1. Scheduling

2. Definition of scheduling
Establishing the timing of the use of equipment, facilities and human activities in an organization
In the decision-making hierarchy, scheduling decisions are the final step in the transformation process before actual output occurs.
Effective scheduling can yield
Cost savings
Increases in productivity

3. Volume
Scheduling tasks are largely a function of the volume of system output.
High-volume systems
Intermediate-volume systems
Low-volume systems

4. High-Volume Systems
Flow system: High-volume system with Standardized equipment and activities
Flow-shop scheduling: Scheduling for high-volume flow system
Goal: a smooth rate of flow of goods or customers through the system to get a high utilization of workforce and equipment
Highly repetitive nature system leads to:
…the determination of many loading and sequence decisions during the design of the system,
…highly specialized: tools and equipnment, arrangement, division of labour
automatization

5. Balancing the line
Allocating the required tasks to workstations so that they satisfy technical (sequencing) constraints and are balanced with respect to equal work times among stations.
Goal: maximum utilization and highest possible output rate

6. Hindrances of highly specialized jobs
Discontent of workers:
Too simple tasks: monotonous, boring
Give rise to fatigue, absenteeism, turnover
Reduce productivity

7. High-Volume Success Factors
Process and product design: manufacturability
Preventive maintenance: to minimize disruption of the flow of work
Rapid repair when breakdown occurs
Optimal product mixes: linear programming
Minimization of quality problems: to minimize disruption
Reliability and timing of supplies: to avoid shortages (and high carrying costs)

8. Intermediate-Volume Systems
Outputs are between standardized high-volume systems and made-to-order job shops
Usually standard outputs
Not continuous but intermittent production (periodical shifts from one job to another)
Run size (large), timing, and sequence of jobs
Economic run size:
MRP approach

9. Setup costs Depend on the similarity of products
Complex sequencing problem: different setup costs for every combination
Off-line setups, modular set-ups, flexible equipment

10. Scheduling in Low-Volume Systems
Products made to order not to inventory
Orders can be very different
Job-shop scheduling: Scheduling for low-volume systems with many variations in requirements
Schedules cannot be made prior to actual job order
Loading - assignment of jobs to process centres and to various machines in the centres
Sequencing - determining the order in which jobs will be processed

11. Aims of loading Find arrangement to minimize:
Processing and setup costs
Idle time among work centers and machines
Job completion time

12. Gantt load charts Visual aid
Depicts the loading and idle times for a group of machines or departments
Trial-and-error schedule development

13. Loading
Infinite loading: jobs are assigned without regard to the capacity of work centres. This can lead to over- and underloads.
Finite loading: takes into account the work centre capacity and job processing times. Need frequent updating.
Forward scheduling: scheduling ahead from a point in time. ‘How long will it take to complete this job?’
Backward scheduling: scheduling backward from due date. ‘When is the latest job can be started?’

14. Gantt schedule chart
Shows the orders or jobs in progress and whether they are on schedule
horizontal axis: time,
vertical axis: jobs in progress

15. Sequencing
Sequencing: Determine the order in which jobs at a work centre will be processed (and the order in which jobs are processed at individual workstations within work centres). Crucial if work centres are heavily loaded.
Workstation: An area where one person works, usually with special equipment, on a specialized job.

16. Sequencing
Priority rules: Simple heuristics used to select the order in which jobs will be processed.
Job time: Time needed for setup and processing of a job.

17. Priority Rules Top Priority FCFS - first come, first served
SPT - shortest processing time
EDD - earliest due date
CR - critical ratio
S/O - slack per operation
Rush - emergency
Top Priority

18. Effectiveness of a given sequence
Job flow time – the length of time a job is at a particular workstation or work center. (it includes not only processing time, but waiting time, transportation time)
Average flow time = total flow time /number of jobs
Job lateness – length of time the job completion date is exceed the date the job was due to promised to the customer
Average tardiness =total lateness/number of products
Makespan – is the total time needed to complete a group of jobs (time between start the first and completion of the last one)
Average number of jobs =total flow time/makespan (it reflects the average work-in-process inventory if the jobs represent equal amount of inventory)

19. Scheduling Seminar exercises
Process and Production Management

20. Assumptions The set of jobs is known
Setup time is independent of processing sequence
Setup time is deterministic
Process time are deterministic
There will be no interruptions in processing such as machine breakdowns, accidents, or workes illness.

