ChIII-ProcessSelection

ChIII-ProcessSelection - 1/19/2011 MGMT 36100 Operations...

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Unformatted text preview: 1/19/2011 MGMT 36100 Operations Management (OM) III: Process Selection Process/ Production systems types: types: These can be classified in different ways. Classifications I Make-toMake-to-order Assemble-to-order e-toMake-toMake-to-stock Classifications II Job Shop Batch Repetitive Continuous ProcessSelection 1 ProcessSelection 2 Classifications I Make-toMake-to-order Process Classifications I Assemble-toAssemble-to-order Process Raw Material Manufacture Assemble Ship Manufacture W.I.P. Assemble Ship Delivery Lead Time Order Received Delivery Date Characteristics: Mass Customization, medium delivery times, medium costs Delivery Lead Time Characteristics: Customization, Long delivery times, high costs Order Received Delivery Date ProcessSelection 3 ProcessSelection 4 Classifications I Make-toMake-to-stock Process Production Systems Classifications II Job Shop Emergency Room Commercial Bakery Automatic Carwash Petroleum Refinery Manufacture Assemble Ship Repetitive Characteristics: standardization, short delivery times, low costs Delivery Lead Time Continuous Delivery Date Order Received Variety W.I.P. Batch Volume 5 ProcessSelection 6 ProcessSelection ProcessSelection 1 1/19/2011 Classification II: Comparison Process Selection: How to organize production of goods or services? Continuous Highly standardized Very efficient, very high volume Very rigid, lack of variety, costly to change, very high cost of downtime 7 ProcessSelection 8 Job shop Batch Repetitive Customized SemiSemiStandardized standardized Advantages Wide Variety Flexible Low unit cost, high volume, efficient Disadvantages Slow, high Moderate Low unit cost, cost/unit , flexibility, complex moderate high cost of planning & scheduling downtime scheduling complexity Description Major implications • • • • Capacity planning Layout of facilities Equipment Design of work systems of work systems ProcessSelection Process Design We will consider assembly lines. Design Single model: 26” TV sets. I-pods / ovens I(with different colors). Mixed models: Vans and sedans. and sedans. Layout: Serial, cell,.. Conveyor, manual. Equipment selection. Line balancing. Suppose we want to assemble chairs. Precedence Precedence information Management New product learning period. Day to day: absenteeism, motivation, quality, equipment failure equipment failure. Improvements Better balancing. Better methods. Time reduction. 1 75 90 60 60 Precedence diagram Task Description 1 2 3 4 5 6 7 8 Set legs Unpack seat Set back-rest backPrepare box Full assembly Inspect Pack Pred. Time 3, 5 6 4, 7 5 2 6 3 7 8 4 Join legs & seat 1, 2 50 If we do one task per station, we min CT 35 we get min. CT = 90 [sec/unit]. 90 40 If we do all tasks in 1 station, we get max. CT = 500 [sec/unit]. We will discuss only Assembly Line Balancing for single model. Total time (sec.) 500 How do assemblies for - airplane, sandwich, automobile, furniture, p.c. p.c. differ? ProcessSelection Suppose the desired rate: 24 chairs / hour Target Cycle Time: Unidirectional flow 9 = 3600 [sec/hr] / 24 [units / hr] = 150 [sec/unit] ProcessSelection 10 Example 1 5 2 Precedence diagram for chair assembly Task Description Time Effective Cycle Time 75 = maximum station time 50 40 1 2 3 4 5 6 Set legs Unpack seat Set back-rest backPrepare box Join legs & seat