UNIT - 2 computer integrated manufacturing.pptx

computer integrated manufacturing

1. UNIT II PRODUCTION PLANNING & CONTROL SYSTEM AND COMPUTER AIDED PROCESS PLANNING Production planning and Control System - Aggregate Production Planning and Master Production Schedule – Material Requirement Planning (MRP I) – Simple Problems –Capacity Planning – Shop Floor Control – Inventory Control – EOQ, WIP costs & Inventory Holding Costs - Simple Problems – Introduction to Manufacturing Resource Planning (MRP II) & Enterprise Resource Planning (ERP) - Process planning – Manual Process Planning and case studies Computer Aided Process Planning (CAPP)

2. Production Planning and Control Production planning and control (PPC) is concerned with the logistics problems that are encountered in manufacturing, that is, managing the details of what and how many products to produce and when, and obtaining the raw materials, parts, and resources to produce those products. PPC solves these logistics problems by managing information. Computers are essential for processing the tremendous amounts of data involved to define the products and the means to produce them, and for reconciling these technical details with the desired production schedule. In a very real sense, PPC is the integrator in computer-integrated manufacturing. ‹#›

3. Production Planning Production planning consists of deciding which products to make, in what quantities, and when they should be completed; scheduling the delivery and/or production of the parts and products; and planning the manpower and equipment resources needed to accomplish the production plan. Activities ‹#›

4. Production Planning Activities 1. Aggregate production planning This involves planning the production output levels for major product lines produced by the firm. These plans must be coordinated among various functions in the firm, including product design, production, marketing, and sales. 2. Master production planning. The aggregate production plan must be converted into a master production schedule (MPS) which is a specific plan of the quantities to be produced of individual models within each product line. ‹#›

5. Production Planning Activities 3. Material requirements planning (MRP). MRP is a planning technique, usually implemented by computer, that translates the MPS of end products into a detailed schedule for the raw materials and parts used in those end products. 4. Capacity planning. This is concerned with determining the labor and equipment resources needed to achieve the master schedule. ‹#›

6. Activities of Production Planning and Control ‹#›

7. Structure of MRP ‹#›

8. Material Requirements Planning Material requirements planning (MRP) is a computational technique that converts the master schedule for end products into a detailed schedule for the raw materials and components used in the end products. The detailed schedule identifies the quantities of each raw material and component item. It also indicates when each item must be ordered and delivered to meet the master schedule for final products. MRP is often thought of as a method of inventory control. It is both an effective tool for minimizing unnecessary inventory investment and a useful technique in production scheduling and purchasing of materials. ‹#›

9. Material Requirements Planning The distinction between independent demand and dependent demand is important in MRP. Independent demand means that demand for a product is unrelated to demand for other items. Final products and spare parts are examples of items whose demand is independent. Independent demand patterns must usually be forecasted. Dependent demand means that demand for the item is directly related to the demand for some other item, typically a final product. The dependency usually derives from the fact that the item is a component of the other product. Component parts, raw materials, and subassemblies are examples of items subject to dependent demand. ‹#›

10. Material Requirements Planning Whereas demand for the firm’s end products must be forecasted (in the absence of customer orders), the raw materials and component parts used in the end products should not be forecasted. Once the delivery schedule for end products is established, the requirements for components and raw materials can be directly calculated. For example, even though demand for a given model of automobile each month can only be forecasted, once the quantity is established and production is scheduled, it is known that five tires will be needed to deliver the car. ‹#›

11. Material Requirements Planning MRP is the appropriate technique for determining quantities of dependent demand items. These items constitute the inventory of manufacturing: raw materials, work-in-process (WIP), component parts, and subassemblies. That is why MRP is such a powerful technique in the planning and control of manufacturing inventories. For independent demand items, inventory control is often accomplished using order point systems ‹#›

12. Material Requirements Planning The concept of MRP is relatively straightforward. Its implementation is complicated by the sheer magnitude of the data to be processed. The master schedule provides the overall production plan for the final products in terms of month-by-month deliveries. Each product may contain hundreds of individual components. These components are produced from raw materials, some of which are common among the components. For example, several components may be made out of the same gauge sheet steel. The components are assembled into simple subassemblies, and these subassemblies are put together into more complex subassemblies, and so on, until the final products are assembled. ‹#›

13. Material Requirements Planning Each step in the manufacturing and assembly sequence takes time. All of these factors must be incorporated into the MRP calculations. Although each calculation is uncomplicated, the magnitude of the data is so large (at least for products of more than a few components) that the application of MRP is impractical without computer processing. ‹#›

14. INPUTS TO THE MRP SYSTEM To function, the MRP program needs data contained in several files that serve as inputs to the MRP processor. They are (1) the master production schedule (2) the bill of materials file and other engineering and manufacturing data, and (3) the inventory record file. Capacity planning also provides input to ensure that the MRP schedule does not exceed the production capacity of the firm. ‹#›

15. MASTER PRODUCTION SCHEDULE The MPS lists what end products and how many of each are to be produced and when they are to be ready for shipment. Manufacturing firms generally work on monthly delivery schedules, but the master schedule uses weeks as the time periods. Whatever the duration, these time periods are called time buckets in MRP. Instead of treating time as a continuous variable (which of course, it is), MRP makes its computations of materials and parts requirements in terms of time buckets. ‹#›

16. MASTER PRODUCTION SCHEDULE ‹#›

17. BILL OF MATERIALS The bill of materials (BOM) file provides information on the product structure by listing the component parts and subassemblies that make up each product. It is used to compute the raw material and component requirements for end products listed in the master schedule. Product structure for product P1 ‹#›

