This document contains Chapters 23 to 26 Chapter 23 PRODUCT DESIGN AND CAD/CAM IN THE PRODUCTION SYSTEM REVIEW QUESTIONS 23.1 What are manufacturing support systems? Answer: As defined in the text, manufacturing support systems are the procedures and systems used by the firm to manage production and solve the technical and logistics problems associated with designing the products, planning the processes, ordering materials, controlling work-in-process as it moves through the plant, and delivering products to customers. 23.2 What are the six phases of the general design process? Answer: As listed in the text, the six phases of the general design process are (1) recognition of need, (2) problem definition, (3) synthesis, (4) analysis and optimization, (5) evaluation, and (6) presentation (e.g., documenting the design). 23.3 What is computer-aided design? Answer: Computer-aided design (CAD) is any design activity that involves the effective use of the computer to create, modify, analyze, optimize, or document an engineering design. 23.4 Name some of the benefits of using a CAD system to support the engineering design function? Answer: The six benefits listed in the text are (1) to increase the productivity of the designer, (2) to expand the available geometric forms in the design, (3) to improve the quality of the design, (4) to improve design documentation, (5) to create a manufacturing database, and (6) to promote design standardization. 23.5 Give some examples of engineering analysis software in common use on CAD systems. Answer: The text lists the following examples: (1) Mass properties analysis to calculate weight, center of gravity and similar part attributes, (2) interference checking to identify interferences between components in an assembly, (3) tolerance analysis, (4) finite element analysis, (5) kinematic and dynamic analysis, and (6) discrete-event simulation. 23.6 What is rapid prototyping? Answer: Rapid prototyping is a family of fabrication technologies that allow engineering prototypes of solid parts to be made in minimum lead time by fabricating the part directly from the CAD geometric model. This is usually done by dividing the solid object into a series of layers of small thickness and then defining the area shape of each layer. 23.7 What is virtual prototyping? Answer: Virtual prototyping involves the use of the CAD geometric model to construct a digital mock-up of the product, enabling the designer and others to obtain the sensation of the real physical product without actually building the physical prototype. 23.8 What is a product data management system? Answer: As defined in the text, a product data management (PDM) system consists of computer software that provides links between users (e.g., designers) and a central data base, which stores design data such as geometric models, product structures (e.g., bills of material), and related records. The software also manages the data base by tracking the identity of users, facilitating and documenting engineering changes, recording a history of the engineering changes on each part and product, and providing similar documentation functions. 23.9 What is computer-aided manufacturing? Answer: As defined in the text, computer-aided manufacturing (CAM) is the effective use of computer technology in manufacturing planning and control. 23.10 Name some of the important applications of CAM in manufacturing planning? Answer: The seven applications listed in the text are (1) computer-aided process planning (CAPP), (2) computer-assisted NC part programming, (3) computerized machinability data systems, (4) computerized work standards, (5) cost estimating, (6) production and inventory planning, and (7) computer-aided line balancing. 23.11 What is the difference between CAD/CAM and CIM? Answer: CAD/CAM is concerned with the engineering functions in design and manufacturing. CIM includes all of the engineering functions of CAD/CAM, but it also includes the firm’s business functions that are related to manufacturing. 23.12 What is quality function deployment? Answer: As defined in the text, quality function deployment (QFD) is a systematic procedure for defining customer desires and requirements and interpreting them in terms of product features, process requirements, and quality characteristics. Chapter 24 PROCESS PLANNING AND CONCURRENT ENGINEERING REVIEW QUESTIONS 24.1 What is process planning? Answer: Two similar definitions are given in the text: (1) Process planning involves determining the sequence of processing and assembly steps that must be accomplished to make the product. (2) 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. 24.2 Name some of the decisions and details that are usually included within the scope of process planning? Answer: The seven items listed in the text are (1) interpretation of design drawings, (2) selection of processes and their sequence, (3) selection of equipment, (4) deciding the tools, dies, molds, fixtures, and gages that will be needed, (5) methods analysis, (6) work standards, and (7) cutting tools and cutting conditions. 24.3 What is the name of the document that lists the process sequence in process planning? Answer: The document is called a route sheet. 24.4 A typical process sequence for a manufactured part consists of four types of operations. Name and briefly describe the four types of operations. Answer: The four types of operations are (1) basic processes, which determine the starting geometry of the workpart, (2) secondary processes, which transform the starting geometry into the final geometry, (3) operations to enhance physical properties, such as heat treating of metals, and (4) finishing operations, which usually provide a coating on the part surface. 24.5 What is a net shape process? Answer: A net shape process is one that requires no subsequent processing to establish the final geometry of the part. 24.6 Name some of the factors that influence the make-or-buy decision? Answer: The seven factors listed in Table 24.2 in the text are the following: (1) How do part costs compare between the make and buy alternatives? (2) Is the process available in-house? If not, then buy the part. (3) What is the total production quantity and anticipated product life? High quantities favor a make decision. Longer product lives favor a make decision. (4) Is the component a standard catalog item? If yes, then buy. (5) Is the supplier reliable? If yes, then buy. (6) Is the company’s plant already operating at full capacity? If yes, then buy. (7) Does the company need an alternative supply source? If yes, then at least some of the parts should be purchased. 