Introduce About drills

Three pointed and seven sharp edges take the lead, with crescent arc grooves divided on both sides. The outer edge is further grooved, and the horizontal edge is ground low, narrow, and sharp.

The reason why group drills are superior to other drills: 60% of the axial resistance of standard Fried Dough Twists drills comes from the horizontal edge, because the front angle of the horizontal edge is about -60 °. The "group drilling" removes 80%~90% of the horizontal edge of the Fried Dough Twists drill, and forms two internal edges. The front angle of the internal edge increases from -60 ° to 0 °~-10 °, thus reducing the axial resistance by about 50%, and making the feeding feel particularly light.

The group drill is sharpened with a straight outer edge to create a crescent groove, resulting in finer chips and smoother chip removal. The circular reinforcement generated during drilling is conducive to the centering of the drill bit, ensuring that the drilling is smooth and round. Its drilling torque is reduced by about 30%, so it can drill with a larger feed rate. The outer edge has a sharp angle of 135 °, the inner edge has a sharp angle of 120 °, and the drill tip height is 0.06d, which makes it have excellent drilling performance for thin plates. Due to its low cutting resistance, accurate and stable centering, it is particularly suitable for use on hand drills.

Fried Dough Twists drill is a commonly used drilling tool for machining. Although the structure is simple, it is not an easy task to truly sharpen it. The key lies in mastering the methods and techniques of sharpening, and once mastered, problems will be easily solved. Let me introduce the hand sharpening skills of Fried Dough Twists drills. The top angle of Fried Dough Twists drill is generally 118 °, which can also be regarded as 120 °.

The main techniques for grinding drill bits are:

1. The cutting edge should be level with the grinding wheel surface. Before grinding the drill bit, the main cutting edge of the drill bit should be placed on a horizontal plane with the grinding wheel surface, which means that when the cutting edge contacts the grinding wheel surface, the entire edge must be ground. This is the first step in the relative position between the drill bit and the grinding wheel. Once the position is set, slowly lean towards the grinding wheel surface.

2. The axis of the drill bit should be inclined at an angle of 60 ° with the grinding wheel surface. This angle is the sharp angle of the drill bit, and if the angle is not correct at this time, it will directly affect the size of the drill bit tip angle, the shape of the main cutting edge, and the lateral slope angle. This refers to the positional relationship between the axis of the drill bit and the surface of the grinding wheel, which can be accurately observed by taking 60 °. Here, it is important to pay attention to the relative horizontal and angular positions of the drill bit before grinding. Both should be taken into account, and the angle should not be neglected for the sake of flattening the blade edge, or for the sake of flattening the angle, the blade edge should be neglected.

3. Grind back from the blade edge. After the cutting edge contacts the grinding wheel, it needs to be ground from the main cutting edge to the back surface, which means starting from the cutting edge of the drill bit to contact the grinding wheel first, and then slowly grinding down along the entire back cutting surface. When the drill bit cuts in, it can gently touch the grinding wheel. First, perform a small amount of edge grinding, and pay attention to the uniformity of the sparks. Adjust the pressure on the hand in a timely manner. Also, pay attention to the cooling of the drill bit, and do not let it grind too hard, causing discoloration of the edge and annealing of the edge. When a high temperature is found at the cutting edge, the drill bit should be cooled down in a timely manner.

4. The cutting edge of the drill bit should swing up and down, and the tail of the drill bit should not be raised.

This is a standard drill bit grinding action, where the main cutting edge swings up and down on the grinding wheel, that is, the hand holding the front of the drill bit should evenly swing the drill bit up and down on the grinding wheel surface. The hand holding the handle cannot swing, and it is also necessary to prevent the back handle from tilting upwards, that is, the tail of the drill bit cannot be raised above the horizontal centerline of the grinding wheel, otherwise it will make the cutting edge dull and unable to cut. This is the most crucial step, and whether the drill bit is worn well or not is closely related to it. When grinding is almost done, start from the edge of the blade and gently rub against the back corner to make the back of the blade smoother.

5. Ensure that the blade tip is aligned with the axis, and slowly adjust it symmetrically on both sides.

After grinding one edge, the other edge must be ensured to be in the middle of the drill bit axis, and both edges must be symmetrical. Experienced masters will observe the symmetry of the drill tip under bright light and slowly polish it. The back angle of the cutting edge of a drill bit is generally 10 ° -14 °. If the back angle is too large, the cutting edge is too thin, causing severe vibration during drilling. The hole opening is triangular or pentagonal, and the chips are needle shaped; The back angle is small, and the axial force during drilling is large, making it difficult to cut in. The cutting force increases, the temperature rises greatly, and the drill bit heats up severely, even making it impossible to drill. The back angle grinding is suitable, with the tip aligned and the two edges symmetrical. During drilling, the drill bit discharges chips quickly and without vibration, and the aperture does not expand.

