Drilling is one of the most important processes in metal cutting. Normal twist drills greatly limit the drilling efficiency due to the defects of the original structure. China's group drilling is one of the world's well-recognized drills with excellent performance. However, the group drill has a complex structure and is difficult to sharpen and is not widely used in production. In recent years, a series of advanced drills and sharpeners have been developed at home and abroad, which can sharpen some advanced drills and group drills. However, these sharpeners are complex and expensive, and most manufacturers are unacceptable. In the early 1990s, Nishiki Corporation developed a new type of drill and developed a corresponding sharpening machine, quickly gaining market recognition. Fine hole drill bit is not as good as our country's group drill, but because of its simple structure and low price, sharp hole drill bit can be used in production very quickly. Therefore, it is of great significance to develop efficient new drills and to develop sharp grinding machines that are easy to operate and inexpensive. 1 New-type drills proposed to increase drilling efficiency. However, the analysis found that the group drill still has certain disadvantages: 1) It is difficult to achieve complete symmetry of the left and right cutting edges during sharpening, so that a large radial force will be generated in the drilling process, the wear of the drill bit is accelerated, and the aperture is enlarged. 2) The chips of the group drill are divided into two in width, the speed difference between the outer end and the inner end of the chip is still large, and the additional deformation during cutting is still large; 3) the structure is complex and the grinding is difficult.
(a) Small and medium diameter drills (5<Ø<20)
(b) Large diameter drill Ø>20)
Fig. 1 New Drill Tips We have optimized a standard drill and have obtained a new drill type. The new cutting bit has the same cutting edge grinding method as that of the group drill. At the same time, we adopt a better chip separation method, which makes the new drilling type drilling performance better than that of the group drill, and simplifies the structure, so that sharpening is convenient, in which the small diameter (5<Ø<20) The structure of the drill is shown in Figure 1(a). The circular arc edge on the left side of the bit is shorter, about 1/3 of the length of the entire cutting edge, and the outer edge is longer, about 2/3 of the length of the entire cutting edge; the right circular arc edge is longer and is about the entire length of the cutting edge. 2/3, the outer blade is shorter, about 1/3 of the length of the entire cutting edge; while the left outer edge is lower than the right outer edge (height difference should be greater than the drilling feed f, the dotted line in the figure is the right edge (Higher part); Simultaneously simplifying the flank and replacing the helicoid with a plane. The structure of the large diameter drill bit (Ø>20) is shown in Fig. 1(b). The left circular arc edge is approximately 1/5 of the entire length of the cutting edge, and the outer edge is approximately 4/5 of the entire length of the cutting edge; The circular-arc edge is about 2/5 of the length of the entire cutting edge, the outer edge is about 3/5 of the length of the entire cutting edge, and the outer edge of the upper and lower side is opened with a swarf, and the width is about the entire length of the cutting edge. 1/5 of the depth is greater than the amount of feed. During this drilling process, cutting forces are symmetrically distributed throughout the drilling process. When the drill bit first touches the workpiece, the shortened chisel edge plays a good centering role; afterwards, the symmetrical circular-arc cutting edge starts to cut into the workpiece, and the cutting width is reduced due to the shorter circular arc edge; when the two sides of the drill bit touch the workpiece The outer edge begins to participate in cutting. The right outer edge of the bit is higher than the left outer edge, and the left outer edge is longer than the right outer edge. When drilling, the right outer edge cuts only the outer circle, and the left outer edge cuts only the middle one. ring. It can be seen that the special structure of the drill ensures a symmetrical distribution of cutting forces on the cutting edge. For large diameter drills, the chips are divided into five sections in the direction of the main cutting edge, which reduces the cutting distortion better. The other properties are the same as those of small and medium-diameter drills. The new drilling model has the following main advantages: 1) The chip is divided into three or five segments in the direction of the width of the main cutting edge. The cutting speed difference between the outer and inner ends of each cutting edge is significantly reduced, reducing the cutting torque and reducing the drill bit. Wear and additional deformation of the chip; 2) The chip is thick and narrow in the outer edge of the tape, and the chip is easy to remove. After the arc edge is shortened, the amount of curled chip is reduced, reducing the risk of chip jamming, so the chip is removed. The situation is better than the standard group drill; 3) If the cutting edges on the two sides have a slight height error, it will not cause changes in the cutting load on both sides and affect the radial force changes, but there is a radial force at the moment of drilling, and Radial force is balanced during drilling, which is unmatched by other drills; 4) Sharpening is easy.
