning device in iMRI-phantom tests.

Impact performance enhancement of honeycombs through additive manufacturing-enabled geometrical tailoring

We report the enhanced low-velocity impact performance of geometrically tailored honeycomb structures enabled via stereolithography additive manufacturing. Geometrical tailoring of the honeycomb structures was realized by linearly varying the cell wall thickness along the through-thickness direction, while retaining the overall mass of the structures. We examine the effects of cell wall thickness gradient, impact energy, cell topology, geometric scaling and impact direction on the energy absorption capacity and damage mechanisms of tailored honeycombs. For the geometrical and material properties of honeycomb structures considered here, experimental results indicate that, at low impact energy levels (≤30 J), the effect of geometrical tailoring has no significant advantage. Nevertheless, at higher impact energy levels (>30 J), geometrically tailored honeycombs outperform non-tailored counterparts, exhibiting over 60% increase in energy absorption capacity. Experimental observations further reveal that geometrical tailoring results in a change of failure mode from brittle fracture to progressive damage of the cell walls from thinner sections at which the structures were subjected to low-velocity impact, offering superior energy absorption characteristics. The results of this study suggest that the concept of geometrical tailoring in conjunction with additive manufacturing offers new opportunities for the development of high performance architected lattices.

Fabrication of single-crystal superalloy hollow blade based on integral ceramic mold

The integral ceramic mold technique based on stereolithography additive manufacturing and gelcasting technology was applied to casting single-crystal (SX) superalloy parts. The fabrication process for producing alumina-based ceramic molds with kyanite additive and the resultant mold structures were investigated. The results showed that the fabricated alumina-based molds exhibited superior high-temperature mechanical performance and dimensional stability. The high-temperature mechanical performance was attributed to the addition of suitable amounts of kyanite, which led to the mullitization of the raw materials. Moreover, the volume expansion that accompanied kyanite decomposition enabled well-controlled sintering shrinkage and apparent porosity. The ceramic molds prepared with the optimal amount of kyanite exhibited favorable bending strength, creep deformation, sintering shrinkage, and apparent porosity for directional solidification of SX superalloys. Cast trials of a hollow turbine blade using CMSX-4 SX superalloy demonstrated the potential of the proposed approach for rapid-cast SX superalloy parts.

Use of Polymer Scaffolding and Electroplating to Create Porous Metal Structures

Additive manufacturing (AM) offers a fabrication process that provides numerous advantages when compared with traditional fabrication methods. Specifically, AM technology allows for the creation of porous media where porosity and permeability can be precisely controlled. When manufacturing metallic artifacts for biomedical use (e.g., bone implants), the investment in a laser sintering machine can be prohibitive for the budget-conscious enterprises limiting the study and use of this technology. Electroforming, electroplating, and electrotyping have been used for decades to replicate the complex shape of unique artifacts and can be viable techniques to create complex metallic shapes starting from a conductive mandrel. We investigated a fabrication technique that combines the stereolithographic additive manufacturing of a polymeric mandrel with electroforming, to obtain porous composites of polymers and metals. The fabrication method to electroform a porous artifact is presented, and an analytical model of the combined properties of the composite material is provided.

Rapid, continuous additive manufacturing by volumetric polymerization inhibition patterning.

Contemporary, layer-wise additive manufacturing approaches afford sluggish object fabrication rates and often yield parts with ridged surfaces; in contrast, continuous stereolithographic printing overcomes the layer-wise operation of conventional devices, greatly increasing achievable print speeds and generating objects with smooth surfaces. We demonstrate a novel method for rapid and continuous stereolithographic additive manufacturing by using two-color irradiation of (meth)acrylate resin formulations containing complementary photoinitiator and photoinhibitor species. In this approach, photopatterned polymerization inhibition volumes generated by irradiation at one wavelength spatially confine the region photopolymerized by a second concurrent irradiation wavelength. Moreover, the inhibition volumes created using this method enable localized control of the polymerized region thickness to effect single-exposure, topographical patterning.

