Summary Of Reasons For Machining Errors
With the development of intelligent automation, there are more and more orders for machining, but please don't refuse orders for machining. Various unpredictable mistakes may occur when you receive a suitable order for machining. These mistakes will Will bring immeasurable losses to large mechanical processing plants, so what are the reasons for the mistakes in mechanical processing orders? SANS Machining has summarized nine reasons for the mistakes in machining orders.
1. Machine Errors
Spindle rotation error refers to the variation of the actual rotation axis of the spindle relative to its average rotation axis at each moment, which will directly affect the accuracy of the processed workpiece. The main causes of spindle rotation error are spindle coaxiality error, bearing error, coaxiality error between bearings, spindle winding and so on. The guide rail is the benchmark for determining the relative positional relationship of various machine tool components on the machine tool, and it is also the benchmark for machine tool movement. The manufacturing error of the guide rail itself, the uneven wear of the guide rail and the installation quality are important factors that cause the guide rail error. Transmission chain error refers to the error of the relative movement between the transmission elements at both ends of the transmission chain. It is caused by the manufacturing and assembly errors of each component of the transmission chain, as well as the wear during use.
2. Tools Errors
Any tool will inevitably wear out during the cutting process, which will cause the size and shape of the workpiece to change. The influence of tool geometry error on machining error varies with the type of tool: when using a fixed-size tool, the tool manufacturing error will directly affect the machining accuracy of the workpiece; and for general tools (such as turning tools, etc.), the manufacturing error There is no direct influence on machining errors.
3. Fixtures Errors
The function of the fixture is to make the workpiece equivalent to the tool and the machine tool have the correct position, so the geometric error of the fixture has a great influence on the machining error (especially the position error).
4. Positioning Errors
Positioning errors mainly include fiducial misalignment errors and positioning pair manufacturing inaccuracy errors. When processing the workpiece on the machine tool, several geometric elements on the workpiece must be selected as the positioning datum during processing. If the positioning datum and the design datum are selected (the datum used to determine a certain surface size and position on the part drawing) ) Does not coincide, it will produce benchmark misalignment error.
The workpiece positioning surface and the fixture positioning element together constitute a positioning pair. The maximum position change of the workpiece caused by the inaccurate manufacturing of the positioning pair and the matching gap between the positioning pairs is called the inaccurate manufacturing error of the positioning pair. The inaccurate manufacturing error of the positioning pair can only occur when the adjustment method is used, and it will not occur in the trial cutting method.
5. Errors Caused By Force And Deformation Of The Process System
Workpiece rigidity: In the process system, if the rigidity of the workpiece is relatively low relative to the machine tool, cutting tool, and fixture, under the action of cutting force, the deformation of the workpiece due to insufficient rigidity will have a greater impact on machining errors.
Tool rigidity: The rigidity of the external turning tool in the normal (y) direction of the machined surface is very large, and its deformation can be ignored. Boring an inner hole with a small diameter, the rigidity of the tool bar is very poor, and the force and deformation of the tool bar have a great influence on the machining accuracy of the hole.
Machine tool component stiffness: The machine tool component is composed of many parts. So far, there is no suitable simple calculation method for the stiffness of machine tool components. At present, experimental methods are mainly used to determine the stiffness of machine tool components. The factors that affect the rigidity of machine tool components include the influence of the contact deformation of the joint surface, the influence of friction, the influence of low-rigidity parts, and the influence of clearance.
6. Errors Caused By Thermal Deformation Of The Process System
The thermal deformation of the process system has a relatively large impact on the machining error, especially in the precision machining and large parts processing. The machining error caused by the thermal deformation can sometimes account for 50% of the total error of the workpiece.
7. Adjustment Errors
In each process of machining, the process system must be adjusted in one way or another. Since the adjustment cannot be absolutely accurate, an adjustment error occurs. In the process system, the mutual position accuracy of the workpiece and the tool on the machine tool is ensured by adjusting the machine tool, tool, fixture or workpiece. When the original accuracy of machine tools, tools, fixtures and workpiece blanks all meet the process requirements without considering dynamic factors, the adjustment error plays a decisive role in the machining error.
8. Measurement Errors
When measuring parts during processing or after processing, the measurement accuracy is directly affected by the measurement method, the accuracy of the measuring tool, the workpiece, and the subjective and objective factors.
9. Errors Caused By Internal Stress Of The Workpiece
The stress that exists inside the part without external force is called internal stress. Once internal stress is generated on the workpiece, the workpiece metal will be in a high-energy unstable state, which instinctively transforms to a low-energy stable state, and accompanied by deformation, so that the workpiece loses its original machining accuracy .
There are 9 reasons for the mistakes in machining orders. We must first understand these 9 reasons for the mistakes in machining. When machining orders, we should try our best to avoid the influence of these mistakes on the workpiece, so as to better guarantee the quality of machining orders.
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