Nonconventional Technologies Review no. 1/2010 ASPECTS OF SURFACE MICROGEOMETRY MACHINING BY ULTRASONIC AIDED PLANE LAPPING

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1 ASPECTS OF SURFACE MICROGEOMETRY MACHINING BY ULTRASONIC AIDED PLANE LAPPING Liliana TULCAN 1, Miaela NISTORAN BOTIS 2, Aurel TULCAN 3 1 University Politenica from Timisoara, Romania, liliana.tulcan@gmail.com 2 University Politenica from Timisoara, Romania, botis.miaela@gmail.com 3 University Politenica from Timişoara, aurel.tulcan@gmail.com Abstract: Starting from abrasive grain workpiece interaction at lapping and ultrasonic aided lapping it performs microscopic study and qualitative analysis of obtained surfaces and mark out te main tendency of ultrasonic aided lapping. Keywords: abrasive grain, ultrasonic aided lapping. 1. ABRASIVE GRAIN WORKPIECE INTERACTION AT FINISHING PROCESSES Watever abrasion processes are influenced by concerted action of four entrance categories: abrasive tool or abrasive medium and is support, te implicated macine tool, te workpiece and operational factors. Te process seems to be very complex and ard to be described. By finising processes te surface adjustment is realized by two elementary materials processing s: cutting and plastic deformation. In te cutting processes is carried out te removing of te exceeding material necessary for error correction of processing size and sape of te workpiece, a certain quality of surface layers and removed defects caused by previous processing. Cutting processes influences te process efficiency and te processing precision of fine abrasive smooting. Case of a singular grain in fig.1a [1] gives breaking edge sceme and te forces acting on te processed surface. Micro cutting occurs under te action of tangential force F t and start at a certain ratio of te grain penetration dept and radius grinding attacment called penetration relative / and depends on material plasticity and normal force F n [1]. In te initial moment of abrasive grain penetration in te material an elastic deformation occurs, followed by a plastic deformation by extruding te material, pusing it from te resulted micro cannel 55 and formation of a deposit (creast) on te lateral side. On 0,01 0, 1 deformation of material occurs, i.e. a friction of abrasive grain wit te processed surface witout removal of cips. Fig.1. Generation cips. Relative penetration dept at wic te transition occurs from elastic deformation to plastic deformation can be calculated using te formula: 2 c 200 (1) E Were: c Limited creep stress of processed material; E - Elasticity modulus of material. On 0,1 1, 1 plastic deformation of material occurs witout destruction.

2 On 0,2 2 began micro cutting, scratcing and plastic deformation accompanying material. Increased micro cutting wic occurs increases te plasticity workpiece size /. Depending on te cutting edge sape, te penetration dept, te cutting edge position relative to te size of processed surface it can be obtained a micro cannel (a scratc) by plastic deformation or cutting. It as been experimentally found tat te appearance of eiter of te two possibilities of abrasion depends on te angle acieved by te active abrasive grain wit its forward direction. Te critical angle of attack c value over wic appears cutting depends on te material grains and workpiece material and process kinematics. In fig.1b it is called interference angle, i.e. angle tickening of undistorted cips. During te deformation process, te cip will ave tree distinct zones: I slip deformation, II plastic deformation, III cutting. Te lengt of te first areas depends on te angle tat could be extended by a detailed calculation, respectively irremovable cip geometry for different types of cips. Because only a part of material extracted from te abrasion micro cannels is removed, te remainder is pused on te lateral sides. It is defined te coefficient f ab tat care of drawing out te material of piece from te processed cavities; f ab is te ratio between te crest volume deposited on te initial surface and te total displacement volume. For ductile materials it can ave values between 0 (ideal plouging) and 1 (ideal cutting) and by fragile materials it can ave improper value. It is considered tat one abrasive grain removes only a part of te undistorted cip, te remained material saped like crests disposed on te bot sides of grains, being plastic deformed from te next grains as sows in fig.2 [1]. Te crest volume will be a (1-f ab ) weigt from te undistorted cip volume. Fig.2. Te lateral crests forming troug plastic deformation of work piece material Te crest sape can be approximated like a parabola: 2 a 2 cr x cr z (2) cr Te crest area disposed on te side of grains will be: 1 f ab A 4 Acr acrcr (3) 2 3 Were: A te cannel area. 3Acr acr (4) 2tg Acrtg cr 3 (5) 8 In te process of surface plastic deformation occur micro irregularities smooting and gaps filling wit material of crests. On te oter and tere may be situations wen, after several successive passages of abrasive grains, crests are stressed on alternating directions and will be required to come off from te workpiece surface due to fatigue request. Tis process ends formation of te surface rougness and pysical-mecanical processing of te surface layer of material, degree of strengtening and size of te residual stresses. Depending on te conditions and procedures for processing, smooting fine may be reduced to only one of te basic processes described. It must be specified tat te finising processes because of te need to ensure quality processed surface mirror, te abrasive grain trajectory must not to be repeated. Suc features of finising processes appear toward adjustment in respect of kinematics processes and cutting regime. One of te main elements tat influence cutting in finising processes is te coverage and ow te dispersion of 56

