329 ISSN 1392 1207. MECHANIKA. 2015 Volume 21(4): 329 333 Influence of deformtion on metl structure in the forwrd microextrusion process K. Mogielnicki*, J. Piwnik** *Fculty of Mechnicl Engineering, Bilystok University of Technology, Bilystok, Polnd, E-mil: k.mogielnicki@p.edu.pl **Fculty of Mechnicl Engineering, Bilystok University of Technology, Bilystok, Polnd, E-mil: j.piwnik@p.edu.pl http://dx.doi.org/10.5755/j01.mech.21.3.9553 1. Introduction Compring microforming to trditionl forming process it cn e oserved, tht while going to microscle, prmeters such s grin size or surfce structure re not chnged [1, 2]. Reltionships etween the dimensions of the mnufctured items nd morfometric prmeters of their microstructure nd surfce stereometry, oth items nd tools re different in mcro nd microscle. This leds to the size effect formtion, which presence does not permit direct ppliction in microforming of metls ville technologicl knowledge relting to conventionl forming methods [3, 4]. Microforming is young technology, ut more nd more reserch centers in the world del with it. Currently works refer to experimentl dignosis of the impct of size effect on metl forming processes nd of the products mechnicl properties. In prllel, together with the reports of these works results, ttempts to tke into ccount nd pply the identified phenomen in ll sorts of softwre simulting the metl deformtion processes re undertken eg. [5, 6]. Experimentl studies of metl microextrusion hve een presented in themtic literture for two decdes [7]. Influence of the continers nd dies surfces smoothness nd mteril grin size on the mechnicl properties of the product hve een investigted size effect. Similrly, s in the cse of mcroscle, in microscle there re conducted: forwrd microextrusion eg. [8, 9], ckwrd microextrusion eg. [10] nd n ngled one [11, 12]. These processes re crried out in dry conditions, with luriction, t mient nd elevted tempertures. These prmeters pper to hve different, often heightened influence on mechnics of deformtion in the microscle. Minituriztion of these processes introduces need to further understnd the peculirities with it emerging. In microscle mteril cn no longer e treted s homogeneous, ecuse in the re of deformtion it cn e just few grins. It should lso e tken into ccount the influence of continer surfce roughness, which significntly ffects on deformtion processes t the microscle level. 2. Experimentl investigtions In order to determine the influence of tool roughness on metl plstic flow in the forwrd microextrusion process conducted in dry conditions, the toolkit uthor s copyright project ws designed nd mnufctured [6]. There re two continers nd two rectngulr dies of the sme size, differing only in the degree of continers roughness, hollowed in the hlves of the odies (Fig. 1). The dimeter of the continers is D p = 1.8 mm, while the dies D m = 0.9 mm. Toolkit includes lso the piston tht presses on the "floting" over his fce punches. Body nd the piston re mde of X210Cr12 steel, nd punches of ering steel 100Cr6. Smples mde of luminum nd copper were extruded (Fig. 2). In order to illustrte the mteril structures, smples mde of nneled electrolytic copper Cu99.99E hve een used. Fig. 1 View of the toolkit for forwrd microextrusion [6] Fig. 2 Extruded smples [6] Continers nd dies were drilled with the use of the EDM method. In order to otin diverse wll roughness of continers, they were drilled with different degrees of energy pulsed electric dischrge. In order to determine the degree of continers roughness, the roughness profiles were designted using lser microscope LEXT OLS4000 3D, nd verge vlues of prmeter R were determined for ech. As result of the mesurements, following vlues were otined: R = 1.2 μm nd R = 3.5 μm. Frgments of received profiles of the tested continers re shown in Figs. 3 nd 4.
