Papers by Keyword: Optical Lens

Abstract: Precision glass moulding is a technique that enables the production of optical lenses of complex geometries in a single step. However, it has been reported that the product quality highly depends on the properties of a raw material, the design of a die, and the selection of a processing program. This paper aims to reveal the formation mechanism of the residual stresses by optical lens moulding. To this end, a modulus-based constitutive model was developed to integrate with the deformation and stress analyses by the finite element method. The investigation showed that the residual stresses are caused by the variability and heterogeneity of thermal expansion in a lens, but that they can be reduced effectively by decreasing the rate of cooling within the stage from the molding temperature to the glass transition temperature.

Abstract: For higher geometrical accuracy requirement of optical lens, much research has been conducted either by changing the injection process parameters or changing the material of the mold or the mold manufacturing process. Although some degree of improvements was achieved, those were occasional but not-repeatable. One conventional procedure has been: the injection mold core must be polished several times to obtain qualified lens product in preproduction trial, very uneconomical and inefficient. In this paper, modern engineering tools were applied to simplify the correction process in optical lens fabrication. Combining virtual manufacturing with reverse engineering technology, the method was demonstrated very powerful. For the optical lens of 70x29.1mm in this research, the maximum deviation from the flatness after regular plastic injection molding was 0.208mm. While with combined technology of VM and RE the error was reduced to 0.008mm only by once iteration with an improvement of 96.15%. Not only the technology could be extended to larger or more challenging lens fabrication, it could also be applied to curved surfaces. This is really great tool to achieve higher quality optical lens production with much lower expending in labor and funding.

Abstract: According to needs of aspheric lens grinding and measurement with X/Y/Z 3-axis grinding machines, a CAM system is designed and implemented. The system, based on the parallel grinding geometry model, has realized the function of grinding locus planning, form error compensation, NC program auto-generation, on-machine measurement, grinding wheel on-machine measurement, simulation and technical database. To verify the stability of this CAM system, experiments were performed with three independent machining experiments. The experimental results indicate that the system realized the whole process of aspheric grinding, and it improved the machining efficiency and automation. Especially, this system adopted on-machine form error compensation technology and improved the machining accuracy. By implementing the error compensation integrated in the CAM system, the surface form error of a 430mm×430mm aspheric lens is decreased from PV8.2µm to PV4.1µm. The grinding accuracy was improved 100%.

Abstract: Super polishing experiments were carried out to investigate the effects of polishing parameters on surface quality of stainless steel lens moulding inserts, and to optimize polishing conditions. Experimental results indicated that optical quality surface of stainless steel lens moulding inserts can be achieved through a two-step polishing process: fast polishing with a soft wood head and coarse diamond paste, and fine polishing with a nylon-covered steel ball head and fine diamond paste. A diameter of 20 mm stainless steel lens moulding insert with a surface roughness Ra of 7.6 nm has been successfully achieved using the two-step super polishing process.