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A SEMINAR REPORT ON
"GROUP TECHNOLOGY (CODING SYSTEM)" SUBMITTED TO SAURASTRA UNIVERSITY IN PARTIAL FULFILLMENT OF THE BACHELOR’S DEGREE IN MECHANICAL ENGINEERING YEAR 2009 BY
KHAPANDI JITENDRA R. (06ME004) KAWA KAUSHIK M. (06ME019) UNDER THE GUIDANCE OF
PROF. RUPA P. ACHARYA
DEPARTMENT OF MECHANICAL ENGINEERING V.V.P. ENGINEERING COLLEGE RAJKOT- 360 005.
V.V.P. ENGINEERING COLLEGE RAJKOT
CERTIFICATE This is to certify that project report entitled “GROUP TECHNOLOGY (CODING SYSTEM) ” submitted by KHAPANDI JITENDRA R. (06ME004) and KAWA KAUSHIK M. (06ME019) towards the partial fulfillments of the requirements for semester 7’th of bachelor in Mechanical Engineering of V.V.P. Engineering college, Rajkot the record of work carried out by them under our supervision and guidance. The work submitted has in our opinion reached a level for being accepted for examination the results embodied in this major project work to the best of our knowledge have not been submitted to any other university of institution for award of any degree or diploma.
DATE: PROJECT GUIDE:
HEAD OF DEPARTMENT:
By these words I am feeling very lucky for the opportunity that has been given to me for working with PROF. RUPA P. ACHARYA who has been always Supportive and helpful to my work during the seminar work of the 7th semester MECHANICAL ENGINEERING. I acknowledge his assistance and Encouragement extended by his for giving us information clearing Doubts, Obligatory.
I has inflated pleasure to offer my sincere respect to Prof. JIGNASA P. MEHTA (H.O.D.) for providing us with all the necessary facilities and timely centralization during the period I stay with him.
KHAPANDI JITENDRA R. (06ME004) KAWA KAUSHIK M. (06ME019)
INDEX INTRODUCTION PART FAMILIES PART FAMILY CONCEPT METHOD FOR DEVELOPING PART FAMILIES PROCESS LAYOUT PARTS CLASSIFICATION AND CODING CODING SYSTEM STRUCTURE SPECIAL SYMBOL CODES PRINCIPLES OF CODING SELECTION OF CODING SYSTEMS SOME OF THE IMPORTANT SYSTEMS o
OPITZ Classification System
o DCLASS System o
BENEFITS OF GROUP TECHNOLOGY SCOPE AND LIMITATION
Example of GT-based classification and coding system by computer programming
INTRODUCTION Group technology is a manufacturing philosophy in which similar parts are identified and grouped together to take advantage of their similarities in design and manufacturing. Group technology (GT) is a manufacturing philosophy where similar objects are identified and grouped together to take advantage of their similarities in design and manufacturing. ‘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.’ “The technique of identifying and bringing together related or similar parts in a production process in order to utilize the inherent economy of flow production methods.” Parts with similar characteristics are grouped into families. Families may be based on similarities in design attributes such as geometric shape and size, or manufacturing attributes such as sequence of processing steps required, jigs, fixtures, and tooling.
PART FAMILIES Group Technology is a manufacturing concept in which similar parts are grouped together in parts groups families. 1.
In their Design characteristics (differ in the production processes)
In the manufacturing processed required to produce them (differ design) GT exploits the part similarities by utilizing similar processes and tooling to produce them.
PART FAMILY CONCEPT A part that has been designed for manufacturing usually has to be produced by several succeeding manufacturing operations. If there is a large spectrum of parts to be produced, it will be necessary for work pieces to share common processing equipment. It is advantage to group parts together to families either according to their geometric similarities or to similar fabrication methods. A change of parts would only require a new part program to generate a new contour. The parts form a design family, they are similar in design, and in this case can also be produced by a similar manufacturing process.
The cubical parts which are not very similar anymore; however, they also form a production family and can be made on the same multi-axis machining center.
