A STUDY ON THE ULTRA PRECISION PROGRESSIVE DIE MAKINGFOR SHEET METAL FORMING BY COMPUTER SIMULATION

Sung-Bo Sim1, Chung-Whan Kim2, Gwi-Yun Park1

1School of Mechanical Engineering Pukyong National UniversitySan100, Yongdang-Dong, Nam-Gu, Busan, Republic of Korea

2Graduate school of Mechanical Engineering Pukyong National UniversitySan100, Yongdang-Dong, Nam-Gu, Busan, Republic of Korea

INTRODUCTIONA great deal of influence of developmenttechnology of progressive die for press toolingas a top rapidity operation with a minimizingcosts is given to the production part by manykinds of factors, i.e. the complexity of diecomponents of machining and its assembling,pressing machinery capacity, lot size ofproduction part, materials of die componentsand its heat treatment, etc. The interactions of awhole of many factors to the die developmentwith a optimized method are concerned by toolengineers. The important role of tool engineersis strip process layout design and computeraided FEM simulation with a existing data baseand abundant field experiences. The predictionof result on the tryout is critical division on thedie development. We used the part of precisionproduction (Fig. 1) in electronic production line.Hence, this study needs a whole of press tooldata, our field experiences, relative instructions,and ultra precision machine tools and its skilfuloperation and applications. The added processof this work was FEM simulation by DEFORMwith 3D Unigraphics under the WINDOWenvironment. The result of this computer aidedsimulation was successful and very fine as theoutput coming in Fig. 4, Fig. 5. According toupper work, the optimum die design could beaccomplished. Furthermore the goal of leastdefect could be obtained by the tryout and dierevision.

ANALYSIS OF PART DRAWINGFig. 1 shows the production part drawing in thisstudy through the computer aided die designunder the AutoCAD and Window environment.In this drawing the thickness of material is0.8mm for bending part. The direction of burr isdownward regularly, hence we designed stripprocess layout as the cut-off type progressionthrough the modeling of 3D Unigraphics

application. At this time, we could predict thecompleted actual strip process layout after tryoutvisually. Table 1 shows the mechanicalproperties of SPCC material.[1,2]

TABLE 1 Mechanical properties of SPCCUnit Value

Young modules GPa 200Poison ratio - 0.3Tensile MPa 760Yield Strength MPa 380

[ Note ]1. Burr creating direction should be on the "A"surface to the downward.Material : SPCC, Thickness : 0.8 mm

FIGURE 1 Production part drawing

DESIGN OF STRIP PROCESS LAYOUTFig. 2 shows the result of strip process layout inthis study. For the increasing of material usingratio, we selected the couple row type method,at the same time the symmetrical dispositionand guide line of pin method, pilot locatingmethod were used to accurate process [3,4].

1st stageDifferent shape piercing of central position andpiercing to pilot

2rd stage Indirected piloting process for accurate feeding3nd tage Symmetrical notching of bending portion4th stage Idle stage with consideration of die strength5th stage Left and right wing bending to upper direction6th stage Chamfering and embossing of edge portion7th stage 90 degree bending of edge portion to the upper

direction8th stage Idle stage as same effectiveness as 4th stage9th stage Cut-off stage with a consideration of burr

direction for product obtaining

FIGURE 2 Strip process layout of couple rows

FEM SIMULATION OF STRIP LAYOUTThe FEM program used to simulate the stripprocess layout was DEFORM that is capable ofmaterial behaviour, deep and wide deformationand contrast between punch and die shapes. Itwas possible to determine the stress and strainof bending stage in the strip process.

SPRING BACK CREATING SIMULATIONIn this Study, as a outer method of the commontreatment of spring back of sheet metal bending,punch shoulder shape was considered coiningtype shape also it was simulated by DEFORM.Fig. 3 shows the bending punch shoulder shapewith a coining method

hbh1 h2 h3 h4 h5 h6

0.8mm(100%)

0.04(5%)

0.08(10%)

0.12(15%)

0.16(20%)

0.20(25%)

0.24(30%)

FIGURE 3 Bending punch shoulder shape andsize of coining section

The conditions of DEFORM simulation wereopened as same as following Table2

TABLE 2 Condition of DEFORM SimulationItems ContentsPress Mechanical press SPM:60Friction coefficient 0.09-0.12(0.12 fixed)

At this time, the conditions of bending formationwere shown as the Table3.

