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1、附 錄Ⅰ Micro removal of ceramic material (Al2O3) in the precision — Ultrasonic machining Abstract Ultrasonic machining process is an efficient and economical means of precision machining of ceramic materials. However, the mechanics of the process with respect to crack initiation and propagatio

2、n, and stress development in the ceramic workpiece subsurface are still not well understood. This article presents experimental simulation of the process mechanics in an attempt to analyze the material removal mechanism in machining of ceramic (Al2O3). It is found that low-impact force causes only s

3、tructural disintegration and particle dislocation. The high-impact force contributes to cone cracks and subsequent crater damage. ? 1999 Elsevier Science Inc. All rights reserved. Keywords: Ceramic material (Al2O3); Utrasonic machining 1. Introduction Advanced engineering ceramics plays an increa

4、singly important role in the modern manufacturing industries, especially in aerospace, automotive, electronics, and cutting tool industries because of its superior properties such as chemical inertness, high strength and high stiffness at elevated temperatures, high strength to weight ratio, high ha

5、rdness, corrosion resistance, and oxidation resistance [1]. The main barrier hindering further application of advanced ceramics is the inability of the present manufacturing processes to economically and efficiently machine (especially precision machine) ceramics. Currently, grinding is one of the

6、most commonly used processes in the precision machining of ceramic, however,its high energy consumption results in high machining cost. Moreover, grinding also causes workpiece surface damage[2]. Laser beam machining (LBM) has the potential to be aviable alternative for ceramic machining, but surfac

7、e quality of machined parts is relatively poor [3]. Electrical discharge machining (EDM) is another alternative for ceramic machining,and many engine parts have been successfully machined by EDM [4]. Unfortunately, EDM can machine only electrically conductive materials. Other methods such as electro

8、n-beam and ion-beam cutting, and microwave cutting have also been proposed, but require additional research and development efforts [5–7]. Ultrasonic machining (USM), offers an effective alternative for precision machining of ceramics due to its many unique characteristics [8,9]. Unlike EDM, wire-E

9、DM or electro-chemical machining (ECM), which are all suited only for machining electrically conductive materials, USM can machine all hard and brittle materials [10].Furthermore, USM does not cause any thermal or chemical alterations in the subsurface characteristics of the machined material. Such

10、alterations are inevitable in EDM, ECM, wire-EDM, LBM and many traditional machining. Additionally, USM also produces a better precision surface finish compared to other material removal processes. In most USM practices, an average workpiece surface finish of 0.50 mm can be obtained. With appropriat

11、e measures, a surface finish of 0.25 mm can also be achieved [11]. USM has a great potential for applications in precision machining of ceramics, however, the material removal mechanism especially with respect to the microstructure and properties of the work material is not well understood [12]. T

12、he stresses developed in the subsurface are of critical importance when machining brittle ceramics as the inherent microstructural variations and subsurface flaw characteristics influence the resultant stress distributions in the subsurface [13,14]. It is necessary to Corresponding author investig

13、ate and understand the micro-material removal mechanism in ultrasonic mechanism for improving its efficiency and precision in machining of ceramics. In USM, the tool strikes the workpiece about 20,000 times in a second, a machining action occurs as the tool vibrates the fine abrasive particles flo

14、wing through a very small gap (ten to hundred microns) and propels them against the workpiece material. Material removal takes place in the presence of abrasive slurry. Therefore, it is very difficult to monitor directly or indirectly the presence and progress of involved physical processes. One of

15、the alternatives is to experimentally simulate the conditions of each physical processes to study their respective contribution. This article presents the results of experiments conducted to simulate the kinematics of the impact mechanism similar to the actual ultrasonic machining process. An impact

16、 test system was designed to simulate the impact mechanics of single diamond grit impelled by the contact force of the vibrating tool to strike an Al2O3 workpiece. The impact results on Al2O3 are analyzed. The experimental set-up and parameter selection for the impact test are described in second se

17、ction. The experimental results are given in third section. The microstructural analysis for understanding crack propagation and surface fracture is Presented in fourth section. The last section summarizes the conclusions of this study. 2. System set-up for the impact test The testing unit (Fig.

