Topics To Be Covered 1. Tasks of a Shop Control Manager. 2. Do Shop Control Decisions Vary ? 3. Terminology 4. Performance Measures 5. Scheduling Performance Measures 6. Scheduling Work 7. Theory of Constraints 8. Principles of OPT Previous topic decisions

Tasks of a Shop Control Manager What stage of decision making would you classify those decisions performed by a shop floor control manager? What characteristics should a shop floor control manager have, in terms of: Level of Technical Expertise * Interpersonal Skills Level of Control * Knowledge of workers task What are the Main Responsibilities of a Shop Floor Control Manager 1. Sequencing of jobs. (Priorities) 2. Reporting level of WIP information 3. Conveying status of a shop order 4. Reporting actual output data for capacity control 5. Reporting measurement of efficiency, utilization & productivity of the workforce and machines. 6. Establishing and communicating improvements in processes or equipment that result in improved metrics. Can many of these responsibilities be automated?

Do Shop Control Decisions Vary ? What decisions would a shop floor control manager make for the following process types ? Continuous Process Maintaining status quo * Product & Process design Common reporting mechanism * Minimizing quality issues Variations in decision is in how to prevent breakdowns the plant. Repetitive Operation Prioritization based on demand schedule (lumpy demand) Detailed scheduling of activities * Flexibility in Order Sizes mixed model assembly * Flexible manufacturing processes Synchronized scheduling Job Shop Operations Broad level of expertise * Define scheduled completion date Define sequence of events Coordinate priority with other on-going jobs

Terminology Transfer Lot - Batch size of units that are sent on (transferred) to the next workstation. Batch size is typically less than the size of the job Operation Processing Time - estimated time that is required at an operation. Queue - a waiting line or buffer. Planned Lead Time - estimated time that it will take to complete an order. Including processing time & delays Makespan – time from beginning the first operation on the first part to completing the last operation on the last part in a batch. Flow Time - time that the order actually takes to flow through the shop. Also referred to as cycle time. (Processing Time + Wait Time) FIFO - First In - First Out; a method of scheduling

Performance Measures Work -In-Process (WIP): Should be maintained at a minimum level. Commitment of raw material & processing time Indication of long flow times ( too much waiting) Contributes to shop congestion & confusion Throughput: number of units completed in a given time period. Not as relevant in job shop Utilization: Percent of time a resource (workforce or machine) is operating. Can lead to incorrect decisions Bottlenecks are a limiting factor in a performance measure. Actions to improve Performance. Reduce setup time * Reduce queue time Reduce material handling Processing time, in most cases, represents only a small percentage of the total time.

Loading Def: the assignment of jobs to processing centers Infinite Loading: Jobs are assigned to work centers without regard to the capacity of the work center. result is queues when work exceeds capacity Finite Loading: Jobs assigned to work centers taking into account the work center capacity and job processing times. Frequent updating required to ensure capacity is maintained. Vertical Loading: Loading a work center, job by job usually according to some priority criterion, using infinite loading. (localized priority) Horizontal Loading: Loading each job on all work centers required, before scheduling any lower priority jobs, using finite loading. (Global priority) Forward Scheduling: How long will it take to complete the job? Backward Scheduling: What is the latest the job can be completed?

Scheduling Performance Measures Measures of Scheduling Performance 1. Average Flow Time  (Processing time + Wait time) / number of jobs 2. Average number of jobs in system  (Flow time ) /  Processing times 3. Average lateness  (Days Late)/ Number of jobs Maximum lateness MAX (|Due Date (i) – Completion Date (i)|) Note: Flow time equals processing time plus wait time plus any setup time.

Scheduling Work Sequencing Rules for Single Machine 1. First Come - First Serve Least confusing; most fair Long jobs delay shorter jobs; no consideration for due date. 2. Shortest Processing Time Minimizes the number of jobs in work; fewer late jobs Some large jobs can wait forever. 3. Earliest Due Date Less late jobs * Does not consider processing time 4. Slack Time Remaining Needs to be reevaluated after every job 5. Critical Ratio - Difference between the current time and the due date divided by the remaining processing time. - (td - t0 ) / tp

Scheduling Example Processing times ( including setup times) and due dates for six jobs waiting to be processed at a workcenter are given in the following table. Determine the sequence of processing according to each of these rules: a) FCFS b) SPT c) Due Date d) Critical Ratio Use Average completion time; Average job lateness; & Average number of jobs at the work center as performance measurements. Processing Due Job Time (Days) Date (Days) A 2 7 B 8 16 C 4 4 D 10 17 E 5 15 F 12 18

Scheduling Setup Avg # Of Jobs In Work Job Sequence Avg Lateness Processing Time Flow Time Due Date Lateness

Scheduling - Johnson Rule Johnson Rule: Used to minimize the throughput (completion) time for a group of jobs with a fixed sequence and are processed on two machines. Assumptions: Job times are known Job times are independent of sequence All Jobs have same sequence Job priorities can not be used Process: List the jobs and their times at each work center. Select the job with the shortest time. If the shortest time is at the first machine schedule the job first, if the time is on the second machine the schedule the machine last. Repeat for remaining jobs

Johnson Rule Example WC 1 WC 2 A group of six jobs are to be processed through a two -step operation. The first operation involves degreasing , and the second involves painting. Determine a sequence that will minimize the total completion time for this group of jobs. Processing Time Job Workcenter 1 Workcenter 2 A 5 5 B 4 3 C 8 9 D 2 7 E 6 8 F 12 15 WC 1 WC 2 Finished Good

Johnson Rule Example D – A – E – C – F - B Processing Time Job Workcenter 1 Workcenter 2 A 5 5 B 4 3 C 8 9 D 2 7 E 6 8 F 12 15 D – A – E – C – F - B Job Sequence;

Personnel Scheduling in Services Objective: Find the schedule that minimizes the number of five day workers with two consecutive days off, subject to the demand of the daily staffing schedule. Step 1: Assign the first worker to all the days that require staffing. - Copy all the number of workers required each day into this row. Step 2: Circle the two consecutive days with the lowest numbers. - Circled days are the days off for this employee - The circled days could be on opposite ends of the table. Step 3: For worker 2, subtract 1 from each of the days not circled with positive numbers. Step 4: Repeat Steps 2 & 3 until all workers have been assigned days or there are only zero requirements for each day.

Scheduling Days Off 4 3 2 1 # of Workers needed M T W R F SA SU Matt Jean Burt Hazel Sean

Scheduling Days Off 4 3 2 1 # of Workers needed M T W R F SA SU Matt Jean Burt Hazel Sean

Scheduling Difficulties Scheduling Difficulties center around variability in: Setup Processing time Interruptions Changes in set of jobs Aspects of Good Job Scheduling 1. Realistic Job Due dates 2. Focus on bottlenecks 3. Consider lot splitting for large jobs