production planning & control v2 (1).pdf
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Production Planning & Control
Assignment - A
Question 1a: Explain the forecasting process? What are the techniques for monitoring forecasts?
Answer: A Forecasting process provides a mechanism for soliciting participation from individuals who have knowledge of future events and compiling it into a consistent format to develop a forecast. The forecasting process concentrates defining how information will be gathered and reconciled into a consistent picture of the future. In cases where a statistical forecast is used the process will also define how much weight should be given to the mathematical models versus input from participants to develop the final consensus forecast.
There are two basic approaches to forecasting: � Qualitative � Quantitative
Qualitative Approaches to Forecasting Delphi Approach
• A panel of experts, each of whom is physically separated from the others and is anonymous, is asked to respond to a sequential series of questionnaires.
• After each questionnaire, the responses are tabulated and the information and opinions of the entire group are made known to each of the other panel members so that they may revise their previous forecast response.
• The process continues until some degree of consensus is achieved Scenario Writing
• Scenario writing consists of developing a conceptual scenario of the future based on a well defined set of assumptions.
• After several different scenarios have been developed, the decision maker determines which is most likely to occur in the future and makes decisions accordingly.
Subjective or Interactive Approaches
• These techniques are often used by committees or panels seeking to develop new ideas or solve complex problems.
• They often involve "brainstorming sessions". • It is important in such sessions that any ideas or opinions be permitted to
be presented without regard to its relevancy and without fear of criticism. Quantitative Approaches to Forecasting
• Quantitative methods are based on an analysis of historical data concerning one or more time series.
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• A time series is a set of observations measured at successive points in time or over successive periods of time.
• If the historical data used are restricted to past values of the series that we are trying to forecast, the procedure is called a time series method.
• If the historical data used involve other time series that are believed to be related to the time series that we are trying to forecast, the procedure is called a causal method.
Measures of Forecast Accuracy Mean Squared Error (MSE) The average of the squared forecast errors for the historical data is calculated.The forecasting method or parameter(s) which minimize this mean squared error is then selected. Mean Absolute Deviation (MAD) The mean of the absolute values of all forecast errors is calculated, and the forecasting method or parameter(s) which minimize this measure is selected.The mean absolute deviation measure is less sensitive to individual large forecast errors than the mean squared error measure.
Question 1b: Explain various forecasting models.
Answer:
Managers should always keep themselves abreast of forecasting methods, whether they already have a forecasting package, have built models themselves or plan to invest in one. Most forecasting packages boast of having a variety of models built into them, but then ask the user to choose the model he or she thinks would be most relevant. There are plenty of forecasting models available and "choosing the right one" is not an easy task. A common, erroneous perception is that complex forecasting models always give better results than simple ones.
Different forecasting models work best for different situations- the nature of the business, the nature of data, forecast granularity, forecast horizon, shelf life of the model and the expected accuracy of the forecasts. Forecast granularity is the unit of time of each forecast. Forecast horizon is the number of time units into the future for which forecasts are required. For example, weekly forecasts for the next 2 months have a granularity of a week and a horizon of 8 weeks. Shelf life is the time after which a model becomes useless and there is a need to switch to another model.
Model Type Most Suited Data Types Forecast Hor izon
Shelf L ife of Model
Exponential Smoothing No Trend, Varying Levels Short Short
Holt's Method Varying Trends, Varying Levels, No Seasonality Short Short
Winter 's Method Varying Trends, Varying Levels and Seasonality
Short to Medium Medium
ARIMA Varying Trends, Varying Levels, Seasonality
Short to Medium Long
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Question 2a: What is aggregate production plan? What are the pure strategies for APP?
