According to the motion track, the guide rail can be divided into linear motion guide rail and circular motion guide rail; according to the working nature, it can be divided into main motion guide rail, feed motion guide rail and adjustment guide rail; according to the friction property of contact surface, it can be divided into sliding guide rail, rolling guide rail and hydrostatic guide rail.
- Sliding guide rail
The sliding guide has the advantages of simple structure, convenient manufacturing, good stiffness and high vibration resistance. The traditional cast iron cast iron and cast iron quenched steel guide rail has the disadvantages of large static friction coefficient, dynamic friction coefficient changes with speed, and the friction loss is large. It is easy to crawl at low speed / (1-60 mm / min /), which reduces the positioning accuracy of moving parts. Therefore, it is not used in other CNC machine tools except economical CNC machine tools. At present, most CNC machine tools use plastic guide, that is, a layer of plastic film soft belt composed of plastic and other chemical materials is pasted on the friction surface of moving guide rail.
There are two kinds of guide rail Plastics: PTFE soft belt and epoxy wear-resistant rail coating. The characteristics of plastic sliding guide are good friction characteristics, good wear resistance, smooth movement, good vibration damping and good technology.
- Rolling guide
Rolling guide is to place ball, roller, needle and other rolling elements between the guide surfaces, so that the sliding friction between the guide surfaces becomes rolling friction. Compared with sliding guide, rolling guide has the following advantages: 1) high sensitivity, and little difference between dynamic friction coefficient and static friction coefficient, so it moves stably, and crawling phenomenon is not easy to appear when moving at low speed; (2) high positioning accuracy, repetitive positioning accuracy can reach 0.2 um; 8) low friction resistance, light movement, small wear, good accuracy retention and long service life. However, the anti vibration performance of rolling guide is poor, which requires high protection.
The rolling guide rail is especially suitable for the working parts of machine tools requiring uniform movement, sensitive motion and high positioning accuracy. This is the reason why rolling guide is widely used in CNC machine tools.
- Hydrostatic guide
Hydrostatic guideway can be divided into hydrostatic guideway and aerostatic guideway.
There is an oil chamber between the two guide working faces of hydrostatic guideway. After the lubricating oil with certain pressure is injected, the hydrostatic oil film can be formed, which makes the working surface of the guide rail in pure liquid friction, without wear, and has good accuracy retention. At the same time, the friction coefficient is also very low, which greatly reduces the driving power rate; at low speed In addition, the oil has the function of absorbing vibration and good vibration resistance. Its disadvantage is that the structure is complex, there must be an oil supply system, and the cleanliness of the oil is required to be high. Hydrostatic guideway is widely used in machine tools. The hydrostatic guideway of CNC turret punch press can be divided into open type and closed type. Figure 2.25 shows the working principle of the open hydrostatic guideway.
The aerostatic guideway can form a static pressure air film after passing a certain pressure between the working faces of the two guide rails, so that the two guide surfaces of the CNC punch press can be evenly separated to obtain high-precision movement. At the same time, the friction coefficient is small, and it is not easy to cause heating deformation, but it will change with the air pressure fluctuation, and the bearing capacity is small, which is often used in occasions with small load 。 In addition, we must pay attention to the dust on the guide rail surface, because the dust falling into the air guide surface will cause damage to the guide rail.