X-ray microcomputed tomography (microCT) has become an established method of testing and analyzing additively manufactured parts in recent years, being especially useful and accurate for d...

X-Ray microcomputed tomography in additive manufacturing : a review of the current technology and applications

In this review, the use of x-ray computed tomography (XCT) is examined, identifying the requirement for volumetric dimensional measurements in industrial verification of additively manufactured (AM) parts. The XCT technology and AM processes are summarised, and their historical use is documented. The use of XCT and AM as tools for medical reverse engineering is discussed, and the transition of XCT from a tool used solely for imaging to a vital metrological instrument is documented. The current states of the combined technologies are then examined in detail, separated into porosity measurements and general dimensional measurements. In the conclusions of this review, the limitation of resolution on improvement of porosity measurements and the lack of research regarding the measurement of surface texture are identified as the primary barriers to ongoing adoption of XCT in AM. The limitations of both AM and XCT regarding slow speeds and high costs, when compared to other manufacturing and measurement techniques, are also noted as general barriers to continued adoption of XCT and AM.

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X-ray computed tomography for additive manufacturing: a review

Effects of defects on mechanical properties in metal additive manufacturing: A review focusing on X-ray tomography insights

Nature has developed high-performance materials and structures over millions of years of evolution and provides valuable sources of inspiration for the design of next-generation structural materials, given the variety of excellent mechanical, hydrodynamic, optical, and electrical properties. Biomimicry, by learning from nature's concepts and design principles, is driving a paradigm shift in modern materials science and technology. However, the complicated structural architectures in nature far exceed the capability of traditional design and fabrication technologies, which hinders the progress of biomimetic study and its usage in engineering systems. Additive manufacturing (three-dimensional (3D) printing) has created new opportunities for manipulating and mimicking the intrinsically multiscale, multimaterial, and multifunctional structures in nature. Here, an overview of recent developments in 3D printing of biomimetic reinforced mechanics, shape changing, and hydrodynamic structures, as well as optical and electrical devices is provided. The inspirations are from various creatures such as nacre, lobster claw, pine cone, flowers, octopus, butterfly wing, fly eye, etc., and various 3D-printing technologies are discussed. Future opportunities for the development of biomimetic 3D-printing technology to fabricate next-generation functional materials and structures in mechanical, electrical, optical, and biomedical engineering are also outlined.

Recent Progress in Biomimetic Additive Manufacturing Technology: From Materials to Functional Structures.

Emerging Technologies of Flexible Pressure Sensors: Materials, Modeling, Devices, and Manufacturing

This paper presents a new additive manufacturing (AM) process to directly and continuously print piezoelectric devices from polyvinylidene fluoride (PVDF) polymeric filament rods under a strong electric field. This process, called ?electric poling-assisted additive manufacturing or EPAM, combines AM and electric poling processes and is able to fabricate free-form shape piezoelectric devices continuously. In this process, the PVDF polymer dipoles remain well-aligned and uniform over a large area in a single design, production and fabrication step. During EPAM process, molten PVDF polymer is simultaneously mechanically stresses in-situ by the leading nozzle and electrically poled by applying high electric field under high temperature. The EPAM system was constructed to directly print piezoelectric structures from PVDF polymeric filament while applying high electric field between nozzle tip and printing bed in AM machine. Piezoelectric devices were successfully fabricated using the EPAM process. The crystalline phase transitions that occurred from the process were identified by using the Fourier transform infrared spectroscope. The results indicate that devices printed under a strong electric field become piezoelectric during the EPAM process and that stronger electric fields result in greater piezoelectricity as marked by the electrical response and the formation of sharper peaks at the polar ? crystalline wavenumber of the PVDF polymer. Performing this process in the absence of an electric field does not result in dipole alignment of PVDF polymer. The EPAM process is expected to lead to the widespread use of AM to fabricate a variety of piezoelectric PVDF polymer-based devices for sensing, actuation and energy harvesting applications with simple, low cost, single processing and fabrication step.

https://iopscience.iop.org/article/10.1088/0964-1726/23/9/095044/pdf

Electric poling-assisted additive manufacturing process for PVDF polymer-based piezoelectric device applications

