Modelling Plastic Deformation of A36 Mild Steel Under Extrusion Process

Transcription

1 Mdelling Plastic Defrmatin f A36 Mild Steel Under Extrusin Prcess Mesay Alemu Tlcha Mechanical Engineering Department Jimma institute f Technlgy, Jimma University Jimma, Ethipia Abstract Technlgy f metal frming is used fr shaping any metal int useful prducts by frming prcesses such as Rlling, Frging, Extrusin, Drawing, and Sheet-metal frming. But the research is specifically devted n hydrstatic extrusin finite element mdeling. Hydrstatic extrusin is an advanced metal frming technlgy. In hydrstatic extrusin there is a hydraulic medium that interpses between the billet, that is defrmed and the extrusin punch. Different metals can be extruded under extrusin prcess but this research emphasis n A36 mild steel. A36 mild steel is a lw carbn steel that exhibits gd strength cupled with frmability. A36 mild steel extruded can be used fr a wide range f industrial applicatins, including truck and trailer frame supprts, equipment and machinery frames and supprts, building frames and ther cmpnents. Mdelling the plastic defrmatin f A36 steel under hydrstatic extrusin is cncerned with describing a cmputer based technique fr aiding the ptimizatin f metal defrmatin prcess, prduct design, reduce lead time, and imprve the facility and reliability f the prducts. The ultimate gal f this task is t simulate the plastic defrmatin f A36 steel that defrmed by hydrextrusin prcesses, in rder t reduce trial and errr experimental task and t predict incming difficulties such as defects frmed n end prducts and die angle. In this study, cmmercial abaqus sftware is used fr mdelling. Cmputatinal mdel has been develped t simulate plastic defrmatin f metal by means f hydrextrusin and ptimize the defrmatin prcess with cnsidering the prcess parameters such as pressure, defrmatin rate, die angle, stress distributin. Keywrds Mdeling; Defrmatin rate; Hmgenus defrmatin: Metal frming; Hydrstatic extrusin; Die angle. I. INTRODUCTION Metal frming is the area f metallurgy which is cncerned with cnversin f metal casting ingt int mre useful shape such as flat plate, rd, bar and sheet metal with imprtant analysis. Frming technlgy refers t shaping f metallic materials by means f plastic defrmatin when the term f plastic defrmatin describes permanent shape change, in cntrast t elastic defrmatin. In rder t plastically defrm a metal, a frce must be applied that will exceed the yield strength f the material. There are different metal frming techniques are used tday but the mst widely used is extrusin. Extrusin is the prcess by which a blck/billet f metal is reduced in crss sectin by frcing it t flw thrugh a die rifice under high pressure. In general, extrusin is used t prduce lng parts and unifrm crss-sectin cmpnents. II. BACKGROUND OF THE PROBLEM CONVENTIONAL EXTRUSION PROCESS Extrusin prcess is reducing a blck/billet metal by frcing thrugh a die rifice. During metal defrmatin take place under cnventinal extrusin prcess the flw f the metal is nt nly flw int the die rifice but als fill in the cntainer. The reactin f the extrusin billet with the cntainer results in high stresses which are effective t increase the cracking f materials during primary breakdwn frm the ingt. These prblems are lead t:- Raising the frictin between the wall and billet. Buckling the billet in cntainer befre defrmatin. Surface cracking when the surface f an extrusin splits due t the billet direct cntact with cntainer wall and nn-unifrm lad applied n billet. Internal cracking when the centers f the extruded part develping cracks r vids due t lack f hmgeneity defrmatin. A thin skin will be left in a cntainer finally new metal surface is btained. Wearing and fracture frmed n punch due t direct cntacting with billet material (A36 mild steel). Inhmgeneus defrmatin ( lse istrpy strength) Die wearing due t high perating temperatures. By cnvectinal extrusin wrking f metals that are difficult t frm like steels, nickel- based ally, and ther high temperature materials. There is technique t slve the prblem f billet filling the cntainer, nn-hmgeneity and ther prblems in cnventinal extrusin prcess thrugh replacing ram frce type extrusin by hydrstatic extrusin prcess. 1551

