Presentation on theme: "Managing Capacity Chapter 8. Chapter Objectives Be able to: Explain what capacity is, how firms measure capacity, and the difference between theoretical."— Presentation transcript:
Managing Capacity Chapter 8
Chapter Objectives Be able to: Explain what capacity is, how firms measure capacity, and the difference between theoretical and rated capacity, Describe the pros and cons associated with three different capacity strategies: lead, lag, and match. Apply a wide variety of analytical tools to capacity decisions, including expected value and break-even analysis, decision trees, waiting line theory, and learning curves.
Capacity Decisions Defining and measuring capacity Strategic versus tactical capacity Evaluating capacity alternatives Advanced perspectives –Theory of Constraints –Waiting lines –Learning curves
Measure of an organizations ability to provide goods or services Jiffy Lube Oil changes per hour Law firm Billable hours College Student hours per semester Defining and Measuring Capacity
Consider: Capacity for a PC Assembly Plant: (800 units/shift/line) × (% Good) × (# of lines) × (# of Shifts) 1 or 2 shifts? 2 or 3 lines? Employee training? Controllable Factors Uncontrollable Factors Supplier problems? 98% or 100% good? Late or on time?
Strategic versus Tactical Capacity Strategic: –One or more years out –Bricks & Mortar –Future technologies Tactical: –One year or sooner –Workforce level, schedules, inventory, etc.
Capacity Time Strategic Capacity Planning Bricks & mortar decisions High-level planning High risk Tactical Planning Workforce, inventory, subcontracting decisions Intermediate-level planning Moderate risk Planning & Control Limited ability to adjust capacity Detailed planning Lowest risk Days or weeks outMonths out Years out Capacity versus Time
Capacity Strategies: When, How Much, and How? Leader Laggard Demand Lost Business Excess Capacity
How? Make or Buy (e.g., subcontracting) One extreme: Virtual Business Walden Paddlers (Marketing) Hardigg Industries (Manufacturing) General Composites (Design) Independent Dealers (Direct Sales)
Evaluating Capacity Alternatives Economies of scale (EOS) Expected value analysis (EVA) Decision Trees Break-even points (BEP)
Economies of Scale Total Cost for Fictional Line: Fixed cost + (Variable unit cost)×(X) = $200,000 + $4X Cost per unit for X=1? X=10,000?
Fixed & Unit Cost Scenarios
Indifference Point Compares capacity alternatives at what volume level do they cost the same? Suppose one option has zero fixed cost and $750 per unit cost; the other option has $5,000 fixed cost, but only $300 per unit cost. $0 + $750X = $5,000 + $300X What is the volume, X, at the indifference point?
Expected Value Analysis Forecasted demand or volume is uncertain, allows consideration of the variability in the data
Data Requirements Capacity cost structure (alternatives?) Expected demand (multiple scenarios?) Product and service requirements (e.g. time standards) EVA
Expected Value Analysis Pennington Cabinet Company 2000 jobs per year (20% likelihood) 5000 jobs per year (50%) 7000 jobs per year (30%) Each job = $1,200 revenue
We Know: Average job requires: 2 hours of machine time 3-1/3 hours of assembly team time Machines and teams work 2000 hours per year Each machine and team has yearly fixed cost = $200K 3 different capacity scenarios (see next slide!)
