Twist drills are often used to drill holes in stainless steel workpieces. In the case of hardened stainless steel, cemented carbide drills can be used, and if conditions permit, cemented carbide or ultrafine cemented carbide drills can be used. When drilling, the torque and axial force are large, the chips are easy to combine, hard to break, and difficult to remove. Work hardening deteriorates, the corners of the bit are easily worn, and the rigidity of the bit is poor, so that vibration is likely to occur. Therefore, the drill bit is required to grind the chip groove, the cross edge to reduce the axial force, and the double top angle to improve the heat dissipation condition.
L≈0.32d 0, L / 2> L1> L / 3, R≈0.2d 0, h = 0.04d 0, b≈0.04d 0. When drilling 1Cr18Ni9Ti stainless steel with this drill bit, 20 mm, 25 mm and 35 mm diameters, 4 different supplies, d = 0.32 mm / r, 0.4 mm / r, 0.56 mm / for drills with r 0.67 mm / r is adopted. Crushing and removing chips is successful. Stainless steel debris crushing bits (Fig. 2), S-shaped carbide bits (Fig. 3), square belt bits (Fig. 4), and throw-away cemented carbide shallow hole drills can also be used. When machining martensitic stainless steel 2Crl3 using a stainless steel tip breaker bit (Fig. 2), simply grind the tip breaker with E-E. lCrl8Ni9Ti When drilling austenitic stainless steel, it is necessary to open the insert breaker with A-A. Table 1 shows the specific parameters of the stainless steel chip breaker bit and the applicable drilling amount.
The features of the S-shaped carbide drill are as follows. Without the chisel edge, the axial force can be reduced by 50%. The front corner of the core is positive and the edges are sharp. The thickness of the drill core increases and the rigidity of the drill increases. There are two cutting fluid holes. The arcuate cutting edge and chip grooves are reasonably distributed, facilitating chipping into small pieces for discharge.
The features of the carbide shallow hole drill with replaceable cutting edge are as follows. There are two convex triangular blades asymmetrically mounted on the front of the bit. Various parts of the cutting hole can be automatically centered, the hole has good straightness and the cut-in and cut-out lengths are short. The blade has multiple pit-shaped chip breakers on the rake face, which has good cutting performance, especially chip breakage is reliable and the chips are consistently crushed. Internal cooling allows the cutting fluid to be sprayed directly onto the perforated surface to improve the cooling effect, and the removal of chips is very smooth. In particular, different grades of carbide inserts can be used depending on the material of the workpiece, the cutting speed is 80-120 m / min and the drilling is very light.
When drilling stainless steel, it is often found that the drill bit is prone to wear, the surface of the hole is rough, and sometimes deep grooves are formed and cannot be removed. The opening is too large and the hole is not rounded or tilted to one side. Please note the following points when operating.
- 1. Sharpen the shape and make the two cutting edges symmetrical. If the angle of the drill is too large, the phenomenon of “piercing” will occur, chattering will occur, and the drill hole will become polygonal. The chisel edge should be polished to reduce the axial force of the borehole.
- 2. The bit must be attached to keep the drill sharp and should be ground in time after blunting.
- 3. Reasonable selection of bit shape and drilling amount. According to the drilling depth requirements, the length of the drill bit should be shortened and the thickness of the core should be increased to increase rigidity. When using a high speed steel drill bit, do not cut too fast to prevent the blade from burning out. Make sure that the feed amount is not too large. It is necessary to adjust the feed amount at the time of cutting appropriately in order to prevent the deterioration of the drill bit and the displacement of the drill hole.
- 4.Well cooled and lubricated, the cutting fluid is generally suitable for vulcanizing oil, the flow rate should not be more than 5-8 L / min, the cooling cannot be stopped prematurely. If the diameter is large, it is necessary to use the internal cooling method as much as possible.
- 5. Pay close attention to the drilling process and observe the chip evacuation condition in time. If you find that the chips are messed up, immediately retract the knife to prevent the chips from getting clogged. You also need to pay attention to the sound of the machine tool. If anomalies are found, the tool should be retracted in time and the drill bit should not be allowed to stay on the drilled surface to prevent increased surface hardening of the drilled surface.