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2. Lecture # 13-18 Group Technology/ Coding systems2 3. Group Technology Batch manufacturing is estimated to be the mostcommon form of production in the United States, constituting more than 50% of total manufacturing activity. There is a growing need to make batch manufacturing more efficient and productive. In addition, there is an increasing trend toward achieving a higher level of integration between the design and manufacturing functions in a firm. An approach directed at both of these objectives is group technology (GT). 3 4. Group Technology Group technology is a manufacturing philosophyin which similar parts are identified and grouped together to take advantage of their similarities in design and production. Similar parts are arranged into part families, where each part family possesses similar design and/or manufacturing characteristics. For example, a plant producing 10,000 different part numbers may be able to group the vast majority of these parts into 30-40 distinct families.4 5. Group Technology The manufacturing efficiencies are generallyachieved by arranging the production equipment into machine groups or cells, to facilitate work flow. Grouping the production equipment into machine cells, where each cell specializes in the production of a part family, is called cellular manufacturing.5 6. Group Technology GT is most appropriately applied under the followingconditions: The plant currently uses traditional batch production and a process type layout and this results in much material handling effort, high inprocess inventory, and long manufacturing lead times. The parts can be grouped into part families. This is a necessary condition. Each machine cell is designed to produce a given part family or limited collection of part families, so it must be possible to group parts made in the plant into families.6 7. Group Technology There are two major tasks that a company mustundertake when it implements group technology. These two tasks represent significant obstacles to the application of GT. Identifying the part families. If the plant makes 10,000 different parts, reviewing all of the part drawings and grouping the parts into families is a substantial task that consumes a significant amount of time. Rearranging production machines into machine cells. It is time consuming and costly to plan and accomplish this rearrangement and the machines are not producing during the changeover.7 8. Group Technology - Part Families Grouptechnology offers substantial benefits to companies that have the perseverance to implement it. The benefits include: GT promotes standardization of tooling, fixturing and setups. Material handling is reduced because parts are moved within a machine cell rather than within the entire factory. Process planning and production scheduling are simplified. Setup times are reduced, resulting in lower manufacturing lead times. Work-in-process is reduced. Worker satisfaction usually improves when workers collaborate in a GT cell. Higher quality work is accomplished using group technology. 8 9. Group Technology - Part Families Part Families A part family is a collection of parts that are similareither because of geometric shape and size or because similar processing steps are required in their manufacturing. 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 family9 10. Group Technology - Part Families Two parts that are identical in shape and size butquite different in manufacturing: (a)1,000,000 units/yr, tolerance = 0.010 inch, 1015 CR steel, nickel plate (CR = Cold Rolled ) (b)100/yr, tolerance = 0.001 inch, 18-8 stainless steel10 11. Group Technology - Part Families Ten parts that are different in size and shape, butquite similar in terms of manufacturing All parts are machined from cylindrical stock by turning; some parts require drilling and/or milling11 12. Group Technology - Part Families The biggest single obstacle in changing over to group technology from a conventional production shop is the problem of grouping the parts into families. There are three general methods for solving this problem, which involve the analysis of much data by properly trained personnel.12 13. Group Technology - Part Families 1) Visual inspection - using best judgment to group partsinto appropriate families, based on the parts or photos of the parts 2) Production flow analysis - using information contained on route sheets to classify parts 3) Parts classification and coding - identifying similarities and differences among parts and relating them by means of a coding scheme13 14. Group Technology 1) The visual inspection method is the leastsophisticated and least expensive method. 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. Although this method is generally considered to be the least accurate of the three, one of the first major success stories of GT in the United States made the changeover using the visual inspection method. 14 15. Group Technology15 16. Group Technology 2) Production flow analysis: Parts that go through common operations are groupedinto part families. The machines used to perform these common operations may be grouped as a cell, consequently this technique can be used in facility layout (factory layout)16 17. Group Technology Initially, a machinecomponent chart must beformed. This is an M x N matrix, where M = number of machines N = number of parts x = 1 if part j has an operation on machine i; 0 otherwise. If the machinecomponent chart is small, parts with similar operations might be grouped together by manually sorting the rows and columns.17 18. 