One-step volumetric additive manufacturing of complex polymer structures.

Two limitations of additive manufacturing methods that arise from layer-based fabrication are slow speed and geometric constraints (which include poor surface quality). Both limitations are overcome in the work reported here, introducing a new volumetric additive fabrication paradigm that produces photopolymer structures with complex nonperiodic three-dimensional geometries on a time scale of seconds. We implement this approach using holographic patterning of light fields, demonstrate the fabrication of a variety of structures, and study the properties of the light patterns and photosensitive resins required for this fabrication approach. The results indicate that low-absorbing resins containing ~0.1% photoinitiator, illuminated at modest powers (~10 to 100 mW), may be successfully used to build full structures in ~1 to 10 s

Design for Additive Manufacturing: A Method to Explore Unexplored Regions of the Design Space

Additive Manufacturing (AM) technologies enable the fabrication of parts and devices that are geometrically complex, have graded material compositions, and can be customized. To take advantage of these capabilities, it is important to assist designers in exploring unexplored regions of design spaces. We present a Design for Additive Manufacturing (DFAM) method that encompasses conceptual design, process selection, later design stages, and design for manufacturing. The method is based on the process-structure-property-behavior model that is common in the materials design literature. A prototype CAD system is presented that embodies the method. Manufacturable ELements (MELs) are proposed as an intermediate representation for supporting the manufacturing related aspects of the method. Examples of cellular materials are used to illustrate the DFAM method.Mechanical Engineerin

Thermophysical Phenomena in Metal Additive Manufacturing by Selective Laser Melting: Fundamentals, Modeling, Simulation and Experimentation

Among the many additive manufacturing (AM) processes for metallic materials, selective laser melting (SLM) is arguably the most versatile in terms of its potential to realize complex geometries along with tailored microstructure. However, the complexity of the SLM process, and the need for predictive relation of powder and process parameters to the part properties, demands further development of computational and experimental methods. This review addresses the fundamental physical phenomena of SLM, with a special emphasis on the associated thermal behavior. Simulation and experimental methods are discussed according to three primary categories. First, macroscopic approaches aim to answer questions at the component level and consider for example the determination of residual stresses or dimensional distortion effects prevalent in SLM. Second, mesoscopic approaches focus on the detection of defects such as excessive surface roughness, residual porosity or inclusions that occur at the mesoscopic length scale of individual powder particles. Third, microscopic approaches investigate the metallurgical microstructure evolution resulting from the high temperature gradients and extreme heating and cooling rates induced by the SLM process. Consideration of physical phenomena on all of these three length scales is mandatory to establish the understanding needed to realize high part quality in many applications, and to fully exploit the potential of SLM and related metal AM processes

Comparison between Eight-Axis Articulated Robot and Five-Axis CNC Gantry Laser Metal Deposition Machines for Fabricating Large Components

Featured Application: Laser metal deposition of large axisymmetric components. Laser metal deposition (LMD) is an additive manufacturing (AM) process capable of producing large components for the aerospace and oil and gas industries. This is achieved by mounting the deposition head on a motion system, such as an articulated robot or a gantry computer numerical control (CNC) machine, which can scan large volumes. Articulated robots are more flexible and less expensive than CNC machines, which on the other hand, are more accurate. This study compares two LMD systems with different motion architectures (i.e., an eight-axis articulated robot and a five-axis CNC gantry machine) in producing a large gas turbine axisymmetric component. The same process parameters were applied to both machines. The deposited components show no significant differences in geometry, indicating that the different performances in terms of accuracy of the two machines do not influence the outcome. The findings indicate that LMD can consistently produce large-scale axisymmetric metal components with both types of equipment. For such an application, the user has the option of using an articulated robot when flexibility and cost are essential, such as in a research context, or a CNC machine where ease of programming and process standardization are important elements, such as in an industrial environment

Coordination of spatial and temporal laser beam profile towards ultra-fine feature fabrication in laser powder bed fusion

Laser powder bed fusion (LPBF) is a metal additive manufacturing technology that provides high shape and application flexibilities. Although dimensional flexibility is high in theory thanks to the non-contactless micro range processing tool (i.e., laser beam) and powder, the fabrication robustness of thin and ultra-thin features (dnominal?200 ?m) is still a challenge for the technology. In particular, geometrical fidelity and dimensional accuracy problems have been raising towards the ultra-thin fabrication segment. Although there were different studies that presented solutions for robust and sustainable fabrication strategy in ultra-thin segment in the literature, the vast majority of them focused on process itself directly, and the technological feasibility of the LPBF systems was not considered. However, without considering technological feasibility of the LPBF systems, the presented solutions in the literature are far from providing solid basis and they may mislead the users in the case of direct application. In this sense, this study mainly focused on the scanning capability of the systems for features under 200 µm dimensional range with temporal and spatial laser beam management in the case of conventional scanning strategy (contour and hatch). For this purpose, the fabrication process reduced to the two dimensions (scanning region) via the laser marking tests, and custom laser parameters, which are provided by the industrial grade open architecture LPBF system, has been used. Here, it has been reported that two different errors related to scanning performance and process parameters for continuous and pulsed wave laser emission modes, separation, and compensation of these two errors, and investigation methodology for technological feasibility of the LPBF machines. Moreover, in the pulsed wave laser emission mode, two linear parameters have been presented to optimize spatial energy distribution. Considering the results coming from the practical observations and measurements, it is possible to indicate that the technological feasibility of the utilized LPBF system should be key concern before laser or scan related parameters optimization. The results show that if correct scanning parameters have been selected in the technological feasibility window of the system, scan trajectories based on conventional hatching method can be carried out with sufficient geometrical accuracy

