Topic 14

Production Activity Control

Production Activity Control (PAC)

Objectives of PAC:

1. Meeting Job Due-Dates (Customer Service Level).

2. Controlling Work-In-Process Inventory level.

3. Reducing shop Congestion Level and Job lead-times.

4. Controlling the queues at each work center.

5. Preventing "bottleneck" machines in advance.

6. Increasing shop utilization.

Five Major Data Files in PAC:

1. Item Master File: (Item No./Description/BOM/...)

2. Job Routing File: (Operations/Time/Sequence/...)

3. Work Center Master File: (Capacity/Machine/...)

4. Shop Order Master File: (Release Date/Due Date/...)

5. Shop Order Status File: (Current Location/Rem. Ope./...)

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Data Requirements

The files generally required for a PAC system are:

Planning Files Control Files

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Scheduling and Shop Floor Decisions in Process- Focused Operations

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Functions of Production Activity Control

The major functions of an efficient production activity control system consist of the following:

Releasing order to the production on schedule having verified material, tool, equipment and personnel availability

Preparing shop packet (shop order, drawing, pick list, route sheet, tool request form, labor ticket, move ticket, etc.)

Establishing scheduled start and completion dates so steps in the production process as well as the schedules completion date of the order, as milestones to measure progress.

Comparing future workload with planned capacity to allow for a determination of appropriate action for balancing work

Ranking orders in designed priority sequence by work center and issuing a dispatch list.

Tracking the current status of each order in process. Providing timely and accurate feedback on activities not

proceeding according to plan Revising order priorities on the basis of performance and

changing conditions Monitoring and controlling lead time, work center queue and

work in process Providing exception and performance evaluation reports

(scrap, rework, late order, and work center efficiency analysis reports)

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Production Control Overview

The functions of production control are:

Releasing orders

o Control shop workload

o Meet job’s due-date

o Maintain shop work-in process level

Dispatching

o Determine job processing priority for jobs waiting at each

work center

Tracking the status

o Monitor job processing progress

o Examine job order completion status

Collecting performance data

o For every job order:

Actual cost vs. planned cost

Actual lead-time vs. planned lead-time

o For each work center:

Utilization level

Average job waiting time

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Job Dispatching (Sequencing) Rules

Dispatching Rule:

determine which job will be processed next among the jobs waiting

in queue.

Common Dispatching Rules:

1. FCFS (First-Come, First-Served).

2. SPT (Shortest Processing Time - Job First).

3. LPT (Longest Processing Time - Job First).

4. EDD (Earliest Due-Date - Job First).

5. MRO (Most Remaining Operations - Job First).

6. CR (Critical Ratio: Smallest CR Job First).

CR =

If CR = 1, this order is in “critical”,

If CR ‹ 1, this order is late already,

If CR › 1, this order has some slack time.

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(Due-Date) – (Current Time)

Total Remaining Operation Time

Most Dispatching Rules are Heuristic in nature. Different Rules

perform differently under different measures.

Examples of Evaluation Criteria for

Production Scheduling

1. Minimize average lateness for completed jobs

2. Minimize average flow time for completed jobs

3. Minimize maximum lateness for completed jobs

4. Minimize maximum flow time for completed jobs

5. Maximize machine utilization in facility

6. Minimize average value of work-in-process

7. Maximize worker utilization

8. Balance workload assigned to each worker/machine

9. Maximize volume of work completed in each time period

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Job Dispatching Example

There are three jobs waiting for processing. Their processing time requirement and due-dates are given below:

Job Processing Time (day) Due-Day (from now)A 2 7B 3 15C 9 11

Dispatching jobs by SPT, LPT, and EDD. Comparing the Average

Job Flow Time and the Number of Jobs Late.

a) SPT:

b) LPT:

c) EDD:

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Exercise: Job Dispatching Problem

There are eight jobs waiting in the queue for processing on machine1. The jobs are arranged in the order of their arrival with A, B, C, . . . G, H.

Jobs A B C D E F G HProcessing Times (days) 27 14 7 31 9 27 3 21Due-Date (days from now) 32 33 17 40 28 52 9 44

A) Use FCFS (first-come-first-serve) dispatching rule. Compute total job completion time, average job flow time, and average job lateness.

