Precision Engineering-Journal of the International Societies for Precision Engineering and Nanotechnology最新文献

Electrochemical machining (ECM) is an effective technique for producing both macroscopic and microscopic components of industrial devices. However, achieving high precision in ECM necessitates overcoming the challenge of stray corrosion. This study introduces a novel approach for enhancing the precision of ECM by employing bipolar pulses and an auxiliary electrode to significantly reduce stray corrosion. The innovative strategy utilizes the substantial production of hydrogen bubbles at the cathode surface to localize the electrolytic current to the intended machining area. During the negative pulse phase, both the workpiece and the tool act as cathodes, promoting intensive hydrogen bubble formation in regions not designated for machining, while minimizing bubble generation in the target area. Consequently, these bubbles decrease the stray current traversing the untargeted area during the positive pulse phase. This study reveals the underlying machining principles and the circuitry designed to facilitate this method. Through simulations and experimental validation. Simulations and experiments were performed to demonstrate the effectiveness of the proposed method. The results reveal a significant reduction in stray current in non-machining areas due to hydrogen bubble formation. When compared to conventional ECM employing unipolar pulses, the bipolar pulsed ECM produces holes with superior precision, characterized by reduced overcut and increased depth. Additionally, the surface roughness (Ra) at the base of the machined groove is enhanced by approximately 1.3 times.

The paper presents the procedures developed to correctly assess the geometric condition of large crankshafts using a novel measurement system equipped with a specially designed prism support system with computer monitoring of support reaction forces. These procedures were developed for three variants of measurement execution corresponding to conditions: non-referenced (fixing of the shaft to be measured with the outer extremes of the faces in the spherical prisms and supporting the shaft in the central part with a set of supports referred to as ‘elastic’), referenced (fixing of the shaft to be measured by the outer extremes of the main journals in prisms and support of the crankshaft in the central part, as in the case of the previous variant, by a set of supports referred to as ‘elastic’) and realised in conditions similar to the traditional ones (fixing and support of the crankshaft by a set of prism supports maintaining a constant height position). Considering the utilitarian potential of the developed procedures, exemplary applications of their practical use in the measurement of large crankshafts are presented.

Reluctance actuators (RA) are a type of electromagnetic actuator that offers high forces for short-range motions. The RA takes advantage of the electromagnetic reluctance force property in air gaps between the stator core and mover parts. The stator generates a magnetic flux that produces a magnetic attraction force between the stator and the mover, where the output force is dependent on the air gap displacement nonlinearly. It is demonstrated that the RA can produce a force that is effective and suitable for millimeter-range high-acceleration applications. One application for the RA is the short-stroke stage of photolithography or lithography machines, for example. The RA is available in a wide variety of configurations, such as C-Core, E-Core, Maxwell, and Plunger-type designs. The RA requires precise dynamic models and control algorithms to help linearize the RA for better control and optimization. Some nonlinear dynamics include magnetic hysteresis, flux fringing, and eddy currents. The RA is shown to have a larger force density than any other traditional actuator designs, with the main disadvantage being the nonlinear and hysteresis nonlinearities, making it difficult to control precision motion applications without proper dynamic and control models in place. This review documents currently available knowledge of the RA such as available applications, configurations, dynamic models, measurement systems, and control systems for the RA.

Single-crystal silicon (Si) has important applications in semiconductor, infrared optics, and photovoltaic industries. However, Si is difficult to be machined precisely due to its hard and brittle characteristics. Ion irradiation is proposed as an advanced technology to reduce the hardness and brittleness for a covalent crystal, which is beneficial for the ductile machining process. In the present research, the simulation and experimental investigation of Si with Au ion irradiation were carried out firstly. As following, the grooving experiment is carried out by elliptical vibration cutting (EVC). the machining performance is compared with ordinary cutting (OC) and the material removal mechanism is elaborated. The critical depth of cut for brittle-to-ductile transition is nearly 7 times higher by EVC compared to OC. Initial verification of material modification was conducted by Raman spectra and cutting microgrooves. Finally, the ion irradiation damage mechanism and amorphous Si (a-Si)/crystalline Si (c-Si) machining deformation mechanism were analyzed in detail by transmission electron microscopy. The irradiated sample contains an amorphous layer of 1050 nm, a transition layer containing dislocations and nanocrystals, and a fully crystalline layer. During machining a-Si/c-Si interface, the machining defects in the amorphous layer will first absorb the energy and ensure that the crystalline layer does not produce subsurface damage. In summary, ion-irradiated Si can be achieved in the amorphous region at any depth position and the substrate ductile machining without subsurface damage generation by EVC.

