Advanced Materials Research Vols. 189-193

Abstract: This paper dealt with the outstanding problems which were forging cracks existing in the process of forging.The forming reasons of forging cracks were analyzed. From the perspective of damage mechanics, the conventional mesoscopic models and fracture criteria of ductile metal material damage were introduced. The problems in recent research of forging cracks were pointed out. Some corresponding suggestions for the future research of forging carcks were put forward based on the existing problems. The existed ductile fracture criteria have only predicted the damage of specific process yet ,while the diversities of metal forming processes require ductile fracture criterion to have wide scope of application,so,for reason given above,the emphasis is placed on the necessity of establishing new ductile fracture criteria and fracture parameter library with the method of combination of theory and experiment and numerical simulation.

Abstract: Ball spinning is an effective process to manufacture thin-walled tubular product of superalloy Inconel 718, which has been used widely in aerospace and other fields. In this literature, ball spinning process of superalloy thin-walled tube was investigated using software DEFORM. The build-up phenomenon and its influencing factors like principal axis speed, axial feed rate and wall thichness reduction were investigated using the finite element method (FEM). The experiment of ball spinning process was perfomed based on the proper technical parameters obtained by simulation. The simulated results agreed well with the experimental results.

Abstract: Coping with the characteristic of flow shop scheduling problem with uncertain due date, fuzzy arithmetic on fuzzy numbers is applied to describe the problem, and then a new hybrid algorithm model which integrate particle swarm optimization into the evolutionary mechanism of the knowledge evolution algorithm is presented to solve the problem. By the evolutionary mechanism of knowledge evolution algorithm, we can exploit the global search ability. By the operating characteristic of PSO, we can enhance the local search ability. The algorithm is tested with MATLAB simulation. The result, compared with Genetic algorithm and modified particle swarm optimization, shows the feasibility and effectiveness of the proposed algorithm.

Abstract: Spin-forming of trapezoidal inner gear is a new technology of the near-net forming in gear manufacturing field. Processing parameters, such as the initial thickness of blank and radial reductions of each roller, greatly influence the forming quality of spun part. The forming quality of trapezoidal inner gear involves the filling status of gear tooth and dimensional accuracy of root circle. An approach for processing parameter optimization of the forming quality of the trapezoidal inner gear stagger spinning is proposed. The proposed approach integrates the orthogonal experiment design, gray relational analysis, and analysis of variance (ANOVA). The experiment result indicates that the proposed approach is effective in determining the optimized processing parameters for the stagger spinning of trapezoidal inner gear.

Abstract: Grinding is widely used as a precision process for machining difficult-to-cut materials. Grinding productivity is still greatly dependent on the experience and skill of human operators. Focusing on the indirect method, an attempt was made to build up an intelligent system to monitor the condition of grinding wheels with force signals and the acoustic emission (AE) signals. An artificial immune algorithm based multi-signals processing method was presented in this paper. The intelligent system is capable of incremental supervised learning of grinding conditions and quickly pattern recognition, and can continually improve the monitoring precision. The experiment indicates that the accuracy of condition identification is about 87%, and able to meet the industrial need on the whole.

Abstract: Automatic identification of flaws is very important for ultrasonic nondestructive testing and evaluation of large shafts. A novel automatic identification model of defects is presented. Empirical Model decomposition (EMD) is applied to feature extraction of ultrasonic signals, and possibility Support Vector Machine (SVM) with Dempster-Shafer (DS) theory to perform the identification task. Meanwhile, comparative study on convergent velocity and classified effect is done among SVM and artificial neural network (ANN) with DS models. To validate the method, some experiments are performed and the results show the proposed system has very high identification performance for large shafts and the possibility SVM processes better classification performance and spreading potential than ANN with DS model under the small study sample condition.

Abstract: The steel wheel centre discs are usually stamped by multi-stage sheet metal forming. The stage number and the content of every stage decide if the structure-pieces can be formed successfully and the final forming quality. In this paper, the forming characteristics of wheel centre disc were analyzed firstly and the reasonable two-stage stamping scheme of drawing and inverse-drawing are adopted. The numerical simulations of multi-stage stamping process are performed and connected together through deformation transmission. By means of FLD and changes of sheet metal chickness, the formability is analyzed and the forming process is optimized. The feasibility of multi-stage forming process simulation and the validity of the optimized scheme were verified by stamping in practice.

Abstract: Warm compacting behaviors of pure titanium powders were studied. The results show that warm compaction can be applied to titanium powders. The green densities obtained through warm compaction are generally higher than obtained through cold compaction at the same pressure. The optimal warm compacting temperature is about 140 . At the compacting pressure of 500 Mpa, the ejection force of titanium powders through warm compaction is 32.4% lower than through cold compaction. At the same pressure, the effective compression force through warm compaction is bigger than one through cold compaction. In addition, the densification mechanism of warm compaction was discussed.

Abstract: The warm-cold forming process is researched for complex-DOJ-type spherical housing by means of numerical simulation. Each step of the process is simulated, especially for the reverse extrusion process. Focusing on analysis of the material flow, temperature distribution as well as the load curve, a reasonable process for DOJ-type spherical housing is obtained. The reasonable forming process for DOJ-typed spherical housing offers favorable basis for forming and mold design.

Abstract: In rotary-draw bending process of thin-walled rectangular tube, cross-sectional distortion is an unwanted byproduct, which is closely related to geometry parameters. To study the effects of geometry parameters on cross-sectional distortion, a 3-D finite-elements model was built under the ABAQUS/Explicit environment, and its reliability was validated by experiments. Then, simulation and analysis of the influence laws of geometrical parameters on cross-sectional deformation degree were carried out. The results show that increases with the increase of b/h and decreases with the increase of R/h when b/h>1. However, R/h has little influence on δh when b/h≤1. And the influence of b on δh is larger than that of h, and the effect of h on δh is larger than that of R.