tailieunhanh - Manufacturing Design, Production, Automation, and Integration Part 7

Tham khảo tài liệu 'manufacturing design, production, automation, and integration part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 7 Metal Forming Metal forming processes transform simple-geometry billets blanks into complex-geometry products through the plastic deformation of the metal in open or closed dies. Due to the high costs of the dies however these processes are primarily reserved for mass production. Metals to be formed under normally compressive stress must be ductile and have low yield strength. These properties can be favorably induced when necessary by preheating the billets blanks prior to their placement in the press. Furthermore one should note that metal forming processes may take one or a few iterations . using one or multiple dies in yielding near net shape desired geometries with no or little scrap. Metal forming processes may be classified into two primary categories 1. Massive forming processes for bulk deformation where parts undergo large plastic deformation. 2. Sheet-metal forming processes where thin-walled sheets of metal undergo change in overall shape but not much in their cross sections. In this chapter we will first briefly overview several common metal forming processes but present detailed descriptions for only two of those that are targeted for discrete parts manufacturing versus continuous production such as for tubes and pipes forging and sheet metal forming. Copyright 2003 by Marcel Dekker Inc. All Rights Reserved. OVERVIEW OF METAL FORMING Mechanical Behavior of Metals Deformation of a solid body can be classified as elastic or plastic when unloaded an elastically deformed body always returns to its original shape regardless of history rate time and path of loading the plastic deformation of a body on the other hand depends on all these variables and is subjected to permanent loss of original shape when unloaded. Although the theory of elasticity is well established and yields accurate predictions of strain due to mechanical stress the theory of plasticity normally yields approximate solutions to plastic deformation problems. The typical .