Analysis of linear guides for machine tools
The new rail system allows the machine to achieve fast traverse speeds. At the same spindle speed, rapid traverse is a linear guide. Linear guides, like flat guides, have two basic components; one for the fixed assembly and the other for the moving assembly. Since linear guides are standard components, for machine tool builders. The only thing to do is to machine the parallelism of the plane of the mounting rail and the alignment rail. Of course, in order to ensure the accuracy of the machine tool, a small amount of scraping of the bed or column is essential, and in most cases, the installation is relatively simple.
The guide rail as a guide is hardened steel, which is finely ground and placed on the mounting plane. Compared with the planar guide rail, the geometry of the cross section of the linear guide is more complicated than that of the planar guide. The reason for the complexity is that the groove needs to be machined on the guide rail to facilitate the movement of the sliding assembly. The shape and number of the groove depend on the machine tool to be completed. The function. For example: a rail system that withstands both linear forces and subversive moments, compared to rails that only accept linear forces. There are big differences in design.
A rolling steel ball is used between the moving component of the linear guide and the fixed component without using an intermediate medium. Because the rolling steel ball is suitable for high-speed movement, small friction coefficient and high sensitivity, it can meet the working requirements of moving parts, such as tool holders and carriages of machine tools. The basic function of the fixed component (rail) of the linear guide system is like a bearing ring, a bracket for mounting a steel ball, and the shape is a "v" shape. The bracket wraps around the top and sides of the rail. In order to support the working parts of the machine tool, a set of linear guides has at least four brackets. Used to support large work pieces, the number of brackets can be more than four.
When the working part of the machine tool moves, the steel ball circulates in the groove of the bracket, and the wear amount of the bracket is distributed to each steel ball, thereby extending the service life of the linear guide. In order to eliminate the gap between the bracket and the guide rail, the preloading can improve the stability of the rail system and obtain the preload. An oversized steel ball is placed between the rail and the bracket. The diameter tolerance of the steel ball is ¡À20 ¦Ìm. In the increment of 0.5 ¦Ìm, the steel balls are sorted and classified into the guide rails. The magnitude of the preload is determined by the force acting on the steel ball. If the force acting on the steel ball is too large, the steel ball is subjected to the preloading time for too long, resulting in an increase in the kinematic resistance of the bracket. There is a problem of balance here; in order to improve the sensitivity of the system and reduce the resistance to motion, the preload is reduced accordingly, and in order to improve the accuracy of motion and the accuracy, it is required to have sufficient pre-added negative numbers. aspect.
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When the working time is too long, the steel ball begins to wear, and the preload applied to the steel ball begins to weaken, resulting in a decrease in the movement accuracy of the working parts of the machine tool. If you want to maintain the initial accuracy, you must replace the rail brackets or even replace the rails. If the rail system is preloaded. The system accuracy has been lost, the only way is to replace the rolling components.
The design of the rail system strives to maximize the contact area between the fixed component and the moving component. This not only improves the load carrying capacity of the system, but also the system can withstand the impact force generated by intermittent cutting or gravity cutting, spreading the force widely and expanding the bearing capacity. The area of force. In order to achieve this, the shape of the groove of the guide rail system is various, and there are two representative ones, one is called the Gothic type (the pointed arch type), the shape is the extension of the half-circle, and the contact point is the apex; One is a circular arc that can also perform the same function. No matter which type of structure, there is only one purpose, and strive to contact more of the radius of the rolling steel ball with the rail (fixed component). The factor that determines the performance characteristics of the system is how the rolling components come into contact with the rails, which is the key to the problem.