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Review for Exam III This exam will be administered Wednesday, July 31, 2013, beginning at 10 a.m. – 11:50 a.m.
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Exam Format 40-50 multiple choice 2 - 3 problems Closed-book Closed-notes Closed-neighbor BRING---pencil, calculator, scantron sheet
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Exam Coverage Chapters 12, 13, 14 and 16 in that order An overview of MRP in Chap 15 No details No algorithms NO CHAPTER SUPPLEMENTS No simulation
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Typical problems— Forecasting with error calc Inventory calculations involving: EOQ, reorder point, TC, safety stock, price discounting Lean concepts Calculation of the number of kanbans
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FORECASTING--Two basic categories of approaches What are they??
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Smoothing Effects 150 150 – 125 125 – 100 100 – 75 75 – 50 50 – 25 25 – 0 0 – ||||||||||| JanFebMarAprMayJuneJulyAugSeptOctNov Actual Orders Month 5-month 3-month
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Weighted Moving Average WMA n = i = 1 Wi DiWi DiWi DiWi Di where W i = the weight for period i, between 0 and 100 percent W i = 1.00 Adjusts moving average method to more closely reflect data fluctuations
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Weighted Moving Average Example MONTH WEIGHT DATA August 17%130 September 33%110 October 50%90 WMA 3 = 3 i = 1 Wi DiWi DiWi DiWi Di = (0.50)(90) + (0.33)(110) + (0.17)(130) = 103.4 orders November Forecast
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Averaging method Weights most recent data more strongly Reacts more to recent changes Widely used, accurate method Exponential Smoothing
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F t +1 = D t + (1 - )F t where: F t +1 =forecast for next period D t =actual demand for present period F t =previously determined forecast for present period =weighting factor, smoothing constant Exponential Smoothing (cont.)
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Effect of Smoothing Constant 0.0 1.0 If = 0.20, then F t +1 = 0.20 D t + 0.80 F t If = 0, then F t +1 = 0 D t + 1 F t 0 = F t Forecast does not reflect recent data If = 1, then F t +1 = 1 D t + 0 F t = D t Forecast based only on most recent data
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F 2 = D 1 + (1 - )F 1 = (0.30)(37) + (0.70)(37) = 37 F 3 = D 2 + (1 - )F 2 = (0.30)(40) + (0.70)(37) = 37.9 F 13 = D 12 + (1 - )F 12 = (0.30)(54) + (0.70)(50.84) = 51.79 Exponential Smoothing (α=0.30) PERIODMONTHDEMAND 1Jan37 2Feb40 3Mar41 4Apr37 5May 45 6Jun50 7Jul 43 8Aug 47 9Sep 56 10Oct52 11Nov55 12Dec 54
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FORECAST, F t + 1 PERIODMONTHDEMAND( = 0.3)( = 0.5) 1Jan37–– 2Feb4037.0037.00 3Mar4137.9038.50 4Apr3738.8339.75 5May 4538.2838.37 6Jun5040.2941.68 7Jul 4343.2045.84 8Aug 4743.1444.42 9Sep 5644.3045.71 10Oct5247.8150.85 11Nov5549.0651.42 12Dec 5450.8453.21 13Jan–51.7953.61 Exponential Smoothing (cont.)
