Lean Systems Answer Key Part 4

155) What is the difference between the "push" and "pull" methods of material flow? Which method does lean systems use? Answer: With the pull method, customer demand (an order) activates the production of the goods or services. The production system does not anticipate the need for more product until indicated by a customer order. The push method begins with a production schedule and customer demand is assumed (or hoped for). Lean system processes use the pull method of production. 156) What are some of the approaches used to achieve the high quality levels associated with lean systems? Answer: Quality at the source is one principle approach that is used–this is the philosophy that defects are caught and corrected where they are created. Other ways of building in quality include automatically stopping a process when something is wrong and then fixing the problems on the line itself as they occur (called jidoka), and using mistake-proofing methods to design fail-safe systems that minimize human error (called poka-yoke). 157) Explain the meaning of the term takt time, and use a numerical example to illustrate. Answer: Takt time is the cycle time needed to match the rate of production to the rate of sales or consumption. Numerical examples may vary, but one might be as follows: Units are sold at a rate of 240 per day. A plant running one shift (480 minutes) per day would establish a takt time of 2 minutes per unit, or 120 seconds per unit (480 minutes ÷ 240 units). All manufacturing steps in the process would be planned to complete their work within the 2minute takt time. 158) With respect to lean systems, what is the advantage of standardized components? Answer: Standardization tends to increase the repeatability of tasks, which in turn enables a higher degree of efficiency in production. 159) List and briefly define the 5S Practices that serve as an enabler and essential foundation of lean systems. Answer: Refer to Table 8.2, page 283 in the text. 160) What are the four underlying principles of the Toyota Production System? Answer: The four underlying principles are: (1) all work must be completely specified as to content, sequence, timing and outcome; (2) every customer—supplier connection must be direct, unambiguously specifying the people involved, the form and quantity of goods and services, the way requests are made by customers, and the expected time in which the requests will be met; (3) the pathway for every product and service must be simple and direct; and (4) any improvement to the system must be made in accordance with the scientific method, under the guidance of a teacher, and at the lowest possible level. 161) What is group technology and what advantages are accrued from its use? Answer: The theory is to group parts or products into families and set aside groups of machines for their production. By dedicating these groups of machines to specific part families, the overall setup time between parts is minimized, part routings are less complicated, shorter, and therefore faster, and material handling is minimized. Other less tangible benefits may also be realized; for example, it is typically easier to track down the status of an order if the expeditor knows the cell where it should be produced. Inventory levels may also be lower and learning effects may reduce overall production time. 162) How can group technology be used in a service setting? Provide an example and describe two advantages of using this principle in a service setting. Answer: The theory behind group technology is to group parts or products into families and set aside groups of machines for their production. In a service setting, the parts are customers and the groups of machines may be customer service representatives or could be machines. Examples will vary, but in a university setting, student advising is most likely done using group technology principles, e.g., students are assigned to an advisor based on their major rather than alphabetically. This means that the advisor can develop intimate knowledge of a few majors rather than the virtually impossible task of understanding the quirks of all majors and departments at a university. Many businesses parse their customer bases into commercial and residential groups as well. 163) Explain how a line-flow strategy can be used to reduce or eliminate setups. Answer: If line-flow volumes are high enough, a product layout can be used that eliminates setup requirements entirely. Another tactic, the one-worker-multiple-machines (OWMM) approach, can also be used to reduce or eliminate setups by having one person operate several machines simultaneously to achieve line-flow without requiring the machine to be changed over. In low volume processes, line-flow can be achieved through group technology (GT). This technique groups part or products with similar characteristics into families and sets aside groups of machines for their production. The goal is to group products with similar processing requirements and minimize changeover or setup. 164) What are the general operating rules for a single-card kanban system? Answer: The operating rules for the single-card system are simple and are designed to facilitate the flow of materials while maintaining control of inventory levels. 1. Each container must have a card. 2. The assembly line always withdraws materials from the fabrication cell. The fabrication cell never pushes parts to the assembly line because, sooner or later, parts will be supplied that are not yet needed for production. 3. Containers of parts must never be removed from a storage area without a kanban first being posted on the receiving post. 4. The containers should always contain the same number of good parts. The use of nonstandard containers or irregularly filled containers disrupts the production flow of the assembly line. 5. Only nondefective parts should be passed along to the assembly line to make the best use of materials and worker's time. This rule reinforces the notion of building quality at the source, which is an important characteristic of lean systems. 