Twist drill processing precision hole operation skills

Controlled in the following aspects, the precision of the drill hole can be guaranteed.

1. Correctly sharpen the cutting angle and improve the surface roughness:

The drill bit has a similar similarity to the reamer. If there are two main cutting edges and minor cutting edges, the minor cutting edge is spiral, and there are edge belts and chamfers to increase the smoothness of the cutting. As long as the cutting angle and surface roughness of the drill bit are improved and improved with reference to the requirements of the hinge. Basically, it has the condition of a similar hinge, so it can expand the hole with higher precision. Grind out the second corner. According to the processing materials, generally 2 ≤ 75 °. The length of the new cutting edge is about 3 to 4 mm, and the joint between the cutting edge and the minor cutting edge is ground with a small rounded corner of 0.2 to 0.5 mm, and the sharp corners of the outer edge can be completely ground into a circular arc. Special attention: the two new cutting edges should be symmetrical, so that the combined cutting edge of coarse and fine machining can be formed, the cutting thickness and cutting deformation can be reduced, the light-removing ability can be improved, the heat-dissipating condition can be improved, and the surface roughness of the hole can be improved. Grind the secondary back corner. On a section of the edge close to the main cutting edge, the secondary back angle a01=6°~8° is ground, and the edge width is 0.1-0.2mm, and the grinding length is 4~5mm to reduce the friction on the hole wall. Improve the life of the drill bit. Grinding the negative edge of the blade. Generally, the blade inclination angle is l=-10°～-15°, so that the chips flow to the surface to be added to avoid scratching the hole wall, which is beneficial to increase the surface roughness of the hole. The back angle should not be too large, generally a = 6 ° ~ -10 °, in order to avoid vibration, increase stability, improve the accuracy of the hole. The front and back flank of the cutting edge are ground with whetstone to a roughness of Ra0.4.

2, determine the reasonable amount of cutting in the amount of cutting, the impact on the hole accuracy is the depth of cut and feed, the impact on the life of the drill is the cutting depth and cutting speed. For this purpose, the cutting depth, cutting speed and feed rate should be controlled separately. Cutting depth: It is not affected by the diameter of the machined hole. It will retain the cutting depth of 0.5~1mm before drilling the hole. The roughness is not more than Ra6.3 to avoid large cutting amount, reduce heat, avoid impact and vibration, and eliminate Cold work hardening to improve processing quality and extend bit life. Cutting speed: When drilling cast iron, the cutting speed is about v=20m/min. When drilling steel, the cutting speed is about v=10m/min. The conversion to the machine speed can be determined according to the diameter of the drill hole and the cutting speed of the corresponding material. N = 1000 V / (pD). Feeding amount: Try to use a motorized cutter f=0.1mm/r. However, small drills with a diameter of less than 5 mm can only be fed manually due to their weak strength.

3. Cooling lubricating fluid: Due to the precision machining of the fine hole system, the precision and surface roughness are high, and the cutting load is small, so the lubricating lubricating liquid mainly based on lubrication should be selected. A 10% to 20% aqueous solution of emulsified oil is used.

4. Other requirements:

If the drilling machine with higher precision is used, if the radial runout error of the drill spindle is large, the floating chuck can be used to clamp the drill. Use drill bits that are newer or have partial dimensional accuracy close to tolerance requirements. Because the drill bit will wear after repeated use, it will affect the aperture accuracy. The two cutting edges of the drill bit should be ground and symmetrical as much as possible. The axial swing of the two blades should be controlled within 0.05mm to make the load of the two blades uniform, so as to improve the cutting stability. The radial swing of the drill should be less than 0.03mm. Pre-drilling should prevent the formation of more chilled layers, which would increase the drilling load and wear the fine hole drill. There must be sufficient cooling lubricant in the drilling.

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Label: Twist drill processing precision hole operation skills

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