groover ch15 - group technology

Industrial Work GroupIndustrial Work Group

Group Technology and Group Technology and

Cellular ManufacturingCellular Manufacturing

Ramiro Bonaque Rodríguez

Jose Luís Gandia Fornés

Toni Barberà Pastor

Universitat Jaume I de

Castelló

1. Introduction1. Introduction

2. Parts classification and coding2. Parts classification and coding

3. Production flow analysis3. Production flow analysis

4. Cellular manufacturing4. Cellular manufacturing

5. Application considerations in group 5. Application considerations in group

technologytechnology

6. Quantitative analysis in cellular 6. Quantitative analysis in cellular

manufacturingmanufacturing

Table of contentsTable of contentsTable of contentsTable of contents

1. Introduction1. Introduction1. Introduction1. Introduction

Processes types for batch manufacturingProcesses types for batch manufacturing

Process type plant layout Process type group technology

Turning

Milling

Assembly

Drilling

Shipping

Receiving

Machines are arranged by function.

Machines are arranged into cells


DefinitionsDefinitions

Group technology is a philosophy in which similar parts are identified and grouped together to take advantage of their similarities in design and production.

Group technology is a philosophy in which similar parts are identified and grouped together to take advantage of their similarities in design and production.

Part familyPart family

Part family is a collection of parts that are similar either because of geometric shape and size or because similar processing steps are required in their manufacture.

Part family is a collection of parts that are similar either because of geometric shape and size or because similar processing steps are required in their manufacture.

Cellular manufacturingCellular manufacturing

Cellular manufacturing is grouping the production equipment into machine cells, where each cell specializes in the production of a particular part family.

Cellular manufacturing is grouping the production equipment into machine cells, where each cell specializes in the production of a particular part family.

Group technologyGroup technology


ObjectiveObjective

• To make batch production more efficient and productive.

• To integrate design and manufacturing in a firm.

ObstaclesObstacles

BenefitsBenefits

• Identifying the part families.

• Rearranging production machines into machine cells.

• It promotes standardization

• It reduces material handling, setup times and work-in-process

• Workers satisfaction and quality work improve

Features of group technologyFeatures of group technology


The changeover from a conventional The changeover from a conventional production to group technologyproduction to group technology

1) Visual inspection

2) Parts classification and coding

3) Production flow analysis


2) Parts classification and coding

3) Production flow analysis

Three methods to group the parts into families:

It involves the classification of parts into families by looking at either the physical parts or their photographs and arranging them into groups having similar features.

It involves the classification of parts into families by looking at either the physical parts or their photographs and arranging them into groups having similar features.


2. Parts classification and coding2. Parts classification and coding2. Parts classification and coding2. Parts classification and coding

DefinitionDefinition

Each part family is exclusively identified by an alpha-numerical code, which represents their design attributes, manufacturing attributes or both.

Each part family is exclusively identified by an alpha-numerical code, which represents their design attributes, manufacturing attributes or both.

AdvantagesAdvantages

Methods to obtain the code from a particular partMethods to obtain the code from a particular part

• Design retrieval• Automated process planning• Machine cell design

• Looking in tables to match the subject part against the features described.

• Using a computerized classification and coding system to reply questions about the part’s features.

FeaturesFeatures


Parts coding systems Parts coding systems

OpitzOpitz Brisch SystemBrisch System CODECODE CUTPLANCUTPLAN

DCLASSDCLASS MultiClassMultiClass Part Analog SystemPart Analog System

Hierarchical / monocode

Types of structures of coding systemsTypes of structures of coding systems

Chain-type / polycode

Mixed-modee.g. Opitz Classification System

(by H. Opitz)

e.g. Opitz Classification System (by H. Opitz)

e.g. MultiClass (by Organization for Industrial Research)

e.g. MultiClass (by Organization for Industrial Research)


Opitz Coding System Opitz Coding System

12345 6789 ABCD12345 6789 ABCD12345 6789 ABCD12345 6789 ABCD

Digit sequence:Digit sequence:

