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Drilling in the appraisal of fitter operation is a must-read content. The score accounts for 1/5 to 1/4 of the entire appraisal, and the requirement for the accuracy of the drilling position accounts for more than 3/5 of this part. Therefore, controlling the accuracy of the drilling position is a basic skill that fitters must master.
The control of the positional accuracy of the hole is essentially the correct positional control of the bit and the workpiece during the drilling process. In order to check operator's operation skills, the position adjustment of the hole during drilling is only manual and dynamic control process. Drilling dies and other fixtures are not allowed. Therefore, the position accuracy of the hole is affected by the scribe, the precision of the machine tool, the workpiece and the drill bit. The influence of some uncertain factors such as clamping, the sharpness of the drill, the position of the workpiece, and the adjustment of the cutting amount of the machine, together with certain processing skills and necessary assurance measures, therefore, when the position accuracy of the hole is required to be high , it will lead to serious overshoot.
How to effectively avoid and eliminate the hole position overshoot phenomenon is the key to control the quality of the hole when drilling. In the drilling operation, in addition to correct scribe, drilling the bottom hole, accurately correcting the position in time, and repairing the position of the bottom hole are the basis for ensuring the position accuracy of the hole.
Dash
Since the positional accuracy at the time of starting the drilling is basically determined by the position of the rushing eye, the positional accuracy of the dynamic control hole is converted to the punching accuracy of the rushing position to some extent. Considering the important role that proofing plays in controlling the positional accuracy of the hole, attention should be paid in the specific operation: 1 Select the sharp height ruler of the cutter head so that the groove mark of the centerline of the hole can be marked on the processing surface. Deeper, use the resistance of the centerline of the hole to resist its resistance when the sample moves to determine the correct position of the punching eye. 2 In order to reduce the dimensional deviation between the center of the visual inspection hole and the ideal position, the control circle or control box for each size hole should be drawn (due to the accuracy of the scribe, the method of drawing the control box is recommended), and during the drilling process At the same time as visual inspection, using caliper measurement methods to ensure its position accuracy. 3Because the repairing, drilling and expanding the bottom hole to shift the correction method to the correction of the position deviation of the kind of red eye, can effectively reduce the number of holes to correct the position of the hole at the bottom hole, shorten the operation processing time. Carefully check the position accuracy and make necessary corrections.
Assembly of workpiece and drill
Because in the drilling process, if only the visual measurement method is difficult to ensure its position accuracy, vernier calipers must be used to measure, in order to facilitate the measurement, when the workpiece is installed to make the workpiece out of the machine with a certain size jaw vise. The drill bit should be clamped as short as possible to increase its rigidity and strength, which is more conducive to the accuracy of its position.
Drill hole
The bottom hole is in the correct position or the overshoot is small, which can effectively reduce the number of times that the hole is used to correct the position of the bottom hole, shorten the operation processing time, and have a particularly important effect on improving the processing accuracy and processing efficiency.
The first step: the choice of the drill diameter, the drill diameter is too small, the strength is weak, easy to break in the process of processing; when drilling and correcting, the drill bit is bent and deflected, leading to the opposite direction of the direction to be corrected, and the original hole is enlarged. The position error. The diameter of the drill bit is too large, the length of the horizontal blade is long, and the centering performance is poor, and the number of times of repairing and drilling the position of the correction hole is relatively reduced. If the hole diameter of the bottom hole is larger than the one specified on the drawing, there is a possibility that the bottom hole with poor tolerance cannot be eliminated. Therefore, the proper bit should be selected according to the actual situation, because the center drill can not only well position but also ensure enough rigidity and strength, so it is better to use the center drill when drilling the bottom hole.
Step 2: For correcting the red eye, there are two ways to align the center drill with the red eye. One is to turn the drill chuck by hand, and then move the flat jaw or turn the table of the bench drill to make the center drill and the sample. Red eye correction. The second is that the relatively regular parts are floating as much as possible, relying on the pulling force to make the position of the workpiece produce a slight movement, so that the drill bit and the red eye can automatically center.
The third step: detection, in order to improve the detection accuracy of the position of the hole, the test results should be corrected as necessary: ​​First, measure the nearest point and the farthest point of the two-hole wall and take the average value. The second is to insert a corresponding amount of rods after drilling to measure, in order to reduce the influence of non-linear factors of vernier caliper measurement claws on the measurement results.
Reaming position control
The position of the bottom hole is determined to be correct by inspection. Effective measures shall be taken to prevent the new position deviation of the hole during the reaming process. Firstly, the top angle of the drill bit used for reaming holes should be smaller to reduce the radial eccentric force and vibration during drilling and increase the effect and effect of automatic centering. Then turn the drill chuck by hand and move the flat nose pliers or turn the table of the bench drill so that the two main cutting edges of the drill bit contact with the wall of the entry hole of the drill bit of the original bottom hole at the same time, and then start the drilling machine to drill holes. The operation basically ensures that the position of the original bottom hole does not change.
Hole rectification correction
For the bottom hole whose hole position is within 0.20mm, you can push the workpiece in the direction of deviation correction and gradually increase the diameter of the drill to solve the problem. (Note: In order to weaken the automatic centering of the bit, the drill angle should be increased.)
Repair and correction
For the bottom hole whose hole position is more than 0.20mm, if the above method is still adopted, it will inevitably increase the number of times of hole expansion and the amount of drills with different specifications and dimensions, and extend the time for correcting the deviation. The round offset repair technique can be used to remove excess offset margins and then be solved with drill-drilling.
The first step: relevant measurement and calculation, first measure the bottom hole size error, shape error, such as overshoot, relative ideal position, through the calculation and analysis of the hole position error value. Then, determine the direction of repairing the bottom hole (repair the direction of the bottom hole, the direction of the line from the center of the actual hole to the center of the ideal position) and the shape of the repair hole (the shape of the repair hole should be close to elliptical, elliptical The geometric center coincides with the center of the ideal position. The minor axis of the ellipse is the diameter of the original bottom hole, and the minimum bottom hole diameter that eliminates the hole position error is the long axis of the ellipse.
The second step: Select the trowel and repair method. The diameter of the selected repair file is slightly smaller than the original hole diameter. If the diameter is too large or equal to the diameter of the bottom hole, it is difficult to make a circular cut into the bottom hole or repair it. It is too small and easy to repair into a pear-like shape, so that the bit is asymmetrically stressed, and a new hole position offset error is generated when drilling. During repairs, manual repairs can be made on the bench vise, or with the aid of the rotary motion of the drilling spindle, the file can be clamped in the drill chuck and moved up and down to push the workpiece for machining. The thin plate can be repaired from the end of the bottom hole; when the workpiece is thick, for the through hole, it should be repaired from both ends of the bottom hole to reduce the non-vertical error of the arc surface and the end face of the hole.
The third step: expanding the hole, the diameter of the selected reaming bit should be larger than the elliptical major axis of the middle plane of the workpiece thickness. Reaming should try to use a short drill, a small top angle, back angle, low-speed cutting.
Step 4: Check whether the dimensional accuracy and shape accuracy of the inspection hole are qualified. If not, repeat the above process until the technical requirements specified in the drawings are met.
In the drilling process, the principle of first, general, first, and high accuracy should be followed, that is, the hole at the reference position is preferentially machined or guaranteed, or the hole with relatively high dimensional accuracy and shape accuracy is required.
How to effectively avoid and eliminate the hole position overshoot phenomenon is the key to control the quality of the hole when drilling, but due to many influencing factors, it requires repeated intensive training to achieve the purpose of fully controlling the hole position accuracy. This is a long process of gradual and accurate improvement.