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kiran

  1. 1. MODELING AND ANALYSIS OF MANUFACTURING SYSTEMS Session 7 FLEXIBLE MANUFACTURING SYSTEMS E. Gutierrez-Miravete Spring 2001
  2. 2. DEFINITION <ul><li>A FLEXIBLE MANUFACTURING SYSTEM ( FMS ) IS A SET OF NUMERICALLY CONTROLLED MACHINE TOOLS AND SUPPORTING WORKSTATIONS CONNECTED BY AN AUTOMATED MATERIAL HANDLING SYSTEM AND CONTROLLED BY A CENTRAL COMPUTER </li></ul>
  3. 3. ELEMENTS OF FMS <ul><li>AUTOMATICALLY REPROGRAMMABLE MACHINES. </li></ul><ul><li>AUTOMATED TOOL DELIVERY AND CHANGING </li></ul><ul><li>AUTOMATED MATERIAL HANDLING </li></ul><ul><li>COORDINATED CONTROL </li></ul>
  4. 4. FMS FEATURES <ul><li>MANY PART TYPES CAN BE LOADED </li></ul><ul><li>PARTS CAN ARRIVE AT MACHINES IN ANY SEQUENCE </li></ul><ul><li>PARTS IDENTIFIED BY CODES </li></ul><ul><li>MANY MACHINES CAN BE INCLUDED </li></ul><ul><li>SMALL FMS LEAD TO FLEXIBLE CELLS </li></ul>
  5. 5. FMS FEATURES <ul><li>EXPENSIVE TO IMPLEMENT BUT SAVINGS CAN BE SIGNIFICANT </li></ul><ul><li>FLOOR SPACE REDUCIBLE BY 1/3 </li></ul><ul><li>EQUIPMENT UTILIZATION UP TO 85% OR MORE </li></ul><ul><li>DETAILED PRODUCTION SEQUENCE NOT NEEDED WELL IN ADVANCE </li></ul>
  6. 6. FMS FEATURES <ul><li>REDUCED VARIABLE COSTS AND THROUGHPUT TIME LEAD TO ENHANCED MANUFACTURING COMPETITIVENESS </li></ul><ul><li>ELIMINATION OF STARTUP CYCLES LEAD TO STANDARIZED PERFORMANCE </li></ul><ul><li>MODULAR DESIGN </li></ul>
  7. 7. FMS FEATURES <ul><li>REDUCED DIRECT LABOR COSTS </li></ul><ul><li>THREE SHIFTS READILY FEASIBLE </li></ul><ul><li>IDEAL FOR JIT </li></ul><ul><li>CAN EASILY BE TURNED OVER TO NEW SET OF PRODUCTS IF THE NEED ARISES </li></ul>
  8. 8. MANUFACTURING FLEXIBILITY <ul><li>BASIC </li></ul><ul><ul><li>MACHINE (VARIETY OF OPERATIONS) </li></ul></ul><ul><ul><li>MATERIAL HANDLING (PART MOBILITY AND PLACEMENT) </li></ul></ul><ul><ul><li>OPERATION (VARIETY OF OPERATIONS PRODUCING SAME PART FEATURES) </li></ul></ul>
  9. 9. MANUFACTURING FLEXIBILITY <ul><li>SYSTEM </li></ul><ul><ul><li>PROCESS (VARIETY OF PARTS PRODUCIBLE WITH SAME SETUP) </li></ul></ul><ul><ul><li>ROUTING (ABILITY TO USE DIFFERENT MACHINES UNDER SAME SETUP) </li></ul></ul><ul><ul><li>PRODUCT (CHANGEOVER) </li></ul></ul><ul><ul><li>VOLUME (PRODUCTION LEVEL) </li></ul></ul><ul><ul><li>EXPANSION (ADDED CAPACITY) </li></ul></ul>
  10. 10. MANUFACTURING FLEXIBILITY <ul><li>AGGREGATED </li></ul><ul><ul><li>PROGRAM (UNATTENDED RUNNING) </li></ul></ul><ul><ul><li>PRODUCTION (RANGES OF PARTS, PRODUCTS, PROCESSES, VOLUME, EXPANSION) </li></ul></ul><ul><ul><li>MARKET (COMBINATION OF PRODUCT, PROCESS, VOLUME AND EXPANSION) </li></ul></ul>
  11. 11. COMMENTS <ul><li>DOES FLEXIBILITY REMOVE VARIABILITY FROM THE SYSTEM? </li></ul><ul><li>NO, BUT IT ENABLES IT TO PERFORM EFFECTIVELY </li></ul>