Experimental study of the compression behavior of mask image projection based on stereolithography manufactured parts

The article presents the results of a series of compression tests on samples manufactured by means of the mask image projection based on stereolithography additive manufacturing technique (MIP-SL). Recent studies demonstrate the orthotropic nature of the MIP-SL materials. A research is initiated by the authors to attempt to predict the degree of anisotropy from the manufacturing parameters of the MIP-SL parts. The article focuses mainly on the development of the experimental compression tests of the first stage of the research. Special attention is paid to the four methods used to obtain the stress-strain curve of the material: strain gages, 2D Digital Image Correlation, extensometer measurements and crosshead displacement measurements. The article shows the advantages and limitations of each method. Finally, the anisotropic behaviour is verified and a testing procedure is set to obtain the constitutive parameters of the MIP-SL tested materials.

Mechanical property modeling of photosensitive liquid resin in stereolithography additive manufacturing: Bridging degree of cure with tensile strength and hardness

Owing to the unique layer-wise production method, additive manufacturing technologies have been widely adopted in rapid prototyping and tooling areas, which often require superior mechanical properties such as tensile strength and hardness. In current literature, most mechanical property studies focusing on additive manufactured materials mainly adopt experimental or simulation-based approaches, and therefore cannot be directly used to accurately estimate and predict the achieved mechanical properties. In addition, information regarding the mechanical properties of photosensitive liquid resin used in the Stereolithography additive manufacturing process is limited. Hence, in this paper, mathematical models are established to quantify the tensile strength and hardness of Stereolithography fabricated materials by estimating the solidification levels of both green parts and Ultraviolet post-cured parts. The established degree of cure model is shown to have an average prediction accuracy of around 94%. In addition, the mechanical property models have an average accuracy of 88% and 90% for tensile strength prediction, and 98% and 95% for hardness prediction of green parts and post-cured parts, respectively. It is also observed that the Ultraviolet post-curing process has the capability of significantly enhancing the studied mechanical properties.

Mechanical behaviour of additively-manufactured polymeric octet-truss lattice structures under quasi-static and dynamic compressive loading

Two different polymer resins were used to create three different octet-truss lattice structures of different densities. The mechanical behaviour of these structures has been examined under both quasi-static and dynamic compressive loading. The structures were printed using stereolithography (SLA) additive manufacturing. The basic building octet unit has a fixed strut length of L=10mm, with the designed strut radius varying from R=0.7mm to 1.3mm to provide structures of different densities. It has been found that the mechanical behaviour of the printed octet structures depends on both the relative density and the intrinsic material properties. Higher density structures show larger effective yield and compressive strengths, while the basic printing material fundamentally determines its macroscopic properties: one material provides a brittle mechanical response under compression while the other provides a tough response. The former lattice structures behaved in a brittle manner at all relative densities, fracturing at small strains. For the latter resin lattice structures, on the other hand, under quasi-static compression, the stress-strain curves changed from a slightly stress oscillating mode at low relative density (i.e. ρ¯=0.13) to a stable stress plateau mode at high relative density (i.e. ρ¯=0.41). The Specific Energy Absorption (SEA) of both lattice structures had a monotonically increasing relationship with relative density, the SEA of the brittle resin specimen is higher than that of the tough resin specimen, while the tough resin specimen exhibits its excellent energy absorption under a wide displacement range. For the dynamic compressive tests, the tougher resin structures displayed strain-rate effects, while the more brittle ones did not. The numerically predicted response of both lattice structures agreed closely with the experimental results.

