1. Process Guiding Principles
Since Gr1/Gr2 are commercially pure titanium and belong to the α-type titanium alloy, the forging process for the slabs must strictly control the first heat. The initial forging temperature of the titanium ingot should be controlled at (900±10)°C, meaning forging is conducted below the β-transus temperature (Tβ). In this state, the material exhibits good workability, which is conducive to plastic deformation. However, the main forging characteristic when deformation begins in this state is the relatively coarse grain structure. A significant amount of deformation must be applied to refine the grains. Therefore, a large deformation is necessary at the start of forging to achieve a finer grain size and reduce the probability of surface cracks caused by lower temperatures. Once the dimensions are close to the final product size, only a small allowance for final truing should be left.
As the deformation resistance of titanium alloys decreases significantly with increasing temperature, it is essential to maximize the widening during the high-temperature zone when a large deformation is required for spreading. A certain width allowance for truing should be left, and the edges should not be forged prematurely. If edges are formed too early, the rapid temperature drop at the edges creates a constraint effect. The material flow in the high-temperature zone becomes fixed by the cooler edges, ultimately leading to frequent dressing and truing of the forging.
(3) Once sufficient width has been achieved through spreading, the edges can be forged. Since the thickness dimension has already been forged to its final size at this point, the required truing allowance is small, facilitating the quick truing of the final product.
2. Forming Process Characteristics
(1) Conventional Square Block Forging Process: The advantage of the conventional square block forging process is that the method is well-established. The disadvantages include the need for repeated flipping on three sides, the tendency for the workpiece to bend during upsetting when it becomes thin, difficulty in controlling dimensions across three directions, and the complexity of controlling metal flow.
(2) Forging and Drawing Process: Due to the relatively small cross-sectional dimensions of the titanium ingot (approximately φ450 mm), it is impossible to directly forge the cross-sectional dimensions specified in the drawings using a drawing-down method alone. An upsetting operation must be performed first to increase the cross-sectional area, paving the way for subsequent widening. The greatest advantage of the forging and drawing process is the regular pattern of metal flow, which makes controlling the width and thickness dimensions easy, and the length is not limited. The process route is as follows: First, widen to ensure a certain thickness, then upset by standing the workpiece on end. Next, widen again, upset, and forge the four corners. Subsequently, flatten the piece, stand it up to press the edges, rotate it 90° to flatten the thickness, rotate it another 90° to press the edges, and finally flatten to complete the finished product.