Materials Science Forum Vols. 580-582

Abstract: Titanium is one of structural materials. It has several advantages such as high corrosion resistance and high strength-to-weight ratio. The demand of titanium structural panel and the dissimilar joint has been increased in industry. It is well known that joining of steel and titanium is difficult because of generating the brittle intermetallic compound. In the present work, the laser roll welding of dissimilar metals, titanium to low carbon steel been investigated using a 2.4kW CO2 laser and a 2kW fiber laser. The effects of process parameters on the formation of intermetallic compound at the interlayer and on the mechanical properties were investigated to get a sound dissimilar metal joint. As a result, welded joints of titanium to low carbon steel were broken in the base metal of low carbon steel in the tensile-shear test.

Abstract: A zircon coating was applied on the surface of Ti-6Al-4V alloy by plasma spray and its effect on the high temperature tensile properties of the alloy as well as the oxidation behavior of the alloy were studied. Tensile tests were conducted at 850°C with different strain rates of 10-4s-1,10-3s- 1, 10-2s-1 and 10-1s-1. The results show that the elongation of the coated specimens is higher than that of the uncoated ones, while the ultimate tensile strength of the alloy is not changed. An oxide film had formed on the surface of uncoated Ti-6Al-4V alloy, however no such oxide film was found on the coated alloy at the early of stage. The coating can prevent oxygen penetration into the substrate thus prevent embrittlement of the subsurface zone. The ductility could be improved by means of the zircon coating. The optical micrographs of the specimens show little change in microstructures of the coated and uncoated specimens. Zircon coating has no effect on the microstructure of the substrate alloy.

Abstract: High power lasers, including CO2 laser, Nd:YAG laser, Excimer laser, Diode laser, LD pumped YAG laser, LD pumped Disk laser, LD pumped Fiber laser and Femto second laser, are now used as a modern tool for industries as well as a computer alike in the 4th wave of modernization. Lasers are currently used for welding, cutting, drilling, cladding, direct fabrication, marking, cleaning, micro-machining peening and forming of materials in modernized factories. The joining speed (= product of welding speed and penetration depth) of 45,000mm2/min for steel sheet can be obtained by a 10kW Yb: fiber laser and is that of 50kW electron beam welding, which require the vacuum chamber. As a result of large numbers of research and developments the Advanced Laser Integrated Manufacturing System (ALIMS) using high power diode lasers has been developed and used for modernization in many industrialized countries. The laser materials processing is now penetrated as a machining tool into many industries. In the present paper, an advanced laser integrated manufacturing systems and its applications to industries such as automotive, electronics, ship building and steel making industry are introduced. In addition, development of an advanced laser integrated manufacturing system using a 2kW fiber laser for welding a car panel and “Laser Roll Welding” system for dissimilar metal joints such as mild steel/high strength steel to aluminium alloys, titanium to aluminium and steel to titanium, is described for modernization of industries. It will be a magnificent for the industries. And the 4th wave of modernization and opto-mechatronics will be promoted more by laser/photon technology in the future.

Abstract: Recently, in the loading tests for steel members, the deformation value is measured by calculating a distance of both cross-heads. This measuring method encounters a test error due to various environmental factors, such as initial slip, etc.. Especially, in the case of welded members, the non-uniform deformation behavior in welded joints is observed because of the effect of welding residual stress and weld metal. This is mainly responsible for a test error and a loss of the reliability for used test instruments. Therefore, to improve the accuracy and the applicability of measuring system, it is necessary to employ a visual monitoring system which can accurately measure the local and overall deformation of welded members. In this paper, to accurately measure a deformation of welded members, a visual monitoring system (VMS) was developed by using three-dimensional digital photogrammetry. The VMS was applied to the loading tests of a welded member. The accuracy and the applicability of VMS was verified by comparing to the deformation value measured by a test instrument (MTS-810). The characteristics of the behavior near a welded joint were investigated by using VMS.