24.7 Name some of the benefits derived from computer-aided process planning? Answer: The five benefits named in the text are (1) process rationalization and standardization to obtain more logical and consistent process plans than when process planning is done manually, (2) increased productivity of process planners, (3) reduced lead time for process planning, (4) improved legibility over manually prepared route sheets, and (5) ability to incorporate other application programs, such as cost estimating and work standards. 24.8 Briefly describe the two basic approaches in computer-aided process planning. Answer: The two basic approaches are (1) retrieval CAPP and (2) generative CAPP. A retrieval CAPP system is based on the principles of group technology (GT) and parts classification and coding; in this type of CAPP, a standard process plan (route sheet) is stored in computer files for each part code number and then retrieved for new parts that have the same or similar code numbers. A generative CAPP system creates the process plan based on logical procedures similar to those used by a human planner, but the computer plans the process sequence without human assistance and without a set of predefined standard plans. 24.9 What is concurrent engineering? Answer: Concurrent engineering is an approach used in product development in which the functions of design engineering, manufacturing engineering, and other functions are integrated to reduce the elapsed time required to bring a new product to market. 24.10 Design for Manufacturing and Assembly (DFM/A) includes two aspects: (1) organizational changes and (2) design principles and guidelines. Identify two of the organizational changes that might be made in implementing DFM/A? Answer: The possible organizational changes mentioned in the text are (1) create project teams consisting of product designers, manufacturing engineers, and other specialties (e.g., quality engineers, material scientists) to develop the new product design; (2) require design engineers to spend some career time in manufacturing to witness first-hand how manufacturability and assemblability are impacted by a product’s design; and (3) assign manufacturing engineers to the product design department on either a temporary or fulltime basis to serve as producibility consultants. 24.11 Name some of the universal design guidelines in DFM/A. Answer: The universal DFM/A design guidelines listed in Table 24.3 are the following: (1) Minimize the number of components. (2) Use standard commercially available components. (3) Use common parts across product lines. (4) Design for ease of part fabrication. (5) Design parts with tolerances that are within process capability. (6) Design the product to be foolproof during assembly. (7) Minimize flexible components. (8) Design for ease of assembly. (9) Use modular design. (10) Shape parts and products for ease of packaging. (11) Eliminate or reduce adjustments. 24.12 Name the four activities often included within the scope of advanced manufacturing planning? Answer: The four categories identified in the text are (1) evaluation of new technologies to determine which ones will play a role in the company’s future, (2) managing investment projects that relate to new manufacturing technologies and equipment, (3) facilities planning for new equipment and new buildings, and (4) manufacturing research and development to learn more about processes and technologies of value to the company. Chapter 25 PRODUCTION PLANNING AND CONTROL SYSTEMS REVIEW QUESTIONS 25.1 What is production planning? Answer: As defined in the text, production planning consists of (1) deciding which products to make, how many of each, and when they should be completed; (2) scheduling the delivery and/or production of the parts and products; and (3) planning the manpower and equipment resources needed to accomplish the production plan. 25.2 Name the four activities within the scope of production planning? Answer: The four activities identified in the text are (1) aggregate production planning, (2) master production planning, resulting in the master production schedule, (3) material requirements planning, and (4) capacity planning. 25.3 What is production control? Answer: As defined in the text, production control consists of determining whether the necessary resources to implement the production plan have been provided, and if not, it attempts to take corrective action to address the deficiencies. 25.4 What is the difference between the aggregate production plan and the master production schedule? Answer: The aggregate production plan indicates the output levels for the major product lines of the company, both products that are currently being produced and future products. The master production schedule takes the product line quantities listed in the aggregate plan and converts them into a very specific schedule of individual products and models to be manufactured, when they should be completed and delivered, and in what quantities. 25.5 What is material requirements planning (MRP)? Answer: As defined in the text, material requirements planning is a computational technique that converts the master production 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. 25.6 What is the difference between independent demand and dependent demand? Answer: Independent demand means that demand for a product is unrelated to demand for other items. Final products are examples of items whose demand is independent. Independent demand patterns are usually forecasted. Dependent demand means that demand for the item is directly related to the demand for some other item, usually a final product, so that dependency derives from the fact that the item is a component of the other product. Not only component parts but also the raw materials and subassemblies used in the final product are examples of items subject to dependent demand. 