TABLE 3 Condition of bending formationItems ContentsPunch radius R 0.3mm fixedClearance 0.4-0.08mmDie radius 0.8, 1.6, 2.4, 3.2mm

Height of Coining0.04, 0.08, 0.12, 0.16,0.20, 0.24mm

(a) Bending deformation rp=.3mm, rd=1.6mm

(b) Bending deformation rp=0.3mm, rd=2.4mm

FIGURE 4 FEM Simulation of bending Dieradius

Fig. 4 shows the representatives of bendingdeformation among the conditions of bendingformation as showing on the Table3. In this FEMsimulation, it could be known that the bendingdie radius 1.6mm of couple times of materialthickness of production part which was satisfiedwith a reduction of stress and strain under therelieving of transformation of material thickness.It was considered that the bending die radius2.4mm was become to the lower effect of stress

and strain, hence, the actual production part bytryout was satisfied as a very important factor.

Fig. 5 shows the representatives of FEMsimulation of stress and strain by DEFORM. Atthis time, bending die radius 2.4mm with acoining height 0.08mm pressing was satisfiedwith a lower stress and strain appearance butspring back phenomena occurred within 10% ofmaterial thickness. The production part could bepredicted as a good quality.

(a) FEM simulation of stress of 0.08 coining

(b) FEM simulation of strain of 0.08 coining

(c) FEM simulation of stress of 0.12 coining

(d) FEM simulation of strain of 0.12 coining

FIGURE 5 Stress and Strain deformation of 0.08and 0.12mm coining on the corner at thebending portion

DIE MAKING AND TRYOUTFig. 6 shows the assembling drawing of diedesign result. At this time, we considered theautomatic roll feeding of strip for the massproduction part above one hundred thousandpieces. Also, the die set was selected specialtype tool steel die with a outer and inner guidepost. For aiding the roll feeding, the guide lifterpin was used[5-7].

(a) Front view of assembly

(b) Top view of Upper and Lower Die

FIGURE 6 Die assembling drawing

Fig. 7 shows the critical points of die making andassembling for increasing of accuracy

FIGURE 7 Fitting accuracy for die assembling

Fig. 8 shows the upper and lower die after diemaking at opening status. The SKD11 high alloytool steel was selected for punch and die blockas a cause of containing of minimized wearamong whole of die materials. In this diemaking, we used many kinds of precisionmachine tools i.e. EDM, Wire-cut, jig grindingmachine, tool, CNC machining center, mirrormachine tool and vacuum type heat treatmentfurnace etc.

(a) Upper Die Assembly (b) Lower Die Assembly

FIGURE 8 Upper and lower die assembly

TRYOUTFig. 9 shows the actual production part aftertryout completed. At this time it was confirmedthat the result of tryout and its revision werepreformed very exactly

(a) Actual strip by tryout

(b) Actual Production part

(c) Actual test part

FIGURE 9 Actual part and strip by tryout

CONCLUSIONThe result of this study was obtained as follows.1. Even in small details of production part, itcould be considered sincerely. For theincreasing of material using ratio, productivity,smoothing of strip feeding on the die blocksurface, and balancing of bending power, itcould be fine method that is two lines blank

disposition type strip process layout with 9stages. Also it was applied to reduce the springback phenomena by coining type punchshoulder. Then, it could be performed DEFORMsimulation before the strip process layoutdesign, die making, tryout and its revisionthrough the analysis of actual production part.Upper methods produced outcome to coincidebetween simulation and tryout.2. Under the condition of clearance of bendingsite 5~10% aided to material thickness ofproduction part and die radius 2.0_3.0 times ofmaterial thickness of production part, the outview of actual production part was satisfied andthe coining site of bending to 0.1_0.15 times ofmaterial thickness of production part wasbrought into existence in allowing tolerance.3. It was possible that the prediction of result oftryout was successful through the FEMsimulation. Also it could be done the optimizingdesign of strip process layout for the satisfieddie making and tryout through the computersimulation

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Development of the Practical and Adaptive Diefor Sheet Metals(1), Proceedings of KCOREConference: 141-148

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3. Sim, Sung-Bo, Jang, Chan-Ho, and Sung Yul-Min, 2001, Development of the Pilotless TypeProgressive Die for Thin Sheet Metal, TheProceeding of KCORE Conference: 289-294.

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