Form code: design attributes

Supplementary code: manufacturing attributes

Secondary code: operation sequence and particular needs



Part ClassPart Class

0

Rotational

L/D ≤ 0,5

1 0,5 < L/D < 3

2 L/D ≥ 3

3With deviation

L/D ≤ 2

4With deviation

L/D > 2

5 Special

6 Non-rotational

A/B ≤ 3

A/C ≥ 4

7 A/B > 3

8A/B ≤ 3

A/C < 4

9 Special

External Shape

Element

External Shape

Element

Main ShapeMain

Shape

Internal Shape

Element

Internal Shape

Element

Rotational MachiningRotational Machining

Main bore and

rotational machining

Main bore and

rotational machining

Main ShapeMain Shape Rotational MachiningRotational Machining

Machining of plane surface


Plane Surface Machining

Plane Surface Machining





Other holes and

teeth

Other holes and

teeth

Additional Holes Teeth and Forming

Additional Holes Teeth and Forming

Other holes,

teeth and forming

Other holes,

teeth and forming

Other holes,

teeth and forming

Other holes,

teeth and forming

Digits

6 7 8 9

Dim

ensions

Material

Original shape of raw

materials

Accurany

Main ShapeMain

Shape

Main ShapeMain

Shape

Main ShapeMain

Shape

Digit 1 Digit 2 Digit 3 Digit 4 Digit 5

Su

pp

lemen

tary co

deForm code




0

Rotational

L/D ≤ 0,5

1 0,5 < L/D < 3

2 L/D ≥ 3

3With deviation

L/D ≤ 2

4

5

6 Non-rotational

7

8

9

0Smooth, no shape

elements

1

Stepped to one end

No shape elements

2

Or sm

ooth

Thread

3Functional

groove

4

Stepped to both ends

No shape elements

5 Thread

6 Functional groove

7 Functional cone

8 Operating thread

9 All others

External shape, external shape

elements


elements

Digit 1 Digit 2

0No hole, no

breakthrough

1

Sm

ooth or stepped to one end

No shape elements

2 Thread

3Functional

groove

4S

tepped to both ends

No shape elements

5 Thread

6 Functional groove

7 Functional cone

8 Operating thread

9 All others

Internal shape, internal shape

elements


elements

Digit 3

0 No surface machining

1Surface plane and/or

curved in one direction, external

2External plane surface related by graduation

around the circle

3 External groove and/or slot

4 External spline

5 External plane surface and/or slot, external spline

6 Internal plane surface and/or slot

7 Internal spline

8Internal and external

polygon, groove and/or slot

9 All others

Plane surface machining


Digit 4

0

No gear teeth

No auxiliary hole

1Axial, not on pitch

circle diameter

2Axial on pitch circle

diameter

3Radial, not on pitch

circle diameter

4Axial and/or radial

and/or other directions


on PCD and/or other directions

6 With gear teeth

Spur gear teeth

7 Bevel gear teeth

8 Other gear teeth

9 All others

Auxiliary holes and gear teethAuxiliary holes and gear teeth

Digit 5



ExampleExample Given this rotational part design, determine the form code in the Opitz parts classification and coding system.