Abstract: As the demand of higher throughput in high volume surface mounting technology (SMT) industry, inspection and testing have been notably emphasized. To alleviate concerns associated with board level soldering inspection, automatic optical inspection (AOI) has been actively used in SMT industry [1]. In this paper, statistical quality control method has been applied for board level inspection to maximize the performance of a commercially available AOI system. Considering its complication of SMT assembled board, implementing the quality control scheme for the measured variable data is fairly expensive. However, the proposed system efficiently utilizes both attribute and variable data collected for the daily/weekly based production yield reports, and further utilize as a method for in-line diagnostics in SMT manufacturing process.

Abstract: In order to obtain a good result in the laser welding process, the laser welding technology for manufacturing an automobile body is studied in this research. The monitoring of the welding quality and the seam tracking are studied to improve the productivity. The robot, the seam tracking system and CW Nd:YAG laser are used for the robot laser welding system. The laser system is 4kW Nd:YAG laser_(HL4006D) of Trumpf and the robot system is IRB6400R of ABB. The robot laser welding system is equipped with the seam tracker and plasma sensor. The seam tracking system is composed of SMART-20LS and RAPAL of Servo-Robot and MVS-5 sensor of MVS. The precise positioning of the laser beam on the joint to be assembled is obtained by seam tracker. The welding joints of steel plate are butt and lap joint. The three dimensional welding for non-linear tailored blank is performed after the fundamental experiments of bead-on-plate. Finally, the welding process for non-linear tailored blank and front side member is studied. The monitoring method of welding quality and seam tracking along the butt-joint are studied. The artificial defects in joint are well observed by the plasma intensity signal from the plasma sensor of UV and IR. The robot based laser welding system is developed for the precision seam tracking and the real-time monitoring of welding quality.

Abstract: The robot industry of the 21st century is focused on humanoid robot. It has more intelligence and is able to move dexterously like a biological organ than existing sequence robot. The key technology of this robot is the design of the actuator. To realize the anthropomorphic motion, artificial muscles, such as shape memory alloy and electro active polymer are used. The SMA actuator has good power density and simple structure, but the control scheme of the actuator is difficult. The electro active polymer has good elasticity, but it is difficult to get the required power. In this paper, the performance according to the motion control of segmented SMA wire is evaluated. SMA wire is segmented by thermoelectric modules. The displacement of SMA wire according to load is measured and its hysteresis is surveyed.

Abstract: Recently, stress corrosion cracking (SCC) of primary piping of stainless steel has been observed. SCC is considered to initiate and progress at near the welding zone in butt-welded pipes, because of the tensile residual stress introduced by welding. In present work, three-dimensional and axisymmetric thermo-elastic-plastic finite element analyses have been carried out, in order to clarify the effect of geometrical and welding conditions on through-thickness residual stress. In particular, butt-welding joints of SUS316L pipes have been examined. The residual stress was simulated by three-dimensional and axisymmetric models and the results were compared and discussed in detail.

Abstract: The welding residual stress of a butt-welded pipe joint is evaluated, using inherent strain analysis. The residual stress distribution is obtained in detail along the thickness direction. The residual stresses are similar to values obtained by direct measurement on the specimen surface; as if though direct measurement is not used for the inherent strain analysis. These results indicate that inherent strain analysis is effective in evaluating through-thickness residual stress in primary piping of girth welded joint.

Abstract: In steel structures, the mechanical characteristics and the hysteretic behavior during dynamic behavior is different to those during static deformation. This is due to the coupled effect of strain rate hardening and temperature rise. To predict hysteretic behavior of steel structures under dynamic/cyclic loading such as earthquake, it is therefore necessary to develop a rate-dependent hysteresis model which can accurately describe the static-dynamic mechanical characteristics considered the coupled effect of strain rate hardening and temperature rise as well as the hysteretic behavior. In this paper, to develop a rate-dependent hysteresis model of SM490(structural steel according to Korean standard), the monotonic and cyclic loading tests were performed for strain rate. Based on the test results, the rate-dependent hysteresis model of SM490 was formulated and with the material parameters used, the model was derived. The validity and the accuracy of the developed model were verified by comparing between the analyses and the experiments. The comparison results show that the rate-dependent hysteresis model of SM490 developed by the authors can accurately predict the static-dynamic hysteretic behavior of steel structures under cyclic loading.