Study on chip deformation during high speed millin

Research on chip deformation during high-speed milling titanium alloy in different media (Part 2)

micro analysis of chip deformation

it can be seen from Figure 4 that the surface micro morphology of chips in different media is also different, and there are some microcracks on chips in nitrogen oil mist medium (Figure 4 (c)), which are mainly distributed at the edges and ends of chips, and most of the microcracks are the same as the sliding direction of chips along the rake face (zone I of Figure 5), A small number of microcracks are perpendicular to the chip slip direction (zone II in Figure 5). The possible causes of chip microcracks under nitrogen oil mist medium are as follows: first, nitrogen oil mist is sprayed into the cutting area, which instantly takes away a lot of heat, causing chip thermal stress and thermal cracks; 2、 Nitrogen in the nitrogen oil mist reacts with titanium in the chips to produce brittle titanium nitride, which is distributed on the surface and inside of the chips, making the chips easy to embrittle under strong extrusion and friction

since the air oil mist also takes away a lot of heat in cutting, but its chips do not have microcracks (Fig. 4 (a)), the first possibility is not tenable, so it can be considered that microcracks are caused by the presence of nitrogen. The chip is easy to embrittle, which will reduce the impact of the chip on the milling cutter when it flows through the rake face, thus reducing the milling force to a certain extent. Metallographic analysis of chips comparison of metallographic photos

during the formation of titanium alloy chips, the plastic deformation of the material is large, and the stress of the chips on the shear slip surface increases during work hardening. The TP ⑴ heightening small spring fatigue testing machine produced by Shandong Sida high tech Bureau is the instrument department that does professional mechanical experiments on the fatigue life of springs such as coil springs. At this time, The chips are only crushed at the upper part, but the lower part is still connected, that is, the side close to the rake face with a working voltage of 5V is very smooth, and the other side is serrated, forming concentrated shear sliding chips

Figure 6 shows that under the nitrogen oil mist, the chip has a very obvious nodal trend, and the connection at the bottom of the chip has become very few, and sometimes the chip nodes are almost separated from each other. Although the tendency of chip fragmentation under air oil mist is more obvious than that during dry milling, it is not as good as that under nitrogen oil mist

the reason why the chip nodulation under nitrogen oil mist and air oil mist is more obvious than that in dry milling is that the cooling effect of oil mist reduces the plasticity of titanium alloy on the shear slip surface of chips. 5. For C, D, e-belts, chips are easy to shear along the slip surface. Under nitrogen oil mist, because nitrogen and titanium generate brittle tin on the shear slip surface, at high speed, the high shear force strengthens the concentrated shear slip effect of chips, which makes the nodal characteristics of chips more prominent

Fig. 7 Effect of milling speed on shear angle (r=1.6)

comparison of shear angle f

Fig. 7 is the curve of shear angle f changing with speed

the figure shows that with the increase of milling speed, the cutting angle of titanium alloy chips under air oil mist, nitrogen oil mist and dry milling conditions has an increasing trend, that is, the trend of chip deformation decreases, especially when the milling speed exceeds 275m/min. There are two main reasons for this result: on the one hand, the deformation time is shortened, and the deformation of titanium alloy is reduced; On the other hand, because the chip speed has an impact on the average friction coefficient of the rake face, the higher the cutting speed is, the smaller the average friction coefficient of the rake face is. When the cutting speed is very high, due to the high cutting temperature, the chip bottom layer softens and forms a thin micro soluble layer. In this case, the change of cutting speed has little effect on the chip deformation

in addition, at the same speed, the shear angle of chips under nitrogen oil mist is greater than that under air oil mist. The reason is that there is titanium nitride on the shear slip surface of the chip in nitrogen medium, so the plasticity of the shear slip surface is reduced, and the chip is more prone to plastic instability in the process of concentrated shear slip, so the deformation of the chip is reduced, and the shear angle f is reduced. 3 conclusion

through the high-speed milling experimental research on the deformation of titanium alloy chips under different media, the following conclusions can be drawn: during dry milling, the friction between the tool and chips is large, the temperature in the milling area is high, the deformation of chips after flowing through the rake face is large, the strip wrinkles on the chip surface are more, and the flatness is poor. With the increase of milling speed, the chip shape becomes more and more regular. The surface morphology of chips under different media is also different. The nodal ratio of chips under air oil mist and dry milling is obvious, but it is not as good as nitrogen oil mist. There are many microcracks on the chips in the medium of nitrogen oil mist, and the chips are easier to brittle fracture. At the same speed, the chip shear angle f under displacement stop nitrogen oil mist and air oil mist is greater than that of dry milling and air oil mist, that is, the chip deformation coefficient is lower than that of dry milling and air oil mist, and the air oil mist shear angle f is greater than that of dry milling