In order to make the thermal calibration work, the suitable heating temperature, holding time and forming pressure must be selected.Hot calibration when the pressure on the parts, as long as the parts can be guaranteed to press stick in the mold, then a large pressure on the branches of the role is not big, but may lead to mold and table shape.Therefore, the effect of thermal calibration is mainly affected by temperature and time, and temperature is the decisive factor.In order to eliminate rebound satisfactorily, only at a certain temperature.The so-called thermal specification is mainly to determine the calibration temperature and time.In summary, a proper thermal specification for titanium sheet forming must ensure that the parts meet the following basic requirements after being in shape:
1. The parts are well pasted and basically do not need manual repair.Shape, size and surface quality meet the inspection requirements of titanium plate parts;
2. The mechanical properties of the materials are basically stable, and the main performance indexes at room temperature and service temperature meet the requirements;
3, the residual stress in the parts of the basic elimination;
4. The average hydrogen content of the materials after thermal calibration does not exceed the allowable value of 150p.P.M;
5. The total thickness of oxide skin and permeable layer shall not exceed half of the allowable negative deviation of sheet thickness;
6. No changes in metallographic structure, no obvious growth and overheating of grain;
7. Under the premise of meeting the above requirements, the temperature shall be as low as possible, and the time shall be as short as possible, and the pressure shall be as appropriate to ensure that the parts can be pressed and pasted.
Our calibration specification test was carried out on domestic RX – 1 machine tools.The materials are TA2 and TC1, and the thickness is 0.5, 0.8 and 1.0 mm.Thermocouple indicates the temperature of mold or working area, which can be controlled within ±10℃;Time is controlled by time relay, which is calculated from the time when the specimen is put into the mold, mold closing or working cavity until the time when it is taken out.
The problem of forming accuracy is emphasized.Forming accuracy is the most basic requirement of forming parts, and it is the main index to measure the suitability of temperature and time specification.The method to judge the forming accuracy is to measure the degree of non-sticking mold after the parts are cooled to room temperature, that is, the amount of remaining springback.Take the wide circular curved plate for example.It can represent aircraft parts with small curvature and precise shape.The relative bending radius of such parts is relatively large (such as R/t = 200 before rebound).If the elastic modulus E = 10500 kg/m2;Yield limit alpha 0.2. Let’s take 40 for TA2.5 kilograms per square millimeter, take 60 for TC1.5 kilograms per square millimeter.
In conclusion, on the premise of basically maintaining the forming accuracy, the specification of thermal calibration of titanium plate can be preliminarily determined.
Editor : Carrie Qi (firstname.lastname@example.org)