Cellular Manufacturing Systems - ADDVALUE - Nilesh Arora

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Cellular Manufacturing
by
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ORIGINS

• FLANDERS PRODUCT ORIENTED DEPARTMENTS FOR
  STANDARIZED PRODUCTS WITH MINIMAL TRANSPORTATION
  (1925)
• SOKOLOVSKI/MITROFANOV PARTS WITH SIMILAR
  FEATURES MANUFACTURED TOGETHER

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BASIC PRINCIPLE

• SIMILAR THINGS SHOULD BE DONE SIMILARLY
• THINGS
• PRODUCT DESIGN
• PROCESS PLANNING
• FABRICATION ASSEMBLY
• PRODUCTION CONTROL
• ADMINISTRATIVE FUNCTIONS

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TENETS OF GROUP TECHNOLOGY

• DIVIDE THE MANUFACTURING FACILITY INTO SMALL
  GROUPS OR CELLS OF MACHINES (1-5)
• THIS IS CALLED CELLULAR MANUFACTURING

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SYMPTOMS FOR RE-LAYOUT

• Symptoms that allow us to detect the need for a
  re-layout
• Congestion and bad utilization of space.
• Excessive stock in process at the facility.
• Long distances in the work flow process.
• Simultaneous bottle necks and workstations with
  idle time.
• Qualified workers carrying out too many simple
  operations.
• Labor anxiety and discomfort. Accidents at the
  facility.
• Difficulty in controlling operations and
  personnel.

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What is Group Technology (GT)?

• GT is a theory of management based on the
  principle that similar things should be done
  similarly
• GT is the realization that many problems are
  similar, and that by grouping similar problems, a
  single solution can be found to a set of problems
  thus saving time and effort
• GT is a manufacturing philosophy in which similar
  parts are identified and grouped together to take
  advantage of their similarities in design and
  production

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Implementing GT

• Where to implement GT?
• ?Plants using traditional batch production and
  ?process type layout
• ? If the parts can be grouped into part families
• ?How to implement GT?
• ?Identify part families
• ?Rearrange production machines into machine cells

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Types of Layout

• In most of todays factories it is possible to
  divide all the made components into families and
  all the machines into groups, in such a way that
  all the parts in each family can be completely
  processed in one group only.
• The three main types of layout are
• Line (product) Layout
• Functional Layout
• Group Layout

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Line (product) Layout

• It involves the arrangements of machines in one
  line, depending on the sequence of operations. In
  product layout, if there is a more than one line
  of production, there are as many lines of
  machines.
• Line Layout is used at present in simple process
  industries, in continuous assembly, and for mass
  production of components required in very large
  quantities.

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Functional Layout

• In Functional Layout, all machines of the same
  type are laid out together in the same section
  under the same foreman. Each foreman and his team
  of workers specialize in one process and work
  independently. This type of layout is based on
  process specialization.

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Group Layout

• In Group Layout, each foreman and his team
  specialize in the production of one list of parts
  and co-operate in the completion of common task.
  This type of layouts based on component
  specialization.

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The Difference between group and functional
layout
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Evaluations of cell system design are incomplete
unless they relate to the Cell Design.
Evaluation criteria of Cell Design

• A few typical performance variables related to
  system operation are
• Equipment utilization (high)
• Work-in-process inventory (low)
• Queue lengths at each workstation (short)
• Job throughput time (short)
• Job lateness (low)

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Cell Formation Approach

• Machine - Component Group Analysis
• Machine - Component Group Analysis is based on
  production flow analysis

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Machine - Component Group Analysis

• Production flow analysis involves four stages
• Stage 1 Machine classification.
• Machines are classified on the basis of
  operations that can be performed on them. A
  machine type number is assigned to machines
  capable of performing similar operations.

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Production flow analysis involves four stages
Machine - Component Group Analysis

• Stage 2 Checking parts list and production
  route information.
• For each part, information on the operations to
  be undertaken and the machines required to
  perform each of these operations is checked
  thoroughly.

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Production flow analysis involves four stages
Machine - Component Group Analysis

• Stage 3 Factory flow analysis.
• This involves a micro-level examination of flow
  of components through machines. This, in turn,
  allows the problem to be decomposed into a number
  of machine-component groups.

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Production flow analysis involves four stages
Machine - Component Group Analysis

• Stage 4 Machine-component group analysis.
• An intuitive manual method is suggested to
  manipulate the matrix to form cells. However, as
  the problem size becomes large, the manual
  approach does not work. Therefore, there is a
  need to develop analytical approaches to handle
  large problems systematically.