330 the outer edge of its upper prt (Fig. 7, photo, c nd d). Core of this prt, s in the previous cse, hs n uniform grin structure (Fig. 7, photo e nd f). Fig. 3 Profile of the continer roughness R = 1.2 μm, mesured long n xis [6] Fig. 4 Profile of the continer roughness R = 3.5 μm, mesured long n xis [6] Extruded smples were sunk in epoxy resin nd their metllogrphic sections were prepred. The microscopy imges t the longitudinl sections of smples efore nd fter extrusion were otined. Width mesurements of the strips with highly deformed structure cused y continers roughness in the plces where these nds re the widest were relized. Mesurements were conducted using MultiScn softwre, tht llows morfometric nlysis of ojects in the scled photogrphs. Fig. 5 shows the mteril structure in the longitudinl section of the smple efore extruding. At the edge (Fig. 5, photo ) nd inside (Fig. 5, photo ) of the smple homogeneous grins distriution ppers. Fig. 6 Grin structure of forwrdly extruded copper in continer with roughness R = 1.2 μm; mgn. 500 Fig. 5 Initil copper grin structure At the section of extruded in continer with the roughness R = 1.2 μm smple nrrow strip of deformed structure t the outer edges of its upper prt is visile (Fig. 6, photo d nd e). Core of the smple remined unchnged nd grins in this re hve n originl, uniform lyout (Fig. 6, photo nd ). In the res of the upper outflow nd die frgmented structure ppers (Fig. 6, photo c nd f), cused y intensifiction of deformtion. Lower prt of the smple shows lso significnt frgmenttion of the structure, especilly t its outer edge (Fig. 6, photo g). Smple extruded in the continer with roughness R = 3.5 μm hve roder rnge of deformed grins t Fig. 7 Grin structure of forwrdly extruded copper in continer with roughness R = 3.5 μm; mgn. 500 Figs. 8 nd 9 show the differences in the width of the nds of strongly deformed grins in the vicinity of continers roughness. Photos showing the nds t hlf height of the continers hve een selected. In the smple extruded in continer with the roughness R = 1.2 μm rnge of frgmented grins ws estimted to e out 50 μm. In turn, in smple extruded in continer with the roughness R = 3.5 μm this rnge hs width pproximtely 200 μm.
331 d. Fig. 8 Bnds of strongly deformed grins width mesurement in the smple extruded in the continer with roughness R = 1.2 μm Fig. 10 Adopted for clcultions model for forwrd micro-extrusion roughness of the continers. Motives method ccording to the PN-EN ISO 12085:1999/AC:2009 divides roughness profile into soclled motives. A motive is prt of the originl profile etween the highest points of two locl, not necessrily neighoring, peks of the profile. Using the motives method, the verge length AR nd verge depth R of the motives for oth roughness profiles hve een determined, with given 95% confidence intervl using the norml distriution: 1. R = 4.89 ± 1.09 μm AR = 16.66 ± 2.05 μm, 2. R = 13.87 ± 2.30 μm AR = 26.27 ± 3.41 μm. c. Fig. 9 Bnds of strongly deformed grins width mesurement in the smple extruded in the continer with roughness R = 3.5 μm 3. Microextrusion process modeling conditions Axilly symmetric extrusion process llowed to crry out simultions in hlf sections wht reduced time of clcultion. Simultions hve een performed using softwre DEFORM sed on the theory of plsticity nd using FEM. Tool elements were treted s rigid odies. Simultions hve een crried out with keeping constnt punch velocity equl v 0 = 0.01 mm/s nd workpiece temperture T = 20 C. Workpiece mteril ws considered s homogeneous, plstic with isotropic hrdening, descried y the stress-strin curve defined for the experimentlly investigted one. Its model ws introduced to the softwre lirry of curves. The continer ws D p = 1 mm in dimeter, while the die D m = 0.5 mm (Fig. 10). Initil length of the workpiece model ws 2.5 mm. Modeled meshes hve een designed with the gretest possile numer of elements, wht ws intended to tke into ccount the vrile geometry of the continers surfces. These meshes hd respectively: 7 nd 9 thousnd of elements. Workpieces were designed in the form of rectngles, connected with the peeks of continers roughness. While extruding the mteril filled tringles, which ws the signl, tht the mesh sensitivity is sufficient nd tkes into ccount the surfce Fig. 11 Averge profiles of continers roughness: ) R = 1.2 μm; ) R = 3.5 μm In order to illustrte the influence of continer roughness on metl deformtion process during microextruding the numericl models of roughness were designed nd introduced into simultions (Fig. 11). At the toolworkpiece interfce zero friction fctor hs een given. The friction ws the resistnce of the mteril movement cused y continer roughness wve. 4. Results of the microextrusion numericl nlyses Fig. 12 shows hlf sections of the forwrdly extruded workpieces in continers with top lyers chrcterized y tringulr profiles. Finite element meshes re dense enough to tke into ccount vriility of the mteril geometry in the vicinity of the continers roughness.
