and Associated Companies throughout the world

Transcription

1

2 Editorial Director: Sally Yagan Editor in Chief: Donna Battista Senior Acquisitions Editor: Chuck Synovec Editorial Assistant: Ashlee Bradbury Director of Marketing: Maggie Moylan Executive Marketing Manager: Anne Fahlgren Senior Managing Editor: Judy Leale Production Project Manager: Jane Bonnell Publisher, International Edition: Angshuman Chakraborty Acquisitions Editor, International Edition: Somnath Basu Publishing Assistant, International Edition: Shokhi Shah Print and Media Editor, International Edition: Ashwitha Jayakumar Project Editor, International Edition: Jayashree Arunachalam Senior Manufacturing Controller: Trudy Kimber Creative Director: Blair Brown Senior Art Director/Supervisor: Janet Slowik Art Director: Steve Frim Cover Design: Jodi Notowitz Interior Design: Frubilicious Design Group Associate Media Project Manager, Editorial: Sarah Peterson Media Project Manager, Production: John Cassar Full-Service Project Management: PreMediaGlobal Cover Printer: Courier/Kendallville Pearson Education Limited Edinburgh Gate Harlow Essex CM0 JE England and Associated Companies throughout the world Visit us on the World Wide Web at: Pearson Education Limited 0 The rights of Cecil C. Bozarth and Robert B. Handfield are to be identified as authors of this work has been asserted by them in accordance with the Copyright, Designs and Patents Act 1. Authorized adaptation from the United States edition, entitled Introduction to Operations and Supply Chain Management, 3 rd edition, ISBN by Cecil C. Bozarth and Robert B. Handfield published by Pearson Education 0. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without either the prior written permission of the publisher or a licence permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency Ltd, Saffron House, Kirby Street, London EC1N TS. All trademarks used herein are the property of their respective owners. The use of any trademark in this text does not vest in the author or publisher any trademark ownership rights in such trademarks, nor does the use of such trademarks imply any affiliation with or endorsement of this book by such owners. Microsoft and/or its respective suppliers make no representations about the suitability of the information contained in the documents and related graphics published as part of the services for any purpose. All such documents and related graphics are provided as is without warranty of any kind. Microsoft and/or its respective suppliers hereby disclaim all warranties and conditions with regard to this information, including all warranties and conditions of merchantability, whether express, implied or statutory, fitness for a particular purpose, title and non-infringement. In no event shall Microsoft and/or its respective suppliers be liable for any special, indirect or consequential damages or any damages whatsoever resulting from loss of use, data or profits, whether in an action of contract, negligence or other tortious action, arising out of or in connection with the use or performance of information available from the services. The documents and related graphics contained herein could include technical inaccuracies or typographical errors. Changes are periodically added to the information herein. Microsoft and/or its respective suppliers may make improvements and/or changes in the product(s) and/or the program(s) described herein at any time. Partial screen shots may be viewed in full within the software version specified. Microsoft and Windows are registered trademarks of the Microsoft Corporation in the U.S.A. and other countries. This book is not sponsored or endorsed by or affiliated with the Microsoft Corporation. British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Typeset in / Minion Regular by PreMediaGlobal Printed and bound by Courier/Kendallville in The United States of America The publisher s policy is to use paper manufactured from sustainable forests. ISBN : X ISBN :

