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Reasons for machining accuracy out of tolerance and countermeasures

Reasons for machining accuracy out of tolerance and countermeasuresReasons for machining accuracy out of tolerance and countermeasures

The biggest machining attribute of the vertical machining center is that the consistency of the batch size of the workpiece is very high. We know that the traditional machining of the original workpiece from one process to another process has to go through a clamping process. This process is manual It is difficult to achieve the same cnc machining aluminum size of each component. Of course, this does not mean that the workpiece is out of tolerance. As long as the workpiece is within the tolerance band of the workpiece, it is qualified, which means that the size of some workpieces may be large. The workpiece is on the middle difference, and some workpieces may be on the small difference. It is difficult to guarantee the dimensional consistency of the workpiece.

Therefore, at this stage, the utilization rate of vertical machining centers is the highest in small and medium-sized machining enterprises. Of course, vertical machining centers are also the most cost-effective machine tool among CNC machine tools. They have high machining efficiency and high machining accuracy. These two aspects also solve the problem of maintaining workpieces. The problem of size consistency. Of course, if the numerical control parameters are set improperly or the operation is improper, the vertical machining center will sometimes appear out of tolerance in the actual machining. This article briefly introduces the common causes and solutions for machining tolerances of vertical machining centers:
The machining accuracy of the vertical cnc machining aluminum center is out of tolerance mainly as follows: high surface roughness value of the inner hole machining, the reamed inner hole is not round, the reamed hole position accuracy is out of tolerance, the inner surface of the hole has obvious edge faces and reamed holes The center line of the rear hole is not straight, the hole diameter increases, the hole diameter decreases, etc.

1. The accuracy of the reamed hole position is too poor

Cause: It may be caused by wear of the guide sleeve of the vertical machining center, the bottom end of the guide sleeve is too far from the workpiece, the length of the guide sleeve is short, the accuracy is poor, and the spindle bearing is loose.

Solution: If the position accuracy of the hole is out of tolerance when the vertical cnc machining aluminum center is reaming, the following repairs can be made according to the above-mentioned easy problems. Regularly replace the guide sleeve, lengthen the guide sleeve, improve the coordination accuracy of the guide sleeve and the reamer gap, and repair the machine tool in time , Adjust the spindle bearing clearance.

2. The surface roughness of the inner hole is high

Cause: The surface roughness of the inner hole of the vertical machining center is high, and there are many reasons, which may be due to the high cutting speed, improper cutting fluid selection, excessive main deflection angle of the reamer, and too much reaming allowance. Uneven or too small reaming allowance, unsharp edge, too wide reaming cutting edge band, poor chip removal during reaming, excessive wear of the reamer, and mismatch between the selected milling tool and the part material, etc. .

Solution: Because there are many reasons for the high roughness of machining, it is more complicated to solve it. You can start from the following aspects: reduce the cutting speed, select the cutting fluid according to the machining material, appropriately reduce the reaming allowance, and improve the reaming The position accuracy and quality of the bottom hole may increase the margin of reaming, increase the space of the chip pocket or adopt a reamer with an inclination of the blade to make chip removal smooth, change the reamer regularly, and choose a reasonable tool, such as selecting suitable tools when machining steel parts Measures such as cutting tools for steel machining.

3. Increased machining aperture

Reasons: The gradual increase in the diameter of the vertical machining center during machining may be caused by: the design value of the outer diameter of the reamer is too large or the reamer edge has burrs, the cutting speed is too high, the feed rate is inappropriate, or the machining allowance is too large , The main deflection angle of the reamer is too large, the reamer is bent, the edge of the reamer is adhered to the built-up edge, the edge swing of the reamer is out of tolerance during sharpening, the cutting fluid selection is inappropriate, and it may be a problem of the CNC machine tool itself. The above problems may also occur if the spindle is bent or the spindle bearing is too loose or damaged.

Solution: According to the actual inspection situation, the following countermeasures can be taken: appropriately reduce the outer diameter of the reamer, reduce the cutting speed, appropriately adjust the feed or reduce the machining allowance, appropriately reduce the entering angle, straighten or scrap Bent unusable reamer, choose cutting fluid with better cooling performance, adjust or replace spindle bearing, or replace the entire spindle.

4.The reamed inner hole is not round

Reasons: The machining of the inner hole is not round and the roundness is not enough mainly due to the following factors: the reamer is too long, the rigidity is insufficient, vibration occurs during reaming, the main deflection angle of the reamer is too small, and the reaming allowance is too small. Small, there are gaps, cross holes on the surface of the inner hole, especially blisters, air holes on the surface of the hole, and it may be that the machine tool spindle bearing is loose.
Solution: You can start from the following aspects: the installation of the reamer should adopt rigid connection, select qualified reamer, control the hole position tolerance of the pre-machining process, use unequal pitch reamer, select qualified blanks, and timely adjust the machine tool spindle Adjust the gap and so on.

5. The center line of the hole after reaming is not straight

Cause: When the vertical machining center is machining the hole, the center line may not be straight. The possible reasons may be: the hole is inclined during drilling, especially when the hole diameter is small, due to the poor rigidity of the reamer, the original curvature cannot be corrected. The main deflection angle of the reamer is too large and the guidance is poor, which makes the reamer easy to deviate from the direction during reaming, the cutting part is too large, and the reamer displaces intermittently in the gap in the middle of the hole.
Solution: Increase the hole reaming or boring process to correct the hole, reduce the entering angle, adjust the appropriate reamer, exchange the reamer with the guiding part or lengthen the cutting part, and pay attention to correct operation.