International Journal of Precision Engineering and Manufacturing

In this study, low cycle fatigue (LCF) tests of IN738LC were conducted under high-temperature conditions. The tests were performed with various mechanical strain amplitudes and the relationship between strain amplitude and fatigue life was obtained. In addition, an equation for LCF life prediction was derived from the test results. After obtaining a strain-life diagram from the LCF test results, additional LCF tests were conducted according to the extent of damage. The LCF tests were taken at various degrees of damage in order to observe the change in mechanical properties the severity of damage. For this purpose, indentation tests were conducted and the relationship between hardness and damage was obtained. To nondestructively assess the low cycle fatigued IN738LC, the subharmonic nonlinearity parameter was first introduced because of the high attenuation properties of IN738LC. Until now, the subharmonic technique has been applied only to crack evaluation problems. This technique is presented as an effective tool for assessing low cycle fatigued IN738LC in this paper.

Variable blank holder force (VBHF) is an important process parameter in sheet metal forming. The purpose of this study is to propose a sharing niching radial basis function (SNRBF) neural network for VBHF optimization. Two methods are put forward to improve the prediction accuracy of a RBF neural network. (1) A RBF neural network is trained by a sharing niching technique to achieve global optimal nodes. (2) In Latin hypercube design, Spearman correlation analysis is employed to decrease sample correlation. In addition, in order to improve the performance of the non-dominated sorting genetic algorithm (NSGA-II), excellent individuals in each class of non-dominated individuals are selected by employing immune operators. Based on the Spearman correlation analysis and the Latin hypercube method, training samples are generated and numerical simulations are performed for a double C part. The surrogate models between VBHF and forming quality are constructed by a SNRBF neural network. The Pareto frontier solutions are achieved by employing the improved NSGA-II algorithm. Grey relational analysis is applied to determine the optimal VBHF loading trajectory. The results show decreased wrinkles in the optimized forming part and greater uniformity in the plastic deformation by employing the optimized VBHF, thereby leading to improvement in the forming quality of the double C.

This paper introduces an effective approach for trajectory-tracking control of an electrohydraulic rotary actuator (EHRA). The key feature of this control approach is to utilize a gain-adaptive fuzzy sliding mode control technique to realize the control objective wherein the mathematical model of the system dynamics does not need to be known exactly. Firstly, a state space form of the system model is reviewed. Secondly, an adaptive sliding mode modifier is constructed to derive an equivalent control signal while an additional fuzzy tuning scheme is employed to maintain the system robustness. Convergence of the closed loop system is then ensured by using Lyapunov analyses. Finally, effectiveness and feasibility of the proposed control method are confirmed through three experimental cases in different working conditions.

According to current development trends for automotive parts, light-weight is a key issue in improving fuel efficiency and CO2 reduction. Compared to steel and aluminum, magnesium has a relatively low specific gravity. However, it is challenging to use magnesium to produce a product at room temperature because magnesium has a hexagonal close-packed crystal structure. Therefore, the structure is not suitable for plastic deformation without using a heating system. As a result, a magnesium alloy sheet and die need to be heated from 250 to 300ºC. This paper presents the development of warm forming technology for automotive dash panel using magnesium alloy sheet.

Aluminum alloys, which are suitable for lightweight applications, are being applied widely in diverse industries, especially to the external bodies of automobiles, ships, and aircraft. The external bodies of these vehicles have a three-dimensional geometric shape with various double curvatures. However, aluminum sheets with double curvatures are difficult to form because of their elastic recovery characteristic, known as the springback effect. As a consequence, the stretch-forming process is widely used to reduce the springback phenomenon and to obtain the desired quality product. In the stretch-forming process for aluminum sheets, the stretching conditions should be precisely designed to achieve high accuracy and minimum product defects. In particular, thickness reduction and elastic recovery of the formed plate must be considered during the determination of the stretching force. In this study, the deformation of an aluminum plate according to the magnitude of a tension force was analyzed and an optimal tension force proposed, while considering changes in the mechanical properties of the formed material. FE simulations and experiments show that the proposed tension force can be used to manufacture doubly curved aluminum surfaces with minimum thickness reduction and high accuracy

This paper presents the effect of the contact angle between the retaining ring and the polishing pad in chemical mechanical polishing (CMP) on the profile of the material removal rate (MRR) around the wafer edge and on the within-wafer nonuniformity (WIWNU). This study demonstrates that the mechanical interaction among the polishing pad, wafer, and retaining ring influences the ability to achieve planarization from the CMP process. In particular, the purpose of this study is to understand the effect of the contact conditions between the retaining ring and the pad on the CMP process. In order to verify the mechanical aspects of the MRR near the wafer edge, retaining rings with different contact angles were prepared. Finite element analysis (FEA) verified the effect of the contact angle between the retaining ring and the polishing pad on the stress distribution around the edge of the wafer. The results of the analysis were corroborated by conducting CMP experiments with 200-mm blanket oxide wafers. As expected, the FEA results were in good agreement with the MRR profile around the edge area. Through simulations and experiments, we concluded that the contact angle is an important factor to achieve a flatter edge profile and the material removal profile around the edge of the wafer was optimum at a 0o contact angle. In particular the WIWNU was below 4% when a flat retaining ring was used. The results of this study make it possible to improve the yield of chip production by ensuring the retaining ring maintains perfect flatness without making any special design changes to the CMP equipment.