18、1a) in the experiments consists of three rigid tubular rods bolted to a solid mild steel base, and clamped to a triangular plate at the top. The length of these rods which determine the maximum drop heights are 3 m. An “N” Brale diamond tipped hardness tester (Wilson Instruments, PA) is used to si

19、mulate a single abrasive particle. Once the tool assembly, comprising of the diamond tip fitted to a plexiglas frame (Fig. 1b), is positioned at the predetermined drop height, an electromagnetic release mechanism which also activates a trigger device controlling the start of the time measurements re

20、leases the indenter. This setup permits the indenter assembly to accelerate due to gravity without any disturbances or delays. The tool head provides a base for a unidirectional ENTRAN-EGB 125 accelerometer, which is a small-sized low-weight device capable of measuring accelerations up to 5000 g. Si

21、gnals transmitted by a miniature semiconductive wheatstone bridge of the accelerometer device are amplified by a storage oscilloscope, and the data is stored in a 386 PC connected to the data acquisition system. Because the impact force is a function of the mass of the indenter, the weight of the to

22、ol assembly was designed for this test. 2.1. Experimental parameter selection In most cases for an USM machining, the diameter of a vibrating tool ranges from 4 to 6 mm. The size of the abrasive particles are between 50 and 75 mm. In practice forces applied in ultrasonic machining are within a ran

23、ge of 4.0 and 6.0 N [11]. Approximately, 100 particles are assumed to be covered under the tool during each down strike, and the mass of the indenter assembly is estimated by Newton’s second law of motion, Mass (M) 5 0.51 (kg)/ 9.806(m/s2) 5 52.0 g. To simulate the effect of a particle striking on a

24、 workpiece surface in an USM machining process, a lightweight plexiglas frame was designed to hold the indenter assembly. The assembly with total weight of 50.0 g drops from a precalculated height to strike the workpiece. The drop heights for the indenter are between 45–250 cm to obtain the impact v

25、elocities observed during the actual USM processes. A set of five drop heights were used in this experiment and a time device is automatically triggered when the indenter is released from its predetermined drop position. Fine grained (5 mm) Alumina (Kadco Ceramics, NJ) is impacted at two locations

26、under predetermined impact velocities; the impact locations are far apart to avoid any interaction effects. The diameter of the indenter tip is selected close to the size of particles used in USM machining. The test is aimed at analyzing the dynamic parameters of a single particle during impact and

27、 the fracture characteristics of the damage. The impact parameters are calculated based on free fall up to the point of impact and the characteristics during contact are estimated either directly from measurements or indirectly from calculations. When graphically represented over time, the character

28、istics of a single particle during impact are illustrated by different parameters such as force, velocity, or distance. An understanding of the mechanics of the material removal process based on observations of the microstructure were performed with the aid of a high resolution scanning electron mic

29、roscope. Fig. 2. a) Impact force and velocity over time; b) Impact force and depth over time; c) Impact velocity and depth over time. 3. Results: Impact force, velocity, and penetration depth The output from the accelerometer and the time measurements provide specific impact characteristics such

30、as the force exerted, the impact velocity, and the depth of penetration. The results of the different impact characteristics, are presented in Table 1. The impacts are identified by the workpiece number (p01, p02, and p03), and the impact number (i01, . . . i05). The maximum points sampled indicate

31、the number of data points collected at a sampling rate of a million points per second. Relative time values are computed with the aid of computer software, which identifies the peak position and triggers a relative time clock to store data up to 500 points before the maximum depth (peak) and up to 6

32、000 points after the peak. The end time in seconds is the instant when the indenter leaves the workpiece surface after impact. Fig. 2 (a, b, and c) represent the comparative results of the impact parameters of force, velocity, and depth of penetration at a drop velocity of 1.92 m/sec. Fig. 2a comp

