Why do cutting circular blades wear out when cutting round blades

[Author/Source] Webmaster on June 10, 2015 [Number of clicks] 2504

After improving the cutting speed of the new cutting round blade, the cold welding wear of cemented carbide round blade is reduced. For certain cutting tools and workpiece materials, cutting temperature has a decisive influence on the wear of cutting circular blades.

Cold welding the wear

When cutting, there is a lot of pressure and friction between the chip, the workpiece and the front and rear surface of the knife, so there will be cold welding between them. Therefore, through the reasonable choice of cutting parameters, tool material and Angle, can reduce the cutting heat generation and increase the heat out.

The thermoelectric wear

Because the workpiece, chip and tool are of different materials, the thermoelectric potential will be generated in the contact area when cutting. This thermoelectric potential has the effect of promoting diffusion and accelerating the wear of the tool. In general, the air is not easy to enter the knife chip contact area, oxidation wear is most easily formed in the working boundary of the main and auxiliary knife edge. Because the chips and workpieces are moving at high speed, the surface of the cutting tools and their surfaces maintain the concentration gradient of the diffusing elements in the contact area, so that the diffusion phenomenon continues. Because of the relative motion between the friction surfaces, the cold solder joints will break and be taken away by one side, thus causing cold solder wear. The cutting temperature depends on the heat generated and outgoing, it is affected by the cutting dosage, workpiece material, cutting circular blade material and a few. This diffused wear under the action of thermoelectric potential is called thermoelectric wear. Therefore, the front and the back of the cutting surface with the cutting will gradually produce wear.

At the normal working speed of the HSS cutting circular blade and the low working speed of the carbide circular blade, the cold welding can be satisfied, so the proportion of the cold welding wear is relatively large. The working temperature of HSS cutting circular blade is low, and the diffusion action between cutting chip and workpiece is slow, so the proportion of diffusion wear is far less than that of cemented carbide tool. Abrasive wear exists at all cutting speeds, but for low speed cutting tools (such as broach, grinding teeth, etc.), abrasive wear is the main cause of wear. The diffusion wear is often accompanied by cold welding wear and abrasive wear, and the wear rate is very high. The abrasion and cost resistance of cutting circular blades are related to the efficiency, quality and cost of cutting, so it is one of the most important problems in cutting. The bonding phase CO decreases, and the bonding strength of WC (TiC) in cemented carbide decreases. But because of the alternating capacity, contact fatigue, thermal stress and the surface structure of the tool defects, the fracture of the cold welding joint may also occur in the tool this side, the tool material particles were chip or workpiece away, thus causing the tool wear.

Generally speaking, the hardness of the workpiece material or chip is lower than that of the cutting round blade material, and the fracture of cold welding junction often occurs in the workpiece or chip side. This is because low speed cutting, cutting temperature is relatively low, other causes of wear is not obvious, so it is not the main. In this paper, the causes of abrasive wear, cold welding wear, diffusion wear, oxidation wear and thermoelectric wear of different materials are analyzed. In addition to the nature of tool and workpiece material itself, temperature is the most important factor affecting diffusion wear. It is an important way to reduce tool wear to reduce cutting zone temperature effectively.

Abrasive wear

The hardness of the chip, the workpiece is lower than the hardness of the tool, but they often contain some of the hardness of very high micro hard point, can be engraved on the tool surface groove, this is abrasive wear. It has been proved that the thermoelectric wear can be reduced if the electromotive force contrary to the thermoelectric force is applied at the contact of the workpiece and the tool. The hardness and wear resistance of high speed steel tool is lower than that of hard alloy and ceramics, so its abrasive wear accounts for a larger proportion. Working under the above conditions, tool wear is usually the result of a combination of mechanical, thermal and chemical wear, which can produce the following wear patterns. The results show that brittle metals have stronger resistance to cold welding than plastic metals. The cold welding tendency of metals with the same metal or lattice type, lattice spacing, electron density and similar electrochemical properties is small; Metal compounds have less tendency to cold welding than single phase solid melts. Group B elements in the periodic table are less prone to cold welding than iron. Hard points include carbides (such as Fe3C, TiC, VC), nitides (such as TiN, Si3N4), oxides (such as SiO2, Al2O3) and intermetallic compounds. When cutting metal, in the process of contacting the chip, the workpiece and the cutting round blade, the chemical elements of both sides diffused each other in the solid state, changing the composition and structure of the original material, making the tool material become fragile, thus exacerbating the wear of the tool. Tool wear during cutting has the following characteristics: the contact surface between tool and chip, workpiece is often fresh surface; The contact pressure is very high, sometimes exceeding the yield strength of the material being cut. The temperature of the contact surface is very high, up to 800 ~ 1000℃ for carbide round blades and 300 ~ 600℃ for high-speed cutting tools.

In short, the cause and strength of wear are different for different workpiece materials, tool materials and cutting conditions. All of these, the cutting of circular blade wear intensified.

In the process of cutting, the front knife surface, the back knife surface often contact with the chip, the workpiece, in the contact area there is a strong friction, at the same time, in the contact area and there is a high temperature and pressure. The oxidation wear is related to the adhesion strength of the oxide film. The lower the adhesion strength is, the faster the wear will be. The reverse can reduce the wear and tear. In addition to the abrasive wear on the front surface of the knife, grooves caused by abrasive wear can also be found on the back surface of the knife.

Diffusion wear

Diffusion wear occurs at high temperatures. For example, when cemented carbide is cutting steel, starting from 800℃, the chemical elements in cemented carbide are rapidly diffused into the chips and workpieces, and WC is decomposed into W and C and then diffused into steel. As a result, the cemented carbide surface is carbon - and tungsten - poor. The Fe in the chip and workpiece diffused into the hard alloy, diffused into the hard alloy Fe, will form a new hardness, high brittleness of the composite carbide.

Oxidative wear

When the cutting temperature reaches 700 ~ 800℃, oxygen in the air will oxidized with cobalt, tungsten carbide, titanium carbide, etc., and produce soft oxides (such as Co3O4, CoO, WO3, TiO2, etc.) which will be wiped off by chips or workpieces and form wear, which is called oxidation wear.

In the process of cutting tools will gradually wear, when the tool wear to a certain extent, it can be significantly found that the cutting force increases, cutting temperature rises, chip color changes, and even vibration.

Cold welding wear is generally severe at medium and low cutting speeds. Tool wear and cost related to the efficiency, quality and cost of cutting. At the same time, the size of the workpiece may exceed the tolerance range, and the quality of the machined surface also deteriorates significantly. Ti(N, C) particles in cutting act as ploughs on the tool.

Because the circular cutting blade wear to a certain extent, will reduce the workpiece dimension accuracy and machining surface quality, but also increase the cost of processing and the consumption of the blade, therefore, reducing the circular blade wear has a very important practical significance.