25.7 What are the three inputs to the MRP processor? Answer: As identified in the text, the three inputs to the MRP processor are (1) the master production schedule, (2) the bill of materials file and other engineering and manufacturing data, and (3) the inventory record file. 25.8 What are common use items in MRP? Answer: Common use items are raw materials and components that are used on more than one product. The MRP processor collects these common use items from different products to effect economies in ordering the raw materials and producing the components. 25.9 Name the benefits of a well-designed MRP system? Answer: The text lists the following six benefits: (1) reduction in inventory, (2) quicker response to changes in demand than is possible with a manual requirements planning system, (3) reduced setup and product changeover costs, (4) better machine utilization, (5) improved capacity to respond to changes in the master schedule, and (6) as an aid in developing the master schedule. 25.10 What is capacity planning? Answer: As defined in the text, capacity planning consists of determining what labor and equipment resources are required to meet the current master production schedule as well as long-term future production needs of the firm. It also serves to identify the limitations of the available production resources so that an unrealistic master schedule is not planned. 25.11 Capacity adjustments can be divided into short-term adjustments and long-term adjustments. Name some of the capacity adjustments for the short term? Answer: Capacity adjustments for the short term include the following: (1) Employment in the plant can be increased or decreased in response to changes in capacity requirements. (2) Temporary workers can be used to increase capacity. (3) The number of shifts worked per production period can be increased or decreased. (4) The number of labor hours per shift can be increased or decreased, through the use of overtime or reduced hours. (5) Inventory stockpiling to maintain steady employment levels during slow demand periods. (6) Order backlogs - deliveries of the product to the customer could be delayed during busy periods when production resources are insufficient to keep up with demand. (7) Subcontracting - letting jobs to other shops during busy periods, or taking in extra work during slack periods. 25.12 What is shop floor control? Answer: As defined in the text, shop floor control is the set of activities in production control that is concerned with the release of 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. 25.13 What are the three phases of shop floor control? Provide a brief definition of each activity. Answer: The three phases of shop floor control are (1) order release, (2) order scheduling, and (3) order progress. Order release provides the documentation needed to process a production order through the factory. Order scheduling assigns production orders to the various work centers in the plant by preparing a dispatch list that indicates which production orders should be accomplished at the various work centers. Order progress monitors the status of the various orders in the plant, work-in-process, and other measures that indicate the progress and performance of production. 25.14 What does the term machine loading mean? Answer: Machine loading involves assigning orders to work centers in the plant. 25.15 What is MTConnect? Answer: MTConnect is an open-source protocol based on Internet standards that allows the retrieval of data from factory equipment for shop floor control and other applications. 25.16 What are carrying costs in inventory control? Answer: The term carrying costs refers to the costs of holding inventory, which include (1) investment costs of tying money up in inventory, (2) storage costs, and (3) cost of possible obsolescence or spoilage. 25.17 What is a reorder point system in inventory control? Answer: A reorder point system is a method of determining when to restock an item; specifically, 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. 25.18 What is the difference between material requirements planning (MRP) and manufacturing resource planning (MRP II)? Answer: Manufacturing resource planning includes material requirements planning, but it also adds capacity planning and shop floor control, two features that are absent in material requirements planning 25.19 What is enterprise resource planning (ERP)? Answer: As defined in the text, 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, operations, logistics, distribution, inventory control, accounting, finance, and human resources. The operations function can include service activities as well as production, so ERP can be used by service provider companies. ERP operates on a company-wide basis; it is not a plant-based system as MRP applications often are. PROBLEMS Answers to problems labeled (A) are listed in the Appendix at the back of the book. Material Requirements Planning 25.1 Using the master schedule of Figure 25.2(b), and the product structures in Figures 25.4 and 25.6, determine the time-phased requirements for component C6 and raw material M6. Lead times are as follows: for P1, assembly lead time is 1 week; for P2, assembly lead time is 1 week; for S2, assembly lead time is 1 week; for S3, assembly lead time is 1 week; for C6, manufacturing lead time is 2 weeks; and for M6, ordering lead time is 2 weeks. Assume that the current inventory status for all of the above items is zero units on hand, and zero units on order. The format of the solution should be similar to that presented in Figure 25.7. Answer: Period 1 2 3 4 5 6 7 8 9 10 Item: Product P1 50 100 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 50 100 Planned Order Releases 50 100 Item: Product P2 70 80 25 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 70 80 25 Planned Order Releases 70 80 25 Item: Subassembly S2 100 200 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 100 200 Planned Order Releases 100 200 Item: Subassembly S3 70 80 25 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 70 80 25 Planned Order Releases 70 80 25 Item: Component C6 140 260 50 200 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 140 260 50 200 Planned Order Releases 140 260 50 200 Item: Raw material M6 70 130 25 100 Gross Requirements Scheduled Receipts On hand 0 0 0 Net Requirements 70 130 25 100 Planned