The dissimilar parts requiring at least one common process, which is to drill four holes. In this case, the other processes needed to shape the part would have to be done with different machine tools. These parts are typical for companies producing a wide spectrum of products.
Two completely identical designed parts, one made from plastic and the other from steel. The manufacturing processes would be injection molding for the plastic reel and turning for the metal reel. In this case we have a common design family; however, the production processes are unrelated.
If the parts were to be manufacturing according to group technology considerations, the plant would have to be realigned. The production process assumes a flow line operation with machine tools located in the flow line where they are needed. It can readily be seen that intra-plant transportation is minimized. Setup operations and tool changes are also reduced.
Method for Developing Part Families Visual inspection - This is a simple and crude method of examining and grouping parts and machines through the bare eye according to the judgment of an inspector. Classification of parts into families is simply made by looking at their shapes and these shapes are usually design features. Inaccuracies become magnified when the complexity of the parts increases or the number of machines and parts used are numerous. Classification based on visual inspection is hence the least accurate though the least costly as compared to the other types. Therefore, it should be the last choice. But it can be used as a starting point by which one can begin to judge whether or not Group Technology seems to make sense in his environment.
Production flow analysis - using information contained on route sheets to classify parts Production flow analysis (PFA) is a method for identifying part families based on the sequence of operation and machine routing needed to produce the part [8,24]. Since PFA uses manufacturing attributes rather than design attributes to identify and form part families, it can overcome two possible anomalies. First, parts whose basic geometries are quite different may have similar or identical process routings. However, the disadvantages with this method of part family formation is that it accepts previously set routes sheets without consideration of its being logical or consistent, there is no mechanism for rationalizing the manufacturing routings .
Parts classification and coding - identifying similarities and differences among parts and relating them by means of a coding scheme
PROCESS LAYOUT By grouping parts into families, manufacturing personnel can cut down significantly on the amount of materials handled and movement wasted in producing them by grouping manufacturing machines into specialized work cells instead of arranging them according to function figure shows a processtype layout for batch production in a machine shop. The process machine tools are arranged by function. During the machining of given part, the work piece must be moved between sections, with perhaps the same section being visited several times. This results in a significant amount of material handling, a large in-process inventory, usually more setups than necessary, long manufacturing lead times, and high cost. Figure shows a production shop of equivalent capacity, but with the machines arranged into cells. Each cell is organized to specialize in the manufacture of a particular part family. Advantages are gained on the form of reduced work piece handling, lower setup times, less inprocess inventory, and shorter lead time.
2. Group technology layout
PARTS CLASSIFICATION AND CODING 1. Design Attribute Group Dimensions Tolerances Shape Finnish Material Function 2. Manufacturing Attribute Group Production process Operational sequence Production time Tools required Fixtures required Batch size Machine tool Annual production 3. Combined Attribute Group This system combines the best characteristics of both the design and manufacturing attributes.
Coding System Structure GT begins with data input, usually through a classification and coding system. A classification and coding system is a means of describing the attributes of parts and grouping them according to those descriptions A part coding scheme consists of a sequence of symbols that identify the part’s design and/or manufacturing attributes. The most common approach recommended is to start classification and coding with only those parts currently being released to the shop. The nature of most manufacturing is such that the number of new component shapes released begins to level out within a short time after a classification and coding system, is implemented, and, therefore, an increasingly high percentage of ‘new’ part drawings can be retrieved easily from the existing files. There is no universal classification-and-coding system that can be directly applied to GT; most GT approaches have been implemented with system developed for the specific needs of the organization. Coding systems can be constructed with only numerical symbols, only alphabetical symbols, or a combination of numbers and letters. Numerical codes have certain advantages over alphabetical codes because of a lower risk of reading errors. On the other hand, alphabetical codes have 26 different values per position while the decimal system only has ten possible values. There are basically three types of code constructions used for GT applications. 1. Hierarchical codes (or monocodes or tree structures.) 2. Attribute codes (or polycodes or chain type structures.)
