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Cellular Manufacturing Systems - ADDVALUE - Nilesh Arora

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Title: Cellular Manufacturing Systems - ADDVALUE - Nilesh Arora


1
Cellular Manufacturing
by
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2
ORIGINS
  • FLANDERS PRODUCT ORIENTED DEPARTMENTS FOR
    STANDARIZED PRODUCTS WITH MINIMAL TRANSPORTATION
    (1925)
  • SOKOLOVSKI/MITROFANOV PARTS WITH SIMILAR
    FEATURES MANUFACTURED TOGETHER

3
BASIC PRINCIPLE
  • SIMILAR THINGS SHOULD BE DONE SIMILARLY
  • THINGS
  • PRODUCT DESIGN
  • PROCESS PLANNING
  • FABRICATION ASSEMBLY
  • PRODUCTION CONTROL
  • ADMINISTRATIVE FUNCTIONS

4
TENETS OF GROUP TECHNOLOGY
  • DIVIDE THE MANUFACTURING FACILITY INTO SMALL
    GROUPS OR CELLS OF MACHINES (1-5)
  • THIS IS CALLED CELLULAR MANUFACTURING

5
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.

6
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

7
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

8
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

9
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.

10
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.

11
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.

12
The Difference between group and functional
layout
13
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)

14
Cell Formation Approach
  • Machine - Component Group Analysis
  • Machine - Component Group Analysis is based on
    production flow analysis

15
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.

16
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.

17
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.

18
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.

19
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
20
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
21
Cellular Layout
Process (Functional) Layout
Group (Cellular) Layout
A cluster or cell
Similar resources placed together
Resources to produce similar products placed
together
22
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

23
Process Flows before the Use of GT Cells
24
Process Flows after the Use of GT Cells
25
Designing Product Layouts
  • Designing product layouts requires consideration
    of
  • Sequence of tasks to be performed by each
    workstation
  • Logical order
  • Speed considerations line balancing

26
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

27
Step 1 Identify Tasks Immediate Predecessors
28
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)

29
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

30
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

31
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

32
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

33
LINE BALANCING
34
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

35
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

36
Terminology and Definitions
  • Minimum Work Element
  • Total Work Content
  • Workstation Process time
  • Cycle Time
  • Precedence Constraints
  • Balance Delay

37
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

38
Total Work Content
  • Aggregate of work elements

39
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

40
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

41
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

42
Balance Delay
  • Measure of line inefficiency due to imbalances in
    station times

43
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

44
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
45
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
46
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

47
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
48
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
49
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
50
A Line Process
  • The theoretical minimum number of stations is

where ?t total time required to assemble each
unit
51
A Line Process
  • Idle time, efficiency, and balance delay

Idle time nc ?t
where n number of stations
Balance delay () 100 Efficiency
52
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
53
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
54
Solved Problem 2
  • b. The sum of the work-element times is 720
    seconds, so

which may not be achievable.
55
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
56
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
57
Solved Problem 2
  • d. Calculating the efficiency, we get

96
Thus, the balance delay is only 4 percent
(10096).
58
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