18. BILL OF MATERIALS Product P1 is composed of two subassemblies, S1 and S2, each of which is made up of components C1, C2, and C3, and C4, C5, and C6, respectively. Finally, at the bottom level are the raw materials that go into each component. The items at each successively higher level are called the parents of the items feeding into it from below. For example, S1 is the parent of C1, C2, and C3. The product structure must also specify the number of each subassembly, component, and raw material that go into its respective parent. These numbers are shown in parentheses in the figure. ‹#›

19. INVENTORY RECORD FILE The inventory record file is referred to as the item master file in a computerized inventory system. The types of data contained in the inventory record are divided into three segments: 1. Item master data: This provides the item’s identification (part number) and other data about the part such as order quantity and lead times. 2. Inventory status: This gives a time-phased record of inventory status. In MRP, it is important to know not only the current level of inventory, but also any future changes that will occur against the inventory. Therefore, the inventory status segment lists the gross requirements for the item, scheduled receipts, on-hand status, and planned order releases. 3. Subsidiary data: The third file segment provides subsidiary data such as purchase orders, scrap or rejects, and engineering changes. ‹#›

20. How MRP Works The MRP processor operates on data contained in the MPS, the BOM file, and the inventory record file. The master schedule specifies the period-by-period list of final products required, the BOM defines what materials and components are needed for each product, and the inventory record file gives the current and future inventory status of each product, component, and material. The MRP processor computes how many of each component and raw material are needed each period by “exploding” the end product requirements into successively lower levels in the product structure. ‹#›

21. How MRP Works The MRP processor operates on data contained in the MPS, the BOM file, and the inventory record file. The master schedule specifies the period-by-period list of final products required, the BOM defines what materials and components are needed for each product, and the inventory record file gives the current and future inventory status of each product, component, and material. The MRP processor computes how many of each component and raw material are needed each period by “exploding” the end product requirements into successively lower levels in the product structure. ‹#›

22. How MRP Works Several complicating factors must be considered during the MRP computations. First, the quantities of components and subassemblies do not account for any of those items that may already be stocked in inventory or are expected to be received as future orders. Accordingly, the computed quantities must be adjusted for any inventories on hand or on order, a procedure called netting. For each time bucket, net requirements = gross requirements less on-hand inventories and quantities on order. ‹#›

23. How MRP Works Second, quantities of common-use items must be combined during parts explosion to determine the total quantities required for each component and raw material in the schedule. Common-use items are raw materials and components that are used on more than one product. MRP collects these common-use items from different products to achieve economies in ordering the raw materials and producing the components. Third, lead times for each item must be taken into account. The lead time for a job is the time that must be allowed to complete the job from start to finish. ‹#›

24. How MRP Works There are two kinds of lead times in MRP: ordering lead times and manufacturing lead times. Ordering lead time for an item is the time required from initiation of the purchase requisition to receipt of the item from the vendor. If the item is a raw material that is stocked by the vendor, the ordering lead time should be relatively short, perhaps a few days or a few weeks. If the item is fabricated, the lead time may be substantial, perhaps several months. Manufacturing lead time is the time required to produce the item in the company’s ownplant, from order release to completion, once the raw materials for the item are available. ‹#›

25. How MRP Works The scheduled delivery of end products must be translated into time-phased requirements for components and materials by factoring in the ordering and manufacturing lead times. ‹#›

26. MRP Outputs The MRP program generates a variety of outputs that can be used in planning and managing plant operations. The outputs include planned order releases, which provide the authority to place orders that have been planned by the MRP system; reports of planned order releases in future periods; rescheduling notices, indicating changes in due dates for open orders; cancelation notices, indicating that certain open orders have been canceled because of changes in the MPS; reports on inventory status; performance reports of various types, indicating costs, item usage, actual versus planned lead times, and so on; ‹#›

27. MRP Outputs exception reports, showing deviations from the schedule, orders that are overdue, scrap, and so on; and inventory forecasts, indicating projected inventory levels in future periods. Of the MRP outputs listed above, the planned order releases are the most important because they drive the production system. Planned order releases are of two kinds, purchase orders and work orders. Purchase orders provide the authority to purchase raw materials or parts from outside vendors, with quantities and delivery dates specified. Work orders generatethe authority to produce parts or assemble subassemblies or products in the company’s own factory. Again, quantities to be completed and completion dates are specified. ‹#›

28. Benefits of MRP reduction in inventory, quicker response to changes in demand than is possible with a manual requirements planning system, reduced setup and product changeover costs, Better machine utilization, improved capacity to respond to changes in the master schedule, and aid in developing the master schedule. ‹#›

29. Limitations of MRP Some MRP systems have not been successful because the application was not appropriate, usually because the product structure did not fit the data requirements of MRP; the MRP computations were based on inaccurate data; and the MPS was not coupled with a capacity planning system, so the MRP program generated an unrealistic schedule of work orders that overloaded the factory. ‹#›

30. Shop Floor Control (SFC) ‹#›

31. Shop Floor Control Shop floor control (SFC) is the set of activities in production control that are concerned with releasing production orders to the factory, monitoring and controlling the progress of the orders through the various work centers, and acquiring current information on the status of the orders . A typical SFC system consists of three phases: Order release, Order scheduling, and Order progress. ‹#›