Effective Capacity What is the effective capacity of each capacity alternative? Number of Machines and Teams Number of Hours Available Each Year Maximum Jobs per Year MachinesTeamsMachinesTeamsMachinesTeams Current356,00010,0003,000 Expanded5910,00018,0005,0005,400 New Site71214,00024,0007,0007,200
Alternate Demand Scenarios What is the expected contribution if demand = 5000 AND we decide to move to a new site? Why does revenue for current capacity max out at $3.6 million? Current LevelExpandedNew Site DemandRevenue Fixed ExpensesRevenue Fixed ExpensesRevenue Fixed Expenses 2,000$2,400,000$1,600,000$2,400,000$2,800,000$2,400,000$3,800,000 5,000$3,600,000$1,600,000$6,000,000$2,800,000$6,000,000$3,800,000 7,000$3,600,000$1,600,000$6,000,000$2,800,000$8,400,000$3,800,000
Net Revenue Table DemandCurrentExpandedNew Site 3,000$800,000($400,000)($1,400,000) 5,000$2,000,000$3,200,000$2,200,000 7,000$2,000,000$3,200,000$4,600,000
Expected Value of Each Capacity Alternative: Current capacity level (20%) × $800K +(50%) × $2000K +(30%) × $2000K =$1,760,000
Expanded capacity level (20%) × – $400K +(50%) × $3200K + (30%) × $3200K =$2,480,000 Expected Value of Each Capacity Alternative:
New Site capacity level (20%) × – $1400K +(50%) × $2200K +(30%) × $4600K =$2,200,000 Expected Value of Each Capacity Alternative:
Conclusions for Pennington Which alternative would you choose if you wanted to minimize the worst possible outcome (Maximin)? Maximize the best possible outcome (Maximax)? Why is it important to know effective capacity? How could this help future capacity decisions?
Decision Trees Visual tool for evaluating choices using expected value analysis Allows use of different outcomes and different probabilities of success for each
Decision Tree Requirements Decision points represented by –Choose the best input the highest EVA, lowest cost, least risk, etc. Outcome points represented by –Summation of all inputs (outcomes) weighted by their respective probabilities. No choice can be made at these points Trees drawn from final decision to the outcomes affecting that decision, then on to lower level decisions that might affect the those outcomes, then the lower level outcomes affecting those lower level decisions, and so on
Ellison Seafood Example Here the probabilities affecting the demand level are the same for the three options considered. But the decision tree does allow them to be different, can you think of situations where this might be true?
Decision Tree Criteria Book example illustrates selecting highest revenue option. Other option choices can be on basis of: –Using total cost for outcomes (useful when selling price is not known) –Using estimated risk for outcomes –Outcomes reflecting a desired result (choose highest EVA) Can you think of an example? –Outcomes reflecting undesirable results (choose lowest EVA) Can you think of an example?
Break-Even Point (BEP) Considers revenue and costs, at what volume level are they equal? Suppose each unit sells for $100, the fixed cost is $200,000 and the variable cost is $4 BEP $100X = $200,000 + $4X What is the breakeven volume, X?
Self Test EBB Industries must decide whether to invest in a new machine which has a yearly fixed cost of $40,000 and a variable cost of $50 per unit. What is the break even point (BEP) if each unit sells for $200? What is the expected value, given the following demand probabilities: 250 units (25%), 300 units (50%), 350 units (25%)
Advanced Perspectives Theory of Constraints Waiting lines Learning curves
Theory of Constraints Concept that the throughput of a supply chain is limited (constrained) by the process step with the lowest capacity. Sounds logical, but what does this mean for managing the other process steps?
Theory of Constraints Pipeline analogy Which piece of the pipe is restricting the flow? Would making parts A or D bigger help?
Dealing with a Constraint Identify the constraint Exploit the constraint Keep it busy! Subordinate everything to the constraint Make supporting it the overall priority Elevate the constraint Try to increase its capacity more hours, screen out defective parts from previous step, … Find the new constraint and repeat As one step is removed as a constraint, a new one will emerge. Which piece of the pipe on the previous slide would be the new constraint if Part C was increased in diameter?
Waiting Lines Waiting lines and services –Waiting and customer satisfaction –Factors affecting satisfaction Waiting Line Theory –Terminology and assumptions – Illustrative example
Waiting at Outback Steakhouse... Waiting to get food... Waiting to pay bill... Leaving restaurant Waiting outside or in bar
Key Points Waiting time DECREASES value-added experience On the other hand, adding serving capacity INCREASES costs Businesses must have a way to analyze the impact of capacity decisions in environments where waiting occurs
Waiting and Customer Satisfaction Cost of waiting Cost of service COST Waiting time Lost customers
Firm-Related Factors Unfair versus fair waits Uncomfortable versus comfortable waits Initial versus subsequent waits Capacity decisions
Waiting Line (Queuing) Theory Application of statistics to allow us to perform a detailed analysis of system –Utilization levels, line lengths, etc. Terminology and assumptions
Terminology and Assumptions I
Terminology and Assumptions II Single-Channel Single-Phase Multiple-Channel Single-Phase
Terminology and Assumptions III Complex service environment... How would you describe this?
