Preface to the Fourth Edition My coauthor,Robert Caddell,died in 1990,and I have greatly missed working with him. The most significant changes from the third edition are a new chapter on friction and lubrication and a major rearrangement of the last third of the book dealing with sheet forming.Most of the chapters in the last part of the book have been modified,with one whole chapter devoted to hydroforming.A new section is devoted to incremental forming.No attempt has been made to introduce numerical methods.Other books treat numerical methods.We feel that a thorough understanding of a process and the constitutive relations that are embedded in a computer program to analyze it are necessary.For example,the use of Hill's 1948 anisotropic yield criterion leads to significant errors. I wish to acknowledge my membership in the North American Deep Drawing Research Group from whom I have learned so much about sheet forming.Particular thanks are due to Alejandro Graf of ALCAN,Robert Wagoner of the Ohio State Uni- versity,John Duncan formerly with the University of Auckland,and Thomas Stoughton of General Motors. William F.Hosford xiiPreface to the Fourth Edition My coauthor, Robert Caddell, died in 1990, and I have greatly missed working with him. The most significant changes from the third edition are a new chapter on friction and lubrication and a major rearrangement of the last third of the book dealing with sheet forming. Most of the chapters in the last part of the book have been modified, with one whole chapter devoted to hydroforming. A new section is devoted to incremental forming. No attempt has been made to introduce numerical methods. Other books treat numerical methods. We feel that a thorough understanding of a process and the constitutive relations that are embedded in a computer program to analyze it are necessary. For example, the use of Hill’s 1948 anisotropic yield criterion leads to significant errors. I wish to acknowledge my membership in the North American Deep Drawing Research Group from whom I have learned so much about sheet forming. Particular thanks are due to Alejandro Graf of ALCAN, Robert Wagoner of the Ohio State Uni￾versity, John Duncan formerly with the University of Auckland, and Thomas Stoughton of General Motors. William F. Hosford xii