Manufacturing system in automated line

1. UNIT 3 :
MANUFACTURING SYSTEMS
M.TECH. : AUTOMATION AND
ROBOTICS
INDUSTRIAL AUTOMATION

2. MANUFACTURING SYSTEMS
1. Introduction to Manufacturing Systems
2. Single-Station Manufacturing Cells
3. Manual Assembly Lines
4. Automated Production Lines
5. Automated Assembly Systems

3. Manufacturing Systems in the
Production System

4. Introduction to
Manufacturing Systems
Sections:
1. Components of a Manufacturing System
2. A Classification Scheme for Manufacturing Systems
3. Overview of the Classification System

5. Manufacturing System Defined
A collection of integrated equipment and human resources,
whose function is to perform one or more processing
and/or assembly operations on a starting raw material,
part, or set of parts
▪ 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

6. Examples of Manufacturing Systems
▪ Single-station cells
▪ Machine clusters
▪ Manual assembly lines
▪ Automated transfer lines
▪ Automated assembly systems
▪ Machine cells (cellular manufacturing)
▪ Flexible manufacturing systems

7. Components of a
Manufacturing System
1. Production machines
2. Material handling system
3. Computer system to coordinate and/or control the
preceding components
4. Human workers to operate and manage the system

8. 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
▪ Classification of production machines:
1. Manually operated machines are controlled or
supervised by a human worker
2. Semi-automated machines perform a portion of the
work cycle under some form of program control, and a
worker tends the machine the rest of the cycle
3. Fully automated machines operate for extended
periods of time with no human attention

9. Manually Operated Machine
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.

10. Semi-Automated Machine
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 parts

11. Fully-Automated Machine
Machine operates for extended periods (longer than one
work cycle) without worker attention

12. Material Handling System
▪ In most manufacturing systems that process or assemble
discrete parts and products, the following material
handling functions must be provided:
1. Loading work units at each station
2. Positioning work units at each station
3. Unloading work units at each station
4. Transporting work units between stations in
multi-station systems
5. Temporary storage of work units

13. Work Transport Between Stations
▪ Two general categories of work transport in multi-station
manufacturing systems:
1. Fixed routing
▪ Work units always flow through the same
sequence of workstations
▪ Most production lines exemplify this category
2. Variable routing
▪ Work units are moved through a variety of different
station sequences
▪ Most job shops exemplify this category

14. (a) Fixed Routing and
(b) Variable Routing

15. Computer Control System
▪ Typical computer functions in a manufacturing system:
▪ Communicate instructions to workers
▪ Download part programs to computer-controlled
machines
▪ Control material handling system
▪ Schedule production
▪ Failure diagnosis when malfunctions occur
▪ Safety monitoring
▪ Quality control
▪ Operations management

16. Types of Manufacturing Systems
▪ 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

17. Types of Operations Performed
▪ Processing versus assembly operations
▪ Type(s) of materials processed
▪ 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

18. 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

19. System Layout
▪ 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

20. Automation and Manning Levels
▪ Level of workstation automation
▪ Manually operated
▪ Semi-automated
▪ Fully automated
▪ Manning level Mi
= proportion of time worker is in
attendance at station i
▪ Mi
= 1 means that one worker must be at the station
continuously
▪ Mi
≥ 1 indicates manual operations
▪ Mi
< 1 usually denotes some form of automation

21. Part or Product Variety:
Flexibility
The degree to which the system is capable of dealing with
variations in the parts or products it produces
▪ Three cases:
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

22. Three Cases of Product Variety
in Manufacturing Systems
(a) Single-model case, (b) batch model case, and
(c) mixed-model case

23. Enablers of Flexibility
▪ 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

24. Classification of Manufacturing System
Three basic types of manufacturing systems can
be identified:
▪Single-station cells,
▪Multi-station systems with fixed routing, and
▪Multi-station systems with variable routing.

26. Single-Station Cells
▪ Applications of single-station cells are widespread.
▪ The typical case is a worker-machine cell.
▪ Two categories are distinguished:
▪ (1) manned cells in which a worker must be present
each work cycle, and
▪ (2) automated cells, in which periodic attention is
required less frequently than every cycle. In either case,
these systems
▪ In either case, these systems are used for processing
as well as assembly operations.