3 trajectories on te surface of abrasive grain processed. 2. PHYSICAL MODELS OF ULTRASONIC AIDED LAPPING By finising processes wit free grains like lapping, ultrasonic aided intensifies te grains movements as a result of ultrasonic oscillations, fig.3 [2, 3]. In te macining process, te great abrasive grains execute active rotation movements, and te low grains oscillation. On te great grains, existing between lapping disk and processed surface it is applied a eavy loading compared wit tat s of remainder abrasive. sectioning of 50%. appearance te penomenon like sandblasting. Tus, it is activating te micro cannels forming processes, te surface rougness improvement, but also te apparition of compressive residual stress [3, 4, 5]. 3. ASPECTS OF EXPERIMENTAL RESEARCH Experimental tests were performed by adapting a drilling ultrasound macine, an experimental model, te plane lapping macine wit ultrasonic activation of te workpiece, te equipment construction permits te obtaining of a specific cinematic lapping process. Fig.3. Simplified model of te abrasive grain action by ultrasonic aided lapping It is produced broking and crumbling of abrasive grains, te grains diameter became rapidly uniform, te dressing effect of cutting edge appear faster. Because of superposition, congestion and destruction of te abrasive grains, te exterior load will be uniform ly distributed on te grains group wit uniform diameter, wic permits te increasing of te processing precision, smooting and omogeneity of te surface and it is avoided te formation of deep scratces on te processed surface. In parallel it is produced te low grains oscillation. Factors influence te ranking was done by a random balance, factorial and unifactorial experiments program for a total of 15 objective functions, of wic tree were considered of great practical interest: te surface rougness Ra, efficiency and processing at a bearing lengt ratio 57 Fig.4. Basic diagram of workpiece ultrasonic aided plane lapping Experimental conditions: Ultrasonic oscillation frequency f = 20 khz te goal real amplitude ultrasonic oscillation m lapping disk speed n I = 60 rpm (current speed lapping industrial macines) alternative rectilinear motion n Il 20 double cut planing/min, n IIl 5 double cut planing/min transmission oil typet90 EP 2, grease Li- Ca-Pb type 2. supplying metod: once to start te process. lapping disk 100 mm cast iron Fc 200, Ra = 0,8 m,

4 workpiece 10 mm, material OSC 8. Te significant factors selected for factorial experiment were: working time, abrasive grains nature, initial surface rougness, ultrasonic power and pressure of contact. Statistical analysis was performed using te rougness profile functions string teory, te microscopic study of te area and qualitative analysis results of te abrasive grains wear. Fig. 5 [7] sows te rougness profile and te percentage bearing profile by turning, grinding and lapping. 4. MICROGEOMETRY STUDY OF INITIAL AND FINAL WORK PIECE AREAS A complete information on te abrasivematerial interaction at ultrasonic aided lapping processes is presented on images tat sown te electronic microscope of macine surfaces by turning R a = 3,2 m (Fig. 6a) grinding R a = 0,4 m (Fig. 6b) and image parts being ultrasonic lapping R a = 0,16 m, respectively R a = 0,22 m (Fig. 6 c, d) [7]. Study of te lapping surface aspect, reflects two material removal mecanisms: surface erosion mecanism by wic small particles displaced piece of material, abrasive grains mecanism determined by moving te sliding action of overlapping fingerprints grain edges, wic leads to a specific aspect of eroded areas; continuously deformation of te surface material and smooting te irregularities caused by moving grain rolling, a mecanism tat determines strengtening te superficial layer of te work piece and a specific micro relief. From tis perspective structure rougness profile corresponding to te analytical model confirms te steps described in [6]. Moreover, te images reveals tat te distribution of surface irregularities at ultrasonic lapping is predominantly random, wic was also noted at te analysis of autocorrelation functions and power spectral density [7]. Fig.5. Rougness profile and te percentage bearing profile by turning, grinding and lapping. 58

5 Fig.6. Te macine surface generated by a) turning, b) grinding c), d) ultrasonic lapping. 5. CONCLUSIONS Te study of processed surfaces verifies te pysical model proposed for flat ultrasonic lapping [6]. Processing must be oriented so tat te application of ultrasonic vibrations to activate te dynamic beavior of abrasive grains, teir movement, te effect of forming te cutting edge. Enance micro cannels training, improves te process of sampling te material, and could increase processing efficiency. It is obtained a better recirculation of te abrasive material, facilitating te supply wit it, decreasing te grains size in parallel wit te development of new cutting edges, particles migration could decrease te abrasive consumption and for decreasing te surface rougness and a iger quality for te processed surface, wouldn t be necessary te abrasive substitution wit a finer one. REFERENCES 1. CHEN X., et al. - Analysis and simulation of te grinding process. Part II: Mecanics of grinding, International Journal of Macine Tools & Manufacture, Vol.36, Nr.8, 1996; 2. KUMABE, J. - Vibrationnoe rezanie, Izd. Mašinostroenie, Moskva, 1985; 3. MARINESCU, I.D. et al. - Handbook of lapping and polising; CRC Press, Taylor and Francis Group, 2006: 4. AMZA G. Ultrasunetele aplicaţii active, Ed. AGIR, Bucureşti, 2006: 5. Nanu, A. (coordonare generală), Marinescu N. I. (coordonator volum) et. al. Prelucrarea prin eroziune cu unde ultrasonice, Ed. BREN, Bucureşti, 2004; 6. TULCAN, L et al.- General analytic model for establising te processed material volume for ultrasonic aided plane lapping, ICNcT, Bucureşti, 2005; 7. TULCAN, L. - Activarea ultrasonică a proceselor de netezire fină abrazivă, Teză de doctorat, Timişoara,