# Effects of Grinding Passes and Direction on Material Removal Behaviours in the Rail Grinding Process

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Simulation Details

#### 2.1. Simulaiton Model

^{−2}. Then, after the analysis of the data from the JB-6C surface roughness measuring instrument (Wilson, Guangzhou, China), it was found that the distribution law of the outburst height of the abrasive grain obeys a normal distribution. The size of the abrasive particle is approximately 1000 microns based on the virtual lattice method. Next, the X, Y and Z coordinates of each abrasive particle that were calculated using compiled MATLAB functions are imported into the AutoCAD software (v2014, Autodesk, San Rafael, CA, USA) as the 3D center point of each abrasive particle. The abrasive particles were then placed at the corresponding points in the simulation domain, and the shape of each abrasive particle is simplified as a pyramid. Finally, after simplifying the grinding wheel bond as a cylinder and assembling it with the abrasive particles, a grinding wheel model is established. Following consideration of the convenience of pre-processing settings and the improvement of the solving speed, this paper reduced the thickness of Han’s grinding wheel bond model from 10 mm to 0.5 mm without affecting the simulation results (Figure 2a). Then, the part 2 mm from the top of the rail head is used to establish the rail model, and the 3D model of rail grinding comprises the combination of the rail and the grinding wheel model, as shown in Figure 2b.

#### 2.2. Simulation and Material Parameters

_{2}O

_{3}, and the rail material is U71Mn (Chinese brand, Pangang Group Company Limited, Panzhihua, China) steel. The physical properties of these materials are given in Table 3 and Table 4, respectively. In addition, since the hardness of the grinding wheel is much greater than that of the rail material, the grinding wheel is set as a rigid body while the rail material is set as a plastic body. The constitutive relation of the materials refers to the relationship between the flow stress and the thermodynamic parameters, such as the temperature, strain and strain rate, which are used to characterize the dynamic responses of the materials during deformation. Under the action of external forces during rail grinding, the rail material will undergo elastic deformation and plastic deformation until fracturing at high temperature, large strain and a large strain rate [22,23,24]. To better simulate the rail grinding process, Johnson–Cook constitutive models are widely used because they are relatively simple (with five parameters) and numerically robust. The constitutive equation of the Johnson-Cook material is as follows:

_{r}and T

_{m}are the room temperature and material melting point temperature, respectively, and T is the temperature of the workpiece [25]. The constitutive parameters assigned to rail materials are given in Table 5.

_{f}), and grinding depth (ap). An illustration of these process parameters is presented in Figure 2b. According to the experiment, the values of the rotational speed and the feed speed are 3600 r/min and 83.33 m/min, respectively, and the grinding depth of each grinding pass is given in Table 2.

^{−9}and 10

^{3}, respectively, according to the experimental values, and the hardness value is assigned to the grinding wheel.

## 3. Results

#### 3.1. Wear Amount for the Grinding Wheel

^{2}after a simplified calculation of a pyramid), and the wear depth h of one abrasive grain approaches the maximum contour level of wear depth. Then, the numerical value of the wear volume of a single abrasive grain is approximately equal to its maximum contour level of wear depth. Therefore, the numerical value of the wear volume of the entire grinding wheel is roughly the sum of the maximum wear depth of all abrasive grains.

#### 3.2. Volume of Removed Rail Material

#### 3.3. Grinding Ratio

#### 3.4. Surface Roughness of the Grinding Rail

#### 3.5. Grinding Force

_{n}), tangential force (F

_{t}) and axial force (F

_{a}). In this study, the variation of the overall loads of the grinding wheel in the three directions versus time is obtained from the post-processing using DEFORM-3D, which is regarded as the variation of the grinding force with the rail grinding process.

_{t}, F

_{n}, and F

_{a}before and after changing the grinding direction. The results suggest that the grinding force is slightly increased after changing the grinding direction. Even the grinding depth after changing the grinding direction in the same grinding pass is almost the same, but changing the orientation of the material on the rail surface also has a certain effect on the grinding force. The direction of the grinding force is the same as the change trend of the material on the rail surface. Therefore, the grinding force increases while the direction of the grinding force in the second grinding pass is the same as that in the first grinding pass.

