In situ process monitoring includes any technologies that monitor or inspect during an additive manufacturing (AM) process. This article presents the types, process considerations, and challenges of in situ monitoring technologies that can be implemented during an AM process. The types include system health monitoring, melt pool monitoring, and layer monitoring. The article discusses data analysis, and provides an overview of the integration of sensors into AM machines.

Piezoelectric jetting is a common form of additive manufacturing technology. With the development of material science and manufacturing devices, piezoelectric jetting of biomaterials has been applied to various fields including biosensors, tissue engineering, deoxyribonucleic acid (DNA) synthesis, and biorobots. This article discusses the processes involved in piezoelectric jetting of biosensors and biorobots and the applications of piezoelectric jetting for tissue engineering and producing DNA. In addition, it reviews the challenges and perspectives of piezoelectric jetting.

Additive manufacturing (AM) has been growing as a significant research interest in academic and industry research communities. This article presents flexible and biocompatible energy-harvesting devices using AM technology. First, it discusses material selection for achieving piezoelectricity and triboelectricity. Then, the article highlights the structures of energy harvesters and describes their working mechanisms. Next, it covers the additively manufactured implantable piezoelectric and triboelectric energy harvesters. Further, the article describes the 3D-printed wearable energy harvesters as well as their applications. An overview of additively manufactured self-powered sensors is highlighted. Finally, the article discusses the issues for 3D-printed energy harvesters and their roadmap.

This article describes various methods of electrochemical analysis, namely coulometry, electrogravimetry, voltammetry, electrometric titration, and nanometer electrochemistry. The discussion covers the general uses, sample requirements, application examples, advantages, and limitations of these methods. Some of the factors pertinent to electrochemical cells are also provided. In addition, the article provides information on various potentiometric membrane electrodes used to quantify numerous ionic and nonionic species.

Thermoelastic stress analysis (TSA) an increasingly popular infrared (IR)-based technique for measuring stress on the surface of a part subjected to time-varying loads. This article begins by providing a theoretical and historical background of thermoelastic stress analysis. It then describes infrared detectors, such as quantum detectors and thermal/nonquantum detectors, for thermoelastic stress analysis. The article discusses the theoretical aspects for producing thermoelastic stress analysis data and the applications amenable to thermoelastic stress analysis. It concludes with information on the qualitative applications of thermoelastic stress analysis.

Temperature control in heat treating is of paramount importance in maintaining the quality and achieving the desired metallurgical results. This article provides a detailed account of the factors affecting temperature control in heat treating furnaces, with information on temperature control systems, including contact sensors, noncontact sensors, controllers, energy-flow regulators, measurement instruments, and set-point programmers. Common contact sensors include temperature scales, thermocouples, and resistance temperature detectors, whereas optical pyrometers and on-line radiation thermometers fall under the noncontact type. The article describes two types of instrumentation used in heat treating: field test instruments for temperature-uniformity surveys and system-accuracy tests; and controlling, monitoring, and recording instruments for digital instrumentation.

The atmosphere within a furnace chamber is a basic factor in achieving the desired chemical reactions with metals during heat treating. This article presents the fundamentals of heat treating atmospheres, and describes two groups of atmosphere control, namely, furnace atmosphere control and supply atmosphere control. The two basic types of atmospheric supply systems are generated atmospheres and nitrogen-base atmospheres. The article provides a brief overview of the gas reactions associated with oxidation and carbon control to ensure either carburization, or to prevent decarburization. It demonstrates how the carbon potential control is achieved by controlling water vapor concentration, carbon dioxide concentration, or oxygen partial pressure. The article also describes the various devices and analyzers used to monitor sampled gas from furnace atmospheres, namely, chromatographs, oxygen probes, Orsat analyzers, infrared analyzers, dewpoint analyzers, and hot-wire analyzers. Finally, it discusses the advantages, disadvantages, and limitations of these analyzers.

This article provides an overview of the basic theory of infrared (IR), including emissivity and E slope. It explains how the IR thermometer works, and provides guidance on choosing a thermometer, in particular, deciding between a two-color and a single-wavelength thermometer and installing and maintaining them. The article discusses typical applications of induction heating, and describes how the IR thermometer controls the temperature. While the majority of the article discusses spot thermometers, thermal imagers, which are fast and are used for both research and control of the induction process, are also addressed.

Melting with induction crucible furnaces (ICFs) is a well-established and reliable technology, and their maintenance must be performed at regularly scheduled intervals to ensure safe operation. This article discusses monitoring of the refractory lining, and presents an overview of the various wear-indication methods, namely, manual checks, ground leakage indication, evaluation of electrical values of the furnace, and temperature measurement. It also presents the working principle, physical restrictions, limitations, and remarks on these methods.

The optical fiber preform is a long cylinder of glass that contains core and cladding glasses. This article describes the relationship between the peak furnace temperature, fiber draw tension, and fiber draw speed. It focuses on temperature requirements such as product viscosity, hot zone length, temperature profile, and heating cycle to draw the glass. The article provides information on process gases in the draw induction furnace, insulation package for induction heating operations, and furnace design and scalability. It reviews the key factors for the selection of susceptor materials, namely, cost, temperature cycling, and the impact on the product.

