Chapter 17 Scheduling

Management 3620Chapter 17 Schedule17-2 Overview of Production Planning Hierarchy Capacity Planning 1. Facility size 2. Equipment procurement Aggregate Planning 1. Facility utilization 2. Personnel needs 3. Subcontracting Master Schedule 1. MRP 2. Disaggregation of master plan Long-term (Chapter 5) Intermediate-term (Chapter 14) Short-term (Chapter 17) Intermediate-term (Chapters 14 and 15) Short-term Scheduling 1. Work center loading 2. Job sequencing

Management 3620Chapter 17 Schedule17-3 The Scheduling Problem Have the correct amount of resources at the right time and in the right place THE CHALLENGE Meet the job’s due date – customer service Utilization of the organization’s resources - productivity

Management 3620Chapter 17 Schedule17-4 Build A A Done Build B B Done Build C C Done Build D Ship JANFEBMARAPRMAYJUN On time! Scheduling Manufacturing Operations High-volume Intermediate- volume Low-volume Service operations

Management 3620Chapter 17 Schedule17-5 Work Center #1Work Center #2 Output High-Volume Systems Flow system: High-volume system with standardized equipment and activities Flow-shop scheduling: Scheduling for high-volume flow system –line balancing (Chapter 6) –design of work systems (Chapter 7)

Management 3620Chapter 17 Schedule17-6 High-Volume Success Factors Process and product design Preventive maintenance Rapid repair when breakdown occurs Optimal product mixes Minimization of quality problems Reliability and timing of supplies

Management 3620Chapter 17 Schedule17-7 Intermediate-Volume Systems (1 of 2) Outputs are between standardized high-volume systems and made-to- order job shops Three basic issues –run size of jobs –timing of jobs –sequence in which jobs should be processed

Management 3620Chapter 17 Schedule17-8 Intermediate-Volume Systems (2 of 2) Economic run size Base production on a master schedule developed from customer orders and forecasts of demand

Management 3620Chapter 17 Schedule17-9 Low-Volume Systems A variety of unique (customized) jobs arrive at the shop Someone must analyze each job regarding its routing (which work centers it will be required to visit), and the required amount of resources needed at each work center Typically the customer is told when the job will be finished (due date) The jobs are moved through the required work centers as each becomes available according to a scheduling system

Management 3620Chapter 17 Schedule17-10 Scheduling Low-Volume Systems Loading - assignment of jobs to process centers Sequencing - determining the order in which jobs will be processed

Management 3620Chapter 17 Schedule17-11 Loading Approaches (1 of 2) Infinite loading –assumes capacity of a work center is infinite –priority sequencing rule then used –managers may need to respond to capacity overload conditions

Management 3620Chapter 17 Schedule17-12 Loading Approaches (2 of 2) Finite loading –projects the starting and stopping times of each job at each work center –takes into account capacities of each work center and the processing times of jobs so that capacity is not exceeded In special cases, an algorithm such as the assignment method may be used

Management 3620Chapter 17 Schedule17-13 Everything is #1 Priority Sequencing Determine the order in which jobs waiting at a work center will be processed One approach is to use priority rules (simple heuristics) to select the order in which jobs waiting in line will be processed

Management 3620Chapter 17 Schedule17-14 Examples of Priority Rules FCFS - first come, first served SPT- shortest processing time DD- due date CR- critical ratio

Management 3620Chapter 17 Schedule17-15 Examples of Performance Measures (1 of 2) Job flow time – the length of time a job is in the shop at a particular workstation; includes processing time, wait time, transportation time Average job flow time – the sum of the flow time for each job in a group divided by the number of jobs Makespan – total time needed to complete a group of jobs

Management 3620Chapter 17 Schedule17-16 Examples of Performance Measures (2 of 2) Job lateness – the length of time the job completion time is expected to exceed the time the job is due Average lateness – the sum of the lateness for each job in a group divided by the number of jobs Average number of jobs – average work-in-process for a group of jobs; total flow time divided by makespan

Management 3620Chapter 17 Schedule17-17 Example 2, FCFS

Management 3620Chapter 17 Schedule17-18 Two Work Center Sequencing Johnson’s Rule –technique for minimizing completion time for a group of jobs to be processed on two processes or at two work centers. –minimizes total idle time of the two processes Several conditions must be satisfied

Management 3620Chapter 17 Schedule17-19 Johnson’s Rule Conditions Job time must be known and constant Job times must be independent of sequence Jobs must follow same two-step sequence (flow shop) Job priorities cannot be used All units must be completed at the first work center before moving to second

Management 3620Chapter 17 Schedule17-20 Example Problem first last

Management 3620Chapter 17 Schedule17-21 Gantt Chart Used as a visual aid for loading and scheduling Purpose is to organize and clarify the actual or intended use of resources in a time framework Two most commonly used types –load chart –schedule chart

Management 3620Chapter 17 Schedule17-22 Figure 17-2 Gantt Load Chart

Management 3620Chapter 17 Schedule17-23 Example Problem first last C A D B Data Entry Verify time

Management 3620Chapter 17 Schedule17-24 Scheduling Approaches Forward scheduling –scheduling ahead, from some point in time Backward scheduling –scheduling by working backward from the job’s due date

Management 3620Chapter 17 Schedule17-25 Input/Output Control Used to manage work flow so that queues and waiting times are kept under control Input to a work center is compared to the output of that work center for some time period An imbalance indicates management should investigate

Management 3620Chapter 17 Schedule17-26 Service Operation Problems Cannot store or inventory services Customer service requests are random Scheduling service involves –Customers –Workforce –Equipment Duh! Where’s Dilbert?

Management 3620Chapter 17 Schedule17-27 Scheduling Service Operations Appointment systems –Controls customer arrivals for service Reservation systems –Estimates demand for service Scheduling the workforce –Manages capacity for service Scheduling multiple resources –Coordinates use of more than one resource