1. High accuracy and precision persistence on the base have many machined surfaces of mounting parts and guide surfaces of moving parts. The accuracy of these surfaces and the accuracy of each other's position are very high, and can be maintained for a long time. In addition, when cutting machine tools, all dynamic and static loads are transmitted to the base, so the force on the base is very complicated. For this reason, in order to ensure the accuracy of the position or relative motion between components, besides the accuracy of geometric size and position, the technical requirements of static, dynamic stiffness, anti-vibration, thermal stability and so on should be met.
2. Sufficient static and dynamic stiffness should be provided, including the structural stiffness, local stiffness and contact stiffness of the base itself. Corresponding measures should be taken to achieve a higher stiffness-mass ratio in the end.
3. Dynamic stiffness directly reflects the motion characteristics of the base. In order to ensure that the base has a higher ability to resist deformation and forced vibration and self-excited vibration under alternating loads, at the same time, the resonance and the noise of the body caused by thin arm vibration can be reduced by increasing the damping and natural frequency appropriately.
4. Better thermal stability for machine tools, thermal stability of high-precision CNC machine tools has become a prominent problem, we must design to reduce the thermal deformation of the whole machine, or reduce the impact of thermal deformation on processing accuracy.
5. High strength and abrasion resistance. Large CNC grinders have sufficient strength whenever each base resists external load without exceeding allowable deformation. However, the strength of the parts with large external load and little deformation requirement should be paid attention to. As for the contact part between the base and the moving parts, that is, the guide rail, excellent wear resistance is required.
The sliding guide has the advantages of simple structure, convenient manufacture and high contact stiffness. However, the traditional sliding guides have large friction resistance, fast wear, large difference in dynamic friction coefficients, and crawling occurs at low speed. Therefore, a new type of plastic sliding guide is used.
The plastic guideway used in this design is PTFE guideway soft belt.
1. Characteristics of polytetrafluoroethylene guideway soft belt
Good friction: The static and dynamic friction coefficients of cast iron quenched guideway pairs are almost twice as different as those of dynamic ones, but the static and dynamic friction coefficients of metal PTFE guideway soft belts are generally unchanged. Therefore, this good friction performance can reduce the low-speed crawling, so that the motion is stable and the positioning accuracy is high.
Good wear resistance: besides the low friction coefficient, the PTFE guideway soft belt material has molybdenum disulfide and graphite, therefore, it has lubrication effect itself, and the demand for oil supply is low, so intermittent oil supply can be used. In addition, the plastic is soft, even if it is embedded in metal debris, dust, etc., it will not damage the metal guide surface and the soft belt itself, and can prolong the service life of the guide pair.
Vibration reduction is good: the plastic has a high damping capacity, and its vibration and noise reduction function has a higher significance to improve the relative motion speed of friction pairs.
Good workmanship: It can reduce the hardness and surface quality requirement of the metal guideway matrix pasted with plastic, and because plastic is easy to process, it can make the contact surface of the guideway pair obtain excellent surface quality. At the same time, it has the advantages of high chemical stability, convenient maintenance and good economy.
2. The surface roughness Ra3.2-1.6 is machined by zui. Sometimes, in order to achieve the positioning effect, the surface of the guide rail is machined into grooves 0.5mm to 1mm deep. Large CNC grinder uses gasoline and metal cleaning or acetone to clean the surface of the guide rail, then uses adhesive to bond the soft belt of the guide rail. After 1-2 hours of initial solidification under pressure, it is closed to the matching fixed guide. Applying certain pressure on the rail and curing at room temperature for 24 hours, removing the residual glue, the oil tank can be opened and the finishing process can be carried out, because this kind of guide uses sticking method, commonly known as "sticking plastic guide rail".