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70 70 – 60 60 – 50 50 – 40 40 – 30 30 – 20 20 – 10 10 – 0 0 – ||||||||||||| 12345678910111213 Actual Orders Month Exponential Smoothing (cont.) = 0.50 = 0.30
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AF t +1 = F t +1 + T t +1 where T = an exponentially smoothed trend factor T t +1 = (F t +1 - F t ) + (1 - ) T t where T t = the last period trend factor = a smoothing constant for trend Adjusted Exponential Smoothing
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Adjusted Exponential Smoothing (β=0.30) PERIODMONTHDEMAND 1Jan37 2Feb40 3Mar41 4Apr37 5May 45 6Jun50 7Jul 43 8Aug 47 9Sep 56 10Oct52 11Nov55 12Dec 54 T 3 = (F 3 - F 2 ) + (1 - ) T 2 = (0.30)(38.5 - 37.0) + (0.70)(0) = 0.45 AF 3 = F 3 + T 3 = 38.5 + 0.45 = 38.95 T 13 = (F 13 - F 12 ) + (1 - ) T 12 = (0.30)(53.61 - 53.21) + (0.70)(1.77) = 1.36 AF 13 = F 13 + T 13 = 53.61 + 1.36 = 54.96
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Adjusted Exponential Smoothing: Example FORECASTTRENDADJUSTED PERIODMONTHDEMANDF t +1 T t +1 FORECAST AF t +1 1Jan3737.00–– 2Feb4037.000.0037.00 3Mar4138.500.4538.95 4Apr3739.750.6940.44 5May 4538.370.0738.44 6Jun5038.370.0738.44 7Jul 4345.841.9747.82 8Aug 4744.420.9545.37 9Sep 5645.711.0546.76 10Oct5250.852.2858.13 11Nov5551.421.7653.19 12Dec 5453.211.7754.98 13Jan–53.611.3654.96
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Adjusted Exponential Smoothing Forecasts 70 70 – 60 60 – 50 50 – 40 40 – 30 30 – 20 20 – 10 10 – 0 0 – ||||||||||||| 12345678910111213 Actual Demand Period Forecast ( = 0.50) Adjusted forecast ( = 0.30)
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y = a + bx where a = intercept b = slope of the line x = time period y = forecast for demand for period x Linear Trend Line b = a = y - b x where n =number of periods x == mean of the x values y == mean of the y values xy - nxy x 2 - nx 2 x n y n
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Least Squares Example x (PERIOD) y (DEMAND) xyx 2 173371 240804 3411239 43714816 54522525 65030036 74330149 84737664 95650481 1052520100 1155605121 1254648144 785573867650
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x = = 6.5 y = = 46.42 b = = =1.72 a = y - bx = 46.42 - (1.72)(6.5) = 35.2 3867 - (12)(6.5)(46.42) 650 - 12(6.5) 2 xy - nxy x 2 - nx 2 78 12 557 12 Least Squares Example (cont.)
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Linear trend line y = 35.2 + 1.72 x Forecast for period 13 y = 35.2 + 1.72(13)= 57.56 units 70 70 – 60 60 – 50 50 – 40 40 – 30 30 – 20 20 – 10 10 – 0 0 – ||||||||||||| 12345678910111213 Actual Demand Period Linear trend line
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Seasonal Adjustments Repetitive increase/ decrease in demand Use seasonal factor to adjust forecast Seasonal factor = S i = DiDiDDDiDiDD
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Seasonal Adjustment (cont.) 2002 12.68.66.317.545.0 2003 14.110.37.518.250.1 2004 15.310.68.119.653.6 Total 42.029.521.955.3148.7 DEMAND (1000’S PER QUARTER) YEAR1234Total S 1 = = = 0.28 D1D1DDD1D1DD 42.0148.7 S 2 = = = 0.20 D2D2DDD2D2DD 29.5148.7 S 4 = = = 0.37 D4D4DDD4D4DD 55.3148.7 S 3 = = = 0.15 D3D3DDD3D3DD 21.9148.7
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Seasonal Adjustment (cont.) SF 1 = (S 1 ) (F 5 ) = (0.28)(58.17) = 16.28 SF 2 = (S 2 ) (F 5 ) = (0.20)(58.17) = 11.63 SF 3 = (S 3 ) (F 5 ) = (0.15)(58.17) = 8.73 SF 4 = (S 4 ) (F 5 ) = (0.37)(58.17) = 21.53 y = 40.97 + 4.30 x = 40.97 + 4.30(4) = 58.17 For 2005
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Forecast Accuracy Forecast error difference between forecast and actual demand MAD mean absolute deviation MAPD mean absolute percent deviation Cumulative error Average error or bias
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Mean Absolute Deviation (MAD) where t = period number t = period number D t = demand in period t D t = demand in period t F t = forecast for period t F t = forecast for period t n = total number of periods n = total number of periods = absolute value D t - F t n MAD =
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MAD Example 13737.00–– 24037.003.003.00 34137.903.103.10 43738.83-1.831.83 54538.286.726.72 65040.299.699.69 74343.20-0.200.20 84743.143.863.86 95644.3011.7011.70 105247.814.194.19 115549.065.945.94 125450.843.153.15 55749.3153.39 PERIODDEMAND, D t F t ( =0.3)(D t - F t ) |D t - F t | D t - F t n MAD= = = 4.85 53.39 11
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Other Accuracy Measures Mean absolute percent deviation (MAPD) MAPD = |D t - F t | D t Cumulative error E = e t Average error E = etetnnetetnnn
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Comparison of Forecasts FORECASTMADMAPDE(E) Exponential smoothing ( = 0.30)4.859.6%49.314.48 Exponential smoothing ( = 0.50)4.048.5%33.213.02 Adjusted exponential smoothing3.817.5%21.141.92 ( = 0.50, = 0.30) Linear trend line2.294.9%––
