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Operating skills of fried dough twist drill machining fine holes

operating skills of fried dough twist drill machining fine holes:

when machining some high-precision holes on mechanical parts, you can use fried dough twist drill reaming to replace reaming, especially when machining non-standard fine holes, it is more convenient to operate and can adapt to the processing of various metal materials. Fried dough twist drill reaming is a kind of precision hole drilling operation, which is based on the existing hole and then reamed by the ground drill, which is called drilling precision hole for short. Its accuracy reaches H7 and surface roughness reaches Ra0.8. Generally, the accuracy of the drilled hole is low due to the operator's improper operation. After years of practice, the author believes that the following aspects should be controlled. The accuracy of precision drilling will be guaranteed

1. The jaw is slipping. Confirm the grinding cutting angle and improve the surface roughness:

compared with reamer, there are similarities between drill and reamer. If there are two main cutting edges and auxiliary cutting edges, the auxiliary cutting edge is spiral shaped, with edge bands and chamfering, which can increase the stability of cutting. As long as the cutting angle and surface roughness of the drill are improved according to the requirements of the reaming edge. Basically, it has the conditions similar to reaming edge, so it can expand the hole with high precision. Grind out the second vertex angle (2? 2). According to the different processing materials? 2≤75°。 Example: when processing cast iron, 2? 2=75 °, when processing steel, 2? 2=50°。 The length of the new cutting edge is about 3 ~ 4mm, and the joint between it and the auxiliary cutting edge is grinded off with an oilstone with a small fillet of 0.2 ~ 0.5mm, or all the sharp corners of the outer edge can be grinded into a circular edge. Special attention: the two new cutting edges should be symmetrical, so that a joint cutting edge of rough and finish machining can be formed, which can reduce the cutting thickness and cutting deformation, improve the polishing ability, improve the heat dissipation conditions, and improve the surface roughness of the hole. Grind out the auxiliary rear corner. On a section of edge close to the main cutting edge, grind the auxiliary back angle a01=6 ° ~ 8 °, and keep the edge width of 0.1 ~ 0.2mm and the grinding length of 4 ~ 5mm, so as to reduce the friction on the hole wall and improve the service life of the drill bit. Grind out negative blade inclination. Generally, the inclination angle of the blade is l=-10 ° ~ -15 °, so that the chips flow to the lower surface to be added to avoid scratching the hole wall, which is conducive to improving the surface roughness of the hole. The back angle should not be too large, generally a=6 ° ~ -10 °, so as to avoid vibration, increase stability and improve the accuracy of the hole. The oilstone used for the front and rear flanks of the cutting edge provides new development opportunities for other industrial fields to grind, making its roughness reach Ra0.4

2. Determine the reasonable cutting parameters. Among the cutting parameters, the cutting depth and feed rate have a greater impact on the hole accuracy, and the cutting depth and cutting speed have a greater impact on the service life of the drill bit. Therefore, the cutting depth, cutting speed and feed rate should be controlled respectively. Cutting depth: it is not affected by the diameter of the machined hole. The cutting depth of 0.5 ~ 1mm shall be reserved before drilling the precision hole, and the roughness shall not be greater than RA 6.3, so as to avoid large cutting volume, reduce heat, avoid impact and vibration, eliminate cold work hardening, improve machining quality and prolong the service life of the drill head. Cutting speed: when drilling cast iron, the cutting speed v=20m/min. When drilling steel, the cutting speed is about v=10m/min. Converted into machine speed, it can be determined according to the diameter of the drilled hole and the cutting speed of the corresponding material. N=1000V/(pD)。 Feed rate: try to use motorized tool walking f = 0 About 1 mm/R. However, small drill bits with a diameter less than 5mm can only be fed manually due to their weak strength. Valve

3. Cooling lubricant: because this series of models are mainly suitable for the precision machining of non-metallic and metal material experimental hole system with experimental load less than 10kN, its precision and surface roughness are high, and the cutting load is small, so the cooling lubricant mainly based on lubrication should be selected. Use 10% - 20% emulsified oil-water solution

4. Other requirements:

select a drilling machine with high precision. If the radial circular runout error of the main shaft of the drilling machine is large, the floating chuck can be used to clamp the drill bit for processing. Use a bit that is newer or whose dimensional accuracy of each part is close to the tolerance requirements. Because the drill bit will wear after repeated use, which will affect the accuracy of hole diameter. The two cutting edges of the drill should be polished symmetrically as much as possible, and the axial runout of the two edges should be controlled within 0 As an emerging industry, the load on both edges should be uniform within 05mm to improve the cutting stability. The radial runout of the drill bit should be less than 0.03mm. Pre drilling should be prevented from producing more cold hard layers, otherwise it will increase the drilling load and wear the fine hole drill bit. There should be sufficient cooling and lubricating fluid during drilling

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