What is drilling?
How to drill a hole?
How to make drilling more accurate?
It’s explained very clearly below, let’s take a look.
1. Basic concepts of drilling
Generally speaking, drilling refers to a processing method that uses a drill to process holes on the product surface. Generally speaking, when drilling products on a drilling machine, the drill bit should complete two movements simultaneously:
① Main movement, that is, the rotational movement of the drill bit around the axis (cutting movement);
②Secondary movement, that is, the linear movement of the drill bit along the axis direction toward the workpiece (feed movement).
When drilling, due to shortcomings in the drill bit structure, marks will be left on the processed parts of the product, affecting the processing quality of the workpiece. The processing accuracy is generally below IT10 level, and the surface roughness is about Ra12.5μm, which belongs to the rough machining category. .
2. Drilling operation process
1. Marking: Before drilling, first understand the drawing requirements. According to the basic standard requirements for drilling, use tools to mark the center line of the hole position. The center line must be clear and accurate, and the thinner the better. After drawing the line, Measure with vernier calipers or steel ruler.
2. Draw an inspection square or inspection circle: After drawing the line and passing the inspection, an inspection square or inspection circle with the center line of the hole as the center of symmetry should be drawn as an inspection line during test drilling to facilitate inspection during drilling. and correct drilling orientation.
3. Proofing and punching: After drawing out the corresponding inspection square or inspection circle, proofing and punching should be done carefully. First make a small point, and measure several times in different directions of the cross center line to see if the punch hole is indeed punched at the intersection of the cross center line, and then punch the sample in a straight, round, and wide direction for accurate placement. The knife is centered.
4. Clamping: Use a rag to clean the machine table, fixture surface, and workpiece datum surface, and then clamp the workpiece. The clamping should be smooth and reliable as required, and it is convenient for inquiry and measurement at any time. It is necessary to pay attention to the clamping method of the workpiece to prevent the workpiece from being deformed due to clamping.
5. Test drilling: Test drilling must be done before formal drilling: align the chisel edge of the drill bit with the center of the hole and drill a shallow pit, and then visually check whether the direction of the shallow pit is correct. It is also necessary to constantly correct the deviation to make the shallow pit and the inspection circle Coaxial. If the deviation is small, the workpiece can be pushed in the opposite direction of the deviation while drilling to achieve gradual correction.
6. Drilling: Machine drilling is generally based on manual feed operation. When the test drilling position accuracy is required, drilling can be carried out. When manually feeding, the feeding force should not cause the drill bit to bend to prevent the hole axis from being skewed.
3. Methods for higher drilling accuracy
1. Sharpening a drill bit is the beginning of everything
The corresponding drill bit should be selected for sharpening before drilling. In addition to ensuring accurate vertex angle, clearance angle, and chisel edge bevel, the sharpened drill bit has the same length of the two main cutting edges and is 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 the main cutting edge should also be properly ground (it is best to rough grind on the grinder first, and then fine grind on the oilstone).
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2. Accurate line drawing is the basis
When using a height gauge to mark lines accurately, first of all, you should ensure that the alignment is accurate. When marking, make sure that the angle between the needle angle and the marking plane of the workpiece is 40 to 60 degrees (along the marking direction), so that the lines drawn are clear and even. Pay attention to the selection of the scribing datum plane. The datum plane must be processed accurately and its flatness and perpendicularity to adjacent surfaces must be ensured. After the hole position cross line is drawn, in order to ensure easy alignment when drilling, use the center punch to punch out the center point on the cross line (the punch point must be small and the direction must be accurate).
3. Correct clamping is key
Normally, for holes with a diameter less than 6 mm, if the accuracy is not high, you can use hand pliers to clamp the workpiece for drilling; for holes between 6 and 10 mm, if the workpiece is regular and flat, you can use flat-nose pliers, but the workpiece should be The surface is perpendicular to the drilling machine spindle. When drilling a hole with a larger diameter, the flat-nose pliers must be fixed with a bolt pressure plate; for larger workpieces with a drilling diameter of more than 10 mm, use the pressure plate clamping method to drill.
4. Accurately finding the key is the key
After the workpiece is clamped, do not rush to drop the drill. Alignment should be done first. Alignment includes static alignment and dynamic alignment. The so-called static alignment refers to alignment before the drilling machine is started, so that the center line of the drilling machine spindle and the intersection of the workpiece cross line are aligned. This method is safe and convenient for beginners and is easier to master. However, it does not take into account the swing of the drilling machine spindle, for example. and other uncertain factors, the drilling accuracy is low. Dynamic alignment is performed after the drilling machine is started. During alignment, some uncertain factors are taken into account, and the accuracy is relatively high.
5. Careful inspection is essential
The inspection can accurately and timely discover the accuracy of the hole so that necessary measures can be taken to compensate. For holes with high drilling accuracy, we generally use drilling, reaming, and reaming processing techniques. After drilling the small hole in the first step, use a caliper to detect the error offset from the center of the bottom hole to the datum. After actual measurement, calculate the position of the bottom hole and the ideal center. If the error is not greater than 0.10mm, you can expand the hole. Appropriately increase the drill tip angle, weaken the automatic centering effect, properly push the workpiece in the positive direction, and gradually increase the drill tip diameter to compensate. If the error is greater than 0.10mm, an assorted round file can be used to trim the side walls of the bottom hole. The trimmed part should be connected with the arc of the bottom hole in a smooth transition.
Post time: Feb-22-2024