Full assembly 75 90 60 60 50 35 1 2 90 7 6 5 90 = 150 sec/unit 8 7 6 35 60 8 Effective CT should not exceed Target CT Efficiency = 100 * (total task time) . No. of stations * Effective CT = 100 * (500) = 83.3% 4 * 150 150 St. 4 3 4 3 60 4 Desired rate: 24 chairs / hour 7 Inspect 40 Target Cycle Time: Ti 8 Pack 90 = 3600 [sec/hr] / 24 [units / hr] Total time (sec.) 500 = 150 [sec/unit] Minimum number of stations needed (theoretically): Each station will do the work for 150 sec (max). So, 500/150 = 3.33. That means, we need at least 4 stations. Minimum cycle time = 90 [sec/unit]. Maximum cycle time = 500 [sec/unit]. ProcessSelection Target Cycle Time: Ti 150 [sec/unit] St. 1 St. 2 St. 3 One task / station All tasks in 1 station 11 2, 3 150 1, 5 125 4, 6, 7 135 8 90 ProcessSelection 12 ProcessSelection 2 1/19/2011 Here are two more designs: Target CT = 150 sec. / unit Suppose Target CT = 130 [sec/unit] Minimum number of stations needed (theoretically): Each station will do the work for 150 sec (max). So, 500/130 = 3.85. That means, we need at least 4 stations. 75 Total time = 500 [sec/unit] 1 2 90 50 40 5 90 7 6 35 60 8 75 75 1 50 40 50 40 1 2 90 5 6 35 90 5 2 90 90 3 7 6 35 60 7 8 60 4 8 3 3 2,3 150 60 1,5 125 4 60 6,7 75 4,8 150 60 4 1,3 135 2,5 140 4,6 95 7,8 130 Priority Rules: 1: SPT: Smaller the processing time, higher SPT order 6753 412 8 the priority For tie-breaking we can use rules such as: select smallest / largest tietask number first, largest number of followers, etc. Eligible Eligible task: A task is eligible if all tasks that precede this task have been selected. 13 ProcessSelection 14 Effective CT = 150 sec. / unit Efficiency = 83.3% ProcessSelection Effective CT = 140 sec. / unit Efficiency = 89.3% Example 1 We used this in Ch. 2 Suppose we want 0 to produce 420 units in 7 hours. 1, 20 3, 10 2, 50 4, 40 6, 30 5, 30 7, 20 Example 1 Part (a): SPT rule A task is eligible if all tasks that 0 precede this task have been selected. 1, 20 3, 10 2, 50 4, 40 Target CT = 60 [sec/unit] 6, 30 7, 20 5, 30 This means that we need to produce 1 unit every minute, or Target CT = 60 [sec/unit] Total task time = (20 + 50 + 10 + 40 + 30 + 30 + 20) = 200 [sec] at 60 stat We need at least (200 / 60 ) 4 stations SPT order St I II III IV V Selected Cum. Time Eligible 1 2,3 5 4 6, 7 20 50 , 60 30 40 30 , 50 1 20 1, 2 / 2 3 1 7 5 6 4 2 As soon a task is selected, update everything. Effective cycle time: 60 [sec./unit]. Efficiency: Efficiency: (100 * 200) / (5 * 60) = 66.7%. 5 30 4 40 6, 7 50 Priority Rules: (use appropriate tie-breaker) tie1: SPT: Smaller the processing time, higher the priority 3175642 2: LPT: Higher the processing time, higher the priority For tie-breaking we can use rules such as: select smallest / largest tietask number first, largest number of followers, etc. We will now add a “dummy task 0”, to our diagram (shown in green). ProcessSelection 15 2 / 3,5 / 5, 4 5, 5, 4 / 4 4 /6 6 /7 2, 3 60 SPT order ProcessSelection 16 Example 1 Part (b): LPT rule Target CT = 60 [sec/unit] Total task time = 200 [sec] Lower bound: 4 stations LPT order Station Station 1, 20 3, 10 2, 50 6 1 7 3 4, 40 6, 30 5, 30 7, 20 Assembly Line Balancing (ALB) Objective: To get a layout with minimum number of minimum stations for a specified target cycle time. Procedure: Start with the precedence diagram. Determine target CT. Select a priority rule (SPT, LPT, RPW) and a tie-breaking rule. tieStart with work station 1. Include as many eligible tasks as possible in each work station without exceeding target cycle time. If a task cannot be selected, skip and try the next one. If no eligible task can be selected, create a new station. If all tasks have been included, stop. 2 4 5 Effective CT: 60 [sec./unit]. 