Applied Mechanics and Materials Vols. 395-396

Abstract: To remove the disadvantage of conventional stretch forming machine (CSFM), a flexible stretch forming machine (FSFM) has been developed by authors recently. Based on finite element simulation and experiments, the advantages of FSFM have been detailed discussed. Our results indicated that the discrete multi-gripping jaws can swing and rotate in any direction automatically, which can solve the wasteful production of CSFM by increase the rate of materials utilization and close-fitting dies. Furthermore, the value of springback and thickness gradient in the parts formed by discrete multi-gripping jaws is smaller compare with that of integrally gripping jaws, which can help to achieve a high quality of stretch forming parts. A series of double-curved sheet panels have been formed by FSFM easily and used in the cabinet covers of high-speed train and the Dongdaemun Design Park building successfully. This work has a strong value in enhance the way to flexible and reproducible stretch forming technology.

Abstract: Low formation loads are desirable in metal stamping industries as it reduces the press capacity of the machine and the tooling cost. In the previous study, the author had successfully developed a 2-stage end formation process of a round tube into a square section having small corner radii. However, the formation load in this process increased linearly with the punch stroke in the 1st stage due to the continuous expansion of the tube end by the conical die. Hence, buckling and cracks occurred at the circular section and the bottom end of the square section respectively when the punch stroke was excessive. In this study, the author proposes a circular die having a conical bottom replacing the conical die for the expansion of the tube end. Although the formation load increases when the tube end is expanded at the conical bottom, the amount of increase becomes small when the tube end reaches the circular section of the die due to its constant diameter. At the circular section, the tube end curls and wraps over the die when the punch stroke is increased. In the 2nd stage, the squaring process is performed with a conical bottom square punch and a taper square die for the two different expanded tubes i.e. the one formed with the conical die and the one formed with the conical bottom circular die. Both Finite Element Method (FEM) simulation and experiment were performed to evaluate these two processes. The distribution of plastic strains, forming loads and product appearances are investigated. With the circular die, the maximum forming loads are successfully reduced by 20% and 33% in the 1st and the 2nd stages respectively in the experiment when compared to the ones formed with the conical die. No buckling and cracks are observed for the tube formed with the circular die.

Abstract: Water jet incremental sheet metal forming is the leading research topic in sheet metal forming industry, recently. In this work, a five-axis machine for water jet incremental sheet metal forming is designed and built, which is made up of four parts, namely linear motion unit, nozzle tilt and rotation unit, fixture and seal chamber. The nozzle tilt and rotation unit has two rotation degrees of freedom and the linear motion unit has three translational degrees of freedom. Then, two types of nozzles including L type nozzle and upright nozzle are designed and built. Finally, two different kinds of fixture are designed and built for common sheet metal forming and bellows expansion joints forming, respectively.

Abstract: The procing craft which make cross pipe by hydroforming is recommend. It created finite element model by DYNAFORM and simulated the process of hydroforming four-way tube. Forming result and influencing factor of different loading path is compared and analyzed. As a result, loading path has a great impact on the forming quality of four-way tube.

Abstract: After a brief introduction of state of art of hydraulic forming technology in China and abroad, the simulation experiment and finite element model of the directly forming and step-by-step forming are designed. According to the different characteristics of forming and spring back, the simulation analysis are performed through dynamic display algorithm and statistic implicit algorithm, and analyze the influence on tube thickness, spring back amount and the final residual stress of two different manufacturing processes which is compared with the experimental result. The comparison result can provide some theoretical reference for dashboard beam hydraulic forming process design, process parameter setting and mold design.

Abstract: Due to the apparent advantages of tube hydroforming technology in reducing weight and energy consumption, and saving material and cost, it has been applied in the production of instrument panel beam. By constructing the FEM models of instrument panel beam, three numerical simulation schemes are designed according to the matching relationship between internal pressure load and axial feeding. Then the simulation results are given and compared with the experimental data. The simulation and experimental analysis indicate that the optimal matching relationship between internal pressure load and axial feeding influences hydroforming result of parts. It provides a theoretical reference for the design of hydroforming process and its die, and the setting of critical process parameters.

Abstract: A stress concentration area of big tilling depth rotary blade with 350 mm turning radius is found by ANSYS, and is strengthened by laser shock peening (LSP). The surface properties of rotary blade for LSP, included residual stress, surface micrograph, microstructure and hardness, are researched in this article. The results show that microstructure density is higher after LSP, and the layer is smoother, then the stress concentration is decreased. Meanwhile, the hardness and residual stress of rotary blade surface layer are significantly increased. The average residual stress reaches 390.7 MPa, and the average Rockwell hardness number achieves 45.1 HRC. Measuring results of residual stress, surface micrograph, microstructure and hardness after LSP indicate that LSP can significantly improve the surface properties of rotary blade, and it provides a new basis for further mending surface quality and fatigue property of big tilling depth rotary blade.

Abstract: Under continuous cutting conditions, the reliability of alumina-based ceramic cutting tools wear life with abrasion wear was discussed extensively. An ultimate state equation of alumina-based ceramic cutting tools wear life was proposed according to stress-strength interference theory. Based on the premise that the probability distribution of random parameters has been known, the fracture toughness K_IC and the hardness H which obey Weibull distribution were transformed into normal distribution by means of the equivalent normal distribution method, and then the reliability of alumina-based ceramic cutting tools wear life was analyzed by saddle point approximation method. The probability density function and cumulative distribution function of the ultimate state equation were accurately and quickly obtained by way of saddle point approximation, as a result, the saddle point approximation method was proved accurate with high computing speed in comparison with the Monte-Carlo method. Therefore, the application of the saddle point approximation method developed the reliability analysis theory of alumina-based ceramic cutting tools wear life.

Abstract: In this paper, a new plane magnetic abrasive finishing process by using alternating magnetic field is proposed to improve the efficiency and surface precision. In alternating magnetic field, the forced direction of magnetic particles is changing. Therefore, magnetic particles could produce the up and down movement, which promote the scatter of magnetic particles , improve the roll of abrasive particles and enhance the utilization of abrasive. In order to know well the magnetic intensity distribution in processing area, measured the magnetic flux density. Finishing force is important to understand the mechanism of material removal, investigated to the finishing force and contrasted to the movement changes of magnetic particles in water-soluble finishing fluid and oily finishing fluid. A set of experimental devices have been designed to realize surface polishing on C2801 brass plate, the results proved the feasibility of this method, which can improve the workpiece surface quality.

Abstract: The rationality and advancement of fixture has an important influence on the precision of fine boring which has a direct impact on the performance on auto engines and is one of the key processes of cylinder machining, so a special fixture was designed in this thesis in order to improve the capability of fine boring based on the characteristics of cylinder fine boring. The detail of operating principle, positioning/clamping mechanisms, elevating mechanism and air-operated system were introduce, practical applications indicated that, this fixture can be able to ensure the quality of machining, and improve the flexibility, conveniences and automaticity of the process of machining, so this fixture can greatly reducing the auxiliary time, reduce the production cost and labor intensity, and more satisfying the demand of mass production.