Development of an adaptive toolpath planning strategy for diamond face turning of freeform surfaces

Freeform surfaces are enormously demanded in advanced imaging and illumination applications. Sub-micrometre form accuracy is generally required to guarantee the designed functionality. However, there is a trade-off between the form accuracy and productivity when machining these surfaces, i.e. a sharp tool with finer toolpath segments can improve the form accuracy but at the cost of increased machining time. This paper proposes an adaptive toolpath planning strategy for freeform surfaces machining, which aims to achieve the highest productivity with the given tolerance. Instead of using the constant parameters to plan the toolpath, this strategy calculates the toolpath segment length by taking the tolerance and the curvature into account. Moreover, Fast Fourier Transform (FFT) is used to analyse the frequency components along the toolpath, and an optimized sampling frequency is selected to avoid losing small features on the surface. The toolpaths for diamond turning of a micro-lens array are generated by both conventional and adaptive toolpath planning methods. The results show that the adaptive toolpath can effectively reduce the number of points by one order of magnitude while improving the form accuracy by two-fold.