  12. 12. COMMENTS <ul><li>KEY ISSUE </li></ul><ul><li>CAN A SYSTEM BE DESIGNED WHICH IS USEFUL OVER A SUFFICIENT TIME HORIZON, PART MIX AND SMALL CHANGEOVER TIMES SO AS TO OFFER AN ALTERNATIVE TO SIMULTANEOUS PRODUCTION OF MEDIUM VOLUME PART TYPES? </li></ul>
  13. 13. COMMENTS <ul><li>THE PART TYPES ASSIGNED TO THE FMS SHOULD HAVE SUFFICIENT PRODUCTION VOLUMES TO MAKE AUTOMATION ATTRACTIVE BUT INSUFFICIENT TO JUSTIFY DEDICATED PRODUCTION LINES </li></ul>
  14. 14. ORIGINS OF FMS <ul><li>LINK LINES (1960’S) </li></ul><ul><li>NC MACHINES AND CONVEYORS </li></ul><ul><li>BATCH PROCESSING </li></ul>
  15. 15. ACRONYMS <ul><li>FMS </li></ul><ul><li>NC </li></ul><ul><li>DNC </li></ul><ul><li>CNC </li></ul><ul><li>AGV </li></ul><ul><li>JIT </li></ul>
  16. 16. FMS PRIORITIES <ul><li>MEETING DUE DATES </li></ul><ul><li>MAXIMIZING MACHINE UTILIZATION </li></ul><ul><li>MINIMIZE THROUGHPUT TIMES </li></ul><ul><li>MINIMIZE WIP LEVELS </li></ul>
  17. 17. FMS COMPONENTS <ul><li>MACHINES </li></ul><ul><li>PART MOVEMENT SYSTEMS </li></ul><ul><li>SUPPORTING WORKSTATIONS </li></ul><ul><li>SYSTEM CONTROLLER </li></ul>
  18. 18. MACHINES <ul><li>PRISMATIC VS ROTATIONAL PARTS </li></ul><ul><li>HORIZONTAL MACHINING CENTERS (HMC) AND HEAD INDEXERS (HI) </li></ul><ul><li>TOOL MAGAZINES AND AUTOMATIC TOOL CHANGERS </li></ul>
  19. 19. PART MOVEMENT <ul><li>CONVEYORS </li></ul><ul><li>TOW CARTS </li></ul><ul><li>RAIL CARTS </li></ul><ul><li>AGV’S </li></ul>
  20. 20. SUPPORTING WORKSTATIONS <ul><li>LOAD/UNLOAD STATIONS </li></ul><ul><li>AUTOMATIC PART WASHERS </li></ul><ul><li>COORDINATE MEASURING MACHINES </li></ul>
  21. 21. CONTROLLER <ul><li>COMPUTER </li></ul><ul><li>WORKER (ATTENDANT) </li></ul><ul><li>TRACKING SYSTEM FOR </li></ul><ul><ul><li>PARTS </li></ul></ul><ul><ul><li>MACHINES </li></ul></ul>
  22. 22. PLANNING AND CONTROL HIERARCHY <ul><li>DECISION MAKING PROCESS </li></ul><ul><ul><li>WHICH INFORMATION SHOULD BE COMMUNICATED? </li></ul></ul><ul><ul><li>HOW DO SYSTEM COMPONENTS COMMUNICATE? </li></ul></ul>
  23. 23. COMPONENTS OF THE MANUFACTURING FACILITY <ul><ul><li>FACILITY </li></ul></ul><ul><ul><li>SHOP </li></ul></ul><ul><ul><li>CELL </li></ul></ul><ul><ul><li>WORKSTATION </li></ul></ul><ul><ul><li>EQUIPMENT </li></ul></ul>
  24. 24. MULTILEVEL CONTROL HIERARCHY <ul><li>TREE STRUCTURE OF THE HIERARCHY </li></ul><ul><li>INFORMATION FLOWS ONLY BETWEEN ADJACENT LAYERS </li></ul><ul><li>EACH LEVEL HAS ITS OWN PLANNING HORIZON AND DECISION TYPES </li></ul><ul><li>Fig. 5.5 and Table 5.1 , p. 133 </li></ul>
