Thermal Welds Research Articles

Generating Lap Joints Via Friction Stir Spot Welding on DP780 Steel.

Friction stir spot welding (FSSW), a derivative of friction stir welding (FSW), is a solid-state welding technique that was developed in 1991. An industry application was found in the automotive industry in 2003 for the aluminum alloy that was used in the rear doors of automobiles. Friction stir spot welding is mostly used in Al alloys to create lap joints. The benefits of friction stir spot welding include a nearly 80% melting temperature that lowers the thermal deformation welds without splashing compared to resistance spot welding. Friction stir spot welding includes 3 steps: plunging, stirring, and retraction. In the present study, other materials including high strength steel are also used in the friction stir welding method to create joints. DP780, whose traditional welding process involves the use of resistance spot welding, is one of several high strength steel materials used in the automotive industry. In this paper, DP780 was used for friction stir spot welding, and its microstructure and microhardness were measured. The microstructure data showed that there was a fusion zone with fine grain and a heat effect zone with island martensite. The microhardness results indicated that the center zone exhibited a greater degree of hardness compared with the base metal. All data indicated that the friction stir spot welding used in dual phase steel 780 can create a good lap joint. In the future, friction stir spot welding can be used in high-strength steel welding applied in industrial manufacturing processes.

Thermal Stir Welds in Titanium

Although conventional friction stir welding (FSW) has proven unsuccessful in joining thick sections of alpha and near-alpha titanium alloys, thermal stir welding, a variant of the FSW process in which an external heat source is used to preheat the workpiece, is demonstrated to be able to reliably join 12.3-mm-thick plates of CP titanium. This paper describes the microstructures and textures that develop in these thermal stir welds. The observed microstructure was used to reconstruct the high-temperature microstructure and texture present during the welding process and therefore reveal the genesis of the welding structures.

Microwave Scan Inspection of HDPE Piping Thermal Fusion Welds for Lack of Fusion Defect

In this paper, microwave scan inspection was employed to detect the lack of fusion defect existing in the thermal fusion welds of high-density polyethylene (HDPE) piping. The thermal fusion welds without defects were firstly inspected by microwave scan technique. The obtained microwave interference pattern and the scan image produced were taken as the evaluation standard. Then the thermal fusion welds containing lack of fusion defects obtained under different welding conditions were inspected, and the corresponding scan images were recorded. The problems occurring in the welding processes that lead to lack of fusion defects in thermal fusion welds can be distinguished by analyzing the scan images. Mechanical tests were performed to confirm the effectiveness and reliability of the microwave scan method in detecting the lack of fusion defects in thermal fusion welds of HDPE piping.

Li-Ion Pouch Cells for Vehicle Applications — Studies of Water Transmission and Packing Materials

This study includes analysis of encapsulation materials from lithium-ion pouch cells and water vapour transmission rate (WVTR) measurements. WVTR measurements are performed on both fresh and environmentally stressed lithium-ion pouch cells. Capacity measurements are performed on both the fresh and the environmentally stressed battery cells to identify possible influences on electrochemical performance. Preparation of the battery cells prior to WVTR measurements includes opening of battery cells and extraction of electrode material, followed by resealing the encapsulations and adhesively mounting of gas couplings. A model describing the water diffusion through the thermal welds of the encapsulation are set up based on material analysis of the encapsulation material. Two WVTR equipments with different type of detectors are evaluated in this study. The results from the WVTR measurements show how important it is to perform this type of studies in dry environment and apply a rigorous precondition sequence before testing. Results from modelling confirm that the WVTR method has potential to be used for measurements of water diffusion into lithium-ion pouch cells. Consequently, WVTR measurements should be possible to use as a complement or alternative method to for example Karl Fisher titration.

Experimental and Numerical Investigation of Residual Stress and Distortion Control during Welding of AISI-316L Plates

Welding residual stress and subsequent distortions are a common problem during fabrication. Several techniques for controlling residual stress and distortion during welding, amongst which transient thermal tensioning is one of the more promising methods. Thermal tensioning can be achieved by two side heaters moving along with the weld heat source. The concept of transient thermal tensioning induces a redistribution of the stress field in the welded plate by altering the thermal field. In this paper, the results are presented on the mitigation of out-of-plane deformation during gas tungsten arc butt welding of 2 mm thick AISI-316L stainless steel. Acetylene-air burners are applied as side heaters. The thermal tensioning process induces a number of additional process parameters including the intensity, the size and the location of the heaters. A thermo-mechanical (TM) finite element model is used to cope with the complexity of the process. The model provides a better understanding of the development of the stress field, both in conventional and transient thermal tensioned welds and of the mechanisms which mitigate distortion. The model is validated by temperature, stress and distortion measurements. It appears that the redistribution of stresses and the introduction of tensile stresses by side heating is the main mechanism responsible for the reduction of distortion.

