A helix slope deviation compensation model for milling small modulus copper electrode gears

Zhipeng Feng,Zhao-Yao Shi,Shoujin Lin,Aijun Tong,Peng Wang,Guoqing Wu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.7

When a milling tool is used to mill small modulus copper electrode gears (SMCEG), the deformation is inevitable, thus leading to the helix slope deviation (HSD) of copper electrode gears (CEG). To compensate the influence of milling tool deflection (MTD) on the HSD, a universal HSD compensation model was established for different sizes of milling tools. First, using the principle of orthogonal experiment, a linear regression model of milling parameters and milling tool radius is established. Secondly, the average value of the HSD obtained by the gear measuring instrument is converted into the maximum of MTD according to the principle of helix line formation. The maximum deflections of the milling tools are used as the response value of the regression analysis to fit the maximum deflection curve of the milling tool. Through the reverse adjustment of the rotation angle of the rotating motor, the HSD compensation is realized. Finally, the model was verified by the milling tests. The results showed that the helix deviation reached the requirements of level 4 to 5 in GB/T 38192-2019, and proved the correctness of the established MTD model. The model is significant for milling SMCEG.

Influence of Tool Posture and Position on Stability in Milling with Parallel Kinematic Machine Tool

Muizuddin Azka,Keiji Yamada,Mahfudz Al Huda,Ryutaro Tanaka,Katsuhiko Sekiya 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.12

This paper investigated the machining stability influenced by tool posture and position in ball-end milling with parallel kinematic machine tool (PKM). Initially, the geometric structure was identified, and the machinery stiff ness was measured by impulse respond method at several positions with four tool postures. Then, the milling tests were conducted on fl at work surface using a ball-end mills. Cutting force and acceleration signals of milling tests were measured by three-axis dynamometer and accelerometer. Furthermore, these signals were analyzed by using Fast-Fourier transform and Hilbert–Huang transform (HHT). The results showed that the length of arm change with tool posture, where the machinery stiff ness decreased with the total length of arms for any tool position. The experimental results also demonstrated the machining stability varied with tool posture; the trend of stability corresponds with the machinery stiff ness. The vibration analysis by HHT presented the increasing of power level in the time–frequency plot when the length of arm increase during milling process. Therefore, the geometric influence must be considered to support process planning on the PKM.

Effect of reverse current on tool wear in micro-electrical discharge milling

Cheong, Hyeong Gyun,Kim, Yoo Seok,Chu, Chong Nam Elsevier 2019 Precision engineering Vol.55 No.-

<P><B>Abstract</B></P> <P>An RC-type pulse generator is useful in micro-electrical discharge milling due to its small discharge energy. However, when using this kind of generator, the current between the tool and the workpiece oscillates because of the stray inductance of the circuit. This causes current to flow from the tool to the workpiece in reverse direction to the main discharge current. When the reverse current flows, tool polarity is changed which intensifies tool wear. In this research, the reverse current is eliminated by connecting a MOSFET to a normal RC-type pulse generator. As a result, tool wear was reduced and geometrical accuracy was increased during machining of stainless steel using cemented carbide tool. Tool wear was further reduced through the use of deionized water with low resistivity. However, the use of low resistivity water decreases tool wear but can also reduce geometrical accuracy. The combination of using a MOSFET with low resistivity water therefore reduces tool wear while maintaining geometrical accuracy. The addition of the MOSFET to the RC circuit reduced the relative wear ratio by up to 67%. Thus, removing the reverse current is effective in reducing tool wear in various machining conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The reverse current is caused by oscillation when using an RC-type pulse generator. </LI> <LI> The reverse current worsens the relative wear ratio of the tool. </LI> <LI> The reverse current is removed by the addition of the MOSFET to the RC circuit. </LI> <LI> The addition of the MOSFET reduces the relative wear ratio of the tool. </LI> </UL> </P>

