Necessary Conditions For Thermal Calibration Of Titanium Plates

In order for thermal calibration to be successful, the proper heating temperature, holding time and molding pressure need to be selected. The pressure applied to the part during thermal calibration can be as much as necessary to ensure that the part is pressed into the mold. Large pressures have little effect on the shape of the stub, but may have an effect on the shape of the mold and table. Therefore, the main role of thermal correction is temperature and time, where temperature is the determining factor. In order to eliminate springback satisfactorily, it can only be carried out at a certain temperature. The so-called thermal specification mainly determines the molding temperature and time. In summary, a certain titanium plate molding appropriate thermal specification must ensure that the parts are molded to meet the following basic requirements:

1, the parts fit well, basically no manual trimming. Shape, size, surface quality in line with the titanium plate parts inspection requirements;

2, the basic stability of the mechanical properties of the material, room temperature and working temperature of the main performance indicators in line with the requirements;

3, the parts of the internal residual stress is basically eliminated;

4, the average hydrogen content of the material after thermal calibration does not exceed the permissible value of 150p. p. meters;

5, the total thickness of the oxide skin and gas barrier layer shall not exceed half of the permissible negative deviation of the plate thickness;

6, the material metallographic organization without change, grain without obvious growth and overheating phenomenon;

7, under the premise of meeting the above requirements, the temperature should be as short as possible and the pressure as low as possible to ensure that the parts can be pressed.

Our calibration tests were performed on a domestic RX-1 machine. The materials were TA2 and TC1 with thicknesses of 0.5, 0.8 and 1.0 mm respectively. A thermocouple is used to indicate the temperature of the mold or work area, which can be controlled within ±10°C. The time is controlled by a time relay from the time the specimen is placed in the mold, clamped, or placed in the studio until it is removed.

The problem of molding accuracy now comes to the fore. Forming accuracy is the most basic requirement for parts stamping and forming, and is the main indicator of the appropriate temperature and time specifications. The method of determining forming accuracy is to measure the degree of non-stickiness, i.e., the amount of residual springback, after the part has cooled to room temperature. Take a curved wide-plate bent part as an example. It can represent a class of parts with precise curvature and precise shape in an airplane. The relative bending radius of such parts is large (e.g., relative bending radius before springback R/t=200). If the modulus of elasticity E=10500 kg/mm 2 ; the yield limit α0.2, TA2 is taken as 40.5 kg/mm 2 and TC1 is taken as 60.5 kg/mm 2 .

In summary, under the premise of basically maintaining the forming accuracy, the specification for the thermal calibration of titanium plates can be preliminarily determined.