The U-bending process is a common sheet-metal forming process widely employed to fabricate sheet parts like channels, beams, and frames of various sizes applied in almost all industrial fields. In recent years, the precision requirements are increased on the U-bent parts. To achieve these requirements, in this study, the effects of part geometry on the spring-back/spring-go feature including work piece length, U-channel width, punch and die radii, and work piece thickness, were investigated by using the finite element method (FEM) and laboratory experiments. The FEM simulation results clearly revealed the influence of part geometry on spring-back/spring-go feature via the changes of stress distribution analyses on the bending allowance zone, the bottom of bent part, and the U-leg of bent part. Specifically, the part geometry affected on the bending characteristic on the bending allowance zone, as well as it affected on the spring-back feature. In addition, the part geometry also affected on the formation of reversed bending characteristic on the bottom and U-leg of bent parts, as well as it affected on the spring-go feature. The bending angle could be achieved by compensating these bending and reversed bending characteristics. Therefore, to meet the required bending angle, the suitable design of part geometry was strongly considered to maintain the balancing of the bending and reversed bending characteristics. The laboratory experiments were carried out to validate the accuracy of the FEM simulation results. The FEM simulation results showed good agreement with the experimental results with reference to the bending angle and bending force.

The coined-bead technique is an effective approach for controlling the spring-back characteristics involved in sheet-metal bending. Most previous studies have focused on the application of the coined-bead punch. In this application, bead marks are commonly formed on the inner radii of the bent components. To ensure the precision of the inner bent radius, a coined-bead die can be employed. However, information and data pertaining to coined-bead die applications are currently lacking. In the present research, the influences of the coined-bead die on the spring-back characteristics during V-die bending are investigated for aluminium alloy sheets (AA1100-O), by using the finite element method (FEM) and related physical experiments. Based on material flow and stress distribution analyses, it is found that the bending mechanism of coined-bead die application (particularly in the coining stage) is different from that of coined-bead punch application. Moreover, an increase in the punch radius-to-workpiece thickness ratio and decreases in the bend angle and coined-bead width result in increased spring-back characteristics. It is revealed that the coined-bead die can be applied to prevent spring-back characteristics and the bead mark at the inner radius. However, it was also noted that the V-shape parameters should be carefully considered for coined-bead applications. In addition, it is recommended that the width of the coined-bead die should be larger than that of the coined-bead punch.

In recent years, the engineered materials were developed to improve their mechanical properties. A high-strength steel sheet is one of them, developed to serve the requirement of reducing weight of vehicles. Therefore, as a new material, many researches have been carried out to examine the use of sheet metal forming process applied for high-strength steel sheet. However, the feasibility of shaving process applied for it has not been investigated yet. In the present study, this feasibility was revealed by using experiments on two types of high-strength steel sheets: SAPH 440 and SPFH 590Y (JIS). The relationship between shaved surface feature and shearing clearance of high-strength steel sheets corresponded well with those of their conventional metal sheets. However, due to the high ultimate strength of these materials, it was revealed in this present study that there were not any suitable conditions of shaving process that could be applied to achieve the requirements of smooth cut surface overall material thickness.

The use of Z-bent parts is increasing in many industrial fields. Moreover, the precision requirements for Z-bent part dimensions are becoming more stringent. Z-bent parts are commonly fabricated by two L-or V-bending processes, which cannot provide satisfactory precision. Therefore, a Z-bending process is needed. However, there are few studies on such processes, especially for asymmetrical Z-bent parts. In the present research, which is focused on the wiping Z-bending process, asymmetrical Z-bending die designs with asymmetrical bend radii and bend angles were investigated by using finite element method (FEM) simulations and laboratory experiments. The results showed that when fabricating the same Z-bent parts, different Z-bending die designs produced different stress distributions and different Z-bent part dimensions. Based upon the obtained results, the following die design recommendations were given. To fabricate asymmetrical bend radius Z-bent parts, the Zbending die should be designed with the larger bend radius on the punch side; however, the larger bend radius should be set on the die side when the accuracy of the large bend radius is of paramount importance. To fabricate asymmetrical bend angle Z-bent parts, the Z-bending die should be designed with the larger bend angle on the die side to provide better overall precision for the Z-bent part dimensions. To fabricate asymmetrical bend radius and bend angle Z-bent parts, the Z-bending die should be designed with the larger bend angle on the die side to provide better overall precision for the Z-bent part dimensions. This study confirmed that selecting a suitable Zbending die design is essential to fabricating precise Z-bent parts.

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