60 Efficiency: (100 * 200) / (4 * 60) = 83.3%. Selected Cum. Time Eligible I II III IV V 2 ,3 5 ,1 4 6 ,7 50 , 60 30 , 50 40 30 , 50 2,1 / 5, 1, 3 / 5,1 5,1 / 1 / 4 4 /6 6 /7 Eligible task: A task is eligible if all tasks that precede this task have been selected and there are no other restrictions. 5, 1 50 4 40 6, 7 50 ProcessSelection 2, 3 60 17 ProcessSelection 18 ProcessSelection 3 1/19/2011 Example 2 - SPT Need 1800 units in 7.5 hours. Target CT = 15 [sec. /unit] Total task time = 74 sec. Need at least 5 stations. St Selected C. Time Eligible I II 2, 6 1, 4 , 5 5 , 10 01 6 04 4 5 5 8 09 01 6 04 4 5 5 8 09 05 Example 2 - SPT Target CT = 15 [sec. /unit] /unit] 05 02 5 06 5 10 12 St Selected C. Time Eligible I 2, 6 1 , 4, 5 5, 10 2,1,3 /6,1,3 /1,3 02 5 06 5 10 12 2,1,3 / 6,1,3 /1,3 6 ,10,15 1, 3 / 4,5,3 / 5,9,3 / 10,9,3 5 10, 9, 3 10 03 5 07 9 II 6,10, 15 1, 3 / 4,5,3 / 5,9,3 5, 13 10, 15 6, 12 9 10, 9, 3 / 9, 3 / 3 9, 3 / 7, 8 / 8 7, 8 / 11 / 12 11 12 9 Efficiency: 100*[ 74/ (6*15)] = 82.2% 3, 7 15 8, 11 12 12 9 10 03 08 III 10 III 10, 9 6 6 11 5 07 6 11 9 IV 3, 7 V 8, 11 VI 12 08 6 We will show the remaining solution in one click. SPT order ProcessSelection Effective CT: 15 sec /unit. 4 2 5 6 7 10 1 8 11 9 12 3 19 2, 6 10 ProcessSelection 1, 4, 5 15 10, 9 13 20 Example 2 – SPT, continued Target CT = 15 [sec. /unit] /unit] St Select Cum. T Eligible I 2,6 5,10 2,1,3 / 6,1,3 / 1,3 6,1,3 1,3 II 1,4,5 6,10,15 1, 3 / 4,5,3 /5,9,3 What if tasks 2 & 6 cannot be done in the same station? 01 6 04 4 5 5 09 Back to Ex. 1 8 110 Part (c): RPW rule 1, 20 3, 10 4, 40 90 50 6, 30 20 7, 20 05 02 5 06 5 10 12 180 Target CT = 60 [sec/unit] Total task time = 200 [sec] 2, 50 Lower bound: 4 stations RPW order Station Selected Cum. Time Eligible 100 5, 30 80 4 5 6 7 9 07 5 10 2 1 3 We make task 6 temporarily tem ineligible for the current station. 03 I 08 2 ,3 1,4 5 ,6 7 50 , 60 20 , 60 30 , 60 20 2, 1 / 1, 3, 5 / 1, 5 1, 5 / 4, 5 / 5 5 /6 /7 7 2, 3 60 1, 4 60 5, 6 60 6 11 6 II III IV St Select Cum. T Eligible I 2 1 4 5 11 15 2, 1, 3 / 6,1,3 / 4,5,6,3 / 5, 6, 9, 3 6,1,3 4,5,6 II SPT order ProcessSelection After getting After getting RPW RPW order, do not use weights. Use only task times. 5,6,9,3 Effective CT: 60 [sec./unit]. 7 10 1 8 11 9 12 3 21 ProcessSelection Efficiency: 100 * 200 / (60 * 4) = 83.3% . 7 20 4 2 5 6 22 Ex. 1 Which layout do you prefer? 1, 20 3, 10 2, 50 5 30 4 40 5, 6 60 3, 4 50 4 40 6, 7 50 7 20 6, 7 50 6, 7 50 4, 40 6, 30 5, 30 7, 20 Example 2 R.P.W. method: 01 6 4 04 8 21 5 09 17 37 29 02 19 05 Need 1800 units in 7.5 hours. Target CT = 15 [sec. /unit] Total task time = 74 sec. Need at least 5 stations. stations. 5 19 5 06 14 5 10 9 9 12 1 20 2, 3 60 2, 3 60 2 50 ProcessSelection 2, 3 60 5, 1 50 1, 4 60 1, 5 50 14 36 03 10 5 10 6 11 07 5 21 08 9 12 6 15 11 Weight 6 Time Task 6 1 5 2 10 3 4 4 5 5 5 6 5 7 6 8 8 9 How about this one? 23 1 2 3 37 29 36 24 ProcessSelection ProcessSelection 4 1/19/2011 Example 2 Target C.T.= 15 [sec. /unit ]. Station Selected Cum. Time 37 01 6 21 19 04 4 5 8 09 Example 2 17 Target C.T.= 15 [sec. /unit ]. 