# ELID Dressing Behaviors of Non-Abrasive Iron-Based Grinding Wheels
## 4 Discussion
### Influence of Oxide Layer Mechanical Properties  
The variations of hardness (H), elastic modulus (E), and stiffness (S) of the oxide layer on the iron-based grinding diamond wheel without abrasive particles obtained from nanoindentation testing with respect to the depth of indentation are depicted in Figure 11. It can be observed from the graph that both hardness H and elastic modulus E, as well as stiffness S, increase with the increase in indentation depth. The hardness ranges from 800 to 4900 MPa, the elastic modulus ranges from 23 to 230 GPa, and the stiffness ranges from 0.3 to 11 mN/nm. At relatively shallow indentation depths, the influence of the grinding diamond wheel substrate is minimal, allowing the mechanical properties to be attributed mainly to the oxide layer. As the indentation depth increases, the influence of the grinding diamond wheel substrate becomes more pronounced, resulting in higher measured values of hardness, elastic modulus, and stiffness. When the maximum indentation depth of 0.01 mm is reached, the measured hardness, elastic modulus, and stiffness approach the performance indicators of the grinding diamond wheel substrate. Based on this, it can be inferred that the hardness of the oxide layer is 800 MPa, the elastic modulus is 23 GPa, and the stiffness is 0.3 mN/nm.  
Figure 10: COMSOL simulation of the flow field distribution by ELID electrolytic process.  
The authors previously conducted research on the mechanical properties of oxide films generated after Electrolytic In-Process Dressing (ELID) of abrasive-containing iron-based grinding diamond wheels. The obtained range for stiffness was 27-95 \(\upmu\)N/nm [43]. In contrast, [PERSON] measured a stiffness value of 16.34 \(\upmu\)N/nm for the oxide film on abrasive-containing grinding diamond wheels [44]. These values are of the same order of magnitude. Comparatively, the stiffness of the oxide film on non-abrasive iron-based grinding diamond wheels is significantly higher than that of abrasive-containing ones. As described in Section 4.2, during ELID electrolysis of abrasive-containing iron-based grinding diamond wheels, the presence of abrasive particles disrupts the uniformity of the electric field, leading to weaker oxide film properties. The oxide film becomes discontinuous and unevenly distributed. Conversely, when non-abrasive iron-based grinding diamond wheels undergo ELID electrolysis, the electric field remains uniform, resulting in better oxide film properties. The oxide film is continuous and evenly distributed. The oxide film on the surface of the grinding diamond wheel behaves like a spring. During ELID polishing, a certain \"spring force\" is applied to squeeze \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\) particles within the oxide film onto the workpiece surface, thereby polishing the workpiece. Due to the uniform distribution and mechanical properties of the oxide film on non-abrasive iron-based grinding diamond wheels, \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\) particles are uniformly squeezed onto the workpiece surface, leading to uniform polishing, where the material is evenly removed. Consequently, the polishing performance of non-abrasive iron-based grinding diamond wheel oxide films surpasses that of abrasive-containing ones.