Applied Mechanics and Materials Vol. 372

Abstract: Unlike rigid-body mechanisms, compliant mechanisms (CMs) gain some or all of their motion from relative flexibility of their joints. This paper presents a pseudo-rigid-body model (PRBM) method and virtual work to design and analyze kinematics and dynamics for compliant rotary joints or flexure hinges in the processing of compliant mechanisms. The stress at flexible pivot, the nonlinear-large deflection of flexure hinge, the relationship between displacement and force and/or torque, stress were taken into account in this work based on PRBM. A numerical software package, ANSYS, was exploited to illustrate schematic diagram of the stress versus to horizontal displacement of free end AB of flexure hinge. A mechanism with the desired structure is that one of the most popular aspects, which is needed to take into account in the design phase in advance. The results revealed that the proposed effective approach can be further easily applied in compliant mechanism structures. Future work will focus on multi-objective structural optimization of the flexure hinge.

Abstract: The effect of welding speeds and tool pin profiles on microstructure and mechanical properties of semi-solid metal 356 joints produced by friction stir welding was investigated. In this work, the joints were made by using a fixed rotating speed of 1750 rpm with varying welding speed of 80, 120 and 160 mm/min. In addition, two different types of tool pins, cylindrical and square pin, were applied. The Scanning Electron Microscope (SEM) reveals fine microstructure and uniform dispersion of Si (Silicon) particles obtained from cylindrical pin than that of square pin. Transverse and longitudinal tensile strengths obtained from cylindrical pin are greater than square pin. Furthermore, the joint made from 1750 rpm, 160 mm/min with cylindrical pin shows highest strength.

Abstract: The aim of this research is to study the influence of welding parameters on the metallurgical and mechanical properties of friction stir welded butt joints of dissimilar aluminum alloy sheets between Semi-Solid Metal (SSM) 356-T6 and AA6061-T651 by Friction Stir Welding (FSW). The base materials of SSM 356-T6 and AA6061-T651 were located on the advancing side (AS) and on the retreating side (RS) respectively. The base materials were joined under different tool rotation speeds and welding speeds. The material flows from SSM 356 and AA6061-T651 were clearly visible in the weld nugget. In addition, the mixtures of fine equiaxed grain were observed in the stir zone. The increase in tool rotation speed results in the increase in tensile strength of the joints. As for welding speed associated with various tool rotation speeds, an increase in the welding speed affected lesser the base materials tensile strength up to an optimum value; after which its effect increased. Tensile elongation was generally greater at greater tool rotation speed. An averaged maximum tensile strength of 206.3 MPa was derived for a welded specimen produced at the tool rotation speed of 2,000 rpm associated with the welding speed of 80 mm/min. In the weld nugget, higher hardness was observed in the stir zone than in the thermo-mechanically affected zone. Away from the weld nugget, hardness levels increased back to the levels of the base materials.

Abstract: Laser welding are well reported to be excellent in precision parts joining with high reputations in external finishing. However, the process in obtaining the best processing parameters is not an easy task. In the case of pulse wave laser, the parameter setting constrained by the laser generator specification. Each laser parameters such as pulse width t_p, pulse repetition rate f_p and average laser power P_avg has relation which others. Increasing one parameter will directly decreases the maximum value of other parameters. The limited applicable combination and rage of processing parameters make it difficult to obtain the optimized processing parameters. This study is conducted to investigate the influence of each lasing parameters on the welding penetration capability. The range of applicable parameters for titanium alloy sheet metal has been successfully clarified

Abstract: According to coal-fired power plant’s granulated powder preparation,storage and delivery processes, the existing problems of feed valves in the actual useing environment and job conditions.It was introduced to the principle about a new type of the feed valve,the form of structure and practical application.

