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COMPUTER

INTAGRATED

MANUFACTURING

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Production System

A collection of people, equipment, and proceduresorganized to accomplish the manufacturingoperations of a company

Two categories:• Facilities – the factory and equipment in the facility

and the way the facility is organized (plant layout)

• Manufacturing support systems – the set ofprocedures used by a company to manageproduction and to solve technical and logisticsproblems in ordering materials, moving workthrough the factory, and ensuring that productsmeet quality standards

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TTypes of Manufacturing Systems

1. Continuous-flow processes. Continuous dedicated production of large

amount of bulk product. Continuous manufacturing is represented by

chemicals, plastics, petroleum, and food industries.

2. Mass production of discrete products. Dedicated production of large

quantities of one product (with perhaps limited model variations).

Examples include automobiles, appliances and engine blocks.

3. Batch production. Production of medium lot sizes of the same product.

The lot may be produced once or repeated periodically. Examples: books,

clothing and certain industrial machinery.

4. Job-shop production. Production of low quantities, often one of a kind, of

specialized products. The products are often customized and

technologically complex. Examples: prototypes, aircraft, machine tools

and other equipment.

Production

quantity

Continuous-

flow production

Mass

production

Batch

production

Job shop

production

Product variety

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Category Automation achievements

Continuous-flow process •Flow process from beginning to end•Sensors technology available to measureimportant process variables•Use of sophisticated control and optimizationstrategies•Fully computer automated lines

Mass production of discrete products •Automated transfer machines•Dial indexing machines•Partially and fully automated assembly lines•Industrial robots for spot welding, part handling,machine loading, spray painting, etc.•Automated material handling systems•Computer production monitoring

Batch production •Numerical control (NC), direct numericalcontrol (DNC), computer numerical control(CNC).•Adaptive control machining•Robots for arc welding, parts handling, etc.•CIM systems.

Job shop production •Numerical control, computer numerical control

The Production System

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Production System Facilities

Facilities include the factory, production machinesand tooling, material handling equipment,inspection equipment, and computer systemsthat control the manufacturing operations

• Plant layout – the way the equipment isphysically arranged in the factory

• Manufacturing systems – logical groupings ofequipment and workers in the factory– Production line

– Stand-alone workstation and worker

Manufacturing Support Systems

Involves a cycle of information-processingactivities that consists of four functions:

1. Business functions - sales and marketing, orderentry, cost accounting, customer billing

2. Product design - research and development,design engineering, prototype shop

3. Manufacturing planning - process planning,production planning, MRP, capacity planning

4. Manufacturing control - shop floor control,inventory control, quality control

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Information Processing Cycle in

Manufacturing Support Systems

Automation in Production Systems

Two categories of automation in the

production system:

1. Automation of manufacturing systems in the

factory

2. Computerization of the manufacturing

support systems

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Computer Integrated Manufacturing

Mechanization

• Mechanization is providing human operators

with machinery that assist them with the

muscular requirements of work.

• It can also refer to the use of machines to

replace manual labor or animals.

• A step beyond mechanization is automation.

• The use of hand powered tools is not an

example of mechanization.

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Automation

• What is automation?

• Why automation is required?

• Which are the operations can be automated in

production system?

• Can automation be implemented suddenly?

Automation

• Automation can be defined as the technology

concerned with the application of complex

mechanical, electronic, and computer-based

systems in the operation and control of

manufacturing systems.

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Automation

Automation is the use of control systems

(such as numerical control, programmable logic

control, and other industrial control systems),

in concert with other applications

of information technology

(such as computer-aided technologies [CAD,

CAM,]),

to control industrial machinery and processes,

reducing the need for human intervention.

Automation

• In the scope of industrialization, automation

is a step beyond mechanization.

• Where as mechanization provided human

operators with machinery to assist them

with the muscular requirements of work.

• Automation greatly reduces the need for

human and mental requirements as well.

