Factors affecting the accuracy of the machined hole during drilling:
①The clamping accuracy and cutting conditions of the drill bit, such as tool holder, cutting speed, feed rate, cutting fluid, etc.;
②The size and shape of the drill bit, such as the length of the drill bit, the shape of the blade, the shape of the drill core, etc.;
③The shape of the workpiece, such as the shape of the side of the orifice, the shape of the orifice, the thickness, the state of the card, etc.
The reaming is caused by the oscillation of the drill bit during processing. The swing of the tool holder has a great influence on the hole diameter and the positioning accuracy of the hole, so when the tool holder is seriously worn, a new tool holder should be replaced in time. When drilling small holes, it is difficult to measure and adjust the swing, so it is best to use a thick-shank small-diameter drill with a good coaxiality between the blade and the shank. When machining with a regrind drill, the reason for the decrease in hole accuracy is mostly due to the asymmetry of the back shape. Controlling the edge height difference can effectively restrain the cutting and expanding of the hole.
2. The roundness of the hole
Due to the vibration of the drill bit, the drilled hole pattern is easy to be polygonal, and there are lines on the hole wall like a double line. Common polygon holes are mostly triangles or pentagons. The reason for the triangular hole is that the drill has two centers of rotation when drilling, and they vibrate at a frequency of every 600 exchanges. The main reason for the vibration is the unbalanced cutting resistance. Well, the resistance is unbalanced during the second turn of cutting, and the last vibration is repeated again, but the vibration phase is shifted to a certain extent, resulting in the appearance of double-line lines on the hole wall. When the drilling depth reaches a certain level, the friction between the edge surface of the drill bit and the hole wall increases, the vibration is attenuated, the reciprocating line disappears, and the roundness becomes better. This hole type is funnel-shaped when viewed from the longitudinal section. For the same reason, pentagonal and heptagonal holes may also appear in cutting. In order to eliminate this phenomenon, in addition to controlling the vibration of the chuck, the height difference of the cutting edge, and the asymmetry of the shape of the back and the blade, it is also necessary to improve the rigidity of the drill bit, increase the feed per revolution, reduce the clearance angle, and regrind. Chiseling and other measures.
3. Drill holes on inclined and curved surfaces
When the cutting surface or drilling surface of the drill bit is an inclined surface, a curved surface or a step, the positioning accuracy is poor. Because the drill bit is a radial one-sided cutting surface at this time, the tool life is reduced.
To improve the positioning accuracy, the following measures can be taken:
1) Drill the center hole first;
2) Mill the hole seat with an end mill;
3) Choose a drill with good penetration and rigidity;
4) Decrease the feed rate.
4. Treatment of burrs
During drilling, burrs will appear at the entrance and exit of the hole, especially when machining tough materials and thin plates. The reason is that when the drill bit is about to drill through, the material to be processed is plastically deformed. At this time, the triangular part that should be cut by the edge of the drill bit near the outer edge is deformed and bent to the outside under the action of the axial cutting force, and is at the outer edge of the drill bit. Under the action of the chamfer and the edge of the land, it is further curled to form a curl or a burr.
Post time: Jan-20-2022