Ultra-precision ductile grinding of BK7 using super abrasive diamond wheel

Abstract

fine-grained resin or metal bonded diamond wheels. However, a disadvantage of this technology is the large wear rate of the grinding wheel during the dressing and grinding process, which limits the achievable figure accuracy and the maximum material removal volume, especially in the case of ductile grinding large spherical and aspherical optical surfaces. To solve this problem, a new diamond wheel type with grinding ratio significantly larger than that of finegrained diamond wheels must be applied to guarantee surface form accuracy of the machined surface.Monolayer nickel electroplated coarse-grained diamond grinding wheels have a grain size of approx of 100 µm. Because they can satisfy the requirements mentioned above, they could theoretically be a promising solution to the problem of using fine-grained diamond wheels to obtain topflattened diamond grains with minimized wheel run-out error, provided that they are well conditioned before machining.Based on this idea, several researchers have tried to apply this new diamond wheel in ductile grinding of brittle materials [1−7]. Brinksmeier et al. [1] proposed that a diamond cup wheel be used to dress the coarse-grained diamond wheel: a radial run-out error of less than 2 µm was obtained, and ductile mode taper grinding was realized on the optical glasses. However, no further contour grinding trials had been conducted; Kanai et al. [2] proposed the construction of a new diamond wheel, where the abrasives are monocrystalline pillar diamond and the orientations are aligned. This kind of wheel had perfect grinding performance, but was not easy to manufacture. The unsolved problem for manufacturing electroplated nickel diamond wheels is the uncontrollability of diamond grain concentration and grain protrusion height beyond the bonding material surface [8]; Wakuda et al. [3] proposed a truncating method to dress a coarse-grained CBN wheel in grinding hardened steel, and a mirror-like surface with Ra 0.05 µm was obtained. Hwang et al. [5−7] used unconditioned electroplated diamond wheels on high speed grinding of silicon nitride to investigate wheel wear, wheel life, wheel topography and grinding mechanism. However, there have been no reports so far of the successful application of coarse-grained diamond wheels on ductile contour grinding of optical glasses.Abstract In this paper, a novel conditioning technique using copper bonded diamond grinding wheels of 91 µm grain size and electrolytic in-process dressing (ELID) is first developed to precisely and effectively condition a nickelelectroplated monolayer coarse-grained diamond grinding wheel of 151 µm grain size. Under optimised conditioning parameters, the super abrasive diamond wheel was well conditioned in terms of a minimized run-out error and flattened diamond grain surfaces of constant peripheral envelope. The conditioning force was monitored by a force transducer, while the modified wheel surface status was in-situ monitored by a coaxial optical distance measurement system. Finally, the grinding experiment on BK7...