Among the difficult-to-cut materials, some hardness may be as high as HRC60 or higher, and the tensile strength is about 3 times higher than that of 45 steel, resulting in a cutting force 200% to 250% higher than that of cutting 45 steel; some materials have thermal conductivity Only the thermal conductivity of steel No. 45 is 1/4 to 1/7 or lower, so that the heat in the cutting zone cannot be transmitted quickly, forming a high cutting temperature, which limits the increase of cutting speed; some materials have high temperature hardness and high strength. The cutting force and cutting temperature are high; some materials work hardening degree is 100%-200% higher than the hardness of the substrate, and the hardening depth is 0.1-0.3mm, which makes cutting difficult; some materials are chemically active, causing serious tool cutting. Bonding and diffusion wear; some materials have extremely small elastic modulus and elastic recovery and elongation, making it more difficult to cut. Therefore, in the cutting of various difficult-to-cut materials, according to the properties of the material to be cut, the cutting characteristics and the processing stage, the appropriate cutting fluid is selected to improve the machinability of the difficult-to-cut material, and achieve the purpose of processing.
Selection of cutting fluid for cutting difficult materials:
Commonly used cutting fluids are aqueous solutions, common emulsions, extreme pressure emulsions, mineral oils, composite (plant, mineral, animal) oils, extreme pressure cutting oils. Among them, the aqueous solution has the best cooling effect, and the extreme pressure cutting fluid has the best lubricating effect. The general cutting fluid loses its lubricating ability at around 200 °C, but the addition of extreme pressure additives (such as chlorinated paraffin, carbon tetrachloride, thiophosphate, zinc dialkyldithiophosphate, etc.) into the cutting fluid becomes The well-lubricated extreme pressure cutting fluid can be lubricated at a high temperature of 600 to 1000 ° C and a high pressure of 1470 to 1960 Mpa. Therefore, emulsions or cutting oils containing extreme pressure additives such as sulfur, phosphorus and chlorine are not only suitable for cooling and lubrication of carbon steel and alloy steel, but also suitable for cooling and lubrication during processing of difficult-to-cut materials. The following describes the selection of cutting fluids for the machining of several commonly used difficult-to-cut materials.
stainless steel. In roughing, 3% to 5% emulsion or 10% to 15% extreme pressure emulsion, extreme pressure cutting oil and sulfurized oil are used. In the finishing process, use extreme pressure cutting oil or 10% ~ 20% extreme pressure emulsion, sulfurized oil, sulfurized oil 80% ~ 85% + CCl4 15% ~ 20%, mineral oil 78% ~ 80% + black oil or Vegetable oil and lard 18% + sulfur 1.7%, mechanical oil 90% + CCl4 10%, kerosene 50% + oleic acid 25% + vegetable oil 25%. For broaching, tapping and reaming, use 15% to 20% extreme pressure emulsion or extreme pressure cutting oil, vulcanized soybean oil or vegetable oil; add CCl4 10% to 20% in sulfurized oil, add in lard 20% to 30% CCl4, 10% to 15% kerosene is added to the vulcanized oil for reaming. Add 1.5% to 20% CCl4 to the sulfurized oil or add mechanical oil from lead oil, or dilute chlorinated paraffin with kerosene, or use MoS2 grease for tapping. In the hobbing and gear shaping, 20% to 25% extreme pressure emulsion or extreme pressure cutting oil should be used. When drilling, use 10% to 15% emulsion or 10% to 15% extreme pressure emulsion, extreme pressure cutting oil.
Superalloy. In addition to using the same stainless steel cutting fluid, in the rough processing, use potassium sulfate 2% + potassium nitrite 1% + triethanolamine 7% + glycerol 7% ~ 10% + water balance or with glutamate 7% ~ 10 % + sodium nitrite 5% + triethanolamine 7% ~ 10% + boric acid 7% ~ 10% + glycerol 7% ~ 10% + water balance. For nickel-based superalloys, the use of sulfur-containing cutting fluids should be avoided to avoid stress corrosion and reduce the fatigue strength of the parts.
Titanium alloy. For roughing, 3% to 5% emulsion or 10% to 15% extreme pressure emulsion is used. For finishing, use extreme pressure cutting oil (sodium petroleum sulfonate 10% + oleic acid 3% + petroleum sulfonate lead 6% + triethanolamine 3.5% + chlorinated paraffin 4% + chlorinated stearic acid 3% + 20) Mechanical oil 70.5%), extreme pressure aqueous solution, CCl4+ equivalent amount of alcohol. For broaching, tapping and reaming, extreme pressure cutting oil, oleic acid, sulfurized oil, chlorinated oil, castor oil 60% + kerosene 40%. When broaching, polyether 30% + ester oil 30% + 7 mechanical oil 30% + rust inhibitor and anti-foaming agent 10% can also be used. When drilling, extreme pressure emulsion or cutting oil, sulfurized oil, and electrolytic cutting fluid are used.
High strength steel. In addition to the usual cutting fluids, extreme pressure cutting fluids should be used. Tapping with rapeseed oil or soybean oil is better. When processing molybdenum, use CCl4 plus 20# mechanical oil or MoS2 grease. When finishing pure iron, dilute castor oil with alcohol as a cutting agent. When processing soft rubber, use alcohol or distilled water as a cutting agent.
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