机床切削性能测试.pdf

工具機切削性能測試工具機切削性能測試 財團法人精密機械研究發展中心 徐光漢 2008 04 2006 12 01 精密機械研發中心2 內內容容 一 前言 二 測試方法 三 切削顫振 四 測試工件 五 討論 2006 12 01 精密機械研發中心3 品質 切削效率 尺寸 精度 表面 品質 時間 一 前言 最大移除 率 MRR Cycle Time 2006 12 01 精密機械研發中心4 模 態 主 軸 熱 變 位 循 跡 精 度 靜 動 剛 性 迴 路 增 益 高 速 高 精 度 機 能 加 減 速 參 數 機械特性機械特性 伺服特性伺服特性切削應用技術切削應用技術 切削性能切削性能 刀 具 規 格 切 削 路 徑 工 件 切 削 條 件 顫 振 夾 治 具 評價項目 主 軸 迴 轉 精 度 2006 12 01 精密機械研發中心5 影響切削性能因素 機台方面 結構剛性 功率 轉速 進給速率 刀具方面 材質 硬度 直徑 長度 刀刃數 工件方面 材質 硬度 幾何形狀 周邊 工件夾持 刀具夾持 加工程式 冷卻 2006 12 01 精密機械研發中心6 材料移除率計算方法條件 b b 軸向切削深度軸向切削深度 a a 徑向切削深度徑向切削深度 f f 進給率進給率 n n m m c c n n 主軸轉速主軸轉速 m m 刀刃數刀刃數 c c 切屑厚度切屑厚度chip loadchip load 2006 12 01 精密機械研發中心7 馬力限制 一般以主軸馬達負載表達到130 為上限 振動限制 發生顫振或振動值太大 振動值在0 4G以上 工件夾持限制 切削過程中夾具無法完全固定工件 刀具限制 切刃斷裂或超過刀具可切深 噪音太大限制 噪音值超過安全法規 85dBA 或客戶需求值 80dBA 加工表面粗度不佳 加工表面粗度超過規範或客戶需求 材料移除率的限制 2006 12 01 精密機械研發中心8 ISO CD 230 1 Ed 3 Test code for machine tools Part 1 Geometric accuracy of machines operating under no load or quasi static conditions ISO 230 2 2006 Ed 3 Test code for machine tools Part 2 Determination of accuracy and repeatability of positioning numerically controlled axes ISO DIS 230 3 Ed 2 Test code for machine tools Part 3 Determination of thermal effects ISO 230 4 2005 Ed 2 Test code for machine tools Part 4 Circular tests for numerically controlled machine tools ISO 230 5 2000 Ed 1 Test code for machine tools Part 5 Determination of the noise emission ISO 230 6 2002 Ed 1 Test code for machine tools Part 6 Determination of positioning accuracy on body and face diagonals Diagonal displacement tests ISO FDIS 230 7 2 Ed 1 Test code for machine tools Part 7 Geometric accuracy of axes of rotation ISO CD TR 230 8 Ed 1 Test code for machine tools Part 8 Determination of vibration levels ISO檢驗標準 2006 12 01 精密機械研發中心9 找出 機台 刀具 工件 系統之最佳切削條件 1 主軸轉速 2 進給速度 3 切削深度 4 切削寬度 5 加工路徑 6 穩定切削穩定切削 振動量小振動量小 刀具壽命長刀具壽命長 材料移除率大材料移除率大 二 測試方法 2006 12 01 精密機械研發中心10 實切測試 Trial and Error 刀具與工件架設完成後 設定轉速 切削深度 進 給 直接進行實際切削 並量測切削過程產生的訊 號 例如切削力 振動 聲音等以進行相關的分析 與評估 Exciter Test Predictive 在刀具架設完成之後 提供一已知的輸入力量 衝擊槌 激振器 來激勵刀具 並以感測器 位移計 加速規 量測輸出訊號 以進行相 關的模態參數 頻率 剛性 阻尼 分析與評估 2006 12 01 精密機械研發中心11 切削動力計 三向式力感測器 量取切削時工件所 承受之x y z 三方 向作用力與波型 可建立標準操作程 序 作為日後刀具 判別訊號 2006 12 01 精密機械研發中心12 單刃切削力量測值 2006 12 01 精密機械研發中心13 3D表面粗度量測儀 2006 12 01 精密機械研發中心14 表面粗度紋路頻譜分析 轉速頻 18 33 Hz 刃頻 2006 12 01 精密機械研發中心15 l顫振是一種切削時 發生於工件 刀具間的自激振動 行為 藉由量測可以評價機台切削能力極限 l顫振時 切削力與振動量將會異常增大 以致刀具或 工件發生損害以及惡劣工件表面 l顫振常發生在高速或高馬力切削過程 三 切削顫振 Chatter Ref Dr Smith 2006 12 01 精密機械研發中心16 Machine tools are stiff but not infinitely stiff Cutting performance becomes limited by the dynamic characteristics of the machine Insufficient stiffness and damping lead to problems with chatter Vibration phenomena are not random but can be quantitatively described Basic Principles Ref Dr Smith 2006 12 01 精密機械研發中心17 Ref Dr Smith lThree kinds of stiffnesses Static Stiffness K known static load how much does the tool or spindle point deflect Modal Stiffness ki stiffness associated with a given mode at a given natural frequency fn i ki mi 1 2 Dynamic Stiffness h inverse of real flexibility of the system when excited at a natural frequency inverse resonant flexibility lHow are they related Static stiffness is the inverse sum of all the modal stiffnesses Dynamic stiffness includes the effect of damping and modal stiffness 2006 12 01 精密機械研發中心18 切削顫振發生的原因 切削過程中令人無法接受的振動多屬 