밀링 공구의 마모가 PMMA 임플란트 임시보철물 변연 및 내면적합도에 미치는 영향

신미선 대한치과기공학회 2019 대한치과기공학회지 Vol.41 No.2

Purpose: The purpose of this study is to evaluate the effect of CAD/CAM system milling tool wear on the marginal and internal fit of PMMA implant interim prosthesis three-dimensional manner. Methods: A total of 20 crowns were fabricated with CAD/CAM method. Their designs were unified to first molar of the left maxilla. The Customized abutments were prepared and scanned with on optical model scanner. Five crowns were milled by the newly replaced tool (1st milling), and 15 crowns were milled by 2nd, 3rd, 4th milling tool. The marginal and internal fit of 20 interim crowns were measured using the triple-scan protocol. Results: Statistically significant difference was found between the 1st milling group (51.8±14.6μm) and the 3rd, 4th milling group (128.6±43.8μm, 146.2±38.1μm, respectively) at the distal margins. In the mesial margins, There was a statistically significant difference between the 1st milling group (63.6±25.9μm) and the 3rd, 4th milling group (137.2±25.9μm, 186.8±70.6μm, respectively). In the distal line angle, significant difference was found between the 1st, 2nd, 3rd milling groups and the 4th milling group. In the mesial axial wall, significant difference was found between the 1st milling group (52.2±20.3μm) and the 3rd, 4th milling groups (22.8±8.8μm, 7.8±5.7μm). Conclusion: As a result of the experiment, decrease of the marginal and internal fit was statistically significant as the number of machining cycles increased. In order to produce clinically excellent restorations, it is recommandable to consider the condition of the milling tool wear, when designing the restoration with CAD program.

Tool-Wear Monitoring during Micro-End Milling using Wavelet Packet Transform and Fisher's Linear Discriminant

홍영선,윤해성,문종설,조영만,안성훈 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.7

Tool wear is one of the most important parameters in micro-end milling, and can be used to monitor the condition of the machine and the tool. A micro-end mill has different characteristics from a macro-scale end mill; in particular, shank run-out (which is negligible in the macro-scale tool due to the low aspect ratio) is significant in micro-end milling, inducing excessive tool wear and reduced tool life and leading to sudden, premature failure. In this paper, a novel tool-wear monitoring method is described for determining the state of a micro-end mill using wavelet packet transforms and Fisher’s linear discriminant. Force and torque signals were measured using a dynamometer and were used to reflect geometric changes in the micro-end mill due to wear. Because of the small signal-to-noise ratio, sensor signals measured during the milling process were periodically averaged, and the resulting singleperiod signals provided improved efficiency of feature extraction using wavelet packet transforms. The extracted features were classified in the wavelet domain and used to determine the tool state employing a hidden Markov model. The recognition results were compared with those of an energy-based monitoring technique, and we found that our method could determine the tool state more accurately for both normal wear and premature failure of micro-end mills.

난삭성 소재의 밀링가공시 공구상태감시를 위한 효과적인 신호특성평가

박강휘,김영준,이종환,김정석 한국생산제조학회 2017 한국생산제조학회지 Vol.26 No.6

Difficult-to-cut materials have poor machinability owing to their high stiffness and low thermal conductivity. As the machining proceeds, the tool wear is accelerated and abnormal conditions such as chipping and fracture of the cutting edge occur. Moreover, it is difficult to observe the state of tool in real time because machining is carried out by wet processing. This paper presents an evaluation of effective machining signal characteristics for the condition of a tool in the milling process of difficult-to-cut material. Experiments were conducted with two types of materials and three types of tools. Cutting force signals and vibratory acceleration signals were acquired during the machining experiments. Experiments are conducted until the tool is completely worn out. The correlation between the amount of tool wear and cutting signal characteristics, according to machining distance, is investigated. Finally, we propose effective cutting signal characteristics for tool wear condition monitoring in wet milling process.

