In the above figure, the bottom surface of the sinking hole has roughness and flatness requirements, and there are coaxiality requirements with the following through-holes, the best solution is to use a knife to machine out, the actual cnc machining, in order to speed up, are used with internal cooling of the cemented alloy drill, using G81 drilling cycle, as shown below.
However, the use of G81 drilling cycle only solves the problem of cnc machining efficiency, but whether it can meet the drawing requirements is another problem, for example, how to meet the roughness and flatness of the drawing.
G04X_/P_ refers to the tool pause time (feed stop, spindle does not stop), and the value after address P or X is the pause time. The value after X should be with a decimal point, otherwise it is calculated as one thousandth of the value, in seconds (s), and the value after P cannot be represented by a decimal point (that is, an integer), in milliseconds (ms).
For example, G04X2.0; or G04X2000; Pause for 2 seconds G04 P2000;
However, in some hole precision cnc machining instructions (such as G82, G88 and G89), in order to ensure the roughness of the bottom of the hole, when the tool is machined to the bottom of the hole there needs to be a pause time, at this time can only be represented by address P, if represented by address X, the control system believes that X is the X axis coordinate value for execution.
For example, G82X80.0Y60.0Z-20.0R5.0F200P2000; Drill (80.0, 60.0) to the bottom of the hole and pause for 2 sec
Without a certain amount of dwell time, the tool rotation may not even be able to run a full rotation lap. This will cause unevenness of the surface, unevenness caused by drilling failure, if the drill is the valve seat on the cylinder, or the sealing surface on the hydraulic pipe, which will cause the leakage of gas or liquid, so that the workpiece is scrapped.
Using G81 programming, the bottom surface does not stay, the result is that the bottom surface is uneven, and the stay time is too short.
Use G81 to stay for 1 second, although a second is not much, but has made the tool rotate 30 times, which will make the tool wear quickly, will cause poor surface roughness, this is because the residence time is too long, so we need a correct residence time, not too short and not too long, in order to ensure the accuracy of the parts.
Stopping rotation x 60000 / speed = P value
Stopping rotation means that the tool rotates completely one circle at the bottom of the hole.
60000 is a fixed value because 60 seconds equals one minute, and the formula is converted to milliseconds, not seconds.
P value is generally milliseconds, most of our residence time with the value is very small, two laps of time to stay on the workpiece, only need 15-300 milliseconds, so we use P15-P300, which is the general use of residence time, for contour molding knife, I need to stay 1.5 rpm, write 1.5 in the formula, 60000 unchanged, the speed of the tool is 2000 that is, S2000, by the formula we will get forty-five, which means that we use G81 when the P value should be 45, in the S2000 state, the tool will stay 45 milliseconds, 45 milliseconds will produce 1.5 turns of rotation, this time is enough to clean the workpiece surface, 45 is the best residence time of 2000 rpm, if you do not stay too fast, one second is too much, so we need to calculate the best dwell time before machining , it does not take a lot of time on the program, and the tool does not scratch the surface of the part.
The G04 directive allows the tool to be processed for a short period of time without feed finishing to obtain a rounded and smooth surface. , use the pause command to make the tool for non-feed light whole cutting, and then retract the knife to ensure that the bottom of the hole is flat. 2) When the tool is to be retracted after the boring is completed, in order to avoid leaving a spiral scratch and affecting the surface roughness, the spindle should stop rotating, and pause for a few seconds, and then retract the tool after the spindle is completely stopped. If the tool chuck has a forward and reverse mechanism, a pause command can be used to replace the specified distance with a pause time
The G04 directive allows the tool to be processed for a short period of time without feed finishing to obtain a rounded and smooth surface. Generally used in the following situations:
- When machining blind holes, after the tool feed to the specified depth; , use the pause command to make the tool for non-feed light whole cutting, and then retract the knife to ensure that the bottom of the hole is flat;
- When the tool is to be retracted after the boring is completed, in order to avoid leaving a spiral scratch and affecting the surface roughness, the spindle should stop rotating, and pause for a few seconds, and then retract the tool after the spindle is completely stopped;
- When tapping the thread with a tap. If the tool chuck has a forward and reverse mechanism, the pause command can be used to replace the specified interval with a pause time, and after the tapping thread is completed, the tap exits the workpiece; Then resume the machine’s action instructions.