Group Technology

Flexible manufacturing system(FMS) ,Group Technology Introduction, Part families, Part classification and coding system

1. GROUP TECHNOLOGY Sunith H Guraddi Mtech (CIM ) RVCE,Bangalore

2. Contents Introduction Part families Part classification and coding

3. Introduction Batch manufacturing is estimated to be the most common form of production in the United States, constituting more than 50% of total manufacturing activity. It is important to make batch manufacturing as efficient and productive as possible. Also there has been a trend to integrate the design and manufacturing functions in a firm. An approach directed at both of these objectives is Group technology(GT)

4. GROUP TECHNOLOGY The term group technology was first used by Prof. Mitrofanov in early 1950s. Group technology is manufacturing philosophy in 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. .

5. For e.g : A plant producing 10000 different part numbers may be able to group the vast majority of these parts into 30-40 distinct families. It is reasonable to believe that the processing of each member of a given family is similar and this should result in manufacturing efficiencies. The efficiencies are generally achieved 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

6. Objectives of Group technology Reduce MLT Reduce WIP Improve scheduling Reduce tooling Increase equipment utilization

7. Group technology is most appropriate under the following conditions: The plant currently uses traditional batch production and a process type layout. The parts can be grouped into part families.

8. There are two major tasks that a company must undertake when it implements group technology. These two tasks represent significant obstacles to the application of GT Identifying the part families: If the plant makes 10000 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 . 2. Rearranging production machines into machine cells : It is the time consuming and costly to plan and accomplish this rearrangement and the machines are not producing during the changeover.

9. Group technology offers substantial benefits to companies they are GT promotes standardization of tooling, fixturing and setups. Material handling is reduced because the distances within a machine cell are much shorter 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.

10. PART FAMILIES Part family is a collection of parts that are similar either because of geometric shape and size or because similar processing steps are required in their manufacture. The parts within a family are different, but their similarities are close enough to merit their inclusion as members of the part family.

11. figures 1 and 2 show to different part families. Fig 1. Two parts of identical shape and size but different manufacturing requirements 1,00,000 pc/yr, material = 1015 CR steel,nickel plate 100 pc/yr, material = 18-8 stainless steel

12. Fig.2 A family of parts with similar manufacturing process requirements but different design attributes. All parts are machined from cylindrical stock by turning: some parts require drilling and /or milling

13. One of the important manufacturing advantages of grouping work parts into families can be explained with reference to figures 3 and 4 . figure 3 shows a process type plant layout for batch production in a machine shop. The various machine tools are arranged by function. There is a lathe department, milling machine department, drill press department and so on. To machine a given part , the work piece must be transported between departments. This results in work piece to visit the same department in several times.

14. Fig.3 Process type and plant layout

15. 1. Significant amount of material handling 2. Work in process inventory 3. More machine setups 4. More lead time 5. High cost PROCESS TYPE LAYOUT Results in

16. In the group technology layout machines are arranged into cells. Each cell is organized to specialize in the production of a particular part family.

17. Fig.4 Group technology layout

18. GROUP TECHNOLOGY LAYOUT Results in: Reduced material handling Lower setup time Less in process inventory Shorter lead time Low cost

19. PART FAMILY FORMATION The biggest single obstacle in changing over to GT from conventional production shop is the problem of grouping the parts into families . There are three general methods for solving this problem. Visual inspection Parts classification and coding Production flow analysis All the three methods are time consuming and involve the analyze of much data by properly trained personal.

20. VISUAL INSPECTION This method is the least sophisticated 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. T his 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 change over using the visual inspection. This method is fast and simple and is useful when the part mix is not complex.

21. Fig.5 Visual inspection method

22. PARTS CLASSIFICATION AND CODING This method 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.

23. 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. Simply changing an existing part would take much less time than designing a whole new part from scratch. Automated process planning : The part code for a new part can 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

24. Two categories of part similarities can be distinguished Design attributes Manufacturing attributes Design attributes are concerned with part characteristics such as geometry , size , and material . Manufacturing attributes are concerned with the processing steps required to make a part.

25. Part design attributes Basic external shape Basic internal shape Rotational or rectangular shape Length–to–diameter ratio (rotational parts) Aspect ratio (rectangular parts) Material type Part function Major dimensions Minor dimensions Tolerances Surface finish

26. Part manufacturing attributes Major processes Minor operations Operation sequence Major dimension Surface finish Machine tool Production cycle time Batch size Annual production Fixtures required Cutting tools used in manufacture

27. Parts classification and coding cont… To accomplish parts classification and coding requires examination and analysis of the design and/or manufacturing attributes of each part. The examination is sometimes done by looking in tables . An alternative and more productive approach involves interaction with a computerized classification and coding system , in which the user responds to questions asked by the computer. On the basis of the responses, the computer assigns the code number to part. Whichever method is used, the classification results in a code number that uniquely identifies the part’s attributes.

28. Parts classification and coding cont… A number of classification and coding systems are available and there are a number of commercially available coding packages. However, none of the systems has been universally adopted. One of the reasons for this is that a classification and coding system should be customized for a given company or industry. A system that is best for one company may not be best for another company.