B) Use SPT (shortest processing time) dispatching rule. Compute total job completion time, average job flow time, and average job lateness

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Supplement Scheduling Example a) By ____________ Rule

Job Sequence

Processing Time

Flow Time Due-Date Lateness

(Total) ( ) ( )

Average Flow Time = (Total Flow-Time)/Number of Jobs =

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Average Lateness = (Total Lateness)/Number of Jobs =

B) By ____________ Rule

Job Sequence

Processing Time

Flow Time Due-Date Lateness

(Total) ( ) ( )

Average Flow Time = (Total Flow-Time)/Number of Jobs =

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Average Lateness = (Total Lateness)/Number of Jobs =

Job-Sequencing Problem

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

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

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

Order-sequencing rules:o First-come-first served (FCFS)o Shortest processing time (SPT)o Earliest due date (EDD)o Least slack (LS)o Critical Ratio (CR)o Least Changeover Cost (LCC)

General Performance:o First-come-first-served

o Performs poorly on most evaluation criteriao Does give customers a sense of fair play

o Shortest processing timeo Perform well on most evaluation criteriao But have to watch out for long=processing-time orders

getting continuously pushed backo Critical ratio

o Works well on average job lateness criterion

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o May focus too much on jobs that cannot be completed in time, causing other to be late too.

Scheduling in Service Operations

Major Characteristics of Scheduling in Service Operations:

1. Large demand fluctuation due to customer involvement.

2. Intangible output can not be inventoried, capacity flexibility is

critical (customers will not wait in a long line).

3. Capacity is labor-intensive in customer-contact operations.

Two Major Scheduling Issues:

1. Worker Shift Construction - How many shifts per working

day?

2. Staffing for Each Shift - How many workers will be assigned to

each shift?

Major Scheduling Techniques in Service Operations:

Optimization Analytical Models (e.g., LP, ILP).

Practical-Oriented Scheduling Heuristics.

Queuing (Waiting-Line) Models.

Computer Simulation Search Algorithms.

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Service Operations: Planning and Scheduling

Services are operations with: Intangible outputs that ordinarily cannot be inventoried Close customer contact and short lead times High labor costs relative to capital costs Subjectively determined quality Need better planning, controlling, and management to stay

competitive

Positioning strategies contain two elements: Type of service design

o Standard of customo Amount of customer contacto Mix of physical goods and intangible services

Types of production processo Quasi-manufacturing: production occurs much as

manufacturing, physical goods dominant over tangible services

o Customer-as-participant: high degree of customer involvement physical goods may or may not be significant, service either standard or custom

o Customer-as-product: service performed on customer… usually custom

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Scheduling Challenges in Services:Planning and controlling day-to-day activities difficult due to:

Services produced and delivered by people Pattern of demand for services is non-uniform

Scheduling for Non-Uniform Demand As firms cannot inventory services in advance of high-demand

periods, so businesses use following tactics:o Preemptive actions to make demand more uniformo Off-peak incentives/discountso Appointment scheduleso Fixed scheduleso Make operations more flexible so it is easier to vary

capacityo Part-time personnelo Subcontractorso In-house standby resources

Additional tactics used by business:o anticipated demand and schedule employees during each

time period to meet demando allow waiting lines to form

Scheduling quasi-manufacturing services:o Product-focused operations: customer demand is forecast and

capacity decisions made just as in manufacturing high volumes of standardized products management focused on controlling production costs

product quality and delivery of physical goods

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o Process-focused operations: input-output control important to balance capacity between operations Gantt charts used to coordinate flows between departments Sequence of jobs consider sequencing rules changeover costs

and flow times

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Work Shift Scheduling in Service Operations

Three difficulties in scheduling services:o Demand variabilityo Service time variabilityo Availability of personnel when needed

Managers use two tactics:o Use full-time employees exclusivelyo Use some full-time employees as base and fill in peak

demand with part-time employees

Scheduling Customer-as-Participant Services

Must provide customer ease of use/access features… lighting, walkways, etc…

Layouts must focus on merchandising and attractive display of products

Employee performance crucial to customer satisfaction Waiting lines (queuing models) used extensively to level

demand because:o Demand patterns are irregular or randomo Service times vary among “customers”o Managers try to strike a balance between efficiently

utilizing resources and keeping customer satisfaction high

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Waiting Line in Services: Examples Computer printing jobs waiting for printing Workers waiting to punch a time clock Customers in line at a driven-up window Drivers waiting to pay a highway toll Skiers waiting for chair lift Airplanes waiting to take off

Waiting line analysis: assists managers in determining: How many servers to use Likelihood a customer will have to wait Average time a customer will wait Average number of customer will wait Waiting line space needed Percentage of time all servers are idle

Scheduling customer as product services Wide range of complexity Every facet designed around the customer Highly trained motivated and effective workforce critical to

success Waiting-line analysis can be helpful in determining staffing

levels In more complex operations simulation is a helpful tool in

scheduling resources.

