By Dr. Sumit Gupta SoE, GD Goenka University

Transcription

1 By Dr. Sumit Gupta SoE, GD Goenka University

2 Introduction to Group Technology (GT) Group Technology (GT) is a manufacturing philosophy in which similar parts are identified and grouped together to make advantage of their similarities in design and production. Similar parts bare arranged into part families, where each part family possesses similar design and/or manufacturing characteristics. Grouping the production equipment into machine cells, where each cell specializes in the production of a part family, is called cellular manufacturing.

3 Implementing Group Technology (GT) There are two major tasks that a company must undertake when it implements Group Technology. 1. 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. 2. Rearranging production machines into cells. It is time consuming and costly to plan and accomplish this rearrangement, and the machines are not producing during the changeover.

4 Benefits of Group Technology (GT) 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

5 Part Families A 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. Rotational part family requiring similar turning operations

6 Part Families 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

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

8 Grouping Part Families There are three general methods for solving part families grouping. All the three are time consuming and involve 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.

9 1- Visual Inspection Method The visual inspection 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.

10 2- Parts classification and Coding In parts classification and coding, similarities among parts are identified, and these similarities are related in a coding system. Two categories of part similarities can be distinguished: 1. Design attributes, which concerned with part characteristics such as geometry, size and material. 2. Manufacturing attributes, which consider the sequence of processing steps required to make a part.

11 2- Parts classification and Coding A part coding system consists of a sequence of symbols that identify the part s design and/or manufacturing attributes. The symbols are usually alphanumeric, although most systems use only numbers. The three basic coding structures are: 1. Chain-type structure, also 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 the preceding symbols.

12 2- Parts classification and Coding 2. Hierarchical structure, also known as a monocode, in which the interpretation of each successive symbol depends on the value of the preceding symbols. 3 Hybrid structure, a combination of hierarchical and chain-type structures.

13 Opitz Classification and Coding System It is intended for machined parts and uses the following digits sequence Form Code for design attributes Supplementary Code for manufacturing attributes Secondary Code A B C D for production operation type & sequence

14 Example: Optiz part coding System Given the rotational part design below, determine the form code in the Optiz parts classification and coding system. 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

15 Introduction to Flexible Manufacturing System (FMS) A flexible manufacturing system (FMS) is a highly automated Group Technology machine cell, consisting of a group or processing workstations (usually CNC machine tools), interconnected by an automated material handling and storage system, and controlled by a distributed computer system. The reason the FMS is called flexible is that it is capable of processing a variety of different part styles simultaneously at the various workstations, and the mix of part styles and quantities of production can be adjusted in response to changing demand patterns. 27/08/2015 akhtar kamal 15

16 A flexible manufacturing system is a automated machine cell, consisting of a group of processing workstations, interconnected with automated material handling and storage system. The FMS is most suited for the mid-variety, mid-volume production range

17 Flexible Manufacturing System (FMS) FMS technology can be applied in situations similar to those for cellular manufacturing: The plant either (1) produces parts in batches, or (2) uses manned GT cells and management wants to automate It must be possible to group a portion of the parts made in the plant into part families, whose similarities permit them to be processed on the machines in the flexible manufacturing system The parts or products made by the facility are in the mid-volume, mid-variety production range.

18 High Stand-alone CNC machines Medium Flexible manufacturing systems Low Transfer lines Low Medium High Production Volume Application characteristics of flexible manufacturing systems.

19 The FMS requires a significantly greater capital investment because new equipment is being installed rather than existing equipment being rearranged The FMS is technologically more sophisticated for the human resources who must make it work

20 Increased machine utilisation Fewer machines required Reduction in factory floor space required Greater responsiveness to change. Reduced inventory requirements Lower manufacturing lead times Reduced direct labour requirements and higher labour productivity

21 Flexibility type Definition Dependant on.. Machine flexibility Capability to adapt a given machine (workstation) in the system to a wide range of production operations and part styles. The greater the range of operations and part styles, the greater the machine flexibility. Setup or changeover time. Ease of machine reprogramming (ease with which part programs can be downloaded to machines). Tool storage capacity of machines. Skill and versatility of workers in the system. Production flexibility The range or universe of part styles that can be produced on the system. Machine flexibility of individual stations. Range of machine flexibilities of all stations in the system.

