A self-adaption normal direction and active variable stiffness low-frequency vibration-assisted system for curved surface drilling

The drilling operation occupies an important position in the aircraft assembly workload, and it accounts for a large proportion of the assembly cost. Previous reports show that drilling quality affects aircraft safety factor such as the probability of fatigue failure accidents. This paper proposes an automatic machining system for curved surface drilling. In this scheme, the self-adaption normal direction is realized by using the secondary positioning strategy (primary positioning and precise positioning). An elastic structure and the key positions smooth processing are applied to enhance the positioning guidance. The active variable stiffness mechanism satisfies the different requirements for system stiffness during the positioning stage and the drilling stage. Expansion sleeve locking and state switching of drilling assistance pneumatic cylinder lead to changes in the actuator's DOF and external forces, thereby achieving active control of the stiffness. Vibration-assisted machining technology is introduced to improve drilling quality. Compared with conventional drilling, the results show that this drilling system produces thin and slender chips, smaller burrs, and better internal surface quality.     

Assembly language design and development for reconfigurable flexible assembly line

To improve the efficiency and controllability of our previous proposed cross-category product assembly line, we design an assembly language (A-code) to express a product's assembly process. We further develop an IDE to describe assembly processes as statements, which are organized according to predefined syntax as an A-code file. The interpreter translates statements into executable low-level commands. In addition, a four-layer architecture of the A-code assembly system (ACAS) is proposed to implement this language, thus an A-code files can be run on the assembly line physically. The proposed ACAS can reconfigure each unit for specific products, and control their assembly processes. The expressivity of this language is validated in two assembly cases, a simple shuttle valve and a complex relief valve. The functionality and feasibility of this system are tested by assembling 50 relief valves. The results demonstrate our ACAS can perform complex assembly tasks in a more efficient way.     

Analysis on quantifiable and controllable assembly technology for aeronautical thin-walled structures

Assembly affects the product's performance and reliability directly. The current assembly method based on geometric deviation quantity controlling, cannot guarantee the physical performance for complex aeronautical thin-walled structures effectively, such as assembly geometry accuracy and internal interactive stress. And assembly performance controlling is taken as the bottleneck problem that restricting the new aviation requirement of sub-millimeter assembly. In this paper, by proposing the accurate prediction and process-oriented adjustment&controlling strategies on assembly quality, construction on working mode with “quantifiable and controllable” characteristic was proposed, whose aim was to reduce the phenomenon of out-of-tolerance and deformation rebound error, and the ultimate goal is to reduce the uncertainty of assembly performance parameters. At the technical level, the academic development context and existing problems for assembling thin-walled structures were reviewed and analyzed, such as assembly process parameters optimization, assembly error transfer and accumulation, comprehensive adjustment on assembly quality, and virtual assembly simulation validation. Then the key future research trends for aeronautical structure assembly were also put forward, i.e. the force/deformation coordination among multi-type finite units for non-ideal assemblies, the dynamic construction of stiffness matrix for intermediate assemblies considering geometric nonlinearity, the adaptive balance on assembly performance driven by physical modeling and measured data, and the inverse optimization on assembly quality and parameters with intelligent data processing. This paper would lay a solid foundation for achieving the accurate assembly mode with the characteristics of “intelligent/scientific, and active/collaborative controlling on geometric shape and physical performance”, and higher assembly quality and efficiency could also be gained.     

Towards multi-task transfer optimization of cloud service collaboration in industrial internet platform

Cloud Manufacturing (CMfg) has gained significant attention owing to its capability in reshaping the cooperation paradigm among multiple geographically dispersed enterprises, which is conducive to handle a complex production task flexibly through the industrial internet platform. Cloud Service Assembly (CSA) is concerned with integrating a series of services together for serving a complex manufacturing task, which, as one of bottlenecks for CMfg, plays a critical role in efficient utilization of resources. Evolutionary Algorithms (EAs) have been widely used in resolving CSA in the past. However, they are always executed from scratch for tackling a single task in each run, whereas handling a batch of tasks collectively via leveraging inter-task knowledge transfer has been scarcely studied. Notably, CMfg is often faced with situation of multiple tasks arriving dynamically. In light of this, we propose a Multi-task Transfer EA (MTEA), where several service collaboration tasks are optimized jointly to speed up the search efficiency by exploiting knowledge extraction among tasks. Specifically, data models derived from evolving populations are learned to capture valuable knowledge for transfer so as to boost problem-solving efficacy, a parameter online learning strategy is utilized to tune the intensity of knowledge transfer across tasks. Extensive experiments are conducted on a series of CSA instances, results prove the feasibility and competence of MTEA against state-of-the-art peers.     

Vision-based spatial damage localization method for autonomous robotic laser cladding repair processes

Repair technologies have been considered as sustainable approaches due to their capability to restore value in a damaged component and bring it to like-new condition. However, in contrast to a manufacturing process benefiting from an automated environment, the automation level for repair and remanufacturing processes remains low. With the aim of moving the repair industry towards autonomy, this study proposes a novel repair framework. The developed methodology presents a vision-based Robotic Laser Cladding Repair Cell (RLCRC) that has two features: (a) an intelligent inspection system that uses a deep learning model to automatically detect the damaged region in an image; (b) employing computer vision-based calibration and 3D scanning techniques to precisely identify the geometries of damaged area. The repair of fixed bends is selected as the case study. The results obtained validate the efficacy of the proposed framework, enabling automatic damage detection and damaged volume extraction for worn fixed bends. Following the suggested framework, a time reduction of more than 63% is reported.     

