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Kumagai K.,Hitachi Construction Machinery Co | Ryu S.,Hitachi Construction Machinery Co | Ota M.,Chiba University
International Journal of Fluid Power

The poppet valve is a popular component in hydraulic systems, but it is also well known as trouble maker because it may occasionally induce unpredictable vibration. In former previous studies it has been found that cavitation is an important reason for this kind of vibration, but the causal mechanism between the vibration and cavitation is unclear. In this study, we developed a visualisation experiment system, in which we can observe and analyse the dynamic relationship among the displacement of the poppet, the cavitation quantity and the pressures around the poppet in a visualisation experiment. Based on the observation of the experimental phenomena and data analysis, we propose a hypothesis of a mechanism that can explain how cavitation influences the vibration of the poppet valve. © 2015 Taylor & Francis. Source

Yamane S.,Saitama University | Uji K.,Saitama University | Nakajima T.,Hitachi Construction Machinery Co | Yamamoto H.,Hitachi Construction Machinery Co
Welding International

The formation of stable back beads in a root pass weld during one side multi-layer welding is important to achieve high quality welded metal joints in MAG welding. The authors employed the switch back welding method for V groove joints without backing plates. In this switch back welding method, the torch moves forward and backward with an oscillation frequency of 2.5 Hz. In order to achieve this welding, personal computers control the conventional welding robot, the power source characteristic and the wire feeder unit. During the forward, the torch is weaving on the V groove gap without the weld pool. If the weaving width becomes wider than the proper width, the tip of the wire becomes high and a good back bead cannot be obtained. The weaving width is adjusted so as to get the proper width in the switch back welding. The suitability of the welding conditions for each root gap was verified by observation of the arc, the weld pool and the external appearance of back beads. A good back bead was obtained under V groove welding in 2–4 mm gap. © 2015, © 2013 Taylor & Francis. Source

Usami H.,Meijo University | Horiba Y.,Meijo University | Akita H.,Hitachi Construction Machinery Co | Kobayashi S.,Hitachi Construction Machinery Co
MM Science Journal

The present study proposes a novel surface modification process based on surface deformation, surface plastic flow process, to improve tribological properties of pure titanium (Ti) surfaces. The developed process consists of micro shot peening and roller burnishing: The former and the latter processes are applied to fabricate micro dimples and to penetrate molybdenum disulfide (MoS2) fine powders into the dimples. During the burnishing process, the surface was truncated and the penetrated MoS2 into the dimple was densified simultaneously. As a result, the treated surface was relatively flat and consisted of micro dimples filled with dense MoS2. Tribological properties of the treated surface were evaluated with a ring on disc type testing apparatus using a hardened steel ring as a mated specimen in lubricated condition. Results indicate that the tribological properties of the MoS2 penetrated surface have significantly improved including restriction of occurrence of seizure. © 2014, MM publishing Ltd. All rights reserved. Source

Masuda K.,Hitachi Construction Machinery Co | Nakamura H.,Hitachi Construction Machinery Co
Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A

Recently, many analytical tools have been developed for the structural design and assessment of structural integrity. For welded structures, however, application of the welding simulation as a design tool is relatively limited due to its lack of verification characteristics. So, is necessary to develop a new analytical procedure for evaluation of the welding deformation and residual stresses. For this purpose authors have developed an inversed problem approach based on eigen-strain analysis, where further improvement of accuracy is desired. In this study, eigen-strain characteristics which reproduce both welding deformations and residual stresses are examined by utilizing welding simulations. Eigen-strain components that affect to a specific type of deformations are made clear. By using these results, welding deformations and residual stresses can be reproduced with selected eigen-strain components by image processing of welded plate surface before and after the weld. Source

Yamane S.,Saitama University | Godo T.,Saitama University | Hosoya K.,Hitachi Construction Machinery Co | Nakajima T.,Hitachi Construction Machinery Co | Yamamoto H.,Hitachi Construction Machinery Co
Welding International

The formation of stable back beads in joining of the thick materials is important in order to achieve high-quality welded metal joints. Plasma welding uses the high welding current density, which is suitable for thick materials. The keyhole in the plasma welding depends on the pilot gas and the welding current. The voltage behaviour depends on the keyhole situation. If the torch is moved away from the welding line in conventional GMA welding, the welding voltage and the welding current are changed due to variations of the arc length. But the welding voltage does not change with the arc length in plasma welding, because the welding voltage depends on the situation of the keyhole. The authors tried to observe the weld pool on the top side by using a CCD camera. The timing of the shutter in the CCD camera is investigated to take clear images of the weld pool. As a result, the clear images of the weld pool were taken when the welding current was reduced to 30 A and an interference filter of 950 nm was attached to the CCD camera. The weld pool shape was changed with the torch position in the groove. The image-processing method was developed to detect the top of the weld pool. The torch position was estimated by processing the weld pool images. The digital control was designed to trace the welding line. The performance of the controller was verified by carrying out tracking experiments. © 2014, © 2014 Taylor & Francis. Source

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