Improved Sparrow Search Algorithm Based on Iterative Local Search

This paper solves the shortcomings of sparrow search algorithm in poor utilization to the current individual and lack of effective search, improves its search performance, achieves good results on 23 basic benchmark functions and CEC 2017, and effectively improves the problem that the algorithm falls into local optimal solution and has low search accuracy. This paper proposes an improved sparrow search algorithm based on iterative local search (ISSA). In the global search phase of the followers, the variable helix factor is introduced, which makes full use of the individual’s opposite solution about the origin, reduces the number of individuals beyond the boundary, and ensures the algorithm has a detailed and flexible search ability. In the local search phase of the followers, an improved iterative local search strategy is adopted to increase the search accuracy and prevent the omission of the optimal solution. By adding the dimension by dimension lens learning strategy to scouters, the search range is more flexible and helps jump out of the local optimal solution by changing the focusing ability of the lens and the dynamic boundary of each dimension. Finally, the boundary control is improved to effectively utilize the individuals beyond the boundary while retaining the randomness of the individuals. The ISSA is compared with PSO, SCA, GWO, WOA, MWOA, SSA, BSSA, CSSA, and LSSA on 23 basic functions to verify the optimization performance of the algorithm. In addition, in order to further verify the optimization performance of the algorithm when the optimal solution is not 0, the above algorithms are compared in CEC 2017 test function. The simulation results show that the ISSA has good universality. Finally, this paper applies ISSA to PID parameter tuning and robot path planning, and the results show that the algorithm has good practicability and effect.

Research on Centroid Distribution and Dynamic Characteristics of Irregular Tooth End Milling Cutters

For irregular end milling cutters, the incomplete equality of the pitch angle and helix angle will lead to an uneven mass distribution. The problems of centroid distribution caused by this, and whether it would affect the dynamic characteristics of milling cutters, have not been systematically studied. In this paper, through the proposed mathematical model, the centroid positions of each radial section of four types of end milling cutters, with equal overall eccentricities and different structures, are calculated, respectively. The centroid distribution of end milling cutters is studied and analyzed. Combined with finite element analysis, the vibration mode, frequency, and resonance frequency band of each type of end milling cutter, under the same dynamic excitation, is obtained. Based on a study of the dynamic characteristics of various types of end milling cutters, it is found that the response displacement of the variable pitch variable helix end milling cutter is the smallest, which is 0.043800 mm. With the same level of accuracy, its dynamic performance is the best. On the premise of not changing the overall eccentricity of the end milling cutter, a new idea for the structural design to improve the dynamic characteristics of the end milling cutter is provided.

Validation of variable helix milling instability islands

During machining, it is well-known that unstable self-excited vibrations known as regenerative chatter can limit productivity. There has been a great deal of research that has sought to understand regenerative chatter, and to avoid it through modifications to the machining process. One promising approach is the use of variable helix tools. Here, the time delay between successive tooth passes is intentionally modified, in order to improve the boundary of instability. Previous research has predicted that such tools can offer significant performance improvements whereby islands of instability occur in the stability lobe diagram. By avoiding these islands, it is possible to avoid regenerative chatter, at depths of cut that are orders of magnitude higher than for traditional tools. However, to the authors’ knowledge, these predictions have not been experimentally validated, and there is limited understanding of the parameters that can give rise to these improvements. The present study seeks to address this shortfall. A recent approach to analysing regenerative chatter stability is modified, and its numerical convergence is shown to outperform alternative methods. It is then shown that islands of instability only emerge at relatively high levels of structural damping, and that they are particularly susceptible to model convergence effects. The model predictions are validated against detailed experimental data that uses a specially designed configuration to minimise experimental error. To the authors’ knowledge, this provides the first experimentally validated study of unstable islands in variable helix milling, whilst also demonstrating the importance of structural damping and numerical convergence on the prediction accuracy.