  25. 25. GENERIC CONTROL MODEL <ul><li>GENERIC CONTROL STRUCTURE USED TO ACCOMPLISH PLANNING, EXECUTION AND FEEDBACK </li></ul><ul><li>COMMANDS ARE RECEIVED FROM THE NEXT HIGHER LEVEL AND TASKS ARE BROKEN INTO SUBTASKS </li></ul><ul><li>SUBTASKS ARE ASSIGNED TO COMPONENTS AT NEXT LOWER LEVEL </li></ul>
  26. 26. GENERIC CONTROL MODEL <ul><li>SUBTASK MONITORING PERFORMED THROUGH RECEIPT OF STATUS FEEDBACK FROM LOWER LEVEL </li></ul><ul><li>TASK STATUS INFORMATION RELAYED TO NEXT HIGHER LEVEL </li></ul><ul><li>EACH CONTROLLER HAS A PRODUCTION MANAGER RECEIVING COMMANDS AND SCHEDULING TASKS </li></ul>
  27. 27. GENERIC CONTROL MODEL <ul><li>QUEUE MANAGER MAINTAINED FOR EACH LOWER LEVEL COMPONENTS TO MANAGE ASSIGNED SUBTASKS </li></ul><ul><li>DISPATCH MANAGER RECEIVES DISPATCH ORDERS AND MANAGES SUBTASK EXECUTION FOR EACH QUEUE MANAGER </li></ul><ul><li>Fig. 5.6, p. 134 </li></ul>
  28. 28. BASIC STEPS IN DECISION HIERARCHY <ul><li>LONG TERM PLANNING OR SYSTEM DESIGN (PART TYPES & EQUIPMENT SELECTION) </li></ul><ul><li>MEDIUM RANGE PLANNING OR SETUP (DAILY DECISIONS ABOUT PARTS & TOOLING) </li></ul><ul><li>SHORT TERM OPERATION (SCHEDULING & CONTROL) </li></ul>
  29. 29. SYSTEM DESIGN <ul><li>PROBLEM: SELECTING SYSTEM SIZE, HARDWARE, SOFTWARE AND PARTS FOR THE FMS </li></ul><ul><li>SIZE & SCOPE ARE SELECTED ACCORDING TO CORPORATE STRATEGY </li></ul><ul><li>HARDWARE & SOFTWARE SELECTED TO FIT SCOPE </li></ul>
  30. 30. SYSTEM DESIGN <ul><li>PART SELECTION IS DONE ACCORDING TO AN ECONOMIC CRITERION & STRATEGIC CONSIDERATIONS </li></ul><ul><li>KNAPSACK PROBLEM: LOAD THE FMS TO MAXIMIZE SAVINGS SUBJECT TO FMS CAPACITY </li></ul>
  31. 31. KNAPSACK PROBLEM <ul><li>P = PRODUCTIVE TIME PER PERIOD AVAILABLE ON BOTTLENECK FMS RESOURCE </li></ul><ul><li>p i = TIME PER PERIOD REQUIRED FOR PART i </li></ul><ul><li>s i = SAVINGS PER PERIOD IF PART TYPE i </li></ul>
  32. 32. KNAPSACK PROBLEM <ul><li>maximize  i s i X i </li></ul><ul><li>subject to </li></ul><ul><li>  i p i < P </li></ul>
  33. 33. SOLVING THE KNAPSACK PROBLEM <ul><li>GREEDY HEURISTIC </li></ul><ul><li>Example 5.1, p. 136 </li></ul><ul><li>OPTIMIZATION </li></ul><ul><li>Example 5.2, p. 138 </li></ul>
  34. 34. SYSTEM SETUP <ul><li>ASSIGNMENT OF OPERATIONS AND ACCOMPANYING TOOLING TO MACHINES </li></ul><ul><li>PART SELECTION PROBLEM : BATCH FORMATION </li></ul><ul><li>LOADING PROBLEM : SEQUENCING AND ROUTING OF PARTS </li></ul>
  35. 35. PART SELECTION <ul><li>GOAL: PLACE REQUIRED PARTS INTO COMPATIBLE BATCHES SUCH THAT </li></ul><ul><li>EACH BATCH USES ALL MACHINES </li></ul><ul><li>REQUIRE A LIMITED NUMBER OF TOOLS ON EACH MACHINE </li></ul><ul><li>HAVE SIMILAR DUE DATES FOR PARTS IN THE BACTH </li></ul>