• Processes and systems can also be

automated.

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Automated Manufacturing Systems

Examples:

• Automated machine tools

• Transfer lines

• Automated assembly systems

• Industrial robots that perform processing or assembly operations

• Automated material handling and storage systems to integrate manufacturing operations

• Automatic inspection systems for quality control

Automated Manufacturing Systems

Three basic types:

1. Fixed automation

2. Programmable automation

3. Flexible automation

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Fixed Automation

A manufacturing system in which the sequence of processing (or assembly) operations is fixed by the equipment configuration.

Typical features:

• Suited to high production quantities

• High initial investment for custom-engineered equipment

• High production rates

• Relatively inflexible in accommodating product variety

Programmable Automation

A manufacturing system designed with the capability to change the sequence of operations to accommodate different product configurations

Typical features:

• High investment in general purpose equipment

• Lower production rates than fixed automation

• Flexibility to deal with variations and changes in product configuration

• Most suitable for batch production

• Physical setup and part program must be changed between jobs (batches)

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Flexible Automation

An extension of programmable automation in which the system is capable of changing over from one job to the next with no lost time between jobs

Typical features:

• High investment for custom-engineered system

• Continuous production of variable mixes of products

• Medium production rates

• Flexibility to deal with soft product variety

Product Variety and Production

Quantity for Three Automation Types

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Reasons for Automating

1. To increase labor productivity

2. To reduce labor cost

3. To mitigate the effects of labor shortages

4. To reduce or remove routine manual and clerical tasks

5. To improve worker safety

6. To improve product quality

7. To reduce manufacturing lead time

8. To accomplish what cannot be done manually

9. To avoid the high cost of not automating

Production Concepts and

Mathematical Models

• Production rate Rp

• Production capacity PC

• Utilization U

• Availability A

• Manufacturing lead time MLT

• Work-in-progress WIP

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Production rate Rp• Hourly production rate

• Work units completed/Hr

• Cycle time: Time that one work unit spends being

processed or assembled. It is the time between

when one work unit begins processing and next

unit begins.

• Not all time is productive.

• Cycle time consists of i) actual machining

operation time ii) workpart handling time

iii) tool handling time per workpiece

Operation Cycle Time

Typical cycle time for a production operation:

Tc = To + Th + Tth -------------------1

where

Tc = cycle time, min/pc

To = processing time for the operation, min/pc

Th = handling time (e.g., loading and unloading the production machine), min/pc and

Tth = tool handling time (e.g., time to change tools), min/pc

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Tool handling time

• Time spent changing tools when worn out

• Time required for changing one tool to the

next.

• Tool indexing time for indexable inserts or for

tools on a turret lathe

• Tool positioning for next pass etc..

– These activities do not occur every cycle

– They must be spread over the number of parts

Production rate for

batch production

Time to process one batch(Q units) = Setup time +

processing time, i.e., Tb = Tsu + QTc------------------2

where

Tb = Batch processing time in min

Tsu = Setup time required for one batch in min

Q = Batch quantity, pc

Tc = cycle time per workunit in min/cycle

Tp = Tb / Q ,------------------------3

whereTp= Avg prod. Time/workunit , min/pc

Rp = 60 / Tb ,----------------------4

Where Rp = Hourly prod rate, pc/Hr

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Production rate for

job shop production

Time to process one batch(Q units) = Setup time +

processing time, i.e., Tb = Tsu + QTc

For job shop production, Q = 1

So, Tb = Tsu + Tc = Tp How??

Tp = Tb / Q , whereTp= Avg prod. Time/workunit , min/pc

Rp = 60 / Tb , Where Rp = Hourly prod rate, pc/Hr

Production rate for

mass production

Production rate = cycle rate of the machine

Tb = Tsu + QTc

For mass production, Q = very large

Tp = Tb/Q = (Tsu + QTc ) / Q = Tsu /Q + QTc/Q

Tp = Tsu/Q +Tc

As Q becomes very large, Tsu/Q � 0

So, Tp = Tc

WKT, Production rate is reciprocal of production time

Rp = Rc = 60/Tc

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Production rate for

flow line mass production• Production rate = cycle rate of the production line

• Workstations are interdependent in the line

• Impossible to divide total work equally among all

workstations on the line.

