Scheduling Shop Floor ISQA 459/559 Mellie Pullman 1 Learning Objectives вЂў вЂў вЂў вЂў Explain the different kinds of scheduling Describe different shop loading methods Describe priority rules Describe scheduling performance measures 2 Definitions вЂў Routing: вЂў The operations to be performed, their sequence, the work centers visited, & the time standards вЂў Bottleneck: вЂў A resource whose capacity is less than the demand placed on it вЂў Due date: вЂў When the job is supposed to be finished вЂў Slack: вЂў The time that a job can be delayed & still finish by its due date вЂў Queue: вЂў A waiting line 3 High Volume Operations вЂў High volume flow operations generally have fixed routings вЂў Bottlenecks are easily identified вЂў Commonly use line-balancing to design the process around the required tasks вЂў Examples? 4 Low Volume Operations вЂў Low volume job shop operations are designed for flexibility. вЂў Each product or service may have its own routing (scheduling is much more difficult) вЂў Bottlenecks move around depending upon the products being produced at any given time вЂў Examples? 5 Gantt Charts вЂў Graphical tools used to illustrate workloads & help monitor job progress вЂў Load charts: вЂў Illustrates the workload relative to the capacity of a resource вЂў Progress charts: вЂў Illustrates the planned schedule compared to actual performance 6 Load Chart 7 Progress Chart 8 Loading Workstations вЂў Infinite loading: вЂў Ignores capacity constraints, but helps identify bottlenecks in a proposed schedule вЂ“ enabling proactive management вЂў Finite loading: вЂў Allows only as much work to be assigned as a station should be able to handle вЂ“ but doesnвЂ™t prepare for inevitable slippage 9 Example вЂў Infinite: вЂў Schedule in time period needed вЂў Finite: вЂў Schedule according to capacity limits 10 Forward Vs. Backward Scheduling Start processing when order is received regardless of due date Schedule the jobвЂ™s last activity so it is finished right before the due date 11 Operations Sequencing вЂў A short-term plan of actual jobs based on available capacity & priorities вЂў Priority rules: вЂў Decision rules to allocate the relative priority of jobs at a work center вЂў Local priority rules: determines priority based only on jobs at that workstation вЂў Global priority rules: also considers the remaining workstations a job must pass through 12 Common Priority Rules вЂў вЂў вЂў вЂў вЂў вЂў First come, first served (FCFS) Last come, first served (LCFS) Earliest job due date (EDD) Shortest processing time (SPT) Longest processing time (LPT) Min Critical ratio: (CR) вЂў (Time until due date)/(processing time remaining) 13 How to use priority rules вЂў Decide which rule to use. вЂў List all the jobs waiting to be processed at the work-center and their job time вЂў Job time includes setup and processing time вЂў Using your priority rule, determine which job has the highest priority and should be worked on 1st , 2nd, 3rd ,etc. 14 Machine Shop with 6 jobs waiting вЂў Use SPT (shortest processing time) вЂў Determine sequence of jobs Job Number Job Time (setup & run) A 3 days B 7 days C 6 days D 4 days E 2 day F 5 days 15 Performance Measurement вЂў Job flow time: вЂў Time a job is completed minus the time the job was first available for processing вЂў Average jobs in system: вЂў Measures amount of work-in-progress =Total job flow time/Make-span вЂў Make-span: вЂў The entire time it takes to finish a batch of jobs вЂў Job lateness: вЂў Whether the job is completed ahead of, on, or behind schedule вЂў Job tardiness: вЂў How long after the due date a job was completed 16 More Data on the jobs Job Number Job Time (setup & run) Due Date (days from now) Remaining job time at other WC A 3 days 15 6 B 7 days 20 8 C 6 days 30 5 D 4 days 20 3 E 2 day 22 7 F 5 days 20 5 Critical Ratio 15/(3+6) 17 Completion Data Job Number Competion Date Due Date (days from now) Lateness (days) Tardiness (days) A 5 15 -10 0 B 27 20 +7 7 C 20 30 -10 0 D 9 20 -11 0 E 2 22 -20 0 F 14 20 -6 0 Negative lateness means job is finished ahead of due date. 0=on time 18 Group In-Class Activity вЂў Each team should use each of these rules calculate all performance measures: вЂў Critical Ratio вЂў Longest Process Time вЂў EDD 19 Worksheet for your method:____________ Job # Job Time (setup & run) Due Date -days from now Remaining job time at other WC A 3 days 15 6 B 7 days 20 8 C 6 days 30 5 D 4 days 20 3 E 2 day 22 7 F 5 days 20 5 Job Flow Job Lateness Job Tardiness CR AVE Make-span Job flow-time Average jobs in system ____________ ____________ ____________ 20 What are the companyвЂ™s objectives? What priority rule works best? вЂў Fairness? вЂў Minimizing mean job tardiness? вЂў Minimizing mean job flow time, lateness, and average jobs in the system? 21 Sequencing through 2 work centers JohnsonвЂ™s rule вЂў All jobs are processed through 2 work centers sequentially 1. List the jobs and processing times 2. Find the shortest activity processing time among all jobs (not yet schedule). вЂў вЂў вЂў If it is the first activity, put job needing that activity in the earliest available position in the sequence If it is the second activity, put the job needing that activity in the last avaiable position in the job sequence. One you schedule a job, itвЂ™s eliminated from further consideration 3. Repeat step 2 until every job is on the schedule 22 Sample Problem Metal Job Activity 1 Metal Cutting Activity 2 Deburr & Grind A 1 2 B 3 5 C 2 4 D 5 4 E 4 2 23 Sample Problem (days) Metal Job A Activity 1 Activity 2 Metal Deburr & Grind Cutting 1 (first) 2 B 3 (fourth) 5 C 2 (second) 4 D 5 4 (fifth) E 4 2 (third) 1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 0 1 2 3 4 5 6 7 8 A ACCBBBDDDDDE EEE c t 1 A c t 2 AACCCCBB BBBDDDDEE Ties: pick either 24 Group In-Class Problem Hall A Activity 1 Mopping 4 Activity 2 Buffing 3 B 2 7 C 6 5 D 4 5 E 3 4 F 5 1 25

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