Production activity control cap 11 fall 2007

8/8/2019 Production activity control cap 11 fall 2007

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Production Activity Controlshop floor control

Concerned with controlling theactual activity of making a product

or delivering a service.

Source: Chapman, Fundamentals of Production Planning and Control


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PAC

Planning has already been done and theactual order to produce a product hasbeen executed.

Deals with controlling the priority of the jobs at a work center

Execution control activity.Monitor, prioritize and control.


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PAC inputs:

Newly released orders (MRP)Existing order statusRouting information steps, sequence

needed to complete the jobLead time informationStatus of resources (quantity available,

maintenance schedules, machineproblems, etc.)


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PAC inputs cont.

Resources number, type, conditions People number, skills, time availability Tools equipment for setup or operation of

the machinery Machine or equipment capacity and downtime Materials needed to complete the order


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Information generated by PAC:

Status and location of ordersStatus of critical resources

Performance to standardsScrap / reworkProblems (unscheduled downtime, broken

equipment, etc.)


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Need for PAC

Process industries and repetitive assemblylines with a high volume standard product

dont use detailed PAC systems. Onlyneed to monitor the quantity as it isproduced.Industries with smaller quantities of discrete jobs, often use dispatch lists.


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Dispatch list = list of jobs to be performed

at a given work center in the order inwhich the jobs should be done.Includes information: Scheduled run date, setup and run time Equipment to be used and specific operation Lot sizes Estimates of capacity available Next work center (where to move the job) Jobs expected to be received at the WC in

some specified time period (future jobs)


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The dispatch list is followed by a report tothe PAC system with information on:Part number and quantity producedAny problems (scrap, quality, shortages)

Workforce dataEquipment statusComments, suggestions


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PAC and Gantt charts

Gantt chart = simple visual tool used toschedule work according to priority and toassess the status of all jobs ordered.Used to reprioritize jobs if needed.Shows work to be done, expectation of time required, start and end dates, and job

status.Done for each work center or specificmachine.


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Prioritizing work

Practice exercise dataSuppose thefollowing jobshave arrivedat a WC in theorder listed:

JOB Due in Hrs. workremaining

A 3 hrs. 4

B 9 hrs. 2

C 4 hrs. 1

D 15 hrs. 5E 11 hrs. 3.5

F 19 hrs. 5


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Prioritizing Work methods

1. Due date = Job with earliest due date isdone first. Often used with MRP planning.


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Due date

job Due in Workremaining Start time Completiontime Late?

A 3 hrs. 4 hrs. 0 4 Yes

C 4 hrs. 1 hr. 4 5 Yes

B 9 hrs. 2 hrs. 5 7 No

E 11 hrs. 3.5 hrs. 7 10.5 No

D 15 hrs. 5 hrs. 10.5 15.5 Yes

F 19 hrs. 4 hrs. 15.5 19.5 Yes


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2. SPT Shortest processing time = quick jobs are done first.

A lot of jobs are completed quickly.Leaves long jobs for last and sometimesmakes them late. (customer service andbig orders)


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Shortest processing time

Job Due in Workremaining

Start time Completiontime

Late?

C 4 hrs. 1 hr. 0 1 No

B 9 hrs 2 hrs. 1 3 No

E 11 hrs 3.5 hrs. 3 6.5 No

A 3 hrs. 4 hrs.* 6.5 10.5 Yes

F 19 hrs. 4 hrs.* 10.5 14.5 No

D 15 hrs. 5 hrs. 14.5 19.5 yes


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3. Total slack:

Total time until the job is due-Total processing time____

Total slack

Slack = buffer time, time that can passwithout danger of the job being late.

Work first the jobs with the least total slack(greatest danger of being late)


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Total slack

Job Due in Workremaining Slack Start time Completiontime

A 3 hrs. 4 hrs. -1 hr. 0 4

C 4 hrs. 1 hr. 3 hrs. 4 5

E 11 hrs. 3.5 hrs. 6.5 hrs. 5 8.5

B 9 hrs. 2 hrs. 7 hrs. 8.5 10.5

D 15 hrs. 5 hrs. 10 hrs. 10.5 15.5

F 19 hrs. 4 hrs. 15 hrs. 15.5 19.5


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4. Slack per operation:

Total slack / number of operations left

Work first the job with the least slack per

operation

Gives average slack at each operation

instead of total slack for the entire job.


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Job Due in Slack # operations Slack per operation

Workremaining

A 3 hrs. -1 3 -.33 4 hrs.

B 9 hrs. 7 9 .77 2 hrs.

C 4 hrs. 3 4 .75 1 hrs.

D 15 hrs. 10 15 .66 5 hrs.

E 11 hrs. 6.5 11 .59 3.5 hrs.

F 19 hrs. 15 19 .79 4 hrs.


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Job Due in Slack per operation

Workremaining

Start Completion Late?

A 3 hrs. -.33 4 hrs. 0 4

E 11 hrs. .59 3.5 hrs. 4 7.5

D 15 hrs. .66 5 hrs. 7.5 12.5

C 4 hrs. .75 1 hrs. 12.5 13.5

B 9 hrs. .77 2 hrs. 13.5 15.5

F 19 hrs. .79 4 hrs. 15.5 19.5


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5. First come, first served Assumes that the first job is also neededfirst (doctors office)

Perceived as fair.Really?


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6. Critical ratio:

Time remaining until due / work remaining

Work remaining = total processing time If critical ratio is greater than 1 : there is slack If critical ratio = 1 : there is no slack If critical ratio is less than 1 : past due, late

rule: work first job with lowest critical ratio Considered best rule


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Critical ratio

Job Due in Workremaining

Ratio Start time Completiontime

Late?

