From the development of precision machining to ultra precision machining, is the development direction of the world’s industrial powers. Its precision ranges from micron level to submicron level and even nanometer level (< 10nm).
At present, under the requirement of high machining precision, the machining accuracy of ordinary computer gongs has been increased from ± 10 μ m to ± 5 μ m; the machining accuracy of precision machining center has been increased from ± 3 ~ 5 μ m to ± 1 ~ 1.5 μ m, or even higher; the ultra precision machining accuracy has entered the nano level (0.001 μ m), the spindle rotation accuracy is required to reach 0.01 ~ 0.05 μ m, the roundness is 0.1 μ m, and the surface is machined Roughness Ra = 0.003 μ m, etc. These machine tools generally adopt vector control variable frequency drive motorized spindle (motor and spindle integration), the spindle radial runout is less than 2 μ m, the axial movement is less than 1 μ m, and the shafting imbalance reaches g0.4 level.
There are mainly two types of feed drive of high-speed and high-precision machining machine tools: “rotary servo motor plus precision high-speed ball screw” and “direct drive of linear motor”. In addition, the new parallel machine tool is also easy to realize high-speed feed.
Due to its mature technology and wide application, ball screw not only has a high precision (ISO 3408 grade 1), but also has a relatively low cost to realize high-speed, so it is still used by many high-speed machine tools. The current high-speed machining machine driven by ball screw has a maximum moving speed of 90m / min and an acceleration of 1.5g.
Ball screw belongs to mechanical transmission. In the transmission process, there are inevitably elastic deformation, friction and reverse clearance, which will cause motion lag and other nonlinear errors. In order to eliminate the influence of these errors on machining accuracy, linear motor direct drive was applied to machine tools in 1993. Because of the “zero transmission” without intermediate link, it has small inertia and rigid system High speed and acceleration can be achieved with high speed and fast response, and the stroke length is not limited theoretically. The positioning accuracy can also reach a higher level under the action of high-precision position feedback system. It is an ideal driving mode for high-speed and high-precision machining machine tools, especially for medium and large-scale machine tools. At present, the maximum moving speed of high-speed and high-precision machining machine tools using linear motor has reached 208 M / min and the acceleration is 2G, and there is still room for development.
About the author