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