Answer: Aggregate production planning is concerned with the determination of production, inventory, and work force levels to meet fluctuating demand requirements over a planning horizon that ranges from six months to one year. Typically the planning horizon incorporates the next seasonal peak in demand. The planning horizon is often divided into periods. For example, a one year planning horizon may be composed of six one-month periods plus two three-month periods. Normally, the physical resources of the firm are assumed to be fixed during the planning horizon of interest and the planning effort is oriented toward the best utilization of those resources, given the external demand requirements. Since it is usually impossible to consider every fine detail associated with the production process while maintaining such a long planning horizon, it is mandatory to aggregate the information being processed. The aggregate production approach is predicated on the existence of an aggregate unit of production, such as the "average" item, or in terms of weight, volume, production time, or dollar value. Plans are then based on aggregate demand for one or more aggregate items. Once the aggregate production plan is generated, constraints are imposed on the detailed production scheduling process which decides the specific quantities to be produced of each individual item. There are two pure planning strategies available to the aggregate planner: a level strategy and a chase strategy. Firms may choose to utilize one of the pure strategies in isolation, or they may opt for a strategy that combines the two. LEVEL STRATEGY A level strategy seeks to produce an aggregate plan that maintains a steady production rate and/or a steady employment level. In order to satisfy changes in customer demand, the firm must raise or lower inventory levels in anticipation of increased or decreased levels of forecast demand. The firm maintains a level workforce and a steady rate of output when demand is somewhat low. This allows the firm to establish higher inventory levels than are currently needed. As demand increases, the firm is able to continue a steady production rate/steady employment level, while allowing the inventory surplus to absorb the increased demand. A level strategy allows a firm to maintain a constant level of output and still meet demand. This is desirable from an employee relations standpoint. Negative results of the level strategy would include the cost of excess inventory, subcontracting or overtime costs, and backorder costs, which typically are the cost of expediting orders and the loss of customer goodwill. CHASE STRATEGY. A chase strategy implies matching demand and capacity period by period. This could result in a considerable amount of hiring, firing or laying off of employees; insecure and unhappy employees; increased inventory carrying costs; problems with labor unions; and erratic utilization of plant and equipment. It also implies a great deal of flexibility on the firm's part. The major advantage of a chase strategy is that it allows inventory to be held to the lowest level possible, and for some firms this is a considerable savings. Most firms embracing the just-in-time production concept utilize a chase strategy approach to aggregate planning.
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Question 2b: The demand and capacities for production of company is given below. Demand for January, February and March are 900, 300 and 700 respectively. The production capacities for each of the month are given below.
January February March
Regular Time 600 300 200
Over Time 300 300 300
Sub Contracted 500 500 500
The production cost per unit during regular time is Rs 60, during over time is Rs 70, and the sub contracted cost is Rs 72. The cost of carrying inventory is Rs 5 per unit per month. The cost of unused regular time capacity is Rs 15. Find the optimum production plan using transportation model.
Answer:
The Optimal Solution is the one shown on the following table:
Supply Period Unused
Capacity
Total
Available
Capacity
(Offer)
Jan Feb Mar
Indian Inventory 0 5 10 15
Regular Time 60
600
65 70 15 600
Over Time 70
300
75 80 0 300
Sub Contracting 72 79 82
150
0
350
500
Regular Time
X
60
300
65 15 300
Over Time
X
70 75
50
0
250
300
Sub Contracting 0
X
72 79
150
0
350
500
Regular Time
X
X
50
50
15
150
200
One Time
X
X
70
50
0
250
300
Sub-Contracting
X
X
72
250
0
250
500
Total Demand 900 300 700 1600 3500
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With this, the Total Cost could be calculated as follows:
Period Cost
Period 1: (January): 600 x (Rs 60) + 300 x (Rs 70) Rs 57,000
Period 2: (February): 300 x (Rs 70) Rs 21,000
Period 3 (March): 150 x (Rs 82) + 50 x (Rs 75) + 150 x (Rs 79) + 50 x (Rs 60) + 50 x (Rs 70) + 250 x (Rs 72) Rs 52,400
Unused Regular Time Capacity: 150 x (Rs 15) Rs 2,250
TOTAL COST: Rs 132,650
Question 3a: What is Master Production Scheduling? Explain various types of Bill of Materials.
Answer: A master production schedule (MPS) is a plan for production, staffing, inventory, etc. It is usually linked to manufacturing where the plan indicates when and how much of each product will be demanded. This plan quantifies significant processes, parts, and other resources in order to optimize production, to identify bottlenecks, and to anticipate needs and completed goods. Since an MPS drives much factory activity, its accuracy and viability dramatically affect profitability. Typical MPS's are created by software with user tweaking.
Due to software limitations, but especially the intense work required by the "master production schedulers", schedules do not include every aspect of production, but only key elements that have proven their control affectivity, such as forecast demand, production costs, inventory costs, lead time, working hours, capacity, inventory levels, available storage, and parts supply. The choice of what to model varies among companies and factories. The MPS is a statement of what the company expects to produce and purchase (i.e. quantity to be produced, staffing levels, dates, available to promise, and projected balance).
The MPS translates the business plan, including forecast demand, into a production plan using planned orders in a true multi-level optional component scheduling environment. Using MPS helps avoid shortages, costly expediting, last minute scheduling, and inefficient allocation of resources. Working with MPS allows businesses to consolidate planned parts, produce master schedules and forecasts for any level of the Bill of Material (BOM) for any type of part.
A bill of materials (BOM) is a list of the raw materials, sub-assemblies, intermediate assemblies, sub-components, components, parts and the quantities of each needed to manufacture an end product. No physical dimension is described in BOM.
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It may be used for communication between manufacturing partners, or confined to a single manufacturing plant.