OPTIMIZATION OF VARIABEL HELIX ANGLE PARAMETERS IN CNC MILLING OF CHATTER AND SURFACE ROUGHNES USING TAGUCHI METHOD

In the manufacturing industries, the main problem in process of operating CNC milling machine was chatter effect (self-excited vibration) which increases the quality of the surface roughness. In this study is to determine optimal value of parameters for chatter and surface roughness. The chatter measured using accelerometer MPU-6050 with Arduino by software LabVIEW-2019 based on peaks-FFT value and the surface roughness measured by SJ-301 tester. The research parameters like variable helix angle, spindle speed, feed rate, and depth of cut using stainless steel 304 by Taguchi method. The optimum parameters value obtained are variable helix 35/38 degrees, spindle speed 3000 RPM, feed rate 150 mm/min and depth of cut 0.4 mm. Based on ANOVA value, the variable helix angle and depth of cut are found to be significant for chatter and surface roughness. The depth of cut was high contribution by ANOVA chatter by 93.84% and surface roughness by 91.93%.

Pengaruh Geometri Pahat Variabel Helix Angle Pada Parameter Mesin Cnc Milling Vertikal Berbasis Mikrokontroler Terhadap Nilai Getaran Chatter

Abstrak Objektif. Getaran yang sering terjadi pada pengerjaan proses produksi menggunakan permesinan CNC milling merupakan hal yang sangat penting untuk diperhitungkan. Getaran ini dapat menyebabkan perubahan dimensi dan mempengaruhi tingkat kualitas benda kerja yang dihasilkan, sehingga efek getaran chatter atau self-excited vibration pada proses pengerjaan produksi menjadi masalah utama dalam proses permesinan milling. Nilai getaran chatter ditentukan menggunakan grafik SLD secara ekperimental untuk mengetahui batas antara chatter free dan chatter occurs. Material and Metode. Material yang digunakan dalam penelitian ini adalah Stanless steel 304, dengan menggunakan sensor MPU 6050 yang terhubung pada mikrokontroler Arduino Uno menggunakan software LabVIEW 2019 student edition yang digunakan untuk mengidentifikasi nilai acceleration getaran chatter. Besar nilai acceleration diukur menggunakan FFT menggunakan software DIAdem 2019 student. Metode yang digunakan dalam penelitian ini adalah dalam bentuk eksperimental, dengan geometri pahat Variabel Helix Angle (VHA) 2 variasi sudut yaitu 40/42 (Derajat), Spindel Speed sebesar 2000,2500,3000 (RPM) , Axial Depth Of Cut sebesar 0.5, 1.0, 1.5 (mm), dan Feed Rate sebesar 100, 125 dan 150 (mm/s). Hasil. Hasil pada Grafik Stability Lobe Diagram yang didapatkan pada proses permesinan slot milling menggunakan pahat variable helix angle 40/42 derajat dengan feed rate 150 mm/mnt memiliki chatter free yang lebih tinggi dibandingkan dengan feed rate 100 dan 125 mm/mnt. Kesimpulan. Dari hasil yang didapatkan bahwa semakin tinggi nilai feed rate maka nilai acceleration getaran chatter semakin rendah. Untuk pengembangan dalam penelitian selanjutkan maka perlu dilakukan pemilihan parameter geometri pahat dengan variasi 3 sudut mata pahat untuk mengetahui nilai getaran chatter yang signifikan. Abstrack Objective.Vibration that often occurs in the production process using CNC milling is very important to be taken into account. This is vibration can cause dimensional changes and affect the level of quality of the workpiece produced. Therefore, effect of chatter vibration or self-excited vibration on production process becomes a major problem in the milling machining process. Chatter vibration values ​​can be determined using experimental SLD for determine boundary between free chatter and chatter occur. Materials and Methods .The material used in this study is stanless steel 304, using the MPU 6050 sensor connected to Arduino Uno mikrokontroler using LabVIEW 2019 student edition software that is used to identify chatter vibration acceleration. Acceleration is measured using FFT using 2019 student DIAdem software. The method used is experimental, geometry Variable Helix Angle 2 angular 40/42 (Degrees), Spindel Speed ​​of 2000,2500,3000 (RPM), Axial Depth Of Cut of 0.5, 1.0, 1.5 (mm), and Feed Rate of 100, 125 and 150 (mm / s). Results. Results in the Graph Lobe Stability Diagram obtained in slot milling machining process using a variable helix angle of 40/42 degrees with feed rate of 150 mm / min have higher chatter free compared to feed rates of 100 and 125 mm / min. Conclusion. The results show that higher the value of feed rate, chatter vibration acceleration value is lower. For further development in research, it is necessary to select tool geometry parameters with variations of 3 tool eye angle to determine chatter vibration significant

