Group Technology

INTRODUCTION

Group technology was introduced by Frederick Taylor in 1919 as a way to improve productivity.

One of long term benefits of group technology is it helps implement a manufacturing strategy aimed at greater automation.

Group Technology

Group technology (GT) is a manufacturing philosophy that seeks to improve productivity by grouping parts and products with similar characteristics into families and forming production cells with a group of dissimilar machines and processes

Similarities among parts permit them to be classified into part families

In each part family, processing steps are similar

The improvement is typically achieved by organizing the production facilities into manufacturing cells that specialize in production of certain part families

Part Families

A group 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 family

But the similarities are close enough that the parts can be grouped into the same family

IDENTIFYING PART FAMILIES

Visual inspection - using best judgment to group parts into appropriate families, based on the parts or photos of the parts

Clustering method - using information contained on route sheets to classify parts

Parts classification and coding - identifying similarities and differences among parts and relating them by means of a coding scheme

Clustering Method

1. For each row of the machine/part matrix (M/P/M) read the pattern of cell entries as a binary word. Rank the rows by decreasing binary value. Equal values stay in same order.

2. Ask if newly ranked rows in the matrix are the same as previous order? – Yes (STOP) No (continue)

3. Re-form the M/P/M with rows in new descending order. Now rank the columns by decreasing binary word weight. Columns of equal weight are left where they are

4. Are current column weights the same as current column order? Yes (STOP), No (continue)

5. Re-form the matrix column order per rank order (highest to left) and return to #1.

Lets try it with our earlier problem:

Part ‘Number’

Machine ID

X 1 2 3 4 5 6

A 1 1

B 1 1

C 1 1

D 1 1 1

E 1 1 1

Step 1:

Part Numbers D. Equiv Rank

Machine ID

1 2 3 4 5 6

B. Wt: 25 24 23 22 21 20

A 1 1 23+21 = 10 5

B 1 1 24+23 = 24 4

C 1 1 25+22=36 2

D 1 1 1 24+23+21 = 26 3

E 1 1 1 25+22+20=37 1

Step 2: Must Reorder!

Step 3:

Part Number

B. WT. 1 2 3 4 5 6

Machine ID

E 24 1 1 1

C 23 1 1

D 22 1 1 1

B 21 1 1

A 20 1 1

D. Equiv 24+23 = 24

22+21= 6

22+21+20=7

24+23=24

22+20=5 24=16

Rank 1 5 4 2 6 3

Step 4: Must Reorder

Back at Step 1:

Part Number D. Eqv Rank

1 4 6 3 2 5

B Wt: 25 24 23 22 21 20

Machine ID

E 1 1 1 25+24+ 23=56 1

C 1 1 25+24= 48 2

D 1 1 1 22+21+ 20 = 7 3

B 1 1 22+21=6 4

A 1 1 22+20=5 5

Order stays the same: STOP!

Great Cluster Result!

PART CLASSIFICATION AND CODING

It involves examination of individual design and manufacturing attributes of parts

Sampling process is used to identify part families

Generally customed –engineered for a given company

DESIGN SYSTEMS

Based on part design attributes

Basic external shape Basic internal shape Length/diameter ratio Material type Part function Major/minor dimensions Tolerances Surface finish

• useful for design retrieval and to promote design standardization

MANUFACTURING SYSTEMS

Based on part manufacturing attributes

Major process Minor operations Major dimensions Length/diameter ratio Surface finish Machine tool Operation sequence Production time Batch size Cutting tools Fixtures needed

• Used for computer aided process planning, tool design and other production-related functions

SYSTEMS BASED ON DESIGN AND MANUFACTURING

It attempts to combine the advantages of both design and manufacturing attributes

There is certain amount of overlapping between design and manufacturing attributes of a part

CODING SYSTEM STRUCTURE

Hierarchical structure, known as a mono-code, in which the interpretation of each successive symbol depends on the value of the preceding symbols

Chain-type structure, known as a polycode, in which the interpretation of each symbol in the sequence is always the same; it does not depend on the value of preceding symbols

Mixed-mode structure, which is a hybrid of the two previous codes

IMPORTANT SYSTEMS

Opitz classification system –the University of Aachen in Germany, nonproprietary, Chain type.

Brisch System –(Brisch-Birn Inc.)

CODE (Manufacturing Data System, Inc.) MultiClass (OIR: Organization for Industrial Research), hierarchical or decision-

tree coding structure

OPITZ CLASSIFICATION