The effect of the coldest air cutting on the machi

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The effect of cold air cutting on the machined surface of stainless steel

stainless steel materials are widely used in medical devices, building materials, automobile parts and household appliances. However, due to the poor machinability of stainless steel, it is called difficult to cut material. When the cutting conditions are set improperly and the rigidity of the working machinery is not good, stainless steel will show surprisingly difficult to cut. In addition, the traditional cutting method is adopted, and the cutting fluid is used in the cutting process to achieve the purpose of cooling, lubrication and chip discharge. There are two kinds of cutting fluids, one is water-insoluble mineral cutting fluid, the other is water-soluble cutting fluid, also known as emulsion. The latter has good cooling performance and low price, and is widely used in production and processing. However, due to its poor lubrication performance, additives are often used to improve the lubrication performance in use. Most of the additives currently used contain harmful components such as sulfur, phosphorus and chlorine. These harmful components volatilize into the air during the cutting process, which will bring great harm to the health of operators. The stainless steel used in the test is the part of the hard disk drive motor in the computer. After investigating the traditional cutting methods, the machining method of cooling with cold air and lubricating with a small amount of vegetable oil was studied. In order to achieve the purpose of improving machining accuracy and prolonging tool life, so as to lay the foundation for realizing the requirements of ISO14000

1 stainless steel material characteristics and cutting problems

stainless steel materials are divided into martensite, ferrite and austenite. The characteristics of stainless steel materials and the resulting cutting problems are described in the following three points

(1) high work hardening:

during the cutting process, the machined material produces plastic deformation, and the machined surface forms a hardened layer. The appearance of hardened layer will aggravate the tool wear, especially the tool boundary wear

(2) low thermal conductivity:

70% ~ 80% of the heat generated by cutting is taken away by the chips. However, when the thermal conductivity of the material is low, the chip carries less heat. When the temperature of the cutting point rises, the tool life will be shortened

(3) high affinity:

the affinity of the processed material is high, which is easy to cause chip buildup on the tool tip and attachments on the back surface, thus reducing the accuracy of the machined surface

the material used in the test is ferritic stainless steel. The domestic brand in Japan is sus430f. The chemical composition is shown in Table 1 for the key parameters and important characteristics of injection molding process analyzed by Moldex3D digimat RP

Table 1 sus430f chemical composition

2 cold air machining test

in general cutting methods, a large amount of cutting fluid should be used for cooling and lubrication, so as to improve the tool life and surface roughness. The cold air cutting method is to cool the cutting point with -10 ℃ ~ -30 ℃ cold air, and supply a small amount of vegetable oil to the front and rear face of the tool, so as to reduce the cutting temperature and lubrication

2.1 Bluebe cutting fluid and cold air supply system

2.1.1 Bluebe cutting fluid lb-1

bluebe cutting fluid is a high lubricating cutting fluid developed by the American aerospace industry for the processing of difficult cutting materials. It is extracted from natural vegetable oil and belongs to natural organic matter. Its natural decomposition rate is higher than that of mineral cutting fluid. It has no public hazards to the environment and no toxicity to human body

2.1.2 cold air and micro cutting fluid supply device

see Fig. 1 and Fig. 2 for test device. As shown in Figure 1, one of the compressed air generated by the air compressor is mixed with Bluebe cutting fluid to atomize the tool rake face and flank through the Bluebe oil feeder, and the other is cooled to -10 ℃ ~ -20 ℃ through the vortex cooling pipe to supply the cutting point

Figure 1 Schematic flow chart of test device system

Figure 2 test device

2.2 test conditions and objectives

tool: cemented carbide K10; Cutting speed v=150 m/min; Feed rate f=0.055 mm/r; Cutting depth ap=0.1mm

in order to compare with general cutting methods, water insoluble cutting fluid gm15 (Japanese domestic brand) was also used in the test. The test is divided into three cases:

use water-insoluble cutting fluid gm15

use -10 ℃ cold air without Bluebe micro cutting fluid

bluebe micro cutting fluid is used together with -10 ℃ cold air

carry out research under the above given test conditions, analyze and compare the test results, so as to evaluate the effect of cold air processing

2.3 test results and discussion

2.3.1 chip build-up tumor

as shown in Figure 3, chip build-up tumor is formed at the tool tip of the tool when water-insoluble cutting fluid gm15 is used. The formation, growth and falling off of debris tumor are irregular and unstable. One part of the fallen chip buildup is taken away by the chips, and the other part will adhere to the machined surface, resulting in the reduction of the roughness of the machined surface. Some people think that the chip buildup tumor can protect the tool, but in fact, when the chip buildup tumor falls off, it often takes away part of the tool material at the same time, which intensifies the wear of the tool. Therefore, chip buildup is very harmful to precision cutting. Compared with the cutting test B, which only supplied cold air, and the cutting test C, which simultaneously used Bluebe micro cutting fluid and cold air, the chip buildup at the tool tip was significantly less than that in test a. This shows that cold air cutting has a very obvious effect on reducing chip buildup. In addition, Bluebe micro cutting fluid can permeate between the tool flank and the machined surface, and between the tool flank and the chip, so as to reduce the friction between the two and reduce the chip buildup

test c

Fig. 3 K10 tool wear micro imaging and machined surface micro imaging

2.3.2 tool wear

as shown in Fig. 4, it can be seen that the tool wear of test a and test C are similar, while the tool wear of test B is large, indicating that Bluebe micro cutting fluid plays an important role in reducing tool wear

Fig. 4 wear curve of K10 tool

2.3.3 machined surface

with the reduction of chip buildup, the accuracy of machined surface is improved. Although the tool wear of test a and test C are similar, the surface roughness of test C is improved and the tool life is prolonged. As shown in Figure 4 and figure 5, the machined surface condition of test C is the best. In other cold air tests, it is also found that the effect of Bluebe micro cutting fluid supplied to the flank of the tool is the best

Fig. 5 surface roughness change curve

2.3.4 cold air machining meets the requirements of environmental protection

the use of a large amount of cutting fluid has played a great role in improving the product accuracy when the lower specimen rotates at a constant or variable speed along with the rotary table 1. However, with the development of modern cutting technology and the limitation of environmental protection, it will be replaced by the cold air cutting technology using trace vegetable oil

the waste liquid produced by general cutting shall be subject to high-temperature combustion treatment. With the expansion of industry, the combustion treatment of waste liquid will accelerate the greenhouse effect of the earth, thus causing a great impact on the environment. In developed countries, the cost of waste liquid treatment is rising year by year, which is also one of the main reasons for the rise of production costs. The chips produced by cold air cutting can be directly used as renewable resources, thus realizing the clean production mode, which is of great significance to protect the environment

3 conclusion

aiming at the difficult cutting of stainless steel sus430f, starting with the general cutting methods, this study analyzes the problems when using cemented carbide K10 cutter and water-insoluble cutting fluid gm15 to stop the use of thermosetting plastics (such as bakelite powder) and condensing plastics (such as epoxy resin + curing agent) as fillers. Then the cold air cutting technology is used to solve the disadvantages of the general cutting methods, and the satisfactory results are obtained. Based on the above research, the following conclusions can be drawn: when the experimental machine adopts Lenovo microcomputer:

the water-insoluble cutting fluid gm15 is used, the chip buildup is easy to form at the tool tip, which directly affects the accuracy of the machined surface and the service life of the tool

when cold air and a small amount of vegetable cutting fluid are used at the same time, the machining surface accuracy is improved and the tool life is prolonged

cold air cutting can reduce the production cost

a small amount of vegetable cutting fluid can prevent the machined parts from rusting

cold air cutting technology can prevent environmental pollution

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