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Flow Analysis

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Flow Analysis Factors that Affect the Flow Pattern Flow Analysis Information Flow Patterns a. Flow within Workstations b. Flow within Departments – PowerPoint PPT presentation

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Title: Flow Analysis


1
Flow Analysis
  • Factors that Affect the Flow Pattern
  • Flow Analysis Information
  • Flow Patterns
  • a. Flow within Workstations b. Flow within
    Departments
  • c. Flow between Departments
  • Flow Planning
  • Measuring Flow
  • Types of Layout
  • a. Fixed Location b. Product
  • c. Group Technology d. Process
  • e. Hybrid
  • Flow Dominance Measure
  • Techniques for Machine Cell Formation
  • a. Row and Column Masking Algorithm
  • b. Single Linkage Clustering c. Average Linkage
    clustering

2
Factors that Affect the Flow Pattern
  • Number of parts in each product
  • Number of operations on each part
  • Sequence of operations in each part
  • Number of subassemblies
  • Number of units to be produced
  • Product versus process type layout
  • Desired flexibility
  • Locations of service areas
  • The building
  • . . . .

3
Flow Analysis Information
  • Assembly Chart
  • Operations Process Chart
  • Flow Process Chart
  • Multi-Product Process Chart
  • Flow Diagram
  • From-To Chart

4
Assembly Chart It is an analog model of the
assembly process. Circles with a single link
denote basic components, circles with several
links denote assembly operations/subassemblies,
and squares represent inspection operations. The
easiest method to constructing an assembly chart
is to begin with the original product and to
trace the product disassembly back to its basic
components.
5
Operations Process Chart By superimposing the
route sheets and the assembly chart, a chart
results that gives an overview of the flow within
the facility. This chart is operations process
chart.
6
Flow Process Chart This chart uses circles for
operations, arrows for transports, squares for
inspections, triangles for storage, and the
letter D for delays. Vertical lines connect these
symbols in the sequence they are performed.
7
Multi-Product Process Chart This chart is a flow
process chart containing several products.
8
Flow Diagram It depicts the probable movement of
materials in the floor plant. The movement is
represented by a line in the plant drawing.
9
From-To Chart This chart is a matrix that
contains numbers representing a measure (units,
unit loads, etc.) of the material flow between
machines, departments, buildings, etc.
10
Flow Patterns Flow within Workstations
  • Motion studies and ergonomics considerations are
    important in establishing the flow within
    workstations. Flow within workstations should
    be
  • Simultaneous coordinated use of hands, arms and
    feet.
  • Symmetrical coordination of movements about the
    center of the body.
  • Natural movements are continuous, curved, and
    make use of momentum.
  • Rhythmical and Habitual flow allows a
    methodological and automatic sequence of
    activities. It should reduce mental, eye and
    muscle fatigue, and strain.

11
Flow Patterns Flow within Departments
  • The flow pattern within departments depends on
    the type of department.
  • In a product and/or product family department,
    the flow follows the product flow.

2 machines/operator
1 machine/operator
1 machine/operator
END-TO-END
BACK-TO-BACK
FRONT-TO-FRONT
More than 2 machines /operator
1 machine/operator
CIRCULAR
ODD-ANGLE
12
Flow Pat. Flow within Departments (cont.)
  • In a process department, little flow should occur
    between workstations within departments. Flow
    occurs between workstations and isles.

Uncommon
DIAGONAL
PARALLEL
PERPENDICULAR
Dependent on interactions among workstations
available space size of materials
13
Flow Pat. Flow between Departments
  • Flow between departments is a criterion often
    used to evaluate flow within a facility.
  • Flow typically is a combination of the basic
    horizontal flow patterns shown below. An
    important consideration in combining the flow
    patterns is the location of the entrance
    (receiving department) and exit (shipping
    department).

