Thermal calibration is a key step in the forming process of titanium plate parts, and the choice of process parameters-especially heating temperature, holding time, and forming pressure-directly determines the calibration effect and the final quality of the part. Reasonable pressure helps the part fit closely with the mold, but excessive pressure may cause deformation of the mold or table, so precise control of temperature and time is more important. Among them, temperature is the core factor affecting the correction effect, and in order to effectively eliminate the rebound, the thermal correction must be carried out within the appropriate temperature range. The core of the so-called thermal correction specification is the scientific setting of temperature and time.
Generally speaking, a mature set of titanium plate thermal correction process should ensure that the parts meet the following basic requirements after calibration:
1. High mold fitting: the parts fit well with the mold, basically no manual trimming, and their shape, size and surface quality meet the inspection standards of titanium plate parts;
2. Stable performance: The mechanical properties of the material are basically stable, and the main performance indicators at room temperature and service temperature meet the design requirements.
3. Low residual stress: the residual stress inside the part is basically eliminated;
4. Controllable hydrogen content: after thermal correction, the average hydrogen content of the material does not exceed the allowable limit of 150 p.p.m;
5. Slight surface oxidation: the total thickness of the oxide layer and the air suction layer does not exceed half of the allowable negative deviation of the plate thickness;
6. No obvious change in structure: there is no significant change in the metallographic structure of the material, and there is no obvious grain growth or overheating;
7. Economical and reasonable parameters: Under the premise of meeting all the above requirements, the heating temperature and short holding time should be used as low as possible, and the pressure should be used to ensure the molding of the parts.
This calibration specification test is carried out on the domestic RX-1 machine tool, the test materials are industrial pure titanium TA2 and titanium alloy TC1, and the plate thickness covers 0.5 mm, 0.8 mm and 1.0 mm. During the test, thermocouples are used to monitor the temperature of the mold or working area in real time, and the temperature control accuracy is kept within ±10°C. The holding time is automatically controlled by the time relay, and the self-test part is put into the mold, closed or entered the working cavity to start the time, and ends when it is taken out.
Forming accuracy is the basic index to measure the pressing quality of parts, and it is also an important basis for judging whether the temperature and time parameters are reasonable. The method of determination is to measure the degree of fit between the part and the mold after cooling to room temperature, that is, the amount of residual springback. Taking the curved wide plate bending parts commonly used in aviation components as an example, this type of part has the characteristics of small curvature and high shape accuracy requirements, and its relative bending radius is large (such as R/T ≈ 200 before calibration). Combined with the test results, the process parameter range of thermal correction of titanium plate can be preliminarily determined under the premise of ensuring the forming accuracy. If the elastic modulus E = 10500 kgf/mm² and the yield limit σ0.2 (40.5 kgf/mm² for TA2 and 60.5 kgf/mm² for TC1), the combination of heating temperature and holding time can be further optimized through theoretical calculation and experimental verification, so as to provide a reliable basis for actual production.
Thermal calibration of titanium plates is a process that requires extremely high temperature, time, and pressure control. By scientifically setting the process parameters, it can not only effectively eliminate rebound and ensure forming accuracy, but also ensure the mechanical properties and structural stability of the material. In actual production, reasonable thermal correction specifications should be formulated according to the material grade, plate thickness and part shape, combined with test data and experience accumulation, so as to improve product quality while achieving efficient, economical and reliable production goals.
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