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.

Quasi-static 3-point bending of additive manufactured sandwich components with auxetic star-4 cores was investigated to obtain information on the influence of geometry parameters of the auxetic structure on the stress distribution of the face sheets. Experiments were carried out on specimens manufactured by fused deposition modelling from a PLA polymer to verify a simulation model for analyses. A hyperelastic material model was used in the finite element models to describe the elastic material behaviour and a hardening model to consider plasticity. Nanoindentation tests on the printed structures were conducted to identify the material parameters with modelling the nanoindentation procedure using the finite element method and applying automated optimisation techniques. This approach enabled an accurate reproduction of the nanoindentation tests in the simulations. The derived models for analysing the auxetic geometry have shown that the stress distribution in the face sheets of the sandwich components can be noticeably influenced with targeted changing the wall thicknesses of the auxetic star-4 structure. The simulations have also made it apparent that more effort is required to take into account the influences of the printing process on the deformation behaviour of the sandwich structure in the simulation model.

Metamaterials with auxetic behaviour have great potential for a new generation of load-bearing lightweight sandwich structures due to their outstanding energy absorption capabilities. As a result of their negative Poisson's ratio, component cross-sections increase under tensile loading transverse to the loading direction and decrease conversely under compressive loading. This paper describes experimental and numerical investigations with the finite element method on the load-deformation behaviour of sandwich structures under bending featuring differently oriented auxetic cores and honeycomb cores with varying specifications and degrees of crystallisation. A star-shaped auxetic structure was chosen and compared with hexagonal honeycomb cores. The fabrication of the specimens was carried out by fused deposition modelling and the materials were characterised by infrared spectroscopy, differential scanning calorimetry, melt flow index determinations, dilatometer measurements, tensile tests, and nanoindentation. The bending results exhibited that the advantages of the auxetic structures in energy absorption were clearly evident for certain orientations to the loading direction and that the material properties significantly influenced the structural deformation behaviour.

Laser welding has become well established for joining Ni-Ti-based shape memory alloys and extends the manufacturability of highly functional components with complex geometries. Published studies on the effect of laser welding on alterations to microstructure and properties of these alloys, however, mainly deal with conventional component dimensions and linear laser beam movement. In view of the increasing importance of microtechnology, research into joining of thin-walled Ni-Ti components is therefore of interest. At the same time, studies comparing oscillating and linear beam movement on other materials and the authors’ own work on Ni-Ti materials suggest that oscillating beam movement has a more favorable effect on alterations in material properties and microstructure. Therefore, laser welding of foils made of Ni55/Ti45 with 125 µm thickness was systematically analyzed using a fiber laser and circular oscillation. Amplitude A and frequency f were varied from 0 to 200 µm and 0 to 2000 Hz, respectively. Microstructural analysis showed that by increasing the frequency, grain refinement could be achieved up to a certain value of f. An increasing amplitude led to decreasing hardness values of the weld seam, while the influence of f was less pronounced. The analysis of the weld material using chip calorimetry (Flash DSC) revealed that the beam oscillation had fewer effects on the change in transformation points compared to a linear beam movement.