Group Technology and Cellular Manufacturing

  

Group Technology and Cellular

Manufacturing _{1. Part Families 2. Parts Classification and Coding}

  3. Production Flow Analysis _{4. Cellular Manufacturing 5. Application Considerations in Group Technology}

  6. Quantitative Analysis in Cellular Manufacturing Group Technology (GT) Defined

• A manufacturing philosophy in which similar parts • A manufacturing philosophy in which similar parts

  are identified and grouped together to take advantage of their similarities in design and production Similarities among parts permit them to be • classified into part families

  ▫ In each part family, processing steps are similar ▫ In each part family, processing steps are similar The improvement is typically achieved by organizing • the production facilities into manufacturing cells Overview of Group Technology

  Parts in the medium production quantity range • are usually made in batches Disadvantages of batch production: •

  ▫ Downtime for changeovers ▫ High inventory carrying costs

  GT minimizes these disadvantages by • GT minimizes these disadvantages by • recognizing that although the parts are different, there are groups of parts that possess Part Families and Cellular Manufacturing

  GT exploits the part similarities by utilizing • similar processes and tooling to produce them

• Machines are grouped into cells, each cell

  specializing in the production of a part family ▫ Called cellular manufacturing

  Cellular manufacturing can be implemented by • Cellular manufacturing can be implemented by • manual or automated methods ▫ When automated, the term flexible When to Use GT and Cellular Manufacturing

  1. The plant currently uses traditional batch

  1. The plant currently uses traditional batch

  production and a process type layout ▫ This results in much material handling effort, high in-process inventory, and long manufacturing lead times

  2. The parts can be grouped into part families

  2. The parts can be grouped into part families

  ▫ A necessary condition to apply group technology ▫ Each machine cell is designed to produce a given part family, or a limited collection of part Problems in Implementing GT

  1. Identifying the part families

  ▫ Reviewing all of the parts made in the plant and grouping them into part families is a substantial task

  2. Rearranging production machines into GT cells

  ▫ ▫ It is time-consuming and costly to physically It is time-consuming and costly to physically rearrange the machines into cells, and the machines are not producing during the The benefits of GT’s GT promotes standardization of tooling, fixturing, and setups. • GT promotes standardization of tooling, fixturing, and setups. • Material handling is reduced because parts are moved within • a machine cells rather than within the entire factory.

• Process planning and production scheduling are simplified.

  Setup times are reduced, resulting in lower manufacturing • lead times.

  WIP is reduced. • Worker satisfaction usually improves when workers • Worker satisfaction usually improves when workers • collaborate in a GT cell. Higher quality work is accomplished using group technology. • Part Family

  A collection of parts that possess similarities in • geometric shape and size, or in the processing steps used in their manufacture

Part families are a central feature of group • technology

  ▫ There are always differences among parts in a ▫ There are always differences among parts in a family ▫ But the similarities are close enough that the parts Part Families Two parts that are identical in shape and size but quite different in •

Part Families

  Ten parts are different in size, • shape, and material, but quite similar in terms of manufacturing All parts are machined from • cylindrical stock by turning; some parts require drilling and/or milling and/or milling Traditional Process Layout

  Cellular Layout Based on GT

  Ways to Identify Part Families

  1. Visual inspection

  1. Visual inspection

  ▫ Using best judgment to group parts into appropriate families, based on the parts or photos of the parts

  2. Parts classification and coding

  ▫ Identifying similarities and differences among ▫ Identifying similarities and differences among parts and relating them by means of a coding scheme

  3. Production flow analysis

  Parts Classification and Coding

• Identification of similarities among parts and • Identification of similarities among parts and

  relating the similarities by means of a numerical coding system Most time consuming of the three methods • Must be customized for a given company or • industry industry

Reasons for using a coding scheme: •

  ▫ Design retrieval ▫ Automated process planning Features of Parts Classification and Coding Systems

Most classification and coding systems are based • on one of the following:

  ▫ Part design attributes ▫ Part manufacturing attributes ▫ Both design and manufacturing attributes

Part Design Attributes

• Basic external shape • Basic external shape
• Basic internal shape
• Rotational or rectangular shape
• Length-to-diameter ratio (rotational parts)
• Aspect ratio (rectangular parts)
• Material type
• Part function • Part function
• Major dimensions
• Minor dimensions
• Tolerances

Part Manufacturing Attributes

• Major processes • Major processes
• Minor operations
• Operation sequence
• Major dimension
• Surface finish
• Machine tool
• Production cycle time • Production cycle time
• Batch size
• Annual production
• Fixtures required

