Development of a mobile robotic system for working in the double-hulled structure of a ship

Shipbuilding processes involve highly dangerous manual welding operations. Welding ship walls inside double-hulled structures presents a particularly hazardous environment for workers. This paper describes the “Rail Runner X” (RRX), a new robotic system that can move autonomously inside the walls of a double-hulled ship and automatically execute the required welding processes. The RRX robotic system is composed of a mobile platform and a welding robot consisting of a 3P3R serial manipulator. The robot is used to weld U-shaped trajectories located between two longitudinal stiffeners. The mobile platform enables traverse movements onto neighboring longitudinal stiffeners. The entire cross section of the robotic system is small enough to be placed inside the double-hulled structure via a conventional access hole from the outside shipyard floor. The overall engineering design process that led to the final robot solution developed is presented in this paper, including kinematic analysis data and experimental results for verifying the autonomous movement and welding performance.     

Tool fabrication for composite forming of aircraft winglet using multi-point dieless forming

Journal of Mechanical Science and Technology - Flexible forming technology such as Multi-point dieless forming (MDF) has benefits for the sheet metal field because it can implement a variety of...     

Constitutive modeling for the dynamic recrystallization evolution of AZ80 magnesium alloy based on stress-strain data

In order to improve the understanding of the dynamic recrystallization (DRX) behaviors of as-cast AZ80 magnesium alloy, a series of isothermal upsetting experiments with height reduction 60% were performed at the temperatures of 523 K, 573 K, 623 K and 673 K, and the strain rates of 0.01 s⁻¹, 0.1 s⁻¹, 1 s⁻¹ and 10 s⁻¹ on a Gleeble 1500 thermo-mechanical simulator. Dependence of the flow stress on temperature and strain rate is described by means of the conventional hyperbolic sine equation. By regression analysis, the activation energy of DRX in the whole range of deformation temperature was determined to be Q = 215.82 kJ mol⁻¹. Based on dσ/d? versus σ curves and their processing results, the ?ow stress curves for AZ80 magnesium alloy were evaluated that they have some characteristic points including the critical strain for DRX initiation (?_c), the strain for peak stress (?_p), and the strain for maximum softening rate (?*), which means that the evolution of DRX can be expressed by the process variables. In order to characterize the evolution of DRX volume fraction, the modified Avrami type equation including ?_c and ?* as a function of the dimensionless parameter controlling the stored energy, Z/A, was evaluated and the effect of deformation conditions was described in detail. Finally, the theoretical prediction on the relationships between the DRX volume fractions and the deformation conditions were validated by the microstructure graphs.     

Interpolating G Bézier surfaces over irregular curve networks for ship hull design

We propose a local method of constructing piecewise G¹ Bézier patches to span an irregular curve network, without modifying the given curves at odd- and 4-valent node points. Topologically irregular regions of the network are approximated by implicit surfaces, which are used to generate split curves, which subdivide the regions into triangular and/or rectangular sub-regions. The subdivided regions are then interpolated with Bézier patches. We analyze various singular cases of the G¹ condition that is to be met by the interpolation and propose a new G¹ continuity condition using linear and quartic scalar weight functions. Using this condition, a curve network can be interpolated without modification at 4-valent nodes with two collinear tangent vectors, even in the presence of singularities. We demonstrate our approach in a ship hull.     

Dynamic response characteristics of seismic isolation systems for building structures

