Manufacturing Economics

1. Manufacturing Economics

2. Economics of Manufacturing Manufacturing: Organized way of converting raw material to end product We talked about Selection of material Product design Selection of manufacturing process Manufacturing cost

3. When evaluating the valueask these questions Can the design be simplified? Are the tolerances and surface finish necessary? Will the assembly be easy? Do you need to design new part or can you use old design?

4. Selection of Material Physical properties Strength Toughness Ductility Hardness Fatigue Creep Density Thermal conductivity Manufacturing property Castability Formability Machinability Weldability

5. Product design and cost of material High production and automation Cost of material becomes a significant part of the cost Design Optimization (FEM) Produce lighter parts Optimum factor of safety Substitution of materials Reduction in cost Improved performance Strength to weight

6. Substitution of material in the Auto industry Metal being replaced by plastics Metal fender, gears, pumps, clamps, tanks are all being made with plastics Engine parts have ceramic components Cast products, powder metallurgy Composite materials for connecting rods

9. Selection of Manufacturing Process Have all the alternate processes investigated Are the methods economical Production rate Tolerances Can the part be cast instead of machined Is there a lot of scrap Are the production methods optimized Automation How the inspection/quality control can be met

12. Selection of Manufacturing Process Selection depends on Characteristics of material (strain rate sensitivity etc) Shape, size, thickness Tolerances, surface finish Production volume Functional requirements (Single crystal blade)

13. Process Capability Mold filling: Complex shapes Metal forming: properties Metal removal: easy cheap Metal joining: composite materials, fabricated

14. Effect of tolerances and surface finish Tolerance and surface finish Cost of manufacturing increases as the required surface finish increases and higher tolerances Production Volume Production volume Rate of production Economic size demand

18. Economics Machining cost Labor cost Machine overhead Time to machine Idle time Cost of setting up machine Cost of loading, unloading tools and work piece Tooling Cost Cost of tool Cost of regrinding tool Cost of tool regrinding machine

20. Machining economics Minimum cost of part Max production rate Cp = Cm + Cs + Cl + Ct Cp : cost per piece Cm : machining cost Cl : cost of load and unload Ct : tool cost Cm = Tm (Lm + Bm) Tm : machining time Lm : labor rate Bm : machine over head

21. Setup Cost Cl = Tl (Lm + Bm) Tl : time involved in loading and unloading Tooling cost Ct = [Tc( Lm + Bm) + Tg(Lg+Bg) + Dc]/Np Np: number of parts machined / tool grind Tc : time to change tool Tg : time to grind Bg : over head for tool grinding Dc : Depreciation of tool in number of grindings

22. Time needed to produce one part Tp = Tl + Tm + Tc/ Np Tm: time for particular operation For turning Tm = pLD / fv L: length of cut D: diameter of work piece f : feed v : cutting speed

24. Solved Problem on MRR A 6 in long 0.5 inch diameter 304 stainless steel rod is being reduced in diameter to 0.480in by turning on a lathe. The spindle rotates at N = 400 rpm and tool is traveling at the speed of 8 in/min. Calculate cutting speed, feed, depth of cut and MRR Cutting Speed V at outer diameter = 3.14* D* N = 3.14*0.5* 400 = 628 in/min Cutting Speed at machined diameter = 3.14*0.48*400 = 603 in/min Depth of cut = (0.5-0.48)/2=0.010 in; feed = 8/400=0.02 in/rev MRR = 3.14* D(avg)*d*f*N= 0.123 in^3/min Cutting time t= 6/0.02*400 = 0.75 min

25. Material Removal Rate- Continued For Drilling � MRR is defined as ratio of volume removed to time Hence MRR = 3.14 * D^2/4 * f * N, where D is diameter of the drill, f is the feed and N =rpm For Milling

26. Material Removal Rate A milling operation is carried out on a 12 in long, 4 in wide, mild steel block, feed = 0.01 in/tooth d= 1/8 in. Cutter Diameter D= 2 in, has 20 teeth, N=100rpm. Calculate mrr, power cutting time for this operation. Linear speed v= f*n*N = 0.01 * 100 * 20 = 20 in/min MRR = w*d*v, = 4* 1/8 * 20 = 10 in^3/min Power = Unit power given in Table 8.4 * MRR = 1.1 * 10 = 11hp Torque = Power / Rotational Speed = 578 lb-ft lc = (Dd)^ � = 0.5 in Cutting time t = (l +l (c) / v)= (12 +0.5 )/20 = 37.5 sec

27. Relation between labor cost and material and capital cost

28. Tool Life Taylor Tool Life vTn = C T = (C/v) 1/n Number of pieces per tool grind Np = T/Tm Np = fC1/n/(pLDv(1/n)-1)

29. Minimum cost calculations We can calculate cost per piece in terms of several variables. Cp = Cm + Cs + Cl + Ct dCp/dV = 0 (see eq. 8.55 of the text) -for getting optimum cutting speed and also optumum tool life for minimum cost (see eq 8.56 and 8.57) dTp/dV = 0 (see eq. 8.58 of the text) for optimum cutting speed and also optimum tool life for maximum production. We can find V and T to achieve this. (see eq 8.59 and 8.60)

30. Relevant tool life curves Time between machining Tool change, tool grinding time Machine overhead etc. Decide Minimum cost Maximum production in minimum time Determine all parameters Machining parameters Cost factors

34. Unit Cost