Download - 20.0 Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
1/48
Production Scheduling.
-
8/6/2019 20.0 Production Scheduling.
2/48
Production Scheduling.
Scheduling can be defined as prescribing of when and
where each operation necessary to manufacture theproduct is to be performed.
It is also defined as establishing of times at which to
begin and complete each event or operationcomprising a procedure.
The principle aim of scheduling is to plan the sequence
of work so that production can be systematically
arranged towards the end of completion of all products
by due date.
-
8/6/2019 20.0 Production Scheduling.
3/48
Production Scheduling.
Production Scheduling and the Hierarchy of Production Decisions.
First, the organization must forecast demand for aggregate
sales over some predetermined planning horizon.
These forecast provides the input for determining the
aggregate production and workforce level for the planning
horizon. The aggregate production plan must then be translated
into master production schedule (MPS).
The MPS results in specific production goals by product and
time period.
Material requirements planning (MRP) is one method for
meeting specific production goals of finished-goods
inventory generated by the MPS.
.
-
8/6/2019 20.0 Production Scheduling.
4/48
Production Scheduling
The MRP system explodes the production levels
one obtains from the MPS analysis back in time toobtain production targets at each level of assembly
by time period.
The result of the MRP analysis is specific planned
order releases for final products, subassemblies andcomponents.
Finally, the planned order releases must be
translated into set of tasks and the due dates
associated with those tasks.
This level of detailed planning results in the shop
floor schedule
-
8/6/2019 20.0 Production Scheduling.
5/48
Production Scheduling.
-
8/6/2019 20.0 Production Scheduling.
6/48
Production Scheduling.
Important Characteristics of Job Shop Scheduling Problems.
1. The job arrival pattern:
It is often viewed that job shop problems are static and
proceeded with solutions on the current state but most practical
shop scheduling problems are dynamic in nature.
2. Number and variety of machines in the shops:
A particular job shop may have unique feature that could make
implementing a solution obtained from scheduling algorithm
difficult.
3. Number of workers in the shop:
Both the number of workers and the variety of machines inthe shop determine shop capacity.
A breakdown of a single machine or loss of critical employee
could result in a bottleneck and reduction in the shop capacity.
-
8/6/2019 20.0 Production Scheduling.
7/48
Production Scheduling.
4. Particular flow patterns:
Because material handling issues are often treated separately
from scheduling issues, infeasible flow pattern may result.
5. Evaluation of alternative rules:
The choice of objective will determine the suitability and
effectiveness of a sequencing rule .
It is common for more than one objective to be important, so that
it may be impossible to determine a unique optimal rule.
-
8/6/2019 20.0 Production Scheduling.
8/48
Production Scheduling.
Objectives of Job shop Management.
One of the difficulties of scheduling is that many, often conflicting,objectives are present. Some of the most common objectives are
1. Meet due dates.
2. Minimum work-in-process(WIP) inventory.
3. Minimize the average flow time through the system.
4. Provide for high machine/worker time utilization. (Minimum
machine/worker idle time).
5. Provide for accurate job status information.6. Reduce setup times.
7. Minimize production and worker costs.
-
8/6/2019 20.0 Production Scheduling.
9/48
Production Scheduling.
Principles of Scheduling.
1. The principle of optimum task size:Scheduling tends to achieve maximum efficiency when
the task sizes are small, and all tasks of same order of
magnitude.
2. Principle of optimum production plan:
The planning should be such that it imposes an equal
load on all plants.
3. Principle of optimum sequence:
Scheduling tends to achieve the maximum efficiency
when the work is planned so that work hours are
normally used in the same sequence.
-
8/6/2019 20.0 Production Scheduling.
10/48
Production Scheduling
Performance Measures.
The following performance measures are commonly
used for scheduling. Job Flow Time: The amount of time a job spends in the
service or manufacturing system. Minimizing job flow
times supports the competitive priorities of cost (lowerinventory) and time (delivery speed).
Job flow time = Time of completion - Time job was
available for first processing operation.
Job flow time is sometimes referred to as throughout
time or time spent in the system, including service.
-
8/6/2019 20.0 Production Scheduling.
