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Metallic tubular micro-components play an important role in a broad range of products,
from industrial microsystem technology, such as medical engineering, electronics and optoelectronics, to sensor technology or microfluidics. The demand for such components is increasing, and forming processes can present a number of advantages for industrial manufacturing. These include, for example, a high productivity, enhanced shaping possibilities, applicability of a wide spectrum of materials and the possibility to produce parts with a high stiffness and strength. However, certain difficulties arise as a result of scaling down conventional tube forming processes to the microscale. These include not only the influence of the known size effects on material and friction behavior, but also constraints in the feasible miniaturization of forming tools. Extensive research work has been conducted over the past few years on micro-tube forming techniques, which deal with the development of novel and optimized processes, to counteract these restrictions. This paper reviews the relevant advances in micro-tube fabrication and shaping. A particular focus is enhancement in forming possibilities, accuracy and obtained component characteristics, presented in the reviewed research work. Furthermore, achievements in severe plastic deformation for micro-tube generation and in micro-tube testing methods are discussed.
Ni–Ti alloys are used as functional materials in numerous sectors such as aerospace, automotive engineering, medical technology, and consumer goods. Their properties in terms of shape memory effect and superelasticity offer a great potential for innovative smart products. However, forming and machining of these alloys into concrete products is challenging. Assembling plain structures by laser welding to complex product shapes offers an economical alternative in many cases, but can be associated with negative effects, such as reduction of strength, development of brittle intermetallic compounds, alteration of transformation temperatures, and modification of shape memory effects and superelastic behavior. Against this background, investigations on laser welding of Ni55/Ti45 foil with a thickness of 125 µ m by a fiber laser were conducted. Supported by methods of design of experiments, optimal parameters were determined with respect to laser power, welding speed, focus position, and beam oscillation, and the welding results were analyzed concerning the microstructure and mechanical characteristics of the welded joints. The effect of laser beam oscillation was investigated for the first time for the welding of this alloy. Due to the very low thickness, the preparation of the foils for the microstructure characterization is quite demanding. Best results were obtained by ion milling. Fracture surfaces and the influence of the welding were also investigated.