# Analysis of the Cutting Abilities of the Multilayer Grinding Wheels—Case of Ti-6Al-4V Alloy Grinding

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

_{2}O

_{3}) or silicon carbide (SiC) [11]. However, abrasive grains made of Al

_{2}O

_{3}or SiC have a lower thermal conductivity than grains made of cBN or diamond, so heat dissipation from the grinding zone is more difficult [12].

_{2}O

_{3}grains. During the grinding of the Ti-6Al-4V alloy, an improvement in the grinding process was proven compared to the conventional tools: (i) increased material removal efficiency; (ii) reduction of side ridges; (iii) reduction of grinding forces, and (iv) reduction of the Sa roughness parameter of the ground surface. The effectiveness of the material removal process with the use of abrasive aggregates could be a result of increasing the abrasives cutting edge length [14].

## 2. Materials and Methods

#### 2.1. Measurement Methodology

#### 2.2. Methodology of the Surface Roughness Assessment

_{e}is the feed (μm). The reason for the application of these parameter is that the active area of the grinding wheel, in the range of the Sz value, should not be entirely involved in the material removal process during the single pass. Thus, because of the need for an estimation of the cutting depth, in order for a proper assessment of the active islands, the level of cutting plane on the measured data could not be obtained by extraction of the cutting depth (grinding process set up) from the top of the peak height. The reason is that the Sp value determined on the basis of only one ordinate value exposures the high variability caused by small changes in the active surface of the abrasive tool. A single high point, like a measurement noise, in the measured topography will change the value of this parameter. The S5p value is determined from the motives using the watershed algorithm and the Wolf pruning [21], and is less variable due to isolated high peaks.

#### 2.3. Methodology of the Surface Feature Variability Assessment after the Grinding Process

_{0}and the alternative H

_{1}were formulated as follows:

_{0}) was determined for R = 10,000 bootstrap samples ${\mathit{x}}_{p\left\{A\right\}}^{*}=[{x}_{p{\left\{A\right\}}_{1}}^{*},{x}_{p{\left\{A\right\}}_{2}}^{*},\dots ,{x}_{p{\left\{A\right\}}_{{n}_{1}}}^{*}]$ and ${\mathit{x}}_{p\left\{B\right\}}^{*}=[{x}_{p{\left\{B\right\}}_{1}}^{*},{x}_{p{\left\{B\right\}}_{2}}^{*},\dots ,{x}_{p{\left\{B\right\}}_{{n}_{2}}}^{*}]$:

_{1}, and ${\overline{x}}_{p\left\{B\right\}}^{*}$, ${s}_{p\left\{B\right\}}^{*2}$–the mean value and variance of the p roughness parameter of the surfaces ground with tool B determined from the bootstrap sample with the size n

_{2}.

_{0}hypothesis was assessed using a p-value. This allowed for the assessment of the H

_{0}hypothesis for any significance level α. If p-value > α, it is false to reject the H

_{0}hypothesis.

_{obs}was calculated using the following equation:

## 3. Results and Discussion

#### 3.1. Analysis of the Grinding Wheel Topography

^{4}and was 40% higher than the Shos value for the conventional layer. This confirms the more advantageous geometry of active surfaces in aggregate layers, affecting the efficiency of the material removal process.

#### 3.2. Ground Surface Roughness Analysis

## 4. Conclusions

- The addition of abrasive aggregates increases the size of the active areas of the grinding wheels. These areas are characterized by favorable geometrical features related, inter alia, to the increased width of the cutting edges compared to the active areas present on the surface of the conventional grinding wheel.
- The assessment of the grinding wheel’s cutting ability was carried out using the Shos parameter. It allows for assessing the elevation of the active surfaces, their sharpness, and the orientation of the cutting edges in relation to the cutting direction. The Shos value for the layer with abrasive aggregates is 40% higher than for the layer with conventional abrasive grains;
- The use of bootstrap for the statistical hypothesis tests makes it possible to evaluate the differentiation of the ground surface features as a result of mean roughness parameters values. Those analyses take into account the actual form of the probability distribution of those parameters. They also express the irregularity of the surface roughness parameter values as a result of the grinding process variability;
- The modification of the grinding wheels as an application of new middle layer containing the addition of abrasive aggregates increases the tool’s ability to smooth the machined surface. In the case of surfaces ground with multilayer grinding wheels, more favorable values of roughness parameters were observed for the group of amplitude parameters (Sa, Sq, and Ssk), functional parameters (Spk, Vmp, and Sxp), and feature parameters (Sha and Shv);
- The effects of the application of an intermediate layer with the participation of abrasive aggregates affects the load-bearing capacity of the machined surfaces. The use of abrasive aggregates, with an impact surface larger than the base grains, results in the formation of a topography characterized by a smaller area (Sha value lower by 12%) and a smaller volume of peaks (Shv value lower by 34%) compared to the surfaces obtained as a result of grinding with a conventional grinding wheel.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