3 PART II Establishing the Operations Environment Combining these results with the appropriate A, D3, and D4 values from Table.4 yields the following control chart limits: UCL X = *0.00 = 0.3 LCL X = *0.00 = 0.31 UCL R =.*0.00 = 0.00 LCL R = 0*0.00 = 0 To calculate the process capability ratio, we must first estimate the standard deviation of the individual observations, sn. We can quickly do this by using the = STDEV(number1, number, ) function of Microsoft Excel, where the values in parentheses represent the raw diameter measurements. Doing so results in the following estimate: sn = 0.00 Therefore, the process capability ratio is C p = (0.00) = = 1.1 The results suggest that the current process is capable of meeting the tolerance limits more than.% of the time. DISCUSSION QUESTIONS 1. What costs of quality were highlighted in the opening case study? How can Delta Air Lines justify spending $0 million to reengineer the baggage-handling process at just one airport?. Why can two people perceive the same product or service as having different quality levels? From a business perspective, why is it important, then, to know your customer? 3. Several years ago, a major automotive manufacturer was sued because the latch on a minivan s rear door failed after the vehicle was hit from the side at 30 miles per hour. The plaintiff argued that the latch was of poor quality because it didn t hold up under the stress. The manufacturer disagreed, noting that the latch had met all government requirements and had been made to specifications. According to our definition of quality, can both sides be right? 4. Recall the DMAIC process described in Chapter 4. At what stage would statistical quality control tools be used?. Suppose that the actual range for a sample falls below the lower control limit for the R chart? Is this a good thing or a bad thing? Explain. PROBLEMS Additional homework problems are available at www. pearsoninternationaleditions.com/bozarth. These problems use Excel to generate customized problems for different class sections or even different students. (* = easy; ** = moderate; *** = advanced) 1. (*) Tyler Apiaries sells bees and beekeeping supplies. Bees (including a queen) are shipped in special packages according to weight. The target weight of a package is 1.4 kg. Historically, Tyler s shipments have weighed on average 1.4 kg, with a standard deviation of 0. kg. Calculate the process capability ratio, assuming that the lower and upper tolerance limits are 1.0 kg and 1. kg respectively. Is Tyler Apiaries currently able to meet the tolerance limits.% of the time?. (*) Suppose Tyler changes its processes so that the average package weight is now 1.3 kg, with a new standard deviation of 0. kg. Tyler still markets the packages of bees as weighing 1.4 kg, and the tolerance limits remain as before. Calculate the process capability index for the weight of the bee packages. Is Tyler able to meet the tolerance limits? 3. (**) Refer to problem 1. What would the standard deviation have to be for Tyler Apiaries to achieve Six Sigma quality levels with regard to the weight of the bee packages? 4. (**) The average bee weighs 0.1 grams. Use this information to convert the target package weight and tolerance limits into number of bees for Tyler Apiaries. How might the company use this information to better control the package weights? Should Tyler Apiaries think about resetting the tolerance limits?. (*) Leah s Toys produces molded plastic baby rattles. These rattles must be completely smooth. That is, there can be no rough edges where the molded halves fit together. Rattles are judged to be either acceptable or defective with regard to this requirement. Leah s has determined that the current process has an underlying p

4 CHAPTER Managing Quality 3 value of 0., meaning that, on average, 1. out of 0 rattles is currently judged to be defective. Calculate the standard deviation for the process and the resulting control limits for samples of 00 rattles each.. (*) Leah s Toys also makes rubber balls. The current process is capable of producing balls that weigh, on average, 4 ounces, with a standard deviation of 0.3 ounces. What is the process capability ratio, assuming upper and lower tolerance limits of 3. and.3 ounces? Is Leah s able to meet the tolerance limits.% of the time? Explain.. (**) Reconsider the data in problem. What would the standard deviation have to be to exactly meet the tolerance limits.% of the time?. (**) Suppose Leah s Toys invests in process improvements that lower the standard deviation in problem to just 0. ounces. Is this enough for Leah s to achieve Six Sigma quality levels with regard to the weight of the balls? Explain.. Leah s Toys guarantees to ship customer orders in 4 hours or less. The following chart contains results for five samples of nine customer orders each: SAMPLE SAMPLE CUSTOMER ORDERS (HOURS TO SHIP) (**) LaBoing produces springs, which are categorized as either acceptable or defective. During a period in which the manufacturing processes are under control, LaBoing takes multiple samples of 0 springs each, resulting in a calculated p value of 0.0. Develop the appropriate control chart for the springs.. AnderSet Laboratories produces rough lenses that will ultimately be ground into precision lenses for use in laboratory equipment. The company has developed the following thickness measures, based on samples of four lenses that were taken when the process was under control: MEAN (MICRONS) (N = 4) MINIMUM MAXIMUM a. (**) Based on these results, estimate the p and S p values. b. (**) A student comments, Time is a continuous variable. We should really be looking at the X and R values. Do you agree or disagree? Explain your rationale.. (**) BlueBolt Bottlers has a bottle-filling process with a mean value of 4 ounces and a standard deviation of ounces. Suppose that the upper and lower tolerance limits are and ounces, respectively. What is the process capability ratio? What would the standard deviation have to be in order for the process to meet the tolerance limits.% of the time?. (***) Now suppose BlueBolt Bottlers makes some process improvements, thereby lowering the standard deviation of the process to 1. ounces, rather than ounces. Using the data in problem and the new standard deviation, calculate the process capability ratio. Is the filling process able to meet the tolerance limits.% of the time? Does the process provide Six Sigma quality levels? Explain.. (*) The River Rock Company sells 0-lb bags of decorative rocks for landscaping use. The current bagging process yields samples with X and R values of 0 lb. and lb., respectively. Each sample consists of observations. Develop the appropriate control charts. a. (**) Use these data to calculate X and R and set up the appropriate control charts. b. (**) Can the process be under control in statistical terms but still fail to meet the needs of AnderSet s customers? Explain, using a numerical example.. (**) Suppose AnderSet Laboratories takes some additional samples of the same size, yielding the following results. Plot these samples on the control charts and circle any observations that appear to be out of control. MEAN (MICRONS) (n = 4) MINIMUM MAXIMUM (**) Lazy B Ranch produces leather hides for use in the furniture and automotive upholstery industry. The company has taken samples of nine observations each,