22 Mix flexibility Ability to change the product mix while maintaining the same total production quantity; that is, producing the same parts only in different proportions. Similarity of parts in the mix. Relative work content times of parts produced Machine Flexibility Product flexibility Ease with which design changes can be accommodated. Ease with which new products can be introduced. How closely the new part design matches the existing part family. Off-line part program preparation. Machine flexibility Routing flexibility Capacity to produce parts through alternative station sequences in response to equipm t breakdowns, tool failures, and other interruptions at individual stations. Similarity of parts in the mix Similarity of workstations Duplication of workstations Cross-training of manual workers. Common tooling.

23 Volume flexibility Expansion flexibility Ability to economically produce parts in high and low total quantities of production, given the fixed investment in the system. Ease with which the system can be expanded to increase total production quantities. Level of manual labour performing production. Amount invested in capital equipment. Expense of adding workstations. Ease with which layout can be expanded. Type of part handling system used. Ease with which properly trained workers can be added.

24 Flexible manufacturing systems can be distinguished according to the number of machines in the system. The following are typical categories: Single machine cell Flexible manufacturing cell Flexible manufacturing system

25 A single machine cell consists of one CNC machining center combined with a parts storage system for unattended operation. Completed parts are periodically unloaded from the parts storage unit, and raw work parts are loaded into it

26 A flexible manufacturing cell consists of two or three processing workstations (typically CNC machining centers) plus a part handling system. The part handling system is connected to a load/unload station.

27 Flexible Manufacturing System (FMS) A flexible manufacturing system has four or more processing workstations connected mechanically by a common part handling system and electronically by a distributed computer system.

28 1. Workstations 2. Automated Material Handling and Storage systems 3. Computer Control System 4. Human Resources

29 Following are the types of workstations typically found in an FMS: 1. Load/Unload Stations. 2. Machining Stations. 3. Other processing Stations. 4. Assembly Station. 5. Other Stations and Equipment.

30 Functions 1.Independent movement of workparts between stations. 2.Handle a variety of workpart configurations. 3. Temporary storage. 4.Convenient access for loading and unloading workparts. 5.Compatible with computer control.

31 The FMS includes a distributed computer system that is interfaced to the workstations, Material handling system, and Other hardware components. A typical FMS computer system consists of a central computer and microcomputers. Microcomputers controlling the individual machines and other components. The central computer coordinates the activities of the components to achieve smooth overall operation of the system

32 Human are needed to manage the operations of the FMS. Functions typically performed by human includes: Loading raw workparts into the system, Unloading finished parts (or assemblies) from the system, Changing and setting tools, Equipment maintenance and repair, NC part programming in a machining system, and Programming and operation the computer system.

33 Progressive or Line Type Loop Type Ladder Type Open field type Robot centered type

34 1.Progressive Layout or Line Layout 2. Loop Layout

35 5. Robot Centered Layout

36 Metal-cutting machining Metal forming Assembly Joining-welding (arc, spot), gluing Surface treatment Inspection Testing

37 To reduce set up and queue times Improve efficiency Reduce time for product completion Utilize human workers better Improve product routing Produce a variety of Items under one roof Improve product quality Serve a variety of vendors simultaneously Produce more product more quickly

38 Fixed-routing manufacturing system that consists of multiple workstations linked together by a material handling system to transfer parts from one station to the next Slowest workstation sets the pace of the line Workpart transfer: Palletized transfer line Uses pallet fixtures to hold and move workparts between stations Free transfer line Part geometry allows transfer without pallet fixtures

39 General configuration of an automated production line consisting of n automated workstations that perform processing operations

40 In-line - straight line arrangement of workstations Segmented in-line two or more straight line segments, usually perpendicular to each other Rotary indexing machine (e.g., dial indexing machine)

41 L-shaped layout U-shaped layout Rectangular configuration

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43 Linear transfer systems: Continuous motion not common for automated systems Synchronous motion intermittent motion, all parts move simultaneously Asynchronous motion intermittent motion, parts move independently Rotary indexing mechanisms: Geneva mechanism Others

44 Side view of chain or steel belt-driven conveyor (over and under type) for linear transfer using work carriers

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46 Transfer lines for machining Synchronous or asynchronous workpart transport Transport with or without pallet fixtures, depending on part geometry Various monitoring and control features available Rotary transfer machines for machining Variations include center column machine and trunnion machine

47 Two important areas in the life cycle of a product are design and manufacturing. Process planning serves as an integration link between design and manufacturing. Process planning consists of preparing a set of instructions that describe how to fabricate a part or build an assembly which will satisfy engineering design specifications. 15 April