37 01 6 21 19 04 4 5 8 09 17 05 05 29 02 I 1, 2, 4, 6, 11, 15 5 19 5 06 14 10 5 9 12 Station Selected I II III IV V 1, 2, 4 3, 5 8, 6 9, 11 7, 10 12 Cum. Time 6, 11, 15 10, 15 6, 11 8, 14 5, 10 9 29 02 5 19 5 06 14 10 5 9 12 9 9 14 36 03 10 07 5 14 36 03 10 07 5 08 6 21 11 6 15 VI 08 6 21 12 9 11 6 15 Effective CT = 15 sec /unit. Efficiency = 100 *74 / (6 * 15) = 82.2% RPW order: 01 03 02 04 08 05 06 09 11 07 10 12 ProcessSelection 25 1, 2, 4 15 ProcessSelection 3, 5 15 8, 6 11 9, 11 14 7, 10 10 26 Ex. 2: Solving by inspection. Target CT = 15 sec/unit inspection. I 1,2,4 II 5,6,10 III 3,7 IV 8,9 V 11,12 Various layouts Line flow, flow shop / product layout Job shop: • New products. • Shifting bottlenecks. • Capacity? • Need skilled operators. 01 6 04 4 5 5 8 09 IV I 02 05 Hybrid 9 12 5 II 06 5 10 98.7% A B 1: A - C - D 2: C - B 3: B - D – C - A C 27 ProcessSelection III 03 10 07 5 V 6 Job Shop D 08 6 11 ProcessSelection 28 MGMT 460 Layout: the configuration of departments, work centers, and equipment, with particular emphasis on movement of work (customers or materials) through the system. 1: Product layout: Layout uses standardized processing operations to achieve smooth, rapid, high-volume flow. highAdvantages: • High rate of output • Low unit cost • Labor specialization • Low material handling cost • High utilization of labor and equipment • Established routing and scheduling • Routing accounting and purchasing ProcessSelection 2. Process layout: Layout that can handle varied processing requirements. Dept. A Dept. B Dept. C Dept. D Dept. E Dept. F Disadvantages: • Creates dull, repetitive jobs • Poorly skilled workers may not maintain equipment or quality of output • Fairly inflexible to changes in volume • Highly susceptible to shutdowns • Needs preventive maintenance • Individual incentive plans are impractical 29 Advantages: • Can handle a variety of processing requirements • Not particularly Not particularly vulnerable vulnerable to equipment failures • Equipment used is less costly • Possible to use individual incentive plans Disadvantages: • WIP inventory costs can be high • Challenging routing and scheduling • Equipment utilization rates are low utilization rates are low • Material handling slow and inefficient • Complexities often reduce span of supervision • Special attention for each product or customer • Accounting and purchasing are more involved 30 ProcessSelection ProcessSelection 5 1/19/2011 3. Fixed Position layout: Layout in which the product or project remains stationary, and workers, materials, and equipment are moved as needed. Airplanes. Ships, PrePrefabricated homes Producing with different layouts Example 3 Suppose we want to 5 make a product with the A precedence diagram shown to the right. Times are in minutes. B 13 E C 12 7 10 D F 5 G J I 5 4 H 8 3 9 K 3 M 4. Cellular Production: Layout in which machines are grouped into a cell that can process items that have similar processing requirements 5. Group Technology: The grouping into part families of items with similar design or manufacturing characteristics with similar design or manufacturing characteristics Service Layouts Warehouse and storage layouts Retail layouts Office layouts Service layouts must be aesthetically pleasing as well as functional A, B, C, D require machine type X. E, F, I require machine require machine type require machine type type Y and G,H,J,K,M require machine type Z. If we plan to make this product in large numbers over many months / years, we should think in terms of either a product layout (line flow) or production cells. For low to moderate amounts we may want to use batch production in an existing departmental layout process layout. ProcessSelection 32 ProcessSelection 31 3A: Line layout Suppose we use a target CT = 20 min / unit. One possible layout is shown below. A, B 18 C, D 19 F, E, I 20 5 A B 13 5 G J I 5 4 H 8 3 9 K 3 M E C 12 7 10 D F J, G, H 15 K, M 12 13 4 B G 5 3 A single worker builds the entire H E 5 9 3 product. We need to provide C 12 A J M K 3 machines to each worker. 