32. Shop Floor Control In modern implementations of shop floor control, these phases are executed by a combination of computer and human resources, with a growing proportion accomplished by computer automated methods. The term manufacturing execution system (MES) is used for the computer software that supports SFC and that typically includes the capability to respond to on-line inquiries concerning the status of each of the three phases. Other functions often included in an MES are generation of process instructions, real-time inventory control, machine and tool status monitoring, and labor tracking. In addition, an MES usually provides links to other modules in the firm’s information system, such as quality control, maintenance, and product design data. ‹#›

33. Shop Floor Control Phase -1 : Order Release The order release phase of shop floor control provides the documentation needed to process a production order through the factory. The collection of documents is sometimes called the shop packet. It typically includes the route sheet, which documents the process plan for the item to be produced. material requisitions to draw the necessary raw materials from inventory. job cards or other means to report direct labor time devoted to the order and to indicate progress of the order through the factory. ‹#›

34. Shop Floor Control Phase -1 : Order Release move tickets to authorize the material handling personnel to transport parts between work centers in the factory if this kind of authorization is required. The parts list, if required for assembly jobs. In the operation of a conventional factory, which relies heavily on manual labor, these are paper documents that move with the production order and are used to track its progress through the shop. In a modern factory, automated identification and data capture technologies are used to monitor the status of production orders, rendering the paper documents (or at least some of them) unnecessary. ‹#›

35. Shop Floor Control Phase -2 : Order Scheduling The order release phase is driven by two inputs The first is the authorization to produce that derives from the master schedule. This authorization proceeds through MRP, which generates work orders with scheduling information. The second input to the order release phase is the engineering and manufacturing database that provides the product structure and process plans needed to prepare the various documents that accompany the order through the shop. ‹#›

36. Shop Floor Control Phase -2 : Order Scheduling The order scheduling phase follows directly from the order release phase and assigns the production orders to the various work centers in the plant. In effect, order scheduling executes the dispatching function in PPC. The order scheduling phase prepares a dispatch list that indicates which production orders should be accomplished at the various work centers. It also provides information about relative priorities of the different jobs, for example, by showing due dates for each job. ‹#›

37. Shop Floor Control Phase -2 : Order Scheduling In shop floor control, the dispatch list guides the shop foreman in making work assignments and allocating resources to different jobs to comply with the master schedule. The order scheduling phase in shop floor control is intended to solve two problems in production control: (1) machine loading and (2) job sequencing. To schedule a given set of production orders or jobs in the factory, the orders must first be assigned to work centers. ‹#›

38. Shop Floor Control Phase -2 : Order Scheduling Allocating orders to work centers is referred to as machine loading. The term shop loading is also used, which refers to the loading of all machines in the plant. Since the total number of production orders usually exceeds the number of work centers, each work center will have a queue of orders waiting to be processed. The remaining question is: In what sequence should these jobs be processed? Answering this question is the problem in job sequencing , which involves determining the sequence in which the jobs will be processed through a given work center. ‹#›

39. Shop Floor Control Phase -2 : Order Scheduling To determine this sequence, priorities are established among the jobs in the queue, and the jobs are processed in the order of their relative priorities. Priority control is a term used in production control to denote the function that maintains the appropriate priority levels for the various production orders in the shop. Some of the dispatching rules used to establish priorities for production orders in the plant include: First-come-first served: Jobs are processed in the order in which they arrive at the machine. One might argue that this rule is the most fair. ‹#›

40. Shop Floor Control Phase -2 : Order Scheduling Earliest due date: Orders with earlier due dates are given higher priorities. Shortest processing time : Orders with shorter processing times are given higher priorities. Least slack time: Slack time is defined as the difference between the time remaining until due date and the process time remaining. Orders with the least slack in their schedule are given higher priorities. Critical ratio: The critical ratio is defined as the ratio of the time remaining until due date divided by the process time remaining. Orders with the lowest critical ratio are given higher priorities. ‹#›

41. Shop Floor Control Phase -2 : Order Scheduling When an order is completed at one work center, it enters the queue at the next machine in its process routing. That is, the order becomes part of the machine loading for the next work center, and priority control is utilized to determine the sequence of processing among the jobs at that machine. ‹#›

42. Shop Floor Control Phase -2 : Order Scheduling The relative priorities of the different orders may change over time. Reasons behind these changes include (1) lower or higher than expected demand for certain products, (2) equipment breakdowns that cause delays in production, (3) cancellation of an order by a customer, and (4) defective raw materials that delay an order. The priority control function reviews the relative priorities of the orders and adjusts the dispatch list accordingly. ‹#›

43. Shop Floor Control Phase -3: Order Progress The order progress phase in shop floor control monitors the status of the various orders in the plant, work-in-process, and other measures that indicate the progress of production. The function of the order progress phase is to provide information that is useful in managing the factory. The information presented to production management is often summarized in the form of reports. Work order status reports. These reports indicate the status of production orders. Typical information in the report includes the current work center where each order is located, processing hours remaining before completion of each order, whether each job is on time or behind schedule, and the priority level of each order. ‹#›

44. Shop Floor Control Phase -3 : Order Progress Progress reports: A progress report is used to report performance of the shop during a certain time period (e.g., a week or month in the master schedule). It provides information on how many orders were completed during the period, how many orders should have been completed during the period but were not, and so forth. Exception reports: An exception report identifies deviations from the production schedule (e.g., overdue jobs) and similar nonconformities. These reports are useful to production management in making decisions about allocation of resources, authorization of overtime hours, and other capacity issues, and in identifying problem areas in the plant that adversely affect achieving the master production schedule. ‹#›