redesign and manufacturing of a metal towing hook via laser additive manufacturing with powder bed

Abstract An approach to redesign and manufacture a metal towing hook via Selective Laser Melting is discussed. Some reference criteria and general guidelines are considered step-by-step to concurrently address lightening, manufacturability and job planning. Grounds are given for the application of Additive Manufacturing for complex components to the purpose of material saving and increased safety factor

3D Micromachining of Optical Devices on Transparent Material by Ultrafast Laser

Ultrafast lasers, also referred to as ultrashort pulse lasers, have played an important role in the development of next generation manufacturing technologies in recent years. Their broad range of applications has been investigated in the field of microstructure processing for the biomedical, optical, and many other laboratory and industrial fields. Ultrafast laser machining has numerous unique advantages, including high precision, a small heat affected area, high peak intensity, 3D direct-writing, and other flexible capabilities When integrated with optical delivery, motion devices and control systems, one-step fabrication of assemble-free micro-devices can be realized. In particular, ultrafast lasers enable the creation of various three-dimensional, laser-induced modifications using an extremely high peak intensity over a short time frame, producing precise ablation of material and a small heat affected area in transparent materials. In contrast, lasers with longer pulse durations are based on a thermal effect, which results in significant melting in the heat affected area. In general, ultrafast laser micromachining can be used either to subtract material from or to change the material properties of both absorptive and transparent substances. Recently, integrated micro-devices including optical fiber sensors, microfluidic devices, and lab-on-chips (LOC) have gained worldwide recognition because of their unique characteristics. These micro-devices have been widely used for a broad range of applications, from fundamental research to industry. The development of integrated glass micro-devices introduced new possibilities for biomedical, environmental, civil and other industries and research areas. Of these devices, optical fiber sensors are recognized for their small size, accuracy, resistance to corrosion, fast response and high integration. They have demonstrated their excellent performance in sensing temperature, strain, refractive index and many other physical quantities. In addition to the all-in-fiber device, the LOC is another attractive candidate for use in micro-electro-mechanical systems (MEMS) because it includes several laboratory functions on a single integrated circuit. LOCs provide such advantages as low fluid volume consumption, improved analysis and response times due to short diffusion distances, and better process control, all of which are specific to their application. Combining ultrafast laser micromachining techniques with integrated micro-devices has resulted in research on a variety of fabrication methods targeted for particular purposes. In this dissertation, the direct creation of three-dimensional (3D) structures using an ultra-fast laser was investigated for use in optical devices. This research was motivated by the desire to understand more fully the relationship among laser parameters, material properties and 3D optical structures. Various all-in-fiber sensors in conjunction with femtosecond laser ablation and irradiation were investigated based on magnetic field, temperature and strain application. An incoherent optical carrier based microwave interferometry technique was used for in-situ weak reflector fabrication and a picosecond laser micromachining technique was introduced for developing LOCs with unlimited utilization potential

AUTOMATIC ERROR DETECTION AND CORRECTION IN LASER METAL WIRE DEPOSITION - AN ADDITIVE MANUFACTURING TECHNOLOGY

Additive manufacturing (AM) technology involves building three-dimensional objects by adding material layer-upon-layer under computer control. Metal additive manufacturing offers new possibilities, not only in design, but also in the choice of materials. However, the additive process remains at a lower maturity level compared to the conventional subtractive processes such as milling, drilling and machining among others. Scientifically, there is a safety concern relating to the accuracy of the AM process, how printed products will perform over time and the consistency of their quality. Process accuracy and eventual part quality is compromised due to errors introduced by each of the building steps in the process.Laser metal deposition with wire (LMD-w) is an additive manufacturing technology that involves feeding metal wire through a nozzle and melting the wire with a high-power laser. The technology is being largely researched for use in the aerospace industry to fabricate large aircraft components. With efficient process control, i.e. sensing, processing, and feedback correction of errors, the LMD-w technology has the potential to change the course of manufacturing. However, a prominent limitation in LMD-w is the difficulty in controlling the process.This work proposes a method for detecting surface geometry errors in a deposited layer in the LMD-w process via laser height scanning and high-speed image processing. The controlled process is simplified into a linear system. The aim is to develop an effective sensing and correction module that automatically detects irregularities in each layer before proceeding to subsequent layers, which will reduce part porosity and improve inter-layer bond integrity