Abstract: Dry machining is environmentally friendly, clean and safe to be performed. Regardless of decreasing tool life due to lack of lubricants, choosing dry machining over wet machining may be a wiser choice since the cost of purchasing and disposing the cutting fluids can contribute to a higher cost. Wear rates, tool wear intensities and material removal rates (MRR) of TiCN coated tools using both dry and traditional wet machining on brass were studied with the aim in finding the optimum cutting condition from four different cutting speeds (207, 279, 372 and 498 m/min) with two sets of cutting parameters; depth of cut and feed rate (d = 0.1 mm, f = 0.2 mm/rev and d = 0.2 mm, f = 0.4 mm/rev). Temperatures at the tool-chip interface were measured to analyze the effects of temperature rise during dry machining. Cost analysis on machining cost per piece between dry and wet machining was performed. The optimum cutting condition for wet and dry machining of brass using TiCN coated cutting tool was found to be 498 m/min at d = 0.2 mm, f = 0.4 mm/rev. The tool tip temperature obtained from dry machining did not influence tool wear since the temperature rise is quite similar to the wet machining temperatures. The machining for the dry machining reduced to about 25-76% per piece when compared with wet machining.

Abstract: In this paper, the wear performance of polymer radial ball bearings (PEEK-PTFE and PPS-PTFE) were investigated. For effective operation of equipment in clean energy facilities environment, the polymer bearings were developed. These polymer bearings were produced by machining and their rolling contact fatigue (RCF) behavior under non-lubricated condition was carried out. PEEK accumulation layer with PTFE and graphite was formed on the bearing's inner ring under 3000 rpm high rotation speed. Due to the self-lubrication of PEEK layer, the wear loss of PEEK-PTFE bearing was lower than PPS-PTFE radial bearing. Moreover, it was found that the thin PEEK layer protected the raceway from the friction heat and wear. The wear durability of PEEK-PTFE bearing was superior to PPS-PTFE one.

Abstract: In this work, wear of reinforced poly-ether-ether-ketone (PEEK) polymer bushes in friction against 7075 aluminium alloy cam plates or titanium crankshafts is investigated in order to establish the application possibilities in transmission parts in humanoid robot joints under high load torque. The PEEK bush wear requires close examination as well as the input axis-output axis transmission error (backlash). Sliding wear tests were performed on bushes under 4000 kgfcm (392 Nm) load torque, while the cam plate oscillated in the humanoid robot leg joint evaluation system. The robot joint using PEEK bush achieved quite small backlash after the fatigue wear test.

Abstract: Machining of Carbon Fibre Composites (CFCs) particularly drilling, is frequently employed in industry especially when dealing with joining, assembly and structural repair of the parts. However, the nature and heterogeneous structure of CFCs often results in rapid wear of the cutting tool. This research studied the relationship and compared the effect of drilling a CFC plaque without cutting fluid, with conventional cutting fluid and with cryogenic cooling at constant cutting speed of 94 m/min and feed rate of 0.065 mm/revolution using tungsten carbide twist drill. The conventional cutting fluid was supplied continuously to the drill and the CFC plaque during the drilling cycle; while for the cryogenic cooling tests, the drill tip was immersed in liquid nitrogen for 10 and 30 seconds prior to drilling the CFC. It was found that the tool wear increased with the increasing number of drilled holes at all machining conditions. After drilling of 325 holes, the largest tool wear observed was 181 μm which was produced when drilling the CFC plaque with conventional cutting fluid. The corresponding tool wear for drilling with cryogenic cooling was 164 μm and the smallest tool wear of 155 μm was observed during dry drilling. Dry drilling produced the smallest tool wear because the heat generated reduced the strength of the CFC, particularly polymer matrix. Therefore, this situation led to easier machining of CFC materials; consequently reduced the wear of the tool.

Abstract: Finite element analysis of a coated SCMV (high-strength alloy steel) substrate with interlayer has been studied with the emphasized of stresses behaviour predicted in the substrate region due to the fretting wear surface profiles modification. The analysis is simulated using a simple cylinder-on-flat contact geometry under gross sliding condition for a given surface profile on a specific number of fretting cycles. The effect of interlayer stiffness on the stresses predicted in the substrate region is studied. It is found that the stresses in the substrate region are generally predicted to reduce with the increase of interlayer stiffness and with the advancement of wear.