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FACULTY OF MECHANICAL ENGINEERING

UNIVERSITI TEKNOLOGI MALAYSIA

LAYOUT DESIGN - Part 1

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PRODUCT, PROCESS AND SCHEDULE

Among the questions to be answered before facility planning can be done

What is to be produced ?

How are the products to be produced ?

When are the products to be produced ?

How much of each product will be produced ?

For how long will the products be produced ?

Where are the products to be produced ?

The answers can be obtained from product design, process design, and schedule design

Product design, process design and schedule design must be done concurrently with facilities design

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PRODUCT DESIGN

Product design involves the determination of which products to be produced and the detailed design of

individual products

DIFFERENT PRODUCT DIFFERENT FACILITY

Basic product design data can be obtained from production drawings, prototypes of the product, etc

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PRODUCT DESIGN assembly drawing

Product

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PROCESS DESIGN

Process design decisions determine whether

a part will be purchased or produced,

Selection of process

Sequence of process

This information can be obtained from parts list, bill of materials, route sheet, assembly chart, precedence

diagram

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PROCESS DESIGN make or buy

Options buy raw materials and do in house fabrication and assembly, or buy component and only do in house

assembly

Scope and magnitude of activities are dependent on level of vertical integration

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PROCESS DESIGN make or buy

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PROCESS DESIGN make or buy

- part lists

The input to the facilities planner is a listing of the items to be made and the items to be purchased.

The listing often takes the form of a parts list or a bill of materials

The parts list provides a listing of the component parts o f a product. In addition, a parts list includes at least

the following

Part number

Part name

Number of parts per product

Drawing references

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PROCESS DESIGN make or buy

- parts list

parts lists

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PROCESS DESIGN make or buy

- bill of materials

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PROCESS DESIGN make or buy

- bill of materials

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PROCESS DESIGN selection of process

Product identification process selection (include CAPP) Route sheet

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PROCESS DESIGN selection of process

route sheet

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PROCESS DESIGN sequence of process

Assembly chart

Operation process chart

Precedence diagram

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PROCESS DESIGN sequence of process

assembly chart

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PROCESS DESIGN sequence of process

operation process chart

purchased or produced (make or buy)

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PROCESS DESIGN sequence of process

precedence diagram

purchased or produced (make or buy)

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SCHEDULE DESIGN

Schedule design decisions provide answers to the questions

How much to produce (volume)

When to produce

Associated with these decisions is the determination of the number of machines, number of shifts, number of

employees, space requirements, storage requirements,

material handling equipment, building size etc.

Consequently, plant layout will be very much affected

Information obtained from Master Production Schedule (MPS)

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SCHEDULE DESIGN volume-variety

Volume-variety chart (paretos law)

Mass production area for 15% of high-volume items and a job shop arrangement for the remaining

85% of the product mix

Very important in determining the layout type

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SCHEDULE DESIGN scrap estimates

The market estimate specifies the annual volume to be produced for each product

To produce the required amount of product, the number of units scheduled through production must

equal the market estimate plus a scrap estimate.

Ik = Ok

1 Pk

I1 = On

(1-P1)(1-P2)(1-Pn)

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SCHEDULE DESIGN scrap estimates

A product has a market estimate of 97,000 components and requires three processing steps (turning, milling

and drilling) having scrap estimates of P1 = 0.04, P2 =

0.01 and P3 = 0.03

Input for drilling, I3 = 97,000 = 100,000

1 0.03

Input for milling, I2 = 100,000 = 101,000

1 0.01

Input for turning, I1 = 101,000 = 105,219

1 0.04

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SCHEDULE DESIGN scrap estimates

Scrap estimates

I1 = 97,000

(1 0.03) (1 0.01) (1 0.04)

= 105,219

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SCHEDULE DESIGN - Machine Assignment

The combination of product, process and schedule design decisions influences the number of employees

involved in producing the product

Decisions regarding the assignment of machine to operators can affect the number of employees

Assumptions

Semiautomatic production equipment

Machines are identical

Times required to load and unload each machine are constant

Automatic machining time is constant

Time for operator to travel between machines is constant

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SCHEDULE DESIGN - Machine Assignment

Multiple activity chart shows the activities of one or more people and one or more machines

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SCHEDULE DESIGN - Machine Assignment -

multi activity chart

Machine Assignment

The

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SCHEDULE DESIGN - Machine Assignment

0.5 minute to travel between machines

1.0 minute to load a machine

1.0 minute to unload a machine

6 minutes of automatic machine time

0.5 minute to inspect and pack a finished part

operator loads M-1, walks to M-2, loads M-2, walks to M-3, loads M-3, walks to M-1, unload M-1, load M-1,

inspects and packs the part removed from M-1, travel

to M-2 and so forth

12 minutes to achieve a steady-state condition, thereafter a repeating cycle of 9 minutes in duration

occurs

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SCHEDULE DESIGN - Machine Assignment -

assignment of three machines to one operator

Machine Assignment

The

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SCHEDULE DESIGN - Machine Assignment

Let a = concurrent activity time (eg loading / unloading )

b = independent operator activity time (walking / inspecting )

t = independent machine activity time (eg automatic machine time)

n = ideal number of identical machines assigned an operator

m = number of identical machines assigned an operator

Tc = repeating cycle time

Io = ideal operator time during a repeating cycle

Im = ideal time for each machine during a repeating cycle

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SCHEDULE DESIGN - Machine Assignment

Excluding idle time, each machine cycle requires a + t minutes to complete a cycle. Likewise, the operator

devotes a + b minutes to each machine during a cycle.

Hence, an ideal assignment is

n = (a + t) / ( a + b)

From the example,

n = (2 + 6) / (2 + 1) = 2.67

Not possible to have 2.67 machines so assume 3 machines.

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SCHEDULE DESIGN - Machine Assignment

Consider what will happen if m machines are assigned

The work content for the operator will be m(a + b) , while a machine cycle will be (a + t) in duration

The repeating cycle will be the larger of the two and the difference in the two will be idle time.

Tc = (a + t) if m n

Im = 0 if m n

Io = Tc m(a + b) if m n

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SCHEDULE DESIGN - Machine Assignment

If we wish to determine the cost per unit produced by an m machine assignment, use the following

Co = cost per operator-hour

Cm = cost per machine-hour v= Co/Cm TC(m) = cost per unit produced based on an

assignment of m machines per operator

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SCHEDULE DESIGN - Machine Assignment

The cost per hour of a combination of m machines and an operator totals Co + mCm

Assuming each machine produces one unit during a repeating cycle, the cost per unt produced during a

repeating cycle can be determined as follows;

TC(m) = (Co + mCm)(a + t)/m if m n

to minimize TC(m) when m n,

m should be made as small as possible.

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SCHEDULE DESIGN - Machine Assignment

To facilitate the determination, let

F = TC(n) / TC(n + 1) = (Co + nCm)(a + t)

n[ Co + (n + 1) Cm ] ( a + b)

which reduces to F = v + n x n v + n + 1 n

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SCHEDULE DESIGN - Machine Assignment If F < 1, then TC(n) < TC(n + 1) and n machines should

be assigned

If F > 1, then TC(n + 1) < TC(n) and n + 1 machines should be assigned

If F = 1, then either n or n + 1 machines should be assigned.

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FACULTY OF MECHANICAL ENGINEERING

UNIVERSITI TEKNOLOGI MALAYSIA

THE END