11/48
-
8/6/2019 20.0 Production Scheduling.
12/48
Production Scheduling
Tardiness and lateness: Tardiness is the positive
difference between the completion time (flow time)
and the due date of the job.
A tardy job is the one that is completed after the
due date.
Lateness refers to the difference between the jobcompletion time and its due date, and differs from
tardiness in that lateness can be either positive or
negative
Minimizing the tardiness supports the competitivepriorities of cost (penalties for missing due dates),
quality (perceptions of poor service) and time (on-
time delivery).
-
8/6/2019 20.0 Production Scheduling.
13/48
Production Scheduling
Work-in-process Inventory:
Any job that is waiting in line, from one operation to
the next, being delayed for some reason, being
processed , or residing in the semi finished state.
Minimizing the WIP Inventory supports the
competitive priority of cost (inventory holding costs).
-
8/6/2019 20.0 Production Scheduling.
14/48
Production Scheduling
Total Inventory: This performance measure is used to
measure how effective schedules for manufacturingprocess are.
The sum of scheduled receipt and on-hand inventories
is the total inventory.
Total inventory = Scheduled receipts for all items + On-
hand inventories of all items.
Minimizing total inventory supports the competitive
priority of cost(inventory holding costs). Essentially, total inventory is the sum of WIP and
finished goods inventories.
-
8/6/2019 20.0 Production Scheduling.
15/48
Production Scheduling
Utilization:
The percentage of work time thatis productively spent by an employee or a
machine is called Utilization.
Maximizing the utilization of a process
supports the competitive priority of cost(slack
capacity).
-
8/6/2019 20.0 Production Scheduling.
16/48
Production Scheduling.
Inputs to Scheduling.
1. Performance standards: The information regarding theperformance standards (standard times for operations)
helps to know the capacity in order to assign required
machine hours to the facility.
2. Units in which loading and scheduling is to be expressed.
3. Effective capacity of the work center.
4. Demand pattern and extent of flexibility to be provided
for rush orders.5. Overlapping of operations.
6. Individual job schedules.
-
8/6/2019 20.0 Production Scheduling.
17/48
Production Scheduling.
Scheduling Strategies.
Scheduling strategies vary widely among firms andrange from no scheduling to very sophisticated
approaches.
These strategies are grouped into four classes:
1. Detailed scheduling:
Detailed scheduling for specific jobs that are
arrived from customers is impracticable in actual
manufacturing situation. Changes in orders, equipment breakdown, and
unforeseen events deviate the plans.
-
8/6/2019 20.0 Production Scheduling.
18/48
Production Scheduling
2. Cumulative scheduling:
Cumulative scheduling of total work load is usefulespecially for long range planning of capacity needs.
This may load the current period excessively and
under load future periods.
It has some means to control the jobs.
3. Cumulative detailed:
Cumulative detailed combination is both feasible and
practical approach if master schedule has fixed and
flexible portions.
-
8/6/2019 20.0 Production Scheduling.
19/48
Production Scheduling
4. Priority decision rules:
Priority decision rules are scheduling guides
that are used independently and in conjunction
with one of the above strategies, i.e., first come
first serve.
These are useful in reducing Work-In-Process
(WIP) inventory.
-
8/6/2019 20.0 Production Scheduling.
20/48
Production Scheduling
Priority sequencing rules:
The rules that specify the job processing sequence when several jobs
are waiting in line at a workstation.
First-Come ,First-Served : The job arriving at the workstation first
has the highest priority under a first-come ,first-served (FCFS)
rule.
Earliest Due Date: The job with the earliest due date (EDD) is thenext job to be processed.
Shortest processing Time: The job requiring the shortest
processing time (SPT) at the workstation is processed next.
Critical Ratio: The critical ratio (CR) is calculated by dividing thetime remaining until a jobs due date by the total shop time
remaining for the job, which is defined as the setup, processing,
move and expected waiting times of all remaining operations,
including the operations being scheduled.
-
8/6/2019 20.0 Production Scheduling.
21/48
Production Scheduling
The formula for Critical ratio is
CR= (Due date - Todays date) / (Total shop time remaining)
The difference between the due date and todays date must be
in the same units as the total shop time remaining.
