An investigation into the challenges of the point grinding machining process

Point grinding is an abrasive machining process that utilises miniature single layer superabrasive tools to remove material. The use of such small diameter tools offers advantages in the manufacturing of small or difficult to access complex 3D geometries, however, in their current state, these tools suffer from several critical challenges preventing their successful implementation. An investigation into the use of a typical commercially available point grinding tool for machining of hardened steel components has been carried out, with the aim of identifying the critical process challenges. The requirement for high rotational speeds, high tool deflection, variation in grit protrusion heights and bond layer thickness, accelerated tool wear, increased sensitivity to runout, zero cutting speed at tooltip and high tool loading have been identified as the main issues affecting the point grinding process. It is crucial that these challenges are correctly understood to facilitate future tool development

Inference of the chromospheric magnetic field configuration of solar plage using the Ca II 8542 {\AA} line

It has so far proven impossible to reproduce all aspects of the solar plage chromosphere in quasi-realistic numerical models. The magnetic field configuration in the lower atmosphere is one of the few free parameters in such simulations. The literature only offers proxy-based estimates of the field strength, as it is difficult to obtain observational constraints in this region. Sufficiently sensitive spectro-polarimetric measurements require a high signal-to-noise ratio, spectral resolution, and cadence, which are at the limit of current capabilities. We use critically sampled spectro-polarimetric observations of the \cair line obtained with the CRISP instrument of the Swedish 1-m Solar Telescope to study the strength and inclination of the chromospheric magnetic field of a plage region. This will provide direct physics-based estimates of these values, which could aid modelers to put constraints on plage models. We increased the signal-to-noise ratio of the data by applying several methods including deep learning and PCA. We estimated the noise level to be $1\cdot10^{-3} I_c$. We then used STiC, a non-local thermodynamic equilibrium (NLTE) inversion code to infer the atmospheric structure and magnetic field pixel by pixel. We are able to infer the magnetic field strength and inclination for a plage region and for fibrils in the surrounding canopy. In the plage we report an absolute field strength of $|B| =440 \pm 90$ G, with an inclination of $10^\circ \pm 16^\circ$ with respect to the local vertical. This value for $|B|$ is roughly double of what was reported previously, while the inclination matches previous studies done in the photosphere. In the fibrillar region we found $|B| = 300 \pm 50$ G, with an inclination of $50^\circ \pm 13^\circ$.Comment: Accepted September 22t

Evolution of electroplated cBN tool surface texture parameters during point grinding

Point grinding is an abrasive machining process that utilises small diameter superabrasive single-layer grinding tools for accurate machining of complex 3D geometries. Due to the small nature of these tools, high wear rates and uneven wear around the tool circumference present a challenge for their successful application for finish machining of metallic components. It is, therefore, essential to monitor the surface condition of the point grinding tools, to ensure their safe and reliable operation. In this investigation, the 3D topography evolution of single-layer B126 cBN point grinding tools was characterised using focus-variation imaging. Given the wealth of information obtained using this method, a decision-matrix methodology was used to identify the most important parameters for monitoring the wear condition of the point grinding tools. Grinding trials were also performed with fixed cutting parameters and varied cutting durations up to 520mm3 of material removed to assess the evolution of the point grinding tool surfaces over time as a result of wear during grinding of hardened D2 tool steel. The best criteria for the characterisation of the surface texture of electroplated cBN point grinding tool surfaces were identified to be the average surface height (Sa), skewness (Ssk), root mean square gradient (Sdq), reduced peak height (Spk), peak material volume (Vmp) and developed interfacial area ratio (Sdr). These parameters performed best for direct measurement of point grinding tool surfaces, paving the way for the application of the imaging technique under manufacturing conditions as an on-machine monitoring method for performance assessment

Physical properties of a fan-shaped jet backlit by an X9.3 flare

Context. Fan-shaped jets sometimes form above light bridges and are believed to be driven by the reconnection of the vertical umbral field with the more horizontal field above the light bridges. Because these jets are not fully opaque in the wings of most chromospheric lines, it is not possible to study their spectra without highly complex considerations of radiative transfer in spectral lines from the atmosphere behind the fan. Aims. We take advantage of a unique set of observations of the Hα line along with the Ca I