33、ares the impact velocity and force during penetration; at the point of contact the velocity is maximum, and as the acceleration at this point is zero, the impact force drops to zero. The velocity reduces on impact and finally reaches zero at a point when the indenter is momentarily stationery, this

34、point corresponds to the instant when the force exerted on the indenter by the material is maximum. This instant is also described by the maximum depth of penetration as described in Fig. 2b and c. The velocity on rebound increases as described by the curve until a combination of the acceleration du

35、e to gravity and material resistance reduces it to zero. A summary of results of the impact characteristics are presented in Table 2. For linearly increasing values of the maximum free fall velocity there is a proportional increase in the maximum force experienced by the diamond tip during impact,

36、and a corresponding increase in the penetration depth. Fig. 3 describes the effect of the maximum free fall velocity on the penetration depth. The depth shows a steep increase at intermediate velocities and a relatively gradual increase at the low and high velocities. Fig. 3. Effect of maximum free

37、fall velocity on penetration depth. Fig. 4. Schematic of the crack morphology in brittle materials [15]. Fig. 5. Surface characteristics at an impact velocity of 0.98 m/sec. (3 750.) 4. Microstructure analysis As the crack propagation and subsurface fractures are mainly responsible for material re

38、moval, the SEM technique is particularly useful in its ability to give a vivid and more definitive representation of the crack types and their modes of propagation with respect to the microstructural characteristics of the material. In a study reported by Smith et al. [15] on indentation fractures

39、in brittle materials, median cracks growing perpendicular to the surface just below the tip of the indenter and are contained within the subsurface, but eventually propagate to the surface. Lateral cracks grow parallel to the impact surface, and propagate toward the top at high-impact velocities. T

40、he characteristics of these cracks are described schematically in Fig. 4, which shows a sectional view of the impacted area. The SEM micrographs of the damaged area at different impact velocities are presented in Fig. 5–9. Fig. 5 shows the surface characteristics at 7503, of the damage under an imp

41、act velocity of 0.98m/sec. It can be seen that fragmentation, chipping, and microfracture due to the impact force have mainly contributed toward material removal. Some material removal may also have resulted from dislodged particles as observed by the presence of cavities in the microstructure. With

42、 an impact velocity of 1.15m/sec., the presence of intergranular microcracks can be observed in Fig. 6. However, most of the material is removed from the impact force. At an impact velocity of 1.5 m/sec., cracks projecting from the deformation zone are clearly visible in Fig. 7. The presence of thes

43、e cracks indicate lateral and median crack propagation to the surface. The presence of intergranular microcracks are also visible and are indicated by arrowheads. Because material removal involves both plastic flow and fracture, a combination of compressive and tensile stresses, respectively, are r

44、esponsible for material removal [11]. Median cracks perpendicular to the surface and propagating below the deformation zone, result from the compressive stresses due to the impact force of the indenter. Lateral Fig. 6. Surface characteristics under an impact velocity of 1.15 m/sec. (3350.) Fig. 7. S

45、urface characteristics under an impact velocity of 1.5 m/sec. (3650.) Fig. 8. Surface characteristics under an impact velocity of 1.9 m/sec.(31200.) Fig. 9. Surface characteristics from an impact velocity of 2.05 m/sec. (3750.)cracks propagate to the surface due to high impact forces [15] and merge

46、with the median cracks (Fig. 8) describes the deformation zone with cracks propagating from the epicenterat an impact velocity of 1.5 m/sec.. These cracks originate in the subsurface and propagate to the top, contributing to material removal by dislodging large sections of the material. The network

47、of intergranular microcracks also contribute to the material removal process. Fig. 9 describes the surface characteristics of the damage under an impact velocity of 2.05 m/sec. The dislodged particles in the crater range from small grain sized particles to chunks of dislodged material in the 40–50 m

48、m. range. In an effort to relate the surface area of the damage to the impact velocity, a measurement technique was applied to estimate the area of each crater. The results of the test shown in Fig. 10 describes an increasing trend for increasing impact velocities. This may be attributed to the ma

