Transcript Document

Produktionsplanering
1
What is planning and control?
Supply of
products
and services
Planning
and
control
Demand for
products and
services
The
operation’s
resources
The activities
which reconcile
supply and
demand
The
operation’s
customers
2
Planning is deciding
what activities should take
place in the operation
when they should take place
what resources should be
allocated to them
Control is
understanding what is actually
happening in the the operation
deciding whether there is a
significant deviation from what
should be happening
(if there is deviation) changing
resources in order to affect the
operation’s activities
3
Long-term Planning and Control
Uses aggregated demand forecasts
PLANNING
Determines resources in aggregated form
Objectives set in largely financial terms
Days/ weeks/ months
Hours/days
Time horizon
Months/years
Significance of planning or control
Medium-term Planning and Control
Uses partially disaggregated demand
forecasts
Determines resources and contingencies
Objectives set in both financial and
operations terms
Short-term Planning and Control
CONTROL
Uses totally disaggregated forecasts or
actual demand
Makes interventions to resources to correct
deviations from plans
Ad hoc consideration of operations
objectives
4
Planning and control needs….
Information on Demand levels
Information on Resources
5
The nature of supply and demand
Purchase
Make
Deliver
Make to stock
D
P
Purchase
Make
Deliver
Make to order
D
P
Purchase
Make
Deliver
Resource
to order
D
P
P=total genomloppstid
D=leveranstid (dvs den tid kunden måste vänta)
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Dependent and independent demand
Dependent demand
e.g. input tyre store in car plant
Demand for tyres is
governed by the number of
cars planned to be made
Inependent demand
e.g. tyre fitting service
ACE
TYRES
Demand for tyres is
largely governed
by random factors
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Resource to order
Dependent demand
Each product or
service large
compared with total
capacity of the
operation
Make to order
Make to stock
Independent demand
Each product or
service small
compared with total
capacity of the
operation
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Pull and push philosophies of
planning and control
PUSH CONTROL
CENTRAL OPS. PLANNING AND CONTROL SYSTEM
OR
Instruction on
what to make
and where to
send it
Work
centre
FORECAST
Work
centre
Work
centre
Work
centre
DEMAND
PULL CONTROL
Work
centre
Work
centre
Delivery
Request
Request
Request
Work
centre
Delivery
Request
Work
centre
Delivery
DEMAND
Delivery
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The activities of planning and control
When to do
things?
Scheduling
In what
Sequencing
order to do
things?
Loading
Monitoring
and control
How much
to do?
Are
activities
going to
plan?
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Loading / beläggning
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Tillgängligheten i en maskin
Maximum available time
Valuable operating time
Quality
losses
Slow
running
Set-up and
Equipment
equipment
changeovers
“idling” “Breakdown”
failure
Not worked
(planned)
Not worked
(unplanned)
12
Finite and infinite loading
Load in
std. hours
Load in
std. hours
140
140
Capacity
120
100
100
80
80
60
60
40
40
20
20
0
1
2
3
4
5
Work centres
Möjligt, nödvändigt eller
begr kostnader för att
begränsa beläggningen
6
Capacity
120
0
1
2
3
4
5
6
Work centres
Omöjligt, onödigt eller mkt
kostsamt att begränsa
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beläggningen
Sequencing
14
for in situations with physical
• Except
constraints, various sequencing rules are
used in operations:
- customer priority;
- due date;
- LIFO - last in, first out;
- FIFO - first in, first out;
- longest operation time first;
- shortest operation time first.