48 Process planning emerges as a key factor in CAD/CAM integration because it is the link between CAD and CAM. After engineering designs are communicated to manufacturing, either on paper or electronic media, the process planning function converts the designs into instructions used to make the specified part. 15 April

49 CIM cannot occur until this process is automated; consequently, automated process planning is the link between CAD and CAM. CAD Conceptual design Mathematical analysis Geometric data (graphical representation) CAM Process design Process planning (CNC codes) Tool selection Facilities management CAPP COMPUTER AIDED PROCESS PLANNING 50

50 Analysis of part requirement Selection of raw workpiece Determining manufacturing operations and their sequences Selection of machine tools Selection of tools, workholding devices, and inspection equipment Determining machining conditions and manufacturing time 51

51 As new age manufacturing processes are evolving, Computer Aided Process Planning (CAPP) helps in simplifying and efficiently carrying out the conventional process planning and optimizing use of resources. Detailed set of instructions, engineering drawings, specifications, parts and materials lists etc. 15 April

52 Development of process plan (route sheet) using following approaches- Variant Computer Aided Process Planning Generative Computer Aided Process Planning E.g. Design changes- changes cost estimates Machine breakdown- alternate solution effective solution Interaction among various functions of an organization and dynamic changes.

53 Design input Material selection, Process selection, Process sequencing, Machine and tool selection, Intermediate surface determination, Fixture selection, Machining parameter selection, Cost/time estimation, Plan preparation, these are the general steps involved in the computer aided process planning.

54 1. Variant CAPP method 2. Generative CAPP method 55

55 Also known as data retrieval method. Process plan for a new part is generated by recalling, identifying and retrieving an existing plan for a similar part and making necessary modifications for new part known as Master Part Coding and classification schemes of group technology (GT) used, number of algorithms, mathematical models are developed for family part formation and plan retrieval. Using existing system can save a tremendous amount of time and manpower.

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57 Form the Part Families by Grouping Partsclassifying parts and formation of group parts Develop Standard Process Plans- developed for each part families based on common part features. Retrieve and Modify the Standard Plans for New Parts- when new part enters the systems, it is designed and coded based on its feature, using the coding and classification scheme, and then assigned to a part family.

58 In generative process planning, process plans are generated by means of decision logic, formulas, technology algorithms, etc. Main aim is to convert a part form raw material to finished state. Input to the system includes the description of the part in the form of part code number..

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61 It can systematically produce accurate and consistent process plans. It leads to the reduction of cost and lead times of process plan. Skill requirement of process planer are reduced to develop feasible process plan. Interfacing of software for cost, manufacturing lead time estimation, and work standards can easily be done. Leads to the increased productivity of process planar.

62 While compared with manual process planning the CAPP systems have few disadvantages: The inability to show special manufacturing techniques. The initial cost of establishing a CAPP system is high while compared with manual process planning.

63 Rapid prototyping (RP) is the process, which allows to rapidly produce accurate, tangible models of products designed on a computer aided design (CAD) system. The early use of these models was to assist the designer in determining optimal form. Now one of major applications of RP is tooling aimed at significant reduction of lead time. April 15,

64 The production of models by machining relies on the removal of material until the required form is achieved. Rapid prototyping differs by adding material layer by layer until the desired shape is achieved. Major advantages of RP in comparison with machining by equipment operated by computer numeric control (CNC) are: The time taken to produce a complicated model is significantly less; Excess material is not wasted April 15,

65 A CAD model to STL format STL to sliced layers of the model. The first layer of the physical model is created, the model is then lowered by one layer thickness, and the process is repeated until completion of the model; Supports will be added for any layers that are not directly supported; The model and any supports are removed; the surface of the model is then finished and cleaned. Note: STL (STereoLithography) is a file format native to the stereolithography CAD software created by 3D Systems. April 15,

66 Object Support Object Support (a) (b) (c) Animation of STL Generation and Slicing April 15,

67 The basic methodology for all current RP techniques can be summarized as follows: 1. A CAD model is constructed, then converted to STL (standard triangular language) format. 2. The RP machine processes the STL file by creating sliced layers of the model. 3. The first layer of the physical model is created. The model is then lowered for the thickness of the next layer, and the process is repeated until completion of the model. 4. The model and any supports are removed. The surface of the model is then finished and cleaned. April 15,

68 Product development time and cost will be greatly reduced compared to the conventional prototyping techniques used. By reducing the prototype development time, the total product design cycle will be shorter thereby getting products to the market sooner. Communications between marketing, engineering, manufacturing, and purchasing are enhanced due to the availability of physical prototypes. April 15,