A 3 hrs. 4 hrs. .75 0 4 Yes

D 15 hrs. 5 hrs. 3 4 9 No

E 11 hrs. 3.5 hrs. 3.14 9 12.5 Yes

C 4 hrs. 1 hr. 4 12.5 13.5 Yes

B 9 hrs. 2 hrs. 4.5 13.5 15.5 Yes

F 19 hrs. 4 hrs. 4.75 15.5 19.5 Yes


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These scheduling rules apply in productionenvironments where integrated productioncontrol systems are not used (smaller jobshop environments).

Integrated approaches (MRP) provide their own scheduling priorities.


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Scheduling: estimation of when a job will reach awork center and when the job will be completed.

Two approaches:1. backward scheduling : start with the due

date (promised date) and use lead timeto estimate when job will reach eachcenter. (MRP)

2. Forward scheduling: start when the job

will be released into the productionprocess. Estimate final completion dateand this becomes the promise date.


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Example data

It is now the start of day 214, and there is

one shift in the operation with 7 productivehours. The job calls for a quantity of 100to be built:


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Day 214; 7 work hours; 100 units

Operation Total lead time for 100 u.

A 21 Hours

B 14 hoursC 35 hours

D 7 hours

E 10.5 hours

F 3.5 hours


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Forward scheduling

Operation Lead timehours

Completed

A 21 End of day 216 (3 shifts:214,215,216)

B 14 End of day 218

C 35 End of day 223

D 7 End of day 224

E 10.5 Half through day 226

F 3.5 End of day 226


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This implies that we can deliver theproduct on day 227.

Lead time includes setup, run, queue and

move time.

queue time = time a job must wait to be

processed once it has been moved to theoperation. Largest and most variable of allthe elements of lead time.


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Backward scheduling

Suppose thesalespersonhas promisedthe job for

delivery on day240 using astandard quotedlead time.

Job must befinished onday 239.

Operation;Lead time

Must becompletedby:

Must startby:

F; 3.5 hrs. End of 239 Mid-day 239

E; 10.5 hrs. Mid-day 239 Start of 238

D; 7 hrs. End of 237 Start of 237

C; 35 hrs. End of 236 Start of 232

B; 14 hrs. End of 231 Start of 230

A; 21 hrs. End of 229 Start of 227


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LoadingWork center load: total time estimate to complete

all the jobs at a given work center. Measured intime units (hours). Two approaches:

1. Infinite loading : jobs are loaded according towhen the customer needs them, regardless of capacity.

Assume the work center has infinite capacity.Need for capacity expanding alternatives(overtime, temporary workers).


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Loading2 .

Finite loading : known measurable finite capacityfor the work center.Work is moved to the next time period if there is no

more capacity in the given period.

Advantages:Smoothing the loadSave on extra expenses

Stability of the work center Disadvantages:

Customer service


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Methods for loading a work center

1. V ertical loading : jobs are loaded into thecenter job by job according to a priorityrule (due date, critical ratio, etc.).Focus is the work center, with the jobloaded work center by work center, one

job at a time.


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Methods for loading a work center

2. H orizontal loading: the highest priority jobis loaded work center by work center intoall the work centers required. Then do thesame for the next jobs.

Used in the finite scheduling system.

Focus is on the job.


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Loading example:

A work center (X) has the following jobs,which are listed in the order in which theyarrived at the work center.

The work center uses due date with firstcome, first serve to break any ties.

The current day is the start of day 137, andthere are 7 productive hours in a day

(420 minutes).


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Job(arrival

order)

Quantity Due day Setup time(min.)

Standard per piece (min.)

A 130 136 10 1.5

B 100 137 30 1.8

C 50 137 10 0.6

D 200 138 25 0.8

E 120 138 15 1.1

F 100 138 20 1.3


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V ertical loading and infinitecapacity

Need to first determine the time it shouldtake to complete each job at standard.

See next table


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Job; Q Time std. X Q Setup time Total time

A; 130 130x1.5=195 min. 10 min. 205 min.

B; 100 100X1.8=180 min. 30 min. 210 min.

C; 50 50X0.6=30 min. 10 min. 40 min.

D; 200 200X.08=160 min. 25 min. 185 min.

E; 120 120X1.1=132 min. 15 min. 147 min.

F; 100 100X1.3=130 min. 20 min. 150 min.


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Infinite loadingLoad the work center according to duedate. Jobs A, B, and C would be loadedinto day 137.

Jobs D, E, and F would be loaded into day138.It will require 455 minutes in day 137 and482 minutes in day 138.

Minutes available =420Need for overtime


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Finite loading : 420 minutes available

Only try to complete jobs A and B in day 137.Total minutes required= 415.5 minutes left. Try to start setup for job C.Day 138: finish job C and then complete jobs Dand E.53 minutes left; do setup and start running job F.Complete approximately 25 of the 100 items (53min.- 20 min. setup =33 min.33 min./1.3 min. per item = 25.4 itemsJobs C and F will be late


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Infinite vs. Finite

Infinite loading assumes flexibility incapacity and gives priority to due dates,regardless of the increase in costs.Finite loading assumes no flexibility incapacity and costs. Problems withcustomer service levels.


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It has been assumed that lead time isknown, constant, and accurate. This is not

always true. We might have different actualLT.

Corrective actions: (different Std. and realtimes) Subcontracting or purchasing components

Lot splitting = work only on minimal amountreally needed. Leave the rest for a later date.


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Corrective actions cont.

Operation overlapping = moving part of theorder to the subsequent operation before theentire order is ready for that next operation.

Operation splitting = assigning moreresources to the order so that processing canproceed more quickly.


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Corrective actions cont.

Alternative routings = moving the job tooperations not normally used for itsproduction. Used when primary production

resources are not available.

Order cancellations = costs to complete arehigher than expected profit from the order.

Production activity control cap 11 fall 2007

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