18 19. Group Technology19 20. Parts Classification and Coding 3) Parts Classification and Coding This is the most time consuming of the three methods. In parts classification and coding, similarities among parts are identified, and these similarities are related in a coding system.20 21. Parts Classification and Coding Most classification and coding systems are one of the following: Systems based on part design attributes Systems based on part manufacturing attributes Systems based on both design and manufacturing attributes Part Design Attributes Major dimensions Basic external shape Basic internal shape Length/diameter ratio Material type Part function Tolerances Surface finish21 22. Parts Classification and Coding Part Manufacturing Attributes Major process Operation sequence Batch size Annual production Machine tools Cutting tools Material type22 23. Parts Classification and Coding Classification and coding systems are devised toinclude both a part's design attributes and its manufacturing attributes. Reasons for using a coding scheme include: Design retrieval A designer faced with the task of developing a new part can use a design retrieval system to determine if a similar part already exists. A simple change in an existing part would take much less time than designing a whole new part from scratch.23 24. Parts Classification and Coding Automated process planning The part code for a new partcan be used to search for process plans for existing parts with identical or similar codes. Machine cell design The part codes can be used to design machine cells capable of producing all members of a particular part family, using the composite part concept.24 25. Parts Classification and Coding Coding methods: These are employed in classifying parts into partfamilies. Coding refers to the process of assigning symbols to the parts. The symbols represent design attributes of parts or manufacturing features of part families.25 26. Parts Classification and Coding The variations in codes resulting from the waythe symbols are assigned can be grouped into three distinct type of codes:Monocode or hierarchical code Polycode or attribute Hybrid or mixed code26 27. Monocode or hierarchical code The structure of Monocode is like a tree inwhich each symbol amplifies the information provided in the previous digit.27 28. 28 29. 29 30. Monocode or hierarchical codeStructure of Monocode 30 31. Monocode or hierarchical code A monocode (hierarchical code) provides a largeamount of information in a relatively small number of digits. Useful for storage and retrieval of design related information such as part geometry, material, size, etc. It is difficult to capture information on manufacturing sequences in hierarchical manner, so applicability of this code in manufacturing is rather limited.31 32. Poly Code Chain-type structure, known as a polycode, in whichthe interpretation of each symbol in the sequence is always the same; it does not depend on the value of preceding symbols, so symbols are independent of each other. Each digit in specific location of the code describes a unique property of the workpiece. It is easy to learn and useful in manufacturing situations where the manufacturing process have to be described. The length of a Polycode may become excessive because of its unlimited combinational features. 32 33. Poly Code33 34. Group Technology Mixed (Hybrid Code) It is the mixture of both monocode and polycodesystems. Mixed code retains the advantages of both systems. Most coding systems use this code structure.36 35. Some of the important systems Opitz classification system the University ofAachen in Germany, nonproprietary, Chain type. Brisch System (Brisch-Birn Inc.) CODE (Manufacturing Data System, Inc.) CUTPLAN (Metcut Associates) DCLASS (Brigham Young University) MultiClass (OIR: Organization for Industrial Research), hierarchical or decision-tree coding structure Part Analog System (Lovelace, Lawrence & Co., Inc.) 37 36. Group Technology The OPITZ classification system: It is a mixed (hybrid) coding system Developed by Opitz, Technical University of Aachen,1970 It is widely used in industry It provides a basic framework for understanding the classification and coding process It can be applied to machined parts, non-machined parts (both formed and cast) and purchased parts It considers both design and manufacturing information 38 37. Group Technology The Opitz coding system consists of three groups of digits:Form code 12345part geometry and features relevant to part designSupplementary code 6789information relevant to manufacturing (polycode)Secondary code ABCDProduction processes and production sequences39 38. 40 39. Opitz System41 40. 42 41. Form code in Opitz system for rotational parts in classes 3, and 443 42. Supplemental code in Opitz system44 43. The OPITZ classification system Example: A part coded 20801 2 - Parts has L/D ratio >= 3 0 - No shape element (external shape elements) 8 - Operating thread 0 - No surface machining 1 - Part is axial45 44. The OPITZ classification system Example46 45. The OPITZ classification system Example: Given the part design shown define the"form code" using the Opitz system Step 1: The total length of the part is 1.75, overall diameter 1.25, L/D = 1.4 (code 1) Step 2: External shape - a rotational part that is stepped on both with one thread (code 5) Step 3: Internal shape - a through hole (code 1) Step 4: By examining the drawing of the part (code 0) Step 5: No auxiliary holes and gear teeth (code 0) Code: 1510047 46. Group Technology SELECTION OF CLASSIFICATION AND