A BOM can define products as they are designed (engineering bill of materials), as they are ordered (sales bill of materials), as they are built (manufacturing bill of materials), or as they are maintained (service bill of materials). The different types of BOMs depend on the business need and use for which they are intended. In process industries, the BOM is also known as the formula, recipe, or ingredients list. In electronics, the BOM represents the list of components used on the printed wiring board or printed circuit board. Once the design of the circuit is completed, the BOM list is passed on to the PCB layout engineer as well as component engineer who will procure the components required for the design.
BOMs are hierarchical in nature with the top level representing the finished product which may be a sub-assembly or a completed item. BOMs that describe the sub-assemblies are referred to as modular BOMs. An example of this is the NAAMS BOM that is used in the automative industry to list all the components in an assembly line. The structure of the NAAMS BOM is System, Line, Tool, Unit and Detail.
The first hierarchical databases were developed for automating bills of materials for manufacturing organizations in the early 1960s. At present this BOM is used as a data base to identify the many parts and their codes in automobile manufacturing companies.
A bill of materials "implosion" links component pieces to a major assembly, while a bill of materials "explosion" breaks apart each assembly or sub-assembly into its component parts.
Question 3b: What are the various disaggregation methods in use?
Answer: One framework for resource planning is divided into three levels:
� Aggregate planning (Level 1),
� Disaggregation (Level 2), and
� Execution (Level 3).
Resource management for service-producing organizations generally does not require as many intermediate levels of planning (Level 2) as it does for goods-producing firms.
Aggregate planning is the development of a long-term output and resource plan in aggregate units of measure.
These typically define output levels over a planning horizon of 1 to 2 years, focusing on product families or total capacity requirements.
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Aggregate planning later translates into monthly or quarterly production plans, taking into account capacity limitations such as supply availability, equipment, and labor.
Level 2 planning, or disaggregation, is the process of translating aggregate plans into short-term operational plans that provide the basis for weekly and daily schedules and detailed resource requirements.
Level 3 focuses on execution, moving work from one workstation to another, assigning people to tasks, setting priorities for jobs, scheduling equipment, and controlling processes.
Disaggregating Service Plans
• Most service organizations do not require as many levels of intermediate planning (Level 2) as goods-producing firms.
• Level 1 and 2 planning are often combined in service businesses.
Two Levels of Disaggregation for Many Service Organizations
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Disaggregating Service Plans
• One way to think of disaggregation in services is to go from aggregate planning (Levels 1 and 2) to front line resource (staff) capacity and scheduling decisions (Level 3). Manufacturers use and need an intermediate level of planning (Level 2), where work-in-process and subassemblies reside.
Disaggregation in Manufacturing
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• Disaggregation (Level 2) provides the link between aggregate plans developed at Level 1 and detailed execution at Level 3 (see Exhibit 13.6).
• This provides the basis for detailed purchasing and production schedules for all of the components that comprise the finished good or support service delivery.
• There are three major components for disaggregating aggregate plans into Level 2 plans.
� Master production scheduling (MPS)
� Materials requirements planning (MRP)
� Capacity requirements planning (CRP)
Master Production Schedule (MPS)
• A master production schedule (MPS) is a statement of how many finished items are to be produced and when they are to be produced.
• Typically developed for weekly time periods over a 6- to 12-month horizon.
Materials Requirements Planning (MRP)
• Materials Requirements Planning (MRP) is a forward-looking, demand-based approach for planning the production of manufactured goods and ordering materials and components to minimize unnecessary inventories and reduce costs.
Capacity Requirements Planning (CRP) is the process of determining the amount of labor and machine resources required to accomplish the tasks of production on a more detailed level, taking into account all component parts and end items in the materials plan.
Question 4a: Explain Materials Requirement Planning. What are the inputs and outputs of MRP?
Answer: Material requirements planning (MRP) is a computer-based inventory management system designed to assist production managers in scheduling and placing orders for dependent demand items. Dependent demand items are components of finished goods—such as raw materials, component parts, and subassemblies—for which the amount of inventory needed depends on the level of production of the final product.
The first MRP systems of inventory management evolved in the 1940s and 1950s. They used mainframe computers to explode information from a bill of materials for a certain finished product into a production and purchasing plan for components. Before long, MRP was expanded to include information feedback
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loops so that production personnel could change and update the inputs into the system as needed. The next generation of MRP, known as manufacturing resources planning or MRP II, also incorporated marketing, finance, accounting, engineering, and human resources aspects into the planning process. A related concept that expands on MRP is enterprise resources planning (ERP), which uses computer technology to link the various functional areas across an entire business enterprise.
