Polycrystalline ZnSe ceramics, an extreme difficult to machine material due to the inherent nature low hardness, low fracture toughness, and high brittleness, has been wildly used in the laser and infrared optics manufacturing field. However, the surface defects are inclined to nucleation and propagation through conventional single point diamond turning, the hybrid technology micro-laser-assisted machining (μ-LAM) has been proposed to combine the laser-assisted machining and ultra-precision single point diamond turning, which demonstrated the potential in improving the machining efficiency and surface integrity. In the study, comparative experiments have been conducted to verify the feasibility of μ-LAM on ZnSe ceramics. Furthermore, orthogonal experiments have been carried out to investigate the effect of machining parameters and laser parameters on surface quality and the optimum parameters subjected to the μ-LAM of ZnSe ceramics.
Optical freeform surfaces can provide a higher degree of freedom in optical design, compared with spherical and aspherical optical components. The application of freeform optical components in imaging optical systems is conducive to simplifying the system structure and improving imaging quality, and has wide applications in illumination, imaging and non-imaging, etc. This paper introduces the basic principle and process of fast tool servo (FTS) diamond turning, and its application in the field of optical processing. A series of machining experiment was carried out on aluminum materials by FTS diamond turning for XY polynomial freeform surface mirrors, and the surface accuracy and roughness were measured. The effects of feed rate, spindle speed, and cutting depth on surface roughness were studied and corresponding functional relationship curves were determined. The results show that the feed rate had the greatest influence on surface roughness of aluminum freeform surfaces, as the feed rate increased, the surface roughness increased gradually; the spindle speed and cutting depth have relatively little influence on surface roughness. The fitting degree of curves was very high, which can predict the surface roughness of machined freeform more accurately. The 3-D surface accuracy PV of the final processed freeform surface was 0.22μm, and the 2-D surface roughness Ra value was 3.5nm, the machined surface reached a mirror finish.
Due to the hard and brittle nature for optical materials, such as single crystal silicon, sapphire and fused silica, it is still difficult to machine those materials directly. Laser assisted turning (LAT) is an advanced method for machining the optical materials, which improve the local cutting performance by softening the workpiece. It has been demonstrated the great potential in LAT process for improving the surface quality and reducing the cutting force. This study reviewed the recent application of LAT in these materials. The material removal mechanisms was also analyzed and summarized. According to the experimental results, the machining efficiency and tool life were significantly increased. Finally, the development trend of LAT is prospected.
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