PREDICTION AND ELIMINATION OF GALLING IN FORMING GALVANIZED ADVANCED HIGH STRENGTH STEELS (AHSS) DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School of The Ohio State University By Hyunok Kim, M.S. * * * * * The Ohio State University 2008 Dissertation Committee: Approved by Professor Taylan Altan, Adviser Professor Bharat Bhushan ____________________________________ Professor Gary L. Kinzel Adviser Associate Professor Mark E. Walter Mechanical Engineering Graduate Program ABSTRACT To improve crash worthiness and fuel economy, the automotive industry is using increasingly Advanced High Strength Steels (AHSS). In addition having limited formability, compared to mild steels, AHSS require high pressures at the tool-workpiece interface. This leads to frequent lubricant film break down and galling as well as reduction in tool life, resulting in a considerable challenge to stamping engineers. Galling is a form of adhesive wear and the economic impact of galling upon stamping production is significant due to the increase of scrap rate and die maintenance cost. The major objective of this study is to predict and reduce galling in forming galvanized AHSS. For this purpose, a preliminary model was developed to predict the severity of galling for given lubricants, die materials and coatings in forming galvanized AHSS. In this study, Finite Element Analysis (FEA) of selected stamping operations with AHSS was conducted to determine the critical pressure conditions that exist in practical stamping. Thus, an attempt was made to develop laboratory tribotests, e.g. Twist Compression Test (TCT), Deep Drawing (DDT) and Strip Drawing Test (SDT) that emulate practical stamping conditions. By using these tribotests, the performance of lubricants, die materials and coatings was evaluated for various grades of AHSS in terms of coefficient of friction (COF) and galling. The results of this study helped to develop a preliminary model for predicting galling by considering the empirical relationships between important tribological parameters (e.g. interface pressure, ii sliding length, surface roughness, lubricant viscosity, hardness of zinc-coatings and tool coatings) and galling in forming galvanized AHSS. This model was applied to estimate the total number of parts that can be formed before severe galling occurs. Therefore, this model can offer a cost effective way to select practical and best combinations of lubricant, tool material and tool coating for reducing galling in forming galvanized AHSS. In addition, it can be further developed for use as a scheduling tool for the die maintenance before galling occurs, thus the unexpected downtime of stamping process can be eliminated. iii DEDICATION To my beloved wife, Haw-Young, my lovely children, Benjamin, Samuel and Joseph. iv ACKNOWLEDGMENTS I would like to express my most sincere gratitude to my adviser, Professor Taylan Altan, for the research opportunity at the Engineering Research Center for Net Shape Manufacturing (ERC/NSM) and his exceptional guidance with thoughtful advice during my Ph.D. program at the Ohio state University. My great appreciation extends to Professor Gary Kinzel, Professor Bharat Bhushan, and Professor Mark Walter for serving on my dissertation committee and providing valuable comments. Sincere thanks are extended to all the students and visiting scholars at the ERC/NSM, for their discussions and assistances in various aspects of this research work. My special thanks to Dr. Soo-Sik Han, Hyunjoong Cho, Yingyot Aue-u-lan, Ajay Yadav, Kyungbo Kim, Hariharasudhan Palaniswamy, Nimet Kardes, Partchapol Sartkulvanich, Ibrahim Al-Zkeri, Serhat Kaya, Johann Mai, Quigguang Yan and Dr. Gracious Ngaile. Also, I would like to thank Mr. Frank Goodwin at the International Lead Zinc Research Organization (ILZRO) for the research grant (#ZCO-51 “Control of Galling During Forming Galvanized Advanced High Strength Steels”) that enabled this study to continue. Finally, I want to thank my parents, pastor Keun Sang Lee and friends in church for their pray, support and encouragement during my Ph.D. program. v VITA January 06, 1974 ..................................Born - Seoul, South Korea 2000.......................................................B.S. Mechanical Engineering, Sung Kyun Kwan University, Seoul, Korea 2002.......................................................M.S. Mechanical Engineering, University of Michigan, Ann Arbor, US 2002 - 2008 ...........................................Graduate Research Associate, Engineering Research Center for Net Shape Manufacturing (ERC/NSM), The Ohio State University, Columbus, Ohio, US PUBLICATIONS Research Publications 1. Kim, H., Sung, J., Sivakumar, R., and Altan, T., “Evaluation of Stamping Lubricants using the Deep Drawing Test”, International Journal of Machine Tools and Manufacturer, Vol. 47/14, pp. 2120-2132, 2007. vi 2. Kim, H., Nargundkar, N., and Altan, T., “Prediction of Bend Allowance and Springback in Air-Bending”, ASME Transactions: Journal of Manufacturing Science and Engineering, Vol. 129, pp. 342-351, 2007. 