Measurement of the high-temperature melt pool region in the laser powder bed fusion (L-PBF) process is a primary focus of researchers to further understand the dynamic physics of the heating, melting, adhesion, and cooling which define this commercially popular additive manufacturing process. This paper will detail the design, execution, and results of high speed, high magnification in-situ thermographic measurements conducted at the National Institute of Standards and Technology (NIST) focusing on the melt pool region of a commercial L-PBF process. Multiple phenomena are observed including plasma plume and hot particle ejection from the melt region. The thermographic measurement process will be detailed with emphasis on the ‘measurability’ of observed phenomena and the sources of measurement uncertainty. Further discussion will relate these thermographic results to other efforts at NIST towards L-PBF process finite element simulation and development of in-situ sensing and control methodologies.

The National Institute of Standards and Technology Standard Reference Material (SRM) 2460/2461 standard bullets and casings project will provide support to firearms examiners and to the National Integrated Ballistics Information Network (NIBIN) in the United States. The SRM bullet is designed as both a virtual and a physical bullet profile signature standard. The virtual standard is a set of six digitized bullet profile signatures originally traced from six master bullets fired at the Bureau of Alcohol, Tobacco and Firearms (ATF) and the Federal Bureau of Investigation (FBI). By using the virtual signature standard to control the tool path on a numerically controlled diamond turning machine, 40 SRM bullets were produced. A profile signature measurement system was established for the SRM bullets. The profile signature differences are quantified by the maximum of the cross correlation function and by the signature difference between pairs of compared profile signatures measured on different SRM bullets. Initial measurement results showed high reproducibility for both the measurement system and production process of the SRM bullets. A traceability scheme has been proposed to establish the measurement traceability for nationwide bullet signature measurements to NIST, ATF and FBI. Prototype SRM casings have also been developed.

This paper presents a comprehensive analysis of the uncertainty in the measurement of the peak temperature on the side face of a cutting tool, during the metal cutting process, by infrared thermography. The analysis considers the use of a commercial off-the-shelf camera and optics, typical of what is used in metal cutting research. A physics-based temperature measurement equation is considered and an analytical method is used to propagate the uncertainties associated with measurement variables to determine the overall temperature measurement uncertainty. A Monte Carlo simulation is used to expand on the analytical method by incorporating additional sources of uncertainty such as a point spread function (PSF) of the optics, difference in emissivity of the chip and tool, and motion blur. Further discussion is provided regarding the effect of sub-scenel averaging and magnification on the measured temperature values. It is shown that a typical maximum cutting tool temperature measurement results in an expanded uncertainty of U = 50.1 • C (k = 2). The most significant contributors to this uncertainty are found to be uncertainties in cutting tool emissivity and PSF of the imaging system.

A bullet signature measurement system based on a stylus instrument was developed at the National Institute of Standards and Technology (NIST) for the signature measurements of NIST RM (Reference Material) 8240 standard bullets. The standard bullets are developed as a reference standard for bullet signature measurements and are aimed to support the recently established National Integrated Ballistics Information Network (NIBIN) by the Bureau of Alcohol, Tobacco and Firearms (ATF) and the Federal Bureau of Investigation (FBI). The RM bullets are designed as both a virtual and a physical bullet signature standard. The virtual standard is a set of six digitized bullet signatures originally profiled from six master bullets fired at ATF and FBI using six different guns. By using the virtual signature standard to control the tool path on a numerically controlled diamond turning machine at NIST, 40 RM bullets were produced. In this paper, a comparison parameter and an algorithm using autoand cross-correlation functions are described for qualifying the bullet signature differences between the RM bullets and the virtual bullet signature standard. When two compared signatures are exactly the same (point by point), their cross-correlation function (CCF) value will be equal to 100%. The measurement system setup, measurement program, and initial measurement results are discussed. Initial measurement results for the 40 standard bullets, each measured at six land impressions, show that the CCF values for the 240 signature measurements are higher than 95%, with most of them even higher than 99%. These results demonstrate the high reproducibility for both the manufacturing process and the measurement system for the NIST RM 8240 standard bullets.

Recent experiments with the National Institute of Standards and Technology (NIST) Electrostatic Force Balance (EFB) have achieved agreement between an electrostatic force and a gravitational force of 10 −5 N to within a few hundred pN/N. This result suggests that a force derived from measurements of length, capacitance, and voltage provides a viable small force standard consistent with the Système International d'Unités. In this paper, we have measured the force sensitivity of a piezoresistive microcantilever by directly probing the NIST EFB. These measurements were linear and repeatable at a relative standard uncertainty of 0.8%. We then used the calibrated cantilever as a secondary force standard to transfer the unit of force to an optical lever-based sensor mounted in an atomic force microscope. This experiment was perhaps the first ever force calibration of an atomic force microscope to preserve an unbroken traceability chain to appropriate national standards. We estimate the relative standard uncertainty of the force sensitivity at 5%, but caution that a simple model of the contact mechanics suggests errors may arise due to friction.

An investigation is reported on high speed grinding of silicon nitride using electroplated single-layer diamond wheels. This article is concerned with wheel wear and wheel life, and a second paper (ASME J. Manuf. Sci. Eng., 122, pp. 42–50) deals with wheel topography and grinding mechanisms. It has been suggested that grinding performance may be enhanced at higher wheel speeds due to a reduction in the undeformed chip thickness. Grinding experiments were conducted at wheel speeds of 85 and 149 m/s with the same removal rate. Contrary to expectations, the faster wheel speed gave no improvements in surface finish, grinding ratio, or wheel life. Microscopic observations of the wheel surface revealed dulling of the abrasive grains by attritious wear, thereby causing a progressive increase in the forces and energy until the end of the useful life of the wheel. For all grinding conditions, a single-valued relationship was found between the wheel wear and the accumulated sliding length between the abrasive grains and the workpiece. A longer wheel life and improved grinding performance can be obtained when the operating parameters are selected so as to reduce the abrasive sliding length per unit volume of material removal. [S1087-1357(00)00301-4]

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Process characteristics and effects of gas-and water-atomized stainless steel powders in laser-based rapid tooling Abstract. Additive manufacturing (AM) has the potential to revolutionize discrete part manufacturing, but improvements in processing of metallic materials are necessary before AM will see widespread adoption. A better understanding of AM processes, resulting from physics-based modeling as well as direct process metrology, will form the basis for these improvements. Infrared (IR) thermography of AM processes can provide direct process metrology, as well as data necessary for the verification of physics-based models. We review selected works examining how IR thermography was implemented and used in various powder-bed AM processes. This previous work, as well as significant experience at the National Institute of Standards and Technology in temperature measurement and IR thermography for machining processes, shapes our own research in AM process metrology with IR thermography. We discuss our experimental design, as well as plans for future IR measurements of a laser-based powder bed fusion AM process.