Order Releases 70 130 25 100 25.2 Solve previous Problem 25.1 except that the current inventory on hand and on order for S3, C6, and M6 is as follows: for S3, inventory on hand is 2 units and quantity on order is zero; for C6, inventory on hand is 5 units and quantity on order is 10 for delivery in week 2; and for M6, inventory on hand is 10 units and quantity on order is 50 for delivery in week 2. Answer: Period 1 2 3 4 5 6 7 8 9 10 Item: Product P1 50 100 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 50 100 Planned Order Releases 50 100 Item: Product P2 70 80 25 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 70 80 25 Planned Order Releases 70 80 25 Item: Subassembly S2 100 200 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 100 200 Planned Order Releases 100 200 Item: Subassembly S3 70 80 25 Gross Requirements Scheduled Receipts On hand 2 2 2 2 2 2 2 Net Requirements 68 80 25 Planned Order Releases 68 80 25 Item: Component C6 136 260 50 200 Gross Requirements Scheduled Receipts 10 On hand 5 5 15 15 15 15 Net Requirements 121 260 50 200 Planned Order Releases 121 260 50 200 Item: Raw material M6 60.5 130 25 100 Gross Requirements Scheduled Receipts 50 On hand 10 10 60 60 Net Requirements 0.5 130 25 100 Planned Order Releases 0.5 130 25 100 25.3 Material requirements are to be planned for component C2 given the master schedule for P1 and P2 in Figure 25.2(b), and the product structures in Figures 25.4 and 25.6. Assembly lead time for products and subassemblies (P and S levels) is 1 week, manufacturing lead times for components (C level) is 2 weeks, and ordering lead time for raw materials (M level) is 3 weeks. Determine the time-phased requirements for M2, C2, and S1. Assume there are no common use items other than those specified by the product structures for P1 and P2 (Figures 25.4 and 25.6), and that all on-hand inventories and scheduled receipts are zero. Use a format similar to Figure 25.7. Ignore demand beyond period 10. Answer: Period 1 2 3 4 5 6 7 8 9 10 Item: Product P1 50 100 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 50 100 Planned Order Releases 50 100 Item: Product P2 70 80 25 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 70 80 25 Planned Order Releases 70 80 25 Item: Subassembly S1 50 100 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 50 100 Planned Order Releases 50 100 Item: Subassembly S4 70 80 25 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 70 80 25 Planned Order Releases 70 80 25 Item: Component C2 140 360 50 400 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 140 360 50 400 Planned Order Releases 140 360 50 400 Item: Raw material M2 140 360 50 400 Gross Requirements Scheduled Receipts On hand 0 0 0 Net Requirements 140 360 50 400 Planned Order Releases 360 50 400 In addition, a planned order release for 140 units of M2 should be included in week 0, not shown in the chart. 25.4 Requirements are to be planned for component C5 in product P1. Required deliveries for P1 are given in Figure 25.2(b), and the product structure for P1 is shown in Figure 25.4. Assembly lead time for products and subassemblies (P and S levels) is 1 week, manufacturing lead times for components (C level) is 2 weeks, and ordering lead time for raw materials (M level) is 3 weeks. Determine the time-phased requirements for M5, C5, and S2 to meet the master schedule. Assume no common use items. On-hand inventories are: 100 units for M5 and 50 units for C5, zero for S2. Scheduled receipts are zero for these items. Use a format similar to Figure 25.7. Ignore demand for P1 beyond period 10. Answer: Period 1 2 3 4 5 6 7 8 9 10 Item: Product P1 50 100 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 50 100 Planned Order Releases 50 100 Item: Subassembly S2 100 200 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 100 200 Planned Order Releases 100 200 Item: Component C5 200 400 Gross Requirements Scheduled Receipts On hand 50 50 Net Requirements 150 400 Planned Order Releases 150 400 Item: Raw material M5 150 400 Gross Requirements Scheduled Receipts On hand 100 100 Net Requirements 50 400 Planned Order Releases 50 400 25.5 Solve the previous problem except that the following additional information is known: Scheduled receipts of M5 are 50 units in week 3 and 50 units in week 4. Answer: Period 1 2 3 4 5 6 7 8 9 10 Item: Product P1 50 100 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 50 100 Planned Order Releases 50 100 Item: Subassembly S2 100 200 Gross Requirements Scheduled Receipts On hand 0 Net Requirements 100 200 Planned Order Releases 100 200 Item: Component C5 200 400 Gross Requirements Scheduled Receipts On hand 50 50 Net Requirements 150 400 Planned Order Releases 150 400 Item: Raw material M5 150 400 Gross Requirements Scheduled Receipts 50 50 On hand 100 150 200 50 50 Net Requirements -50 350 Planned Order Releases 0 350 Order Scheduling 25.6 (A) It is currently day 10 in the production calendar of the Machine Shop. Three orders (A, B, and C) are to be processed at a particular machine tool. The orders arrived in the sequence A-B-C. The table below indicates the process time remaining and production calendar due date for each order. Determine the sequence of the orders that would be scheduled using the following priority control rules: (a) first-come-first-serve, (b) earliest due date, (c) shortest processing time, (d) least slack time, and (e) critical ratio. Order Remaining process time Due date A 4 days Day 20 B 16 days Day 30 C 6 days Day 18 Answer: (a) First-come-first-serve sequence = ABC (b) Earliest due date sequence = CAB (c) Shortest processing time sequence = ACB (d) Least slack time: Order A slack time = (20 - 10) - 4 = 6 Order B slack time = (30 - 10) - 16 = 4 Order C slack time = (18 - 10) - 6 = 2 Sequence = CBA (e) Critical ratio: Order A critical ratio = (20 - 10)/4 = 2.5 Order B critical ratio = (30 - 10)/16 = 1.25 Order C critical ratio = (18 - 10)/6 = 1.33 Sequence = BCA 25.7 For each solution (a) through (e) in the previous problem, determine which jobs are delivered on time and which jobs are tardy. Answer: (a) FCFS: sequence = A - B - C Order Process time Due date Start date Completion Status A 4 days Day 20 Day 10 Day 14 On-time B 16 days Day 30 Day 14 Day 30 On-time C 6 days Day 18 Day 30 Day 36 Tardy (b) Earliest due date: sequence = C - A - B Order Process time Due date Start date Completion Status C 6 days Day 18 Day 10 Day 16 On-time A 4 days Day 20 Day 16 Day 20 On-time B 16 days Day 30 Day 20 Day 36 Tardy (c) Shortest processing time: sequence = A - C - B Order Process time Due date Start date Completion Status A 4 days Day 20 Day 10 Day 14 On-time C 6 days Day 18 Day 14 Day 20 On-time B 16 days Day 30 Day 20 Day 36 Tardy (d) Least slack time: Sequence = C - B - A Order Process time Due date Start date Completion Status C 6 days Day 18 Day 10 Day 16 On-time B 16 days Day 30 Day 16 Day 32 Tardy A 4 days Day 20 (e) Critical ratio: Sequence = B - C - A Day 32 Day 36 Tardy Order Process time Due date Start date Completion Status B 16 days Day 30 Day 10 Day 26 On-time C 6 days Day 18 Day 26 Day 32 Tardy A 4 days Day 20 Day 32 Day 36 Tardy Order-Point Inventory Systems 25.8 (A) Annual demand for a certain part is 1800 units per yr. The part is produced in a batch model manufacturing system. Annual holding cost per piece is $3.00. It takes 1.5 hr to set up the machine to produce the part, and cost of system downtime is $200/hr. Determine (a) economical batch quantity for this part and (b) associated total inventory cost. (c) How many batches are produced per year? Answer: 25.9 Annual demand for a made-to-stock product is 50,000 units. Each unit costs $8.00, and the annual holding cost rate is 18%. Setup time to change over equipment for this product is 2.0 hr, and the downtime cost of the equipment is $180/hr. Determine (a) economic order quantity and (b) total inventory costs. (c) How many batches are produced per year? Answer: 25.10 Demand for a certain part is 22,000 units/yr. Unit cost is $9.35, and holding cost rate is 24%/yr. Setup time between parts is 2.5 hr, and downtime cost during changeover is $125/hr. Determine (a) economic order quantity, (b) total inventory costs, and (c) total inventory cost per year as a proportion of actual annual part production costs. Answer: 25.11 A part is produced in batches size of 2500 pieces. Annual demand is 45,000 pieces, and piece cost is $6.50. Setup time to run a batch is 1.5 hr, cost of downtime on the affected equipment is figured at $220/hr, and annual holding cost rate is 30%. What would the annual savings be if the product were produced in the economic order quantity? Answer: 25.12 In the previous problem, (a) how much would setup time have to be reduced in order to make the batch size of 2500 pieces equal to the economic batch quantity? (b) How much would total inventory costs be reduced if the economic batch quantity = 2500 units compared to the economic batch quantity calculated in the previous problem? (c) How much would total inventory costs be reduced if the setup time were equal to the value obtained in part (a) compared to the 1.5 hr used in the previous problem? Answer: 25.13 A machine tool produces 26 components for an assembled product. These are the only parts produced by the machine. To keep in-process inventories low, a batch size of 75 units is produced for each component. Demand for the product is 900 units/yr. Production downtime costs $120/hr. Changeover time between batches is 1.5 hr, and average cycle time per part = 4.0 min. The annual holding cost for each of the 26 parts is $1.60/pc. (a) Determine total annual inventory cost for the 26 parts. (b) Is the given production schedule feasible for a one-shift operation? That is, can 900 units of each of the 26 components be completed in 2000 hours? If so, how many idle hours of machine time occur in the 2000 hours? If not, how many overtime hours must be authorized during the year? Answer: 25.14 For the data in the previous problem, (a) in how many minutes must the changeover between batches be accomplished in order for 75 units to be the economic batch quantity, and (b) can 900 units of each of the 26 components be completed in 2000 hours? If so, how many idle hours of machine time occur in the 2000 hours? If not, how many overtime hours must be authorized during the year? Answer: 25.15 (A) Annual demand for a certain part is 6,000 units. At present the setup time on the machine tool that makes this part is 4.0 hr. Cost of downtime on this machine is $200/hr. Annual holding cost per part is $2.40. Determine (a) economic batch quantity and (b) total inventory costs for this data. Also, determine (c) economic batch quantity and total inventory costs if the changeover time could be reduced to 12 min. Answer: 25.16 A variety of assembled products are made in batches on a batch model assembly line. Every time a different product is produced, the line must be changed over, which results in lost production time. The assembled product of interest here has an annual demand of 8000 units. The changeover time to set up the line for this product is 12.0 hr. The company figures that the hourly rate for lost production time on the line due to changeovers is $250/hr. Annual holding cost for the product is $7.00 per unit. The product is currently made in batches of 800 units for shipment each month to the wholesale distributor. (a) Determine the total annual inventory cost for this product when produced in batch sizes of 800 units. (b) What is the economic batch quantity for this product? (c) How often would shipments be made using this economic batch quantity? (d) How much would the company save in annual inventory costs, if it produced batches equal to the economic batch quantity rather than 800 units? Answer: 25.17 A two-bin approach is used to control inventory for a certain low-cost hardware item. Each bin holds 300 units of the item. When one bin becomes empty, an order for 300 units is released to replace the stock in that bin. The order lead time is less than the time it takes to deplete the stock in one bin, so the chance of a stock-out is low. Annual usage of the item is 4000 units. Ordering cost is $30. (a) What is the imputed holding cost per unit for this item, based on the data given? (b) If the actual annual holding cost per unit is 5 cents, what lot size should be ordered? (c) How much does the current two-bin approach cost the company per year, compared to using the economic order quantity? Answer: Chapter 26 Just-In-Time and Lean Production REVIEW QUESTIONS 26.1 Define lean production. Answer: As defined in the text, lean production means doing more work with fewer resources. It also means giving customers what they want and satisfying or surpassing their expectations. 