MD 021 - Management and Operations

SYMBOL 183 \f "Symbol" \s 12 \hDefinition of a just-in-time (JIT) system

SYMBOL 183 \f "Symbol" \s 12 \hCharacteristics of JIT systems

SYMBOL 183 \f "Symbol" \s 12 \hTypes of scheduling

SYMBOL 183 \f "Symbol" \s 12 \hScheduling performance measures

SYMBOL 183 \f "Symbol" \s 12 \hPriority sequencing (dispatching) rules

SYMBOL 183 \f "Symbol" \s 12 \hScheduling in services

JIT System

Definition

Just-in-time (JIT) is a dependent demand production control system designed to produce goods or services as needed and minimize inventories.

Environments for Effective JIT

Manufacturing: Firms that tend to have highly repetitive manufacturing processes, well-defined material flows, and reasonably high volumes use JIT systems because the pull method allows closer control of inventory and production at the work stations.

Services: Firms that tend to have repetitive operations, reasonably high volumes, and deal with tangible items can benefit from JIT systems.

In general, JIT works well in stable and predictable environments because there is little forward visibility.

Characteristics of JIT Systems

Pull method

Consistently high quality

Small lot sizes

Short setup times

Uniform workstation loads

Standardization of components and work methods

Close supplier ties

Flexible work force

Product focus

Automated production

Preventive maintenance

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 less efficient than standardization.

However, it is sometimes possible to increase operational efficiency even with customization 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 work centers. Operations schedules are short-term plans designed to implement the master production schedule.

Work-force scheduling - Determines when human resources are available for work

Common Performance Measures for Operations Schedules

Job flow time - The time a job spends in the shop

Makespan - For a group of jobs, the time between the start of the first job and the finish of the last job

Past due

The amount of time late, average job lateness

The percentage of jobs completed late

Work-in-process or pipeline inventory expressed in units, number of jobs, dollar value, or weeks of supply

Total inventory - The sum of scheduled receipts and on-hand inventory

Utilization - The percentage of paid time spent productively

Priority Sequencing Rules

EDD = Select Job With Earliest Due Date

FCFS = Job That Arrives First is Processed First

SPT = Select Job With Shortest Processing Time

Performance of Priority Sequencing Rules

Earliest due date (EDD) - Performs well with respect to: minimizing percentages of jobs past due, minimizing the maximum amount of time a job is late. Performs poorly with respect to: job flow time, work-in-process inventory, utilization.

First come, first serve (FCFS) - Perceived as being fair. Performs poorly with respect to all performance 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 with respect to: minimizing the maximum amount of time a job is late, minimizing total inventory (it pushes 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 of work centers

Slack per remaining operations (S/RO) - Performs similarly to EDD with added advantages of a global view and accounting for the duration of the jobs.

Scheduling in Services

Characteristics of services that have an impact on scheduling:

Services can not buffer demand uncertainties with inventory.

Demand for services is difficult to predict.

Scheduling systems can facilitate the capacity management of service providers.

Two approaches:

Schedule customer demand (capacity remains fixed and demand is leveled)

Appointments

Reservations

Backlogs

Schedule the work force to meet forecasted demand (adjust capacity to demand)

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