27. Single-Station Cells
▪ Examples of single-station cells include the following:
▪ • Worker operating an engine lathe (manually operated
machine)
▪ • Worker loading and unloading a CNC lathe
(semi-automated machine)
▪ • Welder and fitter working in an arc-welding operation
(manually operated equipment)

28. Single-Station Cells
▪ • CNC turning center with parts carousel operating
unattended using a robot to load and unload parts (fully
automated machine).
▪ Single-station cells : This type of manufacturing system is
popular because
▪ (1) it is the easiest and least expensive manufacturing
system to implement, especially the manned version;
▪ (2) it is arguably the most adaptable, adjustable, and
flexible manufacturing system; and
▪ (3) a manned single workstation can be converted to an
automated station if demand for the parts or products
made in the station justify this conversion.

29. Multi-station Systems with Fixed Routing.
▪ A multi-station manufacturing system with
fixed routing is a production line, which
consists of a series of workstations laid out
so that the work unit moves from one
station to the next, and a portion of the total
work content is performed on it at each
station.

30. Multi-station Systems with Fixed Routing.
▪ Transfer of work units from one station to the next
is usually accomplished by a conveyor or other
mechanical transport system.
▪ However, in some cases the work is simply
pushed between stations by hand.
▪ Production lines are generally associated with
mass production, although they can also be
applied in batch production.

31. Multi-station Systems with Fixed
Routing
▪ Examples of multi-station systems with fixed routing
include the following:
▪ • Manual assembly line that produces small power tools
(manually operated workstations)
▪ • Machining transfer line (automated workstations)
▪ • Automated assembly machine with a carousel system
for work transport (automated workstations)
▪ • Automobile final assembly plant, in which many of the
spot welding and spray painting operations are
automated while general assembly is manual (hybrid
system).

32. Multi-station systems with variable routing
▪ variable routing is a group of workstations organized to
produce a limited range of part or
▪ product styles in medium production quantities (typically
100–10,000 units annually). The
▪ differences in part or product styles mean differences in
operations and sequences of operations
▪ that must be performed. The system must possess
flexibility in order to cope with this
▪ variety. Examples of multiple-station systems with variable
routing include the following:
▪ are discussed in Chapter 19.

33. ▪ • Manned machine cell designed to produce a family of
parts with similar geometric
▪ features (manually operated machines)
▪ • Flexible manufacturing system with several CNC
machine tools connected by an
▪ automated conveyor system and operating under
computer control (automated
▪ workstations).
▪ The first example represents cellular manufacturing that
uses the principles of
▪ group technology, discussed in Chapter 18. The flexible
manufacturing system in the second
▪ example is a fully automated system. Flexibility and
Multi-station systems with variable routing

34. Manufacturing Systems for Medium or
High Product Complexity

35. Manufacturing Systems for Low
Product Complexity

36. Overview of 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

37. Single-Station Cells
▪ n = 1
▪ Two categories:
1. Manned workstations - manually operated or
semi-automated production machine (M = 1)
2. 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

38. 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

39. 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

40. Single-Station Manufacturing Cells
Sections:
1. Single-Station Manned Workstations
2. Single-Station Automated Cells
3. Applications of Single-Station Cells
4. Analysis of Single-Station Cells

41. Classification of
Single-Station Manufacturing Cells

42. Single-Station Manufacturing Cells
▪ Most common manufacturing system in industry
▪ Operation is independent of other stations
▪ Perform either processing or assembly operations
▪ Can be designed for:
▪ Single model production
▪ Batch production
▪ Mixed model production

43. Single-Station Manned Cell
One worker tending one production machine (most
common model)
▪ Most widely used production method, especially in
job shop and batch production
▪ Reasons for popularity:
▪ Shortest time to implement
▪ Requires least capital investment
▪ Easiest to install and operate
▪ Typically, the lowest unit cost for low production
▪ Most flexible for product or part changeovers

44. Single-Station Manned Cell Examples
▪ Worker operating a standard machine tool
▪ Worker loads & unloads parts, operates machine
▪ Machine is manually operated
▪ Worker operating semi-automatic machine
▪ Worker loads & unloads parts, starts semi-automatic
work cycle
▪ Worker attention not required continuously during
entire work cycle
▪ Worker using hand tools or portable power tools at one
location

45. Variations of
Single-Station Manned Cell
▪ Two (or more) workers required to operate machine
▪ Two workers required to manipulate heavy forging at
forge press
▪ Welder and fitter in arc welding work cell
▪ One principal production machine plus support equipment
▪ Drying equipment for a manually operated injection
molding machine
▪ Trimming shears at impression-die forge hammer to
trim flash from forged part