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Scheduling
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JOB
Mon
5
Tue
6
Wed
7
Thur
8
Fri
9
Mon
12
Tue
13
Table
Shelves
Kitchen
units
Bed
Scheduled
activity time
V
Actual progress
Time now
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V
JOB
Mon
5
Wood
preparation
T
Assembly
B
Tue
6
Thur
8
S
B
Paint
S
Fri
9
Mon
12
Tue
13
K
S
T
Finishing
B
S
S
K
T
V
V
Scheduled
activity time
Wed
7
K
T
Non-productive time
Time now
Actual progress
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Mon Tue Wed Thu
Number of staff
required
Fri
Sat
Sun
3
5
5
5
3
2
2
Peter
X
X
X
X
O
O
X
Marie
X
X
X
X
X
O
O
Claire
X
X
X
X
O
O
X
Walter
O
X
X
X
X
X
O
Jo
O
X
X
X
X
X
O
Peter
X
Walter
Marie
04:00
08:00
12:00
Full day
O
Day off
Jo
Claire
Jo
16:00
20:00
Shift pattern (24 hour clock)
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Monitoring and control
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The control feedback loop
Input
Operation
Intervention
Output
Monitor
Plans
Compare
/ replan
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Beläggningsplanering
• Beläggning = inplanerade operationer
under en viss tidsperiod på viss/vissa
resurser
• Beläggningsplanering = balansering av
beordrad produktion mot statistiskt
beräknad nettokapacitet
• Kö - uppstår när kapaciteten
understiger tillgänglig beläggning
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Kö
• Nackdelar...
- extra kostnader
- högre genomloppstider
- ökad kapitalbindning
- kräver fysiskt lagringsutrymmer
- irritationsmoment
- kräver särskild administration och ger
upphov till särskilt planeringsarbete
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Kö
• ...men också fördelar
- möjligheter till smart omplanering
(samkörning med artiklar med likartat
ställarbete)
- kompetensanpassning
- högre arbetstempo
- gardering mot störningar
- fullt kapacitetsutnyttjande
• Optimering av kapacitetsutnyttjande kontra
kapitalbindning
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Kö - tumregler
• Trånga/viktiga resurser (styrande
maskiner) beläggs med 100% genom
ökad nettokapacitet och buffertar
• Överkapacitet i billiga resurser där dyra
o/e genomloppstidsmässigt viktiga
artiklar tillverkas (kompletterande
maskiner)
• Utbilda arbetsstyrkan mot ökad
flexibilitet – flödesgrupper
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Volymvärdeanalys
• En operation kan inte starta utan material
• Fullt plock = alla artiklar som krävs för en operation
finns tillgängliga vid start
• Svårt att garantera fullt plock utan betydande
kapitalbindning i mellanlager
• Volymvärdeanalys – rangordning av artiklar med
avseende på kapitalbindning
• Artiklar med hög kapitalbindning (A) planeras och
följs upp mkt noga, just-in-time-lev eftersträvas
• Artiklar med låg kapitalbindning (C) köps
in/produceras i god tid i väl tilltagna kvantiteter
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Flaskhalsar
• Genomloppstiden styr av flaskhalsens kapacitet
• Balansera materialflöde snarare än att utnyttja alla resurser
fullt ut
• PIA accumuleras vid flaskhalsen
• Minskning i flaskhalsens output, sänker systemets hela
output
• Ökning av output i en “icke-flaskahls” ökar inte output i
systemet som helhet
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OPT
• Optimized Production Technology (Goldratt &
Cox, 1986)
– Balansera flöde, inte kapacitet
– Utnyttjandet i en “icke-flaskhals” bestäms av andra begränsningar i
systemet, ej av sin egen kapacitet
– En förlorad timme i en flaskhals är en förlorad timme för systemet
– En vunnen timme i en “icke-flaskhals” är en illusion
– Flaskhalsar styr genomloppstid och PIA i systemet
– Transportvolymen behöver inte, och skall ibland inte, vara lika stor som
processvolymen
– Processvolymen skall vara variabel, inte statisk
– Ledtid beror på planeringen och kan inte bestämmas på förhand
– Planering skall skapas genom att se till alla begränsingar samtidigt
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The drum, buffer, rope, concept
Buffer of
inventory
Activity A
Activity B
Communication rope
controls prior activities
Activity C
Activity D
Activity E
Bottleneck
drum sets
the beat
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Kapacitetsplanering
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Causes of seasonality
Climatic
Festive
Behavioural
Political
Financial
Social
Construction materials
Travel services
Beverages (beer, cola)
Holidays
Foods (ice-cream, Christmas cake)
Tax processing
Clothing (swimwear, shoes)
Doctors (influenza epidemic)
Gardening items (seeds, fertilizer)
Sports services
Fireworks
Education services
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Not worked
(unplanned)
Loading time
Total operating time
Availability
losses
Net operating time Speed
losses
Quality
Valuable
operating time losses
Availability rate = a =
total operating time / loading time
Set-up and
changeovers
Breakdown
failure
Performance rate = p =
net operating time/total
operating time
Equipment
“idling”
Slow
running
equipment
Quality
losses
Quality rate = q =
valuable operating time / net
operating time
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How capacity and demand are measured
Efficiency =
Planned
loss of 59
hours
Design
capacity
168 hours
per week
Effective
capacity
109 hours
per week
Utilisation =
Actual output
Effective capacity
Avoidable
loss - 58
hours per
week
Actual
output 51 hours
per week
Actual output
Design capacity
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Simple queuing system
Low variability narrow
distribution of
process times
Time
High variability wide distribution
of process times
Time
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Period t
Period t - 1
Period t + 1
Current
capacity Updated
estimates forecasts
Outcome
Actual
demand
and actual
capacity
Shortages
Queues
Inventory
Costs
Revenues
Working capital
Customer satisfaction
etc
Decision
How much
capacity
next
period?
