class28 manufacturing economics
TRANSCRIPT
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Manufacturing Economics
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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
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When evaluating the value
ask 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?
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Selection of Material
Physical properties
Strength
Toughness
Ductility
Hardness
Fatigue Creep
Density
Thermal conductivity
Manufacturing property
Castability Formability
Machinability
Weldability
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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
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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
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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
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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)
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Process Capability
Mold filling: Complex shapes
Metal forming: properties
Metal removal: easy cheap Metal joining: composite materials,
fabricated
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Effect of tolerances and surface
finish
Tolerance and surface finish
Cost of manufacturing increases as therequired surface finish increases and
higher tolerancesProduction Volume
Production volume
Rate of production
Economic size
demand
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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
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Machining economics
Minimum cost of part
Max production rate
Cp = Cm + Cs + Cl + CtCp : cost per piece
Cm : machining costC
l: cost of load and unload
Ct : tool cost
Cm = Tm (Lm + Bm)Tm : machining time
Lm : labor rate
Bm : machine over head
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Setup Cost
Cl = Tl (Lm + Bm)
Tl : time involved in loading and unloading
Tooling cost
Ct = [Tc( Lm + Bm) + Tg(Lg+Bg) + Dc]/NpNp: 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
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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 piecef : feed
v : cutting speed
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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
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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)
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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
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Cost per
piece of
machining
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time per piece of
machining
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Unit Cost