3. Hybrids, i.e. combination of monocodes and polycode structures.
MONOCODE (Hierarchical Type) This coding system was originally developed for biological classification in 18th century. Inverted-tree hierarchy Meaning of a digit in the code depends on the values of preceding digits Efficient - relevant information need be considered at each digit and fewer digits needed Useful for storage and retrieval of design-related information such as part geometry, material, size, etc. Difficult to learn because of the large number of conditional inference.
The following figure illustrates the structure of a monocode
POLYCODE (ATTRIBUTE CODE) Each digit position in a polycode has the same attribute or feature of a part (consistent meaning) Each digit has values 0-9 or A-Z, and each value has a particular meaning, which is maintained in a reference table Easy to learn, use and alter Length of code may become excessive of its limited combinatorial features Preferred by manufacturing department Simple items and geometrically complex items have same length of code
It is the mixture of both monocode and polycode systems. Mixed code retains the advantages of both systems. Most coding systems use this code structure. The first digit for example, might be used to denote the type of part, such as gear. The next five position might be reserved for a short attribute code that would describe the attribute of the gear. The next digit (7th digit) might be used to designate another subgroup, such as material, followed by another attribute code that would describe the attributes.
A code created by this manner would be relatively more compact than a pure attribute code while retaining the ability to easily identify parts with specific characteristics
Special Symbol codes This is a type of code that used picture or symbols of an object other than numbers or alphabets to represent an activity, event, words, etc. This special symbol codes can be
hieroglyphically, which can best characterized by the symbolic therbligs, created by Frank and Lillian Gilbreths or of more recent vintage, the flow chart codes for tracking the handling of data within a system. During their study of work and time-and motion, they used an epitomized hieroglyphic code symbols to represent a fundamental motions such as reach, grasp, think, etc. The hieroglyphic code symbols described by the therbligs codes pictorially represent the action they describe. For example, the activity of planning can be represented by planning therbligs symbol by a person with his finger at his brow, denoting a thinking pose. Like wise, in the flow chart symbols, the operation performed on a lathe machine can be represented by a circle. Sometimes a code used in a special symbol codes can have a little or no meaning in their shape or character or the code and the information it represents. The common flow chart symbols established and developed by The American Society of Mechanical Engineers (ASME) show in the table below is a good example of such codes. (ASME) Symbol
Inspection Operation Transportation Delay Storage
Principles of Coding As in the case of classification, an industrial coding has also its own principles. These includes 1.
No code should exceed five characters without a break in the string. That means when the code number becomes shorter it becomes easy to handle and, fewer errors committed. Identity codes should of fixed length and pattern. If we use varying-length codes within a given class of materials it will proliferate error rates and require justification in handling (right or left) to the longest code in use. All-numeric codes produce fewest errors.
Alphanumeric combination codes are acceptable if the alpha field is fixed and used to break a string of numbers.
SELECTION OF CODING SYSTEMS 1. Flexibility for various applications such as part family formation, process planning, costing, and purchasing 2. Accuracy, to provide correct information on parts 3. Expandability, to accommodate information on more part attributes deemed important later on 4. Ease of learning 5. Ease of retrieval 6. Reliability and availability of software 7. Suitability for specific applications 8. Costs and time. 9. Scope and application. 10. Adaptability to other system. 11. Differentiation –to distinguish between different part families. 12. Automation Coding Systems
Some of the important systems OPITZ System DCLASS System MICLASS System MULTICLASS System KK3 System
Opitz Classification System The code number has a maximum of 13 positions. Each position may assume 10 different values (attributes). Basic structure of the Opitz system 12345 Form Code
6789 Supplementary Code
ABCD Secondary Code
Form code: describes the primary design attributes of a part Supplementary code: describes manufacturing related attributes Secondary code: more detail of manufacturing attributes Basic Structure of the Opitz Parts Classification and Coding System
DCLASS System It is a decision-making and classification system. It is a tree-structured system that generates codes for components, material, processes, machines, and tools. Each branch of the system represents a condition in which a code is formed at the junction of each branch. The complete code is obtained by taking multiple passes in the decision tree. Sample of DCLASS code representation
MICLASS System (Developed in the Netherlands): The abbreviation is derived from the name Metal Institute Classification System. Developed to help automate & standardize a number of designs, production and management function. These include: Standardization of engineering drawings Retrieval of drawings according to classification Standardization of process routing Automated process planning Selection of parts processing on particular group of machine tools Machine tool investment analysis etc. The System consists of 30 digits (maximum) 1 2 3 4 ..... 12 13 14 15 ..... 30 Universal Code Special Code (For any part) (For any company or industry including lot size, cost data, time, operation sequence, etc.)