2 Hydrstatic extrusin is an advanced metal frming technlgy that used hydraulic medium between the billet, that is defrmed and the extrusin punch, as shwn in fig.1. IV. METHODS EMPLOYED T meet the bjectives f the research, the fllwing methds have been emplyed. Fr mdelling f plastic defrmatin f A36 mild steel material Abaqus sftware is used. Defrmatin f A36 mild steel was analyzed based n:- By experimental result f effective stress relatin with plastic strain as shwn in fig.2. Fig.1. Wrking principle f hydrstatic extrusin machine. In hydrstatic extrusin triaxial state cmpressin stress is frmed. The triaxial state f the cmpressin stresses that are created during the defrmatin leads t increasing the hmgeneity defrmatin. Hydrstatic extrusin methd is generally severe as a plastic defrmatin and recgnized as a methd f grain refinement in metals. Frmatin f such structures results in a cnsiderable imprvement f the mechanical prperties f materials. In this way results a hydrstatic pressure (P) f a certain level that is unifrmly distributed ver the whle surface f the billet that gets int cntact with the liquid. In this prcess there are n cntainer wall frictin; n cntact between the punch and the billet. III. OBJECTIVES The main bjective f the research is t mdel the plasticity defrmatin f the A36 steel material. Fig.2. Effective stress Vs effective plastic strain fr A36 steel. By cnsidering the fllwing prperties f A36 steel material. It is imprtant t knw the plastic flw prperties f A36 steel fr ptimizing the prcess. TABLE I. A36 STEEL MATERIAL PROPERTIES Density (Kg/m3) 7800 Mdules f elasticity (GPa) 200 Yield stress (MPa) 270 Pissn s rati 0.3 Plastic strain failure 0.36 Specific bjectives are:- Reductin f trial-pressings f extrusin prcesses in hydrstatic fr A36 mild steel Mdelling the plastic defrmatin in hydrstatic extrusin with cncerning the descriptin f flw nature A36 mild steel. Analysis the prcess parameter that affect the hmgeneity defrmatin under hydrstatic extrusin prcess. By applying variatin extrusin lad. By applying Levly Mises flw rule. The metal (A36 mild steel) flw grid pattern has been simulated. 1552

3 atm is unifrm during defrmatin but sme distrtin at inter f die angle. Fig.3. A36 Steel grid pattern during defrmatin. Fig.5. Physical mdeling f A36 steel material defrmatin. T imprve the frming quality and t predict ptential defect areas during extrusin 2D and 3D mdelling have been develped as shwn in fig.4. B. Area f Stress Cncentratin A main purpse f cmputatinal mdelling minimizing a labur effrt and predict the quality f prducts. Stress cncentratin is lcalized stress that can be cnsiderable ver than the average even in the unifrmly lad applied acrss the sectin. This is due t abrupt changes in the gemetry. As shwn in Fig.6 the area f stress cncentratin is near t die angle (red clured prtin). Fig.4. 2D and 3D plasticity mdeling f A36 steel material. V. RESULTS AND DISCUSSION The purpse f cmputatinal mdelling was t simulate nature A36 steel defrmatin (grain dislcatin), stress cncentratin, effect f die angle n plastic stress and effect f pressure n plastic strain. A. Permanent Defrmatin (Grain Dislcatin) In metal frming prcesses, prduct shapes are prduced by plastic defrmatin. Permanent defrmatin is a nn-reversible changing in the shape due t the defrmatin energy is transferred thrugh external frce. The defrmatin f A36 steel is hmgenus due t absence f buckling and flw restrictin by frictin. As shwn in the fig.5 plane bundary f Fig.6. Area f stress cncentratins. C. Effect f Die Angle n Plastic Stress Figure 7 shws in extrusin gemetry cnsisting f a 3D cylindrical billet f diameter D = 60 millimeter which is extruded thrugh a die exit diameter d= 20 millimeter. Die angles f θ = 10, 15, 20, 25, 30, 40 r 45 degrees were used fr the simulatins. At 30, 40 and 45 degree stress levels are increased. This indicates that the die angle has great impact n the quality f prducts under hydrstatic extrusin. S the little die angle is recmmended fr hmgenus defrmatin and stress free prducts. 1553

4 Fig.7. Schematic diagram f hydrstatic extrusin gemetry. E. Defrmatin Rate 1) Stress Rate As shwn in the Fig.9 stress rate is analyzed. The result indicate that as rate f defrmatin increase, stress develpment in metarial als increase with cnstant lad. Stress increase as the time increase in the extrusin prcess but nce the stress increment arrive at certain pint, there is lnger stress develpment in the A36 steel material. If there is n further reductin f dimensin in the prcess, metal start t recvers frm the stress. D. Effect f Pressure Distributin n Plastic Strain In hydrstatic extrusin surces f pressure is frmed frm the fluid that leads t defrmatin f metal. The effect f pressure n plastic strain and internal billet defrmatin is analyzed by using tw cases with cnstant lad 900MPa and varying lad directin. Figure 8 shws different plastic strain during the pressure applied ver the whle f the billet and pressure applied nly frm back side. The pressure applied frm back side nly when the diameter f the billet almst near t the diameter f the wall. In this case cefficient f frictin is zer because the il in hydrstatic extrusin services as the lubricatin n the wall. Fig.9. Schematically representatin f stress Vs time. Fig.8. Schematically representatin f strain difference due t lad directin. 1554

