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									          Cellular Manufacturing




Adapted from:




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  Lamar University
Introduction to Cellular Manufacturing (CM)

• Product layouts (assembly lines, mass production one a few
  products on the same line) is the most efficient of the basic
  layout options
• Many products are not made in volumes that require a
  product layout
• Cellular manufacturing (group technology) – forms families
  of products that have common production requirements
• Locate machines, people, jigs, fixtures, drawings, measuring
  equipment, material handling equipment together (focused
  factory)




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      Lamar University
    Introduction to Cellular Manufacturing

• The cellular approach is to organize the entire manufacturing
  process for particular or similar products into one group of
  team members and machines known as a "Cell".
• These "cells" are arranged in a U-shaped layout to easily
  facilitate a variety of operations.
• Parts or assemblies move one at a time (or in small batch
  sizes).
• The parts are handed off from operation to operation without
  opportunity to build up between operations.




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       Lamar University
Introduction to Cellular Manufacturing




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  Lamar University
Introduction to Cellular Manufacturing




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  Lamar University
   Introduction to Cellular Manufacturing

• Fast setup and quick changeovers are essential to Cellular
  Manufacturing systems since production runs are shorter.

• Setup reduction principles are used to achieve one piece
  flow and mixed model synchronization.

• All cells concentrate on eliminating waste.




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       Lamar University
        Empowered Employees in CM

• Goals and tracking charts are maintained and posted.
• Problems are solved through daily cell meetings and
  problem solving teams.
• The inventory management system is a KANBAN Demand
  Pull instead of a work order/kit picking system.

• Cells are responsible for planning, scheduling and
  expediting directly with vendors.

• They establish and maintain a KANBAN system with the
  vendors.



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      Lamar University
                     Advanced CM

• The cell operates like an independent business with total
  responsibility for quality, manufacturing and delivery of the
  product to the customer.
• All cells have the resources within their organization to
  accomplish their mission.
• The requirements are known and goals are established.
• Cell members are flexible and work in teams to accomplish
  their goals including continuous improvement.




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      Lamar University
                     Benefits of CM

• Common tooling required for many products (fewer setups)
• Tooling can be justified since many products require it (more
  volume when products are grouped)
• Minimized material handling
• Simple production schedule
• Short cycle time
• Low WIP




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      Lamar University
                     Benefits of CM

• Cross-training – employees operate several machines
• Minimized material handling costs – since no paperwork is
  required and distance is small
• Employees accept more responsibility of supervision
  (scheduling of parts within cell, scheduling of vacation,
  purchasing of material, managing a budget)
• Simple flow pattern and reduced paperwork
• Buffers are small if batch size is small




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       Lamar University
                Disadvantages of CM

• Lower equipment utilization
• Increased set-up costs
• Less flexibility than functional departments




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      Lamar University
                  Family Formation

• Various levels – macro and micro
• Macro – entire factories (focused factories) can specialize in
  a particular type of part
• Micro – families can be based on similarities in part
  geometry (group shafts, flat parts, gears, etc…), process
  requirements (castings, forgings, sheet metal parts, heat-
  treated parts, printed circuit boards)
• How are these groupings determined?
   – Coding




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      Lamar University
                     Finding Part Families

• Visual Inspection of physical parts or photographs to identify similarities.
• Coding and Classification of parts by examining design and/or
  manufacturing attributes.
    – OPITZ System
    – MICLASS System
• Here a code is assigned to specific features of the part.
    – Is the part cylindrical or prismatic ?
    – Does it have threads?
    – Does it have through slots?
    – Does it require heat treatment?
• This requires a large initial time investment in coding and classifying all
  parts.



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        Lamar University
                Finding Part Families

• Production Flow Analysis : Since the parts in a part family
  have similar manufacturing processes, it is possible to
  identify similar parts by studying the route sheets.
• Parts with similar routes can be grouped into families.




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      Lamar University
                    Group Analysis

• To create part families and machine groups a part-machine
  matrix is created.
• This is a 0-1 matrix in which a one signifies that a machine is
  required for a given part.
• While creating this matrix the machine refers to a "type" of
  machine.
• Thus, if there are 5 identical CNC lathes we will create one
  row in the matrix for these lathes.
• Also, the number of times a part visits a machine is not
  considered at this stage



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      Lamar University
                    Group Analysis

• Once a the part-machine matrix is created, it is customary to
  remove approximately 10% of the most heavily used
  machines.
• Several copies of these machines are likely to be available
  and thus it is always possible to split these machines
  between different groups later.
• The remaining matrix is then inspected for part families.




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      Lamar University
                       Group Analysis

• To identify the part-families the rows and columns are interchanged such
  that a block-diagonal structure is obtained. There are several algorithms
  that can be used to do this. A simple algorithm for this problem can be
  described as follows:
   – Pick any row and draw a horizontal line through it.
   – For each 1 in the row that has been crossed once draw a vertical line
     through the corresponding column.
   – Pick each new column identified in the previous step. For each 1 in
     the column that has been crossed once draw a horizontal line
     through the row.
   – Repeat this process until there are no singly-crossed 1s in the
     matrix.
   – Remove the rows and columns that have been crossed to form a
     part family-machine group.
   – Continue for the rest of the matrix
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       Lamar University
            Group Analysis




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Lamar University
                          Coding

• GT coding and classification schemes attempt to capture
  design and manufacturing attributes such as the main
  shape, size, features of the product, production quantity, and
  material.
• A large number of GT coding schemes have been
  developed for discrete machined parts including MICLASS,
  Opitz and DCLASS




