Key Engineering Materials Vol. 661

Abstract: Hydraulic system plays an important role in many power systems such as excavator, braking system of vehicle and machine tool. Generally speaking, hydraulic control system can be divided into two different driving concepts. The first one is the well-known valve-controlled system and the second one is the pump-controlled system. The former possesses the feature of fast dynamic response. However, the poor energy-saving performance is its major fault. On the contrary, the pump-controlled system has the significant advantage of energy-saving which meets the current demand in modern machine design, but has the disadvantage of slower dynamic response. With the advancement of electric-motor system, however, this disadvantage has been greatly improved. In this paper, the simulation analysis of a newly developed energy-efficient hydraulic CNC lathe turret based on constant pressure control scheme is presented. Instead of the conventional fixed displacement hydraulic pump, the new energy-efficient system utilizes an internal gear pump together with an AC servo motor as its driving power source. In addition, a closed-loop control scheme using PID control is adopted. From simulation results, the new energy-efficient design can reduce the waste of the output flow-rate of the pump through the relief valve that generally happens in conventional hydraulic lathe and then achieve the purpose of designing an energy-efficient hydraulic lathe.

Abstract: The purpose of this study aims at the kinematic study of generalized Oldham couplings by conducting kinematic analysis, kinematic simulation, and prototype experiment. First, the characteristics of generalized Oldham couplings are presented. Then, kinematic analysis and kinematic are performed. Finally, a prototype and its associated experimental setup are established. An experiment is conducted to evaluate the performance of the coupling. The simulated result shows that the output of the coupling is non-uniform, and close to a sinusoid. The experimental result indicates that the experimental output approximately agrees with the theoretical, but with fluctuations and a phase lag.

Abstract: The focus of this research is the development of a single pulse micro EDM system and to manufacture micro spherical probe used in micro CMM. In the single pulse micro EDM system contain unsteady-state multi-degree oscillation circuits to control the transistors’ switches. This configuration is to achieve the adjustment of pulse-off time of the micro-electrical discharge machining system. Investigating the effect of pulse voltages on the critical discharge gaps, the experimental results show that maximum discharge gaps are linearly proportional to the pulse voltages. This tendency serves as the basis for the machine processing parameters. And used of the single pulse micro EDM system to machining micro spherical probe.The micro spherical probe with a diameter smaller than 100 μm, is made by a single pulse micro EDM system with the method of wire electro discharge grinding (WEDG). The current study uses tungsten carbide (WC) as the material for the stylus. Experimental results show that, the micro spherical probe roundness could amount to 2 μm.

Abstract: A polymer-based capacitive micromachined ultrasonic transducer (CMUT) is developed to measure surface roughness. The transducer is designed with two groups in a ratio of two to one. By using air-coupled ultrasound, the transducer can evaluate surface roughness in five modes: full transmission/ full reception, majority transmission/ majority reception, majority transmission/ minority reception, minority transmission/ majority reception, and minority transmission/ minority reception. Experimentation shows the CMUT can identify the surface roughness using a sample of sandpaper with surface roughness Rrms ranging from 11.4μm to 179.8μm. The results indicate that the full transmission/ full reception mode has maximum signal output and the minority transmission/ majority reception mode can obtain a good signal output with a better energy efficiency rating.

Abstract: This paper develops an enhanced grey variable structure controlled DC-AC inverter in parallel, and is suitable for the application of ultra-precision machining (UPM). The enhanced grey variable structure control methodology consists of a nonlinear sliding function (NSF) and a grey model, GM(2,1). The NSF has finite system-state convergence time, and thus the AC output voltage regulation and balanced current-sharing among the parallel modules can be achieved. However, once the loading of the UPM is a highly nonlinear condition, the chatter still exists in NSF. The chatter may cause heat losses and high voltage harmonics in parallel-connected DC-AC inverter output, and thus deteriorates the stability and reliability of the UPM. To eliminate the chatter, the control gains of the NSF can be adjusted by the use of the GM(2,1) under system uncertainty bounds are overestimated. With the enhanced methodology, the parallel-connected DC-AC inverter yields a high-quality AC output voltage with low voltage harmonics and fast dynamic response under highly nonlinear loading, thus achieving the stability and reliability of the UPM. Experimental results are performed to demonstrate the enhanced methodology.

Abstract: Most cold forging die insert materials are powder sintered tungsten steel materials, which can hardly bear the circumferential tension and stress that the die insert longitudinal fracture is easily caused. For this reason, this study intends to investigate effects of die insert pre-stress resulted from shrink fit interference on the die to prevent the product accuracy and service life from being reduced due to the die failure in the forging process. The die effective stress distribution is also calculated in this study, and the interference is added between tungsten steel die inserts and cases to prevent tungsten steel from being damaged by the circumferential stress. The die stress distribution caused by common shrink fit interference in the industry is also investigated. The optimal interference acquired under the design criteria of decreasing equivalent stress presents 0.4%, 0.2%, 0.1%, 0.8%, and 0.1% at different stages. The research results could be the reference to select the optimal parameter for the die design and further shorten the product development effectiveness and reduce the costs.

Abstract: This study intended to investigate the longitudinal crack on the tungsten carbide alloy die core that caused by the influence of receiving the hoop tensile stress in the process of inverse extrusion. Therefore, the shrink fit is adopted to design the die core and stress ring, and assemble the die case, in order to yield the hoop compressive stress in advance, which can be used to resist the tensile hoop stress yielded from the forging process. It also applied the FEM simulation software and Taguchi Method L₉(3⁴) in this study to simulate various combinations of different shrink fits, in order to obtain the best combination of die. Moreover, it focused on the compressive strength of material characteristics for the tungsten carbide alloy steel die core, and properly adjusted the shrink fit to prevent an early crack on the die core that caused by the hoop compressive stress in advance, in order to achieve the best result.

Abstract: This article aims at the discussion of deformation behavior considering size effect on curl forming process of sheet metal. In this study, the test specimens were made by phosphor bronze sheets for curl forming test. The specimens with different thickness were firstly heated at different temperatures for obtaining the objective grain sizes. And the mechanical properties of specimen were acquired by using tensile test. Through the curl forming test with a curl forming machine, the curled angles, springback and curling load were measured and analyzed for investigating the grain size effect of the chamfer and carbon lubricant during the curl forming process.

Abstract: In this paper, construction of finite element analysis based on DEFORM^TM 3D four-blade face milling cutter aluminum 6061 cutting, explore the finite element analysis of face milling cutter rotating in a circle cutting of aluminum alloy 6061.Tool types used WC milling cutters, cutting speed, feed rate as fixed process parameters. The study analyzed four rotations of the blade face milling chip formation, effective stress, effective strain and material changes in temperature and tool wear.