Specification for safety problems of CNC machines in production

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The development of CNC machine tools is increasingly towards high-precision and high-speed development. With the progress of social technology, high-speed intelligence is the future development direction. Therefore, in such a high-speed and open to closed structure machine tool change, once the operation due to programming and operation errors, there is no time to press the emergency stop button, the tool collides with the workpiece. To avoid machine tool and personal accidents, the following measures can be taken during programming and operation:

Programmer
1. 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 circumstances, the origin of the workpiece coordinate system can be set anywhere, as long as this origin has a certain relationship with the origin of the machine coordinate system. But in actual operation, in case the command value is zero or close to zero, the tool will directly point to the position of zero or close to zero. During milling, the tool will run to the workbench or fixture base surface of the machine tool; during turning, it will run to the chuck base surface. In this way, the tool will penetrate the workpiece and point directly to the datum plane. At this time, if it is fast moving, an accident must occur.

General setting of FANUC System: when the decimal point is omitted, it is the minimum input unit, usually μ m。 When the decimal point is omitted, the entered value will be reduced to one thousandth. At this time, the entered value will be close to zero. Or, for other reasons, the tool should have left the workpiece but actually entered the workpiece without leaving the workpiece. In this case, the zero point of the workpiece coordinate system should be set outside the workpiece or on the base plane of the workbench (or fixture), and the result will be different.

2. Programmers and operators should be careful about decimal points when writing programs
FANUC system is the minimum setting unit when omitting the decimal point, while most domestic systems and some systems in Europe and the United States are mm when omitting the decimal point, that is, the calculator input mode. If you are used to the input method of calculator, there will be problems on FANUC system. Many programmers and operators may use both systems. In order to prevent the size from becoming smaller due to the decimal point, the decimal point should also be added to the program of calculator input mode. This is unnecessary for a certain type of system, but after forming a habit, there will be no problems due to the decimal point.

In order to make the decimal point eye-catching, isolated decimal points are often written in the form of “.0” during programming. Of course, when the system executes, the zero after the decimal point of the value is ignored.

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

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

On the lathe, the reference point can be set at the rotation center of the tool rest, the tip of the reference tool or other positions. If there is no additional movement, the zero commanded by the programmer is that the reference point of the tool rest (machine tool) moves to the zero position of the offset. At this time, if the reference point is set at the rotation center of the tool rest, the tool rest must collide with the workpiece. To ensure no collision, the reference point on the machine tool should be set not only outside the tool holder, but also outside all tools. In this way, the reference point will not collide with the workpiece even if the tool holder is equipped with a tool.

On the milling machine, the datum points of X and Y axes are on the axis of the spindle. However, the reference point of axis Z can be set at the spindle end or at a point outside the spindle end. If it is at the spindle end, when the command is zero, the spindle end will reach the zero position specified in the coordinate system. At this time, the end face key at the spindle end will collide with the workpiece: if the spindle is equipped with a tool again, it will collide with the workpiece. To ensure no collision, the reference point on the Z axis should be set outside the length of all tools. Even if no other motion is attached, the reference point will not hit the workpiece.

2. When adjusting the tool length offset, the operator should ensure that the offset value is negative
When the programmer instructs the tool length compensation, the T code instruction is used for turning, and the G43 instruction is used for milling, that is, add the tool length offset value to the instruction value. In the direction of the coordinate axis of the machine tool, it is specified that the movement direction of the tool away from the workpiece is positive, and the direction of the tool moving close to the workpiece is negative. The operator adjusts the tool offset value to a negative value, which instructs the tool to move to the workpiece. When the program instructs the tool to approach the workpiece, in addition to the command value, the offset value of the tool should be added, and this additional value is moved to the workpiece. At this time, in case this value is omitted, the tool will not reach the target point.

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

3. When canceling the tool length offset (compensation), the tool should be outside the workpiece
Sometimes, it is necessary to cancel the tool length offset during machining. For example, on the machining center, if G28, G30 and G27 commands are issued, the machine tool returns to the tool change point for automatic tool change. In order to ensure the accurate arrival of the tool change position, cancel the tool length offset in the command, such as g30z-g49: where Z – is the middle point of tool movement. When the tool reaches the middle point, the tool length compensation should be cancelled. If this intermediate point is not selected properly, the tool tip may not leave the workpiece, or move to the workpiece instead, and an accident may occur at this time. When programming, the tool length is generally not determined. If the value of the command is not enough to keep the tool tip away from the workpiece, there will be a danger. At this time, incremental value programming should be used to make the incremental value greater than all tool length compensation values. If the tool length compensation value is 200mm, command g30g49g91z200.0. If the reference point on the machine tool is set and the tool length offset (compensation) is adjusted according to the previously recommended method, as long as the command point is outside the workpiece, the tool tip must be far away from the workpiece.

4. The tool number and tool compensation number should be easy to check
The tool number is commanded by T code, and its compensation number is set by the operator in the system offset data area. The turning system uses the T code plus 2 or 4 digits, in which the high digit commands the tool number and the low digit commands the tool compensation number. In the milling system, t code instructs the tool number, H code instructs the tool length compensation, and D code instructs the tool compensation radius. H and D codes use the same group of data. The tool number and compensation number are independent of each other, and the programmer can independently specify them.
In order to facilitate verification and setting, except for special purposes, the tool number of the turning system is the same as the compensation number, such as T11 or T101. That is, No. 1 compensation value is used for No. 1 tool. The milling system uses T1 to call the tool, H1 to call the tool length compensation value, and D21 to call the tool radius compensation value (if the number of tools is less than 20). That is, No. 1 length compensation value and No. 21 radius compensation value are used for No. 1 tool, which is convenient for programming and setting operation, as well as memory, so as to reduce the probability of error.

5. During contour milling, the tool should be lifted after leaving the contour surface of the workpiece
During contour milling, make the cutter leave the contour surface of the workpiece and then lift the cutter. In addition to not leaving knife marks on the contour, you can also form a good habit to avoid accidents in other cases.

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