1 Manufacturing Operations Scheduling B2 [ ] B2 [ ] E5 [ E5 [ P9 [---] P9 [---] D1 [ D1 [ X8 ----] X8 ----] C6 [- C6 [

2 Scheduling Process-Focused Process-Focused Manufacturing Manufacturing

3 Scheduling Decisions Scheduling at Washburn Guitar, Inc.

4 Process-Focused Manufacturing l Process-focused factories are often called job shops. l A job shop’s work centers are organized around similar types of equipment or operations. l Workers and machines are flexible and can be assigned to and reassigned to many different orders. l Job shops are complex to schedule.

5 Scheduling and Shop-Floor Decisions MaterialRequirements Plan (MRP) CapacityRequirements Plan (CRP) Order- Processing or Routing Plans Planned Order Releases Report Work Center Loading and Overtime Plan Assignment of Orders to Work Centers MasterProduction Schedule (MPS) Product Design and Process Plans Day-to-Day Scheduling and Shop-Floor Decisions

6 Pre-production Planning l Design the product in customer order l Plan the operations the product must pass through..... this is the routing plan l Work moves between operations on a move ticket

7 Common Shop Floor Control Activities l The production control department controls and monitors order progress through the shop. l Assigns priority to orders l Issues dispatching lists l Tracks WIP and keeps systems updated l Controls input-output between work centers l Measures efficiency, utilization, and productivity of shop

Capacity requirements planning Routings and work centers Shop- floor dispatching Work- in-process control Input/ output analysis Prioritized queue lists Standard production costs Labor and equipment requirements Work orders Work order scheduling Work order tracking Hewlett-Packard’s Shop-Floor Control System Slide 8 of 31

9 Shop Floor Planning and Control l Input-Output Control l Gantt Chart l Finite and Infinite Loading l Forward and Backward Scheduling

10 Input-Output Control l Input-output control identifies problems such as insufficient or excessive capacity or any issues that prevents the order from being completed on time. l Input-output control report compares planned and actual input, planned and actual output, and planned and actual WIP in each time period

11 Input-Output Control l Input-output control identifies problems such as insufficient or excessive capacity, bottlenecks or any issues that prevents the order from being completed on time l Planned input should never exceed planned output InputOutput Work Center

12 Input-Output Control Report Week: Week: Planned input: labor-hrs Actual input: labor-hrs Cumulative deviation Planned output: labor-hrs Actual output: labor-hrs Cumulative deviation Planned ending WIP: l-h Actual ending WIP: l-h

13 Gantt Charts l Gantt charts are useful tools to coordinate jobs through shop; graphical summary of job status and loading of operations

14 Gantt Charts MachiningFabricationAssemblyTest Tue. Wed. Thu. Fri. Sat. Work Centers Mon. EFG C DE HC F ED H C D ScheduledProgress Setup, Maint.

15 Assigning Jobs to Work Centers: How Many Jobs/Day/Work Center l Infinite loading l Assigns jobs to work centers without regard to capacity l Unless excessive capacity exists, long queues occur l Finite loading l Uses work center capacity to schedule orders l Popular scheduling approach l Integral part of CRP

16 Assigning Jobs to Work Centers: Which Job Gets Built First? l Forward scheduling l Jobs are given earliest available time slot in operation l excessive WIP usually results l Backward scheduling l Start with promise date and work backward through operations reviewing lead times to determine when a job has to pass through each operation l Less WIP but must have accurate lead times

17 Order-Sequencing Problems l Sequencing Rules l Criteria for Evaluating Sequencing Rules l Comparison of Sequencing Rules l Controlling Changeover Costs l Minimizing Total Production Time

18 Order-Sequencing Problems l We want to determine the sequence in which we will process a group of waiting orders at a work center. l Many different sequencing rules can be followed in setting the priorities among orders. l There are numerous criteria for evaluating the effectiveness of the sequencing rules.

19 Order-Sequencing Rules l First-Come First-Served (FCFS) Next job to process is the one that arrived first among the waiting jobs l Shortest Processing Time (SPT) Next job to process is the one with the shortest processing time among the waiting jobs l Earliest Due Date (EDD) Next job to process is the one with the earliest due (promised finished) date among the waiting jobs

20 Order-Sequencing Rules l Least Slack (LS) Next job to process is the one with the least [time to due date minus total remaining processing time] among the waiting jobs l Critical Ratio (CR) Next job to process is the one with the least [time to due date divided by total remaining processing time] among the waiting jobs l Least Changeover Cost (LCC) Sequence the waiting jobs such that total machine changeover cost is minimized

21 Evaluating the Effectiveness of Sequencing Rules l Average flow time - average amount of time jobs spend in shop l Average number of jobs in system - l Average job lateness - average amount of time job’s completion date exceeds its promised delivery date l Changeover cost - total cost of making machine changeovers for group of jobs

22 Experience Says: l First-come-first-served l Performs poorly on most evaluation criteria l Does give customers a sense of fair play l Shortest processing time l Performs well on most evaluation criteria l But have to watch out for long-processing-time orders getting continuously pushed back l Critical ratio l Works well on average job lateness criterion l May focus too much on jobs that cannot be completed on time, causing others to be late too.

23 Scheduling Decisions Priority Rules

24 Controlling Changeover Costs l Changeover costs - costs of changing a processing step in a production system over from one job to another l Changing machine settings l Getting job instructions l Changing material l Changing tools l Usually, jobs should be processed in a sequence that minimizes changeover costs

25 Controlling Changeover Costs l Job Sequencing Heuristic l First, select the lowest changeover cost among all changeovers (this establishes the first two jobs in the sequence) l The next job to be selected will have the lowest changeover cost among the remaining jobs that follow the previously selected job

26 Minimizing Total Production Time l Sequencing n Jobs through Two Work Centers l When several jobs must be sequenced through two work centers, we may want to select a sequence that must hold for both work centers l Johnson’s rule can be used to find the sequence that minimizes the total production time through both work centers

27 Johnson’s Rule 1. Select the shortest processing time in either work center 2. If the shortest time is at the first work center, put the job in the first unassigned slot in the schedule. If the shortest time is at the second work center, put the job in the last unassigned slot in the schedule. 3. Eliminate the job assigned in step Repeat steps 1-3, filling the schedule from the front and back, until all jobs have been assigned a slot.