26.2 Name the two pillars of the Toyota production system. Answer: The two pillars of the Toyota production system are (1) just-in-time production and (2) autonomation (automation with a human touch). 26.3 What is the Japanese word for waste? Answer: The Japanese word for waste is "muda" (無駄). 26.4 Name the seven forms of waste in production, as identified by Taiichi Ohno. Answer: Taiichi Ohno’s seven forms of waste are (1) production of defective parts, (2) production of more than the number of items needed (overproduction), (3) excessive inventories, (4) unnecessary processing steps, (5) unnecessary movement of people, (6) unnecessary transport and handling of materials, and (7) workers waiting. 26.5 What are three reasons why people and materials are sometimes moved unnecessarily in production operations? Answer: The reasons given in the text are (1) inefficient workplace layout, (2) inefficient plant layout, (3) Improper material handling method, (4) production machines spaced too far apart, (5) larger equipment than necessary for the task, and (6) conventional batch production. 26.6 What is a just-in-time production system? Answer: As defined in the text, a just-in-time production system produces and delivers exactly the required number of each component to the downstream operation in the manufacturing sequence just at the time when that component is needed. Each component is delivered "just in time." 26.7 What is the objective of a just-in-time production system? Answer: The primary objective of a just-in-time production system is to minimize inventories, especially work-in-process inventories. 26.8 What is the difference between a push system and a pull system in production control? Answer: In a pull system of production control, the order to make and deliver parts at each workstation in the production sequence comes from the downstream station that uses those parts. When the supply of parts at a given workstation is about to be exhausted, that station orders the upstream station to replenish the supply. When this procedure is used throughout the plant, it has the effect of pulling parts through the production system. In a push system, parts at each workstation are produced irrespective of the immediate need for those parts at their respective downstream station. In effect, this production discipline pushes parts through the plant. 26.9 What is a kanban? What are the two types of kanban? Answer: Kanban means signal card in Japanese. The kanban system of production control used in the Toyota JIT system is based on the use of cards that authorize (1) parts production and (2) parts delivery in the plant. Accordingly, the two types of kanbans are (1) production kanbans, which authorize the upstream station to produce a batch of parts and (2) transport kanbans, which authorize transport of the parts to the downstream station. 26.10 What is the basic starting point in a study to reduce setup time? Answer: The starting point in setup time reduction is to recognize that there are two types of work elements in the task of setting up a machine: (1) internal elements, which can only be accomplished while the production machine is stopped, and (2) external elements, which do not require that the machine be stopped. External elements can be accomplished while the previous job is running on the machine. 26.11 What is production leveling? Answer: Production leveling means distributing the changes in product mix and quantity as evenly as possible over time when it is necessary for the production system to adjust to the ups and downs in demand for the final product. 26.12 How is production leveling accomplished? Answer: The approaches mentioned in the text are (1) authorizing overtime during busy periods, (2) using finished product inventories to absorb daily ups and downs in demand, (3) adjusting the cycle times of the production operations, and (4) producing in small batch sizes that are enabled by setup time reduction techniques. In the ideal, the batch size is reduced to one. 26.13 What does autonomation mean? Answer: Taiichi Ohno referred to autonomation as “automation with a human touch.” The notion is that the machines operate autonomously as long as they are functioning properly. When they do not function properly (e.g., when they produce a defective part), they are designed to stop immediately. Autonomation also includes the notion of mistake-proofing the process. 26.14 What is total productive maintenance? Answer: Total productive maintenance (TPM) is a coordinated group of activities whose objective is to minimize production losses due to equipment failures, malfunctions, and low utilization through the participation of workers at all levels of the organization. TPM involves the integration of preventive maintenance and predictive maintenance to avoid emergency maintenance. 26.15 What does the Japanese word kaizen mean? Answer: The Japanese word "kaizen" (改善) translates to "improvement" or "change for the better." In the context of business and management, kaizen refers to the philosophy or practice of continuous improvement. It emphasizes the concept of making small, incremental changes or improvements in processes, systems, and workflows to enhance efficiency, quality, and overall performance over time. Kaizen involves the active involvement of all employees in identifying problems, proposing solutions, and implementing improvements on a daily basis, fostering a culture of continuous learning and innovation within an organization. 26.16 What is a quality circle? Answer: A quality circle is a worker team that is organized to address specific problems that have been identified in the workplace. The problems are not limited to quality. They include problems relating to productivity, cost, safety, maintenance, and other areas of interest to the organization. 26.17 What is visual management? Answer: Visual management refers to a way of managing and organizing operations so that the status of the work situation is evident just by looking at it. If something is wrong, this condition should be obvious to the observer, so that corrective action can be taken immediately. Also called the visual workplace, the principle applies to the entire plant environment. 