21. Processing time (days)
Example 1
Determine the sequence of jobs/products
Determine average flow time
Determine average tardiness
Determine average number of jobs at the workcenter
Job/ product
Processing time (days)
Due date (days) A 2 7 B 8 16 C 4 D 10 17 E 5 15 F 12 18

22. FCFS ABCDEF Aft=120/6=20 days At=54/6=9 days
Job/ product
Processin time (days)
Due date (days)
(2)
Flow time
(3)
Days tardy (0 if negative)
(3)-(2) A 2 7
2-7=-50 B 8 16
2+8=10
10-16=-60 C 4
10+4=14
14-4=10 D 10 17
14+10=24
25-17=7 E 5 15
24+5=29
29-15=14 F 12 18
29+12=41
41-18=23 41
120 54
Aft=120/6=20 days
At=54/6=9 days
M=41  Aj=120/41=2,93 pieces

23.  ACEBDF SPT Aft=108/6=18 days At=40/6=6,67 days Aj=108/41=2,63 pieces
Job/ product
Processin time (days)
Due date (days)
(2)
Flow time
(3)
Days tardy (0 if negative)
(3)-(2) A 2 7
2-7=-50 C 4
2+4=6
6-4=2 E 5 15
5+6=11
11-15=-40 B 8 16
11+8=19
19-16=3 D 10 17
19+10=29
29-17=12 F 12 18
29+12=41
41-18=23 41
108 40
Aft=108/6=18 days
At=40/6=6,67 days
Aj=108/41=2,63 pieces

24. EDD CAEBDF Aft=110/6=18,33 days At=38/6=6,33 days
Job/ product
Processin time (days)
Due date (days)
(2)
Flow time
(3)
Days tardy (0 if negative)
(3)-(2) C 4
4-4=0 A 2 7
4+2=6
6-7=-10 E 5 15
5+6=11
11-15=-40 B 8 16
11+8=19
19-16=3 D 10 17
19+10=29
29-17=12 F 12 18
29+12=41
41-18=23 41
110 38
Aft=110/6=18,33 days
At=38/6=6,33 days
Aj=110/41=2,68 pieces

25. CR ??? Job/ product Processin time (days) Due date (days) (2) CR0 A 2
Remaining time untill due to dat (on the 0th day)
Job/ product
Processin time (days)
Due date (days)
(2)
CR0 A 2 7
(7-0)/2=3,5 B 8 16
(16-0)/8=2 C 4
(4-0)/4=1 D 10 17
(17-0)10=1,7 E 5 15
(15-0)/5=3 F 12 18
(18-0)/12=1,5 41
CR4
(7-4)/2=1,5
(16-4)/8=1,5
(17-4)/10=1,3
(15-4)/5=2,2
(18-4)/12=1,17 1. 2.

26. Job/ product CR16 A (7-16)/2=-4,5 B (16-16)/8=0 C ------- D
(17-16)/10=0,1 E
(15-16)/5=-0,2 F
-----
CR23
(16-23)/8=-0,875
(17-23)/10=-0,6
CR18
(16-18)/8=-0,25
(17-18)/10=-0,1
(15-18)/5=-0,6 3. 4. 1. 5. 4. 2.

27. CRCFAEBD Aft=133/6=22,16 days At=58/6=9,66 days Aj=133/41=3,24 pieces
Job/ product
Processin time (days)
Due date (days)
(2) C 4 F 12 18 A 2 7 E 5 15 B 8 16 D 10 17 41
Flow time
(3) 4
4+12=16
16+2=18
18+5=23
23+8=31
31+10=41
133
Days tardy (0 if negative)
(3)-(2)
4-4=0
16-18=-20
18-7=11
23-15=8
31-16=15
41-17=24 58
Aft=133/6=22,16 days
At=58/6=9,66 days
Aj=133/41=3,24 pieces

28. Sequencing Jobs through two Work Center
Job time is known and constant
Job time is independent of job sequence
All job must follow the same two-step job sequence
Job priorities cannot be used
All units must be completed at the first work center before moving on to the second work center

29. Thank you for your attention!