As a widely used approach for surface modification, laser cladding plays a significant role in surface hardening and repairing of metallic parts. However, the defects existing in laser cladding parts, such as cracks, tensile residual stress, and pores, significantly affect the performance and the application of the cladding parts. In this study, an SS316L layer was fabricated on a 45 steel substrate using a laser cladding process assisted by three-dimensional vibration. The microstructures and the properties of the coating and the bonding interface with various vibration parameters were analyzed and compared. The microstructures of the cladding layer and the matrix were analyzed by an optical microscope and a scanning electron microscope. The results show that the three-dimensional vibration is able to refine the columnar dendrites in the cladding layer. The oscillation accelerates both the liquid flow and the thermal transfer of the molten pool, which not only reduces the temperature gradient but also increases the solidification growth rate. Meanwhile, the porosity and the maximum pore size in the cladding layer were significantly reduced by the vibration. The average microhardness of the cladding layer significantly increased assisted by the three-dimensional vibration. Experimental results demonstrate that the effects of the three-dimensional vibration are more significant than the single vertical vibration. The proposed approach provides a potential way to improve laser additive manufacturing and remanufacturing.

Fully reconfigurable tactile information sensing is indispensable of intelligent robotics intended for varieties of human-machine interactive applications. Current focus of the existing tactile sensors is still mostly on determining contact forces with high sensitivity or large measuring range, yet other tactile information especially the occurrence of incipient slip is equally noteworthy for stable grasping. Herein this paper, a tactile sensing array consisted of four separate sensing units of similar pattern is proposed, which allows different areas of the gripper-object interface to change individually. A seesaw-like prototype based on floating electrode structure is introduced into the design of each sensing unit, drastically reducing unexpected coupling induced by the coupled response between in-plane stretch and out-of-plane pressure. The fabricated prototype of the tactile sensing array is of great flexibility, and has displayed excellent multi-dimensional force sensing capability in terms of high sensitivity (2.38 kPa ^-1 in normal direction and 0.199 kPa ^-1 for tangential directions) and large measuring range (265 kPa in normal direction and 90 kPa for tangential directions). A feasible scheme based on empirical mode decomposition (EMD) was applied for validation of incipient slippage. Detected vibration component of first intrinsic mode function (IMF1) signals as well as real-time variation of stationary tangential force to normal force ratio were both taken into consideration to further divide actual incipient slip from possible re-grasping. During extensive in-hand experiments, distinguished features were all successfully confirmed of incipient slippage than possible re-grasping circumstances, implying full capability of detecting multi-dimensional contact forces and dividing incipient slippage simultaneously of this presented sensing array.

Laser cladding is a promising surface modification technology to fabricate high-performance parts. However, defects such as porosity, cracks and residual tensile stress are easily produced in laser cladding, leading to significant property reduction and poor reliability. In this study, laser cladding with multidimensional high-frequency vibration was investigated. The effects of multidimensional high-frequency vibration on the improvement of microstructure and mechanical properties were analyzed and discussed based on the vibration-assisted laser cladding experiments. In addition, a numerical model was conducted to help understand the significance of the vibration on flow field and temperature field. Results show that 3D vibration led to the primary dendrite spacing reduction from 11.1 to 6.8 μm, microhardness increase from 199 to 221 HV_0.2, and a nearly 110% improvement in the elongations. The findings of this study confirmed the significant benefits of multidimensional high-frequency vibration applied in laser cladding and provided a basis to uncover the underlying mechanisms of multidimensional vibration on the rapid melting and solidification.

The development of pressure sensors of high sensitivity and stable robustness over a broad range is indispensable for the future progress of electronic skin applicable to the detection of normal and shear pressures of various dynamic human motions. Herein, we present a flexible capacitive tactile sensing array that incorporates a porous dielectric layer with micro-patterned structures on the surface to enable the sensitive detection of normal and shear pressures. The proposed sensing array showed great pressure-sensing performance in the experiments, with a broad sensing range from several kPa to 150 kPa of normal pressure and 20 kPa of shear pressure. Sensitivities of 0.54%/kPa at 10 kPa and below, 0.45%/kPa between 10 kPa and 80 kPa, and 0.12%/kPa at 80 kPa and above were achieved for normal pressures. Meanwhile, for shear pressures, sensitivities up to 1.14%/kPa and 1.08%/kPa in x and y directions, respectively, and below 10 kPa, 0.73%/kPa, and 0.75%/kPa under shear pressure over 10 kPa were also validated. The performance of the finger-attached sensing array was also demonstrated, demonstrating which was a potential electronic skin to use in all kinds of wearable devices, including prosthetic hands, surgical robots, and other pressure monitoring systems.

Electrochemical machining (ECM) has become more prevalent in titanium alloy processing. However, the presence of the passivation layer on the titanium alloys significantly impacts the performance of ECM. In an attempt to overcome the passivation effects, a high-temperature electrolyte or the addition of halogen ions to the electrolyte has been used. Still, it often results in compromised machining accuracy and surface roughness. This study applied laser and shaped tube electrolytic machining (Laser-STEM) for titanium alloy drilling, where the laser was guided to the machining zone via total internal reflection. The performance of Laser-STEM using different types of electrolytes was compared. Further, the effects of laser power and pulse voltage on the machining side gap, material removal rate (MRR), and surface roughness were experimentally studied while drilling small holes in titanium alloy. The results indicated that the use of passivating electrolytes improved the machining precision, while the MRR decreased with an increase in laser power during Laser-STEM. The MRR showed an increase while using aggressive electrolytes; however, at the same time, the machining precision deteriorated with the increase in laser power. Particularly, the maximum feeding rate of 6.0 mm/min for the tool electrode was achieved using NaCl solution as the electrolyte during Laser-STEM, marking a 100% increase compared to the rate without the use of a laser. Moreover, the model and equivalent circuits were also established to illustrate the material removal mechanisms of Laser-STEM in different electrolytes. Lastly, the processing of deep small holes with a diameter of 1.5 mm, a depth of 38 mm, and a surface roughness of Ra 2 µm was achieved via Laser-STEM without the presence of a recast layer and heat-affected zones. In addition, the cross-inner flow channels in the titanium alloys were effectively processed.

Highly sensitive flexible tactile sensors with synergistic normal and shear force perception are urgently required for possible grasping, lifting and other in-hand manipulations of robotic hands. Herein, a capacitive 3-D force tactile sensing array inlaid an enhanced porous dielectric layer was presented. The micro-pores were formed through vacuum-assisted infiltration of polydimethylsiloxane (PDMS) solution applying perfluorotributylamine (C12F27N) as sacrificial solvent, meanwhile, using sugar particles mixed up with PDMS-C12F27N emulsion to create extra macro pores. The surface of the sensing array consisted of numbers of pen-cap-like bumps for reliable traction of objects. When normal or shear forces were applied on the surface, the contacted bumps were compressed or declined. The deflections of bumps resulted in possible capacitance variations, which were corresponded to the applied normal and shear forces. Compared with capacitive sensors inlaid an un-patterned solid dielectric layer, the developed sensing array experimentally displayed a high elasticity, a large sensing pressure range (over 250 kPa for normal pressure and over 60 kPa for shear pressures), a high sensitivity (1.63%/kPa and 1.61%/kPa for normal and shear pressure, respectively), a good repeatability and a good structural stability and durability. Finger attached tests validated the proposed tactile sensing array having great potential for all kinds of robotics and prosthetic hand applications.