How should a CNC four-axis machining center perform tool setting? Here is the most practical method!

1. Knife 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.

(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 low 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 CNC program or parts CNC 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 tool setting points not only depends on the accuracy of the numerical control equipment, but also depends on the requirements of parts processing. Manually check the accuracy of the tool to advance the quality of the parts. 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.

(2) Selection method of tool setting point

As for CNC lathe or turn milling machining center CNC equipment, because the center orientation (x0, Y0, A0) has been determined by CNC equipment, the whole machining coordinate system can be determined by determining the axial orientation. Therefore, only need to determine the axial (Z0 or relative orientation) of a certain end as the tool setting point.

As for the three-dimensional CNC milling machine or three-dimensional machining center, compared with the CNC lathe or turn milling machining center, according to the requirements of the NC program, it is not only necessary to determine the origin orientation of the coordinate system (x0, Y0, Z0), but also related to the determination of the machining coordinate system g54, G55, g56, G57, and sometimes depends on the habits of the operator. The tool setting point can be set on the part to be processed or on the fixture. However, it is necessary to have a certain coordinate connection with the positioning datum of the parts. The Z direction can be determined simply by judging a simple detection plane, while the X and Y direction determination needs to select the plane and circle related to the positioning reference according to the specific parts.

For 4-axis or 5-axis CNC equipment, the 4th and 5th rotation axis is added, which is similar to the selection of tool setting point for three-dimensional CNC equipment. Due to the increasingly messy equipment and intelligent CNC system, more tool setting methods are provided. The coordinate contact of tool setting point relative to the machine coordinate system can be determined according to the specific CNC equipment and processing parts, which can be simply set as mutual correlation If the coordinate of tool setting point is (x0, Y0, Z0), the contact with machining coordinate system can be defined as (x0 + XR, Y0 + yr, Z0 + Zr), and the machining coordinate system g54, G55, g56, G57, etc. can be input only through the control panel or other methods. This method is very flexible and skillful, which brings great convenience for subsequent NC machining

Once the machine tool bumps due to the error of programming parameter input, the impact on the accuracy of the machine tool is fatal. So for high-precision CNC lathe, the collision should be eliminated.

(3) The main causes of collision are as follows

a. Input error on the diameter and length of the tool;

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

c. The workpiece coordinate system of the machine tool is set incorrectly. Maybe the zero point of the machine tool is reset in the process of processing, and the machine tool bumps mostly occur in the process of the rapid movement of the machine tool. At this time, the damage caused by the collision is also the biggest, which should be avoided.

Therefore, the operator should pay special attention to the machine tool in the initial stage of the program and when the machine tool is replaced. At this moment, once the program is modified, and the diameter and length of the tool are input incorrectly, it will be very simple to bump.

At the end of the program, the NC axis's retraction action sequence is wrong, so there may be bumping.

In order to avoid the above-mentioned collision, the CNC operator should give full play to the function of five senses when operating the machine tool, investigate whether the machine tool has abnormal movement, whether there is spark, whether there is noise and abnormal sound, whether there is a sensation, whether there is burning smell. If abnormal situation is found, the program should be interrupted immediately. After the problem of standby bed is solved, the machine can continue to work.