Scanners are the most versatile and flexible of the equipment available to the heat treating industry for induction hardening. This article provides a general overview of scanners, and describes various critical factors, including scan speeds, rotational speeds, and center total indicator runout of vertical scanners. It presents information on the frequency selection parameters for scanning applications. The article also discusses the critical parameters and production rates in specifying and developing a tooth-by-tooth hardening process.

Quenching severity is agitation-dependent and therefore, magnitude and turbulence of fluid flow around a part in the quench zone are critically important relative to the uniformity of heat transfer throughout the quenching process. This article provides an overview of the measurement principles for different types of flow devices used in production quench tanks, namely, vane sensors, fluid-quench sensors, caterpillar quench-evaluation sensors, and thermal probes. Various methods of flow measurement in commercial quench tanks may be acceptable for adequate control to ensure a high-quality production process.

Thermal spray processes involve complete or partial melting of a feedstock material in a high-temperature flame, and propelling and depositing the material as a coating on a substrate. This article describes the properties of sprayed electronic materials, including dielectrics, conductors, and resistors, and discusses their implications and associated limitations for device applications and potential remedial measures. The article presents specific examples of electrical/electronic device applications, including electromagnetic interference/radio-frequency interference shielding, planar microwave devices, waveguide devices, sensing devices, solid oxide fuel cells, heating elements, electrodes for capacitors and other electrochemical devices.

This article describes the benefits that can be achieved by using thermal spray on particular engine parts of an automobile. These include improvement in fuel consumption, wear resistance and bonding, and reduction of oil consumption, exhaust heat loss, and cooling heat loss. Typical engine parts are cylinder blocks, cylinder bores, cast iron cylinder liners, piston rings, connecting rod bearings, turbochargers, engine valve lifters, exhaust system parts, and oxygen sensors. The article also describes the benefits of using thermal spray on transmission parts such as synchronizer rings and torque converters.

This article discusses various control processes carried out in powder feeding, thermal spraying, and gas flow of the thermal spray process to standardize the coating quality. Quality of the entire powder feeding process can be achieved by controlling the processing of feeding equipment as well as the characteristics of the powder being fed. Gas flow control can be achieved by using rotameters, critical orifices, and thermal mass flowmeters, whose ability to provide useful information is defined by their resolution, accuracy, linearity, and repeatability. The commercial thermal spray controls discussed here include the open-loop input-based, open-loop output-based, closed-loop input-based, and closed-loop output-based or adaptive controls. The article discusses the common causes and practical solutions for arc starting problems. It also outlines certain important developments in measuring individual and collective particle velocities, temperature, and trajectories as well as other plume characteristics for the plasma spray process.

A close-interval survey (CIS) is a series of structure-to-electrolyte direct current potential measurements performed at regular intervals for assessing the level of cathodic protection (CP) on pipelines and other buried or submerged metallic structures. This article describes the equipment required to perform the CIS. It provides a discussion on the activities that should be performed during the preparation and execution of the CIS. The dynamic stray current identification and compensation by CIS is discussed briefly. The article also explains various factors involved in the validation of CIS data. It concludes with information on CIS data interpretation.

This article focuses on the various types of corrosion-related failure mechanisms and their effects on passive electrical components. The types include halide-induced corrosion, organic-acid-induced corrosion, electrochemical metal migration, silver tarnish, fretting, and metal whiskers. The passive electrical components include resistors, capacitors, wound components, sensors, transducers, relays, switches, connectors, printed circuit boards, and hardware.

This article explores the use of the electrochemical and nonelectrochemical techniques for measuring the corrosion behavior of buried metals and the types of probes used. The electrical resistance technique is the main nonelectrochemical technique used for measuring corrosion rate. Electrochemical techniques discussed include linear polarization resistance, electrochemical noise, harmonic distortion analysis, electrochemical impedance spectroscopy, and hydrogen permeation. The principles of operation for the corrosion measuring techniques are described along with examples of their use in soils.

This article discusses the installation of the most commonly used force-monitoring devices, namely, load cells and piezoelectric force sensors. It describes the purpose and operation of commonly used displacement sensors, such as linear variable differential transformers, proximity sensors, photoelectric sensors, and ultrasonic sensors. The article provides information on the sensors used for detecting tool breakages and flaws in parts, the measurement of material flow during sheet metal forming, and lubrication. It also describes the operating stages of machine vision systems used for automated quality-control purposes. The theory of eddy-current-based material properties evaluation is also discussed.

Principles of metallic corrosion play a fundamental role in developing industrial processes that employ corrosion for constructive purposes. This article examines the changes in kinetics that occur with differentially small potential changes around the equilibrium electrode potentials of two reversible electrodes, such as copper and silver electrodes, in an electrochemical system. It provides a schematic illustration of a reversible cell with copper and silver electrodes to determine a reversible cell potential between the electrodes. An electrode becomes irreversible when the electrode reactions are displaced from equilibrium and the electrode potential is no longer at the equilibrium potential. The article describes irreversible cell potential by using galvanic cells, electrolytic cells, and corrosion cells.