於自激振動 Self excited Vibration 是何種機制使得主軸穩定能量的輸入 轉換成振動現象 Regeneration of Waviness 2006 12 01 精密機械研發中心19 Regeneration of WavinessRegeneration of Waviness Ref Dr Smith 2006 12 01 精密機械研發中心20 Chatter characteristics The chatter frequency is usually close to but not equal to the natural frequency The lobes are more tightly packed at the left smaller speed change for the same phase change Large stable zones exist in the high speed ranges Surprisingly the largest such gap occurs where the tooth passing frequency is equal to the natural frequency Why When tooth frequency matches natural frequency the surface waves and the tooth vibration are in phase The chip thickness looks the same as if there were no vibration Ref Dr Smith 2006 12 01 精密機械研發中心21 Chatter Frequency Below the limit of stability force or sound spectrum frequencies are dominated by tooth frequency run out harmonics and noise Above the limit of stability a prominent chatter frequency appears Stable and unstable machining may be discriminated using the prominent frequency in the spectrum Additionally we will see that if the cut is unstable the chatter frequency gives guidance for correction Chatter cannot occur at the tooth passing frequency or any of its harmonics Chatter can but normally does not coincide with rotational frequency or its harmonics Ref Dr Smith 2006 12 01 精密機械研發中心22 2006 12 01 精密機械研發中心23 Frequency Response Functions FRF A FRF is a measurement of a system s response to a known excitation as a function of the excitation frequency Negative Real Peak Static Compliance Dynamic flexibility 1 2k Magnitude Response Real part of FRF MM K K C C 2006 12 01 精密機械研發中心24 Real Part of FRF we are concerned with the magnitude response for cutting performance the negative real part of the FRF Static Complianc e H n lr f ff 2 2 2 nf k m H k 2 1 1 k G 4 1 Re min Ref Dr Smith 2006 12 01 精密機械研發中心25 Same frequency and stiffness damping ratio lower by on right Affect of Damping RatioAffect of Damping Ratio Ref Dr Smith 2006 12 01 精密機械研發中心26 Affect of Stiffness Same frequency and damping ratio stiffness lower by on right Ref Dr Smith 2006 12 01 精密機械研發中心27 Affect of Frequency Same damping ratio and stiffness frequency lower by 1 3rd on right Ref Dr Smith 2006 12 01 精密機械研發中心28 切削穩定臨界值極限 Critical Limit of Stability blim crit b KG b G s lim crit lim crit s w here lim it axial depth i e no chatter Kcutting stiffness directional orientation factor real part of the O T F 1 2 R e R e m in Re G Re G min min Ref Dr Smith 2006 12 01 精密機械研發中心29 cutting force angle cutting force angle f feed directionf feed direction F cutting forceF cutting force n cutter rotationn cutter rotation N normal of cutN normal of cut u directional orientationu directional orientation factorfactor X XX X axisaxis Y YY Y axisaxis Directional OrientationDirectional Orientation Ref Dr Smith 2006 12 01 精密機械研發中心30 切削穩定區域圖 Stability Lobe Diagram 主軸轉速 RPM 軸 向 切 削 深 度 bcr Ref Tobias S A and Fishwick W Theory of Regenerative Machine Tool Chatter Engineering London Vol 205 1958 2006 12 01 精密機械研發中心31 Tony L Schmitz University of Florida Dept of Mechanical and Aerospace Engineering Gainesville FL USA Single degree of freedom flexure in order to provide a simple dynamic system Ref Dr Smith 2006 12 01 精密機械研發中心32 Tony L Schmitz University of Florida Dept of Mechanical and Aerospace