Produktionsplanering

What is planning and control? Supply of products and services Planning and control Demand for products and services The activities which reconcile supply and demand The operation’s customers The operation’s resources

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 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

PLANNING CONTROL Significance of planning or control Time horizon Hours/days Days/ weeks/ months Months/years Medium-term Planning and Control Uses partially disaggregated demand forecasts Determines resources and contingencies Objectives set in both financial and operations terms Long-term Planning and Control Uses aggregated demand forecasts Determines resources in aggregated form Objectives set in largely financial terms Short-term Planning and Control Uses totally disaggregated forecasts or actual demand Makes interventions to resources to correct deviations from plans Ad hoc consideration of operations objectives PLANNING CONTROL

Planning and control needs…. Information on Demand levels Information on Resources

The nature of supply and demand Purchase Make Deliver Make to stock D P Purchase Make Deliver Make to order D P Resource Purchase Make Deliver to order D P P=total genomloppstid D=leveranstid (dvs den tid kunden måste vänta)

Dependent and independent demand e.g. input tyre store in car plant Demand for tyres is governed by the number of cars planned to be made Demand for tyres is largely governed by random factors ACE TYRES Inependent demand e.g. tyre fitting service

Dependent demand Resource to order Each product or service large compared with total capacity of the operation Make to order Each product or service small compared with total capacity of the operation Make to stock Independent demand

Pull and push philosophies of planning and control PUSH CONTROL FORECAST CENTRAL OPS. PLANNING AND CONTROL SYSTEM OR Instruction on what to make and where to send it 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

The activities of planning and control Scheduling When to do things? How much to do? Loading In what order to do things? Monitoring and control Are activities going to plan? Sequencing

Loading / beläggning

Tillgängligheten i en maskin Maximum available time Valuable operating time Not worked (planned) Quality losses Slow running equipment Not worked (unplanned) Set-up and changeovers Equipment “idling” “Breakdown” failure

Finite and infinite loading Load in std. hours Load in std. hours 140 140 Capacity Capacity 120 120 100 100 80 80 60 60 40 40 20 20 1 2 3 4 5 6 1 2 3 4 5 6 Work centres Work centres Omöjligt, onödigt eller mkt kostsamt att begränsa beläggningen Möjligt, nödvändigt eller begr kostnader för att begränsa beläggningen

Sequencing

• 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.

Scheduling

JOB Mon 5 Tue6 Wed 7 Thur 8 Fri 9 Mon 12 Tue 13 Table Shelves Kitchen units Bed Scheduled activity time Actual progress V Time now

JOB Mon 5 Tue6 Wed 7 Thur 8 Fri 9 Mon 12 Tue 13 Wood preparation Assembly Finishing Paint Scheduled activity time Actual progress T B S K Non-productive time V Time now

Shift pattern (24 hour clock) Mon Tue Wed Thu Fri Sat Sun Number of staff required 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 Claire Walter Peter Jo Marie 04:00 08:00 12:00 16:00 20:00 Shift pattern (24 hour clock) Jo O X X X X X O X Full day O Day off

Monitoring and control

The control feedback loop Input Operation Output Intervention Monitor Plans Compare / replan

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

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

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

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

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

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

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

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

Kapacitetsplanering

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

Not worked (unplanned) Availability rate = a = total operating time / loading time Loading time Set-up and change-overs Availability losses Total operating time Breakdown failure Performance rate = p = net operating time/total operating time Equipment “idling” Speed losses Net operating time Slow running equipment Quality rate = q = valuable operating time / net operating time Valuable operating time Quality losses Quality losses

How capacity and demand are measured Efficiency = Actual output Planned Effective capacity loss of 59 hours Design Avoidable capacity loss - 58 Effective hours per 168 hours capacity week per week 109 hours Actual per week output - 51 hours per week Utilisation = Actual output Design capacity

Simple queuing system Low variability - narrow distribution of process times Time High variability - wide distribution of process times Time

Actual demand and actual capacity Decision Period t - 1 Period t Period t + 1 Current capacity estimates Current capacity estimates Updated forecasts Updated forecasts Outcome Actual demand and actual capacity Decision How much capacity next period? Outcome Actual demand and actual capacity? Decision How much capacity next period? Shortages Queues Inventory Shortages Queues Inventory Capacity level Costs Revenues Working capital Customer satisfaction etc Costs Revenues Working capital Customer satisfaction etc

Hire and make for inventory Lay off staff Delay any action Overtime Hire temporary staff Short-time Idle time Do nothing Make for inventory Hire and make for inventory Start to recruit Hire staff POOR Outlook < 1 NORMAL Outlook = 1 GOOD Outlook > 1 Short-term outlook Long-term outlook Outlook = Forecast demand Forecast capacity

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.

Long-, medium- and short-term capacity planning 6 tables or Macro operation with might produce 12 chairs a given set of resources or some combination

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. Aggregated output Estimate of current capacity Time

Ways of reconciling capacity and demand Level capacity Chase demand D emand management

Cumulative representations Cumulative capacity Cumulative demand Capacity and demand Unable to meet orders Building stock Time

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

Distribution of demand 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 Distribution of demand DEMAND 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.

Average processing time TIME TO PROCESS ONE UNIT OF DEMAND 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

How do you cope with fluctuations in demand? Adjust output to match demand Absorb demand Change demand

Absorb demand Have excess capacity Keep output level Make to stock Make customer wait Part finished, Queues Finished Goods, or Backlogs Customer Inventory

Adjust output to match demand Hire Fire Temporary Labour Lay off Overtime Short time Subcontract 3rd party work

Change demand Change pattern of demand Develop alternative products and/or services

Actual Demand Forecast Replan Capacity Allocate Refine Key question - “How often do you change capacity in response to deviations from demand forecasts?”