MRP works backward from a production plan for finished goods to develop requirements for components and raw materials. "MRP begins with a schedule for finished goods that is converted into a schedule of requirements for the subassemblies, component parts, and raw materials needed to produce the finished items in the specified time frame," William J. Stevenson wrote in his book Production/Operations Management. "Thus, MRP is designed to answer three questions: what is needed? how much is needed? and when is it needed?"
MRP INPUTS
According to Stevenson, the information input into MRP systems comes from three main sources: a bill of materials, a master schedule, and an inventory records file. The bill of materials is a listing of all the raw materials, component parts, subassemblies, and assemblies required to produce one unit of a specific finished product. Each different product made by a given manufacturer will have its own separate bill of materials. The bill of materials is arranged in a hierarchy, so that managers can see what materials are needed to complete each level of production. MRP uses the bill of materials to determine the quantity of each component that is needed to produce a certain number of finished products. From this quantity, the system subtracts the quantity of that item already in inventory to determine order requirements.
MRP OUTPUT
As Stevenson explained, the main outputs from MRP include three primary reports and three secondary reports. The primary reports consist of: planned order schedules, which outline the quantity and timing of future material orders; order releases, which authorize orders to be made; and changes to planned orders, which might include cancellations or revisions of the quantity or time frame. The secondary reports generated by MRP include: performance control reports, which are used to track problems like missed delivery dates and stock outs in order to evaluate system performance; planning reports, which can be used in forecasting future inventory requirements; and exception reports, which call managers' attention to major problems like late orders or excessive scrap rates.
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Question 4b: Explain the various Lot sizing techniques.
Answer: There are a number of lot-sizing techniques available in addition to EOQ. These include the fixed-order quantity, fixed-order-interval model and the single-period model.
FIXED-ORDER-QUANTITY MODEL EOQ is an example of the fixed-order-quantity model since the same quantity is ordered every time an order is placed. A firm might also use a fixed-order quantity when it is captive to packaging situations. If you were to walk into an office supply store and ask to buy 22 paper clips, chances are you would walk out with 100 paper clips. You were captive to the packaging requirements of paper clips, i.e., they come 100 to a box and you cannot purchase a partial box. It works the same way for other purchasing situations. A supplier may package their goods in certain quantities so that their customers must buy that quantity or a multiple of that quantity.
FIXED-ORDER-INTERVAL MODEL The fixed-order-interval model is used when orders have to be placed at fixed time intervals such as weekly, biweekly, or monthly. The lot size is dependent upon how much inventory is needed from the time of order until the next order must be placed (order cycle). This system requires periodic checks of inventory levels and is used by many retail firms such as drug stores and small grocery stores.
SINGLE-PERIOD MODEL. The single-period model is used in ordering perishables, such as food and flowers, and items with a limited life, such as newspapers. Unsold or unused goods are not typically carried over from one period to another and there may even be some disposal costs involved. This model tries to balance the cost of lost customer goodwill and opportunity cost that is incurred from not having enough inventories, with the cost of having excess inventory left at the end of a period.
Question 5a: Explain assembly line balancing clearly defining various terminologies like cycle time, precedence diagram, work stations, efficiency, utilization, balance delay, etc.
Answer: Consider the assembly of a car: assume that certain steps in the assembly line are to install the engine, install the hood, and install the wheels (in that order, with arbitrary interstitial steps); only one of these steps can be done at a time. In traditional production, only one car would be assembled at a time. If engine installation takes 20 minutes, hood installation takes 5 minutes, and wheel installation takes 10 minutes, then a car can be produced every 35 minutes.
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In an assembly line, car assembly is split between several stations, all working simultaneously. When one station is finished with a car, it passes it on to the next. By having three stations, a total of three different cars can be operated on at the same time, each one at a different stage of its assembly.
After finishing its work on the first car, the engine installation crew can begin working on the second car. While the engine installation crew works on the second car, the first car can be moved to the hood station and fitted with a hood, then to the wheels station and be fitted with wheels. After the engine has been installed on the second car, the second car moves to the hood assembly. At the same time, the third car moves to the engine assembly. When the third car’s engine has been mounted, it then can be moved to the hood station; meanwhile, subsequent cars (if any) can be moved to the engine installation station.
Assuming no loss of time when moving a car from one station to another, the longest stage on the assembly line determines the throughput (20 minutes for the engine installation) so a car can be produced every 20 minutes, once the first car taking 35 minutes has been produced.
Question 5b: Explain the key elements to successful JIT.
Answer: The following five steps must be followed to successfully implement a JIT system
Step One: Awareness Revolution This step includes redesigning old management techniques and implementing new techniques and styles. Furthermore, management should review all new concepts with all interacting employees to build confidence and a belief that the new method will work. It is important that employees are fully engaged in the implementation process and assist in identifying and correcting all noticeable mistakes immediately. Employees should also be informed about new developments and changes within the system and an emphasis should be made on continuous improvements. Continuous improvements can also be defined as improvements with no limits.