Coding Scheme Structures

  1. Hierarchical structure (monocode)

  ▫ Interpretation of each successive digit depends on the value of the preceding digit

  2. Chain-type structure (polycode)

  ▫ Interpretation of each symbol is always the same ▫ No dependence on previous digits ▫ No dependence on previous digits

  3. Mixed-code structure (hybrid)

  ▫ Combination of hierarchical and chain-type Opitz Classification System

• One of the first published classification and

  coding schemes for mechanical parts

• Basic code = nine (9) digits (+ 4 digits)

  ▫ Digits 1 through 5 = form code – primary shape and design attributes (hierarchical structure) ▫ Digits 6 through 9 = supplementary code – ▫ Digits 6 through 9 = supplementary code – attributes that are useful in manufacturing (e.g., dimensions, starting material) Basic Structure of Opitz System

  Opitz Form Code (Digits 1 through 5)

  Example: Opitz Form Code Form code in Opitz system is • 15100

  Production Flow Analysis (PFA) Method for identifying part families and associated • machine groupings based on production route sheets rather than part design data

• Workparts with identical or similar route sheets are

  classified into part families Advantages of using route sheet data • Advantages of using route sheet data • ▫ Parts with different geometries may nevertheless require the same or similar processing Steps in Production Flow Analysis

  1. Data collection – operation sequence and machine routing for each part

  2. Sortation of process routings – parts with same sequences and routings are arranged into “packs”

  3. PFA chart – each pack is displayed on a PFA chart ▫ ▫ Also called a part-machine incidence matrix Also called a part-machine incidence matrix

  4. Cluster analysis – purpose is to collect packs with similar routings into groups

  PFA Chart (Part-Machine Incidence Matrix)

  Rearranged PFA Chart

  Cellular Manufacturing

• Application of group technology in which dissimilar

  machines or processes are aggregated into cells, each of which is dedicated to the production of a part family or limited group of families

• Typical objectives of cellular manufacturing:

  ▫ To shorten manufacturing lead times ▫ To shorten manufacturing lead times ▫ To reduce WIP ▫ To improve quality Composite Part Concept A composite part for a given family is a hypothetical • A composite part for a given family is a hypothetical • part that includes all of the design and manufacturing attributes of the family

• In general, an individual part in the family will have

  some of the features of the family, but not all of them A correlation between part design features and the • A correlation between part design features and the •

production operations required to generate those

features.

Composite Part Concept

  A production cell for the part family would • consist of those machines required to make the composite part Such a cell would be able to produce any family • member, by omitting operations corresponding to features not possessed by that part to features not possessed by that part The cell would be designed to allow for size • variations within the family as well as feature Composite Part Concept

• Composite part concept:

Part Features and Corresponding Manufacturing Operations Label Label Design Feature Design Feature Corresponding Corresponding Manufacturing Operation

  1 External Cylinder Turning

  2 Cylinder face Facing

  3 Cylindrical step Turning

  

4 Smooth surface External cylindrical grinding

  5 Axial hole Axial hole Drilling Drilling

  5

  6 Counterbore Counterboring

  7 Internal threads Tapping Machine Cell Designs 1.

  1. Single machine (Type I M) Single machine (Type I M)

  2. Multiple machines with manual handling (Type

  II M, Type III M) ▫ Often organized into U-shaped layout

  3. Multiple machines with semi-integrated

  handling (Type II M, Type III M) handling (Type II M, Type III M)

  4. Automated cell – automated processing and

  integrated handling (Type II A, Type III A) ▫ Flexible manufacturing cell Machine Cell with Manual Handling

  Cell with Semi-Integrated Handling

  Cell with Semi-Integrated Handling

  Cell with Semi-Integrated Handling

  Four Types of Part Moves in Mixed Model Production System

  Additional factors in the cell design

Quantity of work to be done by the cell • Quantity of work to be done by the cell •

  ▫ Number of parts per year ▫ The processing time per part at station ▫ Number of machines ▫ Total operating cost ▫ The investment ▫ The investment

  Part size, shape, weight, and other physical • attributes ▫ Size and type of material handling and processing key machine) that is more expensive or performs certain critical operations ▫ Other machines in the cell are supporting machines ▫ Important to maintain high utilization of key ▫ Important to maintain high utilization of key machine, even if this means lower utilization of supporting machines