Similar to straight. It is not as long.
L flow
Simplest. Separate receiving/shipping crews
Straight
Very popular. Combine receiving /shipping.
Simple to administer
Circular flow
U flow
Terminate flow. Near point of origin
Serpentine
When line is too long
S flow
14
Flow within a facility considering the locations
of entrance and exit
At the same location
On adjacent sides
15
Flow within a facility considering the locations
of entrance and exit (cont.)
On the same side but at opposite ends
On opposite sides
16
Vertical Flow Pattern
Flow between buildings exists and the connection
between buildings is elevated
Ground level ingress (entry) and egress (exit)
occur on the same side of the building
Ground level ingress (entry) and egress (exit)
are required
Some bucket and belt conveyors and escalators
result in inclined flow
Travel between floors occurs on the same side of
the building
Backtracking occurs due to the return to the top
floor
17
Flow Planning
  • Planning effective flow involves combining the
    above patterns with adequate isles to obtain
    progressive movements from origin to destination.
  • An effective flow can be achieved by maximizing
    directed flow paths, reducing flow, and
    minimizing the costs of flow.
  • A directed flow path is an uninterrupted flow
    path progressing directly from origin to
    destination the figure below illustrates the
    congestion and undesirable intersections that may
    occur when flow paths are interrupted.

Uninterrupted flow paths
Interrupted flow paths
18
Flow Planning (cont.)
  • The reduction of flow can be achieved by work
    simplification including
  • 1. Eliminating flow by planning for the delivery
    of materials, information, or people directly to
    the point of ultimate use and eliminate
    intermediate steps.
  • 2. Minimizing multiple flows by planning for the
    flow between two consecutive points of use to
    take place in as few movements as possible.
  • 3. Combining flows and operations whenever
    possible by planning for the movement of
    materials, information, or people to be combined
    with a processing step.
  • Minimizing the cost of flow can be achieved as
    follows
  • 1. Reduction of manual handling by minimizing
    walking, manual travel distances, and motions.
  • 2. Elimination of manual handling by mechanizing
    or automating flow.

19
Measuring Flow
  • 1. Flow among departments is one of the most
    important factors in the arrangement of
    departments within a facility.
  • 2. Flows may be specified in a quantitative
    manner or a qualitative manner. Quantitative
    measures may include pieces per hour, moves per
    day, pounds per week. Qualitative measures may
    range from an absolute necessity that two
    departments show be close to each other to a
    preference that two departments not being close
    to each other.
  • 3. In facilities having large volumes of
    materials, information, a number of people moving
    between departments, a quantitative measure of
    flow will typically be the basis for the
    arrangement of departments. On the contrary, in
    facilities having very little actual movement of
    materials, information, and people flowing
    between departments, but having significant
    communication and organizational interrelation, a
    qualitative measure of flow will typically serve
    as the basis for the arrangement of departments.
  • 4. Most often, a facility will have a need for
    both quantitative and qualitative measures of
    flow and both measures should be used.
  • 5. Quantitative flow measure From-to Chart
  • Qualitative flow measure Relationship (REL)
    Chart

20
Quantitative Flow Measurement
  • A From-to Chart is constructed as follows
  • 1. List all departments down the row and across
    the column following the overall flow pattern.
  • 2. Establish a measure of flow for the facility
    that accurately indicates equivalent flow
    volumes. If the items moved are equivalent with
    respect to ease of movement, the number of trips
    may be recorded in the from-to chart. If the
    items moved vary in size, weight, value, risk of
    damage, shape, and so on, then equivalent items
    may be established so that the quantities
    recorded in the from-to chart represent the
    proper relationships among the volumes of
    movement.
  • 3. Based on the flow paths for the items to be
    moved and the established measure of flow, record
    the flow volumes in the from-to chart.

