Oblique hole drilling technology and improvement scheme of fried dough twist drill structure

1. Questions raised

In processing the main part of a military product – fixed plate (material 45 steel, overall dimension 1005) × seven thousand × A total of 1071 pieces need to be drilled at 20mm) φ 24mm 30 ° inclined hole, and the surface roughness of the hole wall is required to reach RA6 three μ m。 When drilling, the thickness of the workpiece is greater than the nominal size by 3mm (reserved as finish planing allowance). When the standard fried dough twist drill is used to drill the fixed plate on the z3550 universal radial drilling machine, the following process problems occur:

1) When drilling a 30 ° inclined hole with a standard fried dough twist bit, due to the small included angle between the bit and the workpiece, in order to ensure the processing length, it is necessary to lengthen the drill pipe and bit, so as to reduce the rigidity of the bit. In addition, when drilling inclined holes, the drill bit is in intermittent cutting state for a long time and has great radial resistance. In order to avoid edge collapse 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 stably reach RA6 three μ M surface roughness requirements. However, when drilling 30 ° inclined holes, due to the influence of intermittent cutting and radial resistance, the drill bit always vibrates in the drilling process. Although the use of drill sleeve guidance can partially reduce the radial resistance, the vibration will still accelerate the wear of the drill bit, resulting in the collapse of the outer edge of the drill bit, which seriously affects the normal progress of drilling processing and drilling quality.

In order to solve the above problems, the oblique hole drilling technology and the structure of the standard fried dough twist drill for machining are improved.

2. Improvement of drilling technology

1) . change the oblique hole drilling process from direct drilling to reaming after drilling, that is φ Add another one in the 24mm drill sleeve φ 21mm drill sleeve, first use φ Drill with a 21mm drill bit and then use it again φ Reaming with 24mm drill bit.

2) In order to ensure the dimensional accuracy of the fixed plate hole spacing and improve the stability of the initial stage of bit drilling, a special oblique hole drilling die is designed.

3) In order to eliminate the radial resistance generated by the side tip of the bit at the moment when it just penetrates 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, the long edge fried dough twist drill with thickened drill core and parabolic cutting edge groove is selected, and the drill tip of the drill is machined to ensure that the angles of the two cutting edges are symmetrical and the cutting edges are stressed evenly.

5) Grinding of drill angle: for drilling φ 21mm drill bit. At the beginning of drilling inclined hole, the drill bit is in intermittent cutting state, and the cutting area is from small to large until it enters continuous cutting state. The machining length at this stage is 48mm. 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 radial resistance. In order to reduce the friction, the φ The geometric angle of the drill tip of 21mm drill bit is grinded into group drill type.

As the change of the sharp angle (main deflection angle) of the bit will change the size ratio of the radial cutting force py to 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 two sharp angles when grinding the bit. At the same time, the cross edge of the drill tip is ground narrow to reduce the axial cutting force; The arc edge is ground low and the arc bottom is close to the side edge of the drill bit, so as to narrow the width of the outer straight edge and reduce the axial height between a and B, so as to increase the annular reinforcement and enhance the centering effect of the side tip of the drill bit, so as to improve the cutting stability. In this way, when the drilling length exceeds a and B, the radial cutting force near the drill tip is opposite to and less than the radial component of the outer straight edge.

3. Improved processing effect

After the geometric angle of the bit is determined, the reasonable cutting parameters are selected through the cutting test (rotating speed n = 160r / min, feed rate f = 0.08 ~ 0.10mm / R). After the inclined hole on the fixed plate is drilled, it needs to be grinded manually 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 ra6.5mm three μ m。 After processing, it is found that the hole wall bus at the drill opening of individual holes is not straight. After analysis, this is due to the inaccurate alignment between the machine tool guide rail, the machine tool spindle angle and the drill template, resulting in the inconsistency between the feed direction of the drill bit and the inner hole axis of the drill sleeve on the drill template. In order to solve this problem, each processing machine tool is equipped with an alignment mandrel. After each hole is drilled, move the head of the machine, insert the alignment mandrel installed in the spindle hole of the machine tool into the drilling sleeve of the drilling template, adjust the spindle position of the machine tool, so that the mandrel can rotate freely in the drilling sleeve, and then take out the mandrel and install the drill bit for drilling.

Through production verification, when the improved drilling process and fried dough twist drill are used to process 30 ° inclined 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.