0,70,3

0,5

0,8

½ – 13 UNC

1,5

1,0


0

Rotational

L/D ≤ 0,5

1 0,5 < L/D < 3

2 L/D ≥ 3

3

4

5

6 Non-rotational

7

8

9

0Smooth, no shape

elements

1

Stepped to one end

No shape elements

2

Or sm

ooth

Thread

3Functional

groove

4

Stepped to both ends

No shape elements

5 Thread

6 Functional groove

7 Functional cone

8 Operating thread

9 All others


elements


elements

Digit 1 Digit 2

0No hole, no

breakthrough

1

Sm

ooth or stepped to one end

No shape elements

2 Thread

3Functional

groove

4S

tepped to both ends

No shape elements

5 Thread

6 Functional groove

7 Functional cone

8 Operating thread

9 All others


elements


elements

Digit 3

0 No surface machining

1Surface plane and/or

curved in one direction, external

2External plane surface related by graduation

around the circle

3 External groove and/or slot

4 External spline

5 External plane surface and/or slot, external spline

6 Internal plane surface and/or slot

7 Internal spline

8Internal and external

polygon, groove and/or slot

9 All others



Digit 4

0

No gear teeth

No auxiliary hole

1Axial, not on pitch

circle diameter

2Axial on pitch circle

diameter

3Radial, not on pitch

circle diameter


and/or other directions


on PCD and/or other directions

6 With gear teeth

Spur gear teeth

7 Bevel gear teeth

8 Other gear teeth

9 All others

Auxiliary holes and gear teeth

Auxiliary holes and gear teeth

Digit 5

Form code0,70,3

0,5

0,8

½ – 13 UNC

1,5

1,0

11 55 11 00 00

Length-to-diameter ratio

L/D = 1,5

Length-to-diameter ratio

L/D = 1,5

External shape: stepped on both ends with screw thread on one end

External shape: stepped on both ends with screw thread on one end

Internal shape: part contains a through-hole

Internal shape: part contains a through-hole

Plane surface machining: nonePlane surface machining: noneAuxiliary holes, gear teeth, etc.: noneAuxiliary holes, gear teeth, etc.: none


MultiClass Coding SystemMultiClass Coding System

Coding structure:Coding structure: up to 30 digits divided into 2 regions

Region 1Region 1

Digit Function

01

2, 34

· · ·18

Code system prefixMain shape categoryExternal and internal configurationMachined secondary elements· · · Etc. · · ·Machined element orientation

Region 2:Region 2: designed by the user to meet specific needs and requirements.


MultiClass Coding SystemMultiClass Coding System

ExampleExample Given this rotational part design, determine the form code in the MultiClass parts coding system.


MultiClass Coding SystemMultiClass Coding System SolutionSolution

3. Production Flow Analysis3. Production Flow Analysis3. Production Flow Analysis3. Production Flow Analysis

• Parts whose basic geometries are quite different may nevertheless require similar or even identical process routings.

• Parts whose geometry are quite similar may nevertheless require process routings that are quite different.


Production flow analysis (PFA) is a method for identifying part families and associated machine groupings that uses the information contained on production route sheets rather than on part drawings.

Production flow analysis (PFA) is a method for identifying part families and associated machine groupings that uses the information contained on production route sheets rather than on part drawings.

Workparts with identical or similar routings are classified into part families. Then, the families can be used to form logical machine cells in a group technology layout.

Possible anomaliesPossible anomalies

VirtueVirtueRequire less time than a complete parts classification and coding procedure.


ProcedureProcedure

3. Sortation of process routings: Parts are arranged into groups according to the similarity of their process routings.To make this:a) All operations or machines are reduced to code numbers;b) For each part, operation codes are listed in the order they are performedc) A sortation procedure is then used to arrange parts into packs.

2. Data collection: The minimum data needed in the analysis are the part number and operation sequence.Additional data: lot size, time standards, and annual demand might be useful.

1. Scope of the analysis: The production flow analysis must begin defining the scope of the study (population of parts to be analyzed).


ProcedureProcedure

4. PFA Chart: The processes used for each pack are then displayed in a PFA chart.PFA chart has been referred as part-machine incidence matrix.

xij = 1 Part i requires processing on machine j

xij = 0 Part i is not processed on machine j

3. Production Flow Analysis3. Production Flow Analysis3. Production Flow Analysis3. Production Flow AnalysisProcedureProcedure

5. Cluster analysis: From the pattern of data in the PFA chart, related groupings are identified an rearranged into a new pattern that brings together packs with similar machine sequences.- Different machine groupings are indicated with blocks. - The blocks might be considered as possible machine cells.

WeaknessWeaknessThe data used in the technique are derived form existing production route sheets. The routings may contain operations that are nonoptimal, illogical or unnecessary.

