Analysis on deformation characteristics of die forging technology of titanium bar
Titanium bar blank products process die forgings arrangement and functional uniformity stainless steel forgings. After recrystallization heat treatment, the low-power and high-power equiaxed fine crystals are indistinct crystals in the active zone of metal. In the hard deformation area, because the deformation amount is small or there is no deformation, the arrangement usually preserves the condition before deformation. In die forging some important titanium bar blank products process parts (such as compressor disk, blade, etc.), in addition to the manipulation of the deformation temperature under TB and proper deformation degree, the arrangement of the manipulation of the original blank is very important, otherwise, the coarse grain arrangement or some disadvantages to genetic forgings, and after the heat treatment and cannot eliminate, will incur forgings. Die forging is usually used to make shape and scale close to the product, then only for heat treatment and cutting processing of the final blank. Casting temperature and deformation degree are the basic elements of titanium alloy arrangement and function. The heat treatment of titanium bar blank products is different from that of steel. Therefore, the technological standard of die forging for titanium bar blank products has a unique and important effect. In order to make the die forging of titanium bar blank products together to achieve higher strength and plasticity, it is necessary to make the total deformation of the blank not less than 30%, the deformation temperature does not exceed the phase transition temperature, and should strive for the temperature and deformation degree in the whole deformation of the blank can be distributed evenly.
In the forging process of titanium bar blank products with disordered shape by die forging on the hammer, the temperature of the metal can still exceed that of the alloy even if the heating temperature is strictly controlled in the sharp deformation area where the thermal effect is concentrated. For example, the die forging cross section is i-shaped titanium bar blank products processing blank, hammer strike overweight, the center (web area) some of the temperature due to the thermal effect of deformation effect is about 100 degrees higher than the edge of some. In addition, in the hard deformation region and the region with critical deformation degree, it is easy to form coarse crystal arrangement with low plastic and durable strength in the heating process after die forging. So the shape of die forging on the hammer disorderly forging, its mechanical function is often very unstable. Lowering the die forging heating temperature, while eliminating some of the risk of the blank overheating, would result in a dramatic increase in deformation resistance, additional wear and tear, and power consumption, as well as the need for more powerful equipment. Hammer on the die forging, the use of repeated tapping method can also reduce the blank some overheating. However, it is necessary to add heat to compensate for the heat lost by the blank touch with the cooler mold. For forgings with relatively simple die forging shape, and when the target demand for plasticity and durability of the deformed metal is not too high, hammer forging is preferred. However, it is not suitable to use hammer forging for the alloy, because repeated heating in the process of die forging will have an unlucky effect on the mechanical function. Compared with the forging hammer, the operating speed of the press (hydraulic press, etc.) is greatly reduced, which can reduce the deformation resistance and deformation thermal effect of the alloy. In the process of die forging titanium bar blank products on hydraulic press, the unit die forging force of blank is about 30% lower than that of hammer, and then the die life can be improved. The decline in thermal effects also reduces the risk of metals overheating and rising beyond TB. When die forging with a press, the blank heating temperature can be lowered by 50 ~ 100 ℃ under the same condition of unit pressure and forging hammer. In this way, the interaction between the heated metal and the periodic gas as well as the temperature difference between the blank and the mold also decreases correspondingly, and then the uniformity of deformation, the uniformity of die forging arrangement also greatly improves, and the consistency of mechanical functions also improves accordingly. The decrease of the deformation velocity, the numerical value is the most significant is the surface shrinkage, the surface shrinkage of the formation of the arrangement of the most sensitive defect.
It is more difficult to flow into the deep and narrow die groove than steel. This is because of the high deformation resistance of titanium, the friction with things and the blank touch surface cooling too fast. To improve the activity and die life of titanium bar blank products. The usual practice is to increase the die forging Angle and the radius of the rounded corner and use lubricants: the rough edge of the bridge on the forging die is larger than steel, usually about 2mm larger. In order to make the groove simple filling, sometimes can choose the bridge scale non – uniform burring groove to restrain or accelerate some of the movement of metal groove. For example, a long square box forging with thinner front and rear side walls; The left and right side walls are thicker. When the box around the edge groove, because the metal flow into the left and right side wall resistance is small, resulting in the metal to the thinner front and rear side wall movement difficult, filling dissatisfaction. Later, the front and rear side walls still use the burr grooves as shown in b-b, while the left and right side walls use the burr grooves as shown in a-a. Because of the width of the bridge and the prevention of damping groove, the thinner front and rear side walls completely overflow, and the metal can be saved by using the aforementioned burr grooves. The die forging method is used to die forging titanium bar blank products process, because of the pressure and reduce the die life. Therefore, it is necessary to strictly limit the volume of the original blank in closed die forging, which makes the preparation process chaotic. Whether to choose closed die forging, from the cost and technological feasibility of two aspects of thinking. In open die forging, the loss of rough edge accounts for 15% ~ 20% of the blank component, and the technological wastes (if necessary to keep some of them according to the conditions of die forging) account for 10% of the blank component. The metal relative loss of rough edges is usually added with the reduction of the blank component. For some forging with asymmetrical layout, large section area difference and difficult to fill, the rough edges can consume up to 50%. Although there is no burr loss in closed die forging, the blank making process is messy and needs to add more transition grooves, which will undoubtedly add auxiliary costs. One of the most useful ways to improve the preheating temperature of titanium bar blank products is to reduce the deformation resistance. Isothermal die forging and hot die forging developed in the past 20 or 30 years at home and abroad have provided a feasible method for processing the fine forging of large and disorderly titanium bar blank products.
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