【正文】 7423,91. Kops23,and43,[22]have shown that, in practice, an increase in static load from zero, with other parameters constant, yields an approximately linear relationship between MRR and static load. Above an optimum value, the MRR decreases owing to a reduction in the size of the abrasive grains reaching the tool/workpiece interface and insufficient slurry circulation3up to a frequency,27Fig. 7.Fig. 7.at constant frequency and static load. In general, MRR increases as the amplitude of tool vibration increases (everything else remaining constant)8813,27,and[35]showed that MRR ∝24,4,27and[84]found that the theoretical static load required for the formation of Hertzian cracks in brittle materials was less than that for sliding indentation.. Effect of various operating parameters on material removal rate (MRR)The amplitude,2735,36which will occur simultaneously at the transient surface.With porous materials like graphite as opposed to hardened steels and ceramics, cavitation erosion is a significant contributor to material removalandUSM material removal mechanisms?Chemical action associated with the fluid employed48,?Cavitation effects from the abrasive slurry50,?Micro chipping by impact of the free moving abrasive particles60,35,and prise:?Mechanical abrasion by direct hammering of the abrasive particles against the workpiece surface43[80], Rozenberg et al.40Methods of slurry delivery3,76,12,162,28,N are typically used. The force is particularly critical when drilling small holes less than 40. The applied force must be chosen carefully since too low a setting will not yield the maximum cutting rate whereas too high a setting will cause jamming between the tool and abrasive27,40[72]. When deep hole drilling with a trepanning tool, the ability to feed the abrasive through the centre of the horn and tool is a great advantage thus reducing side friction66,[68].Tools can be attached to the horn by either soldering or brazing, screw/taper fitting. Alternatively, the actual tool configuration can be machined on to the end of the horn16,67.Fig. 4.64,1,2623,59. They are not liable to heat damage and appear to be more easily adaptable for rotary operations[62]with a thickness usually less than 10% of the total ultrasonic transducer length42,5930kHz for a 2057or a piezoelectric device12,17,500SiC/B4C3950Aluminium Oxide1000SiC/B4CZirconia1100B4CSialon1500B4CSilicon Carbide2400B4C2. Basic elements of an ultrasonic machine tool. The ultrasonic generator and ultrasonic transducerWith a conventional generator system, the horn and tool are set up and mechanically tuned by adjusting their dimensions to achieve resonance. Recently, however, resonance following generators have bee available which automatically adjust the output high frequency to match the exact resonant frequency of the horn/tool assemblymm ? ToolMRR(mm3/min) 10[33]is summarised in[36]and surface finishes of Ra –μm deep with microcracking24,26,54. Sintered alumina, silicon carbide and silicon nitride products generally have a hardness 150015and their good chemical stability and high temperature performance offers the possibility of greater thermodynamic efficiency in gas turbine applicationsCarbon