5 4 PART II Establishing the Operations Environment measuring the square footage of each hide. Summary data are as follows: MEAN (SQ. FT.) (n = ) MINIMUM MAXIMUM Use these data to set up control limits for the hides. Why would it be important for the Lazy B Ranch to track this information? Why might it be harder for the Lazy B Ranch to reduce process variability than it would be for a more typical manufacturer? 1. An insurance company has an online help service for its customers. Customer queries that take more than minutes to resolve are categorized as unsatisfactory experiences. To evaluate the quality of its service, the company takes samples of 0 calls each while the process is under control. The resulting p values are as follows: p VALUES (n = 0) a. (**) Calculate the p and S p values and set up control limits so that future sample p values should fall within the control limits.% of the time. b. (**) Suppose the insurance company takes four additional samples, yielding the following p values: 0., 0., 0., and 0.. Plot the results and circle all values which suggest that the process is out of control. Is it possible that a sample result could fall outside the control limits due to pure chance? Explain. c. (**) Now suppose that the sample size is actually 0, not 0. Recalculate the control limits for the p chart. What happened? Explain. 1. EK Chemical Company sells a specialty chemical in packages marked 0 g. In reality, EK has set the process mean at 0. g, and the process currently has a standard deviation of 0.0 g. Suppose the customer will accept anywhere from to g, as long as the average package has at least 0 g. a. (**) Calculate the process capability index for the current manufacturing process. Is the process capable of meeting the tolerance limits more than.% of the time? Explain. b. (***) Now suppose EK recenters the manufacturing process so that the process mean is exactly 0 g, while the standard deviation remains the same. Calculate the process capability ratio. Is the process still capable of meeting the tolerance limits more than.% of the time? Explain. 1. Crawford Pharmaceuticals has developed a new drug, Vaxidene. The target amount for a single dose of Vaxidene is 0 mg. Patients can receive as little as mg or as much as mg without experiencing any ill effects. Because of potential liability issues, Crawford has determined that it is imperative that manufacturing be able to provide Six Sigma quality levels. At present, the manufacturing process has a process mean of 0 mg and a standard deviation of 0. mg. a. (*) What are the upper and lower tolerance limits for Vaxidene? b. (**) Is Crawford s manufacturing process currently able to meet the dosage specifications at least.% of the time? Show your work. c. (**) What would the standard deviation for the process have to be in order for Crawford to achieve Six Sigma quality levels? 0. BHC produces bags of cement. The stated weight for a bag of cement is 0 lb. Customers will accept an occasional bag weighing as little as lb., as long as the average weight is at least 0 lb. At the same time, BHC doesn t want to give away cement, so it has set an upper tolerance limit of 4 lb. The current filling process has an actual process mean of 1 lb. and a standard deviation of 0. lb. a. (**) Calculate the process capability index for BHC. In this example, why should we use the process capability index rather than the process capability ratio to assess capability? b. (**) Can you think of any reason BHC might want a process mean higher than the target value? 1. Central Airlines would like to set up a control chart to monitor its on-time arrival performance. Each day over a -day period, Central Airlines chose 30 flights at random and tracked the number of late arrivals in each sample. The results are as follows: DAY SAMPLE SIZE NO. OF LATE- ARRIVING FLIGHTS

