Chapter 12 Group Technology and Cellular Manufacturing Systems

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Chapter 12Group Technology and Cellular
Manufacturing Systems
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Agenda

• What is GT?
• GT Implementation
• Classification and Coding Systems
• Benefits of GT
• What is Cellular Manufacturing
• Cell Formulation Approaches
• Economics of Group Tooling in CM
• PPC in CMSs

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What is Group Technology?

• GT is a philosophy that implies the notation of
  recognizing and exploiting similarities in three
  different ways
• By performing like activities together
• By standardizing similar tasks
• By efficiently storing and retrieving information
  about recurring problems
• GT decomposition of large manufacturing system
  to produce a set of parts into smaller subsystems
  of part families based on similarities in design
  attributes and manufacturing features
• Design attributes part configuration,
  dimensional envelope, surface integrity, material
  type, raw material state
• Manufacturing features operations and their
  sequences, batch sizes, machine tools and cutting
  tools, processing times,

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GT Implementation

• Classification approaches using coding systems
• Visual inspection method classify parts into
  families by visually inspecting the physical
  characteristics or photograph of the parts
• Coding methods assigning symbols (represent
  design attributes, manufacturing features) to the
  parts
• A GT code is a string of characters capturing
  information about item
• Different between coding systems symbols, the
  assignment of symbols
• Three types of codes mono code, ploy code and
  mixed-code
• Cell formation approaches using production flow
  information

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Monocode and Polycode
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Example 1
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Mixed-code

• E.g. 12345 6789 ABCD
• ? ? ?
• form code supplementary secondary
• Form code part geometry, dimensions and features
  relevant to part design
• Supplementary code polycode, manufacturing raw
  material, tolerances, surface roughness
• Secondary code production processes and
  production sequences

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Example 2
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Classification and Coding Systems

• Application develop part families
• Methods to form part families hierarchical
  clustering algorithm, p-median formulation,
  multi-objective clustering algorithm
• Selection of classification and coding systems
  attributes of the system
• Flexibility for various applications
• Accuracy to provide correct information on parts
• Expendability
• Ease of learning
• Ease of retrieval
• Reliability and availability of software
• Suitability for specific applications

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Benefits of GT

• Engineering design reduction in new part design,
  drawing, drafting effort, etc.
• Layout planning save floor space, reduced
  material-handling effort
• Specification of equipment, tools, jigs, and
  fixtures standardize, CM, reduce number of
  tools, jigs, etc. significant reduction in
  up-front costs
• Manufacturing process planning reduction setup
  time, production time, improve routing, etc.
• Manufacturing production control reduce WIP,
  easy identify bottlenecks, etc.
• Manufacturing quality control reduce number of
  defects, scrap, inspection effort, etc.
• Purchasing standardize, reduce number of parts
  and raw materials, etc.
• Customer service accurate and faster cost
  estimates, efficient spare parts management, etc.

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What is Cellular Manufacturing

• CM is an application of GT to convert the whole
  manufacturing system into cells
• A manufacturing cell is a cluster of machines or
  processes located in close proximity and
  dedicated to the manufacture of a family of parts
• Objective reduce setup times, flow time,
  inventories and market response times.
• Design of CM systems
• Cell design system structure and system
  operation
• Evaluation of cell design decisions consider
  both related issues

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Cell Formulation Approaches

• Machine-Component Group Analysis
• Production flow analysis (PFA)
• Step1 machine classification
• Step2 checking parts list and production route
  information
• Step3 factory flow analysis
• Step4 machine-component group analysis

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Example 3

• Consider a small problem of 4 machines and 6
  parts as shown in Table 12.1. Modify the matrix
  through row and column exchanges to form cells.
  The part operations to be performed on the
  machines are represented by 1 in the matrix, a
  blank means no operation

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Cell Formulation Approaches

• Rank order clustering algorithm (ROC)
• Step1 assign binary weight and calculate a
  decimal weight for each row and column
• Step2 rank the rows in order of decreasing
  decimal weight values
• Step3 repeat step 1 and 2 for each column
• Step4 continue preceding steps until there is no
  change in the position of each element in each
  row and column
• Other sorting algorithms Direct clustering
  algorithm, MODROC, etc.

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Examples 4

• Consider the machine-component matrix in Table
  12.3. Use ROC algorithm to form machine cells

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Example 4
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Cell Formulation Approaches

• Similarity Coefficient-Based Approaches
• Single-Linkage Cluster Analysis (SLCA)
• Step1 compute similarity coefficients for all
  possible pairs of machines
• Step2 select two most similar machines to form
  the first machine cell
• Step3 lower the similarity level (threshold) and
  form new machine cells
• Setp4 continue step 3 until all the machines are
  grouped into a single cell
• Other measures of similarity coefficients

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Example 5

• Consider the matrix of 5 machines and 10
  components given in Table 12.3 Develop a
  dendrogram and discuss the resulting cell
  structures

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Example 5
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Cell Formulation Approaches

• Exceptional parts and bottleneck machines
• Exceptional part processed in more than one cell
• Bottleneck machines processing exceptional parts
• Evaluation of cell designs minimize the total
  material-handling cost of intercell and intracell
  movement parts
• Expected distance for a straight-line layout
  (N1)/3
• Expected distance for a rectangle layout (M x L)
  (ML)/3
• Expected distance for a square layout2?N/3
• Total cost of inter- and intracell movement for
  the ith configuration

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Cell Formulation Approaches

• An alternative approach of evaluating goodness of
  heuristic solutions grouping efficacy
• Where e number of exceptional elements
• v number of voids in the diagonal
  blocks
• o total number of operations
• Mathematical programming models (reading)

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Economics of Group Tooling in CM

• Convention tooling method the unit cost of
  conventional tooling (UCC) using p different jigs
  or fixtures
• Group tooling method
• Notations
• Ci cost of a jig or a fixture
• p number of different fixtures used to produce
  n parts
• Cj cost of an adapter,
• q different types of adapters
• Cg cost of a group fixture