GROUP TECHNOLOGY

Chapter 10

GROUP TECHNOLOGY

GROUP TECHNOLOGY IS A MANUFACTURING TECHNIQUE AND PHILOSOPHY TO INCREASE PRODUCTION EFFICIENCY BY EXPLOITING THE “UNDERLYING SAMENESS” OF COMPONENT SHAPE, DIMENSIONS, PROCESS ROUTE, ETC.

• Group Technology is the realization that many problems are similar, and that by grouping similar problems, a single solution can be found to a set of problems thus saving time and effort. (Solaja 73)

• First book formalize the concept:Mitrofanov,S.P. 1958, "The Scientific

Principles of Group Technology"

Why Group Technology?

• Average lot size decreasing• Part variety increasing• Increased variety of materials With diverse properties• Requirements for closer tolerances

FLEXIBILITY

PRODUCTION CAPACITY

TRANSFERLINE

SPECIAL SYSTEM

FLEXIBLEMANUFACTURING

SYSTEM

MANUFACTURINGCells

STD. AND GEN.MACHINERY

VO

LU

ME

HIGH

VARIETYLOW HIGH

Everyday Examples

1. Fast food chains2. Doctors, dentists and also manufacturing

A FAMILY OF PARTS

Production Family

• Lack Of Common Database For Mfg., Design...

• Don’t “redesign the wheel”• Automated process planning• Database to drive the automated factory

Benefits Of Group TechnologyReductions in

Throughput timeSet-up timeOverdue orders

Production floor spaceRaw material stocksIn-process inventory

Capital expendituresTooling costsEngineering time and costs

New parts designNew shop drawingsTotal number of drawings

Cont’d

Other Benefits Of Group Technology

Easier to justify automation Standardization in design Data retrieval Easier, more standardized process plansIncreases in quality

Gt affects most every operating and staff function. It is more than merely a technique, but a total

Manufacturing philosophy.

GT

DESIGNENGINEERINGDATA

PROCESSING

MAINTENANCE

TOOL ENGINEERING

ESTIMATING

INDUSTRIALRELATIONS

QUALITYCONTROL

R & D

COSTACCOUNTING

SALES

INVENTORY

PLANNING

PURCHASING

ASSEMBLY

MANAGEMENT

MFG.ENGINEERING

SHIPPING &RECEIVING

Three Techniques To Form Part Families

1. Tacit judgment or visual inspection

2. Production Flow Analysis

• May use photos or part prints• Utilizes subjective judgment

• Uses information contained on the route sheet (therefore only mfg. Info)• Parts grouped by required processing

Cont’d

3. Classification And Coding

• Codes geometry/design and mfg. Info about a component• Codes are alphanumeric strings• Easier to use for other analyses

Types Of Classification And Coding Systems

GT coding can benefit many facets of the Firm and fall into one of 3 categories:

1. Systems based on part design Attributes2. Systems based on part mfg. Attributes3. Systems based on design and mfg. Attributes

Examples:

Part Design Attributes

Basic external shapeBasic internal shapeMaterial

Part Mfg. Attributes

Major processesMinor operationsFixtures needed

Length/diameter ratio

Surface finish

Tolerances-----machine tool Operation sequence

Major dimensionTooling

Batch size

GT Code--a Sequence Of Numerical Digits

Three major structures:

1. Monocode (or hierarchical structure)

A code in which each digit amplifies the information given in the previous digit

• Difficult to construct• Provides a deep analysis• Usually for permanent information

cont’d

2. Polycode (Or Chain-type Structure)

Each digit is independent of all others, presents information not dependent On previous ones

• Easier to accommodate Change

3. Mixed Code

Has some digits forming monocodes, but strings them together in the general Arrangement of a polycode

POPULATION SPACE

CODE SPACE

P

C

MAPPING FROM POPULATION SPACE TO CODE SPACE

H

UN

F t

hre

ad

Tra

nsm

issi

on

Hierarchical Structure

Hydraulic Electrical

Mechanical

32XX

321X

322X

No

thre

adU

NC

thread

3222

323X

Power

Receiving

3232

3231 3233

3221 3223

MonocodePolycode Polycode

Hybrid Structure

Reduction Of Mfg. Costs By Various Steps Of Group Technology Applications

(Adapted From Ham442)

Improvements in Engineering Design

Materials Management & Purchasing Benefits

Production Control Benefits

Manufacturing Engineering Benefits

Tooling & Setup Benefits

Management BenefitsOverall Cost Reduction & Increased Productivity

Not All Cost Savings Are Immediate...

