5-axis milling machine generally has two more rotating axes than 3-axis milling machine. First, the three linear axes need to be tested; second, the two rotating axes need to be tested; and finally, the performance of the 5-axis linkage needs to be tested.
The testing method for the three linear axes of 5-axis milling machine is the same as that for 3-axis milling machine, so it will not be described here.
As the accuracy of the rotating axes has a much greater impact on the precision of 5-axis machining than the accuracy of the three linear axes, the focus of testing 5-axis milling machine is on the accuracy of the two rotating axes.
The accuracy of the rotating axes includes two aspects: one is the accuracy of the rotation of the rotating axes, mainly testing the repeatability of each rotating axis; the other is the spatial geometry relationship between the two rotating axes and the spindle axis, mainly testing whether the spatial geometry relationship between the two rotating axes' axes and the spindle axis is correct.
Measuring the repeatability accuracy of the rotating axes
The method is similar to the measurement method of linear axes: for a rotary table-type rotating axis, fix a block on the rotary table, contact the surface of the block with the micrometer, rotate the rotary table a certain angle, and then reverse the rotation for the same angle and return to the original position. Observe whether the readings of the micrometer when it contacts the surface of the block twice are consistent, and what is the error. For a swing-type rotating axis, a checking pin is installed on the spindle to be checked, and the micrometer pointer contacts the pin to check it.
Measuring the spatial geometry relationship between the two rotating axes and the spindle
This needs to be divided into three types according to the5-axis milling machine:
5-axis milling machine with double rotary table structure;
5-axis milling machine with rotary table and single swing head structure;
5-axis milling machine with double swing head structure.
The testing of the 5-axis linkage performance does not need to be classified according to the type of 5-axis milling machine.
There are two purposes of testing the 5-axis linkage performance:
One is to detect the accuracy of the spatial geometry relationship measurement between the axes of the 5-axis milling machine; the other is to detect the compensation function of the machine tool’s CNC system for the spatial geometric relationship of the 5-axis.
Testing the 5-axis linkage performance cannot be directly measured, but is measured by processing some standard shapes and measuring the errors of the machined shapes:
Straight line
A straight line is machined on a plane, and the cutting axis changes continuously during the machining process. Multiple cutting axis control methods can be tried. The processed material can choose an easily machinable non-metallic material or a non-ferrous metal, and a ball cutter is used. After processing, observe whether the line is bent. If it is significantly bent, it is necessary to retest the precision of various parts of the machine tool, especially to re-determine whether the eccentric relationship between the two rotating axes and the spindle is correct.
Plane
A plane is precisely machined with a ball cutter, which is then divided into multiple segments and processed using several fixed cutting axes and continuously changing cutting axes at different angles. After processing, the errors between different segments of the plane are measured. Ideally, the plane should still be flat. If the error is too large, retest whether the eccentric relationship between the two rotating axes and the spindle is correct.
Sphere
A sphere is precisely machined with a ball cutter, with a diameter greater than half the sphere. The cutting axis is perpendicular to the sphere, and both bidirectional cutting along the longitude and spiral cutting along the latitude are used to process a sphere with the same diameter. After processing, the diameter of the two spheres is measured and compared with the standard value for the error. If conditions permit, the roundness of the two spheres and the error value of the standard sphere can also be measured.
The above is a basic method of testing the 5-axis linkage performance of5-axis milling machines by processing standard shapes.