First, the characteristics of drilling The drill usually has two main cutting edges, when processing, the drill at the same time turning the cutting. The rake angle of the drill bit increases from the central axis to the outer edge, and the cutting speed increases as it approaches the outer edge. The chisel edge of the drill is located near the center axis of the gyration. The rake angle of the chisel edge is large, there is no chip space, and the cutting speed is low, so that a large axial resistance is generated. If the chisel edge is sharpened to an R shape, and the cutting edge near the center axis is a positive rake angle, the cutting resistance can be reduced and the cutting performance can be significantly improved.

2. Chip breaking and chip removal The cutting of the drill bit is carried out in a hole with a narrow space. The chip must be discharged through the drill bit groove, so the chip shape has a great influence on the cutting performance of the drill bit. Common chip shapes include flaky crumbs, tubular crumbs, needle crumbs, cone-shaped spiral crumbs, banded crumbs, fan-shaped crumbs, and powdered crumbs.

When the shape of the chip is not appropriate, the following problems will occur:

       (1) Fine cuttings block the cutting edge, affect the drilling accuracy, reduce the life of the drill, and even break the drill (such as powdery shavings, fan-shaped shavings, etc.);

       2 Long chips tangled around the drill bit interfered with the work, causing the drill bit to break or prevent the cutting fluid from entering the hole (eg, swarf, banding, etc.). For this reason, the effects of chip breaking and chip removal can be improved by using methods such as increasing the feed amount, intermittent feed, grinding the chisel edge, and installing the chip breaker, respectively, or eliminating the problems caused by the chips.

Third, the drilling accuracy The accuracy of the hole is mainly composed of the aperture size, position accuracy, coaxiality, roundness, surface roughness and orifice burr and other factors.

The factors that influence the precision of the machined hole during drilling are:

       1Drilling accuracy and cutting conditions such as tool holder, cutting speed, feed amount, cutting fluid, etc.

       2 drill size and shape, such as drill length, blade shape, core shape, etc.;

        3 workpiece shape, such as the shape of the orifice side, orifice shape, thickness, loading status.

        (a) Cutout of the hole The cut-out of the hole is caused by the vibration of the bit during machining. The vibration of the tool holder has a great influence on the positioning accuracy of the aperture and the hole. Therefore, when the tool holder wears badly, the new tool holder should be replaced in time. When drilling small holes, it is difficult to measure and adjust the pendulum. Therefore, it is better to use a rough-shank small-diameter drill with better concentricity between the blade and the shank. When using a regrind drill, the reason for the decrease in hole accuracy is mostly due to the asymmetry of the back shape. Controlled edge height difference can effectively inhibit the hole cut-out.

        (b) The roundness of the hole Due to the vibration of the drill bit, the drilled hole shape is easy to be a polygon, and a pattern like a double-stranded line appears on the wall of the hole. Common polygonal holes are mostly triangular or pentagonal. The reason for producing the triangular hole is that the drill has two rotary centers when drilling, and they vibrate at a frequency of 600 exchanges per interval. The main cause of the vibration is the unbalance of the cutting resistance. When the drill bit rotates one rotation, the roundness of the processed hole is not As a result, the resistance is unbalanced during the second turning cutting, and the previous vibration is repeated again, but the phase of the vibration is shifted to some extent, resulting in double-line appearance on the wall of the hole. When the drilling depth reaches a certain level, the friction between the edge surface of the drill bit and the wall of the hole increases, the vibration attenuates, the double-line disappears, and the roundness becomes better. The aperture is funnel-shaped when viewed from the longitudinal section. For the same reason, pentagonal, heptagonal, etc. may also occur during cutting. In order to eliminate this phenomenon, in addition to controlling the vibration of the chuck, the height difference of the cutting edge, the asymmetry of the back and the shape of the blade, it is also necessary to improve the rigidity of the drill, increase the feed per revolution, reduce the back angle, and trim. Crossbow and other measures.

         (3) Drilling on inclined planes and surfaces When the cutting surface or drilling surface of the drill is inclined, curved or stepped, the positioning accuracy is poor. Since the drill is a radial single-sided knife, the tool life is reduced.

To improve positioning accuracy, the following measures can be taken:

1. First drill the center hole;

2. Milling hole seat with end mill;

3. Select drills with good cutting and rigidity;

4. Reduce the feed rate.

         (4) Treatment of burr Drilling occurs at the entrance and exit of the hole during drilling, especially when processing tough materials and sheets. The reason for this is that when the drill bit is about to drill through, the material to be machined is plastically deformed. At this time, the triangle part that should have been cut near the outer edge part of the bit is deformed to the outside by the axial cutting force, and is bent on the outer edge of the drill bit. The chamfering and edge banding further curl up to form curls or burrs. This burr-like burr is the most common in drilling.

To control the generation of flash, take the following measures:

1. Increase the helix angle of the drill bit to make the cutting edge sharp and reduce the cutting resistance;

2. The bit front angle is designed to be about 60° to reduce the axial resistance;

3. The bit front angle is designed to be about 180°~190°, starting from the cutting edge of the outer edge part, such as the use of a candlestick-shaped or ladder-like drill type; 4. Decrease the feed rate.