Toughness recovery of modified 9Cr–1Mo steel weld metals after long-term thermal ageing and its evaluation by electrochemical measurement

Recently, thermal power plants have tended to operate under higher temperature and pressure steam conditions for CO2 reduction. Modified 9Cr–1Mo steels are used in the ultra-super critical power plant because of their excellent creep properties. However, the toughness of base metal decreases after long-term thermal ageing at operation temperature. Moreover, toughness of weld metal is lowest in the MIG weldment. In this study, metallurgical factors of toughness of the modified 9Cr–1Mo steel weld metals by thermal ageing at operation temperature were investigated. And the evaluation method of toughness by the electrochemical measurement used with 5% sulphuric acid aqueous solution was investigated. The weld metal that received post-welding heat treatment (PWHT: 1023 K and 5.4 ks) decreased toughness by thermal ageing in 873 K and 31.5 Ms. However, toughness of the welds after thermal ageing was recovered to the same level as PWHT welds when the thermal aged welds received the same thermal history as PWHT. A lot of the large Laves phase was observed in the weld metal after the thermal ageing. However, almost all of the Laves phase dissolved in parent phase by the same thermal history as PWHT. Therefore, it seemed that the decrease and the recovery of toughness were mainly determined by the behaviour of precipitation of the Laves phase. The peak of the current density (Ip) in the electrochemical measurement appeared in the weld metals that precipitated a lot of large Laves phase. It seemed that appearance of Ip was caused by the dissolution of the Laves phase. A good correlation between toughness and Ip was observed. Therefore, it can be said that toughness of the weld metals is supposed to be predicted using an Ip of the electrochemical measurement.

長時間熱時効された改良9Cr-1Mo鋼溶接金属のじん性回復と電気化学計測による評価

Recently, the thermal power plants tend to operate under at higher temperature and pressure steam conditions for the CO2 reduction. The modified 9Cr-1Mo steels are used in the ultra super critical power plant because of the excellent creep property. However, the toughness of base metal decreases after long-term thermal aging at operation temperature. Moreover, it paid attention to the toughness of the weld metal because toughness of weld metal is the lowest in the MIG weldment. In this study, metallurgical factors of toughness of the modified 9Cr-1Mo steel weld metals by thermal aging at operation temperature were investigated. And the evaluation method of toughness by the electrochemical measurement used with 5% sulfuric acid aqueous solution was investigated.The weld metal that received post weld heat treatment (PWHT: 1023 K, 5.4 ks) decreased toughness by thermal aging in 873 K, 31.5 Ms. However toughness of the welds after thermal aging were recovered to the same level of as PWHT welds when the thermal aged welds received the same thermal history as PWHT. A lot of large Laves phase was observed in the weld metal after the thermal aging. However almost of the Laves phase dissolved in parent phase by the same thermal history as PWHT. Therefore, it seemed that the decrease and the recovery of toughness was mainly determined by the behavior of precipitation of Laves phase. Peak of the current density (Ip) in the electrochemical measurement was appeared in the weld metals of precipitated a lot of large Laves phase. It seemed that appearance of Ip was caused by the dissolution of the Laves phase. The good correlation between toughness and Ip was observed. Therefore, it can be said that toughness of the weld metals suppose to be predict using Ip of electrochemical measurement.

Potential of Radio-Frequency Balloon Angioplasty: Weld Strengths, Dose-Response Relationship, and Correlative Histology

Previous studies have established the feasibility of combining tissue heat generated by radio-frequency (RF) current and mechanical pressure to manage problems of percutaneous transluminal angioplasty (PTA) that are thought to cause postangioplasty restenosis (PARS). In the current in vitro study of normal and atherosclerotic human aortic layers (intima-media and media-adventitia) separated artificially, the purposes were to identify a dose-response relationship between the total RF energy delivered and the resultant weld strength between vascular tissues and to study the histologic correlates. Twenty-eight control and 100 experimental specimens were evaluated. The mean weld strength for all specimens with no RF current (at 0 J) was 4.1 g +/- 2.0; at 100 J, 5.9 g +/- 2.8; at 200 J, 28.5 g +/- 3.3; at 300 J, 50.0 g +/- 5.5; and at 500 J, 82.0 g +/- 8.2. Inspection of treated specimens revealed vascular molding (depression in the surface corresponding in dimensions to those of the electrode gap in the treatment chamber). Histologic examination revealed necrosis in the region underlying the electrode gap, a hypocellular fusion zone, indistinct boundaries between welded specimen parts, and transition zones to normal histologic characteristics at either end of each specimen. RF energy combined with mechanical pressure produces dose-dependent thermal welds in artificially dissected vascular tissues, molding of vascular tissue, and cellular destruction in the media. These findings may have clinical application in the management or prevention of all forms of PARS in humans and in the treatment of spontaneous aortic dissection.

