Natasha
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pm | Dry goods, the (12th Dec 22 at 12:45am UTC)
Dry goods, the | | Original title: Dry goods, the relationship between geometric angle of twist drill and sharpening accuracy Source: Mechanical Professor Geometric angle of twist drill: 1. Vertex angle 2 Φ It is the angle between the projections of the two main cutting edges in the midplane. The smaller the vertex angle is, the longer the main cutting edge is, the load on the unit cutting edge is reduced, and the axial force is reduced, which is beneficial to the axial stability of the drill. And the tool tip angle at the excircle is increased, thereby being beneficial to heat dissipation and improving the durability of the tool. However, the decrease of the vertex angle will weaken the strength of the drill point, increase the chip deformation, and lead to an increase in torque. A standard twist drill has a vertex angle of about 118 °. HSS high speed steel drill: the top angle is generally 118 degrees, sometimes more than 130 degrees; HM carbide drill: the top angle is generally 140 degrees; straight flute drill is often 130 degrees, and three-edged drill is generally 150 degrees. 2. Front angle The angle between the rake face and the base plane in an orthogonal plane. The relationship between the rake angle of any selected point on the main cutting edge and the helix angle, cutting edge angle and cutting edge inclination angle of the point is tan = tan/sin + tancos (2-3). As the helix angle gradually decreases from the outer diameter to the drill center,mining dth bit, the cutting edge inclination angle also gradually decreases (negative value increases). When the cutting edge angle is constant, the rake angle decreases from + 30 ° to -30 °. The cutting condition near the center of the drill bit is very poor. 3. Rear angle The clearance angle at any point on the cutting edge is the angle between the cutting plane and the flank at that point. The relief angle of the drill is not measured in the main profile, but in the assumed working plane (feed profile). In the drilling process, it is this relief angle that actually plays a role, and it is also convenient to measure. The clearance angle of the drill bit is obtained by sharpening. During sharpening,rock drilling tools, the outer edge of the drill bit shall be sharpened to a smaller angle (about 8 ° ~ 10 °), and the area near the drill center shall be sharpened to a larger angle (about 20 ° ~ 30 °). The reason for sharpening in this way is that the relief angle can be adapted to the change of the rake angle of the main cutting edge, so that the wedge angle of each point is roughly equal, thus achieving the relative balance of sharpness, strength and durability, making up for the influence caused by the reduction of the actual working relief angle of each point on the cutting edge due to the axial feed movement of the drill bit, and improving the working conditions of the chisel edge. 4. Main deflection angle and end edge inclination angle The main cutting angle of a selected point on the main cutting edge of a twist drill is the angle between the projection of the main cutting edge on the base plane of the point and the drilling feed direction. Due to the different base planes of each point on the main cutting edge of the twist drill, the main deflection angle of each point also changes accordingly. After the twist drill is ground to a vertex angle of 2Φ, the main cutting angle of each point is determined, DHD Drill bit ,dth drilling hammer, and the relationship between them is tan = tanΦcos (2-2). The end face cutting edge inclination angle of the selected point is the included angle between the projection of the main cutting edge in the end face and the base surface of the point. Expand the full text Because the absolute value of the edge inclination angle of each point on the cutting edge gradually increases from the outer edge to the drill center, the main deflection angle of each point on the cutting edge is also large at the outer edge and small at the drill center. 5. Angle of chisel edge The chisel edge is a section of cutting edge perpendicular to the axis on the end face of the twist drill, and the angle of the cutting edge includes a chisel edge bevel angle, a chiset edge rake angle, and a chiset edge relief angle. 1) Chisel edge bevel The angle between the chisel edge and the main cutting edge in the end plane. It is naturally formed when sharpening the drill bit. The standard twist drill with normal top angle and back angle sharpening. The larger the back angle, the smaller the angle. Decreasing the angle increases the chisel edge length. 2) Chisel edge rake angle Since the base plane of the chisel edge is located within the tool solid, the chisel edge rake angle is negative. 3) Chisel edge relief angle. For standard twist drills, =- (54 ° ~ 60 °), = 30 ° ~ 36 °. Therefore, during drilling, the metal at the chisel edge is severely squeezed and deformed, and the axial force is very large. Experiments show that about 50% of the axial force is generated by the chisel edge when machining with a standard twist drill. For larger diameter twist drills, it is generally necessary to grind the chisel edge to reduce the axial force. First of all, "less grinding" is "no grinding". Grinding in a hurry when you get the drill bit must be blind grinding. Only by placing the blade in a good position before sharpening can we lay a solid foundation for the next step of "sharpening", which is very important. Four pithy formulas are used here to guide the sharpening process, and the effect is better. Pithy formula 1: "The cutting edge is placed flat against the wheel surface." This is the first step of the relative position of the drill bit and the grinding wheel, and there are often students who lean on the grinding wheel to start sharpening before the cutting edge is flat. This is definitely not good for grinding.
The "cutting edge" here is the main cutting edge, and "flat" means that the main cutting edge of the part to be sharpened is in a horizontal position. "Face" means the surface of a grinding wheel. " "Lean on" means to get closer slowly. At this time, the drill bit cannot contact the grinding wheel. Pithy formula 2: "The drill shaft slants out the sharp angle." This refers to the positional relationship between the drill axis and the surface of the grinding wheel. The point angle is the half of the point angle 118 ° ± 2O, which is about 60 °. This position is very important because it directly affects the point angle, the shape of the main cutting edge and the bevel angle of the chisel edge. Students should be reminded to memorize the angle of 60 ° in a commonly used set square of 30 °, 60 ° and 90 °, which is easy for students to master. Pithy formula 1 and pithy formula 2 both refer to the relative position of the drill bit before sharpening. The two should be considered as a whole. Do not neglect to set the bevel angle in order to level the cutting edge, or neglect to level the cutting edge in order to set the oblique axis. These mistakes are often made in actual use. The drill bit is now in the correct position and ready to contact the grinding wheel. Pithy formula 3: "Grind the back from the blade to the back." This refers to the slow sharpening from the cutting edge of the drill bit along the entire back. This facilitates heat dissipation and sharpening. On the basis of stabilizing and consolidating the first and second pithy formulas, the drill bit can gently contact the grinding wheel at this time for a small amount of sharpening. When sharpening, observe the uniformity of sparks, adjust the pressure in time, and pay attention to the cooling of the drill bit. When you start sharpening again after cooling, you should continue to set the position of the first and second pithy formulas, which is often difficult to grasp at the beginning of learning, and often change the correctness of its position involuntarily. Pithy formula 4: "Swing up and down and don't warp your tail." This action is also very important in the process of drill sharpening. Some students often change "swinging up and down" into "rotating up and down" when sharpening,down the hole bit, which destroys the other main edge of the drill. At the same time, the tail of the drill bit should not be higher than the horizontal center line of the grinding wheel, otherwise the cutting edge will be blunt and can not be cut. Return to Sohu to see more Responsible Editor:. wt-dthtools.com | |
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