What are the main causes of errors in machining mechanical parts?
Machining accuracy refers to the degree of conformity between the actual geometric parameters (size, shape and position) of the machined mechanical part and the ideal geometric parameters. In the machining of mechanical parts, the error is inevitable, but the error must be within the permissible range. Through error analysis, grasp the basic laws of change, so as to take appropriate measures to reduce processing errors, improve processing accuracy.
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 rotation error are: several sections of the spindle journal coaxiality error, bearing itself of various errors, coaxiality error between the bearings, spindle deflection, etc.
2、Guideway error. Guide rail is a machine tool to determine the relative position of the machine components of the benchmark, but also the benchmark of machine 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. Drive chain transmission error is the first and last two ends of the drive chain is linked to the error of the relative motion between the transmission elements. Transmission error is caused by the manufacturing and assembly errors of the components of the transmission chain and the 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 reference does not overlap error. In the parts used to determine the size of a surface, location based on the benchmark known as the design benchmark. In the process diagram used to determine the process is processed on the surface size, location based on the benchmark called the process benchmark. In the machine tool for processing the workpiece, you need to choose a number of geometric elements on the workpiece as a positioning reference for processing, if the chosen positioning reference and the design reference does not overlap, it will produce the reference does not overlap error. Second, the positioning sub 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 relative to the machine tool, tool, fixture is relatively low, 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. The second is the tool stiffness. External turning tool in the direction of the machining surface normal to the stiffness is very large, the deformation can be negligible. Boring smaller diameter bore, toolholder stiffness is very poor, toolholder deformation on the hole machining accuracy has a great impact. Third, the stiffness of machine components. Machine parts by many parts, machine parts stiffness so far there is no suitable simple calculation method, or mainly with experimental methods to machine parts stiffness.
7, the process system caused by thermal deformation of the error. Process system thermal deformation on the impact of machining accuracy is relatively large, especially in precision machining and large parts processing, caused by thermal deformation of the processing error 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 can not be absolutely accurate, thus producing adjustment errors. In the process system, the workpiece, tool in the machine tool position accuracy of each other, is through the adjustment of the machine tool, tool, fixture or workpiece to ensure that. When the machine, tools, fixtures 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. Mechanical parts processing or measurement after processing, due to the measurement method, gauge accuracy and workpiece and subjective and objective factors have a direct impact on the measurement accuracy.