Step Two: Concepts for Workplace Improvement This step requires an evaluation and prioritization of corporate requirements and a disregard for corporate needs that do not promote efficiency. Employees must maintain a clean and orderly work environment by placing inventory or raw materials, supplies and tools in a logical, orderly manner. For example, items that are used most frequently should be located in a convenient location.
Employees can further ensure production efficiency by maintaining all equipment on an ongoing basis. Additionally, rules and employee codes of conduct should be established, practiced and monitored to ensure compliance.
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Employee compliance can be monitored through one on one meetings, observation of employees while at work and check-listed inspections.
Step Three: Flow Manufacturing Step three is the production of a single piece of product at a given time. This can be achieved by hiring and training multi skilled workers. In addition the production manager should follow a strict cycle time to ensure production deadlines are achieved. Furthermore compact machinery should be used in the production facilities to ensure the facilities space is being used most efficiently.
Step Four: Standard Operations Step four of the implementation phase includes following efficiency rules to ensure that quality products are produced as economically as possible. These efficiency rules may suggest arranging people, products and machines in a way that maximizes production efficiency. Furthermore operations charts, work sequence, and maintaining a standard stock of high volume production components have been identified as tools and methods that can be used to improve efficiency.
Step Five: Multiprocessor Handling Step five suggests that one worker is responsible for several processes in a work cell. This can be facilitated by hiring multi skilled workers. These employees should be properly trained so that they are able to perform on several different machines and be capable of handling various production processes.
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Assignment – B
Question 1: Explain, long-range, medium-range and short-term capacity planning methods?
Answer: Plans can be long range, medium range, or short range depending on the time required to complete the action. The time spans of these different ranges depend on the operational environment of the organization. The long-range planning horizon should exceed the time required to acquire new facilities and equipment. This may require 10 years or longer for organizations involved in the extraction process where new mines must be developed. It may be as short as 18 months for the machine shop where facilities and equipment are catalog items,
Medium-range planning is the development of the aggregate production rates and aggregate levels of inventory for product groups within the constraints of a given facility. Expansion of capacity within the medium-range planning period is limited to increasing personnel or shifts, scheduling overtime, acquiring more efficient tooling, subcontracting, and perhaps adding some types of equipment that can be obtained on short notice.
Medium-range planning usually covers a period beginning 1 to 2 months in the future and ending 12 to 18 months in the future. Its exact boundaries depend on the time constraints for changing levels of production in a particular situation. The planning horizon for medium-range planning is usually at least as long as the longest product lead time. In this context, we define lead time as the time from recognizing that an order for material must be placed until that material is present in a finished good. If medium-term planning uses a horizon shorter than this, material planning cannot properly be performed.
There is no precise definition for the length of the short-term planning horizon. Although detailed schedules and assignments of people and machines to tasks usually do not occur until well within the short-range period, the development of the production schedule frequently bridges the medium- and short-range planning periods. Planning is a continuous activity, and refinement of medium-range forecasts and plans to the detail required in preparing the first draft of a short-range version of the production schedule may take place gradually over a number of weeks.
Some interactions of PIM activities frequently take place in more than one time frame. For example, resource requirements planning for facilities may be performed years in advance of production, while some equipment purchases can be initiated a few months before needed. In addition, the master production schedule frequently covers both the medium-range and short-range planning periods.
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Question 2a: What are various batch processing techniques?
Answer: Batch processing is execution of a series of programs ("jobs") on a computer without manual intervention.
Batch jobs are set up so they can be run to completion without manual intervention, so all input data is preselected through scripts or command-line parameters. This is in contrast to "online" or interactive programs which prompt the user for such input. A program takes a set of data files as input, process the data, and produces a set of output data files. This operating environment is termed as "batch processing" because the input data are collected into batches on files and are processed in batches by the program.
Data processing A typical batch processing procedure is End of day-reporting (EOD), especially on mainframes. Historically systems were designed to have a batch window where online subsystems were turned off and system capacity was used to run jobs common to all data (accounts, users or customers) on a system. In a bank, for example, EOD jobs include interest calculation, generation of reports and data sets to other systems, print (statements) and payment processing.
Printing A popular computerized batch processing procedure is printing. This normally involves the operator selecting the documents they need printed and indicating to the batch printing software when, where they should be output and priority of the print job. Then the job is sent to the print queue from where printing daemon sends them to the printer.
Databases Batch processing is also used for efficient bulk database updates and automated transaction processing, as contrasted to interactive online transaction processing (OLTP) applications.
Images Batch processing is often used to perform various operations with digital images. There exist computer programs that let one resize, convert, watermark, or otherwise edit image files.