• So, one station ends up with the longest

operation time ( Bottle neck station).

• Bottle neck station sets the pace to other

workstation.

• Work units should be moved from one

workstation to next (Tr )

Production rate for

flow line mass production

• Cycle time = transfer time + longest processing time

Tc = Tr + Max To -----------------5

• Where Max To = operation time at the bottle neck

station i.e., The maximum of operation times for all

stations on the line

• Tr = Transfer time

Rc = 60/Tc ----------------6

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Production capacity

• maximum rate of output that a production

facility (or production line, work center, or group

of work centers) is able to produce under a given

set of assumed operating conditions

• Operating conditions refer to the number of

shifts per day, number of days in the week (or

month) that the plant operates, employment

levels, and so forth.

Production capacityLet PCw = the production capacity of a given facility under

consideration.

Let the measure of capacity = the number of units produced per

week.

Let n = the number of machines or work centers in the facility.

A work center is a manufacturing system in the plant typically

consisting of one worker and one machine. It might also be one

automated machine with no worker, or multiple workers working

together on a production line.

It is capable of producing at a rate RP unit/hr. Each work center

operates for Hs hr/shift.

Let Sw denote the number of shifts per week.

PCw = n Sw Hs Rp --------------------7

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Production capacity

• If we include the possibility that each work

unit is routed through no operations, with

each operation requiring a new setup on

either the same or a different machine,

• where no = number of operations in the routingo

psw

n

RHnSPC = ---------8

Production Capacity

Plant capacity for facility in which parts are made in one operation (no = 1):

PCw = n Sw Hs Rp

where PCw = weekly plant capacity, units/wk

Plant capacity for facility in which parts require multiple operations (no > 1):

where no = number of operations in the routing

o

psw

n

RHnSPC =

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Production Capacity

Equation indicates the operating parameters that affect plant capacity.

Changes that can be made to increase or decrease plant capacity over the short term are:

1. Change the number of shifts per week (S). For example, Saturday shifts might be authorized to temporarily increase capacity.

2. Change the number of hours worked per shift (H). For example, overtime on each regular shift might be authorized to increase capacity.

o

psw

n

RHnSPC =

Over the intermediate or longer term, the following

changes can be made to increase plant capacity:

3. Increase the number of work centers, n, in the shop.

This might be done by using equipment that was

formerly not in use and hiring new workers.

4. Increase the production rate, Rp by making

improvements in methods or process technology.

5. Reduce the number of operations no required per work

unit by using combined operations, simultaneous

operations, or integration of operations.

Production Capacity

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Utilization• Utilization refers to the amount of output of a

production facility relative to its capacity. Expressing

U=Q/PC------------9

Where U = utilization of the facility,

Q = actual quantity produced by the facility during a given

time period (i.e., pc/wk), and

PC = production capacity for the same period (pc/wk).

It is often defined as the proportion of time that the

facility is operating relative to the time available under

the definition of capacity.

Utilization is usually expressed as a percentage.

Availability

• Availability is defined using two other reliability

terms, mean time between failure (MTBF) and

mean time to repair (MTTR).

• The MTBF indicates the average length of time

the piece of equipment runs between

breakdowns.

• The MTTR indicates the average time required to

service the equipment and put it back into

operation when a breakdown occurs.