  36. 36. PART SELECTION <ul><li>GREEDY HEURISTIC: FORM BATCHES BY ARRANGING PART ORDERS BY DUE DATES </li></ul><ul><li>PART ORDERS ARE SEQUENTIALLY ADDED TO CURRENT BATCH WITHOUT VIOLATING CONSTRAINTS </li></ul><ul><li>BATCH IS THEN READY FOR LOADING </li></ul><ul><li>Example 5.3, p. 140 </li></ul>
  37. 37. Part Selection as a Mixed-Integer Program <ul><li>Time phased set of part orders Dit for part i in time t </li></ul><ul><li>Time available in machine j , Pj </li></ul><ul><li>Time required by product i in machine j pij </li></ul><ul><li>Number of parts of type i made in time t xit </li></ul><ul><li>Number of tool slots in machine j , Kj </li></ul>
  38. 38. Part Selection as a Mixed-Integer Program <ul><li>Number of tool slots required by tool l in machine j , klj </li></ul><ul><li>Set of tools l required on machine j to produce part i , l j(i) </li></ul><ul><li>Holding cost per period for part i hi </li></ul><ul><li>Formulation: p. 142 </li></ul>
  39. 39. Part Selection as a Mixed-Integer Program <ul><li>Goal: Minimize inventory cost while meeting due dates </li></ul><ul><li>Example 5.4 , p. 142 </li></ul>
  40. 40. Incremental Part Selection <ul><li>Several part types in process at any time </li></ul><ul><li>System operates almost continuously </li></ul><ul><li>Goal: Minimize makespan to complete all available part orders </li></ul><ul><li>Procedure: Minimize idle time by balancing work loads subject to part demand and tool magazine capacity </li></ul><ul><li>Formulation: p. 144 </li></ul>
  41. 41. LOADING PROBLEM <ul><li>BATCH TO BE PROCESSED IS KNOWN </li></ul><ul><li>OBJECTIVES REQUIRED </li></ul><ul><li>LOADING SOLUTION MUST BE ROBUST AND FLEXIBLE </li></ul><ul><li>SOLUTION METHODOLOGIES </li></ul><ul><ul><li>MATHEMATICAL PROGRAMMING (p.145) </li></ul></ul><ul><ul><li>HEURISTIC APPROACHES (p. 148) </li></ul></ul>
  42. 42. LOADING PROBLEM: HEURISTIC APPROACH <ul><li>PHASE I : ASSIGN OPERATIONS TO MACHINE TYPES </li></ul><ul><li>PHASE II: </li></ul><ul><ul><li>OPERATIONS COMBINED INTO CLUSTERS TO REDUCE TRANSFERS </li></ul></ul><ul><ul><li>MACHINE GROUPS FORMED </li></ul></ul><ul><ul><li>OPERATIONS AND TOOLS ASSIGNED TO GROUPS </li></ul></ul>
  43. 43. SCHEDULING AND CONTROL <ul><li>BASIC PROBLEM AREAS </li></ul><ul><ul><li>SEQUENCING AND TIMING OF PART RELEASES TO THE SYSTEM </li></ul></ul><ul><ul><li>SETTING OF INTERNAL PRIORITIES IN THE SYSTEM </li></ul></ul><ul><ul><li>ABILITY OF SYSTEM TO TAKE CORRECTIVE ACTION WHEN COMPONENTS FAIL </li></ul></ul>
  44. 44. Flexible Assembly Systems <ul><li>For the combination of raw materials and components into products with functional characteristics. </li></ul><ul><li>Automated vs manned systems </li></ul><ul><li>Example: Vibratory bowl feeders and vision systems </li></ul><ul><li>Role of Design for Assembly </li></ul>

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