The suitable heating temperature, holding time and forming pressure must be selected to make the heat calibration work.The pressure applied to the parts when the shape is hot, as long as it can ensure that the parts are pressed in the mold, then the big pressure for the branches of the role is not big, but may lead to the mold and the table of righteousness.Therefore, temperature and time are the main factors that affect the effect of thermal calibration, and temperature is the decisive factor.To remove rebound satisfactorily, only at a certain temperature.The so-called thermal specification is mainly to determine the calibration temperature and time.In summary, the appropriate thermal specification for the forming of a titanium plate must ensure that the following basic requirements are met after the assembly:
1. The parts are well pasted and need no manual repair.Shape, 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 service temperature are in accordance with the provisions;
3. The residual stress inside the parts is basically eliminated;
4. The average hydrogen content of the material after thermal calibration shall not exceed the allowable value of 150p. P.m.
5. The total thickness of the oxide skin and the gas permeable layer shall not exceed half of the allowable negative deviation of the plate thickness;
6. The metallographic structure of the material has no change, and the grain size has no obvious growth and overheating.
7. On the premise of meeting the above requirements, temperature should be as low as possible and time as short as possible.
Our calibration test was carried out on the domestic rx-1 machine tool.The material is TA2 and TC1 and the thickness is 0.5, 0.8 and 1.0 mm.Thermocouple is used to indicate the temperature of the mold or working area. The temperature can be controlled within ±10℃.Time is controlled by time relay, counting from the time when the specimen is put into the mold, closed the mold or put into the working chamber to the time when it is taken out.
The problem of forming accuracy is emphasized.Forming accuracy is the most basic requirement of parts pressing, is the main index to measure whether the temperature, time specification is appropriate.The method to judge the forming accuracy is to measure the degree of non-sticking after the parts are cooled to room temperature, that is, the amount of residual springback.First take the circular wide plate bending part as an example.It can represent a class of parts in which the curvature of the plane is small and the shape is accurate.The relative bending radius of such parts is large (such as R/t = 200 before springback).If the elastic modulus E = 10500 kg/m2;The yield limit is 0.2, 40.5 kg/m2 for TA2 and 60.5 kg/m2 for TC1.
To sum up, on the premise of keeping the forming accuracy basically, the specification of thermal alignment of titanium plate can be preliminarily determined.