Digital Twins towards Microwave-assisted 3D Printing of Continuous Carbon Fiber Reinforced Composites

Microwave-assisted 3D printing based on the fused filament fabrication (FFF) method is an emerging technology to print lightweight continuous carbon fiber reinforced thermoplastics (CCFRP) at high speed. Different from traditional FFF, microwave offers selective and volumetric heating properties to melt thermoplastic materials instantaneously, and the microwave printing head and nozzle remain at room temperature. These advantages can increase the printing speed of CCFRP significantly, while the belt slippage of a printing bed is noticed during microwave-assisted 3D printing. The slippage of the moving belt happens because the cold nozzle moves at high speed and encounters resistance from the rough surface of the printed filament. To solve this problem, this paper presents a hierarchical digital twin (DT) framework, consisting of core and basic DTs, for the prevention of belt slippage induced printing malfunction. The core DTs use MATLAB Simscape multibody models to simulate the printing process virtually and the printing G-code is corrected before printing. In addition, an accelerometer installed on the printing bed is connected to the core DTs. Abnormal vibration signals due to belt slippage can be measured and communicated with core DTs for interrupting and correcting the process. By monitoring the temperature of the heated filament and the output microwave power, the service life of the nozzle and microwave cable are evaluated in the basic DTs

Tooling design and microwave curing technologies for the manufacturing of fiber-reinforced polymer composites in aerospace applications

The increasing demand for high-performance and quality polymer composite materials has led to international research effort on pursuing advanced tooling design and new processing technologies to satisfy the highly specialized requirements of composite components used in the aerospace industry. This paper reports the problems in the fabrication of advanced composite materials identified through literature survey, and an investigation carried out by the authors about the composite manufacturing status in China’s aerospace industry. Current tooling design technologies use tooling materials which cannot match the thermal expansion coefficient of composite parts, and hardly consider the calibration of tooling surface. Current autoclave curing technologies cannot ensure high accuracy of large composite materials because of the wide range of temperature gradients and long curing cycles. It has been identified that microwave curing has the potential to solve those problems. The proposed technologies for the manufacturing of fiber-reinforced polymer composite materials include the design of tooling using anisotropy composite materials with characteristics for compensating part deformation during forming process, and vacuum-pressure microwave curing technology. Those technologies are mainly for ensuring the high accuracy of anisotropic composite parts in aerospace applications with large size (both in length and thickness) and complex shapes. Experiments have been carried out in this on-going research project and the results have been verified with engineering applications in one of the project collaborating companies

An efficient cache replacement algorithm for multimedia object caching

Multimedia object caching, by which the same multimedia object can be adapted to diverse mobile appliances through the technique of transcoding, is an important technology for improving the scalability of web services, especially in the environment of mobile networks. In this paper, we address the problem of cache replacement for multimedia object caching by exploring the minimal access cost of caching any number of versions of a multimedia object. We first present an optimal solution for calculating the minimal access cost of caching any number of versions of the same multimedia object and its extensive analysis. The performance objective is to minimize the total access cost by considering both transmission cost and transcoding cost. Based on this optimal solution, we propose an efficient cache replacement algorithm for multimedia object caching. Finally, we evaluate the performance of the proposed algorithm with a set of carefully designed simulation experiments for various performance metrics over a wide range of system parameters. The simulation results show that our algorithm outperforms comparison algorithms in terms of all the performance metrics considered. © 2007 CRL Publishing Ltd.link_to_subscribed_fulltex