Nine errors of machining, you know how many
Machining error refers to the degree of deviation between the actual geometric parameters (geometric size, geometric shape and mutual position) and the ideal geometric parameters after machining of the part.
The degree of conformity between the actual geometric parameters and the ideal geometric parameters after machining of the part is the machining accuracy. The smaller the machining error and the higher the degree of conformity, the higher the machining accuracy.
Machining accuracy and machining error are two ways of referring to one problem. Therefore, the size of machining error reflects the level of machining accuracy. The main reasons for machining errors are some of these:
1, the manufacturing error of the machine tool
Machine tool manufacturing errors mainly include spindle rotation error, guide error and drive chain error.
Spindle rotation error refers to the actual axis of rotation of the spindle moment relative to its average axis of rotation of the amount of change, it will directly affect the accuracy of the workpiece being machined. The main reasons for the spindle rotation error are the coaxiality error of the spindle, the error of the bearing itself, the coaxiality error between the bearings, spindle winding, etc. 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.
The manufacturing error of the guide itself, the uneven wear and tear of the guide and the quality of installation is an important factor causing the guide error. Drive chain error refers to the beginning and end of the drive chain between the two ends of the relative movement of the transmission components error. It is caused by the manufacturing and assembly errors of each component link in the transmission chain, as well as the wear and tear in the process of use.
3、Geometric error of the tool
Any tool in the cutting process is inevitable to produce wear and tear, and the resulting change in the size and shape of the workpiece. Tool geometric error on the impact of machining errors vary with the type of tool: the use of fixed-size tool processing, the manufacturing error of the tool will directly affect the machining accuracy of the workpiece; and the general tool (such as turning tools, etc.), the manufacturing error on the machining error has no direct impact.
3, the geometric error of the fixture
The role of the fixture is to make the workpiece equivalent to the tool and machine tool has the correct position, so the geometric error of the fixture on the machining error (especially the position error) has a great impact.
Positioning error mainly includes the benchmark non-coincidence error and positioning vice manufacturing inaccuracy error. When machining the workpiece on the machine tool, several geometric elements on the workpiece must be selected as the positioning datum for processing, if the positioning datum selected does not overlap with the design datum (the datum used to determine the size and position of a surface on the part diagram), the datum does not overlap with the error.
Workpiece positioning surface and fixture positioning elements together constitute the positioning vice, due to the inaccuracy of the positioning vice manufacturing and positioning vice of the maximum position of the workpiece caused by the fit gap, known as the positioning vice manufacturing inaccuracy error. The inaccuracy of the positioning sub manufacturing error is only generated when the adjustment method is used, and will not be generated in the trial cutting method.
5、The error caused by the deformation of the process system
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 of machining errors is relatively large.
Tool stiffness: external turning tool stiffness in the direction of the normal (y) of the machined surface is large, and its deformation can be negligible. Boring smaller diameter bore, tool bar stiffness is very poor, tool bar deformation of the hole processing accuracy will have a great impact.
Machine tool components stiffness: machine tool components consist of many parts, machine tool components stiffness so far there is no suitable simple calculation method, at present the main experimental method to determine the stiffness of machine tool components. Factors affecting the stiffness of machine tool components are combined with the impact of contact deformation, the impact of friction, the impact of low stiffness parts, the impact of clearance.
6, the process system caused by thermal deformation of the error
Process system thermal deformation on the impact of processing errors is relatively large, especially in precision machining and large parts processing, processing errors caused by thermal deformation can sometimes account for 50% of the total error of the workpiece.
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 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 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 adjustment error plays a decisive role in machining errors.
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.
9, internal stress
There is no external force and the existence of internal stress in the parts, known as internal stress. Once the internal stress on the workpiece, the workpiece metal will be in a high-energy unstable state, it instinctively to the low-energy stable state, accompanied by deformation occurs, so that the workpiece loses its original processing accuracy.