The structure of the MICLASS coding system
Basic form: Basic shape (1), Shape element (2 & 3), Location of the shape element (4) Supplementary design and mfg. information: Number of outside diameters (19), Number of inside diameters or specific shape (20), Rotational grooves or knurls (21), Close tolerance diameters (22), Splines (23), Gears (24), Sprockets (25), Pitch diameter/diameter pitch (26), Number of teeth
Multiclass System –developed by the Organization for Industrial Research (OIR):First 18 digits of the Multiclass Classification and Coding System
BENEFITS OF GROUP TECHNOLOGY It affects all areas of a company, including: • engineering • equipment specification • facilities planning • process planning • production control • quality control • tool design • purchasing •
Some of the well-known tangible and intangible benefits of implementing GT: 1. Engineering design • •
Reduction in new parts design Reduction in the standardization
• Reduction of drafting effort in new shop drawings •
Reduction of number of similar parts, easy retrieval of similar functional parts, and identification of substitute parts
2. Layout planning • Reduction in production floor space required •
Reduced material-handling effort
3. Specification of equipment, tools, jigs, and fixtures • Standardization of equipment • Implementation of cellular manufacturing systems •
Significant reduction in up-front costs incurred in the release of new parts for manufacture
4. Manufacturing: process planning • Reduction in setup time and production time • Alternative routing leading to improved part routing •
Reduction in number of machining operations and numerical control (NC) programming time
5. Manufacturing: production control • Reduced work-in-process inventory • Easy identification of bottlenecks • Improved material flow and reduced warehousing costs • Faster response to schedule changes •
Improved usage of jigs, fixtures, pallets, tools, material handling, and manufacturing equipment
6. Manufacturing: quality control • Reduction in number of defects leading to reduced inspection effort • Reduced scrap generation • Better output quality •
Increased accountability of operators and supervisors responsible for quality production, making it easier to implement total quality control concepts.
7. Purchasing • Coding of purchased part leading to standardized rules for purchasing • Economies in purchasing possible because of accurate knowledge of raw material requirements • Reduced number of part and raw materials •
Simplified vendor evaluation procedures leading to justin-time purchasing
8. Customer service • Accurate and faster cost estimates •
Efficient spare parts management, leading to better customer service
Scopes and Limitation Due to the time constraint while conducting the study, the classification and coding system will be made in such a way that to classify and retrieve drawings only for rotational parts made in the machine shop. Although, more than four hundred sample drawings are taken and analyzed, only small numbers are entered into the data base for the demonstration purpose. Therefore, with similar procedures, it is possible to continue for the non-rotational parts and different cast to make the CCS system complete.
Example of GT-based classification and coding system by computer programming
THE START-UP FORM
E GT BASED CCS APPLICATION
A DATA ENTRY FORM
MAJOR DIMENSIONS DATA INPUT FORM
Form used to select the external shape attributes for the rotational work part.
Form used to select the external shape attributes (this is the case for a rotational work-part with two outer diameter)
Form used to select the internal shape attributes for the rotational work part.
Form used to select the internal shape attributes (this is the case for a rotational work-part with one internal diameter)
Form used to select the type of surface plain machining used.
Form used to select the type of auxiliary hole or gear teeth.
Form used to select material type.
THE GENERATED GT- CODE DISPLAY WINDOW
FINAL RESULT DISPLAY WINDOW