fibre posite acceleration lever, holes and outline profile machined by USM26[51]. In addition, there are also greater problems in tuning a plex tool to achieve maximum performance pared to more basic tools.Fig. 2.4,and27,and36,26,rpm.?USM bined with electrical discharge machining (EDM)3928,[19].Wμm3031.In USM, high frequency electrical energy is converted into mechanical vibrations via a transducer/booster bination which are then transmitted through an energy focusing device, . horn/tool assembly8,and26[25], however, the depth to diameter ratio is limited to about 3:12319,15,and8,and preferably those with low ductility USM 系統(tǒng)最大限度地去除材料中發(fā)揮了重要作用。（例如橫截面積和形狀），振幅和磨粒平均尺寸。他們也應(yīng)該是耐腐蝕，具有足夠高的強(qiáng)度來(lái)附加螺絲附件。 USM 推薦使用共振發(fā)生器，自動(dòng)調(diào)整輸出高頻率去匹配變幅桿/刀具組件的精確諧振頻率。RUM 下 H/E 對(duì)不同材料的表面粗糙度的影響圖 最近有限元分析應(yīng)用到軸對(duì)稱變幅桿的設(shè)計(jì),該方法可以考慮到刀具的重量和用于漿料運(yùn)輸?shù)娜靠缀蛯⑵涔潭ㄔ趽Q能器所需的諧振頻率，有限元分析也評(píng)估工作應(yīng)力是否在確定的安全范圍之內(nèi)[67]，Dam 等人表示可以設(shè)計(jì)出一個(gè)變幅桿能將縱向超聲波左右轉(zhuǎn)換成縱向和橫向作用，如圖 18，這種橫向作用有利于輪廓形成。圖 ：180 網(wǎng)狀 SiC，回轉(zhuǎn)速度 200rpm6 變幅桿和刀具的設(shè)計(jì)變幅桿的設(shè)計(jì)理論和結(jié)構(gòu)，很多學(xué)者都研究過(guò)，但是卻還是不明了[7, 63, 67, 104–106]，傳統(tǒng)變幅桿的設(shè)計(jì)是基于一個(gè)考慮彈性力和慣性力的無(wú)窮小的平衡微分方程，然后在其整合的情況下，元件和變幅桿能產(chǎn)生共振[56, 106, 107]，變幅桿的長(zhǎng)度取決于工作頻率，并且對(duì)能量放大器沒(méi)影響，典型的設(shè)計(jì)包括：圓柱形，階梯，錐形和指數(shù)型[11，88，107]，調(diào)諧從換能器這里結(jié)束，其中 1015 毫米應(yīng)要進(jìn)行調(diào)諧[16，25，40，65，107，108]。圖 15 靜負(fù)載對(duì)圓柱度的影響影響尺寸精度和形狀精度的因素還有聲學(xué)元件和超聲波刀具的精度[16, 27, 40, 73]。Dam 等人認(rèn)為當(dāng)切削速度和切削深度降低的時(shí)候能得到更高的表面光潔度。如果刀具硬度增加是由加工硬化引起的，那么磨粒會(huì)進(jìn)入刀具，從而導(dǎo)致工件材料去除率降低，此外，工件的偏移會(huì)更加嚴(yán)重，這樣導(dǎo)致工件形成凸面，也會(huì)使刀具中心產(chǎn)生塑形變形，形成碟狀，此外，研究發(fā)現(xiàn)對(duì)于所有刀具材料而言刀具外緣的硬化程度最高，中間最小[97].所以，例如黃銅和銅是不適合做道具材料，因?yàn)樗鼈冊(cè)诖笳袷幒痛笳穹聲?huì)產(chǎn)生很多毛刺[3, 30]，他們降低聲波頻率衰減應(yīng)力波，使用硬質(zhì)金屬如碳化鎢來(lái)降低塑形變形和刀具磨損量[48]。 RUM 下，不同的H/E對(duì)MRR 的影響圖11 相同截面積的刀具的不同形狀對(duì)MRR的影響在旋轉(zhuǎn)超聲波加工中，刀具的旋轉(zhuǎn)能增強(qiáng) MRR，工件的精度，在一些情況下還能減少切削力[12, 76]，增加了刀具的壽命[27]. 在相同條件下旋轉(zhuǎn)超聲波加工中 MRR 是用金剛石進(jìn)行磨削時(shí)的 6 倍左右，是傳統(tǒng)超聲波加工的 4 倍，Komaraiah et al. [83]等人表示旋轉(zhuǎn)超聲波加工比傳統(tǒng)超聲波加工性能優(yōu)越的原因可以用工件表面的壓痕，工件和刀具之間的游離磨粒，晶粒之間的滑動(dòng)接觸來(lái)解釋，對(duì)于旋轉(zhuǎn)超聲波加工，Prabliakar [66] 和 Komaraiah [90]等人表示較高的轉(zhuǎn)速得到了較高的材料去除率，在一般情況下，最佳的鉆孔深度應(yīng)該是該刀具直徑的 2 到 5 倍之間，但是在懸浮液不斷供給的條件下得到的[16, 87]。有一些學(xué)者[70, 71, 77, 90]研究出套料刀具最佳的條件是內(nèi)部直徑與外部直徑之比大約為 ，刀具的厚度下限是不小于 5 倍的磨粒粒度[16, 27]。雖然超聲波加工允許工件材料可硬可軟，但是脆性材料更適合用這種加工方法，硬性材料通過(guò)脆性斷裂被切除而不是塑形斷裂，像低碳鋼這種塑形材料是通過(guò)塑形斷裂切除的，在這種情況下，磨粒會(huì)容易被嵌進(jìn)工件[12, 13, 28, 36]，降低工件材料斷裂韌度或者以楊氏模量的比率增加刀具的硬度講導(dǎo)致更高的 MMR[25, 41, 55, 84]，如圖 9 和圖 10，工件材料的機(jī)械性能和它的斷裂形式對(duì)于它采用何種加工形式是很重要的。超過(guò)一個(gè)最佳值后，由于到達(dá)變幅桿/工件相接面的磨料顆粒大小的減小和懸浮液循環(huán)不足[7, 16, 26, 43, 60, 75, 88, 90]，MRR 也隨之減少，最大加工速度的最佳靜負(fù)載被發(fā)現(xiàn)是取決于刀具結(jié)構(gòu)（例如橫截面積和形狀）和磨粒平均尺寸，如圖 8 所示，Kops [92]表明，采用一種小于最佳值（基與 MRR）的靜負(fù)載，可以更好地減少磨料磨損和提高刀具壽命。圖 6 USM 材料去除原理 [81]. 各種操作參數(shù)對(duì)材料去除率的影響在加工前可以通過(guò)加速器 [10],電渦流探針[30, 85]，激光多普勒測(cè)量?jī)x（dopplermeter）[86]，激光斑點(diǎn)干涉儀[58]測(cè)量超聲刀具振幅ξ，通過(guò)使用高轉(zhuǎn)化率刀具，如換能器直徑比率 [27, 39]，獲得高頻振幅，理想情況下，為了優(yōu)化切割速度 [3, 4, 6, 10, 13, 24, 49, 66]，振幅應(yīng)該與粗磨料平均直徑相等，Shaw [35] 認(rèn)為了 MRR∝ξ3/4，其他研究者