0 6 12 18 24 36Time (months)

Selection of optical instrument parts in one company, Illustrating the similarity between certain components

• Proliferation Of Parts

• Note: some of the above are almost the same

Conceptual design

Coding (rough model)

Retrieval existing designs

Existing designs

Design modification

New Design

Design archive

Retrieve designs of similarshape or function and usethem as the examples.

Design concept can be coded.

Code is a rough model of theconceptual design.

Technique:

1. Determine part and machine requirements

2. Numerically code each partGeometry (& size)MaterialOther specifications (tolerance, Surface finish)

3. Form a family of similar parts which use (Largely) the same set of machine tools

4. Lay out of each cell (a group of machine Tools) to make a family of parts

5. Design group tooling

Example:

Thirteen parts with similar manufacturing Process requirements but different

Design attributes

Functional Layouts Are Inefficient

PROCESS-TYPE LAYOUT

Lathe Milling Drilling

Grinding

Assembly

Receiving andShipping

L

L L

L

L

L

L

L M

MM

M M

M

A A

A A

D

D D

D

G

G

G

G G

G

Group Technology Layout

Shipping

L L M D

L M D

G

L M GG

A A

Receiving

Department #2

Department #3

Department #1

D D M I

D ML L I

D

M

LM

I

Cellular Layout

1st Digitpart class

Positionswith adigit

2nd Digitmain shape

3rd Digitrotationalmachining

4th Digitplane surface

matching

5th Digitadditional

holes teeth &forming

Form Code

Opitz coding and classification system.

(Reprinted with permission from H. Opitz, A Classification System to Describe Workpieces, Pergamon Press.)

Special

Non

-rot

atio

nal

Special

Rot

atio

nal

9

8

7

6

5

4

3

2

1

0Internal

shapeelement

Rotationalmachining

Main bore & rotationalmachining

Other holesand teeth

Other holesteeth andforming

Other holesteeth andforming

Machiningof planesurfaces

Machiningof planesurfaces

Machiningof planesurfaces

External shape

element

Main shape

Main shape

Main shape

Main shape

Supplim-entarycode

Digit6 7 8 9

Dim

ensi

ons

Mat

eria

lO

rigi

nal s

hape

of

raw

mat

eria

lsA

ccu

racy

Process planningsystem

APT Processor& post-processor

APT Program

Process

XXX

Typical Process

Planning System

Partprogramme

r

Production planner• Scheduling• MPP

Industrial engineer• Time standard• Operation instruction• Layout

Engineeringdrawing

Processplanner

Code orother form

of input

Process Planning

“Process planning” is that function within a manufacturing Facility that establishes which machining processes and Parameters are to be used (as well as those machines capable Of performing these processes) to convert (machine) a piece Part from its initial form to a final form predetermined (usually by a design engineer) from an engineering drawing.

(I.E. The preparation of the detailed work instructions to Produce a part)

Bridge

Design Manufacturing

Process planning bridges design and manufacturing

Variant Process Planning

Uses the similarity among components to retrieve existing process plans (which can be modified)

Overview: Two Stages For VP Systems

1. Preparatory stage

• Existing parts coded & classified (i.E. Gt is a prerequisite)• Part families organized• Standard plans developed• Databases created

(Note: this stage is labor intensive)Cont’d

Part Drawing

Coding

Family Formation

Process Plan

Family One

StandardPlanFile

(Indexedby FamilyMatrix)

1. Preparatory Stage Of Variant

Process Planning

2. Production Stage Of Variant Process Planning

Coding Family SearchStandard

PlanFile

Editing Standard PlanRetrieval

Process Plan