Drilling steps and methods to improve drilling accuracy

Basic concept of drilling

Under normal circumstances, drilling refers to a processing method in which a drill is used to make holes on the product display. Generally speaking, when drilling a product on a drilling machine, the drill bit should complete two movements simultaneously:

① The main motion, that is, the rotary motion of the drill bit around the axis (cutting motion);

②Secondary movement, that is, the linear movement of the drill toward the workpiece along the axis (feeding movement).

When drilling, because of the flaws in the structure of the drill bit, it will leave traces on the processed parts of the product and affect the processing quality of the workpiece. The processing accuracy is generally below IT10, and the surface roughness is about Ra12.5μm, which belongs to the rough processing category. 

Drilling operation process

Underline

Before drilling, first understand the drawing requirements. According to the basic requirements of drilling, use tools to draw the center line of the hole position. The center line must be clear and accurate, and the thinner the better. After the line is drawn, use a vernier caliper or a steel ruler. Take measurements.

Check square or check circle

After the line is drawn and passed the inspection, an inspection grid or inspection circle with the center line of the hole as the center of symmetry should be drawn as the inspection line for the trial drilling, so that the drilling direction can be checked and corrected during the drilling.
Proofing

After marking out the corresponding check square or check circle, you should carefully proof the eye. Make a small spot first, and measure multiple times in different directions of the center line of the cross to see if the punch is indeed hitting the intersection of the center line of the cross, and then punch the punch to the right, round, and big to make it accurate. Knife centered.
Clamping

Use a rag to clean the machine table, fixture surface, and reference surface of the workpiece, and then clamp the workpiece. The clamping is flat and reliable as required, and it is convenient to query and measure at any time. It is necessary to pay attention to the clamping method of the workpiece to prevent the workpiece from deforming due to the clamping.

Test drill

Test drilling is necessary before formal drilling: the drill bit is aligned with the center of the hole to drill a shallow pit, and then visually check whether the shallow pit is in the correct orientation, and continuous correction is needed to make the shallow pit coaxial with the inspection circle. If the violation is small, you can force the workpiece to move in the opposite direction of the violation during the trip to reach the gradual proofreading.

Drilling

Machine-added drilling is generally based on manual feed operation. When the azimuth accuracy of the test drilling is required, the drilling can be carried out. During manual feed, the feed force should not cause the drill to bend and avoid the hole axis from skewing.

A more accurate method of drilling

Sharpening the drill bit is the beginning of everything

Before drilling, choose the corresponding drill bit for sharpening. The sharpened drill bit maintains accurate apex angle, relief angle and chisel edge bevel angle, the length of the two main cutting edges is flat and symmetrical to the center line of the drill bit, and the two main flank surfaces are smooth, in order to facilitate centering and reduce the roughness of the hole wall , The chisel edge and main cutting edge should also be properly ground (it is best to rough ground on the grinder first, and then fine-grind on the oil stone).
Accurate marking is the basis

When using a height ruler to accurately draw a line, the first thing to do is to ensure the correctness of the standard. When scribing, make the angle of the scribing needle and the scribing plane of the workpiece form an angle of 40 to 60 degrees (along the scribing direction), so that the drawn lines are clear and even.
Pay attention to the selection of the datum plane for marking, the datum plane must be processed accurately, and the flatness of itself and the perpendicularity to the adjacent surface must be ensured. After the cross line of the hole position is drawn, in order to ensure easy alignment when drilling, use the center punch to punch out the center point on the cross line (requires the punch point to be small and the direction to be accurate).

Correct clamping is the key

Generally, for holes with a diameter of less than 6mm, if the accuracy is not high, use hand pliers to clamp the workpiece for drilling; for holes of 6 to 10mm, if the workpiece is regular and even, flat-nose pliers can be used to hold the workpiece, but the workpiece should be clamped The surface is perpendicular to the spindle of the drilling machine. When drilling a hole with a larger diameter, the flat-nose pliers must be fixed with a bolt pressing plate; for larger workpieces with a hole diameter of 10mm or more, the pressing plate clamping method is used to drill the hole.

Accurate search is the key

After the workpiece is clamped, do not rush to drop the drill, and firstly perform alignment.
Alignment has static alignment and dynamic alignment. The so-called static alignment refers to alignment before the drilling machine is launched, so that the center line of the drilling machine spindle and the cross line of the workpiece are aligned. This method is safe and convenient for beginners and easier to grasp, but because the swing of the drilling machine spindle is not considered, for example And other uncertain factors, the drilling accuracy is low. The dynamic search is performed after the drilling machine is launched. During the alignment, some uncertain factors are taken into account, and the accuracy is relatively high.

Careful inspection is essential

The detection can accurately and timely find the accuracy of the hole so that necessary measures can be taken to compensate.
For holes with high drilling precision, we generally use drilling, reaming, and reaming processing techniques. After drilling a small hole in the first step, use a caliper to detect the error offset from the center of the bottom hole to the reference plane, and calculate the position of the bottom hole and the ideal center after actual measurement. If the error is not greater than 0.10mm, it can be reamed Properly increase the top angle of the drill bit, weaken the automatic centering effect, properly push the workpiece in the positive direction, and gradually increase the diameter of the drill tip to compensate. If the amount of error is greater than 0.10mm, you can use assorted round files to trim the two side walls of the bottom hole, and the trimming part should be connected with the smooth transition of the bottom hole.

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