8 I Total time needed 7 10 5 = 5 + 13 + .. +9 + 3 D F = 84 min / unit Worker capacity = 420[min / day] / 84[min/unit] = 5 [units / day] # of worker s = 100 [units/day] / 5 [units/day * worker] = 20 workers. workers. Capacity 100 units/day Capacity = 100 units/day Costing for the cell layout - Total workers: 20 Daily salary = 20[workers]*16[$/hr * worker]*8[hrs/day] = 2560 [$ /day ] Overheads = 2560 [$/ day ] * 0.6 = 1536[$/ day ] Production cost = (2560 + 1536) [$/ day ] / 100 [units / day] = $40.96/ unit Unit Product cost = Material cost + Production cost = $125.52 + $40.96= $166.48 3B: Cell layout Effective CT = 20 min / unit. We will produce (7 * 60 / 20) = 21 units per day (7 hour working) If we need to produce 100 units per day, we will need 100 / 5 lines in parallel (with capacity = 21*5 = 105 units per day. ProcessSelection 33 ProcessSelection 34 3C: Batch process We will now calculate number of workers needed for each department. All workers work for 7 hours (420 min) and we need to produce 100 units in one day. X Time/unit Time for 100 units Workers needed Dept. capacity 5 A B 13 E 5 G J I 5 4 H 8 Example 4: 3 9 K 3 M B 5 A 13 E 5 G J I 5 4 H 8 3 9 K 3 M C 12 7 10 D F We We now have the same precedence diagram but 6 different machines are needed. C 12 7 10 D F Y Z 27 min 2700 min 7 108 4A: Line layout We can use the same layout we saw earlier but we will have to move machines to appropriate locations. AB 18 CD 19 FEI 20 J GH 15 KM 12 37 min 5 + 10 + 5 = 20 min 3700 min 100*20 = 2000 min 9 102 2000 / 420 5 5 * 420 / 20 105 4B: Cell layout Calculations will not change from the previous example but we will have to provide all 6 machines to each worker. 35 ProcessSelection 36 Bottleneck ProcessSelection Total workers = 21. Capacity = 102 ProcessSelection 6 1/19/2011 4C: Batch process Machines in departments X, Y, Z are shown below with other calculations in the table. 5 A B 13 E 5 G J I 5 4 H 8 3 9 K 3 M Right to Work Law Alabama Arizona Arkansas Florida Nevada North Carolina North Dakota Oklahoma South Carolina South Dakota Tennessee Texas Utah Virginia Wyoming C 12 7 10 D F X Time/unit Workers Capacity 30 min min 8 112 Y 24 min 6 105 Z 30 min 8 112 H M A, C F Georgia Idaho Iowa Iowa Kansas Louisiana Routing will be very inefficient in this layout; job travels back and fro between departments due to precedence relationships. ProcessSelection D, E B Mississippi Nebraska If you are employed in the states listed, you are probably protected by the state's Right to Work law and cannot be required to join or pay dues or fees to a union. Under federal labor law and the state's Right to Work law, the state Right to Work law, you you have the right to resign from membership in a union at any time. If you resign, you cannot be disciplined by the union for any postpostresignation conduct. I, G J, K 37 ProcessSelection 38 ProcessSelection 7 ...
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