46. Single-Station Automated Cell
Fully automated production machine capable of
operating unattended for longer than one work cycle
▪ Worker not required except for periodic tending
▪ Reasons why it is important:
▪ Labor cost is reduced
▪ Easiest and least expensive automated system to
implement
▪ Production rates usually higher than manned cell
▪ First step in implementing an integrated
multi-station automated system

47. Enablers for
Unattended Cell Operation
▪ For single model and batch model production:
▪ Programmed operation for all steps in work cycle
▪ Parts storage subsystem
▪ Automatic loading, unloading, and transfer between
parts storage subsystem and machine
▪ Periodic attention of worker for removal of finished work
units, resupply of starting work units, and other machine
tending
▪ Built-in safeguards to avoid self-destructive operation or
damage to work units

48. Enablers for
Unattended Cell Operation
▪ For mixed model production:
▪ All of the preceding enablers, plus:
▪ Work unit identification:
▪ Automatic identification (e.g., bar codes) or
sensors that recognize alternative features of
starting units
▪ If starting units are the same, work unit
identification is unnecessary
▪ Capability to download programs for each work unit
style (programs prepared in advance)
▪ Capability for quick changeover of physical setup

49. Parts Storage Subsystem and
Automatic Parts Transfer
▪ Necessary conditions for unattended operation
▪ Given a capacity = np
parts in the storage subsystem, the
cell can theoretically operate for a time
UT = np
Tc
where UT = unattended time of operation
▪ In reality, unattended time will be less than UT because
the worker needs time to unload finished parts and load
raw workparts into the storage subsystem

50. Parts Storage Capacity
▪ Typical objectives in defining the desired parts storage
capacity np
:
▪ Make np
Tc
= a fixed time interval that allows one worker
to tend multiple machines
▪ Make np
Tc
= time between scheduled tool changes
▪ Make np
Tc
= one complete shift
▪ Make np
Tc
= one overnight (“lights-out operation”)

51. Storage Capacity of One Part
▪ Example: two-position automatic pallet changer (APC)
▪ With no pallet changer, work cycle elements of
loading/unloading and processing would have to be
performed sequentially
Tc
= Tm
+ Ts
where Tm
= machine time and Ts
= worker service time
▪ With pallet changer, work cycle elements can be
performed simultaneously
Tc
= Max{Tm
, Ts
} + Tr
where Tr
= repositioning time of pallet changer

52. CNC Machining Center with Automatic
Pallet Changer - Stores One Part

53. Storage Capacities Greater Than One
▪ Machining centers:
▪ Various designs of parts storage unit interfaced to
automatic pallet changer (or other automated
transfer mechanism)
▪ Turning centers:
▪ Industrial robot interface with parts carousel
▪ Plastic molding or extrusion:
▪ Hopper contains sufficient molding compound for
unattended operation
▪ Sheet metal stamping:
▪ Starting material is sheet metal coil

54. Storage Capacities Greater Than One
Machining center and automatic pallet changer with pallet
holders arranged radially; parts storage capacity = 5

55. Storage Capacities Greater Than One
Machining center and in-line shuttle cart system with pallet
holders along its length; parts storage capacity = 16

56. Storage Capacities Greater Than One
Machining center with pallets held on indexing table; parts
storage capacity = 6

57. Storage Capacities Greater Than One
Machining center and parts storage carousel with parts
loaded onto pallets; parts storage capacity = 12

58. Applications of Single Station
Manned Cells
▪ CNC machining center with worker to load/unload
▪ CNC turning center with worker to load/unload
▪ Cluster of two CNC turning centers with time sharing of
one worker to load/unload
▪ Plastic injection molding on semi-automatic cycle with
worker to unload molding, sprue, and runner
▪ One worker at electronics subassembly workstation
inserting components into PCB
▪ Stamping press with worker loading blanks and unloading
stampings each cycle

59. Applications of Single Station
Automated Cells
▪ CNC MC with APC and parts storage subsystem
▪ CNC TC with robot and parts storage carousel
▪ Cluster of ten CNC TCs, each with robot and parts
storage carousel, and time sharing of one worker to
load/unload the carousels
▪ Plastic injection molding on automatic cycle with robot
arm to unload molding, sprue, and runner
▪ Electronics assembly station with automated insertion
machine inserting components into PCBs
▪ Stamping press stamps parts from long coil

