Mechanical Knowledge

How to set the tool in a CNC four-axis machining center

1. Tool position

The tool location point is a datum point on the tool, and the relative movement track of the tool location point is the processing path, also called the programming track.

2. Tool setting and tool setting points

Tool setting means that the index control operator uses certain measurement methods to make the tool position point coincide with the tool setting point before starting the CNC program. You can use a tool setting instrument to measure the tool, its operation is relatively simple, and the measurement data is relatively accurate. After positioning the fixture on the CNC machine tool and installing the parts, use gauge blocks, feeler gauges, dial gauges, etc. to use the coordinates on the CNC machine tool to set the tool. For the operator, it is very important to determine the tool point, which will directly affect the machining accuracy of the part and the accuracy of the program control. In the batch production process, the repeat accuracy of the tool setting point must be taken into consideration. The operator must deepen the understanding of the CNC equipment and master more tool setting skills.

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(1) Selection criteria for tool setting points

Simple alignment on the machine tool, easy to check during processing, easy to calculate during programming, and small error in tool setting.

The tool setting point can be selected from a certain point on the part (such as the center of the positioning hole of the part), or a certain point outside the part (such as a certain point on the fixture or machine tool), but it must be determined with the positioning reference of the part Coordinate contact.

The accuracy and precision of forward tool setting, even if the parts require less precision or the program requirements are not strict, the machining accuracy of the selected tool setting part should be higher than the machining accuracy of other directions.

Select the part with large contact surface, simple monitoring, and stable processing process as the tool setting point.

The tool setting point is as consistent as possible with the planning reference or process reference, so as to avoid the reduction of tool setting accuracy or even machining accuracy due to standard conversion, which increases the difficulty of NC program or part NC machining.

In order to advance the machining accuracy of parts, the tool setting point should be selected as far as possible on the planning datum or process datum of the part. For example, for parts that are positioned with holes, it is more appropriate to use the center of the hole as the tool setting point.

The accuracy of the tool setting point not only depends on the accuracy of the numerical control equipment, but also depends on the requirements of the part processing. Manually check the tool setting accuracy to advance the quality of the part CNC machining. Especially in batch production, the repetitive accuracy of the tool setting point should be considered. The accuracy can be checked by the coordinate value of the tool setting point relative to the machine origin.

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(2) Selection method of tool setting point

Regarding numerical control equipment such as numerical control lathes or turning and milling machining centers, since the center position (X0, Y0, A0) has been determined by numerical control equipment, the entire processing coordinate system can be determined by determining the axial direction. Therefore, it is only necessary to determine a certain end face in the axial direction (Z0 or relative orientation) as the tool setting point.

Regarding the three-coordinate CNC milling machine or three-coordinate machining center, it is much messier than the CNC lathe or the turning-milling machining center. According to the requirements of the CNC program, it is not only necessary to determine the origin of the coordinate system (X0, Y0, Z0), but also the machining coordinate system The judgment of G54, G55, G56, G57, etc. is related, and sometimes depends on the operator's habits. The tool setting point can be set on the part to be processed or on the fixture, but it is necessary to have a certain coordinate connection with the positioning datum of the part. The Z direction can be simply judged by judging a plane of simple detection, and X, Y The direction determination needs to select the plane and circle related to the positioning datum according to the specific part.

Regarding four-axis or five-axis CNC equipment, the 4th and 5th rotary axes are added, which is similar to the selection of tool setting points for three-axis CNC equipment. As the equipment becomes more messy, the CNC system is intelligent and provides more tool setting methods. , According to the specific numerical control equipment and specific processing parts, the coordinate connection of the tool setting point relative to the machine tool coordinate system can be simply set to be related to each other. For example, the coordinate of the tool setting point is (X0, Y0, Z0), which is the same as the machining coordinate system. Contact can be defined as (X0+Xr, Y0+Yr, Z0+Zr), and the processing coordinate system is G54, G55, G56, G57, etc., just input it through the control panel or other methods. This method is very flexible and highly skilled, which brings great convenience to subsequent CNC machining. Friends who are learning UG programming can join the QQ group: 304214709 to receive learning materials and courses.

Once the machine tool bumps due to a programming parameter input error, the impact on the machine tool accuracy will be fatal. Therefore, for high-precision CNC lathes, bumps must be eradicated.

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(3) The main reason for the collision:

a. Input errors in the diameter and length of the tool;

b. The standard and other related standard input errors of the workpiece and the initial position positioning error of the workpiece;

c. The workpiece coordinate system of the machine tool is set incorrectly. Perhaps the zero point of the machine tool is reset during the machining process and changed. Machine tool bumps mostly occur during the rapid movement of the machine tool. The bumps that occur at this time are also the most harmful and should be avoided.

Therefore, the operator must pay special attention to the initial stage of the execution of the program and the time when the machine is replacing the tool. At this moment, once the program is modified incorrectly, the diameter and length of the tool are input incorrectly, then it is very easy to bump.

At the end of the program, if the NC axis retracts the tool in a wrong sequence, then a collision may also occur.

In order to avoid the above-mentioned bumps, the CNC operator should give full play to the functions of the five senses when operating the machine tool, and investigate whether the machine tool has abnormal movements, sparks, noise and abnormal noise, sensation, and burnt smell. If an abnormal situation is found, the program should be interrupted immediately. After the standby bed problem is solved, the machine tool can continue operation.

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