In order to make the thermal calibration successful, it is necessary to select the appropriate heating temperature, holding time and forming pressure. The pressure applied to the part during thermal shape correction ensures that the part is pressed against the mold. However, no matter how much pressure, it can lead to a just shape of the mold and table. Therefore, temperature and time are the main factors that affect the effect of thermal correction, and temperature is the decisive factor. In order to eliminate springback satisfactorily, it must be carried out at a certain temperature. The so-called thermal specification mainly determines the temperature and time of the shape correction. In general, proper thermal specifications for forming a
titanium sheet must ensure that the part meets the following basic requirements after forming:
1. The parts are well bonded to the mold and basically do not need manual trimming. Appearance, size and surface quality meet the inspection requirements of titanium plate parts;
2. The mechanical properties of the material are basically stable, and the main performance indicators at room temperature and operating temperature meet the requirements;
3. The residual stress inside the part is basically eliminated;
4. The average hydrogen content of the material after thermal correction does not exceed the allowable value of 150p.p.m;
5. The total thickness of the oxide skin and the breathable layer shall not exceed half of the allowable negative deviation of the thickness of the metal plate;
6. There is no change in the metallographic structure of the material, no obvious grain growth, overheating and other phenomena;
7. Under the premise of meeting the above requirements, the temperature should be as low as possible and the time should be as short as possible. The pressure is suitable to ensure that the parts can be pressed against each other.
Forming accuracy is the most basic requirement for press forming of parts, and it is also the main indicator to measure whether the temperature and time specifications are appropriate. The method of judging the forming accuracy is to measure the degree of non-adhesion of the part after cooling to room temperature, that is, the amount of residual springback. Under the premise of basically maintaining the forming accuracy, the specifications of the thermal correction of the titanium plate can be preliminarily determined.
