Class28 Manufacturing Economics

7/31/2019 Class28 Manufacturing Economics

1/30

Manufacturing Economics


2/30

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


3/30

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?


4/30

Selection of Material

Physical properties

Strength

Toughness

Ductility

Hardness

Fatigue Creep

Density

Thermal conductivity

Manufacturing property

Castability Formability

Machinability

Weldability


5/30

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


6/30

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


7/30


8/30


9/30

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


10/30


11/30


12/30

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)


13/30

Process Capability

Mold filling: Complex shapes

Metal forming: properties

Metal removal: easy cheap Metal joining: composite materials,

fabricated


14/30

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


15/30


16/30


17/30


18/30

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


19/30


20/30

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


21/30

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


22/30

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


23/30

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


24/30


25/30

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)


26/30

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


27/30

Cost per

piece of

machining


28/30

time per piece of

machining


29/30


30/30

Unit Cost

Class28 Manufacturing Economics

Documents

Transcript of Class28 Manufacturing Economics