Additive Manufacturing (AM) technology is considered as one of the most promising manufacturing technologies in the areas of aerospace and defense industries. However, a lack of assurance of quality with AM parts is a key technological barrier that prevents manufacturers from adopting AM technologies, especially for high value added applications. Therefore, it is critically important to monitor the quality of products during the AM process. In this paper, current process monitoring especially the defects measurement for metal AM in Powder Bed Fusion (PBF) was firstly reviewed. And then, an optical in-situ inspection method based on multi-spectrum is proposed. The optical measuring system with infrared and white light imaging system is designed and optimized. Imaging data fusion algorithms is proposed to obtain the enhanced measuring results from infrared and white light imaging system. Simulation studies were undertaken to verify the validity of the proposed monitoring system. The research work is helpful for the optimization of process parameters so as to control the quality in the AM process.
Precision measurement of three-dimensional (3D) microstructures has drawn great interests from researchers and industries. Currently there are a bunch of high precision measurement methods such as contour-graphs, interferometers and optical computed tomography used in industrial applications. Nonetheless, the loss of information, low efficiency and possible surface damaging of traditional ways still exist. This paper presents a new way to measure micro/nano structures based on light field microscope. The light field information of the microstructures is acquired by using a microlens array which is inserted between the camera sensor and the objective lens. Then a series of regular sub-images are recorded by the photosensor, which is used to reconstruct a 3D image by the developed algorithms. The non-contact shooting process is realized through only one exposure which is much more efficient than the traditional ways. Microlens array with aspheric surface is also designed and used in the developed system, to eliminate aberrations and compensate the loss of spatial resolution. A series of simulation and experimental studies have been undertaken to measure microstructures, and the feasibility of the developed system is validated.
One of the important factors that affect the polishing results is the motion modes of the polishing pad in the process of Computer Controlled Optical Surfacing (CCOS). This paper presents a systematic study for the motion modes in CCOS by using a polishing pad. A series of theoretical and experimental studies have been undertaken to investigate the influences of two typical motion modes, called planet motion and orbital motion, on the polished surface, regarding to material removal rate (MRR), middle-spatial-frequency errors, surface roughness, etc. Firstly, the theoretical removal function of the two motion modes was established, and the experiments were carried out by given polishing parameters. A comparison was made between the results of experiments and simulations by the established polishing model. Then, the effects of the mentioned two motion modes on middle-spatial-frequency errors were simulated by the numerical superposition method, and the results were also verified by actual polishing results. Finally, the surface roughness generated by the two different motion modes was examined and compared. The research work shows that the planet motion has higher material removal rate, lower middle-spatial-frequency errors and lower surface roughness, by compared with orbital motion mode, which is helpful for optimizing the polishing strategy during CCOS.
A new non-contact and wide-range measurement system for lens thickness based on low-coherent interferometry was proposed in this paper. In this system the reference mirror was set moveable, and high-resolution grating ruler was utilized to record real-time position of mirror. Then lens central thickness was calculated on the basis of the relative distance between two interference fringes’ peak. Compared with the traditional thickness measurement technology based on low-coherent interferometry the new method has made great progresses. Firstly beam splitting and interference were separated by use of several fiber couplers which realized appropriate intensity ratio of probe beam and reference beam, and enhanced the contrast of interference fringes. Then zoom lens was designed to improve intensity coupling efficiency between the fiber system and lens system. Finally conversion from optical signal to electronic signal was accomplished by using balance detection, which was good for improving the signal-to-noise ratio. In this paper, firstly the basic principle of measuring device was put forward, namely low-coherent interference technique. Then design of the measuring device and solution for the main problems was introduced in detail. Experimental results of device was given in the end of article, which proved that the relative error of measurement was less than 0.05%.
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