Application of steel cutting materials in machine

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The application of turning steel materials in mechanical parts

the vast majority of mechanical parts are made of carbon and alloy structural steel. When turning this kind of material, it often forms banded chips. In order to cut chips from the blank, the blade needs to bear a huge load. The cut chips slide out of the front knife surface of the blade rapidly. In the relative movement with the blade, it produces a violent friction surface to form a high temperature. Therefore, the blade material should not only be wear-resistant, but also be resistant to high temperature and maintain its hardness at high temperature. Therefore, p-type cemented carbide with a large proportion of tic+tac should be selected for cutting such materials. Nowadays, in order to improve cutting efficiency; Cutting speed; The feed speed is getting higher and higher, and the p-type cemented carbide blade is not competent. In the middle of last century, it was developed to deposit another layer of high hardness film on the p-type hard blade, which is called coating. The coating thickness is only about 0.2% of the blade thickness, which can greatly improve the blade life and adapt to higher cutting speed. In recent decades, coating technology has also been developing continuously, such as from single-layer to multi-layer or even nano multi-layer; How thick is it μ M increases to more than ten μ m. Even more, the types, properties and deposition technology of coating materials are becoming more and more advanced; Cemented carbide, as the base material, has also developed from a single isotropic structure to a structure with tilting properties that meets the processing requirements

according to the cutting requirements of this maximum number of materials, Mitsubishi has successfully launched a new UE series blade material after years of research and development

Figure 1: UE series tool materials for turning steel

Figure 1 succinctly shows the composition of UE series, each brand and their selection concept diagram. The ordinate in the figure can show the cutting depth (back cutting distance) and the abscissa can show the feed rate. A circle with a notch can be seen at the origin of the coordinate, indicating the cutting of each cutting depth and feed rate near the 45 degree line, and then completely lock the black knob condition. When making slight intermittent cutting, the recommended UE series tools are the specific brand of the key technical links of the experimental machine, and the corresponding chip breaking groove can be selected at the same time. For example, when the cutting depth and feed are small, ue6010 and sh chip breaking slots can be selected. If the cutting depth and feed increase roughly along the 45 degree line, it indicates that the chip cross-sectional area gradually increases, and the cutting load gradually increases, ue6010 material and MV and GH chip breaking slots can be selected in turn. When the cutting area is larger, ue6020 material and HX chip breaking slots can be selected. If there is no keyway, notch, etc. on the workpiece, the cutting at this time is called continuous cutting. If the machining allowance is also uniform, it is not to cut the surface layer of the workpiece, but to cut its inner layer. In addition, if the installation rigidity of the workpiece is high, it is not easy to produce vibration. At this time, the cutting force is roughly constant, and the cutting under the above conditions belongs to the stable cutting range, as shown in the upper left of Figure 1. For cutting within this range, with the increase of cutting depth and feed rate, ue6005 material and sh, MV, GH chip breaking groove can be selected respectively. When the cutting depth and feed rate are larger, ue6010 material and HX chip breaking groove can be selected. In the lower right of Figure 1, there is a circle with four notches, which vividly indicates that more intense intermittent cutting is formed when the notches on the workpiece are processed. The machining allowance is uneven, and the R & D investment of non workpiece inner cutting enterprises also increases correspondingly. However, the cutting of high hardness and uneven skin or the cutting of workpiece when the installation rigidity is poor and easy to vibrate belong to the unstable cutting range. At this time, ue6020 material can be mainly selected. With the increase of cutting depth and feed rate, the corresponding chip breaking groove can be selected as before. If the unstable condition is more serious, ue6035 and the corresponding chip breaking groove should be selected. Why do you choose this way? Due to UE series, these four materials are equivalent to different grades of ISO international standards from P01 to P40 as shown in Figure 1. The smaller the number above, the higher the surface hardness, the more wear-resistant, and the more adaptable to higher cutting speed. The larger the number, the higher the surface toughness, and the more impact resistant, but the applicable cutting speed is relatively low, which can also be seen from the recommended cutting conditions on the right side of Figure 1

