Key component technology for ultra-precision machining machines (2)

3 linear guide

The linear guide, which is the relative positioning mechanism of the tool and the workpiece, is an important component next to the spindle. The basic requirements for linear guides for ultra-precision machine tools are: flexible movement, no crawling and other discontinuous movements; straight line accuracy; practicality should be rigid in accordance with the conditions of use; low heat during high-speed movement; easy maintenance . Common guide rails in ultra-Precision Machining machines include VV sliding guides and rolling guides, hydrostatic guides and gas static pressure guides. Traditional VV sliding guides and rolling guides have achieved good results in both the US and Germany. The latter two are non-contact rails, so there is no need to worry about creep. The latter two are also the most suitable guide rails in terms of accuracy. The hydrostatic guide rail generates a large amount of heat due to the viscous shear resistance of the oil, so it is necessary to take cooling measures for the hydraulic oil. In addition, the hydraulic device is relatively large, and the maintenance of the oil circuit is troublesome. The gas static pressure guide rail can obtain a large support rigidity because the support portion is flat, and it has almost no heat generation problem. If the initial design is reasonable, there is almost no problem in subsequent maintenance. However, attention must be paid to the dustproofing of the rail surface. The gap of the air rail is only a few ten micrometers, and the dust of such a size is invisible to the naked eye. Such dust cannot be completely eliminated even in a clean room, and dust falling into the air rail surface may cause damage to the rail surface. In general, the air static pressure guide is the best guide rail at present, but if the dustproof condition cannot be guaranteed, the hydrostatic guide rail must be used instead. At present, the straightness of the air static linear guide can reach 0.1 to 0.2 μm/250 mm.

Figure 1 Pressure distribution on the air floating surface

The HCM-I ultra-precision machining machine uses an air linear guide, and the pressure distribution on the air-floating surface is shown in Figure 1.

By installing the adjusting air static pressure guide, the following conclusions can be drawn: (1) A sufficient exhaust passage must be ensured, otherwise the slide will generate a positional disturbance, sometimes reaching a few micrometers. (2) Theoretically speaking, reducing the orifice diameter and the film thickness can improve the stiffness of the slide, but it brings technical difficulties. It is difficult to process small holes of

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