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Forecast Control Tracking signal monitors the forecast to see if it is biased high or low 1 MAD ≈ 0.8 б Control limits of 2 to 5 MADs are used most frequently Tracking signal = = (D t - F t ) MADEMAD
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Tracking Signal Values 13737.00––– 24037.003.003.003.00 34137.903.106.103.05 43738.83-1.834.272.64 54538.286.7210.993.66 65040.299.6920.684.87 74343.20-0.2020.484.09 84743.143.8624.344.06 95644.3011.7036.045.01 105247.814.1940.234.92 115549.065.9446.175.02 125450.843.1549.324.85 DEMANDFORECAST,ERROR E = PERIODD t F t D t - F t (D t - F t )MAD TS 3 = = 2.00 6.10 3.05 Tracking signal for period 3 –1.002.001.623.004.255.016.007.198.189.2010.17TRACKINGSIGNAL
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Tracking Signal Plot 3 3 – 2 2 – 1 1 – 0 0 – -1 -1 – -2 -2 – -3 -3 – ||||||||||||| 0123456789101112 Tracking signal (MAD) Period Exponential smoothing ( = 0.30) Linear trend line
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Statistical Control Charts = = = = (D t - F t ) 2 n - 1 Using we can calculate statistical control limits for the forecast error Control limits are typically set at 3
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Statistical Control Charts Errors 18.39 18.39 – 12.24 12.24 – 6.12 6.12 – 0 0 – -6.12 -6.12 – -12.24 -12.24 – -18.39 -18.39 – ||||||||||||| 0123456789101112 Period UCL = +3 LCL = -3
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Regression? Correlation? Neither will be on the exam Regression is just the linear trend line in which the independent variables are other than time There will not be exam questions on either regression or correlation But you will see LINEAR TREND LINE
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Inventory for Independent Demand – Chapter 13 EOQ = Economic Order Quantityu Assumes
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Carrying costs Rent Lighting/heating Security Interest (on borrowed capital tied up in inventory) Taxes Shrink/obsolescence/theft Can also be expressed as a % of product cost A rule of thumb is 30%
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Ordering costs—costs related to Transportation Shipping Receiving Inspection
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Shortage costs This is an opportunity cost Is ignored in the simple EOQ models you will be using, by assuming that there are no shortages Consideration is given to shortages when we add safety stock to a Reorder Point, R = d*L + safety stock
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Back-order costs Will assume impatient customers who must have the product they wish to buy NOW. So back-ordering is not considered in the simple models we looked at
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Continuous Inventory Systems Constant order amount, called the EOQ EOQ = Economic Order Quantity Fixed annual deterministic demand Minimizes Holding (carrying) costs Ordering costs Uses re-order point to determine when to order Time between orders is not fixed
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EOQ models also have No shortages/back-ordering Constant lead time Instantaneous or finite replenishment Can take into consideration price discounting When doing so, three costs are minimized jointly: Ordering costs, holding costs and purchase costs taken over a year’s time
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If the quantity ordered is less than the EOQ, then Ordering costs will be greater than holding (carrying) costs
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ABC Classification—what is the point?? To concentrate, focus on the those items in inventory that constitute the highest dollar value to the firm Class A items constitute 5-15% of the items and 70 to 80% of the total dollar value to the firm Class B items constitute 30% of the inventory items but only 15% of the dollar value Class C items constitute 50 to 60% of the items but only 5 to 10% of the dollar value
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ABC Classification.. Class A items are tightly controlled Class B items less so Class C items even less Dollar values are computed by multiplying the unit cost by the annual demand for the item This technique is used in all auto parts inventory control systems and has been for 15 years
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Periodic inventory systems are…. Fixed Time period systems NOT EOQ Models The time between orders is fixed, the re-order point is fixed, but the order amount is not
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Which gives you lowest holding cost? Instantaneous replenishment Finite (non-instantaneous) replenishment Quantity discounts WHICH OF THE ABOVE GIVES YOU LOWEST TOTAL ORDERING COST?