21
Example 1
From-to Chart
Revised Flow Pattern
Original Flow Pattern
22
Flow Patterns
Press
Turning
Store
Milling
Press
Plate
Assembly
Warehouse
Stores Turning
Milling Warehouse Assembly Plate
U-shaped flow
Straight-line flow
Stores Press Plate
Assembly Turning
Milling Warehouse
Stores Milling
Warehouse Turning Press
Plate Assembly
W-shaped flow
S-shaped flow
23
Flow Patterns (cont.)
Press
Turning
Store
Milling
Press
Plate
Assembly
Warehouse
Stores Turning
Milling Warehouse Assembly Plate
U-shaped flow
Straight-line flow
Stores Press Plate
Assembly Turning
Milling Warehouse
Stores Milling
Warehouse Turning Press
Plate Assembly
W-shaped flow
S-shaped flow
24
Qualitative Flow Measurement
  • A Relationship (REL) Chart is constructed as
    follows
  • 1. List all departments on the relationship
    chart.
  • 2. Conduct interviews of surveys with persons
    from each department listed on the relationship
    chart and with the management responsible for all
    departments.
  • 3. Define the criteria for assigning closeness
    relationships and itemize and record the criteria
    as the reasons for relationship values on the
    relationship chart.
  • 4. Establish the relationship value and the
    reason for the value for all pairs of
    departments.
  • 5. Allow everyone having input to the
    development of the relationship chart to have an
    opportunity to evaluate and discuss changes in
    the chart.

25
Relationship Chart
26
Types of Layout
Volume High Medium Low
Product Planning Department
Product Layout
Product Family Planning Department
Fixed Location Layout
Process Layout
Group Technology Layout
Fixed Materials Location Planning Department
Process Planning Department
Low Medium High Variety
27
Fixed Product Layout
Warehouse
Storage
28
Fixed Product Layout (cont.)
  • Advantages
  • 1. Material movement is reduced.
  • 2. Promotes job enlargement by allowing
    individuals or teams to perform the whole job.
  • 3. Continuity of operations and responsibility
    results from team.
  • 4. Highly flexible can accommodate changes in
    product design, product mix, and product volume.
  • 5. Independence of production centers allowing
    scheduling to achieve minimum total production
    time.
  • Limitations
  • 1. Increased movement of personnel and
    equipment.
  • 2. Equipment duplication may occur.
  • 3. Higher skill requirements for personnel.
  • 4. General supervision required.
  • 5. Cumbersome and costly positioning of material
    and machinery.
  • 6. Low equipment utilization.

29
Product Layout
30
Product Layout (cont.)
  • Advantages
  • 1. Since the layout corresponds to the sequence
    of operations, smooth and logical flow lines
    result.
  • 2. Since the work from one process is fed
    directly into the next, small in-process
    inventories result.
  • 3. Total production time per unit is short.
  • 4. Since the machines are located so as to
    minimize distances between consecutive
    operations, material handling is reduced.
  • 5. Little skill is usually required by operators
    at the production line hence, training is
    simple, short, and inexpensive.
  • 6. Simple production planning control systems
    are possible.
  • 7. Less space is occupied by work in transit and
    for temporary storage.
  • Limitations
  • 1. A breakdown of one machine may lead to a
    complete stoppage of the line that follows that
    machine.
  • 2. Since the layout is determined by the
    product, a change in product design may require
    major alternations in the layout.
  • 3. The pace of production is determined by the
    slowest machine.
  • 4. Supervision is general, rather than
    specialized.
  • 5. Comparatively high investment is required, as
    identical machines (a few not fully utilized) are
    sometimes distributed along the line.

31
Process Layout
32
Process Layout (cont.)
  • Advantages
  • 1. Better utilization of machines can result
    consequently, fewer machines are required.
  • 2. A high degree of flexibility exists relative
    to equipment or man power allocation for specific
    tasks.
  • 3. Comparatively low investment in machines is
    required.
  • 4. The diversity of tasks offers a more
    interesting and satisfying occupation for the
    operator.
  • 5. Specialized supervision is possible.
  • Limitations
  • 1. Since longer flow lines usually exist,
    material handling is more expensive.
  • 2. Production planning and control systems are
    more involved.
  • 3. Total production time is usually longer.
  • 4. Comparatively large amounts of in-process
    inventory result.
  • 5. Space and capital are tied up by work in
    process.
  • 6. Because of the diversity of the jobs in
    specialized departments, higher grades of skill
    are required.

