Activity Scheduling and Control Activity Scheduling Control Input

Activity Scheduling and Control

Activity Scheduling & Control • Input: MRP Manufacturing Orders (MO’s) Subject to Capacity Constraints, Not Purchase Orders (PO’s) • Plans Hit the Real World (the Shop Floor)

Activity Scheduling & Control • Planning - Ensure Resources Available - Schedule Order Start & Completion Dates • Implementation - Gather Information Needed to Make Item - Dispatch (Release) Orders to Floor • Control (Feedback) - Rank Orders in Priority Sequence - Track Actual Performance vs. Plans - Monitor WIP, Queues, Lead Time, Etc. - Report Out – Input/Output Reports (p. 175)

Data Requirements - Planning • Item Master File: Part Numbers, Description, Lead Time, On Hand, On Order, Quantity Assigned to Work Center, Lot Sizes • Product Structure or Bill of Materials File • Routing File: Series of Operations Along with Resources Needed, Set Up, Run Times, Lead Times • Work Center Master File Work Center Number, Capacity, Shifts, Machine and Labor Hours Available, Efficiency, Utilization, Queue Time, Alternate Centers

Data Requirements - Control • Shop Order Master File (Each Order): Shop Order Number, Order Quantity, Quantity Completed, Quantity Scrapped, Material Issued, Due Dates, Priority, Balance Due, Costs • Shop Order Detail File (Each Operation): Operation Number, Setup Hours, Run Hours, Quantity Completed, Quantity Scrapped, Due Date or Lead Time Remaining

Types of Manufacturing/Service Systems • Intermittent (Job Shops) - Traditional - Work Cells • Flow (Assembly Lines) • Projects (SOM 466)

Job Shops • Different Items Can be Produced at the Same Job Center – Requires Worker and Machine Flexibility • Design and Fabrication of Item Determines Job Shop Routing • Capacity Required at Each Work Center Depends on Mix of Products. Hard to Predict • Queues (Inventory) Results When Schedule Assigns too Many Jobs to Work Center – Throughput Times Generally Long

Job Shop Example

Work Cells • Intermediate to Job Shops & Assembly Lines • Group of Machines to Make Set of Parts • Minimizes Distances, Related Handling Costs • Minimizes Inventories

Work Cell Example

Work Cell Example

Scheduling in Job Shops and Work Cells • Forward Scheduling – Left to Right – Earliest Dates • Backwards Scheduling – Right to Left – Latest Dates • Infinite Loading – No Capacity Limits • Finite Loading – Capacity Limits • Operations Overlapping • Operations Splitting

Scheduling in Job Shops and Work Cells: Shop Floor Control Job Routing Red Green Purple A(1), B (1), C (1), A (2) B (1), A (1) Work Center A B C 1 PM 2 PM 3 PM 4 PM R P G G R P Gantt Chart

Bottlenecks in Job Shops and Work Cells • Establish Inventory Buffer Before Bottleneck • Control Rate of Material Feed at Gateway Operation • Try to Increase Capacity of Bottleneck • Adjust Loads – Alternate Work Centers or Subcontract • Last Resort – Change Schedule • Use Goldratt’s “Theory of Constraints” 170 -172) (pp.

Sequencing Rules in Job Shops and Work Cells • First – Come, First – Served (FCFS) • Earliest Due Date (EDD) • Earliest Operation Due Date (ODD) • Shortest • Critical Process Time (SPT) Ratio (CR) or Slack Rule CR = (Due Date – Present Date) / Lead Time Remaining Lowest CR Has Priority. CR < 1: Behind Schedule

Flow Manufacturing Assembly Lines • Allows Mass Production • Repetitive Production of Standardized Products • Standard Flow Minimizes Inventories • Routings are Fixed. Work Centers Depend on Routing. • Capacity Fixed by the Assembly Line

Assembly Line Example

Scheduling Assembly Lines: Assembly Line Balance Definitions: Task or Operation – Smallest Definable Unit of Work (Circle) Station Cycle – Work Area (Square) Time – Time Allowed to Do a Cycle of Work 1/(Production Rate)

Assembly Line Balance: Assign Tasks to Stations

Example: Problem 3. 6 Task A B C D E F G Follows --A A A B, C, D E, F Time (Sec. ) 25 25 20 10 15 20 10 Cycle Time = 35 Seconds

Assembly Line Balance Theoretical Minimum Stations = Sum of Task Times / Cycle Time = 125 / 35 ≈ 4 Idle Time = (Stations X Cycle Time) - Sum of Task Times = (4 X 35) – 125 = 15

Assembly Line Balance: Assign Tasks to Stations AD Idle: 0 B + 10 CE + 0 FG + 5 = 15

Assembly Line Balance Nightmare Task Time(s) Cycle Time Solutions: - Divide Task - Decrease Task time - Increase Cycle Time - Parallel Stations