DOM 102 Principles of Operations Management Operations Scheduling

DOM 102: Principles of Operations Management Operations Scheduling Irwin/Mc. Graw-Hill © The Mc. Graw-Hill Companies, Inc. , 1998

Operations Scheduling u Ordering the sequence of workflow through a system to achieve a given objective(s) u Will depend on the type of workflow involved thus; – Job/Batch shop – Flow shop – Project ** Job systems are complex because High variety, skilled manpower, random arrival of orders & use of process technology Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 2

Work Center u Area in a business in which productive resources are organized and work is completed. u May be a single machine, a group of machines, or an area where a particular type of work is done. – – Job shop (by function) Flow (product) Assembly line GT cell Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 3

Capacity and Scheduling u Infinite loading – work is assigned to a center based on what is needed over time u Finite loading – schedules in detail each resource using the setup and run time required for each order. u Forward scheduling u Backward scheduling Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 4

Typical Scheduling and Control Functions u Allocating orders, equipment, and personnel - Loading u Determining the sequence of order performance - Sequencing u Initiating performance of the scheduled work – Dispatching u Shop-floor control- reviewing status, controlling & expediting late & critical orders Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 5

Work-Center Scheduling Objectives u Meet due dates u Minimize lead time u Minimize setup time or cost u Minimize work-in-process inventory u Maximize machine utilization Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 6

Priority Rules for Job Sequencing 1. First-come, first-served (FCFS) 2. Shortest operating time 3. Earliest due date first 4. Earliest start date first (due date-lead time) 5. Least slack time remaining first Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 7

Priority Rules for Job Sequencing 6. Least slack time remaining (per operation as opposed to per job) first 7. Smallest critical ratio first (due date-current date)/(number of days remaining) 8. Smallest queue ratio first (slack time remaining in schedule)/(planned remaining queue time) 9. Last come, first served 10. Random order Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 8

Schedule Performance Measures u Meeting due dates of customers or downstream operations. u Minimizing the flow time (the time a job spends in the process). u Minimizing work-in-process inventory. u Minimizing idle time of machines or workers. Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 9

Job Sequencing Example First-Come First-Served Orders submitted at beginning of week n-jobs on one machine FCFS Schedule Late? On-Time? Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 10

Job Sequencing Example Shortest Operating Time Orders submitted at beginning of week n-jobs on one machine Shortest Operating Time Schedule Late? On-Time? Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 11

Job Sequencing Example Last-Come First-Served Orders submitted at beginning of week n-jobs on one machine Last-Come First-Served Schedule Late? On-Time? Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 12

Job Sequencing Example Earliest Due Date First Orders submitted at beginning of week n-jobs on one machine Earliest Due Date First Late? On-Time? Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 13

Other Scheduling Techniques 1. Johnsons Rule – many jobs Vs Two machines sequentially. Shortest time for first machine do job first otherwise do the job last. 2. The Assignment Method – same No. of Jobs & machines. Make use of the Assignment Algorithm or Hungarian Method Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 14

Shop-Floor Control Major Functions 1. Assigning priority of each shop order 2. Maintaining work-in-process quantity information 3. Conveying shop-order status information to the office Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 14

Shop-Floor Control Major Functions 4. Providing actual output data for capacity control purposes 5. Providing quantity by location by shop order for WIP inventory and accounting purposes 6. Providing measurement of efficiency, utilization, and productivity of manpower and machines Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 15

Hewlett-Packard’s Shop-Floor Control System Work orders Work order scheduling Work order tracking Capacity requirements planning Routings and work centers Shopfloor dispatching Workin-process control Labor and equipment requirements Standard production costs Prioritized queue lists Input/ output analysis Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 16

Input/Output Control Input u Planned Work Center Output input should never exceed planned output u Focuses Irwin/Mc. Graw-Hill attention on bottleneck work centers ©The Mc. Graw-Hill Companies, Inc. , 1998 17

Principles of Work-Center Scheduling 1. There is a direct equivalence between work flow and cash flow. 2. The effectiveness of any job shop should be measured by speed of flow through the shop. 3. Schedule jobs as a string, with process steps back to back. 4. A job once started should not be interrupted. Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 18

Principles of Job Shop Scheduling 5. Speed of flow is most efficiently achieved by focusing on bottleneck work centers and jobs. 6. Reschedule every day. 7. Obtain feedback each day on jobs that are not completed at each work center. 8. Match work center input information to what the worker can actually do. Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 19

Principles of Job Shop Scheduling 9. When seeking improvement in output, look for incompatibility between engineering design and process execution. 10. Certainty of standards, routings, and so forth is not possible in a job shop, but always work towards achieving it. Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 20

Personnel Scheduling in Services u Scheduling consecutive days off u Scheduling daily work times u Scheduling hourly work times Irwin/Mc. Graw-Hill ©The Mc. Graw-Hill Companies, Inc. , 1998 21