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With the high precision requirements and the trend of large-scale composite parts, the development of composite molds is imminent. The short carbon fiber (SCF) composite mold is mainly prepared by the technological process flow of composite sheet injection, the bonding of composite plates, and machining. However, the current process optimization method has not matured adequately, and there are still many shortcomings, for example, low precision and high cost. In this paper, the optimization method of SCF/polyetherimide (PEI) composite molds is proposed. Many experiments have been conducted, and the results show that the coefficient of thermal expansion of composite samples can be effectively reduced and the mechanical properties can be improved by optimizing the SCF weight ratio and carbon fiber length. The bonding strength of composite joints in a high-temperature environment can be improved by optimizing the bonding process parameters and modification by carbon nanotubes. Based on the above optimization method, the SCF/PEI composite mold is prepared, and the C-shaped beam composite part is fabricated by using this mold. Compared with the part made by aluminum mold, the shape accuracy of the C-shaped beam composite part is proven high through digital measurement technology. [ABSTRACT FROM AUTHOR]

Continuous carbon fiber reinforced polymer composite 3D printing has drawn more attention due to its ability to manufacture composite structures with complex shapes. The surface treatment of CF is necessary to improve the combination between carbon fiber (CF) and matrix. In this work, polyurethane with nano‐SiO2 (PU/SiO2) was used to size CF to enhance the compatibility of CF and nylon 6 (PA6). The chemistry and morphology of the CF were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The interface strength between CF and PA6 was tested by the fiber pull‐out test, and eventually obtained optimized concertation of PU/SiO2 sizing agents (with 25 wt% PU and 0.4 wt% nano‐SiO2). The results show that compared with untreated CF, the interfacial shear strength (IFSS) of CF and PA6 after sizing increased by 316.93%. In addition, several CF/PA6 composite specimens printed by a homemade composite 3D printer were used to do mechanical tests. The results show that the flexural strength increased by 33.87%, the tensile strength increased by 20.75%, and the interlaminar shear strength (ILSS) increased by 66.54%. [ABSTRACT FROM AUTHOR]

Background: When performing the spatial large-scale measurements, the measurement accuracy of laser tracker would decreased with the increase of the measurement distances due to the refraction difference of most optical digital measurement devices. Therefore, this paper proposed a method based on photogrammetry system to improve the large-scale measurement accuracy of the laser tracker. Purpose: The purpose of this method is to improve the large-scale measurement accuracy of the laser tracker by considering the advantages of photogrammetry system such as high measurement accuracy and good portability. Methods: The measurement data from the photogrammetry system would be used as a reference to do correction on measurement results from laser tracker. The coordinate correction method based on Rodrigues' rotation formula has been discussed. The measurement accuracy of the long-distance point of laser tracker can be significantly improved through the coordinate correction method. Conclusion: Based on the advantages of using photogrammetry system, the proposed method can achieve higher accuracy when measuring the common points at a closer distance than the laser tracker can do when measuring objects far away from instrument. The feasibility of the proposed method has been demonstrated by experiment. [ABSTRACT FROM AUTHOR]

In traditional multi-axis machining, the linear tool path generated by computer-aided manufacturing systems is still in a broad tool path format, resulting in discontinuities at the corners, which slow down tool motion, and also trigger tool vibration, reducing machining accuracy and surface quality. In order to ensure the C3 continuity of the tool during the multi-axis machining process, this paper proposes an analytical B-spline local smoothing method with curvature control. The tool position trajectory and tool orientation are both smoothed by a 5th spline curve with 9 control points. Optimal control points are determined for position and orientation splines to achieve C3 continuity at the junctions between the spline and linear segment while preserving the predefined geometric tolerance limits and minimizing the maximum curvature of the inserted B-spline curve. The smoothed tool path is expected to have less curvature fluctuation, which can significantly improve both the kinematic performance of the machine tool and the machining efficiency. Both computer simulations and physical printing experiments are carried out to demonstrate the improvements of our proposed method in motion smoothness and tracking accuracy in multi-axis machining tasks. [ABSTRACT FROM AUTHOR]