before describing the characteristics of UE series, briefly explain the damage that causes tool failure. Nowadays, cemented carbide, cermet, ceramics, CBN (francium boron nitride), PCD (Artificial Polycrystalline Diamond) and other sintered materials are the main tool materials, and the utilization rate of high-speed steel has declined. The damage morphology of sintered materials is the same as that of high-speed steel. Wear is a progressive damage, which is related to cutting time and cutting length. Because it is sintered material and has its own characteristics, that is, hard and brittle, insufficient toughness, it will cause instant and low cycle impact due to the change of cutting force and cutting heat during the cutting process, and form brittle fracture. This kind of damage is manifested as (1) some small gaps appear on the blade, which is called defect or chipping. (2) When it is serious, a large gap is called broken fracture. When there is a small notch on the blade, that is, a defect, it can no longer be used for finishing, but in some cases, it can continue to be used for rough machining. (3) In addition, during processing, some chips are bonded and welded near the blade. General bonding and coalescence wear are one of the causes of damage to parts and non sintered tools. For sintered tool materials, bonding and coalescence wear may occur, but more importantly, the chips firmly bonded to the tool surface are bonded. After being impacted by subsequent processing, the coalesced materials and chip nodules are forcibly separated from the tool surface. In this process, part of the tool materials are also taken away with the separation, resulting in bonding, Fusion defects and damages, so the bonding and fusion of chips should be avoided in the field processing. Of course, they also affect the quality of the machined surface. (4) Poor thermal conductivity of sintered materials is prone to thermal cracks and other damage

Mitsubishi UE series coating materials are developed to well resist the above major tool damage and ensure efficient and long-life processing. The four coatings of UE series are made by CVD (chemical vapor deposition), which can be made thick, wear-resistant and high-temperature resistant, and can adapt to high-speed, large feed and deep cutting. Ue6010 and ue6020 are the most widely used four coatings of UE series. It is the most versatile and typical. Figure 2 shows the organizational structure of ue6010 and ue6020

Figure 2: UE series tool material for turning steel

it can be seen from Figure 1 that on the 45 degree line, the first recommendation is ue6010, because it has both quite high hardness and wear resistance and considerable toughness, which can adapt to a certain intermittent cutting and impact. Its matrix cemented carbide is an inclined structure, that is, the performance and function of each layer are different, and the toughness of the top layer combined with the coating is large, so as to ensure that the coating can be firmly combined with it, resistant to defects and damage, The matrix cemented carbide core is hard and has strong deformation resistance. The coating is divided into three layers. The innermost layer combined with the matrix is TiCN fiber columnar crystal. The secondary layer has high hardness and considerable toughness, which can well resist the wear of front and rear knife surfaces

the middle layer is Al2O3 with fine grains. Its hardness can reach hy2100, and its free energy of formation can reach - 100kcal/om. This value represents chemical stability. The smaller the value is, the better the chemical stability is, and the better the heat resistance is. When this layer is in high-speed cutting, it is difficult to produce the mutual diffusion of tool and workpiece material molecules, resulting in the crescent wear caused by the flow of banded chips on the rake face. The melting degree of iron in this layer is almost zero under high temperature conditions, The iron filings are not easy to fuse on its surface, so as to avoid all kinds of damage caused thereby. It is coated by the unique even coating technology, and the surface is particularly smooth. On this basis, the surface is coated with a layer of special titanium compound, which keeps smooth, reduces the friction coefficient, and further reduces the bonding and fusion of iron filings. Because it is golden yellow, it is easy to find possible minor damage. When recommending ue6010, it also particularly recommends the MV chip breaking groove, which is suitable for cutting conditions and first realizes the efficient and safe recovery of single category low value-added waste. The excellent combination of the two increases its versatility. The structure and performance characteristics of each layer of ue6020 are roughly the same as those of matrix cemented carbide ue6010. However, its film layer is thin (Fig. 2), its hardness is lower than that of ue6010, its wear resistance is poor, and its adaptive cutting speed is also low, but it can still maintain a fairly high wear resistance under the recommended cutting speed range (Fig. 1). Its bending strength, toughness and impact resistance are higher than that of ue6010, which is suitable for cutting in the unstable cutting range. Under impact load, the thick film may crack and fail, and the reliability of the film decreases. The thick layer is more impact resistant and has high reliability

for the service conditions of ue6010 and ue6020, for example, in continuous cutting and very stable cutting conditions, ue6005 with higher hardness and wear resistance can be further selected. At this time, the impact load is very small or even not, so it is easy to achieve more efficient cutting at the recommended higher cutting speed. On the contrary, in case of intermittent cutting and greater impact load, ue6035 with higher toughness and bending strength than ue6020 can be selected to work at the recommended cutting speed. Although the speed decreases (Fig. 1), it avoids tool defects and damage, prolongs the service life of the tool, avoids frequent blade replacement, shortens the auxiliary time, and also improves the cutting efficiency

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