Converting Batch processing is also used for converting a number of computer files from one format to another. This is to make files portable and versatile especially for proprietary and legacy files where viewers are not easy to come by.
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Question 2b: Explain the concept of theory of constraints and synchronous manufacturing.
Answer: Theory of Constraints (TOC) is an overall management philosophy introduced by Dr. Eliyahu M. Goldratt in his 1984 book titled The Goal, that is geared to help organizations continually achieve their goal. The title comes from the contention that any manageable system is limited in achieving more of its goal by a very small number of constraints, and that there is always at least one constraint. The TOC process seeks to identify the constraint and restructure the rest of the organization around it, through the use of the Five Focusing Steps.
Synchronous Manufacturing is the most popular application of the Theory of Constraints.
While the Theory of Constraint is certainly best known for its application to production scheduling, Synchronous Manufacturing is a broader concept that implies ALL the elements of a business – not just production – working in sync to achieve the strategic goals of the business.
Still, the heart of a Synchronous Manufacturing implementation is a shop schedule that actually works.
What we mean by "works" is, a schedule that remains valid and keeps the plant pumping out the right products on time to meet delivery schedules, despite "Murphy" – despite inaccurate data, absenteeism, machine breakdowns, unreliable vendors, unexpected scrap, etc.
And yes – we can develop these schedules just as easily in job shops where no two products or routings are ever the same, as in a plant with a standard product line.
One of the beauties of this technique is that schedules developed and managed using the Drum-Buffer-Rope (DBR) technique of Synchronous Manufacturing produce short lead times, fast flow, and low inventory ... yet these schedules are extremely robust, they remain valid while all sorts of things can go wrong in the plant.
Question 2b: Explain the concept of theory of constraints and synchronous manufacturing.
Answer: (a) Kanban: Kanban is a signaling system to trigger action. As its name
suggests, kanban historically uses cards to signal the need for an item. However, other devices such as plastic markers (kanban squares) or balls (often golf balls) or an empty part-transport trolley or floor location can also be used to trigger the movement, production, or supply of a unit in a factory.
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It was out of a need to maintain the level of improvements that the kanban system was devised by Toyota. Kanban became an effective tool to support the running of the production system as a whole. In addition, it proved to be an excellent way for promoting improvements because reducing the number of kanban in circulation highlighted problem areas
b) Scheduling and sequencing Scheduling is the process of deciding how to commit resources between
varieties of possible tasks. Time can be specified (scheduling a flight to leave at 8:00) or floating as part of a sequence of events.
In mathematics, a sequence is an ordered list of objects (or events). Like a set, it contains members (also called elements or terms), and the number of terms (possibly infinite) is called the length of the sequence. Unlike a set, order matters, and the exact same elements can appear multiple times at different positions in the sequence.
c) System nervousness The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous system of vertebrates (such as humans) contains the brain, spinal cord, and retina. The peripheral nervous system consists of sensory neurons, clusters of neurons called ganglia, and nerves connecting them to each other and to the central nervous system. These regions are all interconnected by means of complex neural pathways. The enteric nervous system, a subsystem of the peripheral nervous system, has the capacity, even when severed from the rest of the nervous system through its primary connection by the vagus nerve, to function independently in controlling the gastrointestinal system.
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Case Study
2.- A company is setting up an assembly line to produce 192 units per eight-hour shift. The following table identifies the work elements, items, and immediate predecessors.
Work element Time (seconds) Immediate predecessor(s)
A 40 None B 80 A C 30 D, E, F D 25 B E 20 B F 15 B G 120 A H 145 G I 130 H J 115 C, I
Total 720 Questions:
a) What is the desired cycle time? b) What is the theoretical minimum number of work stations? c) Use the largest work element time rule to work out a solution. d) What are the idle time, efficiency and balance delay for the
solution? Answer.-
On this one, I used a WinQSB Program to solve all needed. Here are the results:
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Question 3.- A laundry has three operations washing drying and ironing for the linen it receives from various customers. The laundry has 7 jobs at hand to be sequenced for the three activities. The activity times for the various jobs on hand is given in the following table.
Job Washing Drying Ironing A 1 7 8 B 3 3 10 C 7 8 9 D 9 2 11 E 4 8 9 F 5 6 14 G 2 1 12
a) Sequence these jobs using Johnson’s method and find the overall processing time.
b) Find out the waiting time for the jobs. c) Find out the idling times for the machines. d) What are the conditions for using Johnson’s rule?
Aswer.- First, Find these data: min Machine 1 – M1 (Washing) max Machine 2 – M2 (Drying) min Machine 3 – M3 (Ironing) If min M1 ≥ max M2 or min M3 ≥ max M2, the sequence can be solved as a 2-machine type. min M1 = 1 max M2 = 8 min M3 = 8
Criteria Result min M1 ≥ max M2 � min M3 ≥ max M2 �
One of conditions apply. Now, M1’ and M2’ are created. M1’i = M1i + M2i M2’I = M2i + M3i New Matrix is created.