332 Forwrd microextrusion in continer with the roughness wve numericl simultions following effective stress σ distriutions reveled (Fig. 13). Effective stress in the mteril is chrcterized y specific distriution in the vicinity of the wve. σ increses with incresing motive prmeters nd with the height of the continer. Fig. 14 shows the deformtion of the mteril using strtified strin effective imges ε. In the vicinity of the wve there is significnt chnge in the conditions of deformtion. With incresing motives depth increses strin vlue in the workpiece section. Prticles velocities distriutions (Fig. 15) revel the slow of movement of the lyers in the continer roughness vicinity. The lrger motives dimensions the igger volume of the mteril with reduced speed ded zone. This dependency compred to imges of the strin fields suggests, tht in the initil phse of mteril flow significnt deformtion of the mteril nd the flow suppression is followed. As result, conicl surfce re rises, in respect of which n intensive shering is followed y. Fig. 12 Workpieces with the finite element mesh during extruding in the continers with roughness modeled in the form of tringle motives: ) R = 14 μm, AR = 26 μm; ) R = 5 μm, AR = 17 μm Fig. 14 Effective strin distriutions while forwrd extruding with motives prmeters: ) R = 14 μm, AR = 26 μm; ) R = 5 μm, AR = 17 μm Fig. 13 Effective stress distriutions while forwrd extruding with motives prmeters: ) R = 14 μm, AR = 26 μm; ) R = 5 μm, AR = 17 μm Fig. 15 Velocity distriutions while forwrd extruding with motives prmeters: ) R = 14 μm, AR = 26 μm; ) R = 5 μm, AR = 17 μm 5. Conclusions Anlyzed microextrusion processes were chrcterized y lrge rtio of the continer roughness vlue R to its dimeter D p. In experimentl prt of investigtions, microextrusion cses with the ove reltion R / D p equ-
333 ling 0.00067 nd 0.00194 hve een exmined. This gives respectively 11 nd 39% of prticiption of the frgmented y the continers roughness grin structure lyers in the inputs cross sections. Volume of the fine grined structure depending on the roughness of continer is the source of size effect in this cse. This phenomenon hs een confirmed experimentlly nd numericlly. Reduction of the degree of roughness or incresing in the dimensions of the input will result in the disppernce of this occurrence. Susequent studies should e focused on identifying nd recognizing the vlue of the prmeter, which llows to specify the ppernce of the size effect resulting from the impct of continers roughness. This prmeter could e the rtio of surfce roughness R to continer dimeter D p : R / Dp. Line forecsting of this rtio vlue, sed on the otined dt suggests, tht when it is equl to 0.0002, the prticiption of fine grined structure t the input cross section will e negligily smll. It will e, therefore, the size effect emergence vlue during forwrd extruding of the tested metl. This estimte should e verified experimentlly. Precise determintion of this strt prmeter vlue would llow to determine the continer dimeter nd its degree of roughness, to which modeling of continer surfce roughness wve in forwrd microextrusion numericl simultions would e pproprite. References 1. Vollertsen, F.; Hu, Z.; Niehoff, H.S.; Theiler, C. 2004. Stte of the rt in micro forming nd investigtions into micro deep drwing, Journl of Mterils Processing Technology 151(1): 70-79. http://dx.doi.org/10.1016/j.jmtprotec.2004.04.266. 