26.18 What is an andon board? Answer: An andon board is a light panel positioned above a workstation or production line that is used to indicate its operating status. If a problem occurs, such as a line stoppage, the andon board identifies where the problem is and the nature of the problem. 26.19 What is the 5S system? Answer: The 5S system is a set of procedures that is used to organize work areas in the plant. It is also a means of involving workers in the visual management of the factory. The five S’s stand for (1) sort things in the workplace and discard things that are not needed, (2) set in order the things that remain after sorting, (3) shine or clean the workplace, (4) standardize locations for items in the workplace, and (5) self-discipline to sustain the order that has been created. 26.20 What is takt time? Answer: Takt time is defined as the effective daily operating time divided by the daily quantity of units demanded. It is the cycle time that corresponds to the demand rate for the item. 26.21 What are standardized work procedures in the Toyota production system? Answer: Standardized work procedures in the Toyota production system consist of determining the following factors for each task: (1) cycle time, which becomes matched to the takt time for the task, (2) work sequence or standard operations routine, which is the order of work elements performed in the task, and (3) standard work-in-process quantity, which refers to the minimum number of WIP parts needed to avoid workers waiting. PROBLEMS Answers to problems labeled (A) are listed in the Appendix at the back of the book. Setup Time Reduction 26.1 (A) A stamping plant supplies sheet metal body panels to an automotive final assembly plant. The following data are values representative of the parts made at the plant. Annual demand is 180,000 pc (for each part produced). Average cost per piece is $15 and holding cost is 18% of piece cost. Changeover (setup) time for the presses is 4 hr and the cost of downtime on any given press is $200/hr. Determine (a) the economic batch size and (b) the total annual inventory cost for the data. If the changeover time for the presses could be reduced to 6 min, determine (c) the economic batch size and (d) the total annual inventory cost. (e) What would the annual savings be for the plant if these annual inventory costs were applied to all 46 different stampings produced by the plant? Answer: 26.2 A supplier of parts to an assembly plant in the household appliance industry is required to make deliveries on a just-in-time basis (daily). For one of the parts that must be delivered, the daily requirement is 100 parts, five days/wk, 52 wk/yr. However, the supplier cannot afford to make just 100 parts each day because of the high cost of changing over the production machine. Instead, it must produce in larger batch sizes and maintain an inventory of the parts from which 100 units are withdrawn for shipment each day. Cost per piece is $16 and holding cost is 24% of piece cost. Changeover time for the production machine used to produce the part is 2.5 hr and the cost of downtime on this machine is $180/hr. Determine (a) the economic batch size and (b) the total annual inventory cost for the data. (c) How many weeks of demand does this batch quantity represent? Answer: 26.3 In the previous problem, it is desired to reduce the economic batch size from the value determined in that problem to 500 units, which would require the supplier to keep a maximum inventory of one week’s demand for the parts. (a) Determine the changeover time that would allow the economic batch size in stamping to be 500 pieces. (b) What is the corresponding total annual inventory cost for this batch size, assuming the changeover time in part (a) can be realized? (c) What are the total annual inventory cost savings to the supplier, compared to the TIC determined in the previous problem? Answer: 26.4 (A) Monthly demand rate for a certain part is 10,000 units. The part is produced in batches and its manufacturing costs are estimated to be $8.00. Holding cost is 20% of piece cost. Currently the production equipment used to produce this part is also used to produce 19 other parts with similar usage and cost data (assume the data to be identical for purposes of this problem). Changeover time between batches of the different parts is now 4.0 hr, and cost of downtime on the equipment is $250/hr. A proposal has been submitted to fabricate a fast-acting slide mechanism that would permit the changeovers to be completed in just 10 min. Cost to fabricate and install the slide mechanism is $125,000. (a) Is this cost justified by the savings in total annual inventory cost that would be achieved by reducing the economic batch quantity from its current value based on a 4-hr setup to the new value based on a 10-min setup? (b) How many months of savings are required to pay off the $125,000 investment? Answer: 26.5 An injection-molding machine produces 25 different plastic molded parts in an average year. Annual demand for a typical part is 20,000 units. Each part is made out of a different plastic (the differences are in type of plastic and color). Because of the differences, changeover time between parts is significant, averaging 5 hr to change molds and purge the previous plastic from the injection barrel. One setup person normally does these two activities sequentially. A proposal has been made to separate the tasks and use two setup persons working simultaneously. In that case, the mold can be changed in 1.5 hr and purging takes 3.5 hr. Thus, the total downtime per changeover will be reduced to 3.5 hr from the previous 5 hr. Downtime on the injection-molding machine is $200/hr. Labor cost for setup time is $20/hr. Average cost of a plastic molded part is $2.50, and holding cost is 24% annually. For the 5-hr setup, determine (a) the economic batch quantity, (b) the total number of hours per year that the injection-molding machine is down for changeovers, and (c) the annual inventory cost. For the 3.5-hr setup, determine (d) the economic batch quantity, (e) the total number of hours per year that the injection-molding machine is down for changeovers, and (f) the annual inventory