A ratio less than 1.0 implies that the job is behind schedule.
A ratio greater than 1.0 implies that the job is ahead of
schedule.
The job with the lowest CR is scheduled next.
-
8/6/2019 20.0 Production Scheduling.
22/48
Production Scheduling
Numerical Problem:
-
8/6/2019 20.0 Production Scheduling.
23/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
24/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
25/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
26/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
27/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
28/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
29/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
30/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
31/48
Production Scheduling
Scheduling Models
-
8/6/2019 20.0 Production Scheduling.
32/48
-
8/6/2019 20.0 Production Scheduling.
33/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
34/48
Two-Machine Flow Shop
Johnsons Rule Example
A 5 6
B 16 5
C 8 2D 9 17
E 4 6
Machine Machine
Job Center 1 Center 2
The minimum processing time, 2, is given by Job C on
Machine 2. So, Schedule Job C in the end.
-
8/6/2019 20.0 Production Scheduling.
35/48
A 5 6
B 16 5
D 9 17
E 4 6
Machine Machine
Job Center 1 Center 2
Two-Machine Flow Shop
Johnsons Rule Example
C
After removing job C, the minimum processing time, 4, is
given by Job E on Machine 1. So, Schedule Job E in the
beginning.
-
8/6/2019 20.0 Production Scheduling.
36/48
A 5 6
B 16 5
D 9 17
Machine Machine
Job Center 1 Center 2
Two-Machine Flow Shop
Johnsons Rule Example
CE
Job E is removed. Now, there is a tie. Minimum processing
time is given by Jobs A and B. Break ties arbitrarily.
Schedule one of Job A or Job B.
-
8/6/2019 20.0 Production Scheduling.
37/48
B 16 5
D 9 17
Machine Machine
Job Center 1 Center 2
Two-Machine Flow Shop
Johnsons Rule Example
CAE
Job A is chosen arbitrarily. Job A is scheduled in the
beginning, because its minimum time is given on Machine 1.
Beginning means position 2 because position 1 is taken.
-
8/6/2019 20.0 Production Scheduling.
38/48
D 9 17
Machine Machine
Job Center 1 Center 2
Two-Machine Flow Shop
Johnsons Rule Example
CBAE
Next, Job B is scheduled. Its scheduled in the end, because
its minimum processing time is given on Machine 2.
-
8/6/2019 20.0 Production Scheduling.
39/48
Machine Machine
Job Center 1 Center 2
Two-Machine Flow Shop
Johnsons Rule Example
CBDAE
The sequencing is complete after assigning the remaining
Job D to the remaining position. Next, the makespan is
computed.
-
8/6/2019 20.0 Production Scheduling.
40/48
E
A
DB
C
CBDAE
Each triplet above shows the starting, processing, and finishing times of an operation.
Johnsons rule guarantees that the above schedule gives the best value (44) of
makespan.
Two-Machine Flow Shop
Johnsons Rule Example
Machine Machine
Job Center 1 Center 2
-
8/6/2019 20.0 Production Scheduling.
41/48
Johnsons Rule
example:2
JOBJOB PROCESS 1PROCESS 1 PROCESS 2PROCESS 2
AA 66 88BB 1111 66
CC 77 33
DD 99 77
EE 55 1010
CE A BD
-
8/6/2019 20.0 Production Scheduling.
42/48
Production Scheduling
d h d l
-
8/6/2019 20.0 Production Scheduling.
43/48
Production Scheduling
P d ti S h d li
-
8/6/2019 20.0 Production Scheduling.
44/48
Production Scheduling
Waiting Line Model.
When job arrivals/order arrivals is random in nature and
we have limited facilities to process jobs or orders, the
jobs or orders pile up in the form of a queue or a waiting
line .
This is particularly true in service organizations or in jobproduction shops.
The production in charge has to use waiting line model
to reduce the waiting time of jobs and to see that
machines are optimally loaded.
P d i S h d li
-
8/6/2019 20.0 Production Scheduling.
45/48
Production Scheduling
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
46/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
47/48
Production Scheduling
-
8/6/2019 20.0 Production Scheduling.
48/48
Thank You