Planning and control needs.

Transkript

1 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 The operation s customers 2 Planning is deciding Control is what activities should take place in the operation when they should take place what resources should be allocated to them 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 1

2 Significance of planning or control Time horizon Hours/days Days/ weeks/ months Months/years PLANNING CONTROL Long-term Planning and Control Uses aggregated forecasts Determines resources in aggregated form Objectives set in largely financial terms Medium-term Planning and Control Uses partially disaggregated forecasts Determines resources and contingencies Objectives set in both financial and operations terms Short-term Planning and Control Uses totally disaggregated forecasts or actual 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 Purchase Make Deliver Make to stock P D Purchase Make Deliver Make to order P D Purchase Make Deliver P P=total genomloppstid D=leveranstid (dvs den tid kunden måste vänta) D Resource to order 6 2

3 Dependent and independent Dependent e.g. input tyre store in car plant Demand for tyres is governed by the number of cars planned to be made Inependent e.g. tyre fitting service ACE TYRES Demand for tyres is largely governed by random factors 7 Resource to order Dependent Each product or service large compared with total capacity of the operation Make to order Make to stock Independent Each product or service small compared with total capacity of the operation 8 Pull and push philosophies of planning and control PUSH CONTROL CENTRAL OPS. PLANNING AND CONTROL SYSTEM Instruction on what to make and where to send it OR FORECAST Work centre Work centre Work centre Work centre DEMAND PULL CONTROL Request Request Request Request Work centre Work centre Work centre Work centre DEMAND Delivery Delivery Delivery Delivery 9 3

4 The activities of planning and control When to do things? Scheduling Loading How much to do? In what order to do things? Sequencing Monitoring and control Are activities going to plan? 10 Loading / beläggning 11 Tillgängligheten i en maskin Maximum available time Valuable operating time Quality losses Slow running equipment Equipment idling Breakdown failure Set-up and changeovers Not worked (planned) Not worked (unplanned) 12 4

5 Finite and infinite loading Load in std. hours Work centres Möjligt, nödvändigt eller begr kostnader för att begränsa beläggningen Load in std. hours Work centres Omöjligt, onödigt eller mkt kostsamt att begränsa 13 beläggningen Sequencing 14 Except for in situations with physical 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. 15 5

6 Scheduling 16 JOB Mon 5 Tue 6 Wed 7 Thur 8 Fri 9 Mon 12 Tue 13 Table Shelves Kitchen units Bed Scheduled activity time Actual progress V Time now V 17 JOB Mon 5 Tue 6 Wed 7 Thur 8 Fri 9 Mon 12 Tue 13 Wood preparation T S K Assembly B T S S S Finishing B T K Paint S B T K Scheduled activity time V Time now V Non-productive time Actual progress 18 6

7 Mon Tue Wed Thu Fri Sat Sun Number of staff required 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 Peter Jo Walter O X X X X X O Jo O X X X X X O X Full day O Day off Marie Claire Jo 04:00 08:00 12:00 16:00 20:00 Shift pattern (24 hour clock) 19 Monitoring and control 20 The control feedback loop Input Operation Output Intervention Plans Monitor Compare / replan 21 7

8 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 22 Kö Nackdelar... - extra kostnader - högre genomloppstider - ökad kapitalbindning - kräver fysiskt lagringsutrymmer - irritationsmoment - kräver särskild administration och ger upphov till särskilt planeringsarbete 23 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 24 8

9 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 25 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 26 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 27 9

10 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 28 The drum, buffer, rope, concept Buffer of inventory Activity A Activity B Activity C Activity D Activity E Communication rope controls prior activities Bottleneck drum sets the beat 29 Kapacitetsplanering 30 10

11 Causes of seasonality Climatic Festive Behavioural Political Financial Social Construction materials Beverages (beer, cola) Foods (ice-cream, Christmas cake) Clothing (swimwear, shoes) Gardening items (seeds, fertilizer) Fireworks Travel services Holidays Tax processing Doctors (influenza epidemic) Sports services Education services 31 Loading time Total operating time Net operating time Valuable Quality operating time losses Speed losses Availability losses Not worked (unplanned) Set-up and changeovers Breakdown failure Equipment idling Slow running equipment Quality losses Availability rate = a = total operating time / loading time Performance rate = p = net operating time/total operating time Quality rate = q = valuable operating time / net operating time 32 How capacity and are measured Design capacity 168 hours per week Utilisation = Planned loss of 59 hours Effective capacity 109 hours per week Actual output Design capacity Efficiency = Actual output Effective capacity Avoidable loss - 58 hours per week Actual output - 51 hours per week 33 11

12 Simple queuing system Low variability - narrow distribution of process times Time High variability - wide distribution of process times Time 34 Period t - 1 Period t Period t + 1 Current capacity Updated estimates forecasts Current capacity Updated estimates forecasts Outcome Actual and actual capacity Shortages Queues Inventory Decision How much capacity next period? level Outcome Shortages Queues Actual Inventory and actual capacity? Decision How much capacity next period? Costs Revenues Working capital Customer satisfaction etc Costs Revenues Working capital Customer satisfaction etc 35 Short-term outlook POOR NORMAL GOOD Outlook < 1 Outlook = 1 Outlook > 1 Long-term outlook POOR Outlook < 1 NORMAL Outlook = 1 Lay off staff Short-time Idle time Delay any action Do nothing Overtime Hire temporary staff Overtime Hire temporary staff GOOD Make for inventory Hire and make for inventory Hire staff Outlook > 1 Short-time Start to recruit Outlook = Forecast Forecast capacity 36 12

13 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 6tables Macro operation with a given set of resources might produce or 12 chairs or some combination 38 Objectives of capacity planning and control Aggregated output Step 1 - Step 2 - Step 3 - Measure aggregate capacity and. Identify the alternative capacity plans. Choose the most appropriate capacity plan. Forecast Estimate of current capacity Time 39 13

14 Ways of reconciling capacity and Demand Demand Demand Level capacity Chase Demand management 40 Cumulative representations Cumulative capacity and Building stock Cumulative Unable to meet orders Time 41 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 42 14

15 Good forecasts are essential for effective capacity planning. But so is an understanding of uncertainty because it allows you to judge the risks to service level. Only 5% chance of Distribution of being higher than this DEMAND TIME DEMAND Only 5% chance of being lower than this TIME When 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 Average processing time FREQUENCY TIME TO PROCESS ONE UNIT OF DEMAND 44 How do do you cope with fluctuations in in? Absorb Adjust output to to match Change 45 15

16 Have excess capacity Absorb Keep output level Make to to stock Part finished, Finished Goods, or Customer Inventory Make customer wait Queues Backlogs 46 Adjust output to to match Hire Temporary Labour Overtime Subcontract Fire Lay off Short time 3rd party work 47 Change Change pattern of Develop alternative products and/or services 48 16

17 Forecast Demand Actual Demand Replan Allocate Actual Refine Forecast Key question - How often do you change capacity in response to deviations from forecasts? 49 17