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Machine - Component Group Analysis
Example Consider a problem of 4 machines and 6
parts. Try to group them.
Components
Machines 1 2 3 4 5 6
M1 1 1 1
M2 1 1 1
M3 1 1 1
M4 1 1 1
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Machine - Component Group Analysis
Solution
Components
Machines 2 4 6 1 3 5
M1 1 1 1
M2 1 1 1
M3 1 1 1
M4 1 1 1
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Cellular Layout
Process (Functional) Layout
Group (Cellular) Layout
A cluster or cell
Similar resources placed together
Resources to produce similar products placed
together
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Group Technology (CELL) Layouts

• One of the most popular hybrid layouts uses Group
  Technology (GT) and a cellular layout
• GT has the advantage of bringing the efficiencies
  of a product layout to a process layout
  environment

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Process Flows before the Use of GT Cells
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Process Flows after the Use of GT Cells
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Designing Product Layouts

• Designing product layouts requires consideration
  of
• Sequence of tasks to be performed by each
  workstation
• Logical order
• Speed considerations line balancing

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Designing Product Layouts cont

• Step 1 Identify tasks immediate predecessors
• Step 2 Determine TAKT TIME
• Step 3 Determine cycle time
• Step 4 Compute the Theoretical Minimum number of
  Stations
• Step 5 Assign tasks to workstations (balance the
• line)
• Step 6 Compute efficiency, idle time balance
  delay

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Step 1 Identify Tasks Immediate Predecessors
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Layout Calculations

• Step 2 Determine TAKT TIME
• Vicki needs to produce 60 pizzas per hour
• TAKT TIME 60 sec/unit
• Step 3 Determine cycle time
• The amount of time each workstation is allowed to
  complete its tasks
• Limited by the bottleneck task (the longest task
  in a process)

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Layout Calculations

• Step 4 Compute the theoretical minimum number of
  stations
• TM number of stations needed to achieve 100
  efficiency (every second is used)
• Always round up (no partial workstations)
• Serves as a lower bound for our analysis

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Layout Calculations

• Step 5 Assign tasks to workstations
• Start at the first station choose the longest
  eligible task following precedence relationships
• Continue adding the longest eligible task that
  fits without going over the desired cycle time
• When no additional tasks can be added within the
  desired cycle time, begin assigning tasks to the
  next workstation until finished

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Last Layout Calculation

• Step 6 Compute efficiency and balance delay
• Efficiency () is the ratio of total productive
  time divided by total time
• Balance delay () is the amount by which the line
  falls short of 100

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Other Product Layout Considerations

• Shape of the line (S, U, O, L)
• Share resources, enhance communication
  visibility, impact location of loading
  unloading
• Paced versus Un-paced lines
• Paced lines use an automatically enforced cycle
  time
• Number of Product Models produced
• Single
• Mixed-model lines

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LINE BALANCING
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The Line Balancing Problem

• The problem is to arrange the individual
  processing and assembly tasks at the workstations
  so that the total time required at each
  workstation is approximately the same.
• Nearly impossible to reach perfect balance

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Things to consider

• Sequence of tasks is restricted, there is a
  required order
• Called precedence constraints
• There is a production rate needed, i.e. how many
  products needed per time period
• Design the line to meet demand and within
  constraints

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Terminology and Definitions

• Minimum Work Element
• Total Work Content
• Workstation Process time
• Cycle Time
• Precedence Constraints
• Balance Delay

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Minimum Work Element

• Dividing the job into tasks of a rational and
  smallest size
• Example Drill a hole, cant be divided
• Symbol Time for element j
• is a constant

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Total Work Content

• Aggregate of work elements

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Workstation Process time

• The amount of time for an individual workstation,
  after individual tasks have been combined into
  stations
• Sum of task times sum of workstation times

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Cycle time

• Time between parts coming off the line
• Ideally, the production rate, but may need to be
  adjusted for efficiency and down time
• Established by the bottleneck station, that is
  station with largest time

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Precedence Constraints

• Generally given, determined by the required order
  of operations
• Draw in a network style for understanding
• Cannot violate these, an element must be complete
  before the next one is started

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Balance Delay

• Measure of line inefficiency due to imbalances in
  station times

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Line Balancing Example

• EXAMPLE
• Green Grasss plant manager just received
  marketings latest forecasts of fertilizer
  spreader sales for the next year. She wants its
  production line to be designed to make 2,400
  spreaders per week. The plant will operate 40
  hours per week.

