Grinding and economics of machining operation

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Transcript of Grinding and economics of machining operation

  • 1. Grinding

2. Common Grinding Processes 3. Details of Surface grinding 4. Mechanics of GrindingUncut Chip thickness per gritft1 =mm ZNWhereZ = Number of active grains N = rpm of the wheel 5. Z = DCb Where D = Diameter of the wheel C = Surface density of active grains (mm-2) b = Average grain width of cut (mm)rg = b/ t1 f t1 = DNCrgPowerAfU c W= Where A cross sectional area of the job 60 Uc = Specific energyForce per single grit 60, 000W1000 fU c Fc=N= N DACN DCN 6. Chip Formation during surface grindingDl 2 D D2dCos = ( d ) / = 1 2 2D2Cos 1 2l Dd 1 ( NDBC ) bmax t1max l = fdB 6 7. 6fd t1max = NDrg C DBfdU c W=W60 60, 000W 1000 BfdU cFc = = ND ND Components of Grinding ForceAverage force per grit60, 000WF =cN NDCB Dd 369U o f 0.8 d 0.4 rg0.2 N Fc = N 0.8 D1.2C 0.8 8. Thermal aspectsEnergy spent per unit surface area ground Fc ND s BfSince0.4 1 s dU c and U c = U o (t1av )and t1av = t1max 2 d 0.9 D 0.3C 0.2 N 0.2 sf 0.2 Grain chip interface temperaturevt1max g = U ck C 9. Residual stress in workpiece after surface grinding 10. Growth of power requirement of different wheel grades 11. Grinding Wheel Specification 12. Grinding Wheel Wear 13. Types of grinding operations 14. Honing Operation 15. Lapping 16. Abrasive Flow Machining (AFM) 17. Magnetic Abrasive Finishing (MAF) Sintered ferromagnetic abrasive particle Ferromagnetic abrasive particle in actionMagnetic Abrasive Finishing 18. MAFExternal Finishing by MAF Internal Finishing by MAF 19. Ideal roughness in turningMaximum height of unevenness wherefH max = side cutting edge angletan + cot end cutting edge angleMaximum height of unevenness, when nose radius (r) is used f2 H max = 8r 20. Generation of Ideal roughness in slab milling 21. Verification of surface roughness with cutting Speedduring turning mild steel bar 22. Economics of Machining Operation 23. Optimizing cutting parameters for Minimum costR = R1 + R2 + R3 + R4 + R5R = Total Cost/ pieceR1 = Material Cost/ pieceR2 = Set up and idle time Cost/ pieceR3 = Machining Cost/ pieceR4 = Tool changing Cost/ pieceR5 = Tool regrinding Cost/ piece 1= Cost/ min of labour and overheads 2= Cost of setting a tool for regrinding3 = Cost/mm of tool groundts = Set-up tme and idel time/ piece, min,tm = Machining time/piece, min,tct = Tool changing time, min 24. Set- up and idle time costR2 = 1tsMachining cost LD L = Length R3 = 1t3 = 1 D =Diameter 1000 fvf = feedTool Changing costV = speedtm R4 = 1 tctTkT = 1/ n 1/ m T = Tool life v f LD R4 = 1tctv1/ n 1 f 1/ m 1 1000 fv 25. Tool regrinding cost = h f tan vs , hf = flank wear = Minimum length of tool to be reground2 + 3 = 2 + 3h f tan stm R5 = (2 + 3 h f tan vs )TVs = Clearance angle LD= (2 + 3 h f tan vs ) v1/ n 1 f 1/ m 11000k If tool cost of new tool is A and the total length that can be reground is B mm , then cost per mm of the toolA 3 = B 1 + hf ta n v s 26. Total cost per piece LD LD LD R = R1 + 1ts + 1 + 1tct v1/ n 1 f 1/ m 1 + (2 + 3 h f tan vs ) v1/ n 1 f 1/ m 11000 fv 1000 fv1000 fvOptimum speed for a given feedR LD 2 1 LD 1/ n 2 1/ m 1= 1v + (1tct + 2 + 3h f tan vs ) 1vf =0v vopt 1000 f n 1000k v = vopt or nnk 1vopt = (1 n) f (1tct + 2 + 3 h f tan s ) 1/ m 27. Optimum speed for minimum cost n nk 1 vopt= (1 n) f (1tct + 4 ) 1/ mOptimum feed for minimum cost m mk 1f opt = (1 m)v (1tct + 4 ) 1/ nf max = 8rH max lim H maxlim= Limiting value of unevenness 28. Machining force Fc = 1000U 0 wt10.6Fc = k1 f 0.6Power consumption Variation of machining cost with v and fW = k1vf 0.6Maximum available power in the machine then limiting cutting speed-feedWlim vf 0.6= k1Selection of optimum feed 29. Variation of various costs with cutting speed. 30. Optimum cutting parameters for maximum productiontmtt = ts + tm + tct minT LD LD= ts ++ v1/ n 1 f 1/ m 1tct min 1000 fv 1000kFor optimum speed to minimize t1tt LD2 1 LD 1/ n 2 1/ m 1 =v + 1vf tct=0vv = vopt 1000 f n 1000kv = voptn nk vopt= (1 n) f 1/ mtct 31. Optimum cutting seed for maximum efficiencyProfit rateSRS = Amount received per piece pr = tt R and tt can be expressed in terms of v as before, thenpr =0vv = vopt