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Drawing is the most important operation in stamping. Shut height has been used as the main control parameter in die setup. But shut height control can not provide a consistent binder force for a drawing operation in a double-action press and often produces formability and/or quality problems. This paper will examine how different input variables will affect the performance of a drawing operation in a double-action press. Three examples of using tonnage control and process optimization are provided in improving part quality and reducing down time and scrap cost.

The surface quality of an outer skin part of a vehicle, smooth and with no waviness, is becoming more and more important in today's more and more competitive automotive industry. Strain analysis has been used for formability evaluation and trouble shooting and process optimization has been used for formability improvement in stamping. In this work, diffracto analysis is used to evaluate the surface quality of a stamping part, the strain magnitude and the strain distribution of a part are examined to analyze the root cause of the waviness in the part and process optimization, including optimization of press tonnage, nitrogen pressure and shut height, is used to improve the surface quality of the part. Test results from using different input parameters are compared in this paper. The optimized process parameters have been used in production resulting in more stable and high surface quality and less scrap cost.

Springback is one of the main problems in sheet metal bending operations. Theoretically, an accurate description of strain distribution and stress distribution is required in order to predict the springback behavior of a bending component. Prediction of strain distribution needs a good geometrical model while prediction of stress distribution needs both an accurate strain description and an accurate stress-strain relationship. In this paper, a new model is developed for strain calculation in plane strain bending. The displacement of the neutral surface, the thickness change, the stress and strain distributions over the sheet thickness, the bending moment and the springback curvature are examined using this new model and useful conclusions are obtained. The new model is also compared with Hill's pure bending model, the membrane theory (plus post-processing) and the shell theory. The application ranges and the limitations of the membrane theory and the shell theory are discussed.

A methodology is presented for springback analysis and control in forming two-step rail-shaped sheet metal parts. A computer system for bending and springback analysis of two-step rails is developed and described. Effects of tool corner radii, material properties and process variables on the springback behavior of two-step rails is investigated using the analysis system, and conclusions are drawn based on the sensitivity analysis result. An example of springback control is provided in obtaining an accurate shape of a given part in the design stage by changing some of the variables.

Stress and strain distributions developed in a tube during the tube bending operation is important in estimating the limit bending radii, springback and structural properties of the tube. In this paper, A new strain distribution model for tube bending, considering stretching, circumferential strain and cross section flattening, is presented. The axial, circumferential, thickness and effective strains on the outer surface, inner surface and mid-surface of a bending tube were calculated from grid measurement, and are shown in different ways. Thickness strain was also obtained from thickness measurement. Comparison is made among the results from measurement and modeling and a very good agreement is obtained between the new model and the measurement.

A bending and springback analysis method for 2D-draw bending parts has been developed based on a new mathematical model. The main feature of the new model is described and the analysis results obtained from this model are compared with those from other methods. These results show consistent springback behavior for the selected cases. Roles of blankholder force and friction are investigated using the new method, as well as the effect of material properties on springback behavior, e.g., strain hardening index, Young's modulus, plastic anisotropy, etc. The trends are illustrated graphically and some conclusions are drawn based on the analysis.

An important extension to the process of roll forming is the production of embossments by a secondary stamping operation. In this paper, a system is described for transforming stamping profiles to roller profiles, thus eliminating the need for the secondary stamping operation. Included in the system are techniques for identifying and avoiding interference between the rollers, and for calculating torque and power requirements. The system is illustrated by describing how the process was used to design a pair of rollers for embossing a profile generated by the LaBarge method [1].

Stretching a circular blank over a circular domed punch is modelled using the ABAQUS finite element code. Hemispherical, elliptical and flat-bottomed punches are investigated as well as the effect of strain hardening, friction, blank diameter, blankholder pressure and die radius. The results are illustrated using forming limit and other diagrams and summarized in a table that illustrates how strain in the different regions of the blank can be controlled and redistributed.