2. Vollertsen, F.; Schulze Niehoff H.; Hu, Z. 2006. Stte of the rt in micro forming, Interntionl Journl of Mchine Tools nd Mnufcture 46(11): 1172-1179. http://dx.doi.org/10.1016/j.ijmchtools.2006.01.033. 3. Engel, U.; Eckstein, R. 2002. Microforming from sic reserch to its reliztion, Journl of Mterils Processing Technology 125: 35-44. http://dx.doi.org/10.1016/s0924-0136(02)00415-6. 4. Zimnik, Z.; Pondel, B. 2007. Micro metl forming, Metl Forming 18: 29-36. 5. Geißdörfer, S.; Engel, U.; Geiger, M. 2003. Mesoscopic model-simultive pproch to the sctter of process fctors in microforming, Hollmnn (Ed.): Strhltechnik 24: 81-88. 6. Piwnik, J.; Mogielnicki, K. 2014. Experimentl nd FE nlysis of luminium lloy plstic flow in the forwrd microextrusion processes, Archives of Metllurgy nd Mterils 59(2): 521-525. http://dx.doi.org/10.2478/mm-2014-0086. 7. Mogielnicki, K.; Grl, K.; Piwnik, J. 2010. Overview of tool concepts for microextrusion, Scientific nd Didctic Equipment 15: 113-118. 8. Withen, C.P.; Mrstrnd, J.R.; Arentoft, M.; Pldn, N.A. 2005. Flexile tool system for cold forging of micro components, First Interntionl Conference on Multi-Mteril Micro Mnufcture 29: 143-146. 9. Co, J.; Krishnn, N.; Wng, Z.; Lu, H.; Liu, W. K.; Swnson, A. 2004. Microforming: experimentl investigtion of the extrusion process for micropins nd its numericl simultion using RKEM, Journl of Mnufcturing Science nd Engineering 126(4): 642-652. http://dx.doi.org/10.1115/1.1813468. 10. Arentoft, M.; Bruschi, S.; Ghiotti, A.; Pldn, N.A.; Holstein, J.V. 2008. Microforming of lightweight metls in wrm conditions, Interntionl Journl of Mteril Forming 1(1): 435-438. http://dx.doi.org/10.1007/s12289-008-0088-y. 11. Rosochowski, A.; Presz W.; Olejnik, L.; Richert, M. 2007. Micro-extrusion of ultr-fine grined luminium, The Interntionl Journl of Advnced Mnufcturing Technology 33(1-2): 137-146. http://dx.doi.org/10.1007/s00170-007-0955-6. 12. Geißdörfer, S.; Rosochowski, A.; Olejnik, L.; Engel, U.; Richert, M. 2008. Micro-extrusion of ultrfine grined copper, Interntionl journl of mteril forming 1(1): 455-458. http://dx.doi.org/10.1007/s12289-008-0093-1. K. Mogielnicki, J. Piwnik INFLUENCE OF DEFORMATION ON METAL STRUCTURE IN THE FORWARD MICROEXTRUSION PROCESS S u m m r y Investigtion results presented in the work relte to the impct of tool roughness on the mteril plstic flow during forwrd microextruding of metl. Investigtion process consists of the experimentl nd numericl prts. In the experimentl one, forwrd microextrusion of nneled mteril using the toolkit uthor s copyright project ws performed. The tests were conducted to compre deformtion of the mteril extruded in continers with different roughness. As result, otined imges of deformed mteril structures re presented nd compred. Numericl prt reltes to simultions of nlogous microextrusion processes conducted using DEFORM softwre. Tool roughness ws modeled in the form of rigid tringulr wves, whose geometric prmeters were sed on the roughness profiles otined for the experimentl tools. Depth nd length of the tringulr elements were determined using the motives method. Distriution fields of the effective stress, strin nd the flow velocities re presented nd compred. Bsed on otined dt, concept of determining of the prmeter which cn help to define the ppernce of structurl size effect resulting from the influence of continer roughness is lso presented. Keywords: microextrusion, tool roughness, mteril structure, FE nlysis. Received Jnury 22, 2015 Accepted Mrch 17, 2015