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How do we calculate a re- order point? Lead time in days times the daily demand plus the safety stock Safety stock equals the service level (usually 3 for z) times the standard deviation of daily demand times the sq. rt. of lead time. (You will be given the formulas)
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How do we calculate… Time between orders? Production days in a year / # of orders Run length EOQ or order quantity / daily Production rate
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How do we calculate… Time between orders? Production days in a year / # of orders Run length EOQ or order quantity / daily Production rate
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Safety Stocks and Service Levels Safety stock = Z value * std. dev. of daily demand * sqrt(lead time) For 95% service level, use Z value of 1.65 For 99% service level, use Z value of 3
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Inventory Terms ABC system Carrying costs Continuous inventory system Dependent demand EOQ Fixed-order quantity system Fixed time period system Capacity Independent demand Inventory In-process inventory Non-instantaneous receipt Order cycle Quantity discount Stockout Service level Efficiency
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Chapter 14 –S&OP
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Copyright 2009 John Wiley & Sons, Inc.14-55 Sales and Operations Planning – Chapter 14 Determines the resource capacity needed to meet demand over an intermediate time horizon Aggregate refers to sales and operations planning for product lines or families Sales and Operations planning (S&OP) matches supply and demand Objectives Establish a company wide game plan for allocating resources Develop an economic strategy for meeting demand
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Copyright 2009 John Wiley & Sons, Inc.14-56 Sales and Operations Planning Process
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What are the inputs to the aggregate planning system?? Demand forecasts Capacity constraints Strategic objectives Company policies Financial constraints NOT… Size of workforce Inventory levels Units subcontracted Overtime scheduled
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Copyright 2009 John Wiley & Sons, Inc.14-58 The Monthly S&OP Planning Process
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Copyright 2009 John Wiley & Sons, Inc.14-59 Meeting Demand Strategies Adjusting capacity Resources necessary to meet demand are acquired and maintained over the time horizon of the plan Minor variations in demand are handled with overtime or under-time Managing demand Proactive demand management
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Copyright 2009 John Wiley & Sons, Inc.14-60 Strategies for Adjusting Capacity Level production Producing at a constant rate and using inventory to absorb fluctuations in demand Chase demand Hiring and firing workers to match demand Peak demand Maintaining resources for high-demand levels Overtime and under-time Increasing or decreasing working hours Subcontracting Let outside companies complete the work Part-time workers Hiring part time workers to complete the work Backordering Providing the service or product at a later time period
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Copyright 2009 John Wiley & Sons, Inc.14-61 Strategies for Adjusting Capacity Level production Producing at a constant rate and using inventory to absorb fluctuations in demand Chase demand Hiring and firing workers to match demand Peak demand Maintaining resources for high-demand levels Overtime and under-time Increasing or decreasing working hours Subcontracting Let outside companies complete the work Part-time workers Hiring part time workers to complete the work Backordering Providing the service or product at a later time period
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Copyright 2009 John Wiley & Sons, Inc.14-62 Level Production Demand Units Time Production
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Copyright 2009 John Wiley & Sons, Inc.14-63 Chase Demand Demand Units Time Production
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Copyright 2009 John Wiley & Sons, Inc.14-64 Strategies for Managing Demand Shifting demand into other time periods Incentives Sales promotions Advertising campaigns Offering products or services with counter- cyclical demand patterns Partnering with suppliers to reduce information distortion along the supply chain
