Non Conventional Machine

Module 9 Non-conventional machining Version 2 ME, IIT Kharagpur Lesson 36 Accelerated Machining (USM) Version 2 ME, IIT Kharagpur Instructional Objectives i. ii. iii. iv. Describe the basal apparatus of actual abatement in USM Identify the action ambit of USM Identify the machining characteristics of USM Analyse the aftereffect of action ambit on actual abatement amount (MRR) v. Advance algebraic archetypal apropos MRR with USM ambit vi. Draw aberration in MRR with altered action ambit vii. Identify above apparatus of USM accessories viii. State the alive assumption of USM accessories ix. Draw schematically the USM accessories x. List three applications of USM xi. List three limitations of USM 1. Introduction Accelerated machining is a non-traditional machining process. USM is aggregate beneath the automated accumulation NTM processes. Fig. 9. 2. 1 briefly depicts the USM process. Force, F Slurry of annoying and baptize Horn Vibration abundance f ~ 19 - 25 kHz Amplitude, a ~ 10 – 50 ? m Apparatus Assignment Fig. 9. 2. 1 The USM action In accelerated machining, a apparatus of adapted appearance vibrates at an accelerated abundance (19 ~ 25 kHz) with an amplitude of about 15 – 50 ? over the workpiece. About the apparatus is apprenticed bottomward with a augment force, F. Amid the apparatus and workpiece, the machining area is abounding with adamantine annoying particles about in the anatomy of a baptize based slurry. As the apparatus vibrates over the workpiece, the annoying particles act as the indenters and bash both the assignment actual and the tool. The annoying particles, as they indent, the assignment material, would abolish the same, decidedly if the assignment actual is brittle, due to able initiation, advancement and breakable breach of the Version 2 ME, IIT Kharagpur aterial. Hence, USM is mainly acclimated for machining breakable abstracts {which are poor conductors of electricity and appropriately cannot be candy by Electrochemical and Electro-discharge machining (ECM and ED)}. 2. Mechanisms of Actual Abatement in USM and its modelling As has been mentioned earlier, USM is about acclimated for machining breakable assignment material. Actual abatement primarily occurs due to the angle of the adamantine annoying grits on the breakable assignment material. As the apparatus vibrates, it leads to angle of the annoying grits. During indentation, due to Hertzian acquaintance stresses, cracks would advance aloof beneath the acquaintance site, again as angle progresses the cracks would bear due to access in accent and ultimately advance to breakable breach of the assignment actual beneath anniversary alone alternation armpit amid the annoying grits and the workpiece. The apparatus actual should be such that angle by the annoying grits does not advance to breakable failure. Appropriately the accoutrement are fabricated of tough, able and adaptable abstracts like steel, stainless animate and alternative adaptable brownish alloys. Other than this breakable abortion of the assignment actual due to angle some actual abatement may action due to chargeless abounding appulse of the abrasives adjoin the assignment actual and accompanying solid-solid appulse erosion, but it is estimated to be rather insignificant. Thus, in the accepted model, actual abatement would be affected to booty abode alone due to appulse of abrasives amid apparatus and workpiece, followed by angle and breakable breach of the workpiece. The archetypal does accede the anamorphosis of the tool. In the accepted model, all the abrasives are advised to be identical in appearance and size. An annoying atom is advised to be all-around but with bounded all-around bulges as apparent in Fig. 9. 2. 2. The annoying particles are characterised by the boilerplate dust diameter, dg. It is added affected that the bounded all-around bulges accept a compatible diameter, db and which is accompanying to the dust bore by db = ? dg2. Appropriately an annoying is characterised by ? and dg. db db db db dg Fig. 9. 2. 2 Schematic representation of annoying dust Version 2 ME, IIT Kharagpur During angle by the annoying dust assimilate the workpiece and the tool, the bounded all-around bulges acquaintance the surfaces and the angle action is characterised by db rather than by dg. Fig. 9. 2. 3 shows the alternation amid the annoying dust and the workpiece and tool. Apparatus db annoying dust db Assignment A B db 2x C D ?w Hemispherical actual removed due to breakable Fig. 9. 2. 3 Alternation amid dust and workpiece and apparatus As the angle proceeds, the acquaintance area amid the annoying dust and workpiece is accustomed and the aforementioned grows. The acquaintance area is annular in attributes and is characterised by its bore ‘2x’. At abounding indentation, the angle abyss in the assignment actual is characterised by ? w. Due to the indentation, as the assignment actual is brittle, breakable breach takes abode arch to hemi-spherical breach of bore ‘2x’ beneath the acquaintance zone. Therefore actual abatement per annoying dust is accustomed as 2 ? w = ? x 3 3 Now from Fig. 9. 2. 3 AB 2 = AC 2 + BC 2 ? db ? ?d ? ? ? = ? b ? ? w ? + x2 ? 2 ? ? 2 ? 2 x = db? w apathy ? w2 as ? w

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