29. FEATURES OF PARTS CLASSIFICATION AND CODING Parts classification system fall into one of three categories Systems based on part design attributes System based on part manufacturing attributes Systems based on both design and manufacturing attributes

30. In terms of the meaning of the symbols in the code, there are three structures used in classification and coding schemes. Hierarchical structure, or monocode Chain type structure or polycode Hybrid, or mixed Hierarchical structure also known as a monocode , in which the interpretation of each successive symbol depends on the value of the preceding symbols. In this type of code, the meaning of each character is dependent on the meaning of the previous character. This type of code is particularly preferred in design departments for part retrieval because this type of system is very effective for capturing shape, material, and size information.

31. The following figure illustrates the structure of a monocode :

32. Chain type structure also known as 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. The meaning of each character in a polycode is independent of all other digits. Each digit is used to completely to classify some feature of the item. I t is easy to learn and useful in manufacturing situations where the manufacturing process have to be described. T he length of a polycode may become excessive because of its unlimited combinational features

33. Mixed-mode structure which is a hybrid of the two previous coding schemes. The mixed mode structure uses a combination of hierarchical and chain type structures. It is the most common structure found in GT parts classification and coding systems. Coding schemes that contain only design data require fewer digits, perhaps 12 or fewer. Most modern classification and coding system include both design and manufacturing data, and this usually requires 20 to 30 digits. This might seem like too many digits for a human reader to easily comprehend, but most of the data processing of codes is accomplished by computer .

34. Some general classification and coding systems developed.

35. Selection of classification and coding systems Some of the important classification and coding system attributes include: Flexibility for various applications such as part family formation, process planning, costing, and purchasing. Accuracy, to provide correct information on parts Expandability, to accommodate information on more part attributes. 4. Ease of learning 5. Ease of retrieval 6. Reliability and availability of software 7. Suitability for specific applications

36. OPTIZ PARTS CLASSIFICATION AND CODING SYSTEM This is the most common and widely used coding system . This system was developed by H.Optiz of the University of Aachen in Germany It is generally a 9 digit code with 5 forming the primary code while the last 4 are secondary code. It represents one of the pioneering efforts in GT and is probably the best known , if not the most frequently used , of the parts classification and coding systems. It is intended for machine parts. The Optiz coding scheme uses the following digit sequences. 12345 6789 ABCD

37. The basic code consists of nine digits, which can be extended by adding four more digits. The first nine are intended to convey both design and manufacturing data. The interpretation of the first nine digits is defined in figure 5. The first five digits, 12345 are called the form code. This describes the primary design attributes of the part. Such as external shape (For example, rotational vs rectangular) and machined features (for example, holes, threads, gear teeth, and so forth) The next four digits ,6789, constitute the supplementary code , which indicates some of the attributes that would be useful in manufacturing. (for example, dimensions, work material, starting shape, and accuracy.) The extra four digits ,ABCD, are referred to as secondary code and are intended to identify the production operation type and sequence. The secondary code can be designed by the user firm to serve its own particular needs.

38. The Opitz coding system consists of three groups of digits:

39. Fig.5 Basic structure of the Opitz system of parts classification and coding

40. Fig.6 Form code for rotational parts in the Opitz coding system

41. let us examine the from code consisting of the first five digits, defined generally in fig 6. The first digit identifies whether the part is rotational or non rotational. It also describes the general shape and proportions of the part. We limit our survey here to rotational parts possessing no unusual features, those with first digit values of 0,1,or 2. for this class of work parts, the coding of the first five digits is defined in fig 6. Consider the following examples to determine the coding of a given parts.

42. EXAMPLE 1 Figure 7

43. Given the rotational part design in figure 7. determine the form code in the Optiz parts classification and coding system. With reference to figure 6 ,the five digit code is developed as follows: Length-to-diameter ratio, L/D = 1.5 digit 1 = 1 External shape: stepped on both ends with screw thread on 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 Hence the form code for the given part is 15100

44. EXAMPLE 2 Figure 8 Develop the opitz form code (first fiive digits) for component given in figure 8

45. Solution 1 2 1 3 2 Part class: Rotational part, L/D =2 External shape: Stepped to one end ,thread Internal shape: Stepped to one end, no shape element Surface machining: External groove Auxiliary holes: Axial on pitch circle diameter

46. EXAMPLE 3 Figure 9 Develop the opitz form code (first fiive digits) for component given in figure 9

47. Solution 1 3 3 3 Part class: Rotational part, L/D =1.52 External shape: Stepped to one end ,smooth , no shape elements Internal shape: no hole Surface machining: External groove Auxiliary holes: Radial , not on pitch circle diameter

48. MICLASS coding system The MICLASS ( Metal Institute Classification)was developed by organisation for Applied Scientific Research in Netherlands in 1960s and 1970s to develop a system for both design and manufacture needs for OIR (Organisation for Industrial Research). The various functions MICLASS was developed for are Standardise engineering drawings Retrieve drawings based on classification Standardise process routing Automate process planning MICLASS is an expandable hybrid code system of up to 30 digits, while the first 12 digits have been standardised.

49. The system can be enlarged to thirty digits to cover any classification attribute desired by the user Computer software is provided by OIR for deriving the part code ,after the user goes through series of questions and answers them interactively. The built in logic is in the form of decision tree

50. KK-3 Coding System This is a code developed by the Japan Society for the promotion of the Machine industry(JSPMI) and was presented first in 1976

51. CODE MDSI System Manufacturing Data Systems, Incorporated(MDSI) has developed this classification and coding system called CODE. It is an 8 digit hybrid code used primarily to classify and code mechanical piece parts. The typical code structure is shown below.