On machine polishing of ultraprecision diamond ground aspherical surfaces on multispectral CVD ZnS lens

For the aspheric machining of zinc sulphide, ultraprecision diamond grinding and the CNC sub- Aperture polishing were applied on the same machine tool. After ultraprecision diamond grinding, CNC sub- Aperture polishing was performed successively without removing the part from workpiece spindle. For making the on machine polishing realized, the tool influence function (TIF) and dwell- Time map need to be achieved. Firstly, the TIF for the process of computer-controlled polishing with soft polishing wheel was theoretically presented based on the Preston equation. For establishing the interfacial pressure distribution model, the Winkler elastic foundation was introduced to model the polishing wheel in the contact zone. A series spot experiments were conducted to obtain the removal spot statistical properties for establishing the TIF. Secondly, the dwell- Time map was calculated through formulating the form correction into the matrix form. For the axis-symmetrical part, the material removal distribution could be calculated by one dimension TIF in a polar coordinate system. To achieve the convergence between actual and simulated removal profile, the TIF matrix need to be corrected by multiplying an adjusting matrix before form correction. Depending on the on machine form error measure equipment, the part error map could be obtained to work out the dwell- Time map. After on machine polishing, the ultraprecision ground aspherical surfaces of the CVD zinc sulphide lens become smoother while the form accuracy does not deteriorate. the experimental result indicate that the on machine polishing technique of ultraprecision diamond ground aspherical CVD ZnS lens was achieved to fulfil the high efficiency machining of infrared aspherical lens which are hard- To-machine via diamond turning .