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Material Type: Notes; Class: Operations Management; Subject: operations,information & strategic mgmt; University: Boston College; Term: Unknown 1989;
Typology: Study notes
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MD 021 - Operations Management Lean Systems/Scheduling Outline
Definition of a just-in-time (JIT) system - Characteristics of JIT systems - Types of scheduling - Scheduling performance measures - Priority sequencing (dispatching) rules - Scheduling in services
JIT System Definition Just-in-time (JIT) is a dependent demand production control system designedto produce goods or services as needed and minimize inventories. Environments for Effective JIT
Manufacturing: Firms that tend to have highly repetitive manufacturingprocesses, well-defined material flows, and reasonably high volumes useJIT systems because the pull method allows closer control of inventory andproduction at the work stations.
Services: Firms that tend to have repetitive operations, reasonably highvolumes, and deal with tangible items can benefit from JIT systems. - In general, JIT works well in stable and predictable environments becausethere is little forward visibility.
Enabling Customization using Standardized Operations Product or service customization has negative effects on both:
Predictability of demand - Predictability of operations Since uncertainty in operations requires extra resources, customization is inherently lessefficient than standardization.However, it is sometimes possible to increase operational efficiency even withcustomization using standardization strategies. Standardization strategies include: • Part standardization – Maximize component commonality across products - Process standardization – Delay customization as late as possible - Product standardization – Carry a limited number of products in inventory
Types of Scheduling
Operations scheduling - Assigns workers to tasks or jobs to machine workcenters. Operations schedules are short-term plans designed to implement themaster production schedule. - Work-force scheduling - Determines when human resources are available forwork
7 Priority Sequencing Rules Single dimension rules: EDD = Select Job With Earliest Due DateFCFS = Job That Arrives First is Processed FirstSPT = Select Job With Shortest Processing Time Multiple dimension rules:^ CR = Time Remaining to Due DateTotal Shop Time Remaining Remaining Operations of Number Remaining Time Shop Total
Date Due to Remaining Time = S/O
Performance of Priority Sequencing Rules
Earliest due date (EDD) - Performs well with respect to: minimizing percentages of jobs pastdue, minimizing the maximum amount of time a job is late. Performs poorly with respect to: jobflow time, work-in-process inventory, utilization. - First come, first serve (FCFS) - Perceived as being fair. Performs poorly with respect to allperformance measures. - Shortest processing time (SPT) - Performs well with respect to: average job flow time, work-in-process inventory, minimizing percentages of jobs past due, utilization. Performs poorly withrespect to: minimizing the maximum amount of time a job is late, minimizing total inventory (itpushes work to finished goods before it is needed), adjusting schedules when due date changes(due date is not used in the calculation of priority). - Critical ratio (CR) - Performs well when we are concerned with global operation of a system ofwork centers. - Slack per operations (S/O) - Performs similarly to EDD with added advantages of a global viewand accounting for the duration of the jobs.