60. CNC Machining Center
Machine tool capable of performing multiple operations that
use rotating tools on a workpart in one setup under NC
control
▪ Typical operations: milling, drilling, and related operations
▪ Typical features to reduce nonproductive time:
▪ Automatic tool changer
▪ Automatic workpart positioning
▪ Automatic pallet changer

61. CNC Horizontal Machining Center

62. CNC Turning Center
Machine tool capable of performing multiple operations on a
rotating workpart in one setup under NC control
▪ Typical operations:
▪ Turning and related operations, e.g., contour turning
▪ Drilling and related operations along workpart axis of
rotation

63. CNC Turning Center

64. Automated Stamping Press
Stamping press on automatic cycle producing stampings
from sheet metal coil

65. CNC Mill-Turn Center
Machine tool capable of performing multiple operations either
with single point turning tools or rotating cutters in one
setup under NC control
▪ Typical operations:
▪ Turning, milling, drilling and related operations
▪ Enabling feature:
▪ Capability to control position of c-axis in addition to x-
and z-axis control (turning center is limited to x- and
z-axis control)

66. Part with Mill-Turn Features
Example part with turned, milled, and drilled features

67. Sequence of Operations of a
Mill-Turn Center for Example Part
(1) Turn smaller diameter, (2) mill flat with part in
programmed angular positions, four positions for square
cross section; (3) drill hole with part in programmed
angular position, and (4) cutoff of the machined piece

68. Manual Assembly Lines
Sections:
1. Fundamentals of Manual Assembly Lines
2. Analysis of Single Model Assembly Lines
3. Line Balancing Algorithms
4. Mixed Model Assembly Lines
5. Workstation Considerations
6. Other Considerations in Assembly Line Design
7. Alternative Assembly Systems

69. Manual Assembly Lines
▪ Factors favoring the use of assembly lines:
▪ High or medium demand for product
▪ Identical or similar products
▪ Total work content can be divided into work elements
▪ It is technologically impossible or economically
infeasible to automate the assembly operations
▪ Most consumer products are assembled on manual
assembly lines

70. Why Assembly Lines
are so Productive
▪ Specialization of labor
▪ Learning curve
▪ Interchangeable parts
▪ Components made to close tolerances
▪ Work flow principle
▪ Products are brought to the workers
▪ Line pacing
▪ Workers must complete their tasks within the cycle time
of the line

71. Manual Assembly Line Defined
A production line consisting of a sequence of workstations
where assembly tasks are performed by human workers
as the product moves along the line
▪ Organized to produce a single product or a limited range
of products
▪ Each product consists of multiple components joined
together by various assembly work elements
▪ Total work content - the sum of all work elements
required to assemble one product unit on the line

72. Manual Assembly Line
Configuration of a manual assembly line with n
manually operated workstations

73. Typical Products
Made on Assembly Lines
Automobiles Personal computers
Cooking ranges Power tools
Dishwashers Refrigerators
Dryers Telephones
Furniture Toasters
Lamps Trucks
Luggage Video DVD players
Microwave ovens Washing machines

74. Manual Assembly Line
▪ Products are assembled as they move along the line
▪ At each station a portion of the total work content is
performed on each unit
▪ Base parts are launched onto the beginning of the line at
regular intervals (cycle time)
▪ Workers add components to progressively build the
product

75. Assembly Workstation
A designated location along the work flow path at which
one or more work elements are performed by one or
more workers
Typical operations performed at manual assembly stations
Adhesive application
Sealant application
Arc welding
Spot welding
Electrical connections
Component insertion
Press fitting
Riveting
Snap fitting
Soldering
Stitching/stapling
Threaded fasteners

76. Work Transport Systems
▪ Two basic categories:
▪ Manual
▪ Mechanized

77. Manual Work Transport Systems
▪ Work units are moved between stations by the workers
without the aid of a powered conveyor
▪ Types:
▪ Work units moved in batches
▪ Work units moved one at a time
▪ Problems:
▪ Starving of stations
▪ Blocking of stations
▪ No pacing

78. Mechanized Work Transport Systems
▪ Work units are moved by powered conveyor or other
mechanized apparatus
▪ Categories:
▪ Work units attached to conveyor
▪ Work units are removable from conveyor
▪ Problems
▪ Starving of stations
▪ Incomplete units