Terminology and Assumptions IV Population: Infinite or Finite Arrival rates:Random or constant rate –Random rates typically defined by Poisson distribution for infinite population Service Rates: Random or constant –Random service rates typically described by exponential distribution Priority rules (aka Queue Discipline) Permissible queue length
Example A single drive-in window for Bank Arrival rate –15 per hour, on average Service rate –20 per hour, on average How many channels? Phases? What kinds of questions might we have?
Drive-In Bank = arrival rate = 15 cars per hour = service rate =20 cars per hour Average utilization of the system: = = 0.75
Drive-In Bank Probability of n arrivals during period T is: e.g., probability of only 4 arrivals during a 45-minute period is:
Drive-In Bank Average number of cars in the system: (waiting plus being served)
Drive-In Bank Average number of cars waiting:
Drive-In Bank Average time spent in the system: (waiting plus being served) (How do we know the answer is in hours?)
Drive-In Bank Average time spent in the line: (How do we know the answer is in hours?)
Question? What happens as the arrival rate approaches the service rate? Suppose is now 19 cars per hour
One Answer: Average number of cars waiting: Implications? What are we assuming here?
Other Types of Systems (Discussed in the supplement to Chapter 8) Single-channel, single-phase with constant service time –Example: Automatic car wash Multiple-channel, multiple-phase (hospital) –Usually best handled using simulation analysis
Self Test I Look back at the drive-in window example. How can we have an average line length > 1 while the average number of cars being served is < 1? Similarly, what happens as the arrival rate approaches the service rate? Suppose the teller at the drive-in window is given training and can now handle 25 cars an hour (a 25% increase in service rate). What happens to the average length of the line?
Self Test II Look back at the Outback Steakhouse example. What kind of queuing system is it?
Question? How can capacity change, even when we do not hire new people or put in new equipment?
Learning Curves Recognize that people (and often equipment) become more productive over time due to learning. First observed in aircraft production during World War II Getting more emphasis as companies outsource more activities
A Formal Definition For every doubling of cumulative output, there will be a set percentage improvement in time per unit or some other measure of input Output Time per unit 10 hrs. 8 hrs. 6.4 hrs hrs hrs. 80% learning curve - Where does the name come from?
A Formal Definition (contd) Where:T n = time for the nth unit T 1 = time for the first unit b = ln(learning percent) / ln2
Example Reservation clerk at Delta Airlines First call (while training) takes 8 minutes Second call takes 6 minutes What is the learning rate? How long would you expect the 4th call to take? The 16th? The 32nd?
Key Points Quick improvements early on, followed by more and more gradual improvements The lower the percentage, the steeper the learning curve Practically speaking, there is a floor Estimates of effective capacity must consider learning effects!
Another Question... How could learning curves be used in long-term purchasing contracts?
Johnston Controls I Johnston Controls won a contract to produce 2 prototype units for a new type of computer. First unit took 5,000 hrs. to produce and $250K of materials Second unit took 3,500 hrs. to produce and $200K of materials Labor costs are $30/hour
Johnston Controls II The customer has asked Johnston Controls to prepare a bid for an additional 10 units. What are Johnstons expected costs?
Johnston Controls IV Additional 10 units means the third through twelfth units. Total labor for units 3 through 12: =5,000 hours × (5.501 – 1.7) = 19,005 hrs is sum of n b for 12 units 1.7 is the sum of n b for the first two units
Johnston Controls V Total material for units 3 through 12: = $250,000 × (7.227 – 1.8) = $1,356,750
Johnston Controls VI Total cost for additional 10 units: = $30 × (19,005 hours) + $1,356,750 = $1,926,900 What if there is a significant delay before the second contract?
Self-Test Assume that there WILL BE a significant delay before Johnston Controls makes the next 10 units. Assuming that Johnston has to start over with regard to learning, estimate total cost for these additional 10 units.
Case Study in Managing Capacity Forsters Market