1. Selection of basic materials
Material: Titanium alloy TC4 The composition of the material is Ti-6Al-4V, which belongs to the ( + type titanium alloy, which is shown in Figure 1 for its structure.
The chemical composition is as follows:
2. Introduction to the basic properties of materials
It has good comprehensive mechanical and mechanical properties, and the service temperature is 300 350. The specific strength is high. The intensity of TC4 is sb=1012gpa, density g=44 103, specific intensity sb g=235, while the specific strength of alloy steel sb g is less than 18. Titanium alloys have low thermal conductivity. The thermal conductivity of titanium alloy is 1 5 of iron, 1 10 of aluminum, and the thermal conductivity of TC4 is l=7955w/m·k。Compared with general titanium alloys, the biggest advantage of titanium-aluminum intermetallic compounds is that they can still maintain good mechanical properties and corrosion resistance under higher temperature conditions, some of which have a maximum service temperature of 816 and individual alloys up to 982, light weight, high temperature resistance, high strength, and good creep resistance, making them the most competitive materials for marine equipment and aviation equipment in the future. Titanium is non-toxic, no heavy metal precipitation, high strength and good biocompatibility with the human body, and is a very ideal medical metal material, such as human bone joints, connectors, fixation plates, etc., which can be used as implants implanted in the human body. At present, the Ti-6Al-4V ELI alloy is still widely used in the medical field.
3. Simulation relationship between material strain, time and temperature
The relationship between strain and temperature at the 815 rate and rheological peak strain plot is shown in Figure 2
The initial strain rate is 5 10-3s-1, the temperature is 900, and the tensile test is carried out for 5, 10 and 15 minutes respectively, and the corresponding curves of strain and stress are obtained, as shown in Figure 3.
As shown in Figure 3, the stress of the material due to the corresponding strain in the tensile process of the test high temperature first reaches the peak value very quickly, and then gradually decreases; And with the increase of the corresponding strain, the later curve gradually becomes flattened. The holding time is within the range of 0 16 min, the strain stress curve changes greatly in a short time, and the pattern forms a rapid rise.
4. Establish mathematical models and simulation selection of mold-related parameters
In the process of establishing the finite element simulation state, the relationship between the fluctuating stress of the simulated deformation of the alloy material and the macroscopic thermal parameters is established, which is particularly important in order to obtain the corresponding numerical simulation final state data. The article is simulated by comparing exponential and concatenation.
Simulation, as well as the parallel model Johnson-cook, as well as the empirical formula of Kumar's five basic types of high-temperature basic type relations, the collection and collation of high-temperature tensile test data, and finally the Kumar model is used to establish the mathematical expression of the high-temperature constitutive equation of the alloy in the range of temperature of 850 930, change rate: 4 10-4 1 10-2S-1, and the actual strain is the real deformation
Pneumatic forming is a deformation process based on the premise of high temperature, the mold and the workpiece will be thermally expanded and contracted at the same time as the temperature changes, and considering the different expansion coefficients of the two materials, the amount of deformation is different, by comparing various types of high-temperature mold materials.
The mechanical properties of the materials at different temperatures, especially the linear expansion coefficients of the alloys and these materials, are compared. Finally, Ni7N, i.e., ZG35Cr24Ni7Sin, will be selected as the TC4 pneumatic forming mold material. According to the high-temperature mechanical property parameters of the two and the empirical data of large-scale mold design, the scaling coefficient of the mold surface is determined to be 6%.
The inner diameter of the mold and the processing air pressure can be found above Lianli.
On this basis, according to the results of FEA's calculations, the structure and dimensions of the upper and lower molds were determined. The above design does not consider the thinning amount of titanium tube processing and the processing process is constant temperature.
5. Conclusion
Through the above simulation calculation and mold simulation design research, a new molding scheme is provided for the manufacturing of parts with high strength and strict tolerance requirements.