45. Shop Floor Control Factory Data Collection System Various techniques are used to collect data from the factory floor. These techniques range from manual methods that require workers to fill out paper forms that are later compiled to fully automated methods that require no human participation. The factory data collection system (FDC system) consists of the various paper documents, terminals, and automated devices located throughout the plant for collecting data on shop floor operations, plus the means for compiling and processing the data. The factory data collection system serves as an input to the order progress phase in shop floor control. ‹#›

46. Shop Floor Control Factory Data Collection System It is also an input to priority control, which affects order scheduling. Examples of the types of data on factory operations collected by the FDC system include: Piece counts completed at each work center Scrapped parts and parts needing rework Operations completed in the routing sequence for each order Direct labor time expended on each order Machine downtime. The data collection system can also include the time clocks used by employees to punch in and out of work. ‹#›

47. Shop Floor Control Factory Data Collection System It is also an input to priority control, which affects order scheduling. Examples of the types of data on factory operations collected by the FDC system include: Piece counts completed at each work center Scrapped parts and parts needing rework Operations completed in the routing sequence for each order Direct labor time expended on each order Machine downtime. The data collection system can also include the time clocks used by employees to punch in and out of work. ‹#›

48. Shop Floor Control Factory Data Collection System The ultimate purpose of the factory data collection system is twofold: to supply status and performance data to the shop floor control system and to provide current information to production foremen, plant management, and production control personnel. To accomplish this purpose, the factory data collection system must input data to the plant computer system. In current CIM technology, this is done using an on-line mode, in which the data are entered directly into the plant computer system and are immediately available to the order progress phase. ‹#›

49. Shop Floor Control Factory Data Collection System The advantage of on-line data collection is that the data file representing the status of the shop can be kept current at all times. As changes in order progress are reported, these changes are immediately incorporated into the shop status file. Personnel with a need to know can access this status in real time and be confident that they have the most up-to-date information on which to base any decisions. Even though a modern FDC system is largely computerized, paper documents are still used in factory operations ‹#›

50. Shop Floor Control Factory Data Collection System Manual Data Input Techniques Manually oriented techniques of factory data collection require production workers to read from and fill out paper forms indicatingorder progress data. The forms are subsequently turned in and compiled, using a combination of clerical and computerized methods. The paper forms include the following: Job traveler Employee time sheets Operation tear strips Prepunched cards ‹#›

51. Shop Floor Control Factory Data Collection System Automated and Semiautomated Data Collection Systems. To avoid the problems associated with the manual and clerical procedures, some factories use data collection terminals located throughout the factory. Workers input data relative to order progress using simple keypads or conventional alphanumeric keyboards. Data entered by keyboard are subject to error rates of around 0.3% (one error in 300 data entries), an order of magnitude improvement in data accuracy over handwritten entry. ‹#›

52. Shop Floor Control Factory Data Collection System Automated and Semiautomated Data Collection Systems. The data entry methods also include automatic identification and data collection (AIDC) technologies such as bar codes and radio frequency identification (RFID). Certain types of data such as order number, product identification, and operation sequence number can be entered with automated techniques using bar-coded or magnetized cards included with the shop documents. Some of the configurations of data collection terminals that can be installed in the factory include One centralized terminal. Satellite terminals Workstation terminals ‹#›

53. CAPACITY PLANNING Capacity planning consists of determining what labor and equipment resources are required to meet the current MPS as well as long-term future production needs of the firm. Capacity planning also identifies the limitations of the available production resources to prevent the planning of an unrealistic master schedule. Capacity planning is often accomplished in three stages first, during aggregate production planning; second, when the master production schedule is established; and third, when the MRP computations are done. ‹#›

54. THREE STAGES OF CAPACITY PLANNING ‹#›

55. CAPACITY PLANNING During aggregate production planning, the term resource requirements planning (RRP) denotes the evaluation process used to make sure that the aggregate plan is feasible. Downward adjustments may be required if the plan is too ambitious. RRP may also be used to plan for future increases in capacity to match an ambitious plan or to anticipate demand increases in the future. Thus, resource requirements planning is used not only to check the aggregate production plan but also to plan for future expansion (or reduction) of capacity. ‹#›

56. CAPACITY PLANNING In the MPS stage, a capacity calculation called rough-cut capacity planning (RCCP) is made to assess the feasibility of the master schedule. Such a calculation indicates whether there is a significant violation of production capacity in the MPS. On the other hand, if the calculation shows no capacity violation, neither does it guarantee that the production schedule can be met. This depends on the allocation of work orders to specific work cells in the plant. ‹#›

57. CAPACITY PLANNING Accordingly, a third capacity calculation is made at the time the MRP schedule is prepared Called capacity requirements planning (CRP), this detailed calculation determines whether there is sufficient production capacity in the individual departments and in the work cells to complete the specific parts and assemblies that have been scheduled by MRP. If the schedule is not compatible with capacity, then either the plant capacity or the master schedule must be adjusted. ‹#›

58. INVENTORY CONTROL Inventory control attempts to achieve a compromise between two opposing objectives: minimizing the cost of holding inventory and maximizing customer service. Minimizing inventory cost suggests keeping inventory to a minimum, in the extreme, zero inventory. Maximizing customer service implies keeping large stocks on hand so that customer orders can immediately be filled. The types of inventory of greatest interest in Process planning and Cost Estimation are raw materials, purchased components, in-process inventory (WIP), and finished products. ‹#›