X-ray computed tomography (CT) is uniquely suited for dimensional measurement of components having internal geometry, difficult-to-reach part features, and easy-to-deform or flexible structures. Through the development of standards it is also becoming accepted as a metrology tool. The objectives of this study are to compare dimensional measurements on artifacts containing internal structures and mechanically compliant features using current state-of-the-art CT and coordinate measure machine (CMM) techniques. It also aims to discuss some of the issues with recently developed standards for CT measurement uncertainty estimation. To illustrate the challenges of CMM and the potential of X-ray CT for reliable dimensional inspection, two different problems are presented: 1) characterization of internal geometry in a metallic artifact that has features inaccessible to tactile or vision-based measurement techniques; and 2) evaluation of dimensional measurement of diameters, form, and relative distances in the components of a flexible object with stems that bend due to mechanical contact by tactile instruments, e.g., CMM. In addition, some issues with the direct application of the ISO 15530 series for the estimation of CT measurement uncertainties are discussed, and a generalized formalism for uncertainty budgeting in CT metrology (still based on the ISO 15530 guidelines but with some differences) is applied to the measurements presented throughout this paper. For dimensions of geometric features ranging from 0.6 mm to 65 mm, a comparison between CT and CMM measurements typically resulted in differences of approximately 5 μm or less for most of the measurements, while expanded uncertainties computed for the CT measurements ranged from 1 to 20 μm. CT measurements on the internal geometries resulted in uncertainties comparable to CMM data that were obtained with the metallic artifact disassembled. However, in the particular case of measuring compliant structures, the conventional CMM strategies led to large systematic errors in the measurements. It is demonstrated that using extrapolation methods, measurements from these two systems converged to within ±2 μm.

Dimensional metrology with X-ray CT: A comparison with CMM measurements on internal features and compliant structures

This paper presents the method of a six-degree-of-freedom (DOF) posture measurement in a linear stage by employing a single unit of an optical encoder. The proposed optical encoder was constructed to simultaneously measure the posture along the traveling axis; angular errors, pitch, yaw and roll; and translational errors, ?X, ?Y and ?Z. It consists of a diffractive optical element, a corner cube, four separate two-dimensional position-sensitive detectors, four photodiodes and auxiliary optics components. The circularly polarizing interferometric technique was integrated to measure the displacement of the stage along the traveling axis in a robust manner and the resolution was estimated to be less than 0.4 nm. Two types of stages were employed for the measurement implementation, the piezoelectric transducer-driven and the ballscrew-driven, and they were feedback-controlled for the traveling axis, respectively. With a single travel of the stage, it provided a six-DOF motion error with a high resolution, less than 0.03 arcsec, 20 nm and 0.4 nm for angular errors, ?Y and ?Z, and ?X, respectively, at the same time. As a result, it was seen that motion errors of the stage have relevance to the driving mechanism and the whole construction of the stage.

https://iopscience.iop.org/article/10.1088/0957-0233/22/10/105901/pdf

Design and construction of a single unit multi-function optical encoder for a six-degree-of-freedom motion error measurement in an ultraprecision linear stage

Recently, in accordance with the increasing market demand for ultraprecision technology, a high precision multi-degree-of-freedom displacement measurement technology has become important for industrial applications such as the field of manufacturing and inspection because those physical quantities, linear and angular displacements, are key parameters for keeping and improving quality control of a production system A number of instruments capable of precise multi-degree-of-freedom measurements have been built and some novel techniques have been introduced The current state-of-art techniques for multi-degree-of-freedom motion error measurement in a linear stage using laser encoder-implemented system are reviewed First, we summarize the basic principles behind the measurement technology of the motion error in a stage and simple encoder system Next, the basic design principles of practical laser encoder system are discussed using the experience of past and existing cases to refer to the important points and the major scientific results The current trends in the field are significantly discussed, including the novel techniques under construction and advanced technologies Lastly, the future of multi-functional laser encoder-implemented system, highlighting the kinds of new science upcoming in the next few years, is discussed

Multi-degree-of-freedom motion error measurement in an ultraprecision machine using laser encoder - Review †

This paper represents a polymeric piezoelectric manufacturing process for sensing and actuation applications. The electric poling-assisted additive manufacturing (EPAM) process combining additive manufacturing (AM) with polymeric poling process has been recently introduced. This process keeps piezoelectric polymer dipoles well-aligned and uniform over a large area in a single-step direct printing process. Here, the EPAM process was employed to directly print polyvinylidene fluoride (PVDF) polymer; sensing and actuation performance was tested with dynamometer, a baseline comparison measuring instrument. Also, the plasma-assisted poling process that potentially increases piezoelectricity was briefly introduced and discussed with a preliminary result. As a result, this study promises new multi-functional materials, novel designs, and approaches in a single AM and fabrication step by combining AM with piezoelectric polymer poling methods in convenient, fast, and precise manner.

ChaBum Lee

Papers

Electric poling-assisted additive manufacturing process for PVDF polymer-based piezoelectric device applications

Dimensional metrology with X-ray CT: A comparison with CMM measurements on internal features and compliant structures

Design and construction of a single unit multi-function optical encoder for a six-degree-of-freedom motion error measurement in an ultraprecision linear stage

Multi-degree-of-freedom motion error measurement in an ultraprecision machine using laser encoder - Review †

Polyvinylidene fluoride (PVDF) direct printing for sensors and actuators