Welding of polymer interfaces

AbstractStudies of strength development at polymer‐polymer interfaces are examined and applications to welding of similar and dissimilar polymers are considered. The fracture properties of the weld, namely, fracture stress, σ, fracture energy, GIc, fatigue crack propagation rate da/dN, and microscopic aspects of the deformation process are determined using compact tension, wedge cleavage, and double cantilever beam healing experiments. The mechanical properties are related to the structure of the interface via microscopic deformation mechanisms involving disentanglement and bond rupture. The time dependent structure of the welding interface is determined in terms of the molecular dynamics of the polymer chains, the chemical compatibility, and the fractal nature of diffuse interfaces. Several experimental methods are used to probe the weld structure and compare with theoretical scaling laws, Results are given for symmetric amorphous welds, incompatible and compatible asymmetric amorphous welds, incompatible semicrystalline and polymer‐metal welds. The relevance of interface healing studies to thermal, friction, solvent and ultrasonic welds is discussed.

Laser balloon angioplasty: effect of exposure duration on shear strength of welded layers of postmortem human aorta.

Laser Balloon Angioplasty (LBA) is a technique that may improve the results of balloon angioplasty by thermally sealing arterial dissections and reducing elastic recoil. To define the relationship between laser-exposure duration and the strength of thermal welds made between separated layers of arterial wall, 360 1-cm discs of human postmortem aorta were lased for six different exposure intervals at three different temperature ranges, comparing shear strength of thermal welds in the different groups. Twenty discs were lased to achieve plateau adventitial temperatures of 95 degrees C-104 degrees C (group A), 105 degrees C-114 degrees C (group B), or 115 degrees C-124 degrees C (group C) at each of the exposure periods (5, 10, 15, 20, 25, and 30 sec). A 400-micron fiberoptic coupled to a 1.06 micron continuous wave neodymium:YAG laser was placed perpendicularly 8 mm above the luminal surface of each disc, which had been split midway between the intimal and adventitial surface and reapposed. Mean laser energy ranged 78-378 J delivered in a decremental stepwise fashion to achieve quickly and maintain the target plateau tissue temperature. Mean weld strength increased in relation to both achieved tissue temperature and laser-exposure duration, with at least 10 sec necessary, at temperatures greater than 95 degrees C, for reliable thermal welding. Laser exposure for greater than 20 sec provided no statistical increment in weld strength. In the anticipated clinical performance of LBA, these data suggest that when thermal fusion of disrupted arterial tissues is desired, a laser-exposure duration of 10-20 sec is optimal.

Laser balloon angioplasty: effect of tissue temperature on weld strength of human postmortem intima-media separations.

Dehiscence of portions of atheromatous plaques fractured during percutaneous transluminal coronary angioplasty may contribute to both abrupt reclosure and gradual restenosis. Laser balloon angioplasty has been shown to be effective in welding human plaque-arterial wall separations in vitro by heating tissues with a Nd:YAG laser during balloon inflation. To define the potentially useful therapeutic range of tissue temperature required to achieve thermal welds, 220 1-cm diameter discs of human postmortem atheromatous aortic tissue, the intimal plaque of which had been separated from the media, were exposed to 3-25 watts of Nd:YAG laser radiation delivered over a 12-mm2 nominal spot size for 20 seconds via a 400-micron core optical fiber. As measured with a thermistor, adventitial temperature reflected the temperature at the plaque-media junction to within 10 degrees C. The degree of tissue temperature elevation was related to delivered energy, while effective tissue penetration increased to maximum depth of 3 mm at the highest power density. Strength of tissue welds was defined as the force required to shear opposing layers of welded segments. Adventitial tissue temperatures below 80 degrees C were not associated with appreciable welds, while equilibrium temperatures between 95 degrees C and 140 degrees C were consistently associated with effective mean weld strengths, which increased linearly from 25 to 110 g, respectively. Temperatures greater than 150 degrees C were associated with rapid tissue dehydration and charring. These data suggest that the therapeutic range of tissue temperature that provides effective thermal fusion of intima-media separations is broad and that the depth and degree of thermal coagulation can be controlled by manipulation of laser energy delivery.