Isolation is an effective method of reducing effects of seismic events on building structures. Steel-reinforced elastomeric isolator (SREI) is one kind of isolation system which is used extensively, but there are some problems associated with its use, such as cost and weight. Fiber-reinforced elastomeric isolator (FREI) has been developed in an attempt to solve the problems of high cost and heavy weight for SREI. In this study, mechanical properties for the SREI and the FREI are investigated. Systematic dynamic response analyses are performed for three different models such as a fixed based, an SREI based and an FREI based low-story building structures. Two-dimensional and three-dimensional dynamic response analysis results for each model are compared in terms of displacement, drift, acceleration and shear force in this study. In the two-dimensional dynamic response analysis, the SREI and the FREI based structures are proven to be the more effective isolation systems against seismic events by comparing with the fixed based one. As a result, the FREI has shown better isolation performances than that of the SREI. Furthermore, to extract the characteristics of the FREI on building structure resisting the seismic effects, two models of three-dimensional framed structure with fixed bases and FREI isolated bases are built, respectively. After the dynamic response analysis of these two structures subjected to bi-directional ground motions, the analyzed results are compared with each other. It is shown that the FREI could effectively absorb the seismic energy, and decreases the destructive effects acting on a building structure due to ground horizontal motions that could occur in an earthquake. This paper was recommended for publication in revised form by Associate Editor Seockhyun Kim Beom-Soo Kang received his B.S. in Mechanical Engineering from Pusan National University in 1981 and his M.S. in Aerospace Engineering from KAIST in 1983, Korea, respectively. He then received his Ph.D. from the University of California at Berkeley, USA, in 1990. Dr. Kang is currently a Professor at the Department of Aerospace Engineering at Pusan National University in Busan, Korea. His research interests include seismic isolation, materials processing, FEM and flexible forming technology. Tae-Wan Ku received his B.S., M.S. and Ph.D. in Aerospace Engineering from Pusan National University, Korea, in 1997, 1999 and 2003, respectively. Dr. Ku is currently a research professor at the Department of Aerospace Engineering at Pusan National University in Busan, Korea. His research interests include multi-stage deep drawing, flexible forming technology, and forming limit surface theory.     

A study on deburring of magnesium alloy plate by magnetic abrasive polishing

Drilling is one of the most important machining operations in manufacture process. When drilling process is applied, unexpected burrs will be formed on the surface of workpiece. Even a small burr can cause unwanted problems, resulting in low quality products. In order to get better drilled parts, it is very important to know characteristics of burr formation and to remove the burr from the drilled surface with machining process. In this study, magnetic abrasive polishing (MAP) was used to research the deburring factors of magnesium alloy. Moreover, design of experiments was performed to evaluate parameters’ effect on the MAP process. As a result, it was seen that the MAP was useful to remove the burrs on the workpiece without damage from its original surface.     

A review of adhesion and friction models for gecko feet

The attachment pads of geckos exhibit the most versatile and effective adhesive known in nature. Their fibrillar structure is the primary source of high adhesion and their hierarchical structure produces the adhesion enhancement by giving the gecko the adaptability to create a large real area of contact with surfaces. Although geckos are capable of producing large adhesive forces, they retain the ability to remove their feet from an attachment surface at will. Detachment is achieved by a peeling motion of the gecko’s feet from a surface. During the last few years, many researches have been conducted to develop the theoretical models that explain the gecko to adhere and detach from surfaces at will, including micro/macroscopic gecko adhesion, friction and peeling models for gecko hierarchical fibrillar structure contacting to rough surface. This review describes the progress in the modeling filed for gecko adhesion, friction and peeling, and discussed the future issues for gecko modeling.     

Average flow model with elastic deformation for CMP

We present a three-dimensional (3D) average flow model considering elastic deformation of pad asperities for chemical mechanical planarization. To consider the contact deformation of pad asperities in the calculation of the flow factor, 3D contact analysis of a semi-infinite solid based on the use of influence functions is conducted for computer-generated rough surfaces. The average Reynolds equation and boundary conditions of both force and momentum balance are used to investigate the effects of pad roughness and external pressure conditions on a film thickness and wafer position angles. It is found that the position angles decrease with the increasing of the applied pressure and the roughest pad has the highest position angles at any given load. Comparing elastic and rigid pads, the minimum film thickness formed between the elastic pad and the wafer is thinner than that between the rigid pad and the wafer.     

Tailored blank design and prediction of weld line movement using the backward tracing scheme of finite element method

To achieve weight and cost reductions in component manufacturing, tailored blank is introduced for forming automotive structural skin components. In order to obtain successful application of tailored blanks without necessarily trimming after the forming process, it is critical to design an initial welded blank and to predict the weld line movement, which is usually determined by intuition and experience with the trial-and-error approach. A systematic approach method of the backward tracing scheme, which is confirmed by experiment, is extended to design the initial tailored blank for net-shape production in this study. The optimised tailored blank by the backward tracing scheme appears to be successful in obtaining a net-shape stamping product. This blank also improves the forming condition during stamping process. All simulation results show that the backward tracing scheme can be applied to more general blank design.