59. INVENTORY CONTROL The major costs of holding inventory are (1) investment costs, (2) storage costs, and (3) cost of possible obsolescence or spoilage. These three costs are referred to collectively as carrying costs or holding costs. Investment cost is usually the largest component. When a company borrows money to invest in materials to be processed in the factory, it must pay interest on that money until the customer pays for the finished product. But many months may elapse between start of production and delivery to the customer. Even if the company uses its own money to purchase the starting materials, it is still making an investment that has a cost associated with it. ‹#›

60. INVENTORY CONTROL Companies can minimize holding costs by minimizing the amount of inventory on hand. However, when inventories are minimized, customer service may suffer, inducing customers to take their business elsewhere. This also has a cost, called the stock-out cost. Most companies want to minimize stock-out cost and provide good customer service. Thus, they are caught on the horns of an inventory control dilemma, balancing carrying costs against the cost of poor customer service. Different inventory control procedures are used for independent and dependent demand items. ‹#›

61. INVENTORY CONTROL For dependent demand items, MRP is the most widely implemented technique. For independent demand items, order point inventory systems are commonly used. Order point systems are concerned with two related problems that must be solved when managing inventories of independent demand items: (1) how many units should be ordered? and (2) when should the order be placed? The first problem is often solved using economic order quantity formulas. The second problem can be solved using reorder point methods. ‹#›

62. Economic Order Quantity Formula The problem of deciding on the most appropriate quantity to order or produce arises when the demand rate for the item is fairly constant, and the rate at which the item is produced is significantly greater than its demand rate. This is the typical situation known as make-to-stock. The same basic problem occurs with dependent demand items when usage of the item is relatively constant over time due to a steady production rate of the final product with which the item is correlated. In this case, it may make sense to endure some inventory holding costs so that the frequency of setups and their associated costs can be reduced. ‹#›

63. Economic Order Quantity Formula. In these situations where demand remains steady, inventory is gradually depleted over time and then quickly replenished To some maximum level determined by the order quantity. The sudden increase and gradual reduction in inventory causes the inventory level over time to have a sawtooth appearance. ‹#› Model of inventory level over time in the typical make-to-stock situation.

64. Economic Order Quantity Formula.   ‹#›

65. Economic Order Quantity Formula. The holding cost C h consists of two main components, investment cost and storage cost. Both are related to the time that the inventory spends in the warehouse or factory. The investment cost results from the money the company must invest in the inventory before it is sold to customers. This inventory investment cost can be calculated as the interest rate paid by the company i (percent), multiplied by the value (cost) of the inventory. ‹#›

66. Economic Order Quantity Formula. Storage cost occurs because the inventory takes up space that must be paid for. The amount of the cost is generally related to the size of the part and how much space it occupies. As an approximation, it can be related to the value or cost of the item stored. This is the most convenient method of valuating the storage cost of an item. By this method, the storage cost equals the cost of the inventory multiplied by the storage rate (s). The term s is the storage cost as a fraction (percent) of the value of the item in inventory. ‹#›

67. Economic Order Quantity Formula. Combining interest rate and storage rate into one factor, h = i + s. The term h is called the holding cost rate. Like i and s, it is a fraction (percent) that is multiplied by the cost of the part to evaluate the holding cost of investing in and storing inventory. Accordingly, holding cost can be expressed as follows: C h = hC pc where C h = holding (carrying) cost, Rs./pc/yr; C pc = unit cost of the item, Rs./pc; and h = holding cost rate, rate/yr. ‹#›

68. Economic Order Quantity Formula. Setup cost includes the cost of idle production equipment during the changeover time between batches. The costs of labor performing the setup changes might also be added in. Thus, C su = T su C dt where C su = setup cost, Rs./setup or Rs./order; T su = setup or changeover time between batches, hr/setup or hr/order; and C dt = cost rate of machine downtime during the changeover, Rs./hr. ‹#›

69. Economic Order Quantity Formula.   ‹#›

70. Economic Order Quantity Formula.   ‹#› where EOQ = economic order quantity (number of parts to be produced per batch, pc/batch or pc/order)

71. Economic Order Quantity Formula. The annual demand for a certain item made-to-stock = 15,000 pc/yr. One unit of the item costs Rs.20.00, and the holding cost rate = 18%/yr. Setup time to produce a batch = 5 hr. The cost of equipment downtime plus labor = Rs.150/hr. Determine the economic batch quantity and the total inventory cost for this case. ‹#› Given: Annual Demand (Da) = 15000 pc/yr Unit cost (Cpc) = Rs.20 Setup cost (Csu) = Rs. 150/hr x 5hr C su = Rs. 750 Holding cost per unit (C h ) = 0.18 x Rs. 20 C h = Rs. 3.6 To Find Economic Order Quantity (EOQ) Total Inventory Cost (TIC)

72. Economic Order Quantity Formula. ‹#› EOQ = 2500 Units  

73. Economic Order Quantity Formula. Reorder Point Systems Determining the economic order quantity is not the only problem that must be solved in controlling inventories in make-to-stock situations. The other problem is deciding when to reorder. One of the most widely used methods is the reorder point system. ‹#› Operation of a reorder point inventory system.