49、terial removed when lateral and median cracks merge at the surface. Thus, the impact zone material removal occurs mainly from a combination of particle coalescence and microstructural disintegration. Below the plastic zone, at the lowimpact forces, material removal occurs from particles dislodged fr

50、om the surface. Fragmentation from the impact force of the diamond tip, and intergranular microcracks also result in material removal. At the higher impact velocities between 1.92 and 2.1 m/sec lateral and median cracks merge at the surface to dislodge large particles of material in the range betwee

51、n 20 to 50mm. At these loads the network of intergranular microcracks also play a significant role in the material removal process. 5. Conclusions This study was aimed at understanding the mechanism of the material removal process in fine grain Alumina during precision ultrasonic machining. Micro

52、structural analysis of the damaged surface due to the dynamic impact of an abrasive particle indicates the presence of two phenomena that contribute to material removal; the deformation at the point of impact, and the brittle structure below the impact zone. From the dynamic impact tests, material r

53、emoval in the USM process appears to be a function of the impact velocity, which is determined by the frequency and amplitude of the vibrating tool. Material in the impact zone is removed by fragmentation and by chipping microfracture due to the high compressive stresses developed in the region. At

54、low-impact velocities, material removal in the brittle substructure occurs mainly due to structural disintegrations and particle dislocations. At higher velocities, material is removed by a network of intergranular microcracks and from the propagation of lateral and median cracks. These cracks merge

55、 at the surface dislodging large sections of the material. Acknowledgments The authors thank the Nebraska Research Initiative Fund for their financial support. The authors also gratefully acknowledge the assistance of Ms. L. Shi and Mr. N. Saxena in the preparation of this article.

56、 附 錄Ⅱ 超聲波加工過程是一個高效和經(jīng)濟的手段，用在精密加工的陶瓷材料上。然而，力學這一過程對裂紋產(chǎn)生和擴大，并強調發(fā)展陶瓷工件表層仍然沒有得到很好的理解。本文介紹的模擬實驗研究的過程力學，試圖分析材料去除機理在加工陶瓷（氧化鋁）過程中。結果發(fā)現(xiàn)，低沖擊力只有助于結構性解體和粒子脫位。高沖擊力有助于錐裂縫和隨后的縫口損壞。 關鍵詞：陶瓷材料（氧化鋁） ;超聲波加工 1 ：導言 先進的工程陶瓷發(fā)揮著越來越重要的作用，現(xiàn)代制造業(yè)，特別是在航空航天，汽車，電子和切割工具行業(yè)，由于其優(yōu)越的性能，如化學惰性，高強度，高剛度在較高高溫，高強度重量比，

57、硬度高，耐腐蝕，抗氧化 目前，磨削是一種最常用的精密加工陶瓷方法，然而，其能源消耗高，結果增加加工費用。此外，還造成磨削工件表面損傷 。激光加工（ LBM ）有可能成為可行的選擇陶瓷加工，但表面質量機械零件的相對較差 。放電加工是另一個替代的陶瓷加工，許多發(fā)動機部件已成功應用電火花加工 。然而，電火花加工機只能用唯一導電材料。其他方法，例如電子束和離子束切割和微波切割也被提出，但需要額外的研究和開發(fā)工作。 超聲波加工（超聲波馬達） ，提供了一個有效的用于精密加工陶瓷的方法由于其有許多獨特的特點。電火花，線切割或電化學加工 ，這些都是只適合加工導電材料，超聲波馬達可用于所有硬脆材料

58、 。此外，超聲波加工會引起加工材料的任何熱或化學的表層特征改變。這種改變在電火花加工，電子對抗，線切割，LBM和許多傳統(tǒng)的機械加工中是不可避免的。此外，超聲波加工作了一個更好的表面加工精度與其他材料去除過程相比。在大多數(shù)超聲波加工法中，平均工件表面光潔度可達0.50毫米。有了適當?shù)拇胧?，表面光潔度也可以實現(xiàn)到0.25毫米 。 超聲波加工大的應用潛力在精密加工陶瓷中，然而，對材料去除率機制，尤其是對微觀結構和工作性質的材料沒有得到很好的理解。在強調發(fā)達國家在地下關于要性脆性陶瓷加工時的固有微觀結構的變化和地下缺陷特征由此造成的影響應力分布在地下微觀材料去除機理的超聲機制為提高其效率和加工精度陶

