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What are the effects of cutting heat and cutting temperature on mechanical parts in metal processing?

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Update time : 2019-12-06 02:01:00
Cutting heat and the resulting cutting temperature will cause thermal deformation of the processing technology system, which not only affects the wear and service life of the tool, but also affects the machining accuracy and surface quality of the parts.

Generation and conduction of cutting heat

Cutting heat comes from the energy consumed by the elastic and plastic deformation of the parts, and the frictional heat generated between the chip and the rake face of the tool, the processed surface and the flank of the tool, is transmitted through the chip, part, tool and surrounding medium. Generally, the chips take the most heat away.

For example, 50% -86% of the cutting heat is taken away by the chip during turning, 10% -40% is passed into the turning tool, 3% -9% is passed into the part, and about 1% is passed into the air; the proportion of the cutting tropical travel during drilling It is about 28% of chips, 14.5% of tools, 52.5% of workpieces, and 5% of surrounding media.

Cutting temperature and its influencing factors

Cutting temperature generally refers to the average temperature of the area where the chips contact the rake face of the tool. The cutting temperature depends on the amount of heat generated and the speed of heat transfer. Therefore, all factors that affect the generation and transmission of cutting heat affect the level of the cutting temperature.

(1) Workpiece material. The higher the strength and hardness of the workpiece material, the greater the unit cutting force, the greater the power consumed during cutting, the more cutting heat generated, and the higher the cutting temperature delay; the greater the plasticity of the workpiece material, the greater the deformation coefficient. Larger, the more heat is generated; the smaller the thermal conductivity of the workpiece material, the less the heat dissipated, and the higher the cutting temperature in the cutting zone; for materials with large heat capacity, the cutting temperature is lower when the cutting heat is the same.

(2) Cutting amount. When the amount of cutting is increased, the cutting power is increased, the cutting heat generated is also increased, and the cutting temperature is increased. The changes in cutting speed, feed rate, and back-eating amount have different effects on the generation and conduction of cutting heat, so the effects on cutting temperature are also different.

(3) Cutting speed υc. Cutting speed υc has the greatest influence on cutting temperature. The reason is that when υc increases, the heat consumed by deformation and frictional heat increase sharply. Although the heat taken away by the chips increases correspondingly, the heat transfer capacity of the tool remains unchanged.

For hard alloy cutting tools, υc should not be lower than 50m / min, the purpose is to prevent the tool from being too brittle and improve the toughness, but υc is generally not greater than 300m / min, the purpose is to prevent the tool from sharp wear due to too high temperature; for high speed steel tools, υc Generally less than 30m / mino.

(4) Feed amount f. The effect of the feed amount f on the cutting temperature is smaller. The reason is that when f increases, the cutting thickness hD increases (the chip heat capacity increases and the heat taken away increases), but the cutting width bD does not change (the heat dissipation area does not change, and the heat dissipation conditions of the cutter head have not improved), and the cutting temperature increases. .

(5) Eat the knife amount ap. The effect of cutting back ap on cutting temperature has the least effect, because if ap is doubled, the cutting width bD is also doubled proportionally, and the heat dissipation area is also doubled accordingly, which improves the heat dissipation conditions of the cutter head. The cutting temperature is only slightly increased.

According to the analysis of the feed amount f and the back knife amount ap, it can be known that the use of a wide and thin (bD large, hD small) cutting layer profile is beneficial to control the cutting temperature.

From the perspective of controlling the cutting temperature, when the conditions of the machine tool allow, it is more advantageous to choose a larger back-feed amount and feed amount than a large cutting speed.

(6) Tool geometry parameters. The rake angle and main declination angle of the tool have a great influence on the cutting temperature. Increasing the rake angle can reduce the cutting deformation and the friction between the chips and the rake face. The cutting heat generated is reduced and the cutting temperature is reduced. However, when the rake angle is too large (≥20 °), the heat dissipation area of ​​the tool head is reduced, but instead Increase the cutting temperature. Reducing the main declination angle can increase the working length of the cutting edge, increase the heat dissipation area of ​​the cutting head, and reduce the cutting temperature.

 
 (7) Other factors. When the wear of the flank of the tool increases, the friction between the tool and the workpiece is aggravated, and the cutting temperature increases. The higher the cutting speed, the more obvious the effect of tool wear on the cutting temperature. The cutting fluid's lubrication function is used to reduce the friction factor and reduce the generation of cutting heat. At the same time, the cutting fluid can also take away a part of the cutting heat, so using cutting fluid is an important measure to reduce the cutting temperature.