Engineering Gainesville FL USA Two degree of freedom system dynamics Ref Dr Smith 2006 12 01 精密機械研發中心33 切削條件 19 mm Diameter 4 fluted end milling of aluminum 7075slotting Ref Dr Smith 2006 12 01 精密機械研發中心34 Cut Records for Cut E Cut Record for Cut F Cut Record for Cut G Ref Dr Smith 2006 12 01 精密機械研發中心35 測試程序 4 3 2 1 EXCITATIO N HAM MER RESPONSE AC CEL MLA Interface Box PC Accelerometer STRIKE Hammer 頻率響應圖 Lobe圖 振動頻譜 TXF模組 2006 12 01 精密機械研發中心36 SHOP FLOOR OPTIMIZATION FOR PERFORMANCE MACHINING Dr Thomas S Delio Tom Delio E Mail delio mfg IRL www mfg Manufacturing Laboratories Inc 2006 12 01 精密機械研發中心37 量測資料圖例 2006 12 01 精密機械研發中心38 實作例 程序 1 依馬達出力 切削型態選用適當刀具 本例為面銑刀 D125 8刃 2 使用Metalmax之TXF模組進行頻率響應量測與顫振條件模擬 3 切削條件選用 切深 由淺至深 每層依TXF資料選用多種轉速 進給 依馬達負載漸加至130 為限 4 切削中使用Metalmax軟體之Harmonizer模組紀錄音頻 5 切削中使用三向加速規量測主軸頭振動 頻率響應圖 2006 12 01 精密機械研發中心39 轉速 645RPM進給 900mm min 切深 7mm量測結果 無顫振無顫振 機台振動頻譜 Lobe圖 轉速 380RPM 進給 600mm min 切深 6mm量測結果 顫振 異常振動 測試結果 2006 12 01 精密機械研發中心40 2006 12 01 精密機械研發中心41 2006 12 01 精密機械研發中心42 2006 12 01 精密機械研發中心43 C Type綜合加工機 直徑10mm3刃端銑刀進行鋁材全槽式切削顫振測試 2006 12 01 精密機械研發中心44 Improving Cutting Performance What are the Options We have a handle on the basic chatter mechanism so what can we do to reduce chatter problems Increase stiffness Increase damping Low speed for process damping Reduce axial or radial depth of cut Change cutting forces non evenly space teeth lead and rake angles etc Structure modification tuned dampers Tool Tuning Chatter Control Spindle speed variation Selection of Optimum Spindle Speed Ref Dr Smith 2006 12 01 精密機械研發中心45 Increase Stiffness Increasing the stiffness without changing anything else raises the critical limit of stability Improved stability across all spindle speeds Lifts the stability lobes Generally desirable Shorten overhang Larger diameter tool and or spindle Stiffen tool holder spindle connections Increase the bearing pre load Stiffen the work piece and or fixture Beware of affect on damping dynamic flexibility 1 dynamic stiffness is most important Ref Dr Smith 2006 12 01 精密機械研發中心46 Cutting Stiffness Cutting Stiffness Ks is equivalent to unit horsepower specific power Psp It is a measure of the cutting force per unit chip area F Ks b f b axial depth f feed or avg chip thickness Units of N mm2 Pspis given as HP m3 min or watts m3 min Ref Dr Smith 2006 12 01 精密機械研發中心47 Mechanical and Thermal Properties of Selected Work piece Materials No Material UTS Ks k Tm c 1 grey cast iron HBN 200 1500 43 12 1220 3 7 2 carbon steel 1020 N 400 2100 43 12 1520 3 7 3 carbon steel 1035 N 500 2300 43 12 1500 3 7 4 carbon steel 1045 N 650 2600 43 12 1490 3 7 5 stainless steel 302 700 2700 15 4 4 1425 3 6 6 alloy steel 4140 H 900 2800 38 10 1510 3 7 7 alloy steel 5140 H 950 2800 40 11 1500 3 7 8 Ni based Inconel X 1450 3500 12 3 2 1370 3 7 9 Ni based Udimet 500 1500 3550 12 3 2 1370 3 7 10 Co based L605 1250 3700 10 2 8 1370 3 6 11 Ti A16 V4 1350 2000 7 2 6 1600 2 7 12 Al 7075 T6 530 850 140 60 540 2 3 Column Heads represent the following UTS ultimate tensile strength N mm2 Mpa Ks specific force N mm2 k thermal conductivity N sec C k c thermal diffusivity mm2 sec Tm melting temperature C c specific heat per volume N mm2 C Ts shear plane temperature C 2006 12 01 精密機械研發中心48 Increase Damping Damping plays the same role as stiffness Identifying the sources of damping