Digital twin-based analysis of volumetric error mapping procedures

The evaluation of the volumetric accuracy of a machine tool is an open challenge in the industry, and a wide variety of technical solutions are available in the market and at research level. All solutions have advantages and disadvantages concerning which errors can be measured, the achievable uncertainty, the ease of implementation, possibility of machine integration and automation, the equipment cost and the machine occupation time, and it is not always straightforward which option to choose for each application. The need to ensure accuracy during the whole lifetime of the machine and the availability of monitoring systems developed following the Industry 4.0 trend are pushing the development of measurement systems that can be integrated in the machine to perform semi-automatic verification procedures that can be performed frequently by the machine user to monitor the condition of the machine. Calibrated artefact based calibration and verification solutions have an advantage in this field over laser based solutions in terms of cost and feasibility of machine integration, but they need to be optimized for each machine and customer requirements to achieve the required calibration uncertainty and minimize machine occupation time.This paper introduces a digital twin-based methodology to simulate all relevant effects in an artefact-based machine tool calibration procedure, from the machine itself with its expected error ranges, to the artefact geometry and uncertainty, artefact positions in the workspace, probe uncertainty, compensation model, etc. By parameterizing all relevant variables in the design of the calibration procedure, this simulation methodology can be used to analyse the effect of each design variable on the error mapping uncertainty, which is of great help in adapting the procedure to each specific machine and user requirements. The simulation methodology and the analysis possibilities are illustrated by applying it on a 3-axis milling machine tool.     

B4C–TiB2 composites fabricated by hot pressing TiC–B mixtures: The effect of B excess

Previous research have reported that B₄C–TiB₂ composites could be prepared by the reactive sintering of TiC–B powder mixtures. However, due to spontaneous oxidation of raw powders, using TiC–B powder mixtures with a B/TiC molar ratio of 6: 1 introduced an intermediate phase of C during the sintering process, which deteriorated the hardness of the composites. In this report, the effects of B excess on the phase composition, microstructure, and mechanical properties of B₄C–TiB₂ composites fabricated by reactive hot pressing TiC–B powder mixtures were investigated. XRD and Raman spectra confirmed that lattice expansion occurred in B-rich boron carbide and B_xC–TiB₂ (x > 4) composites were obtained. The increasing B content improved the hardness and fracture toughness but decreased the flexural strength of B_xC–TiB₂ (x > 4) composites. When the molar ratio of B/TiC increased from 6.6:1 to 7.8:1, the Vickers hardness and the fracture toughness of the composites were enhanced from 26.7 GPa and 4.53 MPa m^1/2 to 30.4 GPa and 5.78 MPa m^1/2, respectively. The improved hardness was attributed to the microstructural improvement, while the toughening mechanism was crack deflection, crack bridging and crack branching.     

Green preparation of vanadium carbide through one-step molten salt electrolysis

Vanadium carbide (VC) as excellent ceramic and functional material is usually prepared by carbothermal reduction of V₂O₅ which must be extracted from a typical V slag by complex processes. Pollutants, such as ammonia-nitrogen wastewater, NH₃ and CO₂ are inevitably discharged. A novel and green method for VC preparation was proposed by one-step co-electrolysis of soluble NaVO₃ and CO₂ in molten salt. It was found that VC with high purity was easily obtained by reducing electrolysis temperature and CO₂ flow rate to 600 °C and 10 mL min⁻¹ at 3.0 V. Besides VC with particles and layered stacking structure in products, a small amount of carbon and oxygen elements existed. The atomic percentage contents of C, V, and O elements in VC were about 50.0%, 44.5% and 3.8%, respectively. During electrolysis, CO₃²⁻ and VO₃⁻ was reduced at about −0.55 V (vs. Ag/AgCl) and −1.38 V (vs. Ag/AgCl), respectively. CO₃²⁻ ions were more easily reduced than VO₃⁻, and was firstly reduced to CO₂²⁻ and then converted to C. Then, VC was prepared by two routes from CO₂ and NaVO₃. One route is that VO₃⁻ ions are firstly electroreduced to VO₂⁻ ions and then are further electroreduced to VC with C. Another route is that VO₃⁻ ions are electroreduced to V which in-situ reacted with C to VC. Both VO₃⁻ and CO₃²⁻ ions are electroreduced by two-step process. In final, VC is in-situ deposited on cathode. It provides a novel and green way to prepare VC and also achieves the high value-added utilization of vanadium slag and CO₂.     

Investigation of thermal residual stresses during laser ablation of tantalum carbide coated graphite substrates using micro-Raman spectroscopy and COMSOL multiphysics

Laser ablation of high-temperature ceramic coatings results in thermal residual stresses due to which the coatings fail by cracking and debonding. Hence, the measurement of such residual stresses during laser ablation process holds utmost importance from the view of performance of coatings in extreme conditions. The present research aims at investigating the effect of laser parameters such as laser pulse energy, scanning speed and line spacing on thermal residual stresses induced in tantalum carbide-coated graphite substrates. Residual stresses were measured using micro-Raman spectroscopy and correlated with Raman peak shifts. Transient thermal analysis was performed using COMSOL Multiphysics to model the single ablated track and residual stresses were reported at low, moderate and high pulse energy regimes. The results showed that the initial laser conditions caused higher tensile residual stresses. Moderate pulse energy regime comprised higher compressive residual stresses due to off centre overlapping of the laser pulses. Higher pulse energy (250 μJ), higher scanning speed (1000 mm/s) and moderate line spacing (20 μm) caused accumulation of tensile residual stresses during the final stage of laser ablation. The deviation of experimental residual stresses from COMSOL numerical model was attributed to unaccounted additional stresses induced during thermal spraying process and deformation potentials in the numerical model.     