3. Kim, H., Sung, J., and Altan, T., “Investigation of Galling in Forming Galvanized AHSS by Using the Twist Compression Test (TCT)”, accepted for the publication to the Journal of Materials Processing Technology, November 2007. 4. Kim, H., Han, S., Yan, Q., and Altan, T., ”Evaluation of Tool Materials, Coatings and Lubricants in Forming Galvanized Advanced High Strength Steels (AHSS)” accepted for the publication to the Annals of the CIRP, January 2008. 5. Kim, H., Shriniwas, P. and Altan, T., “Evaluation of New Lubricants for Cold Forging Without Zinc Phosphate Coating”, the 37th International Cold Forging Group (ICFG) Plenary Meeting, Istanbul, Turkey, Sep. 13-15, 2004. 6. Altan, T., and Kim, H., “Improvement of Tribological Conditions in Tube Hydro-Forming (THF) by using Environmental Friendly Lubricant Systems and Textured Tubes”, Proceedings of the 2005 NSF DMII Grantees Conference, Scottsdale, Arizona, Jan. 3-6, 2005. 7. Altan, T., and Kim, H., “Experimental and Numerical Studies on Friction & Lubrication in Metal Forming Processes”, Proceedings of the 2006 NSF DMII Grantees Conference, St. Louis, Missouri, July 24-27, 2006. FIELDS OF STUDY Major Field: Mechanical Engineering Studies in: Metal Forming Technology, Design and Tribology vii TABLE OF CONTENTS Page ABSTRACT ..................................................................................................................... ii DEDICATION ................................................................................................................ iv ACKNOWLEDGMENTS .............................................................................................. v VITA ……….. ................................................................................................................. vi LIST OF FIGURES ....................................................................................................... xiv LIST OF TABLES ...........................................................................................................xx LIST OF SYMBOLS .................................................................................................... xxii GLOSSARY ................................................................................................................xxiii CHAPTER 1 INTRODUCTION ....................................................................................1 1.1. Application of AHSS in Forming Automotive Structural Parts .....................1 1.2. Galvanized AHSS ..................................................................................................4 1.3. Galling in Forming Advanced High Strength Steels (AHSS) .........................7 1.4. Research Motivation .............................................................................................9 CHAPTER 2 RESEARCH OBJECTIVES ...................................................................10 CHAPTER 3 STATE-OF-THE-ART REVIEW ..........................................................11 3.1. Friction Models Used in Metal Forming Analysis .........................................11 3.2. Lubrication Mechanisms in Metal Forming ....................................................14 viii 3.2.1. Primary Lubrication Mechanisms in Metal Forming .....................14 3.2.2. Secondary Lubrication Mechanisms in Metal Forming .................16 3.3. Galling in Sheet Metal Forming Process ..........................................................16 3.3.1. Studies on Wear Models for Galling .................................................16 3.3.2. Tribotests to Evaluate Galling in Cold Forming Process ...............17 3.3.3. Effect of Surface Texturing on Galling ..............................................19 3.4. Lubrication, Tool Materials and Tool Coatings used in Forming AHSS .....................................................................................................................20 3.4.1. Lubrication in Forming AHSS ...........................................................20 3.4.2. Tool Materials in Forming AHSS ......................................................21 3.4.3. Tool Coatings in Forming AHSS .......................................................25 CHAPTER 4 INVESTIGATION OF GALLING USING THE TWIST COMPRESSION TEST .........................................................................27 4.1. Principle of TCT ..................................................................................................27