Figure 2 grinding adjustment schematic
2 Grinding of new types of drills This type of drill requires grinding, cutting, arcing, chisel, and flank. To complete the grinding of a drill bit, the center height of the grinding wheel must have three height changes relative to the center of the drill bit to ensure that a certain relief angle is worn. When sharpening, the spiral flank of the drill is simplified as a plane, which can facilitate sharpening. The principle of adjustment in the grinding process is shown in Figure 2. The knife is set so that the cutting edge is horizontal, and the outer cutting edge and the circular cutting edge are ground. Adjust the wheel height to ensure that the first rear angle b1=12°, a1=b1, then the center of the grinding wheel is higher than the center of the drill bit H1 H1=Rsina1 (1)
R is the radius of the grinding wheel. Afterwards, one side of the edge is ground by the X and Y feeds. Then the drill is rotated 180° around the straight line, and then the other side of the drill is sharpened. Trim the secondary flank to ensure that the second relief angle b2 is 20°. This is to reduce the flank and avoid the flank face from cutting while drilling, and at the same time ensure the strength of the drill. A2=b2=20°, the wheel needs to be raised H2 H2=Rsin20°+B-H1 (2)
B is the width of the first flank after grinding, which is about 3mm. Trim the chisel edge and raise the grindstone again so that the a3 equals 55°. Then the grindstone needs to be raised again. H3 H3 = Rsin55°-H2-H1 (3) Increase the inner edge rake angle as much as possible while ensuring the strength of the chisel edge. , It helps to reduce the axial force. A3 taking 55° is the result of a comprehensive consideration of these two aspects.
Figure 3 Schematic diagram of the drill grinding machine
3 The development of the sharpening machine theoretically speaking, the space six coordinate movements can realize any spatial movement, thus can finish the spatial arbitrary shape surface processing. How to select the six coordinates is an important consideration in the design of machine tools. The sharpener structure we have developed is shown in Fig. 3. This sharpening machine can realize the above grinding process. The movement in the X and Y directions is to achieve the X, Y direction of the feed movement, so that the cutting point of the grinding wheel relative to the cutting edge of the drill bit to form the desired movement trajectory; a is the rotational movement of the drill around its own axis, with 180 ° indexing and positioning functions, thus achieving symmetrical cutting and grinding of the cutting edge around the drill bit, at the same time, the drill bit can be rotated and positioned freely in the direction of its own axis to complete the cutting edge of the knife and realize the grinding of different back angles. The drill bit axis and the X axis form an angle of 30° to ensure that the cutting edge of the drill bit moves in the horizontal direction (Y axis), forming a 120° front angle of the drill bit; b is the rotation of the fixture around the Z axis, and different angles can be repaired. Grinding; Z' direction of movement has three fixed positions, through the handle to achieve, the handle and the wheel head frame around the fixed fulcrum rotation, the grinding wheel relative to the height of the drill bit will change, so as to achieve the first flank of the drill bit, two The grinding of the secondary flank and chisel edge forms the main posterior, posterior posterior, and transverse cusp. This adjustment method is simple in structure, convenient in operation, and accurate in accuracy. Only three simple movements of the handle are required to perform the complicated adjustment and positioning motion of the grinding wheel. For the wear of the grinding wheel or the drill of different diameters, the grinding wheel can also be accurately positioned through the fine adjustment device to ensure the angle of the drill. This sharpening machine has the following advantages: It can easily grind a new type of drill bit shape, stable grinding quality and good consistency; Simple structure, because the complex spiral movement is transformed into a simple linear motion, so the machine structure is greatly simplified, Reduced cost; Machine tool adjustment is simple and convenient, operation saves time and effort, and with special fixtures, can quickly complete the drill bit part of the grinding; The wheel contour correction is very convenient, the operation is very simple. 4 Conclusions The new drill bit is less difficult to shave than the standard drill, and the drilling performance is significantly improved. The new type of drill bit will better solve the regrind problem of a large number of dulled drill bits existing in the company, and it can realize mechanized sharpening. The regrind time is greatly shortened, and the durability and drilling efficiency are significantly improved. Tests have proved that, under the same conditions, the new drill has a 8.3% to 19.4% reduction in axial resistance when drilling, and a reduction in drilling torque of 2.6% to 21.7% compared to the basic drill. The sharpening machine has simple structure, convenient operation and low cost, which can guarantee the promotion of new drilling type, which is bound to promote the mechanical industry in our country.
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