CODING SYSTEMSFor the purpose of selecting or developing your owncode, it is important to understand the attributes of classification and coding systems.48 47. CELLULAR MANUFACTURING Cellular manufacturing is an application of grouptechnology in manufacturing, in which all or a portion of a firms manufacturing system has been converted into cells.49 48. CELLULAR MANUFACTURING A manufacturing cell is a cluster of machines orprocesses located in close proximity and dedicated to the manufacture of a family of parts. The parts are similar in their processing requirements, such as operations, tolerances and machine tool capacities.50 49. CELLULAR MANUFACTURINGThe primary objectives in implementing acellular manufacturing system are to reduce: Setup times (by using part family tooling and sequencing) Flow times (by reducing setup and move times and wait time for moves and using smaller batch sizes) Reduce inventories Market response times51 50. CELLULAR MANUFACTURING Functional and Cellular layouts of an electronics plant:52 51. CELLULAR MANUFACTURING53 52. Cell Design Design of cellular manufacturing system is a complexexercise with broad implications for an organization. The cell design process involves issues related to both System structure and System operation.54 53. Evaluation of Cell Design Decisions The evaluation of design decisions can be categorizedas related to either the system structure or the system operation.55 54. Typical considerations related to the system structure include: Equipment and tooling investment (low) Equipment relocation cost (low) Material handling costs (low) Floor space requirements (low) Extent to which parts are completed in a cell (high) Flexibility (high)56 55. The system operation Evaluations of cell system design are incompleteunless they relate to the operation of the system. A few typical performance variables related to system operation are: Equipment utilization (high) Work-in-process inventory (low) Queue lengths at each workstation (short) Job throughput time (short) Job lateness (low)57 56. Cell Design A major problem throughout the cell designprocess is the necessity of trading off against each other objectives related to structural parameters and performance variables. For example, higher machine utilization can be achieved if several cells route their parts through the same machine. The drawbacks are increased queuing and control problems.58 57. Cell Design System cost and performance are affected by everydecision related to system structure and system operation.59 58. CELL FORMATION APPROACHES Machine - Component Group Analysis: Machine - Component Group Analysis is basedon production flow analysis Production flow analysis involves four stages:60 59. Production flow analysis Stage 1: Machine classification. Machines are classified on the basis of operations that canbe performed on them. A machine type number is assigned to machines capable of performing similar operations.61 60. Production flow analysis Stage 2:Checking parts list and production route information.For each part, information on the operations to beundertaken and the machines required to perform each of these operations is checked thoroughly.62 61. Production flow analysis Stage 3: Factory flow analysis. This involves a micro-level examination of flow ofcomponents through machines. This, in turn, allows the problem to be decomposed into a number of machine-component groups.63 62. Production flow analysis Stage 4:Machine-component group analysis. An intuitive manual method is suggested tomanipulate the matrix to form cells. However, as the problem size becomes large, the manual approach does not work. Therefore, there is a need to develop analytical approaches to handle large problems systematically.64 63. EXAMPLE: Consider a problem of 4 machines and 6 parts. Try to group them. Components Machine s123456M1111M2111M3111M411165 64. Components Machine s246135M1111M2111M3111M411166 65. Quantitative Analysis in Cellular Manufacturing Rank Order Clustering Algorithm: Rank Order Clustering Algorithm is a simplealgorithm used to form machine-part groups.67 66. Rank Order Clustering Algorithm Step 1: Assign binary weight and calculate a decimal weight foreach row and column using the following formulas:mDecimal weight for rowi = b ip 2 m-p p =1nDecimal weight for column j = b pj 2 n p p =1Where i is row no.; j is column number; m is number of columns; n is number of rows; p is the component/part row or column number 68 67. Step 2: Rank the rows in order of decreasing decimalweight values. Step 3: Repeat steps 1 and 2 for each column. Step 4: Continue preceding steps until there is no change in the position of each element in the row and the column.69 68. EXAMPLE: Consider a problem of 5 machines and 10 parts. Try to group them by using Rank Order Clustering Algorithm. Components Machines12345M111111111M2 M31M4 M51 11 11910111 11111181171 161 1111 70 69. Binary weight 2928272625242322212078910Decimal equivalent1111100711451Components Machines12345M111111111M2 M31M4 M51 111 1111116568 1111111455 1020 71 70. Binary weight 29 28 2726 25 2423 2221 20910Components Binary weightMachines1234567824M51111111123M111111111122M3121M411111120M211111Decimal equivalent11128 27 27 27 28 20 28 26 11 1172 71. Binary weight 292827262524232221209Components Binary weightMachines1572348624M51111111123M1111111122M311121M411120M2111Decimal equivalent101020 111 1Decimal equivalent1019 900111231111528 28 28 27 27 27 26 20 11 1173 72. Solve using Rank Order Clustering Technique Components Machines1M123167891 11M3 1M4111 111M6 M751M2M541 11 11 74