6. Total production should not exceed the total amount authorized on the kanbans in the system. 165) How does Toyota's two-card kanban system work? Answer: Toyota uses a two-card system, based on a withdrawal card and a productionorder card, to control inventory quantities more closely. The withdrawal card specifies the item and the quantity the user of the item should withdraw from the producer of the item, as well as the stocking locations for both the user and the producer. The production-order card specifies the item and the quantity to be produced, the materials required and where to find them, and where to store the finished item. Materials cannot be withdrawn without a withdrawal card, and production cannot begin without a production-order card. The cards are attached to containers when production commences. By manipulating the number of withdrawal and production cards in play at any time, management can control the flow of materials in the production system. 166) When determining the number of kanban containers, discuss the impact of alpha, the policy variable, on the total amount of inventory in the system. If alpha is set equal to zero, is system inventory zero? What would be required to achieve a system-wide inventory of zero? Answer: The policy variable alpha adds safety stock to cover for unexpected circumstances, for example a quality issue or delays in supply. Even if alpha is zero, there is still inventory in the system as dictated by the average demand during lead time DDLT. The DDLT is calculated by multiplying the daily demand for parts by the sum of the average container travel time plus the average container process time. One unappealing way for system-wide inventory of zero would be for demand to drop to zero. Another way for system-wide inventory to be close to zero would be for a manufacturer to have very large capacity and fast processing. Such capacity and speed would be prohibitively expensive for processing tangible goods. 167) Briefly outline the steps to be followed in evaluating and improving a process using value stream mapping. Answer: VSM analysts begin by selecting a product family for which the mapping will be done. This is followed by drawing a current state map of the existing production situation, and gathering and including all pertinent information on material and information flows (cycle times, scrap rates, machine uptime, batch sizes, etc.). Once the current state map is completed, the analysts use lean systems principles (e.g., load leveling, pull scheduling, Kanban systems) to create a future state map with more streamlined product flows. In this step, sources of waste are highlighted, and means for eliminating them are identified. Finally an implementation plan for achieving the future state is developed, which then becomes the blueprint for implementing and fine tuning a lean system. The process does not stop here, but provides continuous improvement opportunities as a new future state map is drawn after the lean system has been further improved. 168) Choose a simple, common process and create a value stream map containing the current state, plus a realistic future state, and implementation plan. Answer: Answers will vary. See the outline below for steps to be followed and information to be included. VSM analysts begin by selecting a product family for which the mapping will be done. This is followed by drawing a current state map of the existing production situation, and gathering and including all pertinent information on material and information flows (cycle times, scrap rates, machine uptime, batch sizes, etc.). Once the current state map is completed, the analysts use lean systems principles (e.g., load leveling, pull scheduling, Kanban systems) to create a future state map with more streamlined product flows. In this step, sources of waste are highlighted, and means for eliminating them are identified. Finally an implementation plan for achieving the future state is developed, which then becomes the blueprint for implementing and fine tuning a lean system. The process does not stop here, but provides continuous improvement opportunities as a new future state map is drawn after the lean system has been further improved. 169) Briefly discuss the House of Toyota, including its origins and key points. Answer: The House of Toyota is a graphic presentation of all the essential elements of lean systems that make the Toyota Production System (TPS) work well. It was originally used by Toyota to define TPS to its employees and suppliers. Its roof represents the primary goals of high quality, low cost, waste elimination, and short lead times. The roof is supported by the twin pillars of JIT and jidoka, which stand on a base of operational stability that comes from leveraging a number of lean concepts. For additional details refer to Figure 8.3, page 285 in the text. 170) What are the organizational issues companies must address before implementing a lean system? Answer: The organizational issues faced by companies include the human cost of lean systems (tends to create stress in workers), cooperation and trust (changes activities of workers and the relationships between them), and changing reward systems and labor classification. 