is not so easy Can add mass or damper Best used on a system exhibiting a single flexible mode Location in tool is best Only effective when located on at an active location Ref Dr Smith 2006 12 01 精密機械研發中心49 Low Speed For Process Damping Many conventional cutting processes use this phenomenon Dampening imposed due to the variation of radial force due to the interaction of the tool flank rake face with the cut surface Force is proportional to the velocity of the vibration and therefore is a damping force Higher values occur when tool is worn or when the tool has a low or no rake angle Speed at which damping is effective is dependent on frequency of flexible mode and tool wear Short wavelengths are not easily reproduced by the tool High speed spindles generally have low power at low speeds Generally leads to a large reduction in MRR Lower speeds in general produce higher amounts of process damping Ref Dr Smith 2006 12 01 精密機械研發中心50 Illustration for Process Damping Depth of cut increases as speed in decreased Ref Chatter Theory Section for mechanics Trends Less influence with sharp tools Dull tools will increase stability however power requirements increase Ref Dr Smith 2006 12 01 精密機械研發中心51 Reduce Axial or Radial Depths of Cut Reduce axial depth of cut to get below the critical limit of stability Reduce the radial depth of cut to reduce the average number of teeth in the cut and to change the orientation factors Reductions improve stability but decrease the metal removal rate Errors in the selection of these parameters require reprogramming the tool path Ref Dr Smith 2006 12 01 精密機械研發中心52 Cutting Force Distribution Change tool geometry Shift forces from flexible lateral direction to stiff axial direction Lead angle and angular position of multiple boring inserts Non evenly Spaced teeth Disturbs the regeneration of waviness In the stability lobe picture non proportional spacing raises the critical limit of stability but also reduces the ability to use the highly stable speeds Because the feed does not vary one tooth carries the full load and the others are under utilized The spacing works best when tuned to one speed and one set of spindle dynamics Ref Dr Smith 2006 12 01 精密機械研發中心53 Structure Modification Tuned Dampers In some cases it is possible to modify the structure to improve stability Eliminate unnecessary flexibility Change the orientation of the cutting force toward stiff directions Add dynamic absorbers or tuned dampers to improve the dynamic stiffness of particular modes Dynamic absorbers and tuned dampers require space and an active location on the relevant mode It is difficult to add tuned dampers to rotating components Ref Dr Smith 2006 12 01 精密機械研發中心54 Tool Tuning So far we assumed that the tool was fixed and adjusted the spindle speed to match the tool characteristics An alternate point of view would say that we should accept the spindle characteristics as fixed and adjust the tool to match For example the length of the tool can be adjusted to make a large stable gap fall at the top speed of the spindle Some unusual things can happen Ref Dr Smith 2006 12 01 精密機械研發中心55 l工件 鋁材 l尺寸 240 x30mm l刀具 三支程式均使用 6 2刃球刀 l幾何特徵 斜面165 85度 圓角R2 R50 l觀察重點 高速下轉角過切情況 四 測試工件 2006 12 01 精密機械研發中心56 l幾何特徵 二次方拋物線接R5導角 l觀察重點 高速下轉角過切情況 l走刀方式 往返運動 lintol outtol 3 m 8470 260 8470 750 2006