Ultra-precision Ductile Grinding of Off-Axis Biconical Free-Form Optics with a Controllable Scallop Height Based on Slow Tool Servo with Diamond Grinding Wheels

Free-form optics made of hard and brittle materials possesses the reflection and imaging functions that are difficult to be achieved by traditional optics and are widely used in various high energy space optical systems. However, free-form optics made of hard and brittle materials poses great challenges to ultra-precision machining due to its extreme demands of complex surface shapes with nonrotational asymmetric, submicron profile accuracy, controllable scallop height, nanometer surface roughness and ductile grinding surfaces. The freeform generation technique of the slow tool servo with diamond grinding wheel (STS-DGW) previously proposed by us was used to manufacture free-form optics made of hard and brittle materials. First, a theoretical model of scallop height during grinding of biconical free-form surface was established, and the effects of curvature changes on scallop height were studied. Subsequently, the profile error caused by the centering error of diamond wheel was calculated theoretically, and an accurate adjustment method of the grinding wheel position was proposed. Then, an undeformed chip thickness model for achieving ductile grinding was established, and the simulation calculation of critical grinding parameters was carried out. Ultimately, a typical off-axis biconical free-form optics with submicron profile accuracy, a controllable scallop height, nanometer surface roughness, and ductile grinding surfaces was successfully fabricated on single-crystal silicon using the proposed STS-DGW. Compared with the previous research, the profile accuracy was further improved, a controllable scallop height and ductile grinding surface was achieved.