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Copyright 2009 John Wiley & Sons, Inc.14-65 Quantitative Techniques For AP Pure Strategies Mixed Strategies Linear Programming Transportation Method Other Quantitative Techniques
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Copyright 2009 John Wiley & Sons, Inc.14-66 Pure Strategies Hiring cost= $100 per worker Firing cost= $500 per worker Inventory carrying cost= $0.50 pound per quarter Inventory carrying cost= $0.50 pound per quarter Regular production cost per pound= $2.00 Regular production cost per pound= $2.00 Production per employee= 1,000 pounds per quarter Production per employee= 1,000 pounds per quarter Beginning work force= 100 workers Beginning work force= 100 workers QUARTERSALES FORECAST (LB) Spring80,000 Summer50,000 Fall120,000 Winter150,000 Example:
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Copyright 2009 John Wiley & Sons, Inc.14-67 Level Production Strategy Level production = 100,000 pounds (50,000 + 120,000 + 150,000 + 80,000) 4 Spring80,000100,00020,000 Summer50,000100,00070,000 Fall120,000100,00050,000 Winter150,000100,0000 400,000140,000 Cost of Level Production Strategy (400,000 X $2.00) + (140,00 X $.50) = $870,000 SALESPRODUCTION QUARTERFORECASTPLANINVENTORY
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Copyright 2009 John Wiley & Sons, Inc.14-68 Chase Demand Strategy Spring80,00080,00080020 Summer50,00050,00050030 Fall120,000120,000120700 Winter150,000150,000150300 10050 SALESPRODUCTIONWORKERSWORKERSWORKERS SALESPRODUCTIONWORKERSWORKERSWORKERS QUARTERFORECASTPLANNEEDEDHIREDFIRED Cost of Chase Demand Strategy (400,000 X $2.00) + (100 x $100) + (50 x $500) = $835,000
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Copyright 2009 John Wiley & Sons, Inc.14-69 Items Product lines or families Individual products Components Manufacturing operations Resource Level Plants Individual machines Critical work centers Production Planning Capacity Planning Resource requirements plan Rough-cut capacity plan Capacity requirements plan Input/ output control Sales and Operations Plan Master production schedule Material requirements plan Shop floor schedule All work centers Hierarchical Nature of Planning Disaggregation: process of breaking an aggregate plan into more detailed plans
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Copyright 2009 John Wiley & Sons, Inc.14-70 Collaborative Planning Sharing information and synchronizing production across supply chain Part of CPFR (collaborative planning, forecasting, and replenishment) involves selecting products to be jointly managed, creating a single forecast of customer demand, and synchronizing production across supply chain
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Copyright 2009 John Wiley & Sons, Inc.14-71 Available-to-Promise (ATP) Quantity of items that can be promised to customer Difference between planned production and customer orders already received Capable-to-promise quantity of items that can be produced and made available at a later date ATP in period 1 = (On-hand quantity + MPS in period 1) – (CO until the next period of planned production) ATP in period n = (MPS in period n ) – (CO until the next period of planned production)
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Copyright 2009 John Wiley & Sons, Inc.14-72 ATP: Example
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Copyright 2009 John Wiley & Sons, Inc.14-73 ATP: Example (cont.)
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Copyright 2009 John Wiley & Sons, Inc.14-74 ATP: Example (cont.) ATP in April = (10+100) – 70 = 40 ATP in May = 100 – 110 = -10 ATP in June = 100 – 50 = 50 = 30 = 0 Take excess units from April
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Chapter 15 – ERP & Material Requirements Planning Inventory for Dependent Demand
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MRP is applied mostly to Project operations Batch operations Assembly line operations Continuous operations
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What is the relationship between MRP and LEAN (JIT—Kanbans)? There is no relationship MRP is used by older manufacturing firms MRP is used for execution, LEAN for planning MRP is used for planning, LEAN for execution
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Material requirements planning is a system for Computing EOQ’s Determining when to release orders Computing safety stocks Determining service levels WHICH????
