Analysis and optimization of temperature distribution in carbon fiber reinforced composite materials during microwave curing process

Vacuum assisted microwave curing technologies and modified optical sensing systems have been employed to investigate the influence of ply orientation and thickness on through-thickness temperature distribution of carbon fiber reinforced composite laminates. Two different types of epoxy systems have been studied. The results demonstrated that the ply orientation did not affect the temperature distribution of composite materials. However, the thickness was an important influencing factor. Nearly 10 ◦C temperature difference was found in 22.5 mm thick laminates. Through analyzing the physical mechanisms during microwave curing, the temperature difference decreased when the heat-loss in surface laminates was reduced and the absorption of microwave energy in the center laminates was improved. The maximum temperature difference of the samples formed using the modified microwave curing technologies in this research could be reduced by 79% to 2.1 ◦C. Compared with the 5.29 ◦C temperature difference of laminates using thermal heating process, the maximum temperature difference in laminates using modified microwave curing technologies was reduced by 60%, and the curing time was cut down by 25%

LiDAR Based Multi-Robot Cooperation for the 3D Printing of Continuous Carbon Fiber Reinforced Composite Structures

3D printing of lightweight continuous carbon fiber reinforced plastics (CCFRP) in three dimensions changes the traditional composite manufacturing processes. The continuous carbon fibers reinforced plastic filament can be printed along the load transmission path and significantly improve the strength of composite structures. Compared to the three-axis computer numerical controlled (CNC) machine based printing process, industrial robots provide the possibility to manufacture complex, spatial and large-scale composite structures. Here, the concept to use multi-robot to print complex spatial CCFRP components simultaneously has been presented. More than one 6 degrees of freedom industrial robots can cooperate with each other and solve the contradiction between structural complexity and printing reachability. During the printing process, the deformation of composite structures may happen, especially for the self-supporting components. Thus, in this paper, a Light Detection and Ranging (LiDAR) method is introduced to detect the deformation of printed composite structure and the movements of two UR robots. To obtain the point clouds of the printed structure, a LiDAR camera D435i has been installed on one robot. A new approach by combining coordinate transformation and iterative-closest-point (ICP) algorithm has been developed to merge the point clouds collected from different shooting angles of the camera

Small-Size Coaxial Resonant Applicator for Microwave Heating Assisted Additive Manufacturing

This article introduces the design and analysis of a small-size coaxial resonant applicator for high-speed microwave heating-assisted additive manufacturing of multiple materials, such as continuous carbon fiber reinforced polymer composites, thermoplastic, and metal parts. The elaborated coaxial resonant applicator reduces the size and has a resonant frequency between 2.4 and 2.5 GHz. A TEM wave is stimulated in the applicator where the electrical field is polarized perpendicular to the filaments and, therefore, allows a maximum penetration depth. The electrical conductive filament is designed as a part of the inner conductor to enhance coupling efficiency. To prevent microwave leakage induced by the conductive material, a compact quarter wavelength filter was developed. The equivalent circuit of the filter was used to analyze the influence of structural parameters on the resonance frequency. The filter has been tested and good agreement between measured and simulated results is obtained. The heating behavior with varying input power has been investigated for polyamide, polylactic acid, and continuous carbon fiber reinforced polyamide filaments

Microwave additive manufacturing of continuous carbon fibers reinforced thermoplastic composites: Characterization, analysis, and properties

Traditional additive manufacturing (also known as 3D printing) of continuous carbon fiber reinforced plastic (CCFRP) lacks the ability to manufacture parts with high speed and energy efficiency. This is mainly because of the contact needed and the slow heat transfer from the conventional hotend to the composite filaments. A microwave heating assisted additive manufacturing method is here presented which allows manufacturing CCFRP with a higher speed as compared to conventional methods. The permittivity of printed specimens with different fiber volume fraction was investigated. By using the measured dielectric properties, a micro-scale microwave radiation and heat transfer model between the fiber and resin matrix has been established. The skin-core temperature difference of the moving CCFRP filaments during conventional thermal and microwave heating has been simulated to reveal the relationship between the temperature difference, filament diameter and printing speed. Non-isothermal crystallization behavior and mechanical strengths of thermal and microwave printed specimens have been studied, and the reasons for the different results have been analyzed

Load-dependent path planning method for 3D printing of continuous fiber reinforced plastics

3D printing, to print continuous fiber reinforced plastics (CFRPs) has advantages of manufacturing complex shape and short production cycle. Due to anisotropic mechanical properties of continuous fibers, the paving direction of the fibers determines the mechanical strengths of the printed CFRPs. In this paper, a novel load-dependent path planning (LPP) method has been proposed to generate printing path for CFRPs, which exactly follows the load transmission path of the parts and could provide higher mechanical properties. A topology optimization method is applied to simplify the original disordered load distribution. In the developed Stress Vector Tracing (SVT) algorithm, the printing paths are generated along the load transmission path with the variable spacing of adjacent paths. The LPP method has been compared with the state-of-the-art printing path planning method for continuous fibers and shown better load-bearing and printability

A new process control method for microwave curing of carbon fibre reinforced composites in aerospace applications

For the fabrication of carbon fibre reinforced composites used in aerospace industry, microwave curing technologies are more effective than traditional thermal curing technologies. However, the manufacturer’s recommended cure cycles used in traditional autoclave curing are directly adopted into current microwave curing technologies without thorough validation. Here, a new cyclic heating and cooling methodology for microwave curing process control of composite is proposed by analyzing mechanisms of heat conduction, stress generation and curing kinetics. The results of the experiment carried out show significant reductions in residual strain, warpage, total curing time and energy consumption, compared with both traditional thermal curing and current microwave curing technologies. The mechanical properties of samples cured by the new process are compared with the autoclave cured ones

Path-designed 3D printing for topological optimized continuous carbon fibre reinforced composite structures

In current 3D printing technologies, it remains a great challenge to print continuous carbon fibre reinforced composites with complex shapes and high mechanical performances. The main reason lies in the limitation of printing path design, which cannot guarantee to print carbon fibres along load transmission paths of composite parts. Here we address this issue by proposing an ingenious path-designed 3D (PD-3D) printing approach that considers the load transmission path and anisotropic property of the continuous carbon fibre reinforced filament. Complex structures of carbon fibre reinforced composites, with enhanced lightweight, were demonstrated. Such structures of carbon fibres paving along load transmission paths, greatly reduce stress concentration and achieve a quasi-isotropic performance. By comparing printed specimens with drilled holes and semicircles, the PD-3D printed specimens with holes and semicircles are 67.5% and 62.4% higher in tensile and flexural strength, respectively. And the strength to weight ratio of the tensile and flexural specimens also increase by 55.1% and 35.2%, compared with the drilled ones