## 4. Discussion

_{2}O

_{3}grinding wheel. The reciprocating grinding of rails is achieved by changing the grinding direction between down-grinding and up-grinding. In addition, the material removal behaviours on the interface between the rail and the grinding wheel play a vital role in the analysis of the rail grinding process. Since the simulation results of this paper are similar to those from the experiment, and the experimental data are in good agreement with the field data, it is concluded that the rail grinding simulation in this study can effectively model the rail grinding in the field, and the method of analyzing the material removal behaviours on the interface between the rail and grinding wheel is feasible. It is worth noting that, because the numerical value of grinding wheel wear volume is estimated in the simulation analysis, a modified coefficient is needed according to further analysis of wheel wear in a reciprocating rail grinding experiment. A modified coefficient for the grinding ratio can then also be presented.

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 1.**Schematic diagram of the grinding band after rail grinding: (

**a**) down grinding; (

**b**) up grinding; and (

**c**) up grinding after down grinding.

**Figure 2.**3D model of rail grinding in the field showing (

**a**) the grinding wheel and (

**b**) rail grinding.

**Figure 3.**Meshed model of rail grinding in the field showing (

**a**) the grinding wheel and (

**b**) the rail.

**Figure 4.**Verification of the grinding band between (

**a**) the field, (

**b**) the experiment and (

**c**) the simulation.

**Figure 5.**Verification of the wear region of the worn grinding wheel between (

**a**) the experiment and (

**b**) the simulation.

**Figure 6.**Change in the grinding wheel wear with (

**a**) the number of grinding passes and (

**b**) a change in the grinding direction.

**Figure 7.**Change in the volume of removed rail material with the number of grinding passes in the simulation and the experiment.

**Figure 9.**Change in the grinding ratio with (

**a**) the number of grinding passes and (

**b**) a change in the grinding direction.

**Figure 10.**Schematic diagram of the surface roughness: (

**a**) definition and (

**b**) cross section direction.

**Figure 11.**Change in the surface roughness with the number of grinding passes in (

**a**) the simulation and (

**b**) the experiment.

**Figure 13.**Change in the grinding force with the number of grinding passes: (

**a**) F

_{t}; (

**b**) F

_{n}; and (

**c**) F

_{a}.

**Figure 14.**Change in the grinding force with a change in the grinding direction: (

**a**) F

_{t}, (

**b**) F

_{n}, and (

**c**) F

_{a}.

Normal Force (N) | Rotational Speed (r/min) | Feed Speed (mm/min) | Grinding Angle (°) | Grinding Mode |
---|---|---|---|---|

1800 | 3600 | 83.33 | 2 | down-up-down |

Grinding Pass | Ⅰ | Ⅱ | Ⅲ | |
---|---|---|---|---|

Width (mm) | Average | 12 | 13.66 | 14.3 |

Deviation | 0.1 | 0.3 | 0.35 | |

Depth (mm) | Average | 0.06 | 0.01776 | 0.007456 |

Deviation | 0.05 | 0.15 | 0.175 |

Rail Material | Young’s Modulus (MPa) | Poisson’s Ratio | Thermal Conductivity (N·s ^{−1}·°C^{−1}) | Heat Capacity (N·mm ^{−2}·°C^{−1}) |
---|---|---|---|---|

U71Mn | 2.06754 × 10^{5} | 0.3 | Change with temperature |

Grinding Wheel Material | Young’s Modulus (MPa) | Poisson’s Ratio | Density (kg·m ^{−3}) |
---|---|---|---|

Al_{2}O_{3} | 3.7 × 10^{5} | 0.22 | 3960 |

A (MPa) | B (MPa) | n | C | m |
---|---|---|---|---|

792 | 510 | 0.26 | 0.014 | 1.03 |

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**MDPI and ACS Style**

Zhang, S.; Zhou, K.; Ding, H.; Guo, J.; Liu, Q.; Wang, W.
Effects of Grinding Passes and Direction on Material Removal Behaviours in the Rail Grinding Process. *Materials* **2018**, *11*, 2293.
https://doi.org/10.3390/ma11112293

**AMA Style**

Zhang S, Zhou K, Ding H, Guo J, Liu Q, Wang W.
Effects of Grinding Passes and Direction on Material Removal Behaviours in the Rail Grinding Process. *Materials*. 2018; 11(11):2293.
https://doi.org/10.3390/ma11112293

**Chicago/Turabian Style**

Zhang, Shuyue, Kun Zhou, Haohao Ding, Jun Guo, Qiyue Liu, and Wenjian Wang.
2018. "Effects of Grinding Passes and Direction on Material Removal Behaviours in the Rail Grinding Process" *Materials* 11, no. 11: 2293.
https://doi.org/10.3390/ma11112293