tailieunhanh - Mechanical Systems Design Handbook P7

Process and Control Objectives Forming of metallic materials is the process of choice when complex net shapes with high levels of productivity are desired. Myriad processes, ranging from job-shop metal bending machines to very high speed stamping and forging presses are available. | 7 Forming Processes Monitoring and Control Introduction Process and Control Objectives David E. Hardt Process Control Issues The Process Material Diagram The Machine Control Diagram The Plant or Load Forming Physics Mechanics of Deformation Machine Load Dynamics Mechanics of Forming Bending Stretching and Springback Machine Control Sensors Machine Control Force or Displacement Process Resolution Issues Limits to Process Control Process Resolution Enhancement Massachusetts Institute Direct Shape Feedback and Control of Technology Summary Introduction Process and Control Objectives Forming of metallic materials is the process of choice when complex net shapes with high levels of productivity are desired. Myriad processes ranging from job-shop metal bending machines to very high speed stamping and forging presses are available. In all cases the processes involve plastic deformation of the workpiece and the resulting strong forces required to create plastic stresses. In this chapter the problem of controlling such processes is considered from both the viewpoint of controlling the forming equipment and the deformation process itself. Several unique aspects of forming processes arise when considering control system design 1. The process or plant transfer function becomes a static block with variable gain and severe hysteresis. 2. The plant the forming process is inherently variable owing to the sensitivity to the workpiece material properties. 3. An inherent lack of process degrees of freedom with respect to controlling overall part shape exists. Metal forming can be divided into sheet-forming processes and bulk-forming processes typically forging . The major difference is that the latter involves a complex three-dimensional flow of the material while the former tends to be dominated by plane strain conditions and the process is not intended to change material thickness only the curvatures. In what follows the sheet-forming processes are .