Influence of Wear and Tool Geometry on the Chatter, Cutting Force, and Surface Integrity of TB6 Titanium Alloy with Solid Carbide Cutters of Different Geometry

In this paper, vibration-free milling cutters (variable helix (VH) and variable pitch (VP) end mills) and standard (SD) end mills are used to machine TB6 (Ti-10V-2Fe-3Al) titanium alloy in order to study the influence of wear and geometric structure parameters of milling cutters on chatter, cutting force and surface integrity of machined surfaces. The results of the tests show that the wear of milling cutters has a significant influence on the chatter, cutting force, roughness, residual stress, and microhardness. Geometric structure parameters of milling cutters also have a clear impact on both chatter and cutting force. Also, chatter and cutting force have significant effects on roughness and residual stress, which are in turn affected by tool geometric structure parameters, separately.

Chatter Vibration Comparison Between Normal Helix Angle and Variable Helix Angle in End Milling Process Based on Spectrum Analysis

Chatter vibration in machining processes is often found in cutting processes which will decrease the machining efficiency and the surface quality of the products. Chatter is a relative vibration of the cutting tool and workpiece caused by the fluctuation of cutting force that is concerned to be a self-excited vibration. The variable Helix Angle Cutting tool which has pitch angle variation will also inflict different tooth passing frequencies on the flute that stand contiguous and trim the resonance frequency. This research aims to compare chatter vibrations that occurred between Normal Helix Angle and Variable Helix Angle cutting tool based on spectrum analysis on cutting parameter variety (depth of cut; rotation speed; feed rate milling). The outcome is spectrum analysis can detect the chatter phenomenon, measure the natural frequency (38-42 Hz), and also compare chatter vibrations between two tools appropriately.

Stability Analysis for Milling Process with Variable Pitch and Variable Helix Tools by High-Order Full-Discretization Methods

Chatter is one of the significant limitations in the milling process, which may cause poor surface quality, reduced productivity, and accelerated tool wear. Variable pitch and variable helix tools can be used to suppress regenerative chatter. This study extends the high-order full-discretization methods (FDMs) to predict the stability of milling with variable pitch and variable helix tools. The time-periodic delay-differential equation (DDE) with multiple delays is used to model the milling process using variable pitch and variable helix tools. Then, the DDE with multiple delays is reexpressed by the state-space equation. Meanwhile, the spindle rotational period is divided into many small-time intervals, and the state space equation is integrated on the small-time interval. Then, the high-order interpolation polynomials are used to approximate the state term, and the weights related to the time delay are employed to approximate the time-delay term. The second-order, third-order, and fourth-order extended FDMs (2nd EFDM, 3rd EFDM, and 4th EFDM) are compared with the benchmark in terms of the rate of convergence. It is found that the 2nd EFDM, 3rd EFDM, and 4th EFDM converge faster than the benchmark method. The difference between the curves obtained by different EFDMs and the reference curve is very small. There is no need to extend hypersecond FDMs to analyze the stability of milling with variable pitch and variable helix tools.