Question raising
Fixed plate (material: 45 steel, overall dimension: 1005 × seven thousand × 20mm), a total of 1071 pieces need to be drilled φ 24mm 30 ° inclined hole, and the surface roughness of the hole wall is required to reach Ra6.3 μ m。 When drilling, the thickness of the workpiece is 3mm greater than the nominal size (reserved as fine planning allowance). When the standard fried dough twist drill is used to drill the fixed plate on the z3550 universal rocker drilling machine, the following process problems occur:
1) When drilling a 30 ° oblique hole with a standard fried dough twist drill bit, the included angle between the drill bit and the workpiece is small. In order to ensure the processing length, it is necessary to lengthen the drill rod and drill bit, thus reducing the rigidity of the drill bit. In addition, when drilling inclined holes, the drill bit is in intermittent cutting state for quite a long time and has a large radial resistance. In order to avoid blade breakage and ensure normal processing, the cutting amount must be reduced, which directly affects the processing efficiency and production progress.
2) When drilling straight holes, the drilling and expanding process can be used to reach Ra6.3 μ M surface roughness requirements. However, when drilling 30 ° inclined holes, due to intermittent cutting and radial resistance, the drill bit always has vibration in the drilling process. Although the radial resistance can be partially reduced by using the drill sleeve guidance, the vibration will still accelerate the wear of the drill bit, causing the external edge of the drill bit to break, which seriously affects the normal drilling and drilling quality.
In order to solve the above problems, the oblique hole drilling technology and the standard fried dough twist drill structure used for processing were improved.
2. Improvement of drilling technology
1) . Change the drilling process of inclined hole from direct drilling to reaming after drilling, i.e φ One more in 24mm drill sleeve φ 21mm drill sleeve, first use φ Drill holes with a 21mm drill bit and then use φ Reaming with 24mm drill.
2) In order to ensure the dimensional accuracy of the fixed plate hole spacing and improve the stability of the drill at the beginning of drilling, a special oblique hole drilling die is designed.
3) In order to eliminate the radial resistance generated by the drill tip at the moment of just drilling through the workpiece, a layer of A3 material process plate is set under the workpiece during drilling.
4) Selection of drill type: in order to improve the rigidity and drilling accuracy of the drill bit, the long edge fried dough twist drill bit with thickened core and parabolic cutting edge groove is selected, and the drill tip of the drill bit is ground by machine to ensure that the angles of the two edges are symmetrical and the cutting edges are evenly stressed.
5) Grinding of bit angle: for drilling φ 21mm drill bit. At the beginning of drilling inclined holes, the drill bit is in intermittent cutting state, and the cutting area is from small to large to continuous cutting state. The processing length at this stage is 48 mm. In the intermittent cutting stage, the friction between the edge of the drill bit and the inner wall of the drill sleeve is large under the action of the radial resistance. To reduce the friction φ The geometric angle of the 21mm drill point is grinded into the group drill type.
Because the change of the bit sharp angle (main deflection angle) will change the size ratio of the radial cutting force Py and the axial cutting force (cutting force) Px, that is, the radial cutting force Py will decrease with the increase of the sharp angle, so it is necessary to increase the two sharp angles when grinding the bit. At the same time, the transverse edge of the drill point is sharpened to reduce the axial cutting force; Grind the arc edge low, and the arc bottom is close to the side edge of the drill bit to narrow the width of the external straight edge, reduce the axial height between A and B, so as to increase the annular rib, enhance the centering effect of the drill bit side tip, and achieve the purpose of improving the cutting stability. In this way, when the drilling length exceeds A and B, the radial cutting force near the drill point is opposite to and smaller than the radial component of the external straight edge.
3. Improved processing effect
After the geometric angle of the drill bit is determined, the reasonable cutting parameters (rotating speed n=160r/min, feed rate f=0.08~0.10mm/r) are selected through the cutting test. After the oblique hole on the fixed plate is drilled, it needs to be manually grinded with a grinding wheel (the diameter after grinding is φ 24 ～ 24.5mm), and then polish with emery cloth to make the surface roughness of each hole basically reach Ra6.3 μ m。 After processing, it is found that the generatrix of the hole wall at the drill opening of some holes is not straight. Through analysis, this is because the misalignment between the guide rail of the machine tool, the angle of the machine tool spindle and the drill template results in the inconsistent feed direction of the drill bit and the axis of the inner hole of the drill sleeve on the drill template. To solve this problem, each machine tool is equipped with a aligning mandrel. After each hole is drilled, move the position of the head of the machine, insert the aligning mandrel installed in the spindle hole of the machine tool into the drill sleeve of the drill template, adjust the position of the spindle of the machine tool, so that the spindle can rotate freely in the drill sleeve, and then take out the spindle and install the drill to drill.
Through production verification, when using the improved drilling technology and fried dough twist drill to process 30 ° oblique holes of fixed plate parts, the processing effect is good, and the drilling quality and processing efficiency are significantly improved. Each shift can drill 30 ~ 35 holes.