Reasons for simulating operations Experimentation with the real system is impossible impractical

or uneconomical System is so complex that mathematical formulas cannot be

developed Values of the system’s variables are not known with certainty.

Exercise: Operations Scheduling

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1. Six jobs are waiting to be processed at a workstation. Their job code numbers, estimated production times, and promised delivery times are given in the following table:

Job Code Number Production Time (hours) Time to Promised Delivery (hours)

A 3.8 6.0B 2.1 3.0C 4.5 14.0D 3.0 10.0E 4.2 20.0F 2.9 19.0

Determine the sequence of producing the jobs using the following rule:a) Shortest processing time rule, Longest Processing Time rule, and Critical ratio ruleb) Calculate the Average Job Flow-Time and Average Job Lateness for each of the three

dispatching rules above.

2. Seven jobs are waiting to be processed at a workstation. Their job code number estimated production times, and promised delivery times are given below.

Job Code Number Production Time (hours) Time to Promised Delivery (hours)A 2.4 31.0B 3.7 12.0C 5.2 19.0D 3.3 14.0E 5.6 10.0F 6.1 27.0G 4.0 24.0

Determine the sequence of producing the jobs using the following rule:a) Shortest processing time rule, Longest Processing Time rule, Critical ratio ruleb) Calculate the Average Job Flow-Time and Average Job Lateness for each of the

three dispatching rules above.

3. A company does heat-treating for industrial customers on a first-come first-served basis, but wonders if shortest processing time would be better. The jobs that are now waiting to be

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produced are listed in the order in which they arrived, with their estimated production times, time to promised delivery, and the necessary computations:

Job Estimated Production Time (hours)

Job Sequence(FCFS)

Flow Time (days)

Job Sequence(SPT)

Flow Time (days)

A 6 1 6 4 16B 3 2 9 2 5C 2 3 11 1 2D 5 4 16 3 10

a. Rank the two sequencing rules on two evaluation criteria: average flow time and average job lateness.

b. Which sequencing rule would you recommend? Why?

4. A production planner must decide the sequence in which to produce four customer orders.

Customer Order

Estimated Production Time (days)

Time to Promised Delivery (days)

First-Come First-Served Order Sequence

Flow Time (days)

Lateness (days)

A 10 15 1 10 0B 21 30 2 31 1C 26 60 3 57 0D 19 77 4 76 1

Rank the first-come first-served, shortest processing time, and critical ratio sequencing rule on two evaluation criteria: average flow time, and average job lateness.

Review Questions for Topic 14:

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< PRODUCTION/OPERATIONS SCHEDULING>

(1) In class we discussed the implementation of a scheduling system (and general management information system) for a job shop production facility. Identify several dispatching rules which might be used in such a system. How should the choice of a dispatching rule depend on the firm's strategy?

(2) Define dispatching and expediting. Where does each fit in the general production controlcycle?

(3) Be prepared to sequence several jobs on one machine by the SPT rule, the EDD rule, the FCFS rule, and the LPT rule. Be prepared to evaluate the resulting schedules on the basis of average flow time and average lateness. In addition, what is the impact of these rules on work-in-process?

(4) What is the critical ratio scheduling rule? Be prepared to apply this rule for sequencingseveral jobs on a machine.

(5) Identify several scheduling evaluation criteria for production shops, i.e., given two different schedules for a production shop for the same day, how would one determine which one isbest?

(6) Why is the “job release” an important function for a shop manager? What are the impacts of releasing jobs too early (or too late) to the shop floor?

(7) Describe/draw a job scheduling GANTT chart. For what purpose is it used?(8) Based on class discussions and the text presentation, what job shop scheduling performance

results (in terms of minimizing job flow time and lateness) would be expected from the use of the SPT, LPT, FCFC, and EDD heuristic rules?

(9) Based on our in-class discussions, what is the objective function in scheduling telephone(information) operators or airline reservationists? What are the constraints?

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