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The main optical characteristic of pyrometers is the dependence of their spot diameter on the distance between the pyrometer and the measured object. However, this dependence is currently not amenable to strict calculation and is measured experimentally, emphasizing the importance of selecting the adequate method for measuring the spot diameter. This parameter can be determined using either circular (iris) or slit diaphragm. The first method utilizes the results of measuring the diameter of a variable iris diaphragm installed near the emitter aperture. However, this method is suboptimal due to high cost of labor associated with the measurements. The second method is based on the results of measuring the width of a slit diaphragm, which is also placed near the emitter aperture and moved in a plane perpendicular to the optical axis of the pyrometer. The results obtained by these two methods are slightly different due to the difference in areas of the iris diaphragm and the surface cut by the slit diaphragm, with the width of the slit being equal to the diameter of the iris diaphragm. A relationship has been derived linking the results of measuring the spot diameter of the pyrometer by both circular and slit diaphragm methods. This relationship enables the accurate measurement of this parameter using the slit diaphragm, which is a faster and less labor-intensive method compared to the iris diaphragm. The obtained results are important for non-contact temperature measurements in both technological processes and R&D projects.

Ohmic pulse-heating with sub-microsecond time resolution is used to obtain thermophysical properties for aluminum in the liquid phase. Measurement of current through the sample, voltage drop across the sample, surface radiation, and volume expansion allow the calculation of specific heat capacity and the temperature dependencies of electrical resistivity, enthalpy, and density of the sample at melting and in the liquid phase. Thermal conductivity and thermal diffusivity as a function of temperature are estimated from resistivity data using the Wiedemann–Franz law. Data for liquid aluminum obtained by pulse-heating are quite rare because of the low melting temperature of aluminum with 933.47 K (660.32 °C), as the fast operating pyrometers used for the pulse-heating technique with rise times of about 100 ns generally might not be able to resolve the melting plateau of aluminum because they are not sensitive enough for such low temperature ranges. To overcome this obstacle, we constructed a new, fast pyrometer sensitive in this temperature region. Electromagnetic levitation, as the second experimental approach used, delivers data for surface tension (this quantity is not available by means of the pulse-heating technique) and for density of aluminum as a function of temperature. Data obtained will be extensively compared to existing literature data.

This article presents a model for analyzing the effect of misalignments in the optical power gathered by a single-color fiber-optic off-axis pyrometer when there is a tilting angle between the longitudinal fiber axis and the plane of the emitted surface. The model takes into account the fiber parameters, such as the diameter and the numerical aperture, as well as the target object size and measuring distance. Simulations show the simultaneous influence of tilting angle and lateral displacement. This provides key behavioral insights to guide alignment and calibration, helping to avoid temperature measurement errors in advanced manufacturing. The model allows integration of the emissivity angle dependence. Results show that the influence of lateral misalignment is negligible for values below 15 µm (which is 1/10 of the 150 µm minimum distance) when considering a 160 µm object size and a 60° tilting angle. The displacement influence, for a fixed tilting angle, is higher in specific directions of displacement.

In an attempt to find a solution similar to the FDM 3D printers which would allow cost-effective and reliable additive manufacturing of metal components, this paper proposes a three-axis WAAM system capable of reliably printing small, near-net-shape metal objects. The system consists of gas metal arc (GMA) process equipment, a three-axis CNC positioning system, the interpass temperature control and forced cooling of the base plate and the deposit. The main challenge addressed is the minimisation of shape distortions caused by excessive heat accumulation when printing small objects. The interpass temperature control uses an IR pyrometer to remotely measure the last deposited layer and a control system to keep the interpass temperature below the predefined value by stopping the deposition after each layer in order to allow the deposit to cool. This results in a stable and more repeatable shape of the deposit, even when the heat transfer conditions are changing during the build-up process. The combination of adaptive interlayer dwell time and forced cooling significantly improves system productivity. Open-source NC control and path generation software is used, which enables fast and easy creation of the control code. Different control methods are evaluated through the printing of simple walls, and the printing accuracy is evaluated by printing small shell objects. As the results show, the interpass temperature control allows small objects to be printed at near-net shape with a deviation of 2%, which means that successful printing of 3D shapes can be achieved without trial and error approach.

Thermal issues are critical when machining Ni-based superalloy components designed for high temperature applications. The low thermal conductivity and extreme strain hardening of this family of materials results in elevated temperatures around the cutting area. This elevated temperature could lead to machining-induced damage such as phase changes and residual stresses, resulting in reduced service life of the component. Measurement of temperature during machining is crucial in order to control the cutting process, avoiding workpiece damage. On the other hand, the development of predictive tools based on numerical models helps in the definition of machining processes and the obtainment of difficult to measure parameters such as the penetration of the heated layer. However, the validation of numerical models strongly depends on the accurate measurement of physical parameters such as temperature, ensuring the calibration of the model. This paper focuses on the measurement and prediction of temperature during the machining of Ni-based superalloys. The temperature sensor was based on a fiber-optic two-color pyrometer developed for localized temperature measurements in turning of Inconel 718. The sensor is capable of measuring temperature in the range of 250 to 1200 °C. Temperature evolution is recorded in a lathe at different feed rates and cutting speeds. Measurements were used to calibrate a simplified numerical model for prediction of temperature fields during turning.

