Uniformity, Periodicity and Symmetry Characteristics of Forces Fluctuation in Helical-Edge Milling Cutter
Abstract
:1. Introduction
2. Milling Force Fluctuation Mechanism of Helical-Edge Cutter
2.1. Milling Process and Theory Preconditions
- The milling process is general and simple, which means the influences of the tool wear, deformation, runout and chatter are not considered;
- The milling force model is widely accepted [9]. In this model, the tool path is considered as a circle when calculating the chip thickness. The cutting force caused by the size effect coefficients (Ktc, Krc, Kac) is considered as the main factor and the ploughing effect is ignored in side milling;
- The processing parameters are smooth and not extreme. Under this condition, the milling force coefficient is stable and can be considered as an average value.
2.2. Milling Process and Theory Preconditions
3. Milling Force Fluctuation Characteristics
3.1. Virtual-Edge Projection Method of Force Equation Transformation
3.2. Uniformity Characteristics of Force Fluctuation
3.3. Periodicity Characteristics of Force Fluctuation
3.4. Symmetry Characteristics of Force Fluctuation
4. Simulation and Experimental Validation
4.1. Fast Estimation Method of Milling Force Fluctuations
4.2. Accurate Simulation Method of Milling Force Fluctuation
4.3. Experimental Validation of Force Fluctuation Characteristics
5. Conclusions
- A milling force modeling method is proposed to fulfill the requirements of mathematical expression of the milling force fluctuation. By using the peak-to-peak difference of milling force, the milling force fluctuations are quantified and defined, which provides an opportunity to study the characteristics of milling force fluctuations by mathematical methods;
- A virtual-edge projection method, which enables the milling force on every cutting edge to be projected and replaced directly to the same virtual edge, is proposed. Therefore, the milling force fluctuation can be analyzed intuitively from discontinuities and overlaps of the projected virtual edge;
- The relationship between the force fluctuation characteristics and axial depth of cut is revealed. A one-cycle standard of the axial depth of cut (Apoc) is defined. It is also proven that the force fluctuation is always zero when the axial depth of cut is Apoc. In addition, it is demonstrated that the milling force fluctuates periodically and the minimum period is Apoc. Furthermore, in a period, the milling force fluctuation always first ascends and then descends as the value of Ap increases and the amplitude is symmetric about Apoc. Then, the milling force fluctuations of all periods can be understood by experimental test of only half periods, which significantly reduced the milling test workload;
- Two prediction methods of milling force fluctuations are proposed: fast estimation method and simulation method. The fast estimation method has a simple calculation process and does not require determining the milling force coefficient. However, it only displays a percentage result of force fluctuations and there is no specific force value, which makes this method less accurate and suitable for precise engineering applications. In contrast, the simulation method has higher prediction accuracy and the average error is less than 3 N, which meets the experimental requirements.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Nomenclature
x-y-z | Coordinate system of the machine tool and workpiece |
t-r-a | Coordinate system of a milling cutter |
Ktc, Krc, Kac | Tangential, radial and axial cutting force coefficients (N/mm2) |
Ft, Fr, Fa | Tangential, radial and axial cutting forces (N) |
PTdoc | The force valley and the force peak that followed |
Fpp | Peak-to-peak value of the milling force (N) |
Ae, Ap | Radial and axial depths of cut (mm) |
g | A judgment function to determine whether the micro-element is in milling |
G(θ) | A simplified expression of ft × sin(θ) × g(θ) |
C | A simplified expression of fz × ΔZ |
C0 | The constant force generated by the milling tool at axial depth of Apoc |
θi,j | Tool rotating angle of a tooth j at a height i (deg) |
θst | Entrance angle (deg) |
θex | Exit angle (deg) |
θen | Engaged angle (deg) |
θ0 | Initial angle (deg) |
I | The current height of the micro-elements in the z-direction (mm) |
J | Cutting edge index |
ft | Feed per tooth (mm/tooth) |
ΔZ | Height of a micro-element in the z-direction (mm) |
Z0 | An axial offset reference position in the z-direction (mm) |
Nd | Total number of axial micro-elements |
Nt | Total number of cutting edges |
R | Radial of a cutting tool (mm) |
β | Helix angle of a cutter (deg) |
Apoc | Standard axial cutting depth in each period (mm) |
Ii | Intensity indicator of force fluctuation |
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Processing Parameters | Value | Cutter Parameters | Value |
---|---|---|---|
ft | 0.02 (mm/tooth) | Nt | 6 |
Apoc | 5.236 (mm) | β | 45° |
Ap | 2.618–5.236 (mm) | R | 5 (mm) |
Ae | 1.5, 2.5, 3.5 (mm) | Kt | 474 (N/mm2) |
Number | Ae (mm) | Ap (mm) | Feed Speed (mm/min) | Spindle Speed (rpm) |
---|---|---|---|---|
1 | 2.5 | 1 | 240 | 2279.8 |
2 | 2.5 | 2.618 | 240 | 2279.8 |
3 | 2.5 | 4.236 | 240 | 2279.8 |
4 | 2.5 | 5.236 | 240 | 2279.8 |
5 | 2.5 | 6.236 | 240 | 2279.8 |
6 | 2.5 | 0–10 | 240 | 2279.8 |
Processing Parameters | Value | Cutter Parameters | Value |
---|---|---|---|
Milling type | Down milling | Nt | 6 |
Cutting speed | 71.6 (m/min) | β | 45° |
ft | 0.017 (mm/tooth) | R | 5 (mm) |
Chemical Composition (%) | Webster Hardness (HW) | |||||||
---|---|---|---|---|---|---|---|---|
Si | Fe | Cu | Mn | Mg | Cr | Zn | Al | |
<0.25 | <0.4 | <0.1 | <0.1 | 2.2–2.8 | 0.15–0.35 | <0.1 | remain | 11 |
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Meng, B.; Liu, X.; Li, M.; Liang, S.Y.; Wang, L.; Wang, Z. Uniformity, Periodicity and Symmetry Characteristics of Forces Fluctuation in Helical-Edge Milling Cutter. Appl. Sci. 2021, 11, 2693. https://doi.org/10.3390/app11062693
Meng B, Liu X, Li M, Liang SY, Wang L, Wang Z. Uniformity, Periodicity and Symmetry Characteristics of Forces Fluctuation in Helical-Edge Milling Cutter. Applied Sciences. 2021; 11(6):2693. https://doi.org/10.3390/app11062693
Chicago/Turabian StyleMeng, Boyang, Xianli Liu, Maoyue Li, Steven Y. Liang, Lihui Wang, and Zhixue Wang. 2021. "Uniformity, Periodicity and Symmetry Characteristics of Forces Fluctuation in Helical-Edge Milling Cutter" Applied Sciences 11, no. 6: 2693. https://doi.org/10.3390/app11062693