Practicle 7

8/13/2019 Practicle 7

1/12

Practical No.7

Objective:

i. Introduction to Group Technology

ii. On the basis of Optizs classification system, develop a code for the following part

iii. Write down benefits of Group Technology

Tools & Equipment:Computer with Office , Techniques used for Optizs coding system.

Theory:GROUP TECHNOLOGYGroup technology is an operations management philosophy based on the recognition that similarities

occur in the design and manufacture of discrete parts. Similar parts can then be arranged into partfamilies. To implement such a system, some form of classification of parts and coding is required. Partclassification and coding is concerned with identifying the similarities and using these similarities to

evolve a classification code. Similarities are of two types: design attributes (such as geometric shape andsize), and manufacturing attributes (the sequence of processing steps required to make the part). Incompanies which employ several design engineers and manufacturing a diverse range of products, suchclassifications and coding has a number of other uses. One of the major benefits is avoiding the

duplication of similar components. This can result in considerable savings in terms of design cost,processing cost and tooling cost. One prime necessity to realize this is to have a good design retrievalsystem. The parts classification and coding is required in a design retrieval system, and in computer aided

process planning the process routing is developed by recognizing the specific attributes of the part andrelating these attributes to the corresponding manufacturing operations.

PART FAMILIESpart family is a collection of parts which are similar either because of geometry and size or becausesimilar processing steps are required in their manufacture. The parts within a family are different, buttheir similarities are close enough to merit their identification as members of the part family. The major


2/12

obstacle in changing over to group technology from a traditional production shop is the problem ofgrouping parts into families. There are three general methods for solving this problem.

i. Visual inspectionii. Production flow analysisiii. Parts classification and coding system

What is desirable in a computer integrated manufacturing environment is a software which will analyzethe geometric model of the part and come out with a set of alphabetic/ numeric characters which can

broadly embed similarities.

Similar prismatic parts requiring similar milling operations

Dissimilar parts requiring similar machining operations (hole drilling, surface milling

Identical designed parts requiring completely different manufacturing processes


3/12

One of the important manufacturing advantages of grouping workparts into families can beexplained with reference to figures below


4/12

Grouping Part FamiliesThere are three general methods for solving part families grouping. All the three are time consuming andinvolve the analysis of much of data by properly trained personnel .

The three methods are:1. Visual inspection.2. Parts classification and coding.3. Production flow analysis.

1- Visual Inspection Method The visual inspection methodis the least sophisticated and least expensive method.

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

2- Parts classification and Coding

Parts classification and coding systems can be grouped into three general types:i. Systems based on design attributesii. Systems based on part manufacturing attributes

iii. Systems based on both design and manufacturing attributes

Systems in the first category are useful for design retrieval and to promote design standardization.Systems in the second category are used for computer-aided process planning, tool design, and other

production related functions. The third category represents an attempt to combine the functions andadvantages of the other two systems into a single classification scheme. The types of design andmanufacturing attributes typically included in classification schemes are listed below:


5/12

Part Design Attributes

Basic (External/Internal) shape

Axisymmetric/Prismatic/sheet metal

Length/diameter ratio

Material

Major dimensions

Minor dimensions

Tolerances

Surface finishPart Manufacturing Attributes

Major process of manufacture

Surface treatments/coatings

Machine tool/processing equipment

Cutting tools

Operation sequence

Production time

Batch quantity Production rate

Fixtures neededIf we take a look at a machine tool manufacturing industry, large part families can be grouped as:

i. Heavy parts - beds, columns etc.ii. Shafts, characterized by large L/D ratiosiii. Spindles (long shafts, screw rods included)iv. Non-rounds (small prismatic parts)v. Gears, disc type parts (whose L/D ratios are small)

From the manufacturing point of view, group technology can bring in considerable economy in tooling,set up time, part changeover times, machine specifications etc. The classification of components in groupscan lead to formation of cells where similar components are machined. However, these considerations are

extraneous to the process planning function.

The three basic coding structures:

1. Chain-type structure, also known as a polycode, in which the interpretation of eachsymbol in the sequence is always the same, it does not depend on the value of thepreceding symbols.


6/12

2. Hierarchical structure, also known as a monocode, in which the interpretation of eachsuccessive symbol depends on the value of the preceding symbols.

3. Hybrid structure, a combination of hierarchical and chain-type structures.


7/12

Opitz Classification and Coding System It is intended for machined parts and uses the following digits sequence

Form Code 1 2 3 4 5 for design attributes Supplementary Code 6 7 8 9 for manufacturing attributes Secondary Code A B C D for production operation type

. & sequence


8/12

Digits (1-5) for Rotational parts in the Opitz System


9/12

3- Production Flow Analysis (PFA)

Production flow analysis (PFA) is a method for identifying part families and associatedmachine groupings that uses the information contained on process plans rather than onpart drawings.

Work parts with identical or similar process plans are classified into part families. Thesefamilies can then be used to form logical machine cells in a group technology layout.

The procedure in production flow analysis must begin by defining the scope of the study,which means deciding on the population of parts to be analyzed.

The procedure of Production flow analysis (PFA) consists of the following steps: Data Collecti on.The minimum data needed in the analysis are the part number

and operation sequence, which is obtained from process plans. Sortation of process plans. A sortation procedure is used to group parts with

identical process plans. PFA Chart. The processes used for each group are then displayed in a PFA

chart as shown below.

Clustering Analysis.From the pattern of data in the PFA chart, related groupings are identifiedand rearranged into a new pattern that brings together groups with similar machine sequences.


10/12

Activity:

On the basis of Optiz part coding System develope a code for the fol lowing part:

Solution: Length-to-diameter ratio: L/D = 1.5 Digit 1 = 1 External shape: both ends stepped with screw thread on one end Digit 2 = 5 Internal shape:part contains a through hole Digit 3 = 1

Plane surface machining: none Digit 4 = 0 Auxiliary holes, gear teeth, etc.: none Digit 5 = 0

The form code in the Optiz system is 15100


11/12

BENEFITS OF GROUP TECHNOLOGY

Implementation of group technology results in more focused factories. The likely impact of grouptechnology can be seen in Table

When group technology is applied, a manufacturing company will typically realize the followingbenefits:

Product engineering -

Reduce part proliferation

Help design standardizationProvide manufacturing feed back

Manufacturing engineering

Process selectionTool selection

Machine purchasesMaterial handling

Production engineering -

Reduce lead timeReduce delays

Reduce set-up timeImprove product quality

Production planning and control -

Group schedulingStock accountabilityReduce expediting

Improved product designReduced materials handlingBetter employee satisfaction

Other benefits:

Increased productivity


12/12

Improved accuracy in estimation of costs Greater standardization and variety reduction

Reduced set up times Better product delivery (Helps to implement just-in-time (JIT) manufacturing) Reduced cost of purchasing

Improved plant efficiency

Documents

Practicle 7