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1

Prediction of Surface Roughness based on the Machining Conditions with the Effect of Machining Stability

Lin Yung-Chih, Chen You-Chen, Wu Kung-Da, Hung Jui-Pin

Advances in Science and Technology. Research Journal

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2020

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Vol. 14, no 2

171--183

EN

This study was aimed at analyzing the influence of the cutting parameters (spindle speed, feed rate and cutting depth) on the surface roughness of the machined parts with the influence of the machining stability of the cutter. In order to consider the chattering effect, the machining stabilities were calculated based on the measured tool tip frequency response functions. A series of machining tests were conducted on aluminum workpieces under different cutting parameters. Then, the surface roughness prediction models in the form of nonlinear quadratic and power-law functions were established based on the multivariable regression method, in which the input parameters, cutting depth and spindle speed, were respectively defined in the stable and unstable regions, according to the stability lobes diagram. The current results show that both models built with the cutting parameters defined in stable regions demonstrate higher prediction accuracy of the surface roughness, about 90%, when compared with the models defined in full regions with the accuracy of about 80%. In particular, the power-law model is proven to have 90% prediction accuracy when validated with the cutting parameters in a stable region. As a conclusion, the mathematical models based on the cutting parameters with well-defined machining stability were proven to show more accurate prediction ability of the surface roughness. It could be expected that the prediction model can further be applied to optimize the machining conditions in low speed roughing and high speed finishing process with desirable surface quality.

2

Investigation of the Dynamic Characteristics and Machining Stability of a Bi-rotary Milling Tool

Hung Jui-Pin, Lin Wei-Zhu

Advances in Science and Technology. Research Journal

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2019

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Vol. 13, no 1

14--22

EN

Bi-rotary milling head is the primary component of multiple-axis machine tool toward the multiply machining operation. The machining performance is greatly related to the structure characteristics and positioning precisions of the swivel head. This study was aimed at developing a bi-rotary milling head module, which is composed of a direct drive motor, cross roller bearings and motorized spindle unit. In order to evaluate the machining stability at the design phase, the dynamic characteristics of the rotary milling were first analyzed with finite element method. Especially, the variations of the dynamic characteristics of the spindle tool with the changing of the titling configuration of swivel axis were examined. In order to consider the accurate presentation of a spindle tool system and swivel mechanism, the bearings in the rolling components were also included in the finite element model and simulated with surface contact elements with adequate contact stiffness. The dynamic frequency response function of the spindle tool at different swinging positions were predicted for comparisons, which were further used to calculate the machining stability based on the machining mechanics. The current results show that the feeding direction and swinging positions of rotary milling head have a significant influence on the dynamic characteristics and machining ability of the spindle tool. The variations of the cutting depth with the swinging of A axis fall in the range of 11% to 40%, depending on the feeding direction and swinging angle. The analysis results are expected to clearly demonstrate the variation of the machining performance of the spindle tool under different milling configurations. The devised model and modeling approach can be applied to develop a five axis milling machine with desired dynamic and machining performance.

3

Evaluation of the Optimum Machining Stability of a Milling Tool with Different Flutes and Overhangs

Lin Yung-Chih, Wu Kung-Da, Shih Wei-Cheng, Hung Jui-Pin

Advances in Science and Technology. Research Journal

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2019

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Vol. 13, no 2

56--64

EN

In machining practice, the selection of the tooling condition of the cutters is an important task for milling operation with better surface quality and material remove rates. This study was therefore aimed at evaluating the influence of the tooling condition, such as the flutes and overhang length, on the machining efficiency of a milling machine by using the machining stability analysis method. Essentially, the machining stability was calculated based on the measured frequency response functions of the milling cutter, while it was also affected by the changing milling tooling path. Therefore, the machining stabilities in different feeding directions, referred to as polar stability boundary, were evaluated to show the strength and weakness of a specific cutter in contouring machining. The current results show that the overhang length greatly affects the dynamic characteristics and the limited cutting depths of the milling cutter. The stability boundaries of the machining conditions can be enhanced by appropriately adjusting the overhang of the milling cutter. Besides, the 2-flute cutter shows a larger cutting depth for surface contouring as compared to the 4-flute cutter, which is expected to increase the material remove rate under stable machining. As a whole, this study provides valuable references for enhancing the machining efficiency through the use of different tooling conditions.

