Aluminum and its alloys are widely used in various industrial sectors, especially in the aviation field, because of their low density and certain mechanical properties, energy and good electrical conductivity, thermal conductivity and corrosion resistance. But in the drilling process, aluminum alloy has a lot of processing problems. Aluminum alloy according to different manufacturing methods, divided into casting and deformation (can be rolled) two categories. Deformable aluminum alloy is mostly used to manufacture stretched parts, rivets, plates, profiles, etc. In the processing of this kind of parts, the processing of holes is rare, and we will not consider it for the time being. And casting aluminum alloy, relatively speaking, there are many kinds, the most basic is the aluminum silicon alloy is silicon aluminum.

01 Compared with steel and brass, the characteristics of aluminum alloy:

One is the material soft, poor rigidity

Second, the elastic modulus is low.

These two factors significantly affect the machinability of aluminum alloys. Therefore, when machining aluminum alloy workpieces, the workpiece must be fully clamped and supported, and the tool must be kept sharp. Otherwise, the workpiece tends to leave the cutting tool. Sometimes irregular groove marks and bright extrusion spots appear on the surface of the workpiece, one may be caused by abnormal pressure of the tool on the workpiece, and the other may be caused by vibration due to unstable clamping. When the tool rubs on the surface of the workpiece in a gap, extrusion phenomenon and powder cutting occur, and then when the gap or elasticity disappears, the tool bites into the surface of the workpiece, chew out the groove marks. Therefore, in the process of drilling, we should also pay attention to the cutting points of aluminum alloy, and reasonably select the cutting method of aluminum alloy.

02 choose aluminum alloy group drill:

In the drilling process, the standard group drill due to the outer edge angle (2Φ), the inner edge angle (2Φ ') is relatively large, the relief angle (α) is small, the rear face and the cutting surface friction is serious, resulting in a large amount of cutting heat, cutting temperature rise quickly; the rake angle of the inner edge is negative, the work is completely in the extrusion cutting state, the local temperature is high, and the material melting phenomenon is serious. Improvement of geometric parameters and shapes of special group drills for aluminum alloy. After long-term practice, we have improved the geometric parameters and shape of the standard group drill, sharpened it into a special drill for aluminum alloy, and reduced the external edge angle of the original 140 ° to 105 ° ~ 110 °, thus reducing the axial force, increasing the tool tip angle, improving the heat dissipation conditions, aggravating the chip deformation and forming a strip chip. Increase the rear angle, the rear angle α from the original 13 ° ~ 14 ° to 22 ° ~ 23 °, thus reducing the generation of cutting heat, so that the deposition phenomenon is reduced, while the larger rear angle, but also the main cutting edge more sharp, easy to cut into the material, the formation of thick chips, easy to discharge. Changing the original inner edge rake angle of -10 ° to a positive value or close to a positive value can well reduce the cutting resistance and improve the inner edge cutting body. Changing the original bilateral arc groove to a unilateral arc groove can reduce the cutting resistance and increase the chip thickness without causing vibration under the condition of low hardness of aluminum alloy. The chisel edge along the back side of the edge to grind more to increase the chip space.

(2) grinding method of aluminum alloy group drill. Prepare to use A46 ~ 60K, L type grinding wheel, grinding wheel grinding smooth, the outer suburbs of the grinding wheel shall not be greater than the arc radius of the drill bit. When sharpening the straight edge, the cutting edge of the drill bit is aligned with the plane of the grinding wheel, the angle of the peak angle of the cutting chip to the left of the axis of the drill bit is ground from the cutting edge to the rear cutter surface, and the drill shank is swung up and down. The whole process should have a fulcrum, and the tail swing of the drill bit should not be higher than the horizontal plane. When grinding the crescent groove, the main cutting edge of the drill bit contacts the edge corner of the grinding wheel, the cutting edge cannot be warped up, the shank of the drill bit presses down on the grinding flank, the included angle between the grinding wheel and the drill shaft is 55 degrees, and the drill bit is flat and cannot swing up and down. When sharpening the chisel edge, the axis of the drill bit is inclined to the left by 15 °, the tail of the drill bit is pressed down by 55 °, and the outer edge and the side of the grinding wheel form an included angle. Pay attention to cooling the drill bit in time to avoid annealing the drill core. Finally, sharpen the inner groove of the drill bit and use a flake grinding wheel or a small grinding wheel. At this time, pay attention to the angle of the rear angle to avoid the space position of the flank surface higher than the arc cutting edge.

03 cutting edge of the cutting light:

In order to reduce the occurrence of chip accumulation, especially to prevent the residual marks from adhering to the front surface when the chip accumulation disappears, the rake surface (spiral groove) and flank surface of the cutting edge of the drill should be polished to more than 0.8μm with oilstone. It is best to choose a drill with polished edge groove.

04 Select the appropriate amount of cutting

Limit speed, large feed, is the purpose of cutting aluminum alloy drilling. High speed can provide greater centrifugal force, making the chips in the spiral groove more easily present jet-like discharge, but also can shorten the chip on the cutting edge of the unit residence time, reduce the possibility of bonding. The larger the amount of feed, can reduce the amount of cutting heat generated within the unit cutting.

05 Fully clamp and support the workpiece

When machining aluminum alloy workpieces, the workpiece must be fully clamped and supported, and the tool must be kept sharp. Otherwise, the workpiece tends to leave the cutting tool. Sometimes irregular groove marks and bright extrusion spots appear on the surface of the workpiece. One possibility is caused by the abnormal pressure of the tool on the workpiece, and the other is that when the vibration is caused by the unstable clamping, the tool rubs on the surface of the workpiece in a gap type, causing extrusion and powder cutting. Then, when the gap or elasticity disappears, the tool bites into the surface of the workpiece, chew out the groove marks.

06 Select a reasonable process

In order to obtain a smooth surface of the workpiece, the combination of drilling first and then reaming is used as much as possible, because all kinds of qualified aluminum alloy workpiece blanks will always have some oxide layer, which will aggravate the wear of the drill bit.

07 Select the matching cutting fluid

The choice of aluminum alloy cutting fluid is very important. It must ensure good lubricity, cooling, filterability and rust resistance. Therefore, the cutting fluid that can be used for aluminum alloy processing is different from ordinary cutting fluids. When drilling, due to high-speed processing, a large amount of heat can be generated. If the generated heat cannot be taken away by the cutting fluid in time, sticking will occur, and serious chip accumulation will occur, which will seriously affect the machining roughness of the workpiece and the service life of the tool. At the same time, the heat can also deform the workpiece, seriously affecting the accuracy of the workpiece. Therefore, the choice of cutting fluid should not only take into account its own lubricity, but also its cooling performance. For finishing, it is advisable to choose emulsified anti-friction cutting fluid or low viscosity cutting oil; for semi-finishing and roughing, you can choose a low concentration of emulsified anti-friction cutting fluid, or semi-synthetic anti-friction cutting fluid, etc. Cutting fluid with good cooling performance.