Causes of errors in machining inner holes of CNC lathes

 

Causes of errors in machining inner holes of CNC lathes

Automatic CNC lathes use the same turning tool to process two inner holes with a large difference in diameter. It often appears that the processing size of one hole is very accurate and consistent with the programmed value, but the processing size of the other hole is larger than the programmed size.
After preliminary inspection, the CNC lathe has no faults in the control system and machinery, and there is no problem with the parts processing technology. To further confirm that the cause of the problem is not in the machine tool itself, the two-step axis is machined with an external turning tool. The machining result is that the machining diameter of the two-step axis is the same as the programmed size. This basically shows that the reason for the inner hole machining error is not on the machine tool, and should be looked for in other ways.

Analysis of Causes of Errors in CNC Lathe Inner Hole Machining:
There are many factors that affect the inner hole and outer circle machining of CNC lathes. For example, the length of the tool bar is long, the diameter is small, the rigidity is poor, cooling and chip removal are difficult, the height of the tool tip and the axis of the machine tool is not well controlled, and it is very fast. At the same time, the hole processing accuracy is high.

Before turning on a CNC lathe, the installation of the tool is generally to keep the tip of the tool at the same height as the spindle axis of the machine tool. For the inclined bed CNC lathe, there are strict requirements on the relative height of the turret and the spindle axis of the machine tool during manufacturing, as long as the standard tool does not need to adjust the height of the tool tip.

Most machine tool manufacturers do not have a unified standard for the relative height of the tool post and the axis of the spindle, and the respective heights are different. Even when standard tools are used, shims should be used to adjust the height of the tool tip.

In the actual machining process, machining errors rarely occur on the machining step shaft surface. The main reason is that the operator can check whether the tool center height is consistent with the spindle by testing the end face, which is convenient for measuring the tool nose deviation, and the machining error is small and easy to solve.

There are many reasons for machining errors when machining stepped inner holes, and it is difficult to find the cause of the errors. The operator usually thinks it is a problem with the accuracy of the machine tool. It is difficult to adjust the inner hole tool. Sometimes the processed hole is relatively small. In order to avoid the collision of the tool holder with the workpiece hole, the tool is often placed higher. In this case, the machining diameter of the tool segment is accurate, and the machining size error will occur if the stepped hole is machined.

Analyzing the cause of the error, it is found that the cylindrical machining tool is tested during the tool processing to check whether the center height of the tool end face is consistent with the spindle, which is convenient for measuring the tool tip deviation and the error is small.

When machining a hole on a knife, since it is impossible to detect the height of the end face to check the center of the tool, most of the inner hole diameter is measured directly, so the diameter of the tool segment is accurate, but the height of the tool center is inconvenient to measure. The height difference of the hole diameter will cause errors.