6. After grinding the two edges, pay attention to grinding the tip of the drill bit with a larger diameter.

After grinding the two edges of the drill bit, there will be a flat surface at the tip of the two edges, which affects the center positioning of the drill bit. It is necessary to chamfer the angle behind the edge and grind the flat surface of the tip as small as possible. The method is to raise the drill bit vertically, align it with the angle of the grinding wheel, and at the root behind the blade, pour a small groove towards the blade tip. This is also an important point for the centering of the drill bit and the ease of cutting. Be careful not to grind the chamfer of the cutting edge onto the main cutting edge, as this will cause the front angle of the main cutting edge to be too large, directly affecting the drilling process.

Improvement of Drilling Processing by Grinding and Strengthening the Cutting Edge of Drill bits

Hole machining plays an important role in metal cutting, generally accounting for about one-third of the machining volume. Among them, drilling accounts for about 22% to 25%, and other hole processing accounts for about 11% to 13%. Due to the harsh conditions of hole machining, the technological development of hole machining tools is slower than that of turning and milling tools. In recent years, with the continuous improvement of production efficiency, automation level, and machining center performance requirements for medium and small batch production, the development of tool sharpening technology and multi axis CNC tool sharpening equipment has driven the development of hole machining tools. The most typical example is the gradual maturity of the drill bit grinding technology, which has been widely used in mechanical production for many years and is the most widely used overall structure. By grinding and strengthening the cutting edge of the drill bit to improve drilling conditions, solutions should be sought from the structural characteristics and actual usage of the drill bit.

Ways to improve drilling processing

1. Improve the cutting edge of the drill bit

Adopting a new type of edge grinding method to improve the geometric shape of drill tips and horizontal edges. In the past, the grinding of drill bits was carried out using the ordinary grinding method, which first produced a sharp angle of 2 φ After the corner is formed, the 90 ° edges of the grinding wheel circumference are manually ground to the drill core. Due to the limitations of traditional grinding methods, the symmetry and accuracy of the drill bit after grinding are poor. Only by using a traditional 118 ° sharp angle can the cutting edge be guaranteed to be straight. In recent years, our company has introduced a CNC universal tool grinder, which adopts a relatively advanced five axis CNC system. It can achieve scraping and grinding of the cutting edge of the drill bit, modify the cutting edge form of the drill bit, and still ensure high tool accuracy. So, we tried to improve the geometric angle of the drill bit tip by improving the service life of the drill bit, enhancing the drill bit, and improving the drilling processing conditions.

According to the structural characteristics of the drill bit, we first measured the sharp angle (2 φ The angle was changed and experiments were conducted using sharp angles ranging from 118 ° to 140 °. Tracking and mastering the processing situation on the production site, we found that using a drill bit with an increased sharp angle has a certain effect on processing cast iron: during drilling, the processing becomes light and fast, the sound and vibration are significantly reduced, and the surface roughness of the hole is improved. Judging the smoothness of the machining process from the shape of the chips. But as the sharp angle of the drill bit increases, the wear of the drill bit intensifies. After multiple attempts, it was found that the processing was most stable at a sharp angle of around 130 °, and the quantity and quality of processing were significantly improved.

When improving the axial force on the transverse edge of the drill bit during machining, it is necessary to overcome adverse cutting conditions such as negative rake angle at the transverse edge. When processing the cross cutting edge, we use a large cutting method to scrape and grind the cross cutting edge, shorten the width of the cross cutting edge, make the cross cutting edge of the drilling center close to the main cutting edge, and reduce the axial force and torque during drilling. Through practical testing, it has been found that after improving the axial force situation of the drill bit, the centering accuracy has been greatly improved. By using this structure of drill bits on the shell machining center, it is possible to cancel the center drill under certain conditions, improve machining efficiency, and shorten production time. This drill bit has been gradually tested and promoted in our company's production.

Compared with high-speed steel drill bits, hard alloy drill bits have more stringent processing conditions. The hard alloy drill bit used in the screw hole processing on the flange in our company has lower original processing quantity and processing efficiency. We have also attempted to make some improvements:

Based on the advantage of high hardness of hard alloy materials, a large sharp angle of 140 ° is adopted to increase the cutting rake angle, change the force situation of the drill bit, reduce cutting force, and make machining smoother. Based on the characteristics of the processed materials, the lateral edge of the drill bit is improved by using an R-shaped edge transition. On the basis of the R-shaped edge, the front angle of the lateral edge is increased, and the drilling center part is cut and positioned before drilling, achieving self centering. The central drilling process is cancelled, meeting the positional requirements. Edge cutting treatment is carried out at the diameter to form a protective edge, which makes it less likely for the drill bit to collapse during drilling, Greatly improves the lifespan of the drill bit.

This structure is particularly suitable for improving small diameter drill bits. Now our company's synchronizer workshop processes the diameter of the lock pin hole for the two speed synchronizer φ 7.5mm, with a tolerance range of 0~+0.016mm, a total of 6 holes are machined on each part, with a relative positional tolerance requirement of 0.05mm.

The original processing method was drilling, centering, drilling, and reaming, which made it difficult to ensure positional accuracy and resulted in longer processing cycles and lower efficiency. Currently, direct drilling with hard alloy drill bits can ensure the machining accuracy and positional accuracy of holes, meet the needs of process products, and greatly improve machining efficiency.