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Manufacturing Operations SchedulingManufacturing Operations Scheduling

B2 [----------]B2 [----------] E5 [--------------E5 [-------------- P9 [---]P9 [---] D1 [--------D1 [-------- X8 ----]X8 ----] C6 [-C6 [-

3 3 44 55 66 77 88

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SchedulingScheduling

Process-FocusedProcess-Focused

ManufacturingManufacturing

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Scheduling DecisionsScheduling DecisionsScheduling DecisionsScheduling Decisions

Scheduling at Washburn Guitar, Inc.Scheduling at Washburn Guitar, Inc.

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Process-Focused ManufacturingProcess-Focused ManufacturingProcess-Focused ManufacturingProcess-Focused Manufacturing

Process-focused factories are often called Process-focused factories are often called job shopsjob shops.. A job shop’s work centers are organized around A job shop’s work centers are organized around

similar types of equipment or operations.similar types of equipment or operations. Workers and machines are flexible and can be Workers and machines are flexible and can be

assigned to and reassigned to many different orders.assigned to and reassigned to many different orders. Job shops are complex to schedule.Job shops are complex to schedule.

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Scheduling and Shop-Floor DecisionsScheduling and Shop-Floor DecisionsScheduling and Shop-Floor DecisionsScheduling and Shop-Floor Decisions

MaterialMaterialRequirementsRequirementsPlan (MRP)Plan (MRP)

CapacityCapacityRequirementsRequirementsPlan (CRP)Plan (CRP)

Order-Order-Processing orProcessing orRouting PlansRouting Plans

Planned Planned Order ReleasesOrder Releases

ReportReport

Work CenterWork CenterLoading andLoading and

Overtime PlanOvertime Plan

Assignment ofAssignment ofOrders toOrders to

Work CentersWork Centers

MasterMasterProductionProduction

Schedule (MPS)Schedule (MPS)

Product DesignProduct Designandand

Process PlansProcess Plans

Day-to-Day Scheduling and Shop-Floor DecisionsDay-to-Day Scheduling and Shop-Floor Decisions

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Pre-production PlanningPre-production PlanningPre-production PlanningPre-production Planning

Design the product in customer orderDesign the product in customer order Plan the operations the product must pass through ..... Plan the operations the product must pass through .....

this is the this is the routing planrouting plan Work moves between operations on a Work moves between operations on a move ticketmove ticket

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Common Shop Floor Control ActivitiesCommon Shop Floor Control ActivitiesCommon Shop Floor Control ActivitiesCommon Shop Floor Control Activities

The production control department controls and The production control department controls and monitors order progress through the shop.monitors order progress through the shop. Assigns priority to ordersAssigns priority to orders Issues dispatching listsIssues dispatching lists Tracks WIP and keeps systems updatedTracks WIP and keeps systems updated Controls input-output between work centersControls input-output between work centers Measures efficiency, utilization, and productivity Measures efficiency, utilization, and productivity

of shopof shop

Capacityrequirements

planning

Routingsand

work centers

Shop-floor

dispatching

Work-in-process

control

Input/output

analysis

Prioritizedqueuelists

Standardproduction

costs

Labor andequipment

requirements

Work orders

Work orderscheduling

Work ordertracking

Hewlett-Packard’sShop-Floor ControlSystem

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Shop Floor Planning and ControlShop Floor Planning and ControlShop Floor Planning and ControlShop Floor Planning and Control

Input-Output ControlInput-Output Control Gantt ChartGantt Chart Finite and Infinite LoadingFinite and Infinite Loading Forward and Backward SchedulingForward and Backward Scheduling

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Input-Output ControlInput-Output ControlInput-Output ControlInput-Output Control

Input-output controlInput-output control identifies problems such as identifies problems such as insufficient or excessive capacity or any issues that insufficient or excessive capacity or any issues that prevents the order from being completed on time.prevents the order from being completed on time.

Input-output control reportInput-output control report compares planned and compares planned and actual input, planned and actual output, and planned actual input, planned and actual output, and planned and actual WIP in each time periodand actual WIP in each time period

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Input-Output ControlInput-Output ControlInput-Output ControlInput-Output Control

Input-output controlInput-output control identifies problems such as identifies problems such as insufficient or excessive capacity, bottlenecks or any insufficient or excessive capacity, bottlenecks or any issues that prevents the order from being completed issues that prevents the order from being completed on timeon time

Planned input should never exceed planned outputPlanned input should never exceed planned output

Input OutputWorkCenter

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Input-Output Control ReportInput-Output Control ReportInput-Output Control ReportInput-Output Control Report