33
Group Layout
34
Group Layout (cont.)
  • Advantages
  • 1. Increased machine utilization.
  • 2. Team attitude and job enlargement tend to
    occur.
  • 3. Compromise between product layout and process
    layout, with associated advantages.
  • 4. Supports the use of general purpose
    equipment.
  • 5. Shorter travel distances and smoother flow
    lines than for process layout.
  • Limitations
  • 1. General supervision required.
  • 2. Higher skill levels required of employees
    than for product layout.
  • 3. Compromise between product layout and process
    layout, with associated limitations.
  • 4. Depends on balanced material flow through the
    cell otherwise, buffers and work-in-process
    storage are required.
  • 5. Lower machine utilization than for process
    layout.

35
Hybrid Layout
  • Combination of the layouts discussed.
  • A sample hybrid layout that has characteristics
    of group, process and product layout is shown in
    the following figure.
  • A combination of group layout in manufacturing
    cells, product layout in assembly area, and
    process layout in the general machining and
    finishing section is used.

36
Flow Dominance Measure
  • Notations
  • M number of activities.
  • Nij number of different types of items moved
    between activities i and j.
  • fijk flow volume between i and j for item k
    (in moves/time period).
  • hijk equivalence factor for moving item k with
    respect to other items moved between i and j
    (dimensionless).
  • wij equivalent flow volume specified in
    from-to chart (in moves/time period),

37
Flow Dominance Measure (cont.)
  • Flow dominance measure f
  • where
  • f? is the coefficient of variation.
  • fL and fU are lower and upper bounds on f?,
    respectively (fL ? f? ? fU).
  • The upper bound fU is only guaranteed to work
    when each process plan includes all activities.
    In this case, 0 ? f ? 1.

38
Flow Dominance Measure (cont.)
  • Three cases
  • 1. f ? 0 ? a few dominant flows exist. ? product
    layout.
  • ? can use operations process chart as starting
    point for developing layout and material
    handling system design.
  • ? quantitative measures principal source of
    activity relationship.
  • 2. f ? 1 ? many nearly equal flows exist.
  • ? any layout equally good with respect to flows
    .
  • ? qualitative measures principal source of
    activity relationship.
  • 3. 0 ltlt f ltlt 1 ? no dominant flows exist. ?
    difficult to develop layout.
  • ? process or product family layout .
  • ? both quantitative and qualitative measures
    important source of activity
  • relationship.

39
Example 2
  • Given three machines (activities) labeled 1, 2
    3,

Product A B C
Process Plan 1 - 2 - 3 2 - 1 3 - 1 - 2
Quantities/Shift 10 5 15
  • Assume Product B is twice as difficult to move
    as A or C ? hijB 2 and hijA hijC 1

To
1 0 2 ? 5 10 1 ? 15 15
2 1?10 1 ? 15 25 0 0
3 0 1 ? 10 10 0
From
1 2 3
Equivalent Flow Volume From-To Chart
? w12 25, w21 10, etc
40
Example 2 (cont.)
M 3 and
? no dominant flows exist (likely, since 3
different process plans)
41
Qualitative Measures
  • Closeness values (A, E, I, O, U, X) used to
    indicate physical proximity requirements between
    activities.
  • Relationship Chart can only show symmetric
    relationships, as compared to From-to Chart (wij
    ? wji possible).
  • Relationship Chart is starting point for
    developing layout when 0 ltlt f ? 1.
  • If f ? 1, then dont need to consider flow (only
    qualitative relationship)
  • If f ltlt1, then one can convert equivalent flow
    volumes to closeness values so that material flow
    relationships can be considered along with
    qualitative relationship.
  • If f ? 0, then can still convert to relationship
    chart if significant qualitative relationship
    exists, otherwise, just use operations process
    chart.