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**Figure 1.**The structure and the geometrical layers properties of the multilayer grinding tool: (

**a**) SEM image of a conventional grains in the external layers, (

**b**) the profile of the internal cylindrical layer, (

**c**) profile of the external conical layer, and (

**d**) SEM image of an abrasive aggregate (the admixture to the conventional grains).

**Figure 2.**Measurement set- up: (

**a**) Olympus OLS LEXT 4000 microscope and (

**b**) measurement set-up with Taylor Hobson CCI 6000 and Nikon 20× WD 4.2 lens.

**Figure 5.**Change in the value of the grinding wheel topography assessment parameters with an increase in the distance from the highest ordinate: (

**a**) mean island area, (

**b**) mean island volume, (

**c**) number of islands, (

**d**) shape factor Sw, and (

**e**,

**f**) visualization of the grinding wheel topography.

**Figure 6.**Shos values’ frequency for the aggregate and conventional layers of new abrasive tools in the height range from Sp to Δ.

**Figure 7.**Topographies of the exemplary ground surfaces: (

**a**) surface machined with conventional grinding wheel and (

**b**) surface machined with a multi-layer grinding wheel.

**Figure 8.**Illustration of the features of five surface elevations (parameter S5p) after Wolf pruning (5% Sz).

Process Parameters | |

grinding method | reciprocating grinding |

workpiece material | Ti-6Al-4V |

grinding wheel speed | v_{s} = 18 m/s |

lateral feed | a_{p} = 1 mm/stroke |

feed rate | v_{w} = 4 m/min |

depth of cut | a_{e} = 0.1 mm |

dresser | single-point diamond dresser |

dressing depth (ad) | a_{d} = 0.05 mm |

dressing speed (vd) | v_{d} = 5 mm/s |

grinding condition | wet grinding |

coolant | EMU 12 in 5% water solution |

coolant preassure | 7 bar |

coolant flow rate | 20 L/min |

Ti-6Al-4V Workpiece Properties | |

Average tensile strength MPa | 895 |

Yield point MPa | 825 |

Young’s Modulus GPa | 110 |

Thermal conductivity W/(m·K) | 6.7 (20 °C) |

Density g/cm^{3} | 4.43 |

Grinding Wheel Topography Measurement | |

Equipment | Confocal microscope LEXT OLS4000 with Anti Vibrant AV1 table |

Lenses | Olympus 20×, WD = 0.4 |

Magnification | ×428 |

Elementary measurement area | 646 μm × 646 μm for Olympus × 20 lense, with numerical magnification x1 |

Applied stitching | 5 × 5 cells with 10% overlap |

Number of areas measured | 3 × (2972 μm × 2972 μm) for each tool |

Specimen Topography Measurement | |

Equipment | Interference profilometer Taylor Hobson CCI 6000 |

Lenses | Nikon × 20/0.40DI WD 4.7 |

Magnification | ×428 |

Elementary measurement area | 899 μm × 899 μm for Olympus ×20 lense, with numerical magnification ×1 |

Number of areas measured | 60 × (899 μm × 899 μm) |

**Table 3.**Average values of the roughness parameters [21] of the ground surfaces and the results of the bootstrap test of the statistical significance of their differences.

Parameter | Conventional Tool | Multilayer Tool | Unit | p-Value | Statistically Significant Difference |
---|---|---|---|---|---|