BackgroundA novel numerical method for calculating the contributions of individual diodes in a set of light emitting diodes (LEDs), aimed at simulating a blackbody radiation source, is examined. The intended purpose of the light source is to enable calibration of various types of optical sensors, particularly optical radiation pyrometers in the spectral range from 700 nm to 1070 nm.ResultsThis numerical method is used to determine and optimize the intensity coefficients of individual LEDs that contribute to the overall spectral distribution. The method was proven for known spectral distributions: “flat” spectrum, International Commission on Illumination (CIE) standard daylight illuminant D65 spectrum, Hydrargyrum Medium-arc Iodide (HMI) High Intensity Discharge (HID) lamp, and finally blackbody radiation spectra at various temperatures.ConclusionsThe method enables achieving a broad range of continuous spectral distributions and compares favorably with other methods proposed in the literature.

Significant efforts have been spent determining or monitoring interlayer temperatures (IT) to increase quality in Wire Arc Additive Manufacturing (WAAM). However, an uneven thermal profile in the wall and a temperature gradient along the layer length are expected after a thin wall layer deposition, questioning the effectiveness of IT and its measuring approaches. After identifying the holistic meaning of IT, this work aimed at confronting two strategies using infrared pyrometers, elucidating their advantages and limitations for both open and closed-loop control. The proposed Upper and Sideward Pyrometer strategies were presented in detail and then assessed at different distances from the heat source. A calibration procedure was proposed. The results confirmed the existence of a natural temperature gradient along the wall. In addition, they showed how differently the arc heat affects the measured points (in intensity and steadiness) according to the strategy. Therefore, the interlayer temperature measured at a specific point on a part manufactured by WAAM should be taken as a reference and not an absolute value; the absolute value changes according to the measuring approach, sensor positioning and calibration. Using a temperature reference, both strategies can be used in open-loop control to reach repeatability (geometrical and metallurgical) between layers. However, the Sideward Pyrometer strategy is more recommended for feedback control of production, despite being less flexible.

There are presented results of experimental research on calibration of tungsten–rhenium thermocouples at the temperatures exceeding the upper limit of measurements (1700 °C) of standard type B thermocouple. The research was carried out using the high-temperature installation UKT-2500 designed for practical use in production of temperature sensors based on refractory thermocouples. Available types of insulating ceramics for thermocouples have been tested in the temperature range of (1500–2500) °C. The effects of signal shunting and thermocouples stability in inert atmosphere have been investigated at upper limit of the operating temperature range. There was proved practical feasibility of the method for calibration of several contact temperature sensors (up to 10) in one run relative to radiation pyrometer readings. Its suitability for thermocouple calibration and certifying of thermocouple wires in the temperature range (1200–2200) °C was shown. Installation enables to use reference fixed-points of Me-C type to get the highest accuracy calibration of a single tungsten–rhenium thermocouple. Type A bare-wire thermocouple was calibrated in the whole measuring range from 1200 °C to 2500 °C against an accurate radiation pyrometer.

In metal cutting, the magnitude of the temperature at the tool-chip interface is a function of the cutting parameters. This temperature directly affects production; therefore, increased research on the role of cutting temperatures can lead to improved machining operations. In this study, tool temperature was estimated by simultaneous temperature measurement employing both a K-type thermocouple and an infrared radiation (IR) pyrometer to measure the tool-chip interface temperature. Due to the complexity of the machining processes, the integration of different measuring techniques was necessary in order to obtain consistent temperature data. The thermal analysis results were compared via the ANSYS finite element method. Experiments were carried out in dry machining using workpiece material of AISI 4140 alloy steel that was heat treated by an induction process to a hardness of 50 HRC. A PVD TiAlN-TiN-coated WNVG 080404-IC907 carbide insert was used during the turning process. The results showed that with increasing cutting speed, feed rate and depth of cut, the tool temperature increased; the cutting speed was found to be the most effective parameter in assessing the temperature rise. The heat distribution of the cutting tool, tool-chip interface and workpiece provided effective and useful data for the optimization of selected cutting parameters during orthogonal machining.

CMT welding sources are garnering attention as alternative heat sources for wire arc additive manufacturing because of their low-heat input. A comprehensive experimental and numerical study on the multi-layer deposition of STS316L was performed to investigate effect of heat accumulation during the deposition. The numerical model which is appropriate for WAMM was developed considering the characteristics of the CMT heat source for the first time. Using a high-speed camera, the transient behavior of the CMT arc was investigated, and applied to the heat source of the numerical model. The model was then used to analyze 10-layered deposits of STS316L, fabricated using CMT-based WAAM. During deposition, the temperature is measured using a pyrometer to analyze the microstructure, after which the cooling rate of each layer is estimated. The measured and simulated SDAS were compared. Based on the comparison, a guideline for the equation regarding the SDAS size and cooling rate was suggested.