74. Economic Order Quantity Formula. Reorder Point Systems When to reorder cannot be predicted with the precision that would exist if demand rate were a known constant value. In a reorder point system, when the inventory level for a given stock item falls to some point specified as the reorder point, then an order is placed to restock the item. The reorder point is specified at a sufficient quantity level to minimize the probability of a stock-out between when the reorder point is reached and the new order is received. Reorder point triggers can be implemented using computerized inventory control systems that continuously monitor the inventory level as demand occurs and automatically generate an order for a new batch when the level declines below the reorder point. ‹#›

75. Manufacturing Resource Planning (MRP II) The initial versions of material requirements planning in the early 1970s were limited to the planning of purchase orders and factory work orders and did not take into account such issues as capacity planning or feedback data from the factory. MRP was strictly a materials and parts planning tool whose calculations were based on the master production schedule (MPS), product structure data, and inventory records. Over time, it became evident that MRP should be tied to other software packages to create a more integrated PPC system. The PPC software packages that evolved from MRP have gone through several generations and enlargements, two of which are described in this section and the following: (1) manufacturing resource planning and (2) enterprise resource planning. ‹#›

76. Manufacturing Resource Planning (MRP II) Manufacturing resource planning evolved from material requirements planning in the 1980s. It came to be abbreviated MRP II to distinguish it from the original abbreviation and to indicate that it was second generation, that is, more than just a material planning system. Manufacturing resource planning can be defined as a computer-based system for planning, scheduling, and controlling the materials, resources, and supporting activities needed to meet the master production schedule. MRP II is a closed-loop system that integrates and coordinates the major functions of the business involved in production. ‹#›

77. Manufacturing Resource Planning (MRP II) This means that MRP II incorporates feedback of data on various aspects of operating performance so that corrective action can be taken in a timely manner; that is, MRP II includes shop floor control. MRP II can be considered to consist of three major modules (1) material requirements planning, or MRP, (2) capacity planning, and (3) shop floor control ‹#›

78. Manufacturing Resource Planning (MRP II) The MRP module accomplishes the planning function for materials, parts, and assemblies, based on the master production schedule, and it provides a factory production schedule that matches the arrival of materials determined by MRP. The capacity planning module interacts with the MRP module to ensure that the schedules created by MRP are feasible. Finally, the shop floor control module performs the feedback control function using its factory data collection system to implement the three phases of order release, order scheduling, and order progress. ‹#›

79. Manufacturing Resource Planning (MRP II) ‹#›

80. Manufacturing Resource Planning (MRP II) There is an overlap between the elements of MRP II in Figure and CAM (manufacturing planning and control). MRP II does not include NC part programming, which is a significant component of CAM, and it does not include quality control or process control of individual operations in the factory. The overlap occurs in the production planning and control functions. So, MRP II can be considered a software package that is used to implement the PPC functions in computer-aided manufacturing and CAM is an essential part of computer-integrated manufacturing. ‹#›

81. Manufacturing Resource Planning (MRP II) Manufacturing resource planning is an improvement over material requirements planning because it includes production capacity and shop floor feedback in its computations. But MRP II is limited to the manufacturing operations of the firm. As further enhancements were made to MRP II systems, the trend was to consider all of the operations and functions of the enterprise rather than just manufacturing. The culmination of this trend in the 1990s was enterprise resource planning. ‹#›

82. Enterprise Resource Planning (ERP) Enterprise resource planning (ERP) is a computer software system that organizes and integrates all of the business functions and associated data of an organization through a single, central database. The functions include sales, marketing, purchasing, design, production, distribution, finance, human resources, and more. In the software of an ERP system, these business functions are organized into modules, each focused on a different function or group of functions within the organization. Each module and the business functions within it are designed with “best practices” in mind, which means that the software vendor has attempted to incorporate the best way to accomplish the business function. ‹#›

83. Enterprise Resource Planning (ERP) The modules are integrated through the ERP framework to accomplish transactions that may affect several functional areas. ‹#›

84. Enterprise Resource Planning (ERP) Because it uses a single database, ERP avoids problems such as data redundancy, conflicting data in different databases, and communication difficulties between different databases and the modules that operate on these databases. Before ERP, departments within an organization would typically have their own databases and computer systems. For example, the database of the Human Resources department would contain the personal data about each employee and the reporting structure within each department. ‹#›

85. Enterprise Resource Planning (ERP) ‹#›

86. PROCESS PLANNING Process planning consists of determining the most appropriate manufacturing and assembly processes and the sequence in which they should be accomplished to produce a given part or product according to specifications set forth in the product design documentation. The scope and variety of processes that can be planned are generally limited by the available processing equipment and technological capabilities of the company or plant. Parts that cannot be made internally must be purchased from outside vendors. The choice of processes is also limited by the details of the product design ‹#›

87. PROCESS PLANNING Process planning is usually accomplished by manufacturing engineers (other titles include industrial engineers, production engineers, and process engineers). They must be familiar with the particular manufacturing processes available in the factory and be able to interpret engineering drawings. Based on the planner’s knowledge, skill, and experience, the processing steps are developed in the most logical sequence to make each part. ‹#›

88. SCOPE OF PROCESS PLANNING Interpretation of design drawings First, the planner must analyze the part or product design (materials, dimensions, tolerances, surface finishes, etc.). Choice of processes and sequence The process planner must select which processes and their sequence are required, and prepare a brief description of all processing steps. Choice of equipment In general, process planners must develop plans that utilize existing equipment in the plant. Otherwise, the company must purchase the component or invest in new equipment. Choice of tools, dies, molds, fixtures, and gages The process planner must decide what tooling is required for each processing step. The actual design and fabrication of these tools is usually delegated to a tool design department and tool room, or an outside vendor specializing in that type of tooling. ‹#›