Week:Week: -1-1 1 1 22 33 44

Planned input: labor-hrsPlanned input: labor-hrs 100100 5050 4040 100100Actual input: labor-hrsActual input: labor-hrs 5050 4040 3030 8080Cumulative deviationCumulative deviation -50-50 -60-60 -70-70 -90-90

Planned output: labor-hrsPlanned output: labor-hrs 120120 7070 5050 100100Actual output: labor-hrsActual output: labor-hrs 110110 5050 2020 7070Cumulative deviationCumulative deviation -10-10 -30-30 -60-60 -90-90

Planned ending WIP: l-hPlanned ending WIP: l-h 5050 3030 2020 2020Actual ending WIP: l-hActual ending WIP: l-h 7070 1010 00 1010 2020

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Gantt ChartsGantt ChartsGantt ChartsGantt Charts

Gantt chartsGantt charts are useful tools to coordinate jobs are useful tools to coordinate jobs through shop; graphical summary of job status and through shop; graphical summary of job status and loading of operationsloading of operations

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Gantt ChartsGantt ChartsGantt ChartsGantt Charts

MachiningMachining

FabricationFabrication

AssemblyAssembly

TestTest

Tue.Tue. Wed.Wed. Thu.Thu. Fri.Fri. Sat.Sat.Work CentersWork Centers Mon.Mon.

E F G

C D E

H C

F

ED

H C D

ScheduledScheduled ProgressProgress Setup, Maint.Setup, Maint.

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Assigning Jobs to Work Centers:Assigning Jobs to Work Centers:How Many Jobs/Day/Work CenterHow Many Jobs/Day/Work CenterAssigning Jobs to Work Centers:Assigning Jobs to Work Centers:

How Many Jobs/Day/Work CenterHow Many Jobs/Day/Work Center

Infinite loadingInfinite loading Assigns jobs to work centers without regard to Assigns jobs to work centers without regard to

capacitycapacity Unless excessive capacity exists, long queues occurUnless excessive capacity exists, long queues occur

Finite loadingFinite loading Uses work center capacity to schedule ordersUses work center capacity to schedule orders Popular scheduling approachPopular scheduling approach Integral part of CRPIntegral part of CRP

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Assigning Jobs to Work Centers:Assigning Jobs to Work Centers:Which Job Gets Built First?Which Job Gets Built First?

Assigning Jobs to Work Centers:Assigning Jobs to Work Centers:Which Job Gets Built First?Which Job Gets Built First?

Forward schedulingForward scheduling Jobs are given earliest available time slot in Jobs are given earliest available time slot in

operationoperation excessive WIP usually resultsexcessive WIP usually results

Backward schedulingBackward scheduling Start with promise date and work backward Start with promise date and work backward

through operations reviewing lead times to through operations reviewing lead times to determine when a job has to pass through each determine when a job has to pass through each operationoperation

Less WIP but must have accurate lead timesLess WIP but must have accurate lead times

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Order-Sequencing ProblemsOrder-Sequencing ProblemsOrder-Sequencing ProblemsOrder-Sequencing Problems

Sequencing RulesSequencing Rules Criteria for Evaluating Sequencing RulesCriteria for Evaluating Sequencing Rules Comparison of Sequencing RulesComparison of Sequencing Rules Controlling Changeover CostsControlling Changeover Costs Minimizing Total Production TimeMinimizing Total Production Time

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Order-Sequencing ProblemsOrder-Sequencing ProblemsOrder-Sequencing ProblemsOrder-Sequencing Problems

We want to determine the sequence in which we will We want to determine the sequence in which we will process a group of waiting orders at a work center.process a group of waiting orders at a work center.

Many different sequencing rules can be followed in Many different sequencing rules can be followed in setting the priorities among orders.setting the priorities among orders.

There are numerous criteria for evaluating the There are numerous criteria for evaluating the effectiveness of the sequencing rules.effectiveness of the sequencing rules.

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Order-Sequencing RulesOrder-Sequencing RulesOrder-Sequencing RulesOrder-Sequencing Rules

First-Come First-Served (FCFS)First-Come First-Served (FCFS)Next job to process is the one that arrived first Next job to process is the one that arrived first among the waiting jobsamong the waiting jobs

Shortest Processing Time (SPT)Shortest Processing Time (SPT)Next job to process is the one with the shortest Next job to process is the one with the shortest processing time among the waiting jobsprocessing time among the waiting jobs

Earliest Due Date (EDD)Earliest Due Date (EDD)Next job to process is the one with the earliest Next job to process is the one with the earliest due (promised finished) date among the waiting due (promised finished) date among the waiting jobsjobs