4. Cellular Manufacturing4. Cellular Manufacturing4. Cellular Manufacturing4. Cellular Manufacturing

• To shorten manufacturing lead times.


Cellular manufacturing is an application of group technology in which dissimilar machines or processes have been aggregated into cells, each of which is dedicated to the production of a part or product family or limited groups of families.

Cellular manufacturing is an application of group technology in which dissimilar machines or processes have been aggregated into cells, each of which is dedicated to the production of a part or product family or limited groups of families.

ObjectivesObjectives

• To reduce work in process inventory.

• To improve quality.

• To simplify production scheduling.

• To reduce setup times.


Composite Part Concept is a hypothetical part for a given family which includes all of the design and manufacturing attributes of the family.

Composite Part Concept is a hypothetical part for a given family which includes all of the design and manufacturing attributes of the family.

4.1. Composite Part Concept4.1. Composite Part Concept


A production cell designed for the part family would include all the machines required to make the composite part. Such a cell would be capable of producing any member of the family, simply by omitting those operations corresponding to features not possessed by the particular part.

Production cell designProduction cell design

The cell would also be designed to allow size variations within the family as well as feature variations.

An individual part in the family will have some features that characterize the family but not all of them. The composite part possesses all of them.


4.2. Machine cell design4.2. Machine cell design

Types of Machine Cells and LayoutsTypes of Machine Cells and Layouts

Manufacturing cells can be classified according to the number of machines and the degree to which the material flow is mechanized between machines.

Four common GT cell configurations:

1. Single machine cell: Consists on one machine plus supporting fixtures and tooling. This type of cell can be applied to workparts whose attributes allow them to be made on one basic type of process such as turning or milling.


2. Group machine cell with manual handling: an arrangement of more than one machine used collectively to produce one or more part families. - There is no provision for mechanized parts movement between the machines in the cell. Instead, the human operators who run the cell perform the material handling function.- The cell is often organized into a U-shaped layout. This layout is appropriate when there is variation in the work flow and to allow the multifunctional workers in the cell to move easily between machines.


3. Group machine cell with semi-integrated handling: uses a mechanized handling system to move parts between machines in the cell.

4. Flexible manufacturing system (FMS): combines a fully integrated material handling system with automated processing stations.- FMS is the most highly automated of the group technology machines cell.- Variety of layouts: U-shape, in-line, loop, and rectangular.

4. Cellular Manufacturing4. Cellular Manufacturing4. Cellular Manufacturing4. Cellular ManufacturingCell designCell design

Part movementFour types of part movement:

1. Repeat operation: a consecutive operation is carried out on the same machine so the part does not actually move.

2. In-sequence move: the part moves from the current machine to an immediate neighbor in the forward direction.

3. By-passing move: the part moves forward from the current machine to another machine that is two or more machines ahead.

4. Backtracking move: the part moves from the current machine in the backward direction to another machine.


Additional factors

Additional factors that must be accounted for in the cell design:

• Quantity of work to be done by the cell: number of parts per year and processing time per part at each station. Determine the workload and therefore the number of machines that must be included.

• Part size, shape, weight, and other physical attributes: determine the size and type of material handling and processing equipment that must be used.

Movement Layout

Repeat operations

In-sequence move

Passing moves

Backtracking move

Multiple stations (machines)

In-line layout / U-shaped layout

U-shaped layout

Loop or rectangular layout


Key machine conceptKey machine concept

Key machine is a certain machine in a cell that is more expensive to operate than the other machines or that performs certain critical operations in the plant.

Key machine is a certain machine in a cell that is more expensive to operate than the other machines or that performs certain critical operations in the plant.

The other machines are referred to as supporting machines, and they should be organized in the cell to keep the key machine busy. In a sense, the cell is designed so that the key machine becomes the bottleneck of the system.

The key machine concept is sometimes used to plan the GT machine cell. The approach is to decide what parts should be processed through the key machine and then determine what supporting machines are required.