  Key Machine Concept

• Applies in cells when there is one machine (the

Manufacturing Applications of Group Technology

Different ways of forming machine cells: •

  ▫ Informal scheduling and routing of similar parts through selected machines to minimize setups ▫ Virtual machine cells – dedication of certain machines in the factory to produce part families, but no physical relocation of machines but no physical relocation of machines

  ▫ Formal machine cells – machines are physically relocated to form the cells Manufacturing Applications of Group Technology

  Automated process planning • Family tooling (Modular fixtures) •

  ▫ Common base fixture is designed and adaptations are made to switch between different parts in the family

  NC part programs (Parametric programming in • NC part programs (Parametric programming in • NC)

  ▫ Preparation of a common NC program that covers Product Design Applications of Group Technology The use of design retrieval systems that reduce part • The use of design retrieval systems that reduce part • proliferation in the firm

  ▫ Industry survey: For new part designs, Existing part design could be used - 20% Existing part design with modifications – 40% New part design required – 40%

  Simplification and standardization of design • parameters parameters ▫ Tolerances, inside radii on corners, chamfer sizes, hole sizes, thread sizes, and so on.

  ▫ Reduces tooling and fastener requirements in Product Design Applications of Group Technology

Aim: •

  ▫ Simplify design procedures and reduce part proliferation ▫ Reducing amount of data and information ▫ Fewer part designs, design attributes, tools, fasteners, and so on mean fewer and simple fasteners, and so on mean fewer and simple design documents, process plans, and other data records

Benefits of Cellular Manufacturing

• Reduce throughput time (manufacturing lead time) • Reduce throughput time (manufacturing lead time)
• Reduce work in process
• Improve part and/or product quality
• Reduce response time for customer orders
• Reduce move distances
• Increase manufacturing flexibility
• Reduce unit costs • Reduce unit costs
• Simplify production planning and control
• Facilitate employee involvement
• Reduce setup times

Quantitative Analysis in Cellular Manufacturing

  Grouping parts and machines by Rank Order • Clustering Arranging machines in a GT Cell •

Rank Order Clustering

  Specifically applicable in production flow • analysis It is an efficient and easy-to-use algorithm for • grouping machines into cells ROC works by reducing the part-machine • incidence matrix to a set of diagonalized blocks incidence matrix to a set of diagonalized blocks that represent part families and associated machine groups Rank Order Clustering Algorithm 1.

  1. In each row of the matrix, read the series of 1’s and In each row of the matrix, read the series of 1’s and 0’s (blank entries = 0’s) from left to right as a binary number. Rank the rows in order of decreasing value. In case of a tie, rank the rows in the same order as they appear in the current matrix.

  2. Numbering from top to bottom, is the current order of rows the same as the rank order order of rows the same as the rank order determined in the previous step? If yes, go to step

  7. If no, go to the following step.

  3. Reorder the rows in the part-machine incidence Rank Order Clustering Algorithm 4.

  4. In each column of the matrix, read the series of 1’s and In each column of the matrix, read the series of 1’s and 0’s (blank entries = 0’s) from top to bottom as a binary number. Rank the columns in order of decreasing value. In case of a tie, rank the columns in the same order as they appear in the current matrix.

  5. Numbering from left to right, is the current order of columns the same as the rank order determined in the previous step? If yes, go to step 7. If no, go to the previous step? If yes, go to step 7. If no, go to the following step.

  6. Reorder the columns in the part-machine incidence matrix by listing them in decreasing rank order, starting with the left column. Go to step 1. Rank Order Clustering: Example

  Rank Order Clustering: Example

  Rank Order Clustering: Example

  Rank Order Clustering: Example

ROC: Example of Overlapping Machine Requirements

  Parts Parts Machines A B C D E F G H

  I

  1

  1

  1

  1

  1

  2

  1

  1

  3

  1

  1

  1

  4

  1

  1

  1

  5

  1

  1

  6

  1

  1

  7

  1

  1

  1 ROC: Example of Overlapping Machine Requirements _{8 7 6 5 4 3 2 1 Binary value 2 2 2 2 2}

₂

_{2 2 2} Machines A B C D E F G H ^{I rank} _{1 1 1 1 1 418 1 2 1 1 17 7}

  3 ^{1 1 1 81 5} _{4 1 1 1 168 3 5 1 1 258 2} ^{Parts decimal equivalent} _{5 1 1 258 2}