5 2) Strain Rate Strain rate is directly related t the stress and time. A greater rate f defrmatin f the A36 steel will mean a higher strain rate. As shwn in fig.10 even stress develped at certain level crrespnding t certain time but a metal n underging t strain defrmatin. Fig.10. Schematically representatin f strain Vs time. VI. CONCLUSION A successful cmputatinal mdelling f A36 steel material under hydrstatic was carried ut with purpse analyzing plasticity defrmatin and effect f die angle n the extrusin. Defrmatin lad was determined by incrpratin f yield stress and ther prperty f A36 steel material. Die angle is significant rll play n the hmgeneity defrmatin under extrusin prcess. Extruded part f A36 steel material start t recver frm the stress (stress free cnditin) frm central prtin at the end f die rifice. This is indicate the material f end prduct can pssess unifrm mechanical prperties. In general, mdelling f plastic defrmatin has a ptential t predict metal flw and grain dislcatin in extrusin prcess. Amng different extrusin technlgy hydrstatic extrusin is the autmated fr prductin f:- Large length/defrmatin rati. Hmgeneity defrmatin. A36 mild steel is cmmn engineering material, it is defrm under hydrstatic extrusin effectively. REFERENCES [1] M. PRAKASH and P., W., CLEARY. Mdelling f cld metal extrusin using sph. CSIRO Mathematical and Infrmatin Sciences, Claytn, VIC [2] Z. ZHANG and F. WANG. Numerical simulatin n prcess f Hdrstatic Extrusin fr tungsten ally thrugh cncave dies with Equal-strian cntur lines. J.Mater.Sci.Technl, VOl.17, Suppl.1, [3] P.,E., Armstrng, J.,E., Hckett, and O.,D., Sherby. Large strain multidirectinal defrmatin f 1100 aluminium at 300K, J. Mech. Phys. Slids 30 (1 2) (1982) 132. [4] E.,H., LEE, R.,L., YANG and W., H., YANG. Mallett stress and defrmatin analysis f the metal extrusin prcess. Cmputer Methds In Applied Mechanics And Engineering I (1977) , Received August [5] K. Jawad, A. Khleif and M., Q., abbd. plane flw analysis fr a prfile extrusin die using digital image prcessing technique. Eng. & Tech. Jurnal, Vl. 30, N.9, [6] J. Hung and C.Hung. The design and develpment f a hydrstatic extrusin apparatus. Jurnal f Materials Prcessing Technlgy Vl.104, [7] P. Tiernan, M.,T., Hillery, B. Draganescu and, M.Gherghe. Mdelling f cld extrusin with experimental verificatin. Jurnal f Materials Prcessing Technlgy 168 (2005) [8] H. Lng, R. Balendra. FE simulatin f the influence f thermal and elastic effects n the accuracy f cld extruded cmpnents, J.Mater. Prc. Tech. 84 (1998) , Elsevier. [9] K. Dae-Chel, Kim Byung-Min. The predictin f central burst defects in extrusin and wire drawing, J. Mat. Prc. Technl. 102 (2000) 19 24, Elsevier. [10] P.K. Saha. Thermdynamics and triblgy in aluminium extrusin, Wear 218 (1998) , Elsevier. [11] G.W. Rwe. Principles f Industrial metalwrking prcesses, Arnld, Lndn, [12] C.H. Lee, T. Altan. Influence f flw stress and frictin upn metal flw in upset frging f rings and cylinders, J. Eng. Ind. 94 (1972) [13] L. Lazzartt, L. Dubar, A. Dubis, P. Ravassard, J. Oudin. Three selectin criteria fr the cld metal frming lubricating ils cntaining. [14] A.F. Castle, T. Sheppard. Ht wrking thery applied t extrusin f sme aluminium allys, Met. Technl. 3 (10) (1976) 42. [15] P.TIERNAN, M.,T., HILLERY, B. DRAGANSECU M. GHEORGHE. Mdelling f cld extrusin with experimental variatin, Jurnal f Materials Prcessing Technlgy, 168, [16] C., P., Blankensip. Sme Effects f Cld by Hydrstatic Extrusin n Mechanical Prperties f High Strength Steels, NASA, Wasingtn DC,Feb.,(1991). [17] E. Whalley, A. Lavergne. Mdifed unsupprted-area hydraulic seal fr pressure f 50 kbar, Rev. Sci. Instrum. 47 (1) (1976). 1555