Utilization measures Utilization measures

Two measures of utilization:

1. Utilization of the key machine: using the usual definition. The utilization of each of the other machines can also be evaluated similarly.

2. Utilization of the overall cell: obtained by taking a simple arithmetic average of all the machines in the cell.

5. Application considerations in 5. Application considerations in group technologygroup technology


5.1. Applications of Group Technology5.1. Applications of Group Technology

5.1.1. Manufacturing Applications5.1.1. Manufacturing Applications

1. Formation of cells

Informal scheduling and routing of similar parts through selected machines

Virtual machine cells

Formal machine cells

2. Process planning of new parts

3. Family tooling

4. Parametric programming



5.1. Application of Group Technology5.1. Application of Group Technology

5.1.2. Product Design Applications5.1.2. Product Design Applications

1. Use of design retrieval systems Design savings

2. Simplification and standardization of design parameters

• Simplify design procedures

• Reduce part proliferation

• Reduce the required number of tools

• Reduce the amount of data and information that the company must deal with



5.2. Survey of Industry Practice5.2. Survey of Industry Practice

Rank Reason for installing Manufacturing Cells

1 Reduce throughput time (Manuf. Lead time)

2 Reduce work-in-process

3 Improve part and/or product quality

4 Reduce response time for customer orders

5 Reduce move distances

6 Increase manufacturing flexibility

7 Reduce unit costs

8 Simplify production planning and control

9 Facilitate employee involvement

10 Reduce setup times

11 Reduce finished goods inventory



5.2. Survey of Industry Practice5.2. Survey of Industry Practice

Rank Costs of Introducing Cellular Manufacturing

1 Relocation and installation of machines

2 Feasibility studies, planning and design

3 New equipment and duplication of equipment

4 Training

5 New tooling and fixtures

6 Programmable controllers, computers and software

7 Material handling equipment

8 Lost production time during installation

9 Higher operator wages

6. Quantitative analysis in 6. Quantitative analysis in cellular manufacturingcellular manufacturing


• Quantitative techniques have been developed to deal with problem areas in GT

• Two main problem areas

Grouping parts and machines into families

Rank order clusteringRank order clustering

Arranging machines in a GT cell

An heuristic approach by Hollier

An heuristic approach by Hollier



6.1. Rank Order Clustering Technique6.1. Rank Order Clustering Technique

• Specially applicable in production flow analysis

• It works by reducing the part-machine incidence matrix to a set of diagonalized blocks that represent part families and machine cells.

• Algorithm 1. Read each row of the matrix as a binary number and reorder them in decreasing order.

2. Do the same with the columns of the matrix

3. Repeat steps 1 and 2 until no change in the matrix is needed.




6.1.2. Example6.1.2. Example

Parts

Machines A B C D E F

1 1 1 1

2 1 1

3 1 1 1

4 1 1

Parts

Machines A F D B E C

1 1 1 1

4 1 1

3 1 1 1

2 1 1





Parts


1a 1 1

4 1 1

3 1 1 1

1b 1 1

2 1 1 1

Parts


1 1 1 1 1

4 1 1

3 1 1 1

2 1 1 1



6.2. Hollier Method to Arrange Machines in a GT Cell6.2. Hollier Method to Arrange Machines in a GT Cell

• Uses data contained in From-To charts

• Maximizes the proportion of in-sequence moves within the cell

• Algorithm 1. Develop the From-To chart

2. Determine the From/To ratio for each machine

3. Arrange machines in order of decreasing From/To ratio





• 50 parts processed on 4 machines.

To: 1 2 3 4 “From” Sums

From/To Ratio

From: 1 0 5 0 25 30 0.60

2 30 0 0 15 45 1.0

3 10 40 0 0 50

4 10 0 0 0 10 0.25

“To” Sums 50 45 0 40





• Flow diagram

50 in 3 2 1 4 30 out

20 out

40 30 25

10 15

105

Percentages of in-sequence moves = 70.4%

Percentages of backtracking moves = 11.1%

QuestionsQuestionsQuestionsQuestions

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