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How to avoid safety problems in the machining center

- Sep 03, 2018 -

1. The programmer and the operator should be careful about the decimal point when writing the program.

The FANUC system is the minimum setting unit when omitting the decimal point, and most domestic systems and some systems in Europe and America, when omitting the decimal point, is mm, which is the calculator input mode. If you are used to the calculator input method, there will be problems on the FANUC system. Many programmers and operators may use both systems. To prevent the size from becoming smaller due to the decimal point, a decimal point should be added to the calculator input method. In doing so, it is superfluous for certain types of systems, but after getting into the habit, there will be no problems with the decimal point.


In order to make the decimal point conspicuous, the isolated decimal point is often written in the form of ".0" during programming. Of course, zeros after the decimal point of the value are ignored when the system is executing.


2. When adjusting the workpiece coordinate system, the operator should set the reference point outside the physical (geometric) length of all the tools, at least at the tool point of the longest tool.


For the workpiece coordinate system on the workpiece installation drawing, the operator obtains the machine coordinate system offset on the machine. That is, the operator sets a reference point on the machine tool and finds the size between the reference point and the zero point of the workpiece coordinate system set by the programmer, and sets this size as the workpiece coordinate system offset.


On the lathe, the reference point can be set at the center of rotation of the tool holder, on the tip of the reference tool or at another location. If no additional motion is added, the zero commanded by the programmer moves the reference point of the tool holder (machine) to the zero position of the offset. At this time, if the reference point is set at the center of rotation of the tool holder, the tool holder must collide with the workpiece. In order to ensure that there is no collision, the reference point on the machine tool should be set not only outside the tool holder, but also outside the tool. This way, even if the tool is mounted on the tool holder, the reference point will not collide with the workpiece.

On the milling machine, the reference points of the X and Y axes are on the spindle axis. However, the reference point of the Z axis can be set at the spindle end or at a point other than the spindle end. If at the spindle end, when the command is zero, the spindle end will reach the zero position specified by the coordinate system. At this point, the end face key of the spindle end will collide with the workpiece: if the spindle is loaded with a tool, it must collide with the workpiece. To ensure no collision, the reference point on the Z axis should be set outside of all tool lengths. The reference point does not hit the workpiece even if no other motion is attached.


3. When adjusting the tool length offset, the operator should ensure that the offset value is negative.


When the programmer commands the tool length compensation, the T code command is used for turning, and the G43 command for milling is used to add the tool length offset value to the command value. In the direction of the machine axis, it is specified that the direction of movement of the tool away from the workpiece is positive, and the direction of the tool moving closer to the workpiece is negative. The operator adjusts the tool offset value to a negative value, which is to command the tool to move toward the workpiece. When the tool is commanded to approach the workpiece, in addition to the command value, the offset value of the tool is added. This additional value is moved to the workpiece. At this point, if the value is missed, the tool will not reach the target point.


In order to set the tool offset value to a negative value, it must be set outside the tool length when specifying the reference point on the machine, at least at the tool point (point) of the reference tool.

4. The origin of the workpiece coordinate system set by the programmer during programming should be outside the workpiece blank, at least on the workpiece surface.


Under normal conditions, the origin of the workpiece coordinate system can be set anywhere, as long as the origin has a certain relationship with the origin of the machine coordinate system. However, in actual operation, if the command value is zero or close to zero, the tool will point to zero or close to zero. During milling, the tool will run toward the work surface or the base of the fixture: during turning, it will run toward the base of the chuck. In this way, the tool will penetrate the workpiece directly to the reference plane. At this time, if it is moving quickly, an accident will occur.


The FANUC system generally sets: when the decimal point is omitted, it is the minimum input unit, usually μm. When the decimal point is missed, the value entered will be reduced to one thousandth, at which point the value entered will be close to zero. Or, for other reasons, the tool should have left the workpiece but did not actually leave the workpiece and enter the workpiece. When this happens, the zero point of the workpiece coordinate system should be set outside the workpiece or on the base of the table (or fixture), and the result will be different.