Static analysis of spatial parallel manipulators by means of the principle of virtual work

It is presented a comprehensive approach for the static analysis of spatial parallel manipulators using the principle of virtual work, equipped with a recursive and systematic formulation, which is intended for conducting an efficient manipulation of the kinematics associated with the problem. Thus, it is possible omitting all internal forces and nonworking external constraint forces in the problem formulation. As a result, the actuator drive forces and/or torques can be directly related with the external loads supported by the manipulator, including the weight of the mobile platform and also the weight of the links of the connecting legs. A thorough understanding of these forces and/or torques is important for proper sizing of actuators at the design stage. In order to prove the feasibility and the validity of the proposed method, two fully detailed examples are presented.     

Hydrogenation effect on magnetic properties of rareearth–Fe/Co amorphous alloys

The effect of hydrogenation on the magnetic properties of rareearth–Fe/Co alloys was investigated by means of measuring the magnetization and hysteresisloops. Hydrogenation leads to an increase of positive exchange interactions in 3D-transition metalmagnetic subsystem and magnetization of the alloys. Hydrogenation effect on coercivity isdetermined by a type of the magnetization processes in a particular alloy. Various mechanisms ofphenomena were observed.     

Drilling thick fabric woven CFRP laminates with double point angle drills

Carbon fiber reinforced plastics (CFRPs) have many desirable properties, including high strength-to-weight ratio, high stiffness-to-weight ratio, high corrosion resistance, and low thermal expansion. These properties make CFRP suitable for use in structural components for aerospace applications. Drilling is the most common machining process applied to CFRP laminates, and it is difficult due to the extremely abrasive nature of the carbon fibers and low thermal conductivity of CFRP. It is a challenge for manufacturers to drill CFRP materials without causing any delamination on the work part while also considering the economics of the process. The subject of this study is the drilling of fabric woven type CFRP laminates which are known to be more resistant to delamination than unidirectional type CFRP laminates. The objective of this study is to investigate the influence of double point angle drill geometry on drilling performance through an experimental approach. An uncoated carbide and two diamond coated carbide drills with different drill tip angles are employed in drilling experiments of aerospace quality thick fabric woven CFRP laminates. Force and torque measurements are used to investigate appropriate drilling conditions based on drill geometry and ideal drilling parameters are determined. Tool life tests of the drills were conducted and the condition of the diamond coating is examined as a function of drilling operational parameters. High feed rate drilling experiments are observed to be favorable in terms of drill wear. Feed is observed to be more important than speed, and the upper limit of feed is dictated by the drill design and the rigidity of the machine drill. Hole diameter variation due to drill wear is monitored to determine drill life. At high feeds, hole diameter tolerance is observed to be more critical than hole exit delamination during drilling of fabric woven CFRP laminates.     

双酚A型邻苯二甲腈树脂改性硅炔杂化树脂及其复合材料性能

采用双酚A型邻苯二甲腈预聚树脂(BAPh-P)改性聚(间二乙炔基苯-二甲基硅烷)树脂(PDMP)制备了双酚A型邻苯二甲腈/聚(间二乙炔基苯-二甲基硅烷)树脂(PBA),利用DSC、FTIR、流变分析、TGA等技术分析其固化行为、黏度以及耐热性变化。结果表明,PBA树脂固化峰值温度较PDMP升高;固化反应主要为炔基的Diels-Alder和加成反应、氰基进一步交联生成三嗪环和酞菁环等结构反应;BAPh-P的加入提升了PDMP在空气下的耐热性,PBA-1(PDMP:BAPh-P质量比为5∶1)树脂固化物在N₂和空气氛围质量损失5%的温度(T_d5)分别为640.6℃和591℃,1000℃质量保留率为89.0%和26.9%;随着BAPh-P质量增加,PBA树脂固化物T_d5呈下降趋势,但空气中T_d5均高于PDMP;石英纤维增强PBA树脂基(QF/PBA)复合材料随BAPh-P质量增加室温弯曲强度逐渐升高,高温弯曲强度先升高后降低;其中QF/PBA-2复合材料室温和400℃弯曲强度分别为363 MPa和330 MPa,较PDMP分别提升91%和214%,室温和400℃的层间剪切强度(ILSS)分别为37.5 MPa和22.2 MPa。      

Critical properties of Cu6Sn5 in electronic devices: Recent progress and a review

As the most common of the intermetallic compounds (IMCs) formed between Sn-based solders and Cu substrates during the packaging of integrated circuits (ICs), Cu₆Sn₅ is frequently involved in the fabrication of solder joints and plays an important role in the integrity of electronic devices. This is especially true for recently developed micro-bumps in 3-dimensional (3D) high-density integrated circuits (ICs), in which the volume fraction of Cu₆Sn₅ is significantly higher than in conventional ball grid array (BGA) or through hole pin (THP) arrangements. Recently, with the use of advanced characterization techniques, significant progress has been made in the understanding of Cu₆Sn₅ intermetallics in terms of their crystal structure, solidification behaviour, role in interface reactions, thermal expansion and mechanical properties. This improved understanding is of fundamental importance for the production of next generation electronic devices, however there is no existing comprehensive summary of this research available. Here, we provide a review on the properties of Cu₆Sn₅ with a focus on: (1) identification of crystal structure and possible phase transformations of Cu₆Sn₅ in real solder joints; (2) formation of Cu₆Sn₅ during solidification of commonly used Pb-free alloys and its influence on the final microstructure; (3) the formation and growth texture of interfacial Cu₆Sn₅; (4) thermal expansion and mechanical properties of Cu₆Sn₅ and the relationship between crystal structure and temperature. The effects of selected alloying elements that have remarkable influences on the above properties are also discussed. The aim of this paper is to identify the key factors that affect the properties of this important IMC and the relationship between these properties and the integrity of solder joints under various conditions.