The accuracy error of CNC milling and machining center is caused by external conditions and is greatly affected by external conditions. It can be divided into: the positioning accuracy error affected by the load of the tooling, the geometric accuracy error caused by the internal stress, and the shape error caused by the thermal deformation.
The accuracy error of CNC milling and machining center is caused by external conditions and is greatly affected by external conditions. It can be divided into: the positioning accuracy error affected by the load of the tooling, the geometric accuracy error caused by the internal stress, and the shape error caused by the thermal deformation.
1. Cutting force, tooling load impact accuracy error
When the workpiece is processed, it is often subjected to cutting force, clamping force, inertial force, gravity, etc., resulting in corresponding deformation, which ultimately destroys the correct relative position between the tool and the workpiece, and reduces the machining accuracy of the workpiece. For example, when the workpiece stiffness is much smaller than the rigidity of the tool and the clamp, the workpiece will be deformed due to insufficient rigidity under the action of the cutting force, thereby reducing the machining accuracy. Conversely, when the stiffness of the workpiece is much larger than the rigidity of the tool and the fixture, the tool and the fixture will be deformed during the machining of the workpiece, which will also reduce the accuracy of the workpiece.
Therefore, it is necessary to rationally select the tool material, increase the forward and main declination of the tool, and perform reasonable heat treatment on the workpiece material to improve its processing performance. At the same time, it is necessary to increase the rigidity of the process system, reduce the cutting force and compress their amplitude of variation.
2. Internal stress affects geometric accuracy error
The internal stress is the stress that exists inside the part without external force. Once the internal stress occurs on the workpiece, the workpiece is placed in an unstable state of high energy position, which instinctively transforms to a stable state of low energy level, accompanied by deformation of the workpiece, and finally the workpiece loses the original machining accuracy. For example, after the heat treatment of the workpiece, internal stress is generated due to uneven wall thickness, uneven cooling, etc., thereby causing deformation, and finally reducing the machining accuracy.
Therefore, when designing parts, try to achieve uniform wall thickness and structural symmetry to reduce the generation of internal stress.
3. Thermal deformation causes shape error
In
Precision Machining and large-piece machining, the thermal deformation of the process system has a great influence on the machining accuracy of the workpiece. The machining error caused by thermal deformation can sometimes account for 40%~70% of the total error of the workpiece. Machine tools, tools and workpieces are subjected to various heat sources, and the temperature gradually increases, while they transfer heat to the surrounding matter and space. As a result, the workpiece and the entire process system are deformed, and when the heat transferred from the unit time is equal to the heat dissipated by the unit, the process system reaches a thermal equilibrium state. For example, in the process of turning large parts, the spindle bearing and the Z-axis screw are heated due to excessive cutting force, which causes large deformation and ultimately affects the machining accuracy of the workpiece.
4. In summary, in addition to the above-mentioned main influencing factors, the accuracy factors affecting CNC milling and machining centers are multifaceted. Product specialization, product structure design, process design, finishing equipment, assembly technology precipitation, working environment are the key to determining the accuracy of CNC machine tools. Therefore, the accuracy of CNC milling and machining centers is caused by many factors.
The accuracy of the machining center and CNC milling machine is mainly determined by the stability of the casting. To stabilize the casting, the design is reasonable, the structure is reasonable, the casting process is reasonable, the machining process is reasonable, and the mechanical aging and 3D vibration aging are required after rough machining. .
In the optomechanical assembly production, in order to eliminate the internal stress of the casting, the size is more stable, and the casting is rough-processed at room temperature for a long time, and is finished at the time of order. This is the last aging process in the production process.
The casting of the machine tool is stable, not only the machine tool has high precision, but also reduces the wear of the machine tool and greatly improves the service life of the machine tool.
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