High precision small diameter positioning pin hole machining

First, the issue of the problem

When processing the fan motor seat, the processing of the two positioning pin holes on the machine base is always unqualified.

The equipment used by the company is the CNC TK6920 milling and boring machine produced by Qier Machine Tool Plant. The machine tool has no cutting fluid supply system. Most of the tools are domestically produced common cutting tools, such as twist drills, ordinary reamers, and some use Sandvik Coromant tools.

When machining the pin hole, the process we use is: drilling the center hole → drilling → reaming → reaming. The drilling and expansion process uses a common twist drill, and the hinge uses a domestically used reamer. These tools are connected to the holder by a drill sleeve (reducing sleeve).

After the first sample trial processing is completed, the laser measuring instrument measures the pin hole unqualified, mainly has the following problems: 1 The pin hole center distance is out of tolerance. 2 pin hole cylindricity is super poor, forming a trumpet shape. 3 pin hole surface roughness is out of tolerance. 4 pin hole roundness is out of tolerance, an ellipse appears.

Second, the cause analysis

Through the analysis of the processing technology and production process, we believe that there are mainly the following reasons:

(1) Machine tool control accuracy factors The accuracy error of each axis of the machine tool is too large, resulting in the deviation of the pin hole center distance.

(2) Tool factor Drilling and reaming with an ordinary drill bit makes the drill bit easily biased, resulting in deflection of the bottom hole. When reaming, the reamer cannot correct the deviation of the bottom hole, and the hole shape error cannot be guaranteed.

(3) Tool and tool holder factors The tool is connected to the tool holder through the reducer sleeve. The precision of the tool is not high and the rigidity is poor, which causes the hole diameter and roundness of the pin hole to be out of tolerance.

(4) Cutting fluid factor The machine does not have a cooling system. Since the pin hole is a blind hole, the chip and the cutting heat cannot be punched out (band) in time, resulting in an excessive surface roughness of the pin hole.

Third, the solution process

In order to solve the above problems, we have processed and produced qualified pin holes, and we have further studied and improved the above various factors.

1. Solve problems with machine tools

We use a laser measuring instrument to measure the accuracy of each axis of the machine to determine the deviation of the column accuracy (ie, the center of the pin hole). Through testing, it is found that the failure of the installation of the Y-axis scale of the machine tool is the main reason for the accuracy deviation of the error column. Finally, the grating ruler is cleaned and reinstalled, and the precision of each axis of the machine tool is detected by a laser interferometer to make it qualified.

Since the machine itself is not equipped with a cutting fluid system, we have designed a separate cutting fluid system to meet the requirements of advanced tools for machine tools.

2. Improve the current tool

After adjusting the accuracy of the machine, we explore and troubleshoot the factors of the tool:

(1) Determining the direction of the clamping tool During the trial processing, the same material, the same drill bit, and the same feed amount were found, but the results were different each time. This is because the direction of the clamping tool is different each time. Such factors as the angle of the tool will change, causing deviations.

(2) Correcting the tool error When using the new reamer for trial processing, it is found that the reamer has a large runout in the circumferential direction. Therefore, we use the dial indicator to check the runout error before use, and the blade with a larger runout error is used. Grinding, making its radial circular runout within a controllable range.

(3) Changing the tool feed parameter Reset the feed amount of the reaming drill and the reamer, and select the feed amount when the machining accuracy is the best.

(4) Selecting the reducer sleeve and the reamer are connected by the reducer sleeve and the shank, so that there will be errors in each setup, and the reducer sleeve and the shank taper shank and the drill reamer Coordination is not a complete perfection in theory. By observing on the tool setting tool, the drill bit (reasing knife) will go off after each clamping, and basically 90% of the reducer sleeves are unqualified. We chose the trial sleeve with a small error on the tool.