Cost modeling and analysis for Mask Image Projection Stereolithography additive manufacturing: Simultaneous production with mixed geometries

Additive manufacturing has obtained widespread and continuously increasing interest, owing to its distinguished advantages (e.g., reduced material waste and enhanced manufacturing complexity) compared to traditional manufacturing processes. Currently, the implementation of additive manufacturing in the industrial sector is limited to small-scale production with high customization level. In current literature, the cost analysis for complex production layouts especially with mixed geometries are not fully studied, and some popular additive manufacturing processes are not well investigated for cost performance. Therefore, in this paper, a comprehensive cost model is established to theoretically evaluate the cost performance of the Mask Image Projection Stereolithography process for simultaneously fabricating multiple mixed geometries. In addition, an optimization problem is formulated to reduce the additive manufacturing costs considering the set of decision variables (layer thickness and surface stratification angle) under the constraints of production throughput and part quality. The case study results indicate that 26% of cost savings can be achieved by solving the proposed optimization problem. Furthermore, a sensitivity analysis is conducted which shows that the raw material unit price and the initial investment on additive manufacturing hardware and software are the main cost drivers.

Plasticization of PMMA Components Using Imidazolium-Based Ionic Liquids in Stereolithography Additive Manufacturing

Additive manufacturing (AM), most commonly known as 3D printing, has become the preferred method for many industries to produce prototype objects and temporary replacement parts because of its precise, rapid, and cost-efficient production of sophisticated geometric shapes. Ionic liquids (ILs) have provided solutions while simultaneously impacting various areas of research in the polymer field. For example, ILs can act as plasticizers—affecting both the polymer’s toughness and flexibility. Thus, the incorporation of ILs as additives to stereolithography (SLA) should also provide similar effects. ILs can contribute to current AM methodologies by furnishing the final 3D printed product with a broad range of properties, from increased durability and thermal stability over a longer time span. The final product will not only be a highly-detailed object but will also possess the chemical functionality of the embedded IL. This study will illustrate that ILs indeed affect the mechanical properties of SLA-produced PMMA and have similar effects to traditional phthalate plasticizers.

Design and Fabrication of Sound Absorption Structures for Thermal Spraying by Using Stereolithographic Additive Manufacturing

Design and Fabrication of Sound Absorption Structures for Thermal Spraying by Using Stereolithographic Additive Manufacturing

Fabrication of Bio-ceramic Implants by Stereolithographic Additive Manufacturing

Fabrication of Bio-ceramic Implants by Stereolithographic Additive Manufacturing

Stereolithographic Additive Manufacturing by Using Nanoparticles Paste Materials

Stereolithographic Additive Manufacturing by Using Nanoparticles Paste Materials

材料テクトニクス工学と光造形アディティブ・マニュファクチャリング

材料テクトニクス工学と光造形アディティブ・マニュファクチャリング

ゆらぎを付与した水流制御構造の光造形アディティブ・マニュファクチャリング

ゆらぎを付与した水流制御構造の光造形アディティブ・マニュファクチャリング

Total volatile organic compound emission evaluation and control for stereolithography additive manufacturing process

Additive manufacturing has gained rapidly increasing public interest as it has shown to be a viable and promising alternative to traditional manufacturing processes. Since a great number of additive manufacturing processes are used in indoor environments without proper emission control, there is an urgent need to assess and prevent any potentially harmful effects on the environment and human health. The stereolithography process utilizes photosensitive liquid resins, which might cause hazardous gaseous emissions due to the volatilization process as well as additive manufacturing production activities. Current studies fail to theoretically evaluate these emissions and propose efficient emission control approaches. This paper aims to advance the state-of-the-art on emission evaluation for stereolithography-based additive manufacturing by establishing an analytic model for the total volatile organic compound emissions. The proposed analytical model is experimentally validated. In addition, the measured emission levels are significantly higher than the reported values in literature as well as the recommended emission standards. Therefore, two emission control strategies are proposed as follows: (1) the adoption of Titanium Dioxide photo catalytic oxidation method, and (2) the employment of activated Carbon absorption approach. Compared to current commercial technology, the two proposed strategies are tested and lead to 44.15% and 71.06% reductions in the average total volatile organic compound concentration, and 62.74% and 68.54% in the total volatile organic compound caused by additive manufacturing activities, respectively.