4

The dynamic repeatability of a machine tool–holder–workpiece system

Jasiewicz M.

Technical Transactions

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2018

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Vol. 115, iss. 1

177--185

EN

Knowledge of the dynamic properties of a machine tool–holder–workpiece system is crucial for the appropriate selection of machining parameters based on stability lobes. One of the most convenient methods allowing for the experimental identification of these properties is impact testing. However, the repeatability of such measurements may be different depending on the machine–workpiece setup and can lead to incorrect cutting parameter calculations. The article presents this issue on the example of a latheworkpiece system. The experimental setup and obtained measurement results are presented and discussed.

PL

Znajomość właściwości dynamicznych układu obrabiarka–uchwyt–przedmiot obrabiany jest kluczowa przy doborze odpowiednich parametrów technologicznych obróbki przy wykorzystaniu krzywych workowych. Jedną z podstawowych eksperymentalnych metod wyznaczania tych właściwości są testy impulsowe. Jednakże, w ramach rozpatrywanego układu obrabiarka–przedmiot wyniki uzyskane w ramach przeprowadzania takich pomiarów mogą się różnić, co jednocześnie prowadzić może do doboru niewłaściwych parametrów obróbki. W pracy przedstawiono niniejsze zagadnienie na przykładzie tokarki. Zaprezentowano badany układ, wyniki przeprowadzonych pomiarów oraz interpretację wyników.

5

Wpływ parametrów skrawania na właściwości modalne przedmiotu obrabianego

Jasiewicz M., Powałka B.

Modelowanie Inżynierskie

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2014

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T. 21, nr 52

93--100

PL

W pracy zaprezentowano wyniki badań mających na celu określenie charakteru zmian właściwości dynamicznych części podatnych podczas frezowania w zależności od parametrów skrawania oraz ich wpływu na rozwój drgań samowzbudnych w procesie obróbki. W tym celu zbudowano stanowisko badawcze charakteryzujące się wysoką podatnością. Przeprowadzono klasyczny test impulsowy, którego to wyniki stanowiły punkt odniesienia do kolejnej części eksperymentu polegającej na wykonaniu szeregu testów impulsowych podczas obróbki przeprowadzanej przy różnych głębokościach skrawania i prędkościach obrotowych narzędzia. Przedstawiono porównanie wyników badań oraz ich interpretację.

EN

This paper presents the results of a study to determine the nature of changes in the dynamic properties of flexible parts during milling depending on the cutting parameters and their implications for the simulation of vibration in the machining process. For this purpose a test stand was build, which is characterized by high flexibility.. The first step was to conduct an impulse test, which results provide a benchmark for the next part of the experiment involving the execution of a series of impulse tests during machining at different cutting depths and spindle speeds. Furthermore the test results and their interpretation is presented.

6

Computational diagnostics of self-excited vibration in a machine tool-cutting process system.

Bodnar A.

Postępy Technologii Maszyn i Urządzeń

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1998

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vol. 22, nr 2

53-72

EN

The paper presents a methodology of computational diagnostics of self-excited vibration, i.e. detecting the weak links - in term of the machine tool's cutting process system stability - in the machine mass-dissipation-spring system (the MDS system). A way of creating a mathematical model of the machine tool-cutting process system in the convention of the rigid finite element method is outlined. For such a definited computational model an algorithm for seeking weak links in the machine tool MDS system is presented. The algorithm action effectiveness is ilustrated by a computational example done for the FWD 32J milling machine.

PL

Przedstawiono metodykę obliczeniowej diagnostyki drgań samowzbudnych obrabiarki, czyli wykrywania w jej układzie masowo-dyssypacyjno-sprężystym (MDS) słabych ogniw ze względu na wibrostabilność systemu obrabiarka-proces skrawania. Pokazano w zarysie sposób tworzenia matematycznego modelu systemu obrabiarka-proces skrawania w konwencji metody sztywnych elementów skończonych. Dla tak zdefiniowanego modelu obliczeniowego opracowano algorytm poszukiwania słabych ogniw w układzie MDS obrabiarki. Skuteczność działania algorytmu ilustruje przykład obliczeniowy wykonany dla frezarki FWD 32J.