close

Вход

Забыли?

вход по аккаунту

?

Scheduling Shop Floor

код для вставкиСкачать
Scheduling Shop Floor
ISQA 459/559 Mellie Pullman
1
Learning Objectives
•
•
•
•
Explain the different kinds of scheduling
Describe different shop loading methods
Describe priority rules
Describe scheduling performance
measures
2
Definitions
• Routing:
• The operations to be performed, their sequence, the
work centers visited, & the time standards
• Bottleneck:
• A resource whose capacity is less than the demand
placed on it
• Due date:
• When the job is supposed to be finished
• Slack:
• The time that a job can be delayed & still finish by its
due date
• Queue:
• A waiting line
3
High Volume Operations
• High volume flow operations
generally have fixed routings
• Bottlenecks are easily identified
• Commonly use line-balancing to
design the process around the
required tasks
• Examples?
4
Low Volume Operations
• Low volume job shop operations are
designed for flexibility.
• Each product or service may have its own
routing (scheduling is much more difficult)
• Bottlenecks move around depending upon
the products being produced at any given
time
• Examples?
5
Gantt Charts
• Graphical tools used to illustrate workloads &
help monitor job progress
• Load charts:
• Illustrates the workload relative to the capacity of a
resource
• Progress charts:
• Illustrates the planned schedule compared to actual
performance
6
Load Chart
7
Progress Chart
8
Loading Workstations
• Infinite loading:
• Ignores capacity constraints, but helps identify
bottlenecks in a proposed schedule – enabling
proactive management
• Finite loading:
• Allows only as much work to be assigned as a
station should be able to handle – but doesn’t
prepare for inevitable slippage
9
Example
• Infinite:
• Schedule
in time
period
needed
• Finite:
• Schedule
according
to
capacity
limits
10
Forward Vs. Backward Scheduling
Start processing when order is received regardless of due date
Schedule the job’s last activity so it is finished right before the due date
11
Operations Sequencing
• A short-term plan of actual jobs based on available
capacity & priorities
• Priority rules:
• Decision rules to allocate the relative priority of jobs at a
work center
• Local priority rules: determines priority based only on jobs at
that workstation
• Global priority rules: also considers the remaining
workstations a job must pass through
12
Common Priority Rules
•
•
•
•
•
•
First come, first served (FCFS)
Last come, first served (LCFS)
Earliest job due date (EDD)
Shortest processing time (SPT)
Longest processing time (LPT)
Min Critical ratio: (CR)
• (Time until due date)/(processing time remaining)
13
How to use priority rules
• Decide which rule to use.
• List all the jobs waiting to be processed at the
work-center and their job time
• Job time includes setup and processing time
• Using your priority rule, determine which job
has the highest priority and should be worked
on 1st , 2nd, 3rd ,etc.
14
Machine Shop with 6 jobs waiting
• Use SPT
(shortest processing time)
• Determine sequence of
jobs
Job Number Job Time
(setup &
run)
A
3 days
B
7 days
C
6 days
D
4 days
E
2 day
F
5 days
15
Performance Measurement
• Job flow time:
• Time a job is completed minus the time the job was
first available for processing
• Average jobs in system:
• Measures amount of work-in-progress
=Total job flow time/Make-span
• Make-span:
• The entire time it takes to finish a batch of jobs
• Job lateness:
• Whether the job is completed ahead of, on, or behind
schedule
• Job tardiness:
• How long after the due date a job was completed
16
More Data on the jobs
Job
Number
Job Time
(setup &
run)
Due Date
(days from
now)
Remaining
job time at
other WC
A
3 days
15
6
B
7 days
20
8
C
6 days
30
5
D
4 days
20
3
E
2 day
22
7
F
5 days
20
5
Critical
Ratio
15/(3+6)
17
Completion Data
Job
Number
Competion Date
Due Date
(days from
now)
Lateness
(days)
Tardiness
(days)
A
5
15
-10
0
B
27
20
+7
7
C
20
30
-10
0
D
9
20
-11
0
E
2
22
-20
0
F
14
20
-6
0
Negative lateness means job is finished ahead of due date. 0=on time
18
Group In-Class Activity
• Each team should use each of these rules
calculate all performance measures:
• Critical Ratio
• Longest Process Time
• EDD
19
Worksheet for your method:____________
Job #
Job
Time
(setup
& run)
Due
Date
-days
from
now
Remaining
job time at
other WC
A
3 days
15
6
B
7 days
20
8
C
6 days
30
5
D
4 days
20
3
E
2 day
22
7
F
5 days
20
5
Job Flow
Job
Lateness
Job
Tardiness
CR
AVE
Make-span
Job flow-time
Average jobs in system
____________
____________
____________
20
What are the company’s objectives?
What priority rule works best?
• Fairness?
• Minimizing mean job tardiness?
• Minimizing mean job flow time, lateness, and
average jobs in the system?
21
Sequencing through 2 work centers
Johnson’s rule
•
All jobs are processed through 2 work centers
sequentially
1. List the jobs and processing times
2. Find the shortest activity processing time among all
jobs (not yet schedule).
•
•
•
If it is the first activity, put job needing that activity in the
earliest available position in the sequence
If it is the second activity, put the job needing that activity in
the last avaiable position in the job sequence.
One you schedule a job, it’s eliminated from further
consideration
3. Repeat step 2 until every job is on the schedule
22
Sample Problem
Metal Job
Activity 1
Metal
Cutting
Activity 2
Deburr & Grind
A
1
2
B
3
5
C
2
4
D
5
4
E
4
2
23
Sample Problem (days)
Metal
Job
A
Activity 1 Activity 2
Metal
Deburr &
Grind
Cutting
1
(first)
2
B
3
(fourth)
5
C
2
(second)
4
D
5
4
(fifth)
E
4
2
(third)
1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1
0 1 2 3 4 5 6 7 8
A ACCBBBDDDDDE EEE
c
t
1
A
c
t
2
AACCCCBB BBBDDDDEE
Ties: pick either
24
Group In-Class Problem
Hall
A
Activity 1
Mopping
4
Activity 2
Buffing
3
B
2
7
C
6
5
D
4
5
E
3
4
F
5
1
25
Документ
Категория
Презентации
Просмотров
5
Размер файла
1 438 Кб
Теги
1/--страниц
Пожаловаться на содержимое документа