Abstract
Free-form surfaces have been widely used in complex optical devices to improve the functional performance of imaging and illumination quality and reduce sizes. Ultra-precision grinding is a kind of ultra-precision machining technology for fabricating free-form surfaces with high form accuracy and good surface finish. However, the complexity and variation of curvature of the free-form surface impose a lot of challenges to make the process more predictable. Tool path as a critical factor directly determines the form error and surface quality in ultra-precision grinding of free-form surfaces. In conventional tool path planning, the constant angle method is widely used in machining free-form surfaces, which resulted in non-uniform scallop-height and degraded surface quality of the machined surfaces. In this paper, a theoretical scallop-height model is developed to relate the residual height and diverse curvature radius. Hence, a novel tool-path generation method is developed to achieve uniform scallop-height in ultra-precision grinding of free-form surfaces. Moreover, the iterative closest-point matching method, which is a well-known algorithm to register two surfaces, is exploited to make the two surfaces match closely through rotation and translation. The deviation of corresponding points between the theoretical and the measured surfaces is determined. Hence, an optimized tool-path generator is developed that is experimentally verified through a series of grinding experiments conducted on annular sinusoidal surface and single sinusoidal surface, which allows the realization of the achievement of uniform scallop-height in ultra-precision grinding of free-form surfaces.
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Abbreviations
- N s :
-
Rotational speed of grinding wheel spindle (mm)
- N w :
-
Rotational speed of workpiece spindle (rpm)
- R s :
-
Wheel radius (mm)
- r s :
-
Nose radius of the grinding wheel (mm)
- V f :
-
Feed speed (mm/min)
- R :
-
Rotation transformation matrix
- R w :
-
Workpiece radius (mm)
- S :
-
Tool path interval (mm)
- ρ w :
-
Curvature radius of workpiece surface (mm)
- R t :
-
Scallop height (mm)
- H :
-
Depth of cut (μm)
- Q ij :
-
Points on the measured surface
- A :
-
Amplitude of sinusoidal surface (mm)
- φ :
-
Phase angle (rad)
- λ :
-
Wave length of sinusoidal surface (mm)
- M :
-
Machining transformation matrix
- T :
-
Translation matrix
- P ij :
-
Points on the measured surface
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Acknowledgements
This work was supported by a Ph.D. studentship (Project Account Code: RU3K) from The Hong Kong Polytechnic University and a grant from the Innovation and Technology Commission (ITC) (Project No. GHP/031/13SZ) of the Government of the Hong Kong Special Administrative Region. This research work was also supported by the State Key Basic Research and Development Program, China (973 Program, Grant No. 2011CB 013202) and Guangdong Provincial Department of Science and Technology, Guangdong, P. R. China for The Introduction of Innovative R&D Team Program of Guangdong Province (Project No.: 201001G0104781202).
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Chen, S., Cheung, C.F., Zhang, F. et al. Optimization of Tool Path for Uniform Scallop-Height in Ultra-precision Grinding of Free-form Surfaces. Nanomanuf Metrol 2, 215–224 (2019). https://doi.org/10.1007/s41871-019-00048-0
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DOI: https://doi.org/10.1007/s41871-019-00048-0