Geometry compensation for additive manufacturing

Durant el procés de fabricació additiva (AM), els gradients de temperatura són substancials i transitoris, resultant en tensions residuals irreversibles i deformació plàstica que tenen un efecte negatiu en la resistència, resistència a la fatiga, ductilitat i tolerància geomètrica del material. Aquestes variants potser no compleixen amb els requisits necessaris. Encara que s'han estudiat i aplicat amb èxit diverses estratègies, com variar el temps de residència, alterar el patró d'escaneig i implementar un preescalfament, per reduir les tensions residuals i les distortions en AM, encara es requereix més estudi sobre mètodes que es concentrin en modificar els paràmetres geomètrics de l'estructura abans d'imprimir. L'estat actual de l'art en aquest camp es focalitza principalment en modificar la malla dels arxius STL (StereoLithography) per compensar les variacions geomètriques. No obstant això, el treball actual presenta un algoritme que modifica l'estratègia d'escaneig en el llenguatge de control numèric utilitzat per AM, en aquest cas GCode, permetent al dissenyador modificar l'estratègia d'escaneig sense haver de modificar la malla i després usar un tallador per generar un nou GCode. El camp de desplaçament d'aquesta tesi es deriva d'un model termo-mecànic (TM) de tres dimensions amb un marc visco-plàstic-elasto-plàstic, i els models emprats són components industrials com engranatges, compressors i impulsors. Els resultats d'aquest estudi indiquen que el mètode de modificació dels nodes de malla va produir resultats superiors en comparació amb l'algoritme de compensació de distorsió per a components industrials. En particular, l'algoritme només va poder reduir les distortions per al mateix component en un 30%, mentre que el mètode de modificació de malla va poder reduir les distortions per a un impulsor en un 50%.Durante el proceso de fabricación aditiva (AM), los gradientes de temperatura son sustanciales y transitorios, lo que resulta en tensiones residuales irreversibles y deformación plástica que tienen un efecto negativo en la resistencia, resistencia a la fatiga, ductilidad y tolerancia geométrica del material. Estas variantes pueden no cumplir con los requisitos necesarios. Aunque se han estudiado y aplicado con éxito diversas estrategias, como variar el tiempo de residencia, alterar el patrón de escaneo e implementar un precalentamiento, para reducir las tensiones residuales y las distorsiones en AM, aún se requiere más estudio sobre métodos que se concentren en modificar los parámetros geométricos de la estructura antes de imprimir. El estado actual del arte en este campo se enfoca principalmente en modificar la malla de los archivos STL (StereoLithography) para compensar las variaciones geométricas. Sin embargo, el trabajo actual presenta un algoritmo que modifica la estrategia de escaneo en el lenguaje de control numérico utilizado para AM, en este caso GCode, lo que permite al diseñador modificar la estrategia de escaneo sin tener que modificar la malla y luego usar un cortador para generar un nuevo GCode. El campo de desplazamiento de esta tesis se deriva de un modelo térmico-mecánico (TM) de tres dimensiones con un marco visco-plástico-elasto-plástico, y los modelos empleados son componentes industriales como engranajes, compresores e impulsores. Los resultados de este estudio indican que el método de modificación de los nodos de malla produjo resultados superiores en comparación con el algoritmo de compensación de distorsión para componentes industriales. En particular, el algoritmo solo pudo reducir las distorsiones para el mismo componente en un 30%, mientras que el método de modificación de malla pudo reducir las distorsiones para un impulsor en un 50%.During the process of Additive Manufacturing (AM), the temperature gradients are substantial and transient, resulting in irreversible residual stresses and plastic deformation that have a negative effect on the material’s strength, fatigue resistance, ductility, and geometrical tolerance. These variants may not meet the necessary requirements. While various strategies, such as varying the dwell time, altering the scanning pattern, and implementing pre-heating, have been studied and successfully implemented to reduce residual stresses and distortions in AM, methods that concentrate on modifying the geometrical parameters of the structure prior to printing require additional study. The current state of the art in this field focuses primarily on modifying the mesh of STereoLithography (STL) files to compensate for geometrical variations. Nevertheless, the current work presents an algorithm that modifies the scanning strategy in the numerical control language used for AM, in this case GCode, allowing the designer to modify the scanning strategy without having to modify the mesh and then use a slicer to generate a new GCode. This dissertation’s displacement field is derived from a three-dimensional coupled Thermal-Mechanical (TM) model with a visco-plastic-elasto-plastic framework, and the employed models are industrial components such as gears, compressors, and impellers. The results of this study indicate that the method of modifying mesh nodes produced superior results when compared to the algorithm for distortion compensation for industrial components. In particular, the algorithm was only able to reduce distortions for the same component by 30%, whereas the mesh modification method was able to reduce distortions for an impeller by 50%. This demonstrates the effectiveness of the mesh modification method in enhancing the geometrical tolerance and minimizing distortions in industrial components, making it a valuable instrument for enhancing the performance