59、瓷。 在超聲波加工中，罷工工件約20000次每秒，發(fā)生運動的工具振動細磨料顆粒流經(jīng)一個非常小的差距（ 10至100微米） ，并推動他們到工件材料。材料去除發(fā)生在在場的磨料泥漿。因此，它是非常困難的監(jiān)測直接或間接的存在和進步涉及的物理過程。一個替代辦法是模擬實驗條件的每個物理過程，研究其各自的貢獻。本文介紹的實驗結果進行運動學模擬的影響類似機制的實際超聲波加工過程。撞擊試驗系統(tǒng)的設計是為了模擬影響力學單鉆石的砂礫促使接觸力的振動工具罷工的氧化鋁工件。 結果影響氧化鋁進行的分析。實驗設置和參數(shù)的選擇影響試驗中描述的第二部分。實驗結果給出了第三節(jié)的微觀結構分析理解和表面裂紋擴展第四部分中提出的。最

60、后一節(jié)總結了這項研究的結論。 2 。系統(tǒng)設置的影響試驗 測試單位（圖1A ）在實驗中包括三個剛性管桿螺栓，以堅實的鋼架為基礎，鉗位到三角形板在頂部。這些長度棒確定的最大下降高度為3米 圖 1 。 表1 結果所產(chǎn)生的影響在不同的特性下降高地測試 圖 a為壓降測試 圖 b為影響的立場 “ N ”形狀鉆石刀具的硬度儀（威爾遜儀器巴勒斯坦權力機構）用在模擬磨粒。當?shù)毒弑话惭b上，組合的鉆石刀具安裝上有機玻璃框架（圖1B） ，在預定下降高度上定位，電磁釋放裝置激活觸發(fā)裝置來控制開始測量時刻的壓頭。此安裝允許，由于加速重力沒有任何干擾或延誤。該工具頭提供了一個基地，單向進

61、入 ，安裝裝置加速度125，這是一個小型體重裝置能測量加速度高達5000克信號轉交的一個縮影半導體壓阻橋梁的加速度裝置擴增存儲示波器，數(shù)據(jù)存儲在一個相當于386個人腦的電腦數(shù)據(jù)采集系統(tǒng)中。由于沖擊力影響是一個功能的質量壓痕，這一試驗的目的是為重量工具安裝。 2.1 實驗參數(shù)的選擇 在大多數(shù)情況下的超聲波馬達加工,直徑振動工具范圍從4至6毫米。磨料顆粒尺寸的大小是50至75毫米。在實踐中其適用于超聲波加工的范圍為4.0和6.0 大約100顆粒子被假定以所涵蓋的工具在每次下跌受塤，和大眾的壓痕一起估計， 牛頓第二定律的運動，質量（男） 5 0.51 （公斤） / 9.806 （ m

62、/s2 ） 5 52.0克 模擬粒子效果顯著的工件表面加工工藝的超聲波馬達，輕巧有機玻璃框架的目的是要舉行壓大會大會的總重量五十○點○克下降了 precalculated高度罷工工件。下拉高地壓為45-250厘米之間取得觀察速度的影響在實際超聲波馬達進程了一套五份下降高地中使用了這個實驗和時間的設備會自動觸發(fā)時壓釋放其預定的下降立場。細粒度（ 5毫米）氧化鋁（ Kadco陶瓷，新澤西州）是影響在兩個地點的沖擊速度下的預定;影響地點相距遙遠，以避免任何互動的效果。直徑的壓痕提示選擇密切的大小顆粒加工中使用的超聲波馬達。 試驗的目的是分析的動態(tài)參數(shù)單粒子在影響和斷裂特征造成的損害。影響參數(shù)的計算