42
Conversion Method
  • To convert equivalent flow volumes to closeness
    values for the example problem, use wij wji to
    make them symmetric.
  • Conversion relations
  • 20 lt wij wji ? A w12 w21 25 10 ? A
  • 12 lt wij wji ? 20 ? E w13 w31 0 15
    ? E
  • 5 lt wij wji ? 12 ? I w23 w32 10 0
    ? I
  • 0 lt wij wji ? 5 ? O
  • wij wji 0 ? U

43
Group Technology
  • Group Technology (GT) is a management philosophy
    that attempts to group products with similar
    design or manufacturing characteristics, or both.
  • Cellular Manufacturing (CM) is an application of
    GT that involves grouping machines based on the
    parts manufactured by them.
  • The main objective of CM is to identify machine
    cells and part families simultaneously, and to
    allocate part families to machine cells in a way
    that minimizes the intercellular movement of
    parts.
  • Potential benefits of CM
  • Setup time reduction. Improvement in
    quality.
  • Work-in-process (WIP) reduction. Improvement
    in material flow.
  • Material handling cost reduction.
    Improvement in machine utilization.
  • Direct/indirect labor cost reduction.
    Improvement in space utilization.
  • Improvement in employee moral.

44
Group Technology (cont.)
  • A cellular manufacturing system (CMS) designer
    must consider a number of constraints
  • Available capacity of machines in each cell
    cannot be exceeded.
  • Safety and technological requirements pertaining
    to the location of equipment and processes must
    be met.
  • The size of a cell and the number of cells must
    not exceed a user-specified value.
  • Design analysis begins with a machine-part
    indicator matrix A aij of size mn, where m
    is the number of machines and n the number of
    parts. Typically the matrix consists of 0 and 1
    entries
  • aij 1 indicates that part j is processed by
    machine i.
  • aij 0 indicates that part j is not processed by
    machine i.
  • Analysis attempt to rearrange the rows and
    columns of the matrix to get a block diagonal
    form as shown in the following example.

45
Example 3
  • Initial Machine Part
  • Processing Matrix
  • Rearranged Machine-Part
  • Processing Matrix

46
Row and Column Masking (RCM) Algorithm
  • 1. Draw a horizontal line through the first
    row. Select any 1 entry in the matrix through
    which there is only one line.
  • 2. If the entry has a horizontal line, go to
    step 2a. If the entry has a vertical line, go to
    step 2b.
  • 2a. Draw a vertical line through the column in
    which this 1 entry appears. Go to step 3.
  • 2b. Draw a horizontal line through the row in
    which this 1 entry appears. Go to step 3.
  • 3. If there is any 1 entries with only one line
    through them, select any one and go to step 2.
    Repeat until there are no such entries left.
    Identify the corresponding machine cell and part
    family. Go to step 4.
  • 4. Select any row through which there is no
    line. If there are no such rows, stop. Otherwise,
    draw a horizontal line through this row, select
    any 1 entry in the matrix through which there is
    only one line, and go to step 2.

47
Example 3 Solution
  • Identification of the First Machine
  • Cell and Part Family
  • Identification of the Second Machine
  • Cell and Part Family

48
Single Linkage (S-Link) Clustering Algorithm
  • S-Link is the simplest of all clustering
    algorithms based on the similarity coefficient
    method.
  • The similarity coefficient between two machines
    is defined as the number of parts visiting the
    two machines divided by the number of parts
    visiting either of the two machines.
  • 1. pairwise similarity coefficients between
    machines are calculated and stored in the
    similarity matrix.
  • 2. The two most similar machines join to form
    the first machine cell.
  • 3. The threshold value (the similarity level at
    which two or more machine cells join together) is
    lowered in predetermined steps and all
    machine/machine cells with the similarity
    coefficient greater than the threshold value are
    grouped into larger cells.
  • 4. Step 3 is repeated until all machines are
    grouped into a single machine cell.

