Machining accuracy is the degree of conformity between the actual geometric parameters (size, shape and position) of the part after machining and the ideal geometric parameters. In machining, errors are inevitable, but the errors must be within the permissible range. Through error analysis, we can grasp the basic law of its change, so as to take corresponding measures to reduce machining errors and improve machining accuracy.
Then there will be an error will be the reason, the reasons for it we summarized, there are roughly the following points.
1, spindle rotation error. Spindle rotation error refers to the actual axis of rotation of the spindle at each instant relative to its average axis of rotation of the amount of change. The main reasons for the spindle radial slewing error are: the coaxiality error of the spindle journals, the various errors in the bearings themselves, the coaxiality error between the bearings, spindle deflection, etc.
2, guide error. Guide rail is a machine tool to determine the relative position of the machine components of the benchmark, but also the benchmark of the machine tool movement. Uneven wear and installation quality of the guide rail, is also an important factor causing the error of the guide rail.
3, the transmission chain error. Transmission error of the transmission chain is the error of the relative motion between the first and last two transmission elements in the transmission chain of the inner contact. Transmission error is caused by the manufacturing and assembly errors of each component link in the transmission chain and wear and tear in the process of use.
4, the geometric error of the tool. Any tool in the cutting process, it is inevitable to produce wear and tear, and the resulting change in the size and shape of the workpiece.
5, positioning errors. First, the benchmark does not overlap error. In the parts used to determine a surface size, location based on the benchmark called the design benchmark. In the process diagram used to determine the size and location of the processed surface of the process based on the benchmark called the process benchmark. In the machine tool for processing the workpiece, you need to select a number of geometric elements on the workpiece as the positioning reference for processing, if the positioning reference selected does not overlap with the design reference, it will produce the reference does not overlap error. Second, the positioning vice manufacturing inaccuracy error.
6, the process system deformation of the error generated by the force. First, the workpiece stiffness. Process system if the workpiece stiffness is relatively low compared to the machine tool, tool, fixture, under the action of cutting force, the workpiece due to insufficient stiffness and deformation caused by the impact on the machining accuracy is relatively large. Second, the tool stiffness. External turning tool stiffness in the direction of the processing surface normal is large, its deformation can be negligible. Boring smaller diameter bore, tool bar stiffness is very poor, tool bar deformation on the hole processing accuracy has a great impact. Third, the stiffness of the machine tool components. Machine parts by many parts, machine parts stiffness so far there is no suitable simple calculation method, or mainly with experimental methods to determine the stiffness of machine parts.
7, the process system caused by thermal deformation of the error. Process system heat deformation on the impact of machining accuracy is relatively large, especially in precision machining and large parts processing, processing errors caused by heat deformation can sometimes account for 50% of the total error of the workpiece.
8, adjustment error. In each process of machining, the process system should always be adjusted in one way or another. Because the adjustment is not absolutely accurate, thus generating adjustment errors. In the process system, the workpiece, tool in the machine tool mutual position accuracy, is through the adjustment of the machine tool, tool, fixture or workpiece, etc. to ensure. When the machine tool, tool, fixture and workpiece blanks, such as the original accuracy of the process requirements and do not take into account the dynamic factors, the impact of the adjustment error, the processing accuracy plays a decisive role.
9, measurement error. Parts in processing or measurement after processing, due to the measurement method, gauge accuracy, as well as the workpiece and subjective and objective factors have a direct impact on the measurement accuracy.