63、基于自由跌落到彈著點和特點在聯(lián)系，估計可以直接從測量或間接計算。當圖形代表隨著時間的推移，一個單一的特點粒子在影響是不同的參數(shù)說明如力量，速度，或距離。了解力學的材料去除過程的意見的基礎上該組織進行的幫助下，高分辨率掃描電子顯微鏡。圖 2 。a）沖擊力和速度隨著時間的推移; b ）影響力和深度隨著時間的推移; c ）影響速度和深度隨著時間的推移。 表2 綜述結果的影響特點 圖a 沖擊力和速度隨著時間的推移 圖b 影響力和深度隨著時間的推移 圖C 影響速度和深度隨著時間的推移 3 結果：沖擊力，速度和穿透深度 輸出加速度和時間的測量提供具體的

64、影響等特點工隊施加的影響，速度和深度滲透。結果的不同影響特點， 列于表1 的影響是確定的工件號碼（ p01 ， p02和p03 ） ，和影響數(shù)量（ i01 - i05 ） 。最高點取樣表明數(shù)據(jù)點數(shù)目收集采樣率萬分每秒。相對時間價值觀在計算機的幫助下，計算機軟件，其中確定該峰的位置和相對時間觸發(fā)時鐘數(shù)據(jù)存儲多達500點之后的最大深度（高峰）和高達6000點后的最高點。結束時間 秒的瞬間時，壓葉片工件表面后產(chǎn)生的影響。 圖 2（ a ， B和C ）代表的比較結果參數(shù)的影響力，速度和深度滲透在下降的速度一點九二米/秒。圖2A型比較沖擊速度和滲透力;在聯(lián)絡點的速度是最大的，并作為加快在這一點上是

65、零，沖擊力降到零速度降低的影響，并最終達到零上點壓時，這一點對應于即時生效時施加的壓痕的材料是最大的。這也是即時所描述的最大深度的滲透所描述在圖2b和c關于反彈的速度增加所描述的曲線之前的組合加速由于重力和材料電阻降低到零。 匯總結果的影響特點列于表2 。 線性增加值最大的自由落體速度有一個比例增加最多部分所經(jīng)歷的鉆石冰山期間的影響，以及 相應增加深度。圖3描述影響最大的自由降落速度的穿透深度。深度顯示在急劇增加中間速度和相對逐步增加在低和高的速度。圖3 ：影響最大的自由降落速度的穿透深度。圖4 ：示意圖裂紋形態(tài)的脆性材料 。 圖5 ：表面特性在沖擊速度為0.98米/秒。 4 ：微

66、觀結構分析 由于裂紋擴展和水下裂縫主要負責材料去除，掃描電鏡技術是特別有用，它能夠讓一個生動和更明確的代表性裂縫類型及其傳播模式方面的微觀結構特征的材料。 在一項研究報告史密斯等人。關于壓痕骨折的脆性材料，中間垂直裂縫越來越表面略低于冰山的壓并包含在地下，但最終傳播到地表。橫向裂縫增長并行影響面，和宣傳的歌曲在高影響速度的特點，這些裂縫描述 schematically圖 4 ，這顯示了截面鑒于影響地區(qū)。 SEM照片損壞的地區(qū)，不同的沖擊速度介紹圖5~9。圖5顯示表面特性在7503 米下的損害的沖擊速度為0.98米/秒可以看出，分裂切和微由于撞擊力主要貢獻的材料去除率。一些材料去除率也可能造成脫落觀察到的粒子的存在空洞的微觀結構。沖擊速度1.15米/秒該間存在裂紋可以看出圖6。 然而，大多數(shù)材料是從沖擊力在沖擊速度為1.5米/秒裂縫預計從變形區(qū)是顯而易見圖7。 存在這些裂紋表明橫向和中間裂紋擴展到地表。在場的情況下 間微也可見，由箭頭并表示。 由于材料去除涉及塑性流動和斷裂，它結合了壓縮和拉伸應力，分別負責材料去除 。中位數(shù)裂紋垂直于表面和宣傳以下的變形區(qū)，因壓強調由于撞擊力的