If CNC Mechanical parts are not good, where is the problem ?

- Nov 19, 2019-

What is the main reason for the error in the CNC-machining of mechanical parts?

Machining accuracy refers to the degree of conformity between the actual geometric parameters (size, shape and position) of the mechanical parts after machining with the ideal geometric parameters. In the machining of mechanical parts, the error is unavoidable, but the error must be within the allowable range. Analyze and grasp the basic laws of its changes, and take corresponding measures to reduce machining errors and improve CNC-machining accuracy.

 

1. Spindle rotation error. Spindle rotation error refers to the variation of the actual rotary axis of the spindle at each moment relative to its average rotary axis. The main reasons for the spindle radial rotation error are: the coaxiality error of the spindle section and the bearing Various errors, coaxiality error between bearings, spindle deflection, etc.

2. Guide rail error. The guide rail is the benchmark for determining the relative position relationship of each machine tool component on the machine tool. It is also the benchmark of the machine tool movement. The uneven wear and installation quality of the guide rail is also an important factor causing the guide rail error.

 

3. Transmission chain error. The transmission error of the transmission chain refers to the relative motion error between the first and last transmission elements in the internal transmission chain. The transmission error is the manufacturing and assembly error and the use process of each component in the transmission chain. Caused by wear and tear.

4, the geometric error of the tool. Any tool in the cutting process, it is inevitable to wear, and thus cause changes in the size and shape of the workpiece.

 

5. Positioning error. First, the reference does not coincide with the error. The reference used to determine the size and position of a surface on the part drawing is called the design basis. It is used to determine the size of the machined surface after processing. The reference on which the position is based is called the process reference. When machining the workpiece on the machine, it is necessary to select several geometric elements on the workpiece as the positioning reference during machining. If the selected positioning reference does not coincide with the design basis, the reference will be generated. Does not coincide with the error. Second, the positioning sub-manufacturing inaccuracy error.

 

6. The error caused by the deformation of the process system. First, the rigidity of the workpiece. If the workpiece stiffness is relatively low relative to the machine tool, tool and fixture in the process system, the deformation of the workpiece due to insufficient rigidity under the action of the cutting force The influence of machining accuracy is relatively large. The second is the rigidity of the tool. The external turning tool has a large rigidity in the normal direction of the machined surface, and its deformation can be neglected. The inner hole with a small diameter and the rigidity of the tool bar are very poor. The deformation of the rod has a great influence on the machining accuracy of the hole. The third is the rigidity of the machine tool. The machine tool components are composed of many parts. There is no suitable simple calculation method for the rigidity of the machine tool components. At present, the experimental method is mainly used to determine the rigidity of the machine tool components.


7. The error caused by the thermal deformation of the process system. The thermal deformation of the process system has a great influence on the machining accuracy. Especially in precision machining and large-piece machining, the machining error caused by thermal deformation can sometimes account for 50% of the total error of the workpiece. .

 

8. Adjusting the error. In each process of machining, the process system should always be adjusted in one way or another. Since the adjustment cannot be absolutely accurate, the adjustment error is generated. In the process system, the workpiece and the tool are on the machine tool. The mutual positional accuracy is ensured by adjusting the machine tool, tool, fixture or workpiece. When the original precision of machine tools, tools, fixtures and workpiece blanks meets the process requirements without considering dynamic factors, the influence of adjustment error , plays a decisive role in the processing accuracy.

 

9. Measurement error. When measuring mechanical parts or after processing, the measurement accuracy is directly affected by the measurement method, the accuracy of the measuring tool, and the workpiece and subjective and objective factors.


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