Influence Of Environmental Temperature On Thermal Characteristics Of Machine Bed

In the high precision machining, the thermal deformation of the machine has become an important role to affect the accuracy, an important measurement to improve the accuracy is to reduce the thermal deformation of the machine. The heat from the processing and the change of the ambient temperature change the temperature field of the machine, and the change of the temperature field of the machine will lead to the change of displacement. The heat is hard to be calculated, so the problem of deciding the temperature and displacement field is really complex. Mastering the regulation of the deformation and taking the reasonable measurement can reduce the deformation effectively.The bed is an important component to make the machine running stably. It is used to support column and other parts. The bed shape, structure and the relative position to other parts of the machine tool will affect the dynamic properties, static properties and thermal properties of the machine tool. This page takes the machine body as the research object, basing on finite element theory and AN SYS simulation, meshing the machine body and loading the boundary. Study how the ambient temperature affects the machine body without any other heat source.The factors such as heat convection coefficient, thermal conductivity, temperature difference and the coefficient of thermal expansion will affect the temperature field and displacement field of the machine body. According to the result of simulation, analysis the trend and the percentage; finding out the best constraint way by comparing lots kinds of it; deformation of the place that guides and column lay on will change the place of guides and spindle, so it is necessary to analysis the regulation and improve the structure of the body; the thermal stiffness is pointing out as the inside factor of the deformation by comparing the thermal stiffness of the key points, the thermal stiffness is the body’s own characters relating to the structure.it won’t change when the temperature changes.Heat convection coefficient makes more contribution than thermal conductivity to change the temperature field, the coefficient of thermal expansion is the most important factor that changes the displacement field; the number of constraint points should be determined according to the actual needs; the point that has the biggest X thermal stiffness will not deform in different situations, the point that has the biggest Y thermal stiffness will not deform, the point that has the biggest Z thermal stiffness will not deform, and those points are the best points for machining in related direction; because of the thermal stiffness is a constant, we can calculate the value of the deformation using the temperature and the thermal stiffness.Some suggestions are given on the base of the analysis. Concrete can be used to make up the body because of its thermal stability, the concrete machine body has a better thermal property than HT250machine body, but the stiffness may not be satisfied. Large machine body is needed to satisfy the need of stiffness and the body is heavier than before. Filling the gap of the HT250machine body with concrete will improve its thermal property, it is proven reasonable by simulating; improve the structure, adding ribs on the body do little to the thermal property, so this method is unreasonable. By reducing the height, the bending stiffness of the bed will decreased, which will make significant improvement to the thermal properties of the bed.The work is sponsored by "High-end CNC Machine Tools and Basic Manufacturing Equipment" major national science and technology project.(NO.2012ZX04006011).