Tool Wear Reduction Using Directional Milling Considering Cutting Angle in Carbon fiber Reinforced Plastic Machining

Gyuho Kim,Hyunho Jo,Jae Seok Shin 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.11

The abrasion of the cutting edge by hard carbon fibers during machining of carbon fiber reinforced plastics (CFRP) causes severe tool wear. In this process, the tool wear volume exhibits a strong dependence on the cutting angle (the angle between the fiber orientation and cutting direction). In industrial applications, the perimeters of CFRP workpieces are frequently machined via contour milling. However, it is difficult to avoid cutting angles that cause rapid tool wear in this type of milling. This study proposes a novel rough milling strategy to maintain the cutting angles within a specific range by adjusting the tool feed direction and radial depth of cut to reduce tool wear. In addition, to implement the proposed method for CFRP machining, a software is developed to generate the tool path. The effectiveness of the proposed method for tool life extension during milling of CFRP is experimentally investigated.

Development and Evaluation of Tool Dynamometer for Measuring High Frequency Cutting Forces in Micro Milling

강익수,김전하,홍진숙,김정석 한국정밀공학회 2010 International Journal of Precision Engineering and Vol. No.

A tool dynamometer is developed for measuring the high frequency cutting forces, and evaluated in micro milling of aluminum 6061-T6 using a tungsten carbide (WC) micro end mill. To improve the accuracy and productivity of the machining process, it is essential to monitor and control the machining process by measuring cutting forces. In order to improve the precision and quality of machined parts, high-speed machining with smaller micro tools is required, causing higher frequency cutting forces. The first natural frequency of tool dynamometers is high enough to precisely measure the high cutting forces. We investigate dynamic characteristics of the tool dynamometer theoretically and experimentally. The measurable frequency range of the developed tool dynamometer was higher than the commercial tool dynamometer, and the measured cutting force signals were not distorted at high-speed of above 60,000 rpm. The results showed that the developed dynamometer is able to measure the static and dynamic force components in high-speed micro milling.

Development and Evaluation of Tool Dynamometer for Measuring High Frequency Cutting Forces in Micro Milling

Kang, Ik-Soo,Kim, Jeon-Ha,Hong, Chin-Suk,Kim, Jeong-Suk 한국정밀공학회 2010 International Journal of Precision Engineering and Vol.11 No.6

A tool dynamometer is developed for measuring the high frequency cutting forces, and evaluated in micro milling of aluminum 606J-T6 using a tungsten carbide (We) micro end mill. To improve the accuracy and productivity of the machining process, it is essential to monitor and control the machining process by measuring cutting forces. In order to improve the precision and quality of machined parts, high-speed machining with smaller micro tools is required, causing higher frequency cutting forces. The first natural frequency of tool dynamometers is high enough to precisely measure the high cutting forces. We investigate dynamic characteristics of the tool dynamometer theoretically and experimentally. The measurable frequency range of the developed tool dynamometer was higher than the commercial tool dynamometer, and the measured cutting force signals were not distorted at high-speed of above 60,000 rpm. The results showed that the developed dynamometer is able to measure the static and dynamic force components in high-speed micro milling.

Milling tool wear diagnosis by feed motor current signal using an artificial neural network

Mehrdad Nouri Khajavi,Ebrahim Nasernia,Mostafa Rostaghi 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.11

In this paper, a Multi-layer perceptron (MLP) neural network was used to predict tool wear in face milling. For this purpose, a series of experiments was conducted using a milling machine on a CK45 work piece. Tool wear was measured by an optical microscope. To improve the accuracy and reliability of the monitoring system, tool wear state was classified into five groups, namely, no wear, slight wear, normal wear, severe wear and broken tool. Experiments were conducted with the aforementioned tool wear states, and different machining conditions and data were extracted. An increase in current amplitude was observed as the tool wear increased. Furthermore, effects of parameters such as tool wear, feed, and cut depth on motor current consumption were analyzed. Considering the complexity of the wear state classification, a multi-layer neural network was used. The root mean square of motor current, feed, cut depth, and tool rpm were chosen as the input and amount of flank wear as the output of MLP. Results showed good performance of the designed tool wear monitoring system.