Amplitude parameters | |||||

Sq | 0.37 ± 0.009 | 0.33 ± 0.006 | µm | 2.62 × 10^{−4} | yes |

Ssk | 0.78 ± 0.09 | 0.03 ± 0.08 | 9.99 × 10^{−6} | yes | |

Sku | 7.5 ± 0.4 | 6.2 ± 0.5 | 6.31 × 10^{−2} | no | |

Sp | 2.6 ± 0.1 | 2.5 ± 0.1 | µm | 3.84 × 10^{−1} | no |

Sv | 2.0 ± 0.1 | 1.8 ± 0.1 | µm | 2.86 × 10^{−1} | no |

Sz | 4.6 ± 0.2 | 4.3 ± 0.1 | µm | 1.94 × 10^{−1} | no |

Sa | 0.27 ± 0.006 | 0.25 ± 0.005 | µm | 3.01 × 10^{−2} | yes |

Functional parameters | |||||

Smr | 0.9 ± 0.1 | 0.9 ± 0.6 | % | 8.91 × 10^{−1} | no |

Smc | 0.42 ± 0.01 | 0.39 ± 0.01 | µm | 2.00 × 10^{−2} | yes |

Sxp | 0.62 ± 0.02 | 0.68 ± 0.02 | µm | 2.20 × 10^{−2} | yes |

Spatial parameters | |||||

Sal | 21.8 ± 0.7 | 14.4 ± 0.3 | µm | 9.89 × 10^{−6} | yes |

Str | 0.0973 ± 0.0060 | 0.0334 ± 0.0009 | 9.99 × 10^{−6} | yes | |

Hybrid parameters | |||||

Sdq | 0.065 ± 0.001 | 0.066 ± 0.001 | 2.74 × 10^{−1} | no | |

Sdr | 0.21 ± 0.01 | 0.22 ± 0.01 | % | 2.59 × 10^{−1} | no |

Volume parameters | |||||

Vv | 0.46 ± 0.01 | 0.41 ± 0.01 | µm³/µm² | 2.30 × 10^{−3} | yes |

Vmp | 0.033 ± 0.001 | 0.019 ± 0.001 | µm³/µm² | 9.99 × 10^{−6} | yes |

Vmc | 0.27 ± 0.01 | 0.27 ± 0.01 | µm³/µm² | 6.69 × 10^{−1} | no |

Vvc | 0.42 ± 0.01 | 0.36 ± 0.01 | µm³/µm² | 8.29 × 10^{−6} | yes |

Vvv | 0.0384 ± 0.0013 | 0.0421 ± 0.0011 | µm³/µm² | 3.29 × 10^{−2} | yes |

Features parameters | |||||

Spd | 0.00025 ± 0.00001 | 0.00030 ± 0.00001 | 1/µm² | 7.70 × 10^{−3} | yes |

Spc | 0.045 ± 0.001 | 0.049 ± 0.000 | 1/µm | 1.20 × 10^{−4} | yes |

S10z | 2.9 ± 0.1 | 2.8 ± 0.1 | µm | 1.71 × 10^{−1} | no |

S5p | 1.76 ± 0.06 | 1.75 ± 0.04 | µm | 9.63 × 10^{−1} | no |

S5v | 1.18 ± 0.07 | 1.03 ± 0.04 | µm | 4.88 × 10^{−2} | yes |

Sda | 3463 ± 155 | 2844 ± 136 | µm² | 3.80 × 10^{−3} | yes |

Sha | 3475 ± 143 | 3060 ± 138 | µm² | 3.10 × 10^{−2} | yes |

Sdv | 104 ± 9 | 71 ± 6 | µm³ | 3.10 × 10^{−3} | yes |

Shv | 129 ± 10 | 83 ± 6 | µm³ | 4.90 × 10^{−4} | yes |

Functional parameters | |||||

Sk | 0.67 ± 0.01 | 0.69 ± 0.01 | µm | 3.07 × 10^{−1} | no |

Spk | 0.52 ± 0.02 | 0.36 ± 0.01 | µm | 9.99 × 10^{−6} | yes |

Svk | 0.33 ± 0.02 | 0.35 ± 0.01 | µm | 4.23 × 10^{−1} | no |

Smr1 | 11.8 ± 0.3 | 9.9 ± 0.2 | % | 9.99 × 10^{−6} | yes |

Smr2 | 89.3 ± 0.2 | 88.3 ± 0.2 | % | 4.90 × 10^{−3} | yes |

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**MDPI and ACS Style**

Lipiński, D.; Banaszek, K.; Rypina, Ł.
Analysis of the Cutting Abilities of the Multilayer Grinding Wheels—Case of Ti-6Al-4V Alloy Grinding. *Materials* **2022**, *15*, 22.
https://doi.org/10.3390/ma15010022

**AMA Style**

Lipiński D, Banaszek K, Rypina Ł.
Analysis of the Cutting Abilities of the Multilayer Grinding Wheels—Case of Ti-6Al-4V Alloy Grinding. *Materials*. 2022; 15(1):22.
https://doi.org/10.3390/ma15010022

**Chicago/Turabian Style**

Lipiński, Dariusz, Kamil Banaszek, and Łukasz Rypina.
2022. "Analysis of the Cutting Abilities of the Multilayer Grinding Wheels—Case of Ti-6Al-4V Alloy Grinding" *Materials* 15, no. 1: 22.
https://doi.org/10.3390/ma15010022