Fig.1 Effect of additive concentration in emulsion mist on roughness values ​​Ra(a) and Rq(b)
a=>Ra,b=>Rq,c=>Rz
Figure 2 Effect of cutting speed Vc on the surface roughness of the material when turning R35 steel (f=0.3 mm/min, P=5.5 m3/h, E=2.5 g/min)
Studies have shown that the minimum amount of lubrication and the addition of additives in turning operations can improve the surface quality over a wide range of cutting speeds. This is because the additive contains compounds that reduce the friction between the workpiece and the blade contact surface.
Emulsions are best used for cutting jobs with minimal lubrication because of their cooling characteristics and grease lubrication characteristics. Smoke-like medium is sucked into the cutting work area by compressed air, and the minimum amount of cooling lubrication (MMS) is increasingly used in the cutting process because it can achieve higher cutting speeds and longer Tool life. Avoid cooling lubricant overflow, can save a lot of cooling lubricant. The minimum amount of cooling lubricant introduced is less than 50 ml/h. Surface quality is the criterion for judging the standard of workpiece quality is the achievable surface quality of turning operations. The following research results are based on the turning of R35 carbon steel (PN-89/H-84023/07) (Figure 1). This steel has the following mechanical properties: hardness HRC125, breaking strength SK = 350 MPa, elongation limit s0.2 = 235 MPa, elongation dK = 25%. In order to carry out the test, the CU 502 turning device was used. The cutting tool is a turning tool with a CSDBM2020M12 shank and a SNUN120408 insert. The insert is made of P25 hard metal, the main knife kr=70°, the secondary knife k'r=20°, the cutting angle g=-8°, and the depth of cut 0.8 Mm. Use 4% Oportet RG-2 emulsion as a cooling lubricant. The additive for the cooling lubricant is an ethylene glycol and methanol-M based RC9601 hydrocarbon consisting of chlorine and sulfur. In order to generate emulsion smoke, a device which is connected to a compressor and sprays gas and emulsion through a nozzle is used. The working pressure is 0.2 MPa. The test was carried out at an incision depth ap=1 mm and under the following process parameters: feed f=0.1-0.5 mm/min, cutting speed vc=50-450 m/min, emulsion flow rate E=1.5-3.5 g/min, compression Air volume P = 4.5~6.5m3/h. Roughness is measured according to the ISO 3274:1997 and ISO 4287:1998 standards. The following roughness values ​​were tested: the arithmetic average Ra of the profile coordinates, the maximum profile height Rz, and the profile square average Rq. In the initial test, the optimal concentration of the additives RC9601 and methanol-M in the emulsion aerosol was determined. For this purpose, the average value of all parameters of the cutting operation was selected: vc=250 mm/min, f=0.3 mm/min, P=5.5 m3/h, E=2.5 g/min. After analyzing the test results, it was found that the roughness of Ra and Rq was minimized when the additive concentration reached 5%. The additive emulsion emulsion significantly reduces the variation between the roughness parameters shown in Figure 2 and the cutting speed. Over the entire range of cutting speeds, the minimum roughness value Ra can be obtained with an emulsion emulsion with additives. This is because additives contain friction-reducing compounds. When the cutting speed is Vc>400m/min, the parameters Ra are basically similar in all cooling modes. The value of the parameter Rz under the cooling of the emulsion mist containing the additive is larger than the value during the dry processing. Compared with the dry machining condition, the value of all roughness parameters will decrease by about 10% to 50% when the cutting speed is less than 200m/min. Cooling with compressed air will reduce the roughness. Comparison of the roughness parameters Ra and Rz after dry-running of R35 steels shown in Figs. 3 and 4 (Cooling: emulsion emulsion containing RC9601 additive and methanol-M). Emulsion sprays containing such additives can be suggested because the roughness Ra can thereby be improved to the greatest extent. Although a better Ra parameter value than dry processing was obtained in the case of an emulsion emulsion containing no additive, the degree of such improvement was extremely limited. When cooled with compressed air, the roughness parameters are reduced compared to dry machining. In the case of emulsion sprays containing additives and methanol-M, roughness parameter values ​​are reduced over a large range of feed and cutting speeds. When turning R35 steel, the smaller the cutting speed, the higher the degree of surface roughness improvement. However, for the roughness parameter Rz, the result obtained when turning with the emulsion mist plus methanol-M is inferior to the dry processing (when Vc=350 m/min). This is related to the fact that the lubricating film is generated on the contact surface between the chip and the blade due to the additive, thereby affecting the reduction of the blade surface.
Fig. 3 Degree of improvement of roughness Ra relative to dry machining in the case of turning R35 steel with emulsion mist plus methanol-M (E = 2.5 g/min, P = 5.5 m3/h)
Fig. 4 When the R35 steel is turned with an emulsion spray plus methanol-M, the roughness parameter Rz is improved relative to the dry process (E = 2.5 g/min, P = 5.5 m3/h) The improved surface quality test showed that when turning R35 steel, the minimum amount of lubricated turning operation can reduce the surface roughness value by 30% compared with the compressed air cooling and dry machining operations. In the case where the cutting speed is greater than 350 m/min, the values ​​of the parameters Rq and Rz when the emulsion mist cools are deteriorated with respect to the dry processing and the cooling of the compressed air. The addition of additives to emulsion sprays can significantly improve the surface roughness compared to other cooling methods. Roughness values ​​can be reduced by up to 50% over a wide range of cutting parameters. The optimum concentration of additive is 5%. The minimum value of surface roughness can be achieved at low speed cutting (<300 m/min).
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