89. SCOPE OF PROCESS PLANNING Analysis of methods Workplace layout, small tools, hoists for lifting heavy parts, even in some cases hand and body motions must be specified for manual operations. The industrial engineering department is usually responsible for this area. Setting of work standards Work measurement techniques are used to set time standards for each operation. Choice of cutting tools and cutting conditions These must be specified for machining operations, often with reference to standard handbook recommendations. Similar decisions about process and equipment settings must be made for processes other than machining. ‹#›

90. PROCESS PLANNING FOR PARTS For individual parts, the processing sequence is documented on a form called a route sheet (some companies call it an operation sheet). Just as engineering drawings are used to specify the product design, route sheets are used to specify the process plan. They are counterparts, one for product design, the other for manufacturing. ‹#›

91. Typical route sheet for specifying the process plan ‹#›

92. Typical route sheet for specifying the process plan In the previous slide, includes the following information: all operations to be performed on the work part, listed in the order in which they should be performed; a brief description of each operation indicating the processing to be accomplished, with references to dimensions and tolerances on the part drawing; the specific machines on which the work is to be done; and any special tooling, such as dies, molds, cutting tools, jigs or fixtures, and gages. Some companies also include setup times, cycle time standards, and other data. It is called a route sheet because the processing sequence defines the route that the part must follow in the factory. ‹#›

93. Typical route sheet for specifying the process plan Decisions on processes to fabricate a given part are based largely on the starting material for the part. This starting material is selected by the product designer. Once the material has been specified, the range of possible processing operations is reduced considerably. The product designer’s decisions on starting material are based primarily on functional requirements, although economics and ease of manufacture also play a role in the selection. A typical processing sequence to fabricate an individual part consists of a basic process, secondary processes, property-enhancing operations, and Finishing operations. ‹#›

94. Typical sequence of processes required in part fabrication. ‹#›

95. Typical route sheet for specifying the process plan Decisions on processes to fabricate a given part are based largely on the starting material for the part. This starting material is selected by the product designer. Once the material has been specified, the range of possible processing operations is reduced considerably. The product designer’s decisions on starting material are based primarily on functional requirements, although economics and ease of manufacture also play a role in the selection. A typical processing sequence to fabricate an individual part consists of a basic process, secondary processes, property-enhancing operations, and Finishing operations. ‹#›

96. Typical route sheet for specifying the process plan A basic process determines the starting geometry of the work part. Metal casting, plastic molding, and rolling of sheet metal are examples of basic processes. The starting geometry must often be refined by secondary processes , operations that transform the starting geometry into the final geometry (or close to the final geometry). The secondary processes that might be used are closely correlated to the basic process that provides the starting geometry. When sand casting is the basic process, machining operations are generally the secondary processes. When a rolling mill produces sheet metal, stamping operations such as punching and bending are the secondary processes. When plastic injection molding is the basic process, secondary operations are often unnecessary, because most of the geometric features that would otherwise require machining can be created by the molding operation. ‹#›

97. Typical route sheet for specifying the process plan Plastic molding and other operations that require no subsequent secondary processing are called net shape processes. Operations that require some minimal secondary processing, usually machining, are referred to as near net shape processes. Once the geometry has been established, the next step for some parts is to improve their mechanical and physical properties. Property-enhancing operations do not alter the geometry of the part, only the physical properties; heat-treating operations on metal parts are the most common type. Similar heating treatments are performed on glass to produce tempered glass. For most manufactured parts, these property-enhancing operations are not required in the processing sequence ‹#›

98. Typical route sheet for specifying the process plan Finally, finishing operations usually provide a coating on the work part (or assembly) surface; examples include electroplating, thin film deposition processes, and painting. The purpose of the coating is to enhance appearance, change color, or protect the surface from corrosion, abrasion, and other damage. Finishing operations are not required on many parts; for example, plastic moldings rarely require finishing. When finishing is required, it is usually the final step in the processing sequence. ‹#›

99. Typical Process Sequences ‹#›

100. Process Planning for Assemblies The type of assembly method used for a given product depends on factors such as (1) the anticipated production quantities; (2) complexity of the assembled product, for example, the number of distinct components; and (3) assembly processes used, for example, mechanical assembly versus welding. For a product that is to be made in relatively small quantities, assembly is generally accomplished at individual workstations where one worker or a team of workers perform all of the assembly tasks. For complex products made in medium and high quantities, assembly is usually performed on manual assembly lines ‹#›

101. Process Planning for Assemblies For simple products of a dozen or so components, to be made in large quantities, automated assembly systems may be appropriate. For high production on an assembly line, process planning consists of allocating work elements to the individual stations of the line, a procedure called line balancing. As in process planning for individual components, any tools and fixtures required to accomplish an assembly task must be determined, designed, and built, and the workstation arrangement must be laid out. ‹#›

102. Make or Buy Decision An important question that arises in process planning is whether a given part should be produced in the company’s own factory or purchased from an outside vendor. If the company does not possess the equipment or expertise in the particular manufacturing processes required to make the part, then the answer is obvious: The part must be purchased because there is no internal alternative. However, in many cases, the part could either be made internally using existing equipment or purchased externally from a vendor that possesses similar manufacturing capability. ‹#›