• What should be the lines cycle time or
  throughput rate per hour be?
• Throughput rate/hr 2400 / 40 60 spreaders/hr
• Cycle Time 1/Throughput rate 1/60 1 minute
  60 seconds

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Line balancing Example

• Assume that in order to produce the new
  fertilizer spreader on the assembly line requires
  doing the following steps in the order specified
• What is the total number of stations or machines
  required?
• TM (total machines) total production time /
  cycle time 244/60 4.067 or 5

Work Element Description Time (sec) Immediate Predecessor(s)
A Bolt leg frame to hopper 40 None
B Insert impeller shaft 30 A
C Attach axle 50 A
D Attach agitator 40 B
E Attach drive wheel 6 B
F Attach free wheel 25 C
G Mount lower post 15 C
H Attach controls 20 D, E
I Mount nameplate 18 F, G
Total 244
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Draw a Precedence Diagram

• SOLUTION
• The figure shows the complete diagram. We begin
  with work element A, which has no immediate
  predecessors. Next, we add elements B and C, for
  which element A is the only immediate
  predecessor. After entering time standards and
  arrows showing precedence, we add elements D and
  E, and so on. The diagram simplifies
  interpretation. Work element F, for example,
  can be done anywhere on the line after element
  C is completed. However, element I must await
  completion of elements F and G.

Precedence Diagram for Assembling the Big
Broadcaster
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Allocating work or activities to stations or
machines

• The goal is to cluster the work elements into
  workstations so that
• The number of workstations required is minimized
• The precedence and cycle-time requirements are
  not violated

• The work content for each station is equal (or
  nearly so, but less than) the cycle time for the
  line

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Finding a Solution

• The minimum number of workstations is 5 and the
  cycle time is 60 seconds, so Figure 5 represents
  an optimal solution to the problem

Firtilizer Precedence Diagram Solution
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Calculating Line Efficiency

• c. Now calculate the efficiency measures of a
  five-station solution

Balance delay () 100 Efficiency 100 -
81.3 18.7
Idle time nc ?t 5(60) 244 56 seconds
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A Line Process

• The desired output rate is matched to the
  staffing or production plan
• Line Cycle Time is the maximum time allowed for
  work at each station is

where c cycle time in hours r desired
output rate
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A Line Process

• The theoretical minimum number of stations is

where ?t total time required to assemble each
unit
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A Line Process

• Idle time, efficiency, and balance delay

Idle time nc ?t
where n number of stations
Balance delay () 100 Efficiency
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Solved Problem 2

• A company is setting up an assembly line to
  produce 192 units per 8-hour shift. The following
  table identifies the work elements, times, and
  immediate predecessors

Work Element Time (sec) Time (sec) Time (sec) Immediate Predecessor(s)
A 40 None
B 80 A
C 30 D, E, F
D 25 B
E 20 B
F 15 B
G 120 A
H 145 G
I 130 H
J 115 C, I
Total 720 Total 720 Total 720
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Solved Problem 2

• a. What is the desired cycle time (in seconds)?
• b. What is the theoretical minimum number of
  stations?
• c. Use trial and error to work out a solution,
  and show your solution on a precedence diagram.
• d. What are the efficiency and balance delay of
  the solution found?

SOLUTION a. Substituting in the cycle-time
formula, we get
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Solved Problem 2

• b. The sum of the work-element times is 720
  seconds, so

which may not be achievable.
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Solved Problem 2

• c. The precedence diagram is shown in Figure 7.6.
  Each row in the following table shows work
  elements assigned to each of the five
  workstations in the proposed solution.

Work Element Immediate Predecessor(s)
A None
B A
C D, E, F
D B
E B
F B
G A
H G
I H
J C, I
Figure 7.6 Precedence Diagram
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Solved Problem 2
Station Candidate(s) Choice Work-Element Time (sec) Cumulative Time (sec) Idle Time(c 150 sec)
S1


S2

S3
S4

S5

A A 40 40 110
B B 80 120 30
D, E, F D 25 145 5
E, F, G G 120 120 30
E, F E 20 140 10
F, H H 145 145 5
F, I I 130 130 20
F F 15 145 5
C C 30 30 120
J J 115 145 5
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Solved Problem 2

• d. Calculating the efficiency, we get

96
Thus, the balance delay is only 4 percent
(10096).
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