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MRP consists of four steps— which is not one of the four? 1. Exploding the BOM 2. Netting out inventory 3. Checking to insure sufficient capacity exists 4. Lot sizing 5. Time-phasing requirements
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Formulas/Rules Projected on-hand = prev projected on-hand + scheduled receipts + planned order receipts – gross requirements Is really the on-hand amount at the end of the period If less than zero, set to zero Net requirements = gross requirements – prev projected on-hand - scheduled receipts If less than zero, set to zero Planned order receipts must be sufficient to accommodate the net requirements Why don’t we just use net requirements for this?? Planned order releases are the same in amount as planned order receipts, just offset one or more periods by the lead time
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MRP led to….. MRP II, which led to…. which led to…. which led to which is where we are today
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Lean Production – Chapter 16 Doing more with less inventory, fewer workers, less space Just-in-time (JIT) Muda waste, anything other than that which adds value to the product or service
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Waste in Operations
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Waste in Operations (cont.)
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Basic Elements 1. Flexible resources 2. Cellular layouts 3. Pull production system 4. Kanban production control 5. Small lot production 6. Quick setups 7. Uniform production levels 8. Total productive maintenance 9. Supplier networks
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Flexible Resources Multifunctional workers perform more than one job general-purpose machines perform several basic functions Cycle time time required for the worker to complete one pass through the operations assigned Takt time paces production to customer demand
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Standard Operating Routine for a Worker
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Cellular Layouts Manufacturing cells comprised of dissimilar machines brought together to manufacture a family of parts Cycle time is adjusted to match takt time by changing worker paths
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Cells with Worker Routes
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Worker Routes Lengthen as Volume Decreases
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Pull System Material is pulled through the system when needed Reversal of traditional push system where material is pushed according to a schedule Forces cooperation Prevent over and underproduction While push systems rely on a predetermined schedule, pull systems rely on customer requests
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Kanbans Card which indicates standard quantity of production Derived from two-bin inventory system Maintain discipline of pull production Authorize production and movement of goods
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Sample Kanban
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Origin of Kanban a) Two-bin inventory systemb) Kanban inventory system Reordercard Bin 1 Bin 2 Q - R Kanban R R Q = order quantity R = reorder point - demand during lead time
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Types of Kanban Production kanban authorizes production of goods Withdrawal kanban authorizes movement of goods Kanban square a marked area designated to hold items Signal kanban a triangular kanban used to signal production at the previous workstation Material kanban used to order material in advance of a process Supplier kanban rotates between the factory and suppliers
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The End
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Ignore what follows
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ERP Large caps have been there and done that Mid and small caps are getting there The road to implementation has been rough
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ERP Modules Sales & distribution Production & Materials Management Quality management Human resource management Project management Accounting and controlling/finance
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Terms Capacity Efficiency Bill of Material Product structure File Master Production File Explosion Expediting Netting
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More terms Load profile MRP II CRP ERP Modular BOM Utilization Time bucket Time fence Order splitting
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Errors 18.39 18.39 – 12.24 12.24 – 6.12 6.12 – 0 0 – -6.12 -6.12 – -12.24 -12.24 – -18.39 -18.39 – ||||||||||||| 0123456789101112 Period UCL = +3 LCL = -3
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Sales and Operations Planning: Capacity Planning and Aggregate Production Planning Long Range Planning Medium Range Planning Aggregate Production Planning
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What are the inputs to the aggregate planning system?? Demand forecasts Capacity constraints Strategic objectives Company policies Financial constraints NOT… Size of workforce Inventory levels Units subcontracted Overtime scheduled
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Capacity planning is…. Long-term strategic decision-making What facilities located where, built exactly when???? NOT Capacity requirements planning
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Aggregate Production Planning Strategies are…. Pure (Trial-and-error) Chase Demand Level production Mixed (optimal) Linear programming Simulation
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Which of the following strategies matches production to demand by hiring and firing workers? Chase demand strategies Level production strategies Strategies that use subcontracting and overtime
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Which of the following is not a strategy for managing demand Shifting demand into other time periods with incentives, sales promotions and advertising campaigns Offering products or services with counter- cyclical demand patterns Partnering with suppliers to reduce information distortion along the supply chain Increasing inventories and laying off workers when demand is soft
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Aggregate production planning provides input to which of the other planning processes? Input/Output Control Shop flow schedule Material requirements plan Forecasting Capacity requirements plan
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The planned order releases are outputs from what planning process ? Input/Output Control Shop flow schedule Material requirements plan Forecasting Capacity requirements plan
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