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Availability

Availability is defined as follows:

Availability: A =

where MTBF = mean time between failures, and

MTTR = mean time to repair

Availability is typically expressed as a percentage

MTBFMTTRMTBF −

-----------10

Availability -

MTBF and MTTR Defined

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1) A production machine operates at 2 shifts/day and 5 days a week at full

capacity. Its production rate is 20 unit/hr. During a certain week, the machine

produced 1000 parts and was idle in the remaining time, (a) Determine the

production capacity of the machine, (b) What was the utilization of the machine

during the week under consideration?

if the availability of the machine is 90%, and the utilization of the machines

is 80%. Compute the expected plant output.

Solution:

(a) The capacity of the machine can be determined using the assumed

80-hr week as follows:

PC = 80(20) = 1600 unit/wk

(b) Utilization can be determined as the ratio of the number of parts

made by the machine relative to its capacity.

U = 1000/1600 = 0.625 (62.5%)

(c) U=Q/PC or

Q= UxPCxA or UAxnSHRp

2) The mean time between failures for a certain production machine is 250 hours,

and the mean time to repair is 6 hours. Determine the availability of the

machine.

Availability: A =

3) One million units of a certain product are to be manufactured annually on

dedicated production machines that run 24 hours per day. 5 days per week, 50

weeks per year, (a) If the cycle time of a machine to produce one part is 1.0

minute, how many of the dedicated machines will be required to keep up with

demand? Assume that availability, utilization, and worker efficiency = 100%, and

that no setup time will be lost, (b) Solve part (a) except that availability = 0.90.

Solution: Tc= 1 min

Tb = Tsu+QTc = 0+QTc

Tp= Tb/Q = Tc

Rp=60/Tp = 60 Parts/Hr

n= PC/SHRp

= 1000000/(50x5x24x60)

= 2.77 = 3 machines

MTBF

MTTRMTBF −

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Manufacturing Lead Time

Manufacturing lead time (MLT) is the total time required

to process a given part or product through the plant,

including any lost time due to delays, time spent in

storage, reliability problems, and so on.

� Production consists of a sequence of individual processing and

assembly operations. Between the operations are material

handling, storage, inspections, and other non productive activities.

� Divide these activities as operation and non operation elements.

� Non operation elements are Handling, temporary storage,

inspection and other sources of delay when work unit is not in

machine.

Let Tc = the operation cycle time at a given machine or workstation,

Tno = the nonoperation time associated with the same machine.

no = the number of separate operations through which the work unit

must be routed

Tsu = Setup time required to prepare each production machine for the

particular product. If we assume batch production, then there are

Q work units in the batch.,

Given these terms, we can define manufacturing lead time as

MLTj = where

MLTj = manufacturing lead time for part or product j (min).

Tsuji = setup time for operation i (min) for the product j,

Qj = quantity of part or product in the batch (pc),

Tcji = operation cycle time for operation i (min/pc),

Tnoji = nonoperation time associated with operation i (min), and

i indicates the operation sequence in the processing; i = I, 2,... noj

∑=

++ojn

inojicjijsuji TTQT

1

)( -----------11

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To simplify and generalize the model,

let us assume that all setup times, operation cycle times, and non

operation times are equal for the noj machines.

Further, let us suppose that the batch quantities of all parts or

products processed through the plant are equal and that they are

all processed through the same number of machines, so that noj =

no , With these simplifications, Eq. becomes:

MLT = no (Tsu + QTc + Tno)

where

MLT = manufacturing lead time,

no = number of operations,

Tsu = setup time,

Q = batch quantity,

Tc = cycle time per part, and

Tno = non-operation time

-----------12

• For a job shop in which the batch size is one (Q = 1), Eq.

(1.12) becomes

MLT=no(Tsu+TC+Tno)------------ (1.13)

For mass production, the Q term in Eq. (1.12) is very large

and dominates the other terms.

In the case of quantity type mass production in which a

large number of units are made on a single machine (no

=1). The MLT simply becomes the operation cycle time for

the machine after the setup has been completed and

production begins.

