Cellular Manufacturing

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Cellular Manufacturing
Adapted from
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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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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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Introduction to Cellular Manufacturing
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Introduction to Cellular Manufacturing
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Introduction to Cellular Manufacturing
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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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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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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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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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Disadvantages of CM

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

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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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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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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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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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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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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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Group Analysis
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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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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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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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Coding Options

• Codes can be chain or hierarchical
• Chain each digits 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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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