Ultra-thin Stainless Steel Sheets Research Articles

Hot stamping of ultra-thin stainless steel sheets for bipolar plates

Hot stamping of ultra-thin stainless steel sheets for bipolar plates

Numerical and experimental study on oscillation mechanism of molten pool during pulsed microplasma arc welding ultrathin sheets

Molten pool oscillation behaviors during pulsed microplasma arc welding ultrathin stainless steel sheets were studied based on the numerical simulation, experimentally visual detection, and theoretical calculation. Without altering the average heat input, the effects of different pulse parameters of welding current on weld pool oscillation frequency and oscillation amplitude were discussed. It showed that the changes either in the weld pool temperature and liquid metal flow rate or in weld pool size cannot keep up with the rapid variations of welding current from base current to peak current or from peak current to base current. The mainly periodic changes of molten pool size and liquid metal flow rate are caused by pulsed current. However, on these main periodic changes, small amplitude fluctuations are superimposed due to weld pool oscillations. The oscillation frequency decreases and the oscillation amplitude increases slightly with the growth of molten pool. Oscillation frequency increased with an elevating in pulsed current frequency, and it rose firstly and then fell when duty cycle of pulsed current increased. Moreover, concerning the fluctuations in weld pool size, the oscillation amplitude reduced with the enhancement in pulsed current frequency though there were no obvious variations in it with the variations in duty cycle of welding current.

Plastic instability and fracture of ultra-thin stainless-steel sheet

A new approach was used to characterise the hardening, instability and fracture behaviour of ultra-thin (0.1 mm) stainless steel sheets under stress triaxiality ranging from 0.37 to 0.66. The Swift and the linear hardening laws were used to capture the stress–strain relationship for the complete level of plastic deformation that exceeds that achievable by a uniaxial tensile test. For this, the Virtual Field Method (VFM) was applied, which uses the strain field measured on the surface of the notched samples, to output the material hardening parameters. To determine one set of hardening parameters that fits all conditions of stress triaxiality, an upper bound of major strain was selected for the VFM fitting that optimises a single set of hardening parameters across all of the stress triaxiality conditions. The void coalescence parameter in a Gurson-Tvergaard-Needleman (GTN) fracture model was calibrated and the model results for fracture initiation were validated experimentally with a quasi-biaxial stretching test.

Analysis on the Action of Oxidant in Chemical Mechanical Polishing of 304 Ultra-Thin Stainless Steel

The ultra-thin stainless steel sheet will be used in flexible displays for substrate material. The application of the substrate requires its surface very smooth, no defects and damage free. Chemical mechanical polishing (CMP) has been considered as a practical and irreplaceable planarization technology in the ultra precision machining of the flexible display substrate. In chemical mechanical polishing of ultra-thin stainless steel, the oxidant of polishing slurry has an important influence on the material removal rate (MRR). In this paper, the influences of oxidant in slurry on MRR and surface roughness had been studied in CMP of ultra-thin 304 stainless steel based on alumina (Al2O3) abrasive. The research results show that the oxidant of the hydrogen peroxide and the oxalic acid have the interaction in CMP 304 stainless steel and when using the only one oxidant in polishing slurry, the hydrogen peroxide or oxalic acid, the MRR is less than the maximum. The oxalic acid can provide a strong acidic environment to ensure the stability of the hydrogen peroxide in polishing slurry and to improve the MRR in CMP 304 stainless steel. The research results can provide the reference for studying the slurry in CMP of ultra-thin stainless steel.

Design and optimization of stamping process of ultra-thin stainless sheet into bidirectionally corrugated shape for finless high-efficiency heat exchanger

The stamping of an ultra-thin stainless steel sheet into a wave shape for a finless heat exchanger was investigated. As an alternative to fins made by the extrusion or drawing, a bidirectionally corrugated shape is advantageous because of its higher efficiency in heat exchange with smaller resistance to an ambient air flow. A greater wave height is advantageous, but is suppressed by fracture during stamping. A new stamping method was developed to realize a high-efficiency heat exchanger using an ultra-thin stainless steel sheet with an optimized corrugated shape in terms of the plan-view pattern and cross-sectional profile.

Mechanical Properties Involved in the Micro-forming of Ultra-thin Stainless Steel Sheets

The objective of this paper is to characterize the mechanical behavior of an ultra-thin stainless steel, of 0.15-mm thickness, that is commonly used in the manufacturing of miniature connectors. The main focus is the relationship between some microstructural features, like grain size and surface roughness, and the macroscopic mechanical behavior investigated in uniaxial tension and simple shear. In tension, adaptations to the very small sheet thickness, in order to hold the specimen under the grips, are presented. Yield stress, initial elastic modulus, and evolution of the loading–unloading slope with plastic deformation were evaluated. Moreover, the kinematic contribution to the hardening was characterized by monotonic and cyclic simple shear test and reproduced by a mixed hardening law implemented in Abaqus finite element code. Then, the evolution of surface roughness with plastic strain, both in tension and simple shear, was analyzed. It was shown that in the case of an ultra-thin sheet, the stress levels, calculated either from an average thickness or when considering the effect of the surface roughness, exhibit a significant difference. Finally, the influence of surface roughness on the fracture of a tensile specimen was also investigated.

Design of Lapping Paste in Lapping 304 Ultra-Thin Stainless Steel Sheet

Ultra-thin stainless steel sheet is likely to be the ideal substrate materials used for flexible display. In order to obtain ultra-thin stainless steel substrate with high accuracy, low surface roughness and without damage, the ultra-precision lapping and chemical mechanical polishing technology must be used. In this paper, the lapping paste for stainless steel has been designed using the orthogonal experiment method. According to the range analysis method, an optimal lapping paste had been obtained. Tests lapping the 304 stainless steel sheet with the optimal lapping paste have been done. The test results show that the MRR is about 240nm/min and the surface rough Ra is about 128 nm. This research results can provide theory support for ultra precision machining the stainless steel.

Experimental Investigation on Micro-Welding of Thin Stainless Steel Sheet by Fiber Laser

Problem statement: The miniaturization of components plays an important role for manufacturing in electrical and electronic industries. The joining technology of thin metal sheets has been strongly required. Laser welding with micro-beam and high-speed scanning is a promising solution in micro-welding, because it has high-potential advantages in welding heat sensitive components with precise control of heat input and minimal thermal distortion. Approach: In this study, the characteristics of laser micro-welding of thin stainless steel sheets by using a single-mode CW fiber laser with high-speed scanning system were experimentally investigated. Results: It was clarified that the welding bead width and depth increased with increasing the scanning velocity under a constant energy density condition and high efficient welding was expected by using high-speed laser scanning with Galvano scanner. The utilization of shielding gas was very effective to obtain smooth fusion bead and the combination of micro beam spot and high-speed laser scanning made it possible to obtain good overlap welding of ultra-thin stainless steel sheets. Conclusion: A faster and high quality welding could be achieved by using a single-mode fiber laser with micro-beam and high-speed scanning.