171) An item sells at a rate of 240 units per day. If a plant works one shift per day (480 minutes), what takt time is required for the plant to meet this demand? Answer: 480 minutes per day ÷ 240 units = 2.0 minutes per unit, or 120 seconds per unit 172) A plant's manufacturing process has a takt time of 90 seconds per unit. This results in a process output of how many units per hour? Answer: 60 minutes per hour x 60 seconds per minute = 3600 seconds per hour 3600 seconds per hour ÷ 90 seconds per unit = 40 units per hour output 173) An item is used in Process B at a rate of 150 units per day. Process A works one shift per day (480 minutes) and supplies Process B's requirements. What takt time is required in Process A to meet Process B's demand? Answer: 480 minutes per day ÷ 150 units = 3.2 minutes per unit, or 192 seconds per unit 174) What is the output for a process that has a takt time of 1.25 minutes per unit?Answer: 60 minutes per hour ÷ 1.25 minutes per unit = 48 units per hour output 175) An item sells at a rate of 600 units per day. If a plant works two shifts per day (480 minutes each shift), what takt time is required for the plant to meet this demand?Answer: 480 minutes per shift × 2 shifts = 960 minutes per day 960 minutes per day ÷ 600 units = 1.6 minutes per unit, or 96 seconds per unit 176) A plant's manufacturing process has a takt time of 72 seconds per unit. This results in a process output of how many units per hour? Answer: 60 minutes per hour × 60 seconds per minute = 3600 seconds per hour 3600 seconds per hour ÷ 72 seconds per unit = 50 units per hour output 177) Jones Electric Motors uses a Kanban system to make motors for several garage door companies in the southeastern United States. The daily demand for motor housings used in manufacturing is 100 units. The average waiting time for a container of parts is 0.2 day. The processing time for a container of housings is 0.1 day, and a container holds 5 housings. If Jones wishes to use a 10% policy variable, how many containers are needed? Answer: 100(.2 .1)(1 .10) d( w p)(1  ) k= = = 6.6 → 7 containers 5 c 178) Happiness, Inc. uses a Kanban system. The daily demand for the most critical part, the Smylie, is 400 units over an eight-hour production period. The average waiting time for a container of Smylies is 30 minutes. The processing time for a container filled with Smylies is 6 minutes, and a container holds 5 units. If the company wishes to use a 5% policy variable, how many containers are needed? Answer: k= d( w p)(1  ) c = 400(.0625 .0125)(1 .05) = 6.3 → 7 containers 5 179) Burdell Salad Dressings uses a Kanban system. The daily demand for corrugated boxes used in packaging its dressings is 300 boxes. The average waiting time for a container of boxes is 0.25 day. The processing time for a container of boxes is 0.1 day, and a container holds 10 boxes. If Burdell wishes to use a 10% policy variable, how many containers are needed? Answer: k= d( w p)(1  ) c = 300(.25 .10)(1 .05) = 11.025 →12 containers 10 180) Champion Cooling Company uses a kanban system at their two locations in the Oklahoma City Metroplex. The daily demand for fans is 2000 at each location and management insists on using the same alpha level (0.1) at both locations. Location Reno uses containers that hold 20 items and takes 0.04 of a day to process a container. It takes 0.07 of a day to get a container filled and for it to wait during its cycle. Location Western uses containers that hold 24 items and takes 0.02 of a day to process a container. It takes 0.08 of a day to get a container filled and for it to wait during its cycle. Which location has the higher level of inventory? Assume that both locations round up to the next highest integer number of containers. Answer: 2000(.04 .07)(1 .1) d( w p)(1  ) kReno = = = 12.1 →13 20 c WIPReno = 20 × 13 = 260 d( w p)(1  ) c WIPWestern = 24 × 10 = 240 kWestern = = 2000(.02 .08)(1 .10) = 9.16 →10 24 181) Champion Cooling Company uses a kanban system at their location in the Oklahoma City Metroplex. The daily demand for fans is 2000 and management insists on using an alpha level of 0.1. They use containers that hold 20 items and takes 0.04 of a day to process. It takes 0.07 of a day to get a container filled and for it to wait during its cycle. How many containers should they use? If they use the nearest integer value number of containers, what is the actual system alpha? Answer: 2000(.04 .07)(1 .1) d( w p)(1  ) = = 12.1 → 12 containers 20 c 2000(.04 .07)(1  ) d( w p)(1  ) = 12 = 20 c 240 = 2000 (.04 + .07)(1 + α) 240 = .11(1 + α) 2000 .12 =1+α .11 1.09 - 1 = α . 09 = α k= 182) Champion Cooling Company uses a kanban system at their location in the Oklahoma City Metroplex. The daily demand for fans is 2000 and management insists on using an alpha level of 0.1. They use containers that hold 24 items and takes 0.02 of a day to process. It takes 0.08 of a day to get a container filled and for it to wait during its cycle. How many containers should they use? If they use the nearest integer value number of containers, what is the actual system alpha? Answer: 2000(.02 .08)(1 .10) d( w p)(1  ) k= = = 9.16 → 9 containers 24 c 2000(.02 .08)(1 ) d( w p)(1  ) = 9= 24 c 24 × 9 = 2000(.02 + .08)(1 + α) 216 = .10(1 + α) 2000 . 108 =1+α .10 1.08 - 1 = α 0.08 = α 183) Burdell Salad Dressings uses a Kanban system. The daily demand for corrugated boxes used in packaging its dressings is 300 boxes. The average waiting time for a container of boxes is 0.25 day. The processing time for a container of boxes is 0.1 day, and a container holds 10 boxes. If Burdell wishes to use a 5% policy variable, what is the level of work in process inventory in their plant? Answer: 300(.25 .10)(1 .05) d( w p)(1  ) = = 11.025 →12 containers 10 c WIP = 10 × 12 = 120 units k= Assuming they round up, their WIP is 120 units. If they round down, they would have 110 units of WIP. 184) The Peeps factory can be described as a three step process consisting of Mixing, Forming, and Packaging. Peeps are made in batches of 1000 and have a daily demand of 75,000 units during what the plant manager likes to call "the Peep season." Mixing has a cycle time of .02 seconds with a setup time of 30 seconds; Forming has a setup time of 24 seconds and a cycle time of .03 seconds, and Packaging has a setup time of 15 seconds with a cycle time of .04 seconds. Each process step is handled by one operator, who is available for 8 hours a day. What is the process bottleneck if each process step is assumed to have 100% uptime? Answer: