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'Module 9 Non-conventional machining discrepancy 2 ME, IIT Kharagpur Lesson 36 Ultrasonic Machining (USM) variate 2 ME, IIT Kharagpur Instructional Objectives i. ii. iii. iv. Describe the staple fiber mechanism of textile remotion in USM Identify the process parameters of USM Identify the machining characteristics of USM snap the effect of process parameters on existent removal rate (MRR) v. Develop mathematical model relating MRR with USM parameters vi. Draw variation in MRR with different process parameters vii. Identify major components of USM equipment viii. State the operationing principle of USM equipment ix.Draw schematically the USM equipment x. List 3 applications of USM xi. List three limitations of USM 1. Introduction Ultrasonic machining is a non-traditional machining process. USM is sorted nether the mechanical group NTM processes. Fig. 9. 2. 1 briefly depicts the USM process. Force, F Slurry of rasping and piddle Horn Vibration frequency f ~ 19 †25 kH z Amplitude, a ~ 10 †50 ? m hawkshaw Work Fig. 9. 2. 1 The USM process In ultrasonic machining, a brute of in demand(p) shape vibrates at an ultrasonic frequency (19 ~ 25 kHz) with an amplitude of around 15 †50 ? over the domesticatepiece. Generally the tool is pressed downward with a guide force, F. Between the tool and endurepiece, the machining partition off is inundate with hard spotty particles generally in the form of a water establish slurry. As the tool vibrates over the workpiece, the scratchy particles act as the indenters and indent some(prenominal) the work material and the tool. The raspy particles, as they indent, the work material, would remove the same, particularly if the work material is toffee, payable to crack initiation, times and toffy fracture of the stochastic variable 2 ME, IIT Kharagpur aterial. Hence, USM is mainly used for machining brittle materials {which are poor conductors of electricity and thus cannot be processed by Elect rochemical and Electro-discharge machining (ECM and ED)}. 2. Mechanisms of strong Removal in USM and its modelling As has been mentioned earlier, USM is generally used for machining brittle work material. Material removal primarily occurs ascribable to the crudeness of the hard abrasive surface on the brittle work material. As the tool vibrates, it oversteps to choppiness of the abrasive coat.During indentation, due to Hertzian concern stresses, cracks would develop fitting below the allude site, then as indentation progresses the cracks would propagate due to amplification in stress and ultimately lead to brittle fracture of the work material under each individual fundamental interaction site in the midst of the abrasive coat and the workpiece. The tool material should be much(prenominal) that indentation by the abrasive common senses does not lead to brittle failure. frankincense the tools are made of tough, strong and pliant materials like steel, stainless stee l and opposite ductile metallic alloys.Other than this brittle failure of the work material due to indentation some material removal whitethorn occur due to free current impact of the abrasives against the work material and associate solid-solid impact erosion, precisely it is estimated to be sooner insignificant. Thus, in the current model, material removal would be assumed to take mastermind only due to impact of abrasives between tool and workpiece, followed by indentation and brittle fracture of the workpiece. The model does consider the distortion of the tool.In the current model, all the abrasives are considered to be identical in shape and size. An abrasive particle is considered to be spherical but with local spherical bulges as shown in Fig. 9. 2. 2. The abrasive particles are characterised by the fairish grit diam, dg. It is further assumed that the local spherical bulges have a changeless diameter, db and which is related to the grit diameter by db = ? dg2. Thus an abrasive is characterised by ? and dg. db db db db dg Fig. 9. 2. 2 stately representation of abrasive grit Version 2 ME, IIT KharagpurDuring indentation by the abrasive grit onto the workpiece and the tool, the local spherical bulges contact the surfaces and the indentation process is characterised by db rather than by dg. Fig. 9. 2. 3 shows the interaction between the abrasive grit and the workpiece and tool. pecker db abrasive grit db Work A B db 2x C D ?w hemispherical material removed due to brittle Fig. 9. 2. 3 Interaction between grit and workpiece and tool As the indentation proceeds, the contact zone between the abrasive grit and workpiece is established and the same grows.The contact zone is circular in nature and is characterised by its diameter ‘2x’. At full indentation, the indentation depth in the work material is characterised by ? w. Due to the indentation, as the work material is brittle, brittle fracture takes repoint leading to hemi-spherical fra cture of diameter ‘2x’ under the contact zone. Therefore material removal per abrasive grit is given 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 neglecting ? w2 as ? w\r\n'