Continuous multi-axis printing has drawn more and more attention owing to its unique advantages of eliminating the need of support (at least in theory) when printing complex models with overhang features and significantly reducing the stair-step effect of the conventional three-axis printing. For continuous multi-axis printing, the printing layers are typically not planar but curved, so to capitalize the extra DOFs provided by the rotary axes of the printer. When a printing layer is concave (i.e., its curvature vector points inward at the printing point), the potential nozzle-layer local gouging becomes a serious concern, which is especially problematic for metal printing wherein the size of the nozzle head is usually large. Unfortunately, this convexity issue has received little attention in the existing curved slicing algorithms, making them prone to the local gouging quandary. In this paper, we propose a novel curved layer decomposition algorithm based on the use of (only the positive sides of) ellipsoidal surfaces. To facilitate the generation of ellipsoidal printing layers for an arbitrary freeform solid model with a complex topology (e.g., having a non-zero genus number), the powerful algebraic technique of skeletonization is employed by our algorithm to first decompose the model into a suitable set of sub-entities, for each of which a series of ellipsoidal printing layers are then generated, wherein the parameters of ellipsoidal layers are adaptively adjusted to satisfy the necessary constraints such as support-free and other requirements. Preliminary experiments in both computer simulation and physical printing of the proposed algorithm are conducted, and the results give a positive validation on the effectiveness and feasibility of the proposed methodology. • A new curved-layer decomposition method based on ellipsoidal surface is developed. • The algebraic technique of skeletonization is employed to do the model segmentation. • An ellipsoid fitting scheme is proposed to allow continuous layer propagation. • The use of ellipsoids can reduce support structure and avoid local gouging problem. [ABSTRACT FROM AUTHOR]

The inherent defects of the layer‐by‐layer manufacturing process limit the mechanical performance of 3D‐printed composite parts. This paper explores a process optimization method for continuous fiber composites 3D printing to improve the mechanical performance of 3D‐printed CF/PA6 (Carbon Fiber/Nylon 6) parts. First, the effects of printing temperature, printing speed, layer thickness, and side step on the mechanical performance of 3D‐printed CF/PA6 were studied by conducting variable parameter printing experiments. All optimal printing parameters for CF/PA6 were obtained, and their impact mechanisms were analyzed. Second, the coupling effect of temperature and pressure of post‐processing reduced the internal voids of 3D‐printed CF/PA6 and improved its mechanical properties. The influence mechanism of the coupling effect of temperature and pressure was summarized, and the optimal post‐processing parameters applicable to CF/PA6 were obtained. Based on the above process optimization, the fiber volume content of the printed CF/PA6 reached 41.05%, and the bending strength and elastic modulus reached 651.54 MPa and 79.08 GPa, which were 209.05% and 179.53% higher than those before optimization. Moreover, the tensile strength and elastic modulus reached 730 MPa and 29.23GPa, which were 98.10% and 81.10% higher than those before optimization. The experimental results give a positive validation of the effectiveness and feasibility of the proposed methodology. Highlights: The effects of printing temperature, printing speed, layer thickness, and side step on the mechanical properties of 3D‐printed CF/PA6 were investigated. The optimal printing parameters applicable to CF/PA6 were obtained and their influence mechanisms were analyzed.The effects of the heat press processing method on the internal voids and mechanical properties of 3D‐printed CF/PA6 were investigated, and the optimal post‐processing parameters applicable to CF/PA6 were obtained.The study resulted in optimal printing parameters and post‐processing parameters for 3D printing CF/PA6, which greatly enhanced its tensile and flexural strength and modulus. [ABSTRACT FROM AUTHOR]

Laser tracker has been used in a diverse range of applications due to its high accuracy and efficient, specifically as measuring the coordinates of points or scanning shape of objects. In real applications, we often need to measure common points on multi-stations by using this technology if objects are large scale. To ensure every common point within the range of laser tracker, common points are usually placed far from the laser tracker. However, the long distance between common points and laser tracker will decrease the accuracy of the result. In this research, we proposed a new method where photogrammetry and laser tracker are integrally used to measure common points to reduce measurement error. With the help of photogrammetry, we first constructed the geometric constraints of common points. Then, by using graphic correction method, the coordinates of common points on laser tracker will be corrected. Both of the theoretical and experimental study results indicated the great success of improving the measurement accuracy of laser tracker. We consider that this method we reported can highly increase the accuracy of measurement on laser tracker station-transfer. [ABSTRACT FROM AUTHOR]