Check the accuracy of vertical machining center

Check the accuracy of vertical machining center

The biggest processing attribute of vertical machining center is that the consistency of batch workpiece size should be very high. We know that the traditional processing of workpiece from one process to another has to go through a clamping process. This process is difficult to achieve the complete consistency of the processing size of each part by human operation. Of course, this does not mean that the workpiece is out of tolerance, as long as the tolerance of the workpiece is within the tolerance All parts within the band are qualified parts, which means that some workpieces may be in large difference, some parts may be in medium difference, and some parts may be in small difference, so it is difficult to ensure the consistency of workpiece size.

Therefore, at present, the utilization rate of vertical machining center is the highest in small and medium-sized processing enterprises. Of course, the vertical machining center is also the most cost-effective machine tool in CNC machine tools. It has high processing efficiency and high processing precision. From these two aspects, it also solves the problem of maintaining the size consistency of workpieces. Of course, if the numerical control parameters are not set properly or the operation is improper, the vertical machining center will also appear the phenomenon of machining out of tolerance from time to time in the actual processing. This paper briefly introduces the causes and solutions of machining out of tolerance in vertical machining center

The out of tolerance of machining accuracy of vertical machining center mainly includes: high surface roughness of inner hole, out of roundness of reamed inner hole, out of tolerance of position precision of reamed hole, obvious edge of inner surface of hole, irregularity of center line of hole after reaming, increase and decrease of hole diameter.

1、 The position accuracy of reamed hole is out of tolerance

Causes: it may be caused by the wear of the guide sleeve of the vertical machining center, the distance between the bottom end of the guide sleeve and the workpiece, the short length of the guide sleeve, the poor accuracy and the looseness of the spindle bearing.

Solution: if the position accuracy of the hole is out of tolerance during reaming of the vertical machining center, the following maintenance can be carried out according to the above-mentioned problems. The guide sleeve shall be replaced regularly and the guide sleeve shall be lengthened to improve the matching accuracy of the clearance between the guide sleeve and the reamer, the machine tool shall be maintained in time, and the spindle bearing clearance shall be adjusted.

2、 The surface roughness of inner hole is high

Causes: the surface roughness of the inner hole machined by the vertical machining center is high, and there are many reasons, which may be caused by too high cutting speed, improper selection of cutting fluid, excessive reamer main deflection angle, too large reaming allowance, uneven or small reaming allowance, unsharp edge, too wide reaming edge, poor chip removal during reaming, excessive wear of reamer, and possibly selected milling Tool and part material mismatch and other reasons.

Solution: there are many reasons for the high machining roughness, so the solution is more complex. We can start from the following aspects: reduce the cutting speed, select the cutting fluid according to the processing materials, appropriately reduce the reaming allowance, improve the position accuracy and quality of the bottom hole before reaming, or increase the reaming allowance, increase the space of chip holding groove or use the reamer with edge inclination angle to make the chip removal smooth The reamer should be changed regularly and the cutting tool should be selected reasonably. For example, when machining steel parts, the suitable tool should be selected.

3、 Increase of machining aperture

Causes: the diameter of the reamer increases gradually when machining in the vertical machining center. The causes may be: the design value of the reamer’s outer diameter is too large or the reamer edge has burr, the cutting speed is too high, the feed rate is improper or the machining allowance is too large, the reamer’s main deflection angle is too large, the reamer is bent, the reamer edge adheres to the chip, the reamer edge swing is out of tolerance during grinding, the cutting fluid is not suitable, and It may be the problem of CNC machine itself. The spindle is bent or the spindle bearing is too loose or damaged.

Solution: according to the actual situation, the following countermeasures can be made: according to the specific situation, reduce the reamer outer diameter, reduce the cutting speed, adjust the feed rate or reduce the machining allowance, properly reduce the main deflection angle, straighten or scrap the bending reamer that can not be used, select the cutting fluid with good cold performance, adjust or replace the main shaft bearing, or replace the whole spindle.

4、 The reamed inner hole is not round

Causes: the machining of the inner hole is not round and the roundness is not enough. It is mainly due to the following factors: the reamer is too long, the rigidity is not enough, the vibration is generated during reaming, the reamer’s main deflection angle is too small, the reaming allowance is too small, there are gaps on the inner hole surface, cross holes, especially sand holes and air holes on the surface of the hole, as well as the looseness of the spindle bearing of the machine tool.

Solution: we can start from the following aspects: the installation of reamer should adopt rigid connection, select qualified reamer, control the hole position tolerance of pre-processing process, adopt unequal pitch reamer, select qualified blank, timely adjust the spindle clearance of machine tool, etc.

5、 After reaming, the center line of the hole is not straight

Causes: when the vertical machining center is machining holes, the center line is not straight. The possible reasons may be: the hole is inclined when drilling, especially when the diameter is small, Due to the poor rigidity of reamer, the original bending can not be corrected, the reamer’s main deflection angle is too large and the guide is poor, so that the reamer is easy to deviate from the direction in reaming, the inverted cone of the cutting part is too large, and the reamer is displaced intermittently at the gap in the middle of the hole.

Solution: increase reaming or boring process to correct the hole, reduce the main deflection angle, adjust the appropriate reamer, replace the reamer with guide part or lengthening cutting part, and pay attention to correct operation.

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