Novel TiC-based composites with enhanced mechanical properties

Novel TiC-based composites were synthesized by reactive hot-pressing at 1800 °C for 1 h with ZrB₂ addition as a sintering aid for the first time. The effects of ZrB₂ contents on the phase composition, microstructure evolution, and mechanical properties were reported. Based on the reaction and solid solution coupling effects between ZrB₂ and TiC, the product ZrC may be partially or completely dissolved into the TiC matrix, and then phase separation within the miscibility gap is observed to form lamellar nanostructured ZrC-rich (Zr, Ti)C. The TiC-10 mol.% ZrB₂ (starting batch composition) exhibits good comprehensive mechanical properties of hardness 27.7 ± 1.3 GPa, flexural strength 659 ± 48 MPa, and fracture toughness of 6.5 ± 0.6 MPa m^1/2, respectively, which reach or exceed most TiC-based composites using ceramics as sintering aids in the previous reports.     

Influence of SiC microstructure on its corrosion behavior in molten FLiNaK salt

The influence of the microstructure on the corrosion rate of three monolithic SiC samples in FLiNaK salt at 900 °C for 250 h was studied. The SiC samples, labeled as SiC-1, SiC-2, and SiC-3, had corrosion rates of 0.137, 0.020, and 0.043 mg/cm²h, respectively. Compared with grain size and the presence of special grain boundaries (i.e., Σ3), the content of high-angle grain boundaries (HAGBs) appeared to have the strongest influence on the corrosion rate of SiC in FLiNaK salt, since the corrosion rate increased six times as the concentration of high-angle grain boundaries increased from 19 to 32% for SiC-2 and SiC-1, respectively. These results stress the importance of controlling the content of HAGBs during the production process of SiC.     

A PV installation framework concerning electricity variable rates

This paper assesses building integrated photovoltaic (BIPV) installation parameters based on the profit generated by a photovoltaic system. It takes into consideration a home building case study and it investigates its monthly energy demand based on a specific location and a typical occupancy. The capability of a photovoltaic (PV) system to generate more profit occurs when solar intensity is maximum while the electric energy price is at its highest rate. The paper traces a framework that encompasses different aspects such as energy demand, energy price, and solar intensity. This framework identifies profit alternatives according to different installation parameters. A tool that predicts a PV installation hourly electric energy production is developed. The profit generated is simulated for home buildings located in Beirut (Lebanon) and Xihua (China), both at 33.8° latitude north. The paper highlights a new approach for BIPV installations, taking into account weather conditions, energy demand, and electric energy utility rates.     

Multi-discharge EDM coring of single crystal SiC ingot by electrostatic induction feeding method

A new technique of EDM coring of single crystal silicon carbide (SiC) ingot was proposed in this paper. Currently single crystal SiC devices are still of high cost due to the high cost of bulk crystal SiC material and the difficulty in the fabrication process of SiC. In the manufacturing process of SiC ingot/wafer, localized cracks or defects occasionally occur due to thermal or mechanical causes resulted from fabrication processes which may waste the whole piece of material. To save the part of ingot without defects and maximize the material utilization, the authors proposed EDM coring method to cut out a no defect ingot from a larger diameter ingot which has localized defects. A special experimental setup was developed for EDM coring of SiC ingot in this study and its feasibility and machining performance were investigated. Meanwhile, in order to improve the machining rate, a novel multi-discharge EDM coring method by electrostatic induction feeding was established, which can realize multiple discharges in single pulse duration. Experimental results make it clear that EDM coring of SiC ingot can be carried out stably using the developed experimental setup. Taking advantage of the newly developed multi-discharge EDM method, both the machining speed and surface integrity can be improved.     

水力旋冲钻井工具破岩影响因素模拟及应用

常规的冲击钻井工具不能满足井眼轨迹控制要求、使用寿命有限、缓解脱压不显著等问题,影响了在定向井钻井中的推广应用。建立ø215.9 mm PDC钻头和岩石的有限元模型,分析钻井参数对破岩效率的影响规律,结果表明:冲击频率为17.5 Hz和35 Hz时,破岩效率最优; 破岩效率随钻压增大而增加,而后变化逐渐平缓; 破岩效率随钻头转速增大而增加; 破岩效率随冲击载荷的增加变化平缓。据此研制了新型水力旋冲钻井工具。现场试验表明,该工具符合定向水平井“一趟钻”工艺要求,使机械钻速提高56%,使用寿命达150 h,MWD信号正常。     

Local toolpath smoothing for five-axis machine tools

When five axis CNC machine tools follow series linear toolpath segments, the drives experience velocity, acceleration and jerk discontinuities at the block transition points. The discontinuities result in fluctuations on machine tool motions which lead to poor surface quality. This paper proposes to insert quintic and septic micro-splines for the tool tip and tool-orientation, respectively, at the adjacent linear toolpath segments. Optimal control points are calculated for position and orientation splines to achieve C³ continuity at the junctions while respecting user-defined tolerance limits. The geometrically smoothed corners are traveled at a smoothly varying feed with cubic acceleration trajectory profile. The proposed method is experimentally demonstrated to show improvements in motion smoothness and tracking accuracy in five-axis machining of free-form surfaces found in dies, molds and aerospace parts.