When reaming stainless steel, the frequently encountered problems are: the surface of the hole is easy to be grooved, the roughness is poor, the hole diameter is out of tolerance, it is flared, and the reamer is easy to wear. The machinability of different types of stainless steel is different, and the problems in reaming are different. For example, when reaming austenitic stainless steel such as 1Cr18Ni9Ti and concentrated nitric acid resistant stainless steel, the main problem is the wear of the reamer; while for 2Cr13, etc. When reaming martensitic stainless steel, it is not easy to ensure the roughness and dimensional accuracy of the reaming. In order to avoid these problems, you should pay attention to the following:
1. Reasonable selection of reamer and reaming amount is the key to ensure smooth reaming.
2. Improve the quality of the pre-processing process, and prevent the pre-processed holes from scratching, ellipse, polygon, taper or bell mouth, waist drum shape, axis line bending, deflection, etc.
3. Keep the hardness of the workpiece material moderate, especially for 2Cr13 martensitic stainless steel, the hardness after quenching and tempering is better than HRC28.
4. Install the reamer and the workpiece correctly. The reamer must be installed upright, and the axis of the reamer should be consistent with the axis of the pre-processed hole of the workpiece to ensure uniform cutting of the teeth.
5. Choosing a suitable cutting fluid can solve the problem of stainless steel chip adhesion and make it smoothly chip removal, thereby reducing the surface roughness of the hole and improving the durability of the tool. Generally, it is better to use vulcanized oil. If 10%-20% CCl4 is added to vulcanized oil or 20%-30% CCl4 is added to lard, it will have a significant effect on reducing surface roughness. As CCl4 is harmful to the human body, it is advisable to use a mixture of 85%～90% of sulfurized oil and 10%～15% of kerosene. When the diameter of the reamer is larger, the internal cooling method can be used.
6. Pay careful attention to the process of reaming, and strictly check the runout of the cutter teeth, which is the key to obtain uniform reaming. In the reaming process, pay attention to the shape of the chips. Due to the small reaming allowance, the chips are in the shape of a foil roll or a short spiral roll. If the size of the chips is different, some are broken and some are small, it means that the reaming is uneven. If the chips are spring-like, it means that the reaming allowance is too large. If the chips are needle-shaped or fragmented, the reamer has been blunt. It is also necessary to prevent clogging of chips, and to observe whether the cutter teeth have sticky chips to avoid excessive hole diameter. When a cemented carbide reamer is used to ream a hole, shrinkage of the hole will occur. In order to prevent the hole from being fuzzed when the tool is retracted, the entering angle can be increased to improve this situation.
Stainless steel drilling and chip breaking
Acid-resistant stainless steel has great plasticity and toughness. The main problem when drilling is that it is not easy to break chips, which affects the inflow of cutting fluid, the temperature in the cutting zone is high, the tool durability is low, and the productivity is low. When drilling, the cutting load is large, and the formation of chips consumes a lot of energy. In addition to the high temperature strength and hardness of this type of stainless steel, the drill chips are not easy to break when they are cut away; at the same time, the cold work hardening phenomenon is very serious, and the surface hardening It can reach more than 100%, and the thickness of the hardened layer can reach 0.1～0.2mm. The thermal conductivity of acid-resistant stainless steel is small, only 1/3 to 1/4 of carbon steel. The temperature in the cutting zone is very high. The strong affinity with other metals and the hard spots in the material increase the wear of the tool.
In order to solve the problem of chip breaking when drilling acid-resistant stainless steel, a new type of acid-resistant stainless steel chip-breaking group drill was developed. When drilling with it, the chip length of about 100mm is discharged from the hole in a "firework" shape, and the chip breaking effect is very ideal.
The key to producing this kind of chips during the drilling process is: first, make the chip splitting point in a critical chip splitting state; second, properly grind the drill tip height (h=0.05D～0.07D) and the arc radius (R= 0.2D); Third, the position of L1=1.7～3.3 mm should be selected appropriately, and the feed rate should be appropriately large and the cutting speed should be low, so that the chips can be broken in the state of oblique screwing.
When using acid-resistant stainless steel chip-breaking group drilling holes, a lower cutting speed and a larger feed rate should be selected, which is conducive to achieving chip breaking.