69 It is possible to have the physical model at critical design reviews thereby the decision making process becomes more accurate. In some cases, it is possible to perform functional prototype testing before committing to the actual tooling. By making available an accurate physical prototype it is possible to generate precise production tooling. April 15,

70 The initial cost of the equipment is high. The build material choices for different processes are limited in terms of their properties. In some cases only plastic materials could be used. April 15,

71 Check the feasibility of new design concepts Make functional models with the limitation of the material to do any testing. Conduct market tests/evaluation Create tooling for investment casting, die casting or injection molding Build a prototype sand or metallic molds and cores for sand, permanent mold and die casting Fabricate a master pattern for silicon and epoxy molds Manufacture many exact copies simultaneously April 15,

72 Fused Deposition Modeling (FDM) Stereolithography (SLA) Laminated Object Manufacturing (LOM) Selective Laser Sintering (SLS) 3D Printing (3DP) or Selective Binding April 15,

73 The FDM process was developed by Scott Crump in Currently Stratasys (Eden Prairie, MN) manufactures Fused Deposition Modeling (FDM) machines. April 15,

74 Extrusion nozzle A plastic filament is unwound from a coil and supplies material to an extrusion nozzle. The nozzle is heated to melt the plastic and has a mechanism which allows the flow of the melted plastic to be turned on and off. The nozzle is mounted to a mechanical stage which can be moved in both horizontal and vertical directions. As the nozzle is moved over the table in the required geometry, it deposits a thin bead of extruded plastic to form each layer. The plastic hardens immediately after being sprayed from the nozzle and bonds to the layer below. Several materials are available for the process including investment casting wax. April 15,

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76 This process was developed by an American company called 3D Systems. (Valencia, CA) It was the first RP method available for commercial usage. April 15,

77 1. The 3D CAD model of the part is sliced by software of SLA device. 2. Each slice is then etched onto the surface of a photosensitive ultraviolet (UV) curable resin using a swinging laser. In the areas where the beam of the laser strikes the surface, the resin is cured, each layer of cured resin is, typically, 0.13 mm thick. 3. At the end of each pass, which covers the whole surface of that layer, the platform goes down allowing liquid resin to flow over that previously cured to a depth of 0.13mm. A re-coating blade passes over the surface to ensure a consistent layer thickness is achieved. April 15,

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82 Resin AccuGen Nd a Appearanc e Clear amber Viscosit y 30ºC Flexural modulus, MPa Accura 25 a White to 1660 Clear Accura SI to 10 a amber 3102 Accura Purple to Amethyst 3721 SL a Clear, Watershed b colourless Somos White, White b opaque ProtoGen Clear, O-XT Clear colourless b ProtoCast Green, AF b clear Elongat ion at break (%) Notche d Izod impact (J/cm) General application Prototype parts, master patterns, RTV mould inserts, flow testing, etc. 13 to to to to to to Similar to polypropylene, functional components for mockups, master patterns, RTV and silicone moulding, etc. Investment casting High quality patterns for RTV moulding, design evaluation models, patterns for direct casting Master patterns, investment casting to to to Master patterns, functional parts to to to 0.17 High accuracy master patterns Very low ash, investment casting April 15,

83 The use of advanced software techniques to capture and re-use product and process knowledge in an integrated way.

84 The main objective with a KBE system is to reduce lead-time by automating mundane work activities of the product development process. Capturing knowledge from staff is another objective. This makes the company more resistant to staff turnover.

85 Concept Generation Concept Evaluation Preparation Manufacturing Aspect

86 1. KADS KADS is perhaps the most common methodology for development of KBSs. KADS is an acronym that has many interpretations e.g. Knowledge Acquisition Documentation System or Knowledge-based system Analysis and Design Support.

87 2. MPKA MOKA (methodology and tools oriented to knowledge based engineering applications) is a project that aims to develop a methodology that will serve as an international standard for KBE system development, MOKA aims to state the common patterns instead to create a methodology that fits every industrial scenario. The methodology of MOKA follows six step 1. IDENTIFY, 2. JUSTIFY, 3. CAPTURE, 4. FORMALIZE, 5. PACKAGE 6. ACTIVATE. The focus of MOKA is the CAPTURE and FORMALIZE steps.

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89 BENEFITS Reduced lead-time Product Optimisation Knowledge capture More time for innovation DRAWBACK Time Demanding Building Product Models Knowledge transfer