MLT = QxTc ------------1.14

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For flow line mass production, the entire production line is

set up in advance. Also, the non operation time

between processing steps is simply the transfer time Tr

to move the part or product from one workstation to

the next. The station with the longest operation time

sets the pace for all stations:

MLT =no(Tr +Max To) = noTc --------------1.15

Since , (Tr +Max To) = Tc (1.5)

Since the number of stations is equal to the number of

operations (n = no) Eq. (1.15) can also be stated as

MLT =n(Tr +Max To) = nTc --------------1.16

A certain part is produced in a batch size of 100 units. The batch must be routed

through five operations to complete the processing of the parts. Average

setup time is 3 hr/operation, and average operation time is 6 min . Average

non operation time due to handling, delays, inspections, etc., is 7 hours for

each operation. Determine how many days it will take to complete the batch,

assuming the plant runs one 8-hr shift/day.

Solution:

Given:

Q = 100 units

no = 5

Tsu = 3hr/operation

Tc = 6 min

Tno = 7 hr/operation

The manufacturing lead time is computed from Fq

MLT = no (Tsu + QTc + Tno)

MLT = 5(3 + 100 X 0.1 + 7) = 100 hours

At 8 hr/day. this amounts to L00/8 = 12.5 days.

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A certain part is routed through six machines in a batch production plant. The

setup and operation times for each machine are given in the table below. The

batch size is 100 and the average non operation time per machine is 12 hours.

Determine (a) manufacturing lead time and (b) production rate for operation

3.

Solution:

Given:

Q = 100 units

no = 5

Tsu = 3hr/operation

Tno = 12hr/machine

The manufacturing lead time is computed from Fq

MLT = ∑=

++ojn

inojicjijsuji TTQT

1

)(

A certain part is routed through six machines in a production plant. The

operation times for each machine are given in the table below. Suppose the

part is made in very large quantities on a production line in which an

automated work handling system is used to transfer parts between machines.

Transfer time between stations = 15 s. The total time required to set up the

entire line is 150 hours. Assume that the operation times at the individual

machines remain the same. Determine (a) manufacturing lead time for a part

coming off the line.(b) production rate for operation 3. and (c) theoretical

production rate for the entire production line.

Solution:

Given: a) MLT = no(Tr+MaxTo)

b) Rp3 = 60/Tp ; But Tp = Tc = To

c) Rp = 60/Tp; But Tp = Tc ; But Tc = Tr+Max To

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Work-In-Process

Work-in-process (WIP) is the quantity of parts or

products currently located in the factory that

either are being processed or are between

processing operations.

WIP is inventory that is in the state of being

transformed from raw material to finished

product.

Work-In-ProcessAn approximate measure of work-in-process can be obtained from the following, using terms previously defined:

WIP =

where WIP = work-in-process, pc;

A = availability, U = utilization,

PC = plant capacity, pc/wk;

MLT = manufacturing lead time, hr;

Sw = shifts per week,

Hsh = hours per shift, hr/shift

( ) ( )w sh

AU PC MLT

S H

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TIP Ratio

The TIP ratio measures the time that the product

spends in the plant relative to its actual

processing time.

It is computed as the total MLT for a part divided by

the sum of individual operation time for the

plant.

∑=

oT

MLTTIP

The average part produced in a certain batch manufacturing plant must be processed

sequentially through six machines on average. Twenty (20) new batches of parts are

launched each week. Average operation time = 6 minutes, average setup time = 5

hours, average batch size= 25 parts, and average non operation time per batch = 10

hr/machine. There are 18 machines in the plant working in parallel. Each of the

machines can be set up for any type of job processed in the plant. The plant operates an

average of 70 production hours per week. Scrap rate is negligible. Determine (a)

manufacturing lead time for an average part, (b) plant capacity, and (c) plant utilization,

(d) Determine the average level of work-in-process in the plant.

a) MLT = no( Tsu + QxTc + Tno )

b) PC = A.U. n.SwHs.Rp/no

c) U = Q/PC

d) WIP = A.U.PC.MLT/SwHs