49
Example 4 Initial Machine Part Matrix
50
Example 4 Initial Similarity Coefficient Matrix
Machine
M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11
M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11
0.08 0.00 0.43 1.00
0.08 0.00 0.80 0.00 0.00 0.80
0.00 0.80 0.50 0.00 0.00 0.00 0.00
0.10 0.00 0.00 0.00 0.00 0.25 0.50
0.00 0.00 0.27 0.45 0.00 0.00 0.00
0.00 0.00 0.00 0.83 0.36 0.43 0.45 0.23
0.43 0.43 0.36 0.00 0.17 0.00 0.00 0.00
0.00 0.00 0.00 0.00 0.57 0.37 0.67 0.00
Machine
51
Example 4 Dendrogram Based on S-Link
Similarity Levels
52
Example 4 Machine Part Groups using S-Link
53
Average Linkage (A-Link) Clustering Algorithm
  • The similarity coefficient between two machine
    cells is defined as the average of pairwise
    similarity coefficients between all members of
    the two cells.
  • 1. Compute pairwise similarity coefficients
    between machines and construct the similarity
    coefficient matrix.
  • 2. Merge the two most similar machines into a
    single machine cell.
  • 3. Compute the similarity coefficients between
    the newly formed machine cell and the remaining
    cells. Revise the similarity coefficient matrix.
  • 4. The threshold value (the similarity level at
    which two or more machine cells join together) is
    lowered in predetermined steps and all
    machine/machine cells with the similarity
    coefficient greater than the threshold value are
    grouped into larger cells. Repeat steps 3 and 4
    until all machines are grouped into a single
    machine cell.

54
Example 4 Revised Similarity Coefficient Matrix I
Machine Cell
(M1, M4) (M2, M6) M3 M5 (M7, M9) M8 M10
M11
(M1, M4) (M2, M6) M3 M5 (M7, M9)
M8 M10 M11
0.04 0.00 0.47
0.80 0.00 0.00 0.00 0.00 0.05
0.00 0.00 0.26 0.50 0.00 0.41
0.43 0.41 0.23 0.43 0.00 0.17
0.00 0.00 0.00 0.00 0.62 0.36 0.00
Machine Cell
55
Example 4 Revised Similarity Coefficient Matrix
II
Machine Cell
(M1, M4 , M5) (M2, M6) M3 (M7, M9, M11) M8
M10
(M1, M4, M5) (M2, M6) M3 (M7, M9,
M11) M8 M10
0.02 0.00 0.47
0.00 0.00 0.03
0.00 0.26 0.50 0.39 0.43
0.41 0.23 0.00 0.17
Machine Cell
56
Example 4 Revised Similarity Coefficient
Matrices III IV
57
Example 4 Dendrogram Based on A-Link
Similarity Levels
58
Example 4 Machine Part Groups using A-Link
59
Comparison
  • RCM is the simplest clustering algorithm.
  • A major disadvantage of RCM is that when the
    machine part matrix contains one or more
    bottleneck machines (machines that belong to more
    than one cell) or exceptional parts (parts that
    are processed in more than one cell), the
    algorithm may provide a solution with all
    machines in a cell and all parts in a
    corresponding part family.
  • The major advantages of S-Link are its simplicity
    and minimal computational requirement. In S-Link,
    once pairwise similarity coefficients are
    computed and the similarity coefficient matrix is
    constructed, the matrix can be used to develop
    the dendrogram which represents the machine cells
    at different threshold values.
  • The major drawback of S-Link is the chaining
    problem. Due to the chaining problem, two machine
    cells may join together just because two of their
    members are similar while the remaining members
    may remain far apart in terms of similarity.
  • The chaining problem of S-Link can be overcome by
    using A-Link. Since in A-Link two machine cells
    merge based on the overall similarity coefficient
    between all their members, it is unlikely that
    two similar members in two cells cause the cells
    to merge while other members are not similar
    enough. A-Link provides a more reliable solution
    to the machine cells formation problem.
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