  6 ^{1 1 65 6} _{7 1}

₁

_{1 140 4}

ROC: Example of Overlapping Machine Requirements

  5

  1

  1

  2 ¹

  2

  1

  1

  2 decimal equivalent

  96

  88

  6

  80

  24

  2 ¹ Parts binary values

  8

  96

  7 rank

  1

  3

  8

  4

  9

  5

  6

  2

  7

  6

  Parts Machines A B C D E F G H

  I

  1

  1

  1

  1

  1

  1

  2 ⁶

  5

  1

  1

  2 ⁵

  4

  1

  1

  1

  2 ⁴

  7

  1

  1

  1

  2 ³

  3

  1

  1

  1

  2 ²

  6

  1

ROC: Example of Overlapping Machine Requirements

  Parts Parts Machines A H B D F G

  I C E

  1

  1

  1

  1

  

1

  5

  1

  1

  4

  1

  

1

  1

  7

  1

  1

  1

  3

  3

  1

  1

  1

  1

  1

  1

  6

  1

  1

  2

  1

  1

ROC: Example of Overlapping Machine Requirements

  Parts Parts Machines A H B D F G

  I C E 1a

  1

  1

  5

  1

  1

  4

  1

  

1

  1 1b

  1

  

1

  7

  7

  1

  1

  1

  1

  1

  1

  3

  1

  1

  1

  6

  1

  1 ARRANGING MACHINES IN A GT CELL

  After part-machine groupings have been • identified by ROC or other method, the next problem is to organize the machines into the most logical arrangement.

Two methods suggested by Hollier •

  ▫ Hollier method 1 ▫ Hollier method 1 ▫ Hollier method 2 Hollier Method 1

  1. Develop the From-To chart from part routing

  data

  2. Determine the “From” and “To” sums for each

  machine

  3. Assign machines to the cell based on minimum

  “From” or “To” sums “From” or “To” sums

  4. Reformat the From-To chart Hollier Method 1 Assign machines to the cell based on minimum “From” or • Assign machines to the cell based on minimum “From” or • “To” sums

  ▫ The machine having the smallest sum is selected.

▫ If the minimum value is a “To” sum, then the machine is placed at

the beginning of the sequence.

  ▫ If the minimum value is a “From” sum, then the machine is placed at the end of the sequence. ▫ Tie breaker rules:

  If a tie occurs between minimum “To” sums or “From” sums, then If a tie occurs between minimum “To” sums or “From” sums, then the machine with minimum “From/To” ratio is selected. If both “To” and “From” sums are equal for a selected machine, it is passed over and the machine with the next lowest sum is selected.

Hollier Method 1: Example

  Suppose that four machines, 1, 2, 3, and 4 have • Suppose that four machines, 1, 2, 3, and 4 have • been identified as belonging in a GT machine cell. An analysis of 50 parts processed on these machines has been summarized in the From-To chart. Additional information is that 50 parts enter the machine grouping at machine 3. 20 enter the machine grouping at machine 3. 20 parts leave after processing at machine 1, and 30 parts leave after processing at machine 4.

  Determine a logical machine arrangement using Hollier Method 1: Example

  Hollier Method 1: Example

  Hollier Method 1: Example

  Hollier Method 1: Example

  ▫ Machines with high ratios are placed at the beginning of the work flow, and machines with beginning of the work flow, and machines with low ratios are placed at the end of the work flow. ▫ In case of a tie, the machine with the higher

  Hollier Method 2

• Develop the From-To chart • Develop the From-To chart
• Determine the From/To ratio for each machine
• Arrange machines in order of decreasing

From/To ratio

  “From” value is placed ahead of the machine with Hollier Method 2: Example

  Hollier Method 2: Example

  Flow Diagram for Machine Cell

  Performance Measures

  Percentage of in-sequence moves • ▫ Computed by adding all of the values representing in-sequence moves and dividing by the total number of moves

Percentage of backtracking moves •

  ▫ Determined by summing all of the values ▫ Determined by summing all of the values representing backtracking moves and dividing by the total number of moves Performance Measures: Example

  Percentage of in-sequence moves • Percentage of in-sequence moves • ▫ In-sequence moves = 40 + 30 + 25 = 95 ▫ Total number of moves = 135 ▫ Percentage of in-sequence moves = 95/135 =

  70.4%

Percentage of backtracking moves • Percentage of backtracking moves •

  ▫ Backtracking moves = 5 + 10 = 15 ▫ Total number of moves = 135 ▫ Percentage of backtracking moves = 15/135 =