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Order-Sequencing RulesOrder-Sequencing RulesOrder-Sequencing RulesOrder-Sequencing Rules

Least Slack (LS)Least Slack (LS)Next job to process is the one with the least [time Next job to process is the one with the least [time to due date to due date minusminus total remaining processing total remaining processing time] among the waiting jobstime] among the waiting jobs

Critical Ratio (CR) Critical Ratio (CR) Next job to process is the one with the least [time Next job to process is the one with the least [time to due date to due date divided bydivided by total remaining processing total remaining processing time] among the waiting jobstime] among the waiting jobs

Least Changeover Cost (LCC)Least Changeover Cost (LCC)Sequence the waiting jobs such that total machine Sequence the waiting jobs such that total machine changeover cost is minimizedchangeover cost is minimized

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Evaluating the EffectivenessEvaluating the Effectivenessof Sequencing Rulesof Sequencing Rules

Evaluating the EffectivenessEvaluating the Effectivenessof Sequencing Rulesof Sequencing Rules

Average flow timeAverage flow time - average amount of time jobs - average amount of time jobs spend in shopspend in shop

Average number of jobs in systemAverage number of jobs in system - - Average job latenessAverage job lateness - average amount of time job’s - average amount of time job’s

completion date exceeds its promised delivery datecompletion date exceeds its promised delivery date Changeover costChangeover cost - total cost of making machine - total cost of making machine

changeovers for group of jobschangeovers for group of jobs

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Experience Says:Experience Says:Experience Says:Experience Says:

First-come-first-servedFirst-come-first-served Performs poorly on most evaluation criteriaPerforms poorly on most evaluation criteria Does give customers a sense of fair playDoes give customers a sense of fair play

Shortest processing timeShortest processing time Performs well on most evaluation criteriaPerforms well on most evaluation criteria But have to watch out for long-processing-time But have to watch out for long-processing-time

orders getting continuously pushed backorders getting continuously pushed back Critical ratioCritical ratio

Works well on average job lateness criterionWorks well on average job lateness criterion May focus too much on jobs that cannot be May focus too much on jobs that cannot be

completed on time, causing others to be late too.completed on time, causing others to be late too.

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Scheduling DecisionsScheduling DecisionsScheduling DecisionsScheduling Decisions

Priority RulesPriority Rules

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Controlling Changeover CostsControlling Changeover CostsControlling Changeover CostsControlling Changeover Costs

Changeover costsChangeover costs - costs of changing a processing - costs of changing a processing step in a production system over from one job to step in a production system over from one job to anotheranother Changing machine settingsChanging machine settings Getting job instructionsGetting job instructions Changing materialChanging material Changing toolsChanging tools

Usually, jobs should be processed in a sequence that Usually, jobs should be processed in a sequence that minimizes changeover costsminimizes changeover costs

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Controlling Changeover CostsControlling Changeover CostsControlling Changeover CostsControlling Changeover Costs

Job Sequencing HeuristicJob Sequencing Heuristic First, select the lowest changeover cost among all First, select the lowest changeover cost among all

changeovers (this establishes the first two jobs in changeovers (this establishes the first two jobs in the sequence)the sequence)

The next job to be selected will have the lowest The next job to be selected will have the lowest changeover cost among the remaining jobs that changeover cost among the remaining jobs that follow the previously selected jobfollow the previously selected job

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Minimizing Total Production TimeMinimizing Total Production TimeMinimizing Total Production TimeMinimizing Total Production Time

Sequencing n Jobs through Two Work CentersSequencing n Jobs through Two Work Centers When several jobs must be sequenced through two When several jobs must be sequenced through two

work centers, we may want to select a sequence work centers, we may want to select a sequence that must hold for both work centersthat must hold for both work centers

Johnson’s rule can be used to find the sequence Johnson’s rule can be used to find the sequence that minimizes the total production time through that minimizes the total production time through both work centersboth work centers

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Johnson’s RuleJohnson’s RuleJohnson’s RuleJohnson’s Rule

1. Select the shortest processing time in either work 1. Select the shortest processing time in either work centercenter

2. If the shortest time is at the first work center, put the 2. If the shortest time is at the first work center, put the job in the first unassigned slot in the schedule. If the job in the first unassigned slot in the schedule. If the shortest time is at the second work center, put the job shortest time is at the second work center, put the job in the last unassigned slot in the schedule. in the last unassigned slot in the schedule.

3. Eliminate the job assigned in step 2.3. Eliminate the job assigned in step 2.

4. Repeat steps 1-3, filling the schedule from the front 4. Repeat steps 1-3, filling the schedule from the front and back, until all jobs have been assigned a slot.and back, until all jobs have been assigned a slot.