# In-Process Measurement of Barkhausen Noise for Detection of Surface Integrity during Grinding
## 2 Material and Methods  
The investigations were carried out on a cylindrical grinding machine Studer S41 (Fritz Studer AG, Steffisburg, Switzerland) with a corundum grinding wheel 54A120 H15 VPMP6904W (500 mm \(\times\) 36 mm \(\times\) 203.2 mm). Case-hardened workpieces (O67.7 mm \(\times\) 152 mm) from AISI 4820 (DIN 18 CrNiMo7-6) were machined by a cylindrical outer diameter grinding process. Table 1 gives the target values for the heat treatment (surface carbon content in wt.%/case hardening depth in mm/tempering temperature in \({}^{\circ}\)C) and the resulting surface carbon content, case hardening depth, surface hardness and surface oxidation depth of the different conditions, characterized at coupon samples. Hardness according to Vickers was measured with a LV-700 AT (LECO Instrumente, Monchengladbach, Germany). Surface oxidation depth was determined from oxygen depth profiles measured with a glow discharge spectrometer LECO GDS-750A (LECO Instrumente, Monchengladbach, Germany) as the depth with less than 0.001 wt.% oxygen. On each of the four heat treatment variations, different thermo-mechanical levels were achieved by the grinding process parameters given in Table 2. The total depth of cut a\({}_{\text{e}}\) was 100 \(\upmu\)m for specific material removal rates Q\({}^{\prime}_{\text{W}}\) = 1 mm\({}^{3}\)/(mm\(\cdot\)s) to Q\({}^{\prime}_{\text{W}}\) = 10 mm\({}^{3}\)/(mm\(\cdot\)s), and 300 \(\upmu\)m for Q\({}^{\prime}_{\text{W}}\) = 12 mm\({}^{3}\)/(mm\(\cdot\)s) and Q\({}^{\prime}_{\text{W}}\) = 14 mm\({}^{3}\)/(mm\(\cdot\)s). Cutting speed v\({}_{\text{c}}\) and speed ratio q were constant over all grinding processes, while the specific material removal rate Q\({}^{\prime}_{\text{W}}\) was varied by the radial feed speed v\({}_{\text{fr}}\). Oil (Rhenus EG 10) was supplied with a metal working fluid flow rate Q\({}_{\text{MWF}}\) of 40 L/min. The grinding wheel was dressed with a dressing overlap ratio U\({}_{\text{d}}\) of 3 and a speed ratio q\({}_{\text{d}}\) of \(-\)1. BN was measured with a 3 MA-II device (Fraunhofer IZFP, Saarbrucken, Germany) and a special sensor for in-process use implemented in the grinding machine. The investigations were performed contactless with an air gap of 200 \(\upmu\)m between the sensor and the workpiece surface. As measurement parameters, a magnetization amplitude of 100 A/cm, a magnetization frequency of 120 Hz and an analyzing frequency range from 100 kHz to 1000 kHz were chosen. Detailed information about the setup and repeatability of measurements is given in [22]. The setup with an isolating transformer and potential equalization ensures the elimination of interfering signals by electromagnetic disturbances. \begin{table}
\begin{tabular}{c c c c c} \hline
**Target Values** & **Surface Carbon** & **CHD\({}_{\text{550}}\)** & **Surface Hardness** & **Surface Oxidation** \\ \hline
0.8/2/150 & 0.83 wt.\% & 1.91 mm & 702 \(\pm\) 8 HV1 & 14.1 \(\upmu\)m \\
0.8/1/150 & 0.83 wt.\% & 1.00 mm & 723 \(\pm\) 10 HV1 & 9.8 \(\upmu\)m \\
0.8/2/210 & 0.84 wt.\% & 1.76 mm & 665 \(\pm\) 7 HV1 & 15.8 \(\upmu\)m \\
0.6/2/150 & 0.65 wt.\% & 1.89 mm & 696 \(\pm\) 20 HV1 & 12.5 \(\upmu\)m \\ \hline \end{tabular}
\end{table} 
Table 1: Heat treatment states before grinding. \begin{table}
\begin{tabular}{c c} \hline v\({}_{\text{c}}\) & 35 m/s \\ q & 90 \\ v\({}_{\text{fr}}\) & 0.28/1.69/2.82/3.38/3.95 mm/min \\ Q\({}_{\text{W}}\) & 1/6/10/12/14 mm\({}^{3}\)/(mm\(\cdot\)s) \\ Q\({}_{\text{MWF}}\) & 40 L/min \\ U\({}_{\text{d}}\) & 3 \\ q\({}_{\text{d}}\) & \(-\)1 \\ \hline \end{tabular}
\end{table} 
Table 2: Grinding parameters. The ground samples were characterized by hardness testing, residual stress measurements and micrographs. Surface hardness was measured with the same device used for the characterization of the heat treatment state: LV-700 AT.