cost. Answer: 26.6 In the previous problem, a second proposal has been made to reduce the purging time of 3.5 hr during a changeover to less than 1.5 hr by sequencing the batches of parts so as to reduce the differences in plastic type and color between one part and the next. In the ideal, the same plastic can be used for all parts, thus eliminating the necessity to purge the injection barrel between batches. Thus, the limiting task in changing over the machine is the mold change time, which is 1.5 hr. For the 1.5-hr setup, determine (a) the economic batch quantity, (b) the total number of hours per year that the injection-molding machine is down for changeovers, and (c) the annual inventory cost. Answer: 26.7 The following data apply to sheet metal parts produced at a stamping plant that serves a final assembly plant in the automotive industry. The data are average values representative of the parts made at the plant. Annual demand = 150,000 pc (for each part produced); average cost per piece = $20; holding cost = 25%, changeover (setup) time for the presses = 5 hr; cost of downtime on any given press = $200/hr. (a) Compute the economic batch size and the total annual inventory cost for the data. (b) If the changeover time could be reduced to 30 min, compute the economic batch size and the total annual inventory cost. Answer: 26.8 (A) Given the data in the previous problem, it is desired to reduce the batch size from the value determined in that problem to 600 pieces. The stamping plant operates 250 days per year, so this quantity is consistent with the number of units supplied daily to the final assembly plant. Determine the changeover time that would allow the economic batch size in stamping to be 600 pieces. What is the corresponding total annual inventory cost for this batch size? Answer: 26.9 Annual demand for a part is 500 units. The part is currently produced in batches. It takes 2.0 hr to set up the production machine for this part, and the downtime during setup costs $125/hr. Annual holding cost for the part is $5.00. The company would like to produce the part using a new flexible manufacturing system it recently installed. This would allow the company to produce this part as well as others on the same equipment. However, changeover time must be reduced to a minimum. (a) Determine the required changeover (setup) time, in order to produce this part economically in batch sizes of one. (b) If the part were to be produced in batch sizes of 10 units instead of one, what is the implicit changeover time for this batch quantity? (c) How much are the annual total inventory costs to the company when the batch size = 1 unit? Answer: Overall Equipment Effectiveness 26.10 (A) A production machine has an uptime proportion of 96% and a utilization of 94%. The fraction defect rate of the parts made on the machine is 0.021, and it operates at 75% of its rated speed. What is the overall equipment effectiveness of this machine? Answer: OEE = 0.96(0.94)(1 – 0.021)(0.75) = 0.6626 = 66.26% 26.11 Reliability data on an automated production machine are: mean time between failures = 37.4 hr and mean time to repair = 34 min. The utilization of the machine is 89%. The fraction defect rate of the parts made on the machine is 1.1%. Its rated operating speed is 75 parts/hr, but it only operates at 62 parts/hr. (a) What is the overall equipment effectiveness of this machine? (b) The reliability and fraction defect rate would be difficult to improve upon, but utilization and rated speed could be increased. What values of utilization and operating speed would allow the overall equipment effectiveness to be increase to 85%. Answer: (a) From Equation (3.9), availability A = (37.4 – 34/60)/37.4 = 0.985 Operating capability ros = 62/75 = 0.8267 OEE = 0.985(0.89)(1 – 0.011)(0.8267) = 0.7168 = 71.68% (b) To increase OEE to 85%, the product Uros must equal 0.85/(0.985 × 0.989) = 0.8725 Any combination of values of U and ros whose product = 0.8725 would work. For example, if U = 95%, then ros = 0.8725/0.95 = 0.9185, so the machine speed would have to be 0.9185(75) = 68.9 parts/hr. Check: ros = 68.9/75 = 0.9187, and OEE = 0.985(0.95)(0.989)(0.9187) = 0.8502 = 85.02% Takt Time and Cycle Time 26.12 (A) The weekly demand for a certain part is 600 units. The plant operates two shifts per day, five days per week, with an effective operating time of 440 min per shift. Determine the takt time for this part. Answer: Daily demand Qdd = 600/5 = 120 pc/day Takt time Ttakt = 2(440)/120 = 7.333 min/pc 26.13 The monthly usage for a component supplied to an assembly plant is 3400 parts. There are 21 working days in the month and the effective operating time of the plant is 450 min per day. Currently, the defect rate for the component is 1.2%, and the equipment used to produce the part is down for repairs an average of 18 min per day. Determine the takt time for this part. Answer: Daily demand Qdd = 3400/21 = 161.9 pc/day Takt time Ttakt = 450/161.9.1 = 2.78 min/pc Comment: Defect rate and downtime are ignored to motivate the plant to achieve a zero defect rate and zero downtime. 26.14 Monthly delivery rate for a part supplied to an automotive assembly plant is 12,500 pc. There are 20 working days in February and 22 working days in March. The effective operating time of the plant is 840 min per day (two shifts). The fraction defect rate for the component is 0.017, and the automated machine that produces the part has an availability of 96%. Determine the takt time for this part during (a) February and (b) March. Answer: (a) February daily demand Qdd = 12,500/20 = 625 pc/day Takt time Ttakt = 840/625 = 1.344 min/pc (b) March daily demand Qdd = 12,500/22 = 568.2 pc/day Takt time Ttakt = 840/568.2 = 1.478 min/pc Comments: (a) Defect rate and downtime are ignored to motivate the plant to achieve a zero defect rate and zero downtime. (b) Having the same monthly delivery rate when the number of days in the month differs would be an unusual situation. Much more likely would be that the delivery rate would be expressed as a daily rate, which would result in the same takt time for all months. Solution Manual for Automation, Production Systems, and Computer-Integrated Manufacturing Mikell P. Groover 9780133499612, 9780134605463
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