Study on a 5-axis precision and mirror grinding of glass freeform surface without on-machine wheel-profile truing

• The virtual ball-end algorithm is applied to 5-axis precision freeform grinding.
• A self-dressing diamond freeform grinding replaces on-machine wheel-profile truing.
• Mirror freeform grinding is parameterized by tool, machine, workpiece and mechanism.

The precision freeform grinding depends on the on-machine truing of diamond wheel, leading to the inefficiency of grinding system. Hence, a virtual ball-end algorithm along with a fixed tool posture angle is proposed for the 5-axis grinding of glass by using a self-dressing diamond wheel. The objective is to realize the precision and mirror freeform grinding without any wheel-profile truing. First, virtual ball-end grinding, ground freeform surface and freeform errors compensation were modeled in 5-axis grinding system, respectively; then tool interference, envelope trace height, grain cutting depth and ground surface roughness were systemically investigated in connection with tool posture angle, tool sizes, grain protrusion variables, abrasive parameters and self-dressing coefficient; finally, the 5-axis grinding experiments of F-theta freeform glass lens were performed. It is shown that the virtual ball-end algorithm is valid for the 5-axis freeform grinding with a self-dressing abrasive tool. Increasing tool posture angle decreases the grain cutting depth to the critical cutting depth from brittle cutting to ductile cutting, but it increases the risk of tool interference. The mirror freeform grinding may be parameterized by material behavior, tool size and posture, grinding conditions and abrasive tool performance. On the base of virtual ball-end algorithm, the form errors compensation enhances the mirror-ground freeform accuracy by 26%. It is confirmed that the 3-μm-size diamond grinding without on-machine truing is feasible to fabricate the precision and mirror freeform glass along with the tool posture angle of 30°.

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