1. Production Activity Control

2. Techniques for scheduling different for various manufacturing systems:
When the plan has been developed, the next step is execution of the plan
Production Activity Control (or often called Shop Floor Control) is to have activities performed as planned
Techniques for scheduling different for various manufacturing systems:
Project
Job shop
Batch
Flow shop

3. Scheduling Batch Flow Line
A group of similar items is manufactured on the batch line
The focus is to minimize changeover time
The smaller the changeover time, the greater the scheduling flexibility
It is becoming very complicated when you have sequence-dependent setup

4. How much to produce? Or How long the run time will be?
Depends on:
Available on hand
Demand rate
The changeover time
Production rate
The sequence, if any, in which items should be run
When the setup times are relatively small and independent of the sequence  produce first the item with smallest runout time
Runout time is the period existing inventory will last given forecast usage (= units in inventory / demand rate)

5. Example Item Inventory Demand (units per day) R (in days)
Scheduling priority) A 80 20
4.0 1 B
100 10
10.0 2 C
150 12
12.5 3 D 60 4
15.0

6. Economic Production Time (in days)
Another Example
Item
Inventory
Demand
(Units per day) R
(in days)
EPQ
Economic Production Time (in days) A 80
1.0
400
2.0 B
150 75 C 60 30
300
1.5
Do you see any problem here?
What would be the solution?

7. Job Shop Scheduling Job shop production is characterized by:
Process layout
Many orders with different sequence of processes
Scheduling is assigning of starting and completion times to orders (jobs) and frequently includes the time when orders are to arrive and leave each department.
Sequencing is the assigning of the sequence in which orders are to be processed.

8. Priority Control
To determine the sequence in which orders should be processed
Common Priority Rules:
First come first served (FCFS)
Short processing time (SPT) : results in lowest WIP, lowest MLT, and lowest average job lateness
EDD (Earliest due date): works well when processing times are approximately the same
Slack time (ST): supports the achievement of due date objectives
Critical ratio (CR)

9. Example
Day 125 (all times are in days)
Order
Due Date
Current Operation Time
Total Operation Time Remaining
MLT Remaining
# Operations Remaining
Slack Time
Critical Ratio A
130
1.5
3.0
6.0 3
2.0
0.83 B
132
1.0
4.5
9.5 5
2.5
0.74 C
136
4.0
8.0 4
7.0
1.38 D
138
3.5
9.0 2
1.44
ST = Due Date – Present Date – Total Operations Time Remaining
Due Date – Present Date
CR = CR = 1 means the order is on schedule
MLT Remaining

10. Sequencing Results EDD : A – B – C – D SPT : B – A – C – D
ST : A – B – D – C
CR : B – A – C – D
Observation:
A and B always scheduled earlier than C and D
Important:
The status of WC to which each order goes next should be considered. (If A will go to a work center overloaded with high priority orders, there is little point of scheduling it first in the current WC)

11. Queue Length Management
Affect WIP and manufacturing lead times
Queues are planned to compensate uneven flow of incoming work and the variations in work center processing times
The objective of QLM:
To reduce WIP
To shorten MLT
To better utilize bottleneck resources

12. Operations Overlapping
Dividing a lot into two or more batches
Used to reduce MLT
SU1
1 Run
2 Run
SU2
1 Run
2 Run
To avoid idle of operation B, SU2+TAB+Q1PB>=Q2PA+TAB
Where Q = Q1+Q2

13. Savings in Lead Time SU1 1 Run 2 Run SU2 1 Run 2 Run SU1 1 Run 2 Run
Without overlapping
SU1
1 Run
2 Run
SU2
1 Run
2 Run
With overlapping
SU1
1 Run
2 Run
SU2
1 Run
2 Run
Lead time savings

14. INPUT/OUTPUT CONTROL Short-range control technique (normally daily)
Compare scheduled input and output to actual input and output
Effective for controlling queue, WIP, and MLT
Enable the planner to determine the actions necessary to achieve the desired output , WIP, and MLT

15. Single Work Center Processes

16. Input / Output Control Day 25 26 27 28 29 30 Input Planned (PI) 16
Actual (AI) 12 19 22 10 15
Cumulative Deviation (ICD) -4 -1 5 -2
Output
Planned (PO)
Actual (AO) 17 18
Cumulative Deviation (OCD) 1 3 2
WIP (Ending)
Planned (PWIP) 32
Actual (AWIP) 31 36

17. Normal Situation (Under Control)
PWIP is less than 3 or 4 times of std of the ending WIP
Acceptable deviation is about twice the standard deviation
Typical out of control situations:
Queues exceed upper limit due to equipment failure, inefficient processing, and excessive input. Solution: decreasing input or increasing process output.
Output is below the lower limit due to equipment failure, inefficient processing, inadequate input, or wrong input at assembly work centers.

18. WIP Reduction Day 25 26 27 28 29 30 Input Planned (PI) 14 13
Actual (AI) 12 17 16 9
Cumulative Deviation (ICD) -2 1 3 -1
Output
Planned (PO)
Actual (AO) 15 18
Cumulative Deviation (OCD) -3
WIP (Ending)
Planned (PWIP) 23 20
Actual (AWIP) 32 21

19. Inadequate Input Day 25 26 27 28 29 30 Input Planned (PI) 16
Actual (AI) 12 13
Cumulative Deviation (ICD) -4 -8
-11
-15
Output
Planned (PO)
Actual (AO) 15
Cumulative Deviation (OCD) -1 -2 -5
WIP (Ending)
Planned (PWIP) 20
Actual (AWIP) 17 14