Chapter 4 _ Lecture Notes.pdf

Chapter 4

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CHAPTER 4

INTRODUCTION TO

MANUFACTURING SYSTEMS

Outline

� Components of a Manufacturing System

� A Classification Scheme for Manufacturing Systems

� Overview of the Classification Scheme

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Outline

� Components of a Manufacturing System

� Production Machines

� Material Handling System

� Computer Control System

� Human Resources

� A Classification Scheme for Manufacturing Systems

� Type of Operations Performed

� Numbers of Workstations

� System Layout

� Automation & Manning Levels

� Part or Product Variety

� Overview of the Classification Scheme

� Single Station Cell

� Multi-Station Systems with Fixed Routing

� Multi-Station Systems with Variable Routing

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The position of the manufacturing system in the larger production system

Introduction to Manufacturing Systems

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Manufacturing System Definition:

A collection of integrated equipment &

human resources, whose function is to

perform one or more processing and/or

assembly operations on a starting raw

materials, part, or set of parts.

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� Equipment includes:

� Production machines and tools

� Material handling and work positioning devices

� Computer systems

� Human resources

� are required either full-time or periodically to

keep the system running

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� Manufacturing system is where the value-added

work is accomplished on the part or product

� Manufacturing Systems examples includes:

� Single-station cells

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One worker tending one production machine

that operates on semi-automatic cycle.






� Machine clusters

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One worker tends a group of semi-automatic

machines.

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� Manual assembly lines

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Human workers perform assembly tasks as the

product is moved along the line, usually by

mechanized conveyor.








� Automated transfer lines

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Series of automated workstations that perform

processing operations such as machining.

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� Automated assembly systems

� Machine cells (cellular manufacturing)

� Flexible manufacturing systems

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Production machines and workstations laid out

in a U-shaped configuration. Produce parts /

products that are similar but not identical.









� Automated assembly systems

� Machine cells (cellular manufacturing)

� Flexible manufacturing systems

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Highly automated machine cell that produces

part / product families.

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Components of a Manufacturing System

� A manufacturing system consists of several

components:

1. Production machines plus tools, fixtures & other

related hardware

2. Material handling system

3. Computer systems to coordinate and/or control the

above components

4. Human workers

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1. Production Machines

� In virtually all modern manufacturing systems, most of the actual processing or assembly work is accomplished by machines or with the aid of tools.

� Machines can be classified as:

� Manually operated

� Semi-automated

� Fully automated

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� Manually Operated:

� control or supervised by a human worker.

� machine provides the power for the operation and the worker provides the control.

� worker must be at machine continuously.

� i.e. lathes, milling machines, drill presses.

� Semi-Automated:

� performs a portion of the work cycle under some from of program control, and human worker tends to the machine for the remainder of the cycle, by loading and unloading it or performing some other task each cycle.

� i.e. CNC lathe controlled.

� Fully Automated:

� operates for extended periods of time with no human attention (attention is required not during each cycle but maybe required periodically after certain no. of cycles– i.e. to load raw materials).

� i.e. injection molding machines.

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Manually operated machines are controlled or

supervised by a human worker. The machine provides the

power for the operation and the worker provides the

control. The entire work cycle is operator controlled.

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A semi-automated machine performs a portion of the

work cycle under some form of program control, and a

worker tends to the machine for the remainder of the

cycle. Typical worker tasks include loading and unloading

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A fully-automated machine operates for extended periods (longer than one work cycle) without worker attention

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� In manufacturing systems, term workstation is

used to refer to a location in the factory where

some well-defined task/operation is

accomplished by an automated machine, a

worker-and-machine combination, or a

worker using hand tools and/or portable

power tools

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2. Material Handling System

� The following material handling functions must be provided:

1. Loading work units at each station

2. Positioning the work units at each station

3. Unloading work units at each station

4. Transportation of work units between station in multi-station manufacturing systems

5. Temporary storage function

� To ensure that work is always present for the respective stations.

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� Work Transport Between Stations� Work transport – moving parts between workstations in a multi-station system

� Can be accomplished either manually or using equipment

� 2 general categories:� Fixed routing:

� Work units always flow through the same sequence of workstations.

� It means that works units are identical or similar enough that the processing sequence is identical.

� Most production lines exemplify this category.

� Variable routing:

� Work units are transported through a variety of different station sequences.

� It means that the manufacturing system is processing or assembling different work units.

� Most job shops exemplify this category.

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Two types of routing in multi-station manufacturing systems

(a) Fixed Routing (b) Variable Routing

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3. Computer Control System

� required to control automated & semi-automated equipment, and

� to participate in the overall coordination & managementof the manufacturing system

� Typical functions:� Communicate instructions to workers

� Download part programs to computer-controlled machines

� Control material handling system

� Schedule production

� Failure diagnosis when malfunctions occur

� Safety monitoring

� Maintain quality control

� Operations management – directly / indirectly

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4. Human Resources

� Direct labor� Perform some or all of the value-added work that is accomplished on the parts or products.

� They directly add to the value of the work unit by performing manual work on it or by controlling the machines that perform the work.

� Indirect Labor� Manage/support manufacturing systems, even for fully automated manufacturing systems

� i.e. computer programmers, computer operators, maintenance & repair personnel, etc.

