Process Capability Study and Identification of the Causes of Defects and Rejections in Galvanization Line of Corrugated Sheet Production Case on: Adama steel factory (ASF) By: Balem Limenie Adamu Thesis submitted to Department of Mechanical Design and Manufacturing Engineering School of Mechanical Chemical and Materials Engineering Presented in Partial Fulfillment of the Requirements for the Degree of Master in Mechanical Design and Manufacturing Engineering Office of Graduate Studies Adama Science and Technology University Adama, Ethiopia June, 2019 I | P a g e Process Capability Study and Identification of the Causes of Defects and Rejections in Galvanization Line of Corrugated Sheet Production Case on: Adama steel factory (ASF) By: Balem Limenie Adamu Advisor Dr. Guteta Kabeta Thesis submitted to School of Mechanical Chemical and Materials Engineering Presented in Partial Fulfillment of the Requirements for the Degree of Master in Mechanical Design and Manufacturing Engineering Office of Graduate Studies Adama Science and Technology University Adama, Ethiopia June, 2019 II | P a g e Approval Sheet of Board of Examiners I, the undersigned, members of the Board of Examiners of the final open defense by Balem Limenie have read and evaluated her thesis entitled “process capability study and identification of sources of defects and rejections. Case of Adama steel factory” and examined the candidate. This is, therefore, to certify that the thesis has been accepted in partial fulfillment of the requirement of the Degree of Master’s in Mechanical Design and Manufacturing engineering. ___________________ ___________________ Advisor Signature Date ___________________________ ___________________ ___________________ Chairperson Signature Date ___________________________ ___________________ ___________________ Internal Examiner Signature Date ___________________________ ___________________ ___________________ External Examiner Signature Date III | P a g e Candidate Declarations I hereby declare that the work, which is being presented in thesis, entitled’’ Process capability study and identification of the sources of defects and Rejection in Galvanization line of corrugated sheet production” in ASF. In partial fulfillment of the requirements for the award of the degree of Masters of Science in Manufacturing Engineering is an authentic record of my own work carried out from November 2018 to June 2019 under the supervision of Dr. Guteta Kabeta, Mechanical Design and Manufacturing Engineering program, Adama Science and Technology University, Ethiopia. The matter embodied in this thesis has not been submitted by me for the award of any other degree or diploma. All relevant resources of information used in this thesis have been duly acknowledged. Balem Limenie Adamu Candidate Signature Date This is to certify that above declaration made by the candidate is correct to the best of my knowledge and belief. This thesis has been submitted for examination with our approval: Dr. Guteta Kabeta Advisor Signature Date IV | P a g e ACKNOLOGNMENT First of all, I would like to thank my almightily GOD to give my full health and her support to finalize my thesis study without any adversity. Secondly, I like provision very grateful thank to my advisor GUTETA KABETA (PhD) in school of chemical, material and mechanical engineering in design and manufacturing program for exposing me to such kind of explorative and investigative thesis work. His encouragement, excellent guidance, creative suggestions and critical comments has a great contributed to accomplish my thesis work. I would like to thank Mr. Dagmawi Hailu for such great knowledge and experience in the quality domain and given me very valuable advice and ways to be easy clear my work along the way. Finally, I would like to thank all ASF staff members. Specially Mr. Asabu Molla, a head technician and productivity department for his continuous help and advice, Mr. Mulatu Teshome head of general human resource manager, Mr. Mekonnen operator of quality control department and Mr. Melaku Ygeizu mechanical operator of machine and also to tank my lovely family and my best friends how are not parting in necessary time and support. V | P a g e Abstract The process capability measurement is an important aspect in quality management to decide whether a process is capable of meeting the required specifications. The main objective were to study capability of the process and identify the possible source of defects and rejections in galvanized sheet production line and provide recommendations. The study has done through collected and analyzed sample data with the application of Microsoft excel and Minitab software to determine the capability of process, applied statistical quality control tool in order to determine the cause and rate of defects and examine the quality of different products using process capability indices. The result showed that the manufacturing process was incapable and in acceptable in both parameters of coating thickness and weight according to Thumb law and six sigma principle; all the values of indices and ppm were out of standard value. All indices values were less than 1.33 and 1.67 and ppm was much greater than 2700 (cp 1) and 0.545 (cp>1.5). The analyzed data, the mount of defects and rejections 3.23% and the overall profit losses are 74,724,240 birr due to the occurrences of different causes of defects and process variations. Key words: Rejection, process capability analysis, Process Capability index, Statistical quality control, defect amount, rework, profit loss. VI | P a g e Table of Contents Approval Sheet of Board of Examiners ........................................................................................... I Candidate Declarations ................................................................................................................. IV ACKNOLOGNMENT ................................................................................................................... V Abstract ......................................................................................................................................... VI Table of Contents ......................................................................................................................... VII List of figures ................................................................................................................................ XI List of tables ................................................................................................................................. XII Abbreviations and Acronyms .................................................................................................... XIII CHAPTER ONE ............................................................................................................................. 1 1. INTRODUCTION ...................................................................................................................... 1 1.1 Back grounds of the study..................................................................................................... 1 1.2 Back ground of the company ................................................................................................ 3 1.3 Process description................................................................................................................ 3 1.4 General Hot dip galvanizing Defects .................................................................................... 4 1.5 Zinc coating section and its defect ........................................................................................ 6 1.5.1 Factors affecting Zn coating ...................................................................................... 7 1.6 Pickling Section and Its Defects ........................................................................................... 7 1.6.1 Under Pickling ........................................................................................................... 8 1.6.2 Over Pickling ............................................................................................................. 8 1.7 Sources of Defects and Rejections ........................................................................................ 8 1.8 Defect Reduction Methodology .......................................................................................... 10 1.8.1 Six Sigma Method.................................................................................................... 10 1.8.2 Process Capability Analysis and Indices ................................................................. 12 1.8.3 Statistical Quality Control l (SQC) .......................................................................... 14 VII | P a g e 1.9 Statement of the Problem .................................................................................................... 18 1.10 Objectives of the study...................................................................................................... 19 1.10.1 General Objective .................................................................................................. 19 1.10.2 Specific objectives ................................................................................................ 19 1.11 Significance of the Study .................................................................................................. 19 1.12Motivation of the study .....................................................................................................