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Job M1’ M2’ A 8 15 B 6 13 C 15 17 D 11 13 E 12 17 F 11 20 G 3 13
a.- Lets get started. Min time registered is 3 in Job G on Column M1’. As it is on M1’, List first. Job G done.
G
Next Min time is 6 in Job B on column M1’. List first cause it is on M1’. Job B done.
G B
Next is 8 in Job A on column M1’. Listed First. Job A done.
G B A
Next min time is a tie on 11, registered by Job D and F. Arbitrarily, Job F selected. Listed First. Job F and also Job D done.
G B A F D
Next is Job E with 12 on M1’. Job E done.
G B A F D E C
And finally, Job C is placed on the missing spot. So, Sequence is:
G B A F D E C
Times for Machine 1:
2 3
Times for Machine 2:
1 3
Times for Machine 3:
12 10
To Find the Overall Processing Time, It’s important to make a Gantt Diagram as follows: As marked, The Overall Processing Time is = 76on M3 process and sum every time amount: 3 (idle) + 12 (G) + 10 (B) + 8 (A) + 14 (F) + 11 (D) + 9 (E) + 9 (C) =
M1
M2
M3
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1 5 9 4
7 6 2 8
8 14 11 9
the Overall Processing Time, It’s important to make a Gantt Diagram as
The Overall Processing Time is = 76 . To get to this number, focus on M3 process and sum every time amount:
12 (G) + 10 (B) + 8 (A) + 14 (F) + 11 (D) + 9 (E) + 9 (C) =
7
8
9
the Overall Processing Time, It’s important to make a Gantt Diagram as
. To get to this number, focus
12 (G) + 10 (B) + 8 (A) + 14 (F) + 11 (D) + 9 (E) + 9 (C) = 76
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b.- To find waiting time for jobs, calculate as follows: JOB G 0 (From M1 to M2) + 0 (From M2 to M3) = 0 JOB B 0 (From M1 to M2) + 9 (From M2 to M3) = 9 JOB A 0 (From M1 to M2) + 12 (From M2 to M3) = 12 JOB F 3 (From M1 to M2) + 14 (From M2 to M3) = 17 JOB D 0 (From M1 to M2) + 25 (From M2 to M3) = 25 JOB E 0 (From M1 to M2) + 26 (From M2 to M3) = 26 JOB C 1 (From M1 to M2) + 27 (From M2 to M3) = 28
Job G B A F D E C
Waiting Time 0 9 12 17 25 26 28
c.- The Idle time for each Machine is as follows: M1 = 76 – 31 = 45 M2 = 2 + 1 + 2 + (76 – 40) = 41 M3 = 3
Machine Washing Drying Ironing
IdlingTime 45 41 3
d.- The conditions are as described on all the problem solution:
Must be valid one of these criteria: (min M1 ≥ max M2) or (min M3 ≥ max M2) to solve easily as a 2-machine model.
Finding a tie assigning Machines and process is to the solver subjective criteria.
Finally, graph a Gantt Diagram to accomplish all jobs, duration times and Machines as well.