103. Factors in the Make or Buy Decision ‹#›

104. Need for Computer Aided Process Planning (CAPP) Problems arise when process planning is accomplished manually. Different process planners have different experiences, skills, and knowledge of the available processes in the plant. This means that the process plan for a given part depends on the process planner who developed it. A different planner would likely plan the routing differently. This leads to variations and inconsistencies in the process plans in the plant. Another problem is that the shop-trained people who are familiar with the details of machining and other processes are gradually retiring and will be unavailable in the future to do process planning. As a result of these issues, manufacturing firms are interested in automating the task of process planning using computer-aided process planning (CAPP). ‹#›

105. Benefits of CAPP Process rationalization and standardization: Automated process planning leads to more logical and consistent process plans than manual process planning. Standard plans tend to result in lower manufacturing costs and higher product quality. Increased productivity of process planners The systematic approach and the availability of standard process plans in the data files permit more work to be accomplished by the process planners. Reduced lead time for process planning Process planners working with a CAPP system can provide route sheets in a shorter lead time compared to manual preparation. ‹#›

106. Benefits of CAPP Improved legibility: Computer-prepared route sheets are neater and easier to read than manually prepared route sheets. Incorporation of other application programs: The CAPP program can be interfaced with other application programs, such as cost estimation and work standards. ‹#›

107. Types of CAPP Retrieval CAPP systems and Generative CAPP systems. Some CAPP systems combine the two approaches in what is known as semi-generative CAPP ‹#›

108. Retrieval CAPP Systems A retrieval CAPP system, also called a variant CAPP system , is based on the principles of group technology (GT) and parts classification and coding. In this form of CAPP, a standard process plan (route sheet) is stored in computer files for each part code number. The standard route sheets are based on current part routings in use in the factory or on an ideal process plan that has been prepared for each family. Developing a database of these process plans requires substantial effort. ‹#›

109. Retrieval CAPP Systems Before the system can be used for process planning, a significant amount of information must be compiled and entered into the CAPP data files. This is refer to as the preparatory phase . It consists of selecting an appropriate classification and coding scheme for the company, forming part families for the parts produced by the company, and (3) preparing standard process plans for the part families. Steps (2) and (3) are ongoing as new parts are designed and added to the company’s design database. ‹#›

110. Retrieval CAPP Systems After the preparatory phase has been completed, the system is ready for use. For a new component for which the process plan is to be determined, the first step is to derive the GT code number for the part. With this code number, the user searches the part family file to determine if a standard route sheet exists for the given part code. If the file contains a process plan for the part, it is retrieved (hence, the word “retrieval” for this CAPP system) and displayed for the user. ‹#›

111. Retrieval CAPP Systems The standard process plan is examined to determine whether any modifications are necessary. It might be that although the new part has the same code number, there are minor differences in the processes required to make it. The user edits the standard plan accordingly. This capacity to alter an existing process plan is what gives the retrieval system its alternative name, “variant” CAPP system. If the file does not contain a standard process plan for the given code number, the user may search the computer file for a similar or related code number for which a standardroute sheet does exist. Either by editing an existing process plan or by starting from scratch, the user prepares the route sheet for the new part. ‹#›

112. Retrieval CAPP Systems This route sheet becomes the standard process plan for the new part code number. The process planning session concludes with the process plan formatter, which prints out the route sheet in the proper format. The formatter may call other application programs into use, for example, to determine machining conditions for the various machine tool operations in the sequence, to calculate standard times for the operations (e.g., for direct labor incentives), or to compute cost estimates for the operations. ‹#›

113. ‹#› General procedure for using one of the retrieval CAPP systems.

114. Generative CAPP Systems Generative CAPP systems represent an alternative approach to automated process planning. Instead of retrieving and editing an existing plan contained in a computer database, a generative system creates the process plan based on logical procedures similar to those used by a human planner. In a fully generative CAPP system, the process sequence is planned without human assistance and without a set of predefined standard plans. Designing a generative CAPP system is usually considered part of the field of expert systems, a branch of artificial intelligence. ‹#›

115. Generative CAPP Systems An expert system is a computer program that is capable of solving complex problems that normally can only be solved by a human with years of education and experience. Process planning fits within the scope of this definition. There are several necessary ingredients in a fully generative process planning system. First, the technical knowledge of manufacturing and the logic used by successful process planners must be captured and coded into a computer program. In an expert system applied to process planning, the knowledge and logic of the human process planners is incorporated into a so-called knowledge base. The generative CAPP system then uses that knowledge base to solve process planning problems (i.e., create route sheets). ‹#›

116. Generative CAPP Systems The second ingredient in generative process planning is a computer-compatible description of the part to be produced. This description contains all of the pertinent data and information needed to plan the process sequence. Two possible ways of providing this description are (1) the geometric model of the part that is developed on a CAD system during product design and (2) a GT code number of the part that defines the part features in significant detail. ‹#›

117. Generative CAPP Systems The third ingredient in a generative CAPP system is the capability to apply the process knowledge and planning logic contained in the knowledge base to a given part description. The CAPP system uses its knowledge base to solve a specific problem—planning the process for a new part. This problem-solving procedure is referred to as the inference engine in the terminology of expert systems . By using its knowledge base and inference engine, the CAPP system synthesizes a new process plan from scratch for each new part it is presented. ‹#›

118. Block Diagram of Expert CAPP System ‹#›

119. Economic Regions for Different Types of Process Planning ‹#›

120. Generative CAPP Systems The majority of existing process planning systems is based on variant process planning approach. Some of them are: CAPP, MIPLAN, MITURN, MIAPP, UNIVATION, CINTURN, COMCAPPV, etc. However, there are some generative system, such as METCAPP, CPPP, AUTAP, and APPAS. ‹#›