79. Types of Mechanized Work Transport
▪ Continuous transport
▪ Conveyor moves at constant speed
▪ Synchronous transport
▪ Work units are moved simultaneously with
stop-and-go (intermittent) motion to next stations
▪ Asynchronous transport
▪ Work units are moved independently between
workstations
▪ Queues of work units can form in front of each
station

80. Continuous Transport
Conveyor moves at constant velocity vc

81. Synchronous Transport
All work units are moved simultaneously to their
respective next workstations with quick, discontinuous
motion

82. Material Handling Equipment for
Mechanized Work Transport
Continuous transport Overhead trolley conveyor
Belt conveyor
Drag chain conveyor
Synchronous transport Walking beam
Rotary indexing machine
Asynchronous transport Power-and-free conveyor
Cart-on-track conveyor
Automated guided vehicles

83. Line Balancing Problem
▪ Given:
▪ Total work content consists of many distinct work
elements
▪ The sequence in which the elements can be performed
is restricted
▪ The line must operate at a specified cycle time
▪ Problem:
▪ To assign the individual work elements to workstations
so that all workers have an equal amount of work to
perform

84. Components of Cycle Time Tc
Components of cycle time at several workstations on a
manual assembly line. At the bottleneck station, there is
no idle time.

85. Precedence Constraints
▪ Restrictions on the order in which work elements can be
performed
Precedence
diagram

86. Other Considerations in Line Design
▪ Line efficiency
▪ Management is responsible to maintain line operation
at efficiencies (proportion uptime) close to 100%
▪ Implement preventive maintenance
▪ Well-trained emergency repair crews to quickly fix
breakdowns when they occur
▪ Avoid shortages of incoming parts to avoid forced
downtime
▪ Insist on highest quality components from suppliers
to avoid downtime due to poor quality parts

87. Other Considerations - continued
▪ Methods analysis
▪ To analyze methods at bottleneck or other troublesome
workstations
▪ Subdividing work elements
▪ It may be technically possible to subdivide some work
elements to achieve a better line balance
▪ Sharing work elements between two adjacent stations
▪ Alternative cycles between two workers

88. Other Considerations - continued
▪ Utility workers
▪ To relieve congestion at stations that are temporarily
overloaded
▪ Changing workhead speeds at mechanized stations
▪ Increase power feed or speed to achieve a better line
balance
▪ Preassembly of components
▪ Prepare certain subassemblies off-line to reduce work
content time on the final assembly line

89. Other Considerations - continued
▪ Storage buffers between stations
▪ To permit continued operation of certain sections of the
line when other sections break down
▪ To smooth production between stations with large task
time variations
▪ Parallel stations
▪ To reduce time at bottleneck stations that have
unusually long task times

90. Other Considerations - continued
▪ Zoning constraints - limitations on the grouping of work
elements and/or their allocation to workstations
▪ Positive zoning constraints
▪ Work elements should be grouped at same
station
▪ Example: spray painting elements
▪ Negative zoning constraints
▪ Elements that might interfere with each other
▪ Separate delicate adjustments from loud noises

91. Other Considerations - continued
▪ Position constraints
▪ Encountered in assembly of large products such as
trucks and cars, making it difficult for one worker to
perform tasks on both sides of the product
▪ To address, assembly workers are positioned on both
sides of the line

92. Alternative Assembly Systems
▪ Single-station manual assembly cell
▪ Worker teams
▪ Automated assembly systems

93. Single-Station Manual Cell
▪ A single workstation in which all of the assembly work is
accomplished on the product or on some major
subassembly
▪ Common for complex products produced in small
quantities, sometimes one-of-a-kind
▪ Custom-engineered products
▪ Prototypes
▪ Industrial equipment (e.g., machine tools)

94. Assembly by Worker Teams
▪ Multiple workers assigned to a common assembly task
▪ Workers set their own pace
▪ Examples
▪ Single-station cell with multiple workers
▪ Swedish car assembly (job enlargement) - product
is moved through multiple workstations by AGVS,
but same worker team follows it from station to
station

95. Reported Benefits of Team Assembly
▪ Greater worker satisfaction
▪ Better product quality
▪ Increased capability to cope with model variations
▪ Greater ability to cope with problems that require more
time rather than stopping the entire production line
▪ Disadvantage:
▪ Team assembly is not capable of the high production
rates of a conventional assembly line