A robot motion position and posture control method for freeform surface laser treatment based on NURBS interpolation

Laser directed energy deposition (DED) offers significant advantages for the integral manufacturing of large-scaled thin-walled workpieces. Nevertheless, how to improve the yield strength (YS) and fatigue properties of thin-walled parts fabricated by DED is a crucial issue. As an advanced surface strengthening technology, ultrasonic surface rolling process (USRP) is aimed to improve the mechanical performances of additively manufactured workpieces. In this work, an optimized bilateral USRP parameter (including the load, repeated times, scanning speed, etc.) with high manufacturing efficiency and surface integrity was developed to fabricate thin-walled CoCrNi medium-entropy alloy (MEA) parts (~1.5 mm thickness). Compared to the as-deposited sample, the sample treated by USRP shows a good strength-ductility balance (ultra-high YS and ductility with 1026.6 MPa and 21.9%, respectively), as well as an impressive improvement in the high-cycle fatigue limit strength of 76.9%. The reasons for high mechanical performance are revealed through multi-scale characterization and calculation. Ultra-high strength is predominantly attributed to the high-density pre-existing dislocations and deformation twins (DTs); Good ductility is related with high hetero-deformation induced stress and the activation of multiple deformation substructures induced by high flow stress, such as dislocations, DTs and hexagonal close-packed phase. Further, the improvement in fatigue performance is ascribed to the closure of manufacturing defects in the surface or subsurface and inhibited surface roughening behavior from stable gradient nanotwinned layer. Finally, the work reveals the quantitative relationship among processing-properties-promotion mechanism (PPP), which provides a criterion to meet the specific mechanical performance of DEDed thin-walled components by precisely tuning the bilateral USRP parameters. 

Optimized bilateral ultrasonic surface rolling process assisting directed energy deposition of thin-walled medium-entropy alloy with high mechanical performance

Ultrasonic surface rolling process (USRP) is a combination of ultrasonic impact and deep rolling techniques. However, the addition of ultrasonic vibrations complicates the working mechanism of USRP tools. Existing studies rarely consider the evolution of dynamic characteristics in USRP tools resulting from changes in ultrasonic amplitudes, which undoubtedly exert a significant influence on surface properties. Moreover, they typically limit the ultrasonic amplitude to a small range. This study aims to identify the boundary process parameters to differentiate between stable and unstable dynamic characteristics during USRP and to compare their effects on the surface integrity and the plastic deformation. Therefore, an equivalent USRP tool model was proposed to analyse the working mechanism at a large-scale ultrasonic amplitude. The boundary USRP parameters responsible for different dynamic characteristics were experimentally explored. Finally, comparative USRP experiments on the Ti-6Al-4V alloy were conducted, and it was observed that USRP parameters under stable dynamic characteristics were beneficial to the excellent surface roughness. Conversely, altering the ultrasonic amplitude to attain unstable dynamic characteristics leads to a notable degradation in the surface quality; however, the extent of plastic deformation is significantly increased. This study provides insights into the effects of dynamic characteristics in USRP, thereby contributing to a deeper understanding of the process and facilitating effective design of process parameters. 

Effect of high-frequency dynamic characteristics in the ultrasonic surface rolling process on the surface properties

In order to separate and purify the reaction raw material ethanol (EtOH) and product acetonitrile (ACN) from the azeotrope of ACN / EtOH / water, an efficient extractive distillation by varying pressure process (EDP) was designed to separate them. Because the feed composition in industrial production was constantly changing, processes of different feed compositions was simulated. Taking into account both economic and environmental factors, the non-dominated sorting genetic algorithm comprehensively optimizes the parameters. The azeotrope was pressure sensitive and the pressure parameter was also optimized in order to improve the efficiency of process energy utilization. Heat exchange network optimization technology was used to fully utilize excess heat in the process. The distillation coupled pervaporation technology has also been designed to explore emerging technologies. Among the three different coupling processes, the performance of EDP-pervaporation (EDPV) was better. Compared with EDP, EDPV under different schemes reduce the total annual cost (TAC) and gas emissions by more than 15% and 21 %, respectively. It was found that the energy consumption was related to the normal distance from the feed composition to the distillation boundary and isovolatility curve. 

Process design and multi-objective optimization for separation of different feed composition of acetonitrile / ethanol / water with extractive distillation by varying pressure / pervaporation

This work presents an approach for the recovery of high purity cyclohexane (CYCLO) and tertiary butyl alcohol (TBA) from wastewater. After thermodynamic analysis, a heterogeneous azeotrope-pressure swing distillation process (HAPSD) with a decanter is proposed. The heterogenous azeotrope distillation with a high-pressure column and a dividing-wall column process (HADWC) is also being developed to propose a green and sustainable process. The novel processes are optimized using simulated annealing algorithm (SAA). Those processes are optimized by simulated annealing algorithm by linking Aspen Plus and MATLAB via taking the total annual cost (TAC) as objective function. Three energy-efficient HADWC processes are proposed based on the process intensification approach of heat pump and heat integration technologies. All processes are evaluated for multi-criteria performance including economy, energy consumption, gas emissions and thermodynamic efficiency. As the result, HADWC-HP-HI process shows the best performance with 31.79%, 53.46%, 50.69%, and 57.94% reducing over the conventional HAPSD process in terms of TAC, energy consumption, gas emissions and thermodynamic efficiency, respectively. 

Economic, environmental, energy, exergy (4E) analysis and simulated annealing algorithm optimization of dividing-wall column-intensified heterogeneous azeotropic pressure-swing distillation process

• Robot-assisted UIT system is developed for aero-engine blades. • A novel non-interference trajectory planning approach is proposed. • Strengthening system can operate without collision even in restricted space. • The proposed strategy can improve fatigue performance of TA19 blades. As a vital component of aero-engine, blade is susceptible to damage from long-term service under cyclic loads. Ultrasonic impact treatment (UIT) can improve the mechanical properties of the material surface. However, applying UIT onto aero-engine blade remains a challenge due to the complex structure. This study investigates robot-assisted ultrasonic impact strengthening strategy for the complex surface in the restricted space. On the one hand, a novel robot-assisted UIT system is developed for a wide range of complex surface features. On the other hand, a non-interference trajectory planning method is introduced for complex surfaces in the restricted space of the blade. The breadth-first search (BFS) strategy based on the criterion of the induced ray is proposed for interference inspecting and optimizing the pose of the UIT tool. Experiments are conducted on real aero-engine blades. The results of numerical and experimental case studies have demonstrated that the proposed strategy can effectively cover the fatigue vulnerable areas without collision. Moreover, compressive residual stresses are generated both on the pressure and suction surface, and the fatigue limit of the UIT blades is improved by 26% as compared with the as-received blades. 

Robot-assisted ultrasonic impact strengthening strategy for aero-engine blades

Control of side-stream pressure-swing distillation and extractive distillation for separating azeotropic mixture of cyclohexane and acetone

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Robot-assisted ultrasonic impact strengthening strategy for aero-engine blades

Control of side-stream pressure-swing distillation and extractive distillation for separating azeotropic mixture of cyclohexane and acetone