Current
capacity Updated
estimates forecasts
Capacity
level
Outcome
Actual
demand
and actual
capacity?
Shortages
Queues
Inventory
Decision
How much
capacity
next
period?
Costs
Revenues
Working capital
Customer satisfaction
etc
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Short-term outlook
POOR
POOR
NORMAL
GOOD
Outlook < 1
Outlook = 1
Outlook > 1
Lay off staff
Delay any
action
Hire temporary
staff
Long-term outlook
Outlook < 1
NORMAL
Outlook > 1
Outlook =
Short-time
Idle time
Do nothing
Overtime
Hire temporary
staff
Outlook = 1
GOOD
Overtime
Make for
inventory
Hire and make
for inventory
Short-time
Start to recruit
Hire staff
Forecast demand
Forecast capacity
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The nature of aggregate capacity
Aggregate capacity of a hotel:
- rooms per night;
- ignores the numbers of guests in each room.
Aggregate capacity of an aluminium producer:
- tonnes per month;
- ignores types of alloy, gauge and batch variations.
37
Long-, medium- and short-term capacity planning
6 tables
Macro
operation with
a given set of
resources
or
might produce
12 chairs
or
some
combination
38
Aggregated output
Objectives of capacity planning and control
Step 1 -
Measure aggregate
capacity and demand.
Step 2 -
Identify the alternative
capacity plans.
Forecast demand
Step 3 -
Choose the most
appropriate capacity
plan.
Estimate of current capacity
Time
39
Ways of reconciling capacity and demand
Demand
Capacity
Level capacity
Demand
Demand
Capacity
Capacity
Chase demand
Demand
management
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Cumulative representations
Capacity and
demand
Cumulative capacity
Cumulative demand
Building
stock
Unable to
meet orders
Time
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OBJECTIVE
To provide an “appropriate” amount of
capacity at any point in time.
The “appropriateness” of capacity
planning in any part of the operation
can be judged by its effect on…...
Costs
Revenue
Working Capital
Service Level
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Good forecasts are essential for effective capacity
planning.
But so is an understanding of demand uncertainty
because it allows you to judge the risks to service
level.
Only 5% chance of demand
being higher than this
DEMAND
DEMAND
Distribution of demand
Only 5% chance of demand
being lower than this
TIME
TIME
When demand uncertainty is high the risks to service level
of underprovision of capacity are high.
43
It is useful to know not only the average capability of
resources but also their variation in capability
FREQUENCY
Average processing time
TIME TO PROCESS ONE UNIT OF DEMAND
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How do you cope with
fluctuations in demand?
Absorb
demand
Adjust
output to
match
demand
Change
demand
45
Absorb
demand
Have
excess
capacity
Keep output
level
Make
to
stock
Part finished,
Finished Goods, or
Customer Inventory
Make
customer
wait
Queues
Backlogs
46
Adjust output
to match
demand
Hire
Temporary
Labour
Overtime
Subcontract
Fire
Lay off
Short time
3rd party work
47
Change
demand
Change pattern of demand
Develop alternative products
and/or services
48
Forecast
Demand
Actual
Demand
Replan
Capacity
Allocate
Capacity
Actual
Capacity
Refine
Forecast
Key question - “How often do you change capacity in response to
deviations from demand forecasts?”
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