The trend of thermal deformation of various types of machine tools and the impact on machining accuracy.
(1) Thermal deformation of car, milling, drilling and boring machine tools The main heat source of such machine tools is the headstock. The heat generated by the frictional heating of the gears and bearings in the headstock and transmitted to the lubricating oil causes the temperature of the headstock and the bed or the main shaft connected thereto to rise and cause large thermal deformation.
(2) Thermal deformation of grinding machine tools.
(3) Thermal deformation of large machine tools. In this case, the surface of the workpiece after machining will produce shape and positional errors.
(4) Thermal deformation of CNC machine tools and machining center machine tools. The machining center machine tool does not change the workpiece clamping conditions, and performs multi-faceted and multi-process processing on the workpiece. The rotation speed is high, the internal heat source is large, the heat dissipation time is short, and large heat deformation is not allowed. Therefore, CNC machine tools, machining center machine tools, to prevent thermal deformation, must take appropriate measures.
The main cause of thermal deformation of the machine tool is the heat generation of the heat source. Reducing the heat generation of the heat source is one of the main measures to reduce the thermal deformation of the machine tool. Improve the quality of rolling bearings. Change the lubrication conditions and assembly quality of the main bearing and the transmission bearing. Due to the temperature rise of the mechanical bearing, the radial load and the friction coefficient are mainly determined. In addition to changing the lubrication condition of the bearing, the dynamic pressure oil film bearing and the hydrostatic bearing may be used to reduce the friction coefficient and reduce the bearing. Heat.
Generally speaking, the fuel tank is designed reasonably and relies on the natural heat dissipation of the fuel tank to meet the oil tank oil temperature control requirements. However, for precision machine tools, the oil temperature of the hydraulic components and the oil temperature of the lubricating oil should be strictly controlled, sometimes requiring constant temperature to maintain The normal working accuracy of the machine tool. In this case, the oil temperature needs to be controlled. In addition to the fan blowing or blowing in the freezer, a serpentine tube cooler or a tube cooler can be arranged in the tank to remove excess heat away by the cooling water. The air-cooled motors can be cooled by hydrogen or helium, because their thermal conductivity is 510 times higher than that of normal gases. Therefore, the cooling effect is much better by switching to hydrogen and helium. Improve surface finish for all parts of the machine. Painting, oxidation and surface treatment can improve the surface endothermic conditions and thus control the effects of various heat sources.
In summary, the control and prevention of the influence of machine tool thermal deformation on the machining accuracy can be based on the reasonable structural design of the machine tool and its technical measures. Another way is to innovate the parts and components of the machine tool in the materials used. Basic materials such as machine bed and column can be made of special materials with small linear expansion coefficient such as granite, light alloy, fine ceramics, etc. It is the ideal material when making precision machine tool spindles from glass ceramics. Due to this special material, the vibration attenuation is good. Good thermal stability, dimensional stability, and easy access to materials. Therefore, the influence of thermal deformation of the machine tool on the machining accuracy can be reduced. In addition, the use of machining error automatic compensation technology is another way to improve machining accuracy. The software compensation of the sensing technology, the size prediction and the automatic applicable control method can be used to control the influence of the thermal deformation of the machine tool on the machining error.
(Finish)
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