臺灣博碩士論文加值系統

本研究為探討工具機之切削動態特性。工具機由五大鑄件組裝而成(底座、鞍座、立柱、主軸頭和工作台)，每一塊組件都有其本身的振動模態，因此，組裝後之工具機最終所表現出的切削動態特性與每一部件都有互相之關聯性。本研究將探討結構、線性元件、主軸以及刀具之動態特性，利用有限元素分析以及振動敲擊試驗，分別進行動態分析，評估每一部件本身之動態特性對工具機切削特性之影響，再將所得之結果相互整合，藉此了解各部件之動態特性互相耦合後對整機切削特性之影響。
工具機結構中，分析模型須包括機柱結構、主軸頭部、進給系統與主軸等關鍵組件。模態分析中可以發現，結構所產生之模態頻率多屬低頻，故在進行低頻切削時，機台之切削特性會受到機柱結構動剛性影響。另外，主軸鎖固部位之結構在影響機台切削特性因素上亦佔有一定程度之影響，若其搭配不同預壓之線性滑軌將改變機台切削特性。
線性滑軌已廣泛應用在各式各樣工具機之進給導軌系統中，其內部滾動鋼珠與滑槽之間的接觸力與接觸點之變形量為非線性關係，將導致鋼珠接觸剛性與阻尼性隨預壓之調整而改變，從而影響工具機平台系統結構之動態特性。對主軸頭部進給系統而言，線軌滑塊預壓等級將是影響刀具對切削力之動態響特性與切削穩定性之重要設計參數。為評估線軌預壓所產生之力學效應，本研究應用振動實驗與切削顫振理論，評估具有不同預壓線軌之主軸刀具系統之動態特性與切削穩定性範圍。研究結果顯示，調整滑軌預壓等級確實會改變刀具端動態響應特性及臨界切深。以本案立式銑床主軸頭進給系統為例，相較於高預壓滑塊，組裝低預壓滑塊反而可以增加刀具動剛性，約4-11%左右，並提升刀具切削穩定性範圍與臨界切深，約增加57％。
主軸系統是工具機重要組件之一，其性能之優劣直接影響到工具機的加工能力與精密度。主軸中接觸介面之強度將影響主軸模態以及整機切削特性之表現，如主軸軸承支滾動接觸介面、刀柄-主軸結合介面、筒夾-刀具夾持介面。結合介面之剛性影響兩個部件結合後其模態之耦合結果。研究中將分別針對刀柄以及刀具進行分析以及實驗，並利用實驗找出刀柄-主軸以及刀具-套筒之振動響應耦合相關性，再將其相關性導入模型進行分析。利用有限元素法與振動實驗分析法探討結合介面對於主軸切削特性之影響，並經由切削實驗來驗證分析之準確性以及對機台實際切削之影響。
完成上述之各部件動態特性分析後，將其結果整合並導入工具機整機實體模型中，搭配整機實際切削實驗，預測刀具之全角度切削穩定性範圍，建立整機分析法則後，將可評估整台機台之全角度切削穩定性，並提供機台設計者對設計中機台之整機動態穩定性的掌握，提升機台加工之效能與穩定性。

This thesis investigates the dynamic characteristics of the machine tool by means of experimental techniques and the finite element method. The results show the greatest impact on the machine’s cutting stability to be from improving the overall stiffness of the spindle-tool holder-tool system, which contributes to the cutting performance.
The machine tool assembly comprises five principle castings: base, table, column, spindle head and spindle. Each module has independent vibration modes, but all the vibration modes are coupled when the machine tool is assembled. This thesis presents the dynamic characteristics of the structure, linear guideway, spindle and tool using the finite element method and vibration tests. We investigate the effect on the machine tool when the components are coupled, assess the effect on the dynamic characteristics of the machine tool of each module and integrate the results.
The analysis of the machine tool model includes the structure of the column, spindle head, feeding system and spindle, which are its key components. Our findings show that the modal frequencies from the machine structure are usually not over 1000 Hz. When the machine tool is cutting workpieces at a low spindle rotating speed, the machine’s structure modal characteristic influences its dynamic characteristics. In addition, the preload of the linear guideway assembly between the column and the spindle head influences the machine tool’s cutting performance; thus, changes to the preload of the linear guideway can either improve or worsen the machine tool’s cutting performance.
The result shows that the overhang of the holder has an amplification effect on the mode amplitude and that the contact stiffness of the interface between the spindle and the holder affects the mode frequency. Choosing a shorter tool holder and increasing the contact area of the interface (using BBT tool holder) can up the dynamic characteristic of the tool holder end. Also, a longer holder overhang negatively affects the cutting stability. In this study, the critical cutting depth is reduced 4.1% in the X-direction and 19.2% in the Y-direction when the tool overhang is increased from 68 to 78 mm.
In addition, the machine positioning affects the accuracy and performance of machine tool during processing. When the spindle head is set in a low position, in the X-direction the critical cutting depth is 13.4% more than in a high position; and in the Y-direction, the critical cutting depth is 3.4% more than in a high position.

ABSTRACT ii
TABLE OF CONTENTS iv
LIST OF TABLES vi
LIST OF FIGURES vii
LIST OF NOMENCLATURE x
CHAPTER 1. INTRODUCTION 1
1.1 Structural Design of Machine Tool 1
1.2 Spindle-bearing System 2
1.3 Linear Feeding Mechanism (linear guides and ball screw) 3
1.4 Research Objective 4
1.5 Organization of the Thesis 4
CHAPTER 2. LITERATURE REVIEW 6
2.1 Spindle 6
2.2 Modeling Analysis of Machine Tool 12
2.3 Cutting Performance of Machine Tool 14
2.4 Interface Coupling 15
CHAPTER 3. FINITE ELEMENT METHOD 20
3.1 Modal Analysis 21
3.2 Modeling of the Rolling Interface 24
3.3 Spindle Model 29
3.4 Response of Spindle Nose and Tool End 31
CHAPTER 4. MODEL ANALYSIS 36
4.1 Spindle Model 36
4.2 Spindle Modal Analysis 38
4.3 Machine Tool Model and Analysis 42
4.4 Spindle-Tool Holder Interface Analysis 50
CHAPTER 5. VIBRATION EXPERIMENT 54
5.1 Spindle Vibration Response 54
5.2 Machine Tool Vibration Response 58
5.3 FRF of Spindle Head in Different Positions 73
CHAPTER 6. RESULTS AND DISCUSSION 76
6.1 Spindle Analysis and Experiment 76
6.2 Machine Tool Analysis and Experiment 78
6.3 Coupling Effect (Spindle and Tool Holder) 81
6.4 Coupling Effect (Tool Holder and Tool) 84
6.5 Tool Effect (Overhang) 86
6.6 Tool Effect (Number of edge) 90
6.7 Spindle Head Position 93
CHAPTER 7. CONCLUSION 96
7.1 Conclusion 96
7.2 Future Work 98
REFERENCE 100

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