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      Lamar University
                            Coding

• Code should contain information about:
• Part or assembly itself
• Manufacturing process (manufacturing engineering,
  industrial engineering, tool engineering, scheduling, line
  supervision, quality assurance, etc…)




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      Lamar University
                Coding Requirements

• Precise nonambiguous meaning, no double or triple
  definitions for the same phrase
• Tightly structured and concise
• Easy to use




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      Lamar University
                     Coding Options

• Codes can be chain or hierarchical
• Chain – each digit’s specific location is fixed for a particular
  meaning
• Chain Example –
   – First digit is reserved for the product type
   – Second digit for material
   – Digits 3-6 for part geometry




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       Lamar University
                   Coding Options

• Chain Advantage – easy to learn
• Chain Disadvantage – requires more digits making it difficult
  to handle manually and with low power computers (not as
  big a problem today as the price of computers has dropped)




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      Lamar University
                    Coding Options

• Hierarchical code – each code character depends on the
  preceding one – a tree type structure
• Advantages – code can be sort since many branches can be
  eliminated
• Disadvantages – difficult to learn




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      Lamar University
                  Code Generation

• CM codes are typically generated manually or interactively
  by answering a series of questions and applying appropriate
  coding rules.
• However, this is a slow and inconsistent procedure which
  inhibited the widespread use of CM.




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      Lamar University
               Opitz Coding Scheme

• Shah and Bhatnagar developed an automated CM coding
  system based on the Opitz coding scheme for machined
  parts.
• The system assigns pre-defined taxonomy codes for each
  feature of its feature-based CAD system.
• The generic information captured by the taxonomy codes is
  used to determine individual feature characteristics and the
  relationships between features and the entire parts.
• The CM code generator uses the resulting feature
  information and Opitz coding rules to generate the CM
  codes.




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      Lamar University
                      Using Codes

• Comparing the CM codes of two products is a quick and
  efficient method for estimating product similarity in selected
  attributes.
• CM codes can be used to search a database of products
  and retrieve the designs and process plans of those
  products which are similar to a given design
• To generate new process plans automatically using a
  knowledge-based system
• To assess manufacturability of a product design




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      Lamar University
                       Cell Layout

• Usually U, L or circular shaped
• Minimizes transportation distance for operators (human or
  robotic)
• Encourages multiple machines per operator
• Most machines are automatic or semiautomatic, resulting in
  considerable idle time
• In a job shop (functional layout) there is one operator for
  each machine




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      Lamar University
                       Supply Push

• Input availability triggers production or work
• Emphasis on “keeping busy” to maximize resource utilization
  as long as there is work to be done
• Will synchronize supply with demand at each stage if:
   – If all information (about product recipe, processing lead
     times, and part inventories) is accurate
   – If forecasts of finished goods are correct
   – If there is no variability in processing




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       Lamar University
                     Demand Pull

• Output need triggers production
• Each station produces only on demand from its customer
  station
• Each station signals demand by picking up a part from its
  input buffer
• The supplier station produces a new unit as a replacement
  in the buffer
• Toyota formalized demand pull with cards called kanbans




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      Lamar University
                         Kanbans

• Kanbans are attached to output flow units in the buffer
  between customer and supplier processes
• Each card lists the following information:
   – Customer process
   – Supplier process
   – Parts description
   – Production quantity




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      Lamar University
                         Kanbans

• As the customer withdraws output flow units from the buffer,
  the attached kanban goes back to the supplier
• It signals an authorization for the supplier to produce the
  listed quantity to be replaced in the buffer
• Upon producing the required quantity, the supplier returns
  the output with an attached kanban to the buffer
• Kanbans control buffer inventory and provide information
  and discipline to the supplier as to when and how much to
  produce
• In the case of a process that handles multiple products, each
  supplier station must also know what to produce


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      Lamar University
    Problem 2 - Test 2 Summer 2001

      A   B        C   D   E   F
1     1   0        0   1   0   1
2     1   1        0   0   1   0
3     1   0        1   0   0   1
4     0   1        0   0   1   0
5     0   0        1   1   0   0
6     0   0        0   0   0   0



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Lamar University
    Problem 2 - Test 2 Summer 2001

      A   B        C   D   E   F
1     1   0        0   1   0   1
2     1   1        0   0   1   0
3     1   0        1   0   0   1
4     0   1        0   0   1   0
5     0   0        1   1   0   0
6     0   0        0   0   0   0



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Lamar University
    Problem 2 - Test 2 Summer 2001

      A   B        C   D   E   F
1     1   0        0   1   0   1
2     1   1        0   0   1   0
3     1   0        1   0   0   1
4     0   1        0   0   1   0
5     0   0        1   1   0   0
6     0   0        0   0   0   0



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Lamar University
    Problem 2 - Test 2 Summer 2001

      A   B        C   D   E   F
1     1   0        0   1   0   1
2     1   1        0   0   1   0
3     1   0        1   0   0   1
4     0   1        0   0   1   0
5     0   0        1   1   0   0
6     0   0        0   0   0   0



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Lamar University
        Problem 2 - Test 2 Summer 2001

          A      B      C     D      E     F
    1     1      0      0     1      0     1
    2     1      1      0     0      1     0
    3     1      0      1     0      0     1
    4     0      1      0     0      1     0
    5     0      0      1     1      0     0
    6     0      0      0     0      0     0
Thus all parts require all machines and only cell is formed

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     Lamar University

								
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