With properties such as high hardness, low density and high-temperature resistance, SiC_f/SiC composites have been widely used in defense and aerospace. Due to its high brittleness and anisotropic characteristics, traditional machining methods are prone to cause serious material damage and affect the service life of SiC_f/SiC composites. The interference trajectories of neighboring grains in longitudinal torsional ultrasonic vibration-assisted grinding were analysed in this study, and comparative experiments between longitudinal torsional ultrasonic vibration-assisted grinding (LTUAG) and conventional grinding (CG) of SiC_f/SiC composites were conducted. Moreover, the trajectory of the grain and the interference situation were combined to analyse the material removal mechanism of SiC fibres in different directions and the SiC matrix section. The impact of different grinding parameters and ultrasonic amplitudes on surface roughness and grinding force was also studied to analyse LTUAG's mechanism of action on machined surfaces. The experimental results show that the material removal mechanism of SiC_f/SiC composites is primarily brittle fracture, which is manifested by the phenomena of fibre breakage, fibre pull-out and shear fracture. Weft yarn fibre pull-out and fibre debonding phenomenon are obvious. Warp yarn fibres are mainly manifested as fibre breakage and shear fracture. Compared with CG, LTUAG reduces fibre pull-out, inhibits interfibre crack expansion and increases the proportion of ductile removal from the material. The maximum reduction of normal and tangential forces in LTUAG compared to CG is about 40 % and 47.7 %, and the surface roughness reduced by a maximum of 12.8 %.

The present work provides an innovative method of composite pattern design for fixed abrasive pads, addressing issues such as machining non-uniformity and passivation blockage arising from uneven lapping flow, pressure, and velocity fields in lapping. First, a multi-physical field modeling method is provided, a material removal distribution model and evaluation criteria for the performance of the abrasive pad are established, and the reliability of this model is validated. Second, based on the model, a composite pattern abrasive pad coupled with a spiral groove and concentric micro groove is designed. Comparative experiments are conducted with the grid abrasive pad. The results show that the clogging and passivation performance of the composite pattern abrasive pad is improved, and the pressure distribution is optimized. Compared with the grid abrasive pad, in the pressure range of 20 N–70 N, the surface roughness Ra of sapphire is reduced by 6.4 %–25.42 %, defects such as brittle fracture pits and scratches on the workpiece surface are reduced, and the surface quality of the workpiece is significantly improved. The material removal rate is between 0.23 μm/min to 0.34 μm/min. This confirms the effectiveness of optimizing abrasive pad pattern design based on multi-physics fields. The research results provide a novel approach for abrasive pad pattern design with engineering application value.

To improve the positioning accuracy of industrial robots and meet the requirements of industrial applications, this study begins with the structural design of multi-jointed industrial robots and proposes a kinematic calibration method based on axis fitting. The proposed method introduces an axis fitting technique based on circle fitting. Utilizing the results of the axis fitting, a method for establishing link coordinate systems by referencing the Modified Denavit-Hartenberg (MD-H) model is presented. Subsequently, a kinematic parameter identification method is proposed. This study primarily investigates the impact of joint rotation angles on the accuracy of axis fitting. The study reveals that when the rotation angle is greater than or equal to 20°, the circularity of the circle fitting is less than 0.008 mm, and the planarity is less than 0.01 mm, indicating that the proposed fitting algorithm meets the required precision for small angle rotations. Finally, the positioning accuracy of the target robot is verified according to ISO 9283:1998. After calibration, the positioning accuracy at point P₁ improves from 1.64 mm to 0.46 mm, an enhancement of 71.95 %, which is the most significant improvement. At point P₂, the positioning accuracy improves from 1.75 mm to 0.69 mm, an enhancement of 60.5 %, which is the least improvement. The advantage of this method lies in its ability to identify kinematic parameters that align with the actual structure of the robot using a simple measurement method, thereby improving the robot's positioning accuracy.

Vat photopolymerization (VPP) based additive manufacturing (AM) technologies print 3D components by using light to selectively cure photosensitive resins. In VPP-based AM, one outstanding challenge remains in controlling the over-curing, which is mainly caused by the diffusive and/or excessive photo-induced species such as free radicals and can severely affect the geometric properties of as-printed parts. Common practices rely on formulating proper resins or optimizing exposure parameters to address the vertical over-curing but often ignore the lateral over-curing. In this work, we develop a new VPP process of photoinhibition aided photopolymer AM (PinPAM) to comprehensively address over-curing issues in both vertical and lateral dimensions for enhancing the properties of as-printed geometry. The PinPAM method incorporates an adaptive photoinhibition zone, generated both surrounding and underneath the curing zone on a layer basis. This differs from current literature approaches that utilize photoinhibition to create a higher deadzone to increase print speed or constrain vertical profiles for achieving volumetric VPP AM. We present several preliminary experimental study cases involving pillar array sample printing. By comparing part dimensions and shapes resulting from traditional VPP and PinPAM, our experiments prove the concept of PinPAM and demonstrate its potential to address over-curing in VPP. Furthermore, we present an initial case study on optimizing the PinPAM process for printing cylinder samples with targeted dimensions, illustrating the planning and implementation of PinPAM. A discussion on future research directions to establish PinPAM is included. The developed PinPAM opens up a new avenue for improving VPP printed parts’ geometrical properties and facilitating its adoption in precision fabrications that demand dimensional accuracy and resolution.