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1. Which of the following is not a characteristic of a production system a) It is a universally applicable model b) Varies from enterprise to enterprise c) It is a framework within which production activities take place d) Ensures coordination of various production operations
2. Which of the following is not a type of production system a) Continuous production b) Job or unit production c) Intermittent production d) Flexible manufacturing
3. All of the following are production functions except a) Aggregate planning b) Pricing of products c) Capacity assessment d) Scheduling of operations
4. Order winner means a) The sales person who gets the order b) The factor of the product that wins the order for the firm c) Order that results in high profits d) Repeat order
5. All of the following are functions of forecasting except a) An estimation tool b) A tool for predicting events related to operations planning and control c) An input for the JIT system d) A vital prerequisite for the planning process
6. Degree of uncertainty in short term forecasting is a) High b) Low c) Nil d) Significant
7. All of the following are key areas of forecasting except a) Better materials management b) Rationalized manpower decisions c) Basis for planning and scheduling d) Routine decisions
8. Which of the following is a dependent demand for an organization manufacturing refrigerators
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a) Compressor b) Requirement for a DG set c) Refrigerators d) Tea coffee vending machine
9. If a forecast repeatedly overestimates actual demand, bias will have a) Positive value b) Negative value c) Zero value d) Infinity
10. Which of the following is not a qualitative method of forecasting a) Delphi method b) Historical data c) Econometric models d) Nominal group technique
11. The most suitable method for forecasting the demand for a brand new product is
a) Moving averages b) Historical data c) Exponential smoothening d) Delphi method
12. The planning that addresses the supply side of a firm’s ability to meet the demand is known as
a) Business plan b) Aggregate production planning c) Aggregate capacity planning d) Master production scheduling
13. Which of the following is not a considerations in developing an aggregate production plan
a) Concept of aggregation b) Goal for aggregate planning c) Forecast of aggregate demand d) Supplier lead time
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14. The aggregate production planning strategy that cannot be employed in a strong union environment is
a) Changing inventory levels b) Changing workforce levels c) Subcontracting d) Influencing demand
15. Which of the following is not an alternative for managing supply a) Inventory based alternatives b) Promotional schemes c) Capacity adjustment d) Capacity augmentation
16. All of the following are capacity adjustment alternatives except a) Hiring/ Firing of workers b) Varying shifts c) Varying working hours d) Subcontracting
17. Which of the following is not an aggregate production planning method
a) Trial-and-error method b) Transportation method c) Linear programming method d) Assignment method
18. All of the following are characteristics of Master Production Scheduling except
a) MPS makes use of actual customer orders b) Product varieties are taken care of in MPS c) MPS is a critical linkage between planning and execution of operations d) It is same as rough cut capacity planning
19. Which is not a characteristic of a Bill Of Materials a) List all parts required for one unit of a product b) Shows dependency relationships c) Gives total number of a part used in a product d) Indicates multi levels of a product
20. All of the following are time phasing requirement of an MRP logic except
a) Gross requirement will occur at the middle of a period b) On hand inventory will be measured at the end of a period c) Planned order release will occur at the beginning of a period d) Lead time considerations are not taken for time phasing
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21. Which of the following is not an input to the MRP system a) The Master Production Schedule b) Bill of materials c) Engineering drawing d) Inventory status file
22. Which of the following is not a Lot sizing technique a) The lot-for lot technique b) The EOQ approach c) Mini-Max approach d) Period order quantity approach
23. The process of tracing the effect of one component in another is called
a) Pegging b) Cycle counting c) Lot sizing d) Time fencing
24. Stability in an MRP is achieved by a) Updating b) Cycle counting c) Lot Sizing d) Time fencing
25. Time fence means a) The shortest lead-time from raw material to finished production of an
item b) Ensuring accuracy of inventory records c) Method used to update MRP at regular intervals d) Calculating net requirements of components
26. All of the following are characteristics of capacity except a) It is the maximum rate at which a system can accomplish work b) Capacity depends on the bottleneck c) Capacity is the productive capability of a facility d) Capacity is measured in monetary terms
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27. Operations managers are concerned with capacity for several reasons. Which of the following is not a concern
a) Enough capacity to meet customer demands b) Capacity affects cost efficiency of operations c) Investment required in capacity d) Machine locations in a facility
28. Which of the following is not a short term strategy for modifying capacity
a) Inventories b) Employment levels c) Subcontracting d) Expansion
29. All of the following are steps in capacity control except a) Monitoring of output b) Comparing with capacity plan c) Assessing demand d) Taking corrective actions
30. Multi-skilling of work force doesn’t results in a) Increasing capacity b) Increasing flexibility c) Improving productivity d) Waste elimination
31. Activity not associated with Dispatching is a) Issue of instructions concerning movement of materials between work
centers b) Issue of instructions to operators c) Loading work centers with jobs d) Issue instructions concerning the issue and return of special tools
32. Routing doesn’t include a) Sequence of processes, operations for a product b) Machines, tools, work stations used in producing the product c) Standard time applicable for each operation d) Detailed skills of the operator for each operation
33. Three planning premises are used in production management. Which of the following is not one among them
a) Make to stock b) Make to order c) Assemble to order d) Make subassemblies
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34. A strategy that is not used for altering lead time is a) Overlapping b) Lot sizing c) Operations splitting d) Lot splitting
35. Backlogs can be reduced by all of the following except a) Increasing work center capacity b) Reducing order release rate c) Increasing lead time d) Subcontracting
36. Priority index in scheduling is also known as a) Critical ratio b) Critical Path c) Random number d) Earliest due date
37. All of the following are characteristics of flow shop production except
a) Special purpose equipment b) Many number of end items c) Low skilled workers d) Low in process inventories
38. Which of the following is not a characteristic of job shop production a) Multipurpose equipment b) Highly skilled workers c) High investment d) Low raw material inventory
39. Bottleneck operation in line balancing means a) Having high operation time b) Having high cycle time c) Having low operation time d) Having more no. of follower operations
40. Which of the following is not associated with line balancing a) Precedence diagrams b) Cycle time c) Closeness matrix d) Minimum number of workstations