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A Classification Scheme of Manufacturing Systems

� Explore variety of manufacturing system types and develop

a classification scheme based on factors that define &

distinguish them

� Factors that define and distinguish manufacturing systems:

1. Types of operations

2. Number of workstations

3. System layout

4. Automation and manning level

5. Part or product variety

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1. Types of Operations Performed

� Manufacturing systems are distinguished by

the types of operations they perform

(Processing versus assembly operations)

� At the highest level, the distinction is between:

� Processing operations on individual work units

� Assembly operations to combine individual processing

and assembled entities

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1. Types of Operations Performed

� Additional parameters of the product that play a role in determining the design of manufacturing systems: � Type of material processed

� Processing operation used for metals are different from those used for plastics or ceramics.

� Differences affect the type of equipment and handling method.

� Size and weight of work units

� Part or product complexity� For assembled products, number of components per product

� For individual parts, number of distinct operations to complete processing

� Part geometry� For machined parts, rotational vs. non-rotational

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2. Number of workstations

� Convenient measure of the size of the system

� Let n = number of workstations

� Individual workstations can be identified by subscript

i, where i = 1, 2, ..., n

� Affects performance factors such as workload

capacity, production rate, and reliability

� As n increases, this usually means greater workload

capacity and higher production rate

� There must be a synergistic effect that derives from n

multiple stations working together vs. n single

stations

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3. System Layout

� The way the system is laid out.

� Applies mainly to multi-station systems

� Fixed routing vs. variable routing

� In systems with fixed routing, workstations are

usually arranged linearly

� In systems with variable routing, a variety of

layouts are possible

� System layout is an important factor in

determining the most appropriate type of

material handling system

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3. System Layout

� Number of Workstations and System Layout� No. of workstations is a key factor in this classification scheme (applicable to both processing or assembly operations)

Type I Single station - the simplest case, consisting of one workstation (n=1), usually including a production machine that can be manually operated, semi- automated, or fully automated.

Type II Multiple stations with variable routing. Consist 2 or more stations (n>1) that are designed and arranged to accommodate the processing or assembly of different part or product styles.

Type III Multiple stations with fixed routing. This system has 2 or more workstations (n>1), which are laid out as a production line.

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4. Automation and Manning Levels

� Level of Automation - another factor that characterizes the manufacturing system.

� Level of workstation automation

� Manually operated

� Semi-automated

� Fully automated

� Manning Level (Mi ) of a workstation � proportion of time that a worker is in attendance at the station.

� If Mi = 1 station i� one worker must be at station i continuously.

� If one worker attends 4 machines, then Mi = 0.25 for each of the 4 machines.

� In general;

� Mi ≥ 1 � indicate manual operations at the workstations

� Mi < 1 � indicate some form of automation operations at the workstations

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4. Automation and Manning Levels

� The average manning level of multi-station

manufacturing system:

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M = average manning level for the system

Wu = no. of utility workers assigned to the system

Wi = no. of workers assigned specifically to the station i, for i=1,2,�,n

W = total no. of workers assigned to the system

n=number of workstations

n

w

n

ww

M

n

i

iu

=

+

=

∑=1

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(Additional Information)

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5. Part of Product Variety

� 5th factor in manufacturing system characterization is the

degree to which the system is capable of dealing with

variations in the parts or products it produces

� Possible variations examples:

� Variations in type and/or color of plastic of molded parts in

injection molding.

� Variations in electronic components placed on a standard size

printed circuit board.

� Variations in the size of printed boards handled by a component

placement machine.

� Variations in geometry of machine parts.

� Variations in parts and options in an assembled product on a

final assembly line.

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� 3 cases of product variety in manufacturing systems:

1) Single-model case

� all parts or products are identical

2) Batch-model case

� different parts or products are produced by the

system, but they are produced in batches because

changeovers are required

3) Mixed-model case

� different parts or products are produced by the

system, but the system can handle the differences

without the need for time-consuming changes in

setup

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(a) Single-model case, (b) batch model case, and

(c) mixed-model case

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� In order to be flexible, a manufacturing systems must possess the following capabilities:

� Identification of the different work units

�The system must be able to identify the differences between work units in order to perform the correct processing sequence

� Quick changeover of operating instructions

�The required work cycle programs must be readily available to the control unit

� Quick changeover of the physical setup

�System must be able to change over the fixtures and tools required for the next work unit in minimum time

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Medium or high part or product complexity (high total work content)

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Low part or product complexity (low total work content)

Overview of the Classification Scheme

� Single-station cells� n = 1

� Manual or automated

� Multi-station systems with fixed routing

� n > 1

� Typical example: production line

� Multi-station systems with variable routing

� n > 1

� Typical case in cellular manufacturing

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1. Single Station Cells

� n = 1

� Two categories:

� Manned workstations - manually operated or semi-

automated production machine (M = 1)

� Fully automated machine (M < 1)

� Most widely used manufacturing system - reasons:

� Easiest and least expensive to implement

� Most adaptable, adjustable, and flexible system

� Can be converted to automated station if demand for part

or product justifies

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2. Multi-Station Systems with Fixed Routing

� n > 1

� Common example = production line - a series of

workstations laid out so that the part or product moves

through each station, and a portion of the total work

content is performed at each station

� Conditions favoring the use of production lines:

� Quantity of work units is high

� Work units are similar or identical, so similar operations are

required in the same sequence

� Total work content can be divided into separate tasks of

approximately equal duration

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3. Multi-Station Systems with Variable Routing

� n > 1

� Defined as a group of workstations organized to achieve some special purpose, such as:

� Production of a family of parts requiring similar (but not identical) processing operations

� Assembly of a family of products requiring similar (but not identical) assembly operations

� Production of a complete set of components used to assemble one unit of a final product

� Typical case in cellular manufacturing

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Chapter 4 _ Lecture Notes.pdf