         4. Processing Conditions for Drilling Some large tool companies have a “Basic Cutting Amount Reference Table” arranged according to the processing materials in the drill bit catalog. The user can select the cutting conditions of the drilling processing with reference to the cutting amount provided. The choice of cutting conditions is appropriate and should be determined through trial cutting, based on factors such as machining accuracy, machining efficiency, and bit life.

        (I) Drill Bit Life and Processing Efficiency Under the premise of meeting the technical requirements of the workpiece being processed, whether the drill bit is used properly or not should be comprehensively measured based on the service life of the bit and the processing efficiency. The evaluation index of the service life of the drill bit can use the cutting distance; the evaluation index of the machining efficiency can select the feed speed. For high-speed steel drills, the service life of the drill bit is greatly affected by the rotation speed, and it is less affected by the feed amount per revolution. Therefore, the machining efficiency can be improved by increasing the feed amount per revolution, and at the same time, a longer bit life can be ensured. However, it should be noted that if the feed per revolution is too large, the chips will be thickened, resulting in difficulty in chip breaking. Therefore, it is necessary to determine the range of feed per revolution that can be smoothly chipped through a test cut. For carbide drills, the cutting edge has a larger chamfer in the negative rake angle direction, and the available range of feed per revolution is smaller than that of high-speed steel drills. If the feed per revolution exceeds the range during machining, the use of the drill bit will be reduced. life. Since the heat resistance of cemented carbide drills is higher than that of high-speed steel drills, the speed of rotation has little effect on the life of drills. Therefore, the method of increasing the speed of rotation can be used to improve the machining efficiency of cemented carbide drills while ensuring the life of the drills.

         (II) Reasonable use of cutting fluid The cutting of the drill is performed in a hole with a narrow space. Therefore, the type of the cutting fluid and the feeding method greatly affect the life of the drill and the machining accuracy of the hole. Cutting fluid can be divided into two major categories: water-soluble and non-water-soluble. Non-water-soluble cutting fluids have good lubricity, wettability and anti-adhesion, and also have rust-preventing effect. Water-soluble cutting fluids have better cooling properties, do not emit smoke and have no flammability. Due to the consideration of environmental protection, the use of water-soluble cutting fluids has increased in recent years. However, if the water-miscible cutting fluid is not properly diluted or if the cutting fluid is deteriorated, the tool life will be greatly shortened, so care must be taken when using it. Regardless of whether it is a water-soluble or non-water-soluble cutting fluid, the cutting fluid must reach the cutting point sufficiently during use. At the same time, the cutting fluid flow rate, pressure, number of nozzles, cooling mode (internal cooling or external cooling) must be strictly controlled.

        Five, re-sharpening drill

        (I) Discriminating the re-grinding period of the drill bit The criterion for re-grinding the drill bit is:

1. The amount of wear of the cutting edge, chisel edge, and edge land.

2. The dimensional accuracy and surface roughness of the processed hole;

3. The color and shape of the chips;

4. Cutting resistance (indirect value of spindle current, noise, vibration, etc.);

5. Processing quantity, etc. The actual use should be based on specific circumstances, from the above indicators to determine the exact and convenient criteria. When using the amount of wear as a criterion, the best regrinding period with the best economy should be found. Because the main sharpening position is the back of the head and the horizontal edge, if the amount of wear of the drill is too large, the wear of the cutting edge is much longer, the grinding amount is large, and the number of times of regrind can be reduced (the total service life of the cutter = the tool life after regrind × can be Re-grinding times will shorten the total service life of the drill bit. When the dimensional accuracy of the machined hole is used as the criterion, the amount of cuts, non-straightness, etc. of the column gauge or check hole shall be applied. Once the control value is exceeded, it shall be immediately Re-grinding; when cutting resistance is used as a criterion, automatic shutdown can be adopted when exceeding the set limit value (such as the spindle current); when using the quantity limit management, the above discriminating contents should be integrated to set the criterion.

         (II) Grinding method of the drill When re-grinding the drill, it is better to use a drill grinding machine or a universal tool grinder, which is very important to ensure the service life and machining accuracy of the drill. If the original drilling process is in good condition, it can be reground according to the original drill type; if the original drill type is defective, the back shape can be appropriately modified and the horizontal edge grinding can be performed according to the purpose of use.

Sharpening should pay attention to the following points:

1. To prevent overheating, to avoid reducing the hardness of the drill bit;

2. The damage on the drill (especially the damage of the edge of the land) should be completely removed;

3. Drilling should be symmetric;

4. Be careful not to bump the edge during sharpening and remove the sharpened burr;

5. For carbide drills, the sharpening shape has a great influence on the drill's performance. The drill type at the time of delivery is the best drill type that has been scientifically designed and tested repeatedly. Therefore, the original edge shape should be maintained when regrinding.