The Speed Of The External Thread Of The CNC Lathe
| When a CNC lathe is machining threads, due to the change of its transmission chain, in principle, its rotation speed can only ensure that the tool moves by one pitch along the main feed axis (mostly Z axis) every one revolution of the spindle, and should not be limited. |
However, when CNC lathes process threads, they are affected by the following aspects:
- 1) The pitch (lead) value commanded in the thread machining block is equivalent to the feed speed F expressed by the feed amount (mm / r). If the spindle speed of the machine tool is selected too high, the converted feed The speed (mm / min) must greatly exceed the normal value;
- 2) At the beginning / end of its displacement, the tool will be constrained by the servo drive system’s up / down frequency and the numerical control interpolation interpolation speed. Because the up / down frequency cannot meet the processing requirements, it may be due to the main feed The “lead” and “lag” produced by the movement caused the pitch of some threads to be inconsistent;
- 3) The turning thread must be realized by the synchronous operation function of the spindle, that is, the turning thread needs a spindle pulse generator (encoder). When the spindle speed is selected too high, the positioning pulse sent by the encoder (that is, a reference pulse signal sent by each revolution of the spindle) may be caused by “overshoot” (especially when the quality of the encoder is unstable). As a result, the thread of the workpiece will be disorderly buckled.
Therefore, when turning threads, the determination of the spindle speed should follow the following principles:
- 1) Under the condition of ensuring production efficiency and normal cutting, a lower spindle speed should be selected;
- 2) When the lead-in length δ1 and cut-out length δ2 (as shown in the figure) in the thread processing block are considered to be sufficient, that is, when the thread feed distance exceeds the length of the specified thread on the drawing, a higher spindle can be selected. Rotating speed;
- 3) When the allowable working speed specified by the encoder exceeds the maximum speed of the spindle specified by the machine tool, you can choose a higher spindle speed as much as possible;
- 4) Under normal circumstances, the spindle speed (n screw) of the thread should be determined according to the calculation formula specified in the manual of the machine tool or numerical control system.
The calculation formula is mostly:
n screw ≤ n allow / L (r / min) where n allows-the maximum working speed (r / min) allowed by the encoder
L—Pitch (or lead, mm) of the workpiece thread.
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