6 CHAPTER Managing Quality a. (*) Calculate p b. (**) Set up a p chart to track the proportion of late arrivals. (Note: Each sample consists of 30 observations.) c. (***) Airline travel is characterized by busy and slow seasons. As a result, what is normal during one time of the year wouldn t be normal at some other time. What difficulties might arise as a result of using a single control chart to track the proportion of late arrivals? What could Central Airlines do about this?. The Oceanside Apparel Company manufactures men s knit shirts. The production process requires material to be cut into large patterned squares, which are then sewn together. If the squares are not the correct length, the final shirt will be either too large or too small. The target length is 3 inches. In order to monitor the cutting process, Oceanside managers took samples of four squares each and measured the lengths. For each sample, they then calculated the sample mean and range. Finally, they calculated the average sample mean (3.0 inches) and average range value (1. inches) for the samples. Managers felt that these values were acceptable; that is, the process was in control. a. (**) Develop the appropriate control chart(s) to monitor the fabric length. b. (**) Using the control chart(s) you developed in part a, plot the following samples. Circle any that appear to be out of control. SAMPLE (n = 4) MEASUREMENTS (IN INCHES) (***) (Microsoft Excel problem) The following Excel spreadsheet calculates the upper and lower control limits for a continuous variable. Re-create this spreadsheet in Excel. You should develop the spreadsheet so that the results will be recalculated if any of the values in the highlighted cells are changed. Your formatting does not have to be exactly the same, but the numbers should be. (As a test, see what happens if all five observations in Sample 1 are 40. Your new upper and lower control limits for the sample means should be 3.0 and 34., respectively.) A B C D E F G H I J K Calculating upper and lower control limits for a continuous variable (sample size = ) Sample ***Observations*** X R Upper control limit for sample means: 3. Lower control limit for sample means: 33. Upper control limit for sample ranges: Lower control limit for sample ranges: Average:

7 PART II Establishing the Operations Environment 4. (***) (Microsoft Excel problem) The following Excel spreadsheet calculates the upper and lower control limits for an attribute (in this case, the proportion of dissatisfied customers). Re-create this spreadsheet in Excel. You should develop the spreadsheet so that the results will be recalculated if any of the values in the highlighted cells are changed. Your formatting does not have to be exactly the same, but the numbers should be. (As a test, see what happens if you change the sample size to 00. The new UCL and LCL values should be.00 and.001, respectively.) A B C D E F G H 1 Setting Up.% Control Limits, Sampling by Attribute 3 No. of dissatisfied Sample size = 0 4 Sample customers p-value p = S p = UCL for sample p values: LCL for sample p values: CASE STUDY DITTENHOEFER S FINE CHINA Peter Ardito/photolibrary.com Introduction Overall, Steve Edwards, vice president of Marketing at Dittenhoefer s Fine China, is very pleased with the success of his new line of Gem-Surface china plates. Gem-Surface plates are different from regular china in that the plates have a special polymer coating that makes them highly resistant to chipping and fading. Not only are the plates more durable, they are also completely dishwasher safe. In order to manufacture the new plates, Dittenhoefer s has leased a special machine to apply the coating and has put in place a drying system to cure the coating on the plates. The research and development (R&D) lab has determined that in order to prevent defective plates, it is important that the machine apply the polymer coating at the proper temperature and in the proper thickness. Specifically, R&D has written up the following guidelines: Coating thickness. The optimal polymer-coating thickness is 4 microns. If the coating is microns, the plates will take too long to dry. If the coating is 3 microns, the plates will be inadequately protected. Coating temperature. The polymer coating needs to be applied at a temperature between 10 degrees Fahrenheit and