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Problems occurred during machining steep aspheric parts with large sagittal height on double-spindle diamond turning
machine are presented and the main reasons of the problems are described. And methods of solving these problems are
also suggested. When we machine steep aspheric parts with large sagittal height on a 2 axis diamond turning machine,
we have such problems as difficult control of part edge accuracy, poor roughness and rapid wear of the cutting tool. The
main reasons for these problems lie in: 1) Measurement. To make accurate measurements, the measurement range of
the profilometer must fall within the sagittal heights of the aspheric parts, and the measurement angle must also meet the
requirements, an insufficient measurement angle, for example, will have a big impact on the measurement and
fabrication accuracy of such parts; and 2) Machine and tool, firstly, the diamond cutting tool will suffer a very big force
when turning the edge section, resulting in bigger micro-vibration in the tool and tool post, thus affecting the part
accuracy and surface roughness. Secondly, the machine itself has location errors in axes X and Z during the processing,
leading to the severest destruction in the steep section of the aspheric part by their resultant force. Lastly, anisotropy of
diamond cutting tool hardness. The indentation hardness of the diamond is maximum in the direction of <1.0.0> of face
(100) and the front clearance has the best strength at tool point in the direction of <1.0.0>. When cutting a steep aspheric
part with large sagittal height, a bigger included angle of the diamond tool point arc will be used, and there will be a
more deviation from the <1.0.0> lattice direction. So the tool hardness is consistently decreased, resulting in a rapid wear
of the cutting tool when turning the steep section of the aspheric part, thus the accuracy and roughness in machining an
aspheric part become more difficult to control. The paper is concluded with the solutions of turning steep aspheric parts
with large sagittal height. Efforts have been made to reach an accuracy within 1.5 um, Ra 0.007 um (mold insert), and no
apparent tool marks on the surface when machining steep aspheric parts with large sagittal height on double-spindle
diamond turning machine.
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