Titanium alloy is known as the "space metal" or "ocean metal" because it combines the strength of steel with the lightness of aluminum and performs well in extreme corrosion and high temperature environments. However, this excellent performance also poses significant machining challenges.Titanium alloy is inherently "stubborn": it has a high deformation resistance, like a hard "stubborn stone"; It has poor thermal conductivity, and heat is easy to collect locally, leading to overheating; It is extremely active at high temperatures and reacts with oxygen, nitrogen, etc. in the air like a hungry wolf, forming a brittle and hard surface layer. Therefore, we cannot treat it like forged ordinary steel. Forging, an ancient and intelligent technology, is not a simple shaping for titanium alloys, but more like a carefully planned "taming" process. Its core purpose is to break its coarse original cast structure through high temperature and pressure, and transform its internal structure into uniform, dense and fine grains, so as to fully stimulate the potential of titanium alloy - high strength, high toughness, fatigue resistance - completely stimulate.
Forging titanium alloy is by no means capable of brute force, it begins with careful preparation and accurate prediction. First, heating is a critical step. Titanium alloys have a very narrow forging temperature window, typically between 850°C and 950°C (for different grades). If the temperature is too low, the material is difficult to deform and easy to crack; If the temperature is too high, the grains will grow quickly or even melt too hot, resulting in product scrapping. This temperature range is strictly controlled and must be "just right". The heating process is usually carried out in an electric or gas furnace, where the atmosphere must remain neutral or slightly oxidized, and sometimes even argon protection is required to minimize the inhalation of harmful gases. Additionally, the billet surface preparation before forging is crucial, as any minor cracks or defects can be magnified after forging, necessitating careful cleanup. It can be said that before the titanium alloy was sent into the forged hammer, engineers had already planned the entire "transformation" path for it through thermodynamic calculations and process design.
When the titanium alloy billet heated to heat is taken out, a "hot processing" in a race against time begins. The forging process is usually divided into multiple fires (i.e., heating-forging-reheating cycles). The first is "blanking", that is, using huge pressure to preliminarily break the loose and coarse grain structure in the ingot. This is followed by "multi-directional forging," which is the essence of titanium forging. The craftsman or manipulator needs to constantly change the direction of the force on the billet and repeatedly upset and lengthen. This process is like kneading, through multi-directional plastic deformation, the internal grains are fully broken, twisted and reorganized, resulting in a fine and uniform isoaxial crystal structure. This not only significantly improves the uniformity of the material, but also greatly improves its comprehensive mechanical properties. During the whole deformation process, the deformation amount, deformation rate and final forging temperature are controlled extremely strictly. The final forging temperature should not be too low, otherwise it will lead to work hardening or even cracking. Modern forging mostly uses hydraulic presses or fast forging presses, which can provide smooth and huge pressure to achieve "gentle and firm" shaping of titanium alloys.
According to the shape and requirements of the final product, titanium alloy forging is mainly divided into two paths: free forging and die forging. Free forging, as its name suggests, is the plastic forming of billets locally or as a whole by simple tools (such as flat anvils, profile anvils). It is highly flexible and suitable for the production of large, relatively simple forgings, such as discs and shafts for aero engines, or for marine pressure-resistant housings. Free forging provides better assurance of the deep quality of forgings, but has limited dimensional accuracy and shape complexity. Die forging involves putting the heated billet into a pre-manufactured precision mold cavity and filling it with pressure to fill the mold cavity. This method can form parts with complex shapes and precise dimensions at one time, such as aircraft landing gear, blades, etc. The die forging has a small processing allowance and high material utilization, but the mold cost is high, and the requirements for forging process parameters are more demanding. Which path to choose is the art of trade-offs between product performance, production costs, and manufacturing cycles.
The end of forging is not the end of the entire process. Titanium parts that have just been forged have huge residual stresses and uneven structure inside, which must be "heat treated" to stabilize and optimize. Through different processes such as annealing and solution aging, its microstructure can be adjusted, internal stresses can be eliminated, and the performance of the material can be achieved in an optimal and stable state. After this series of "tempering" and "fire tests", titanium alloys have finally been reborn as high-end materials that can withstand 10,000 meters of deep-sea pressure, resist high-temperature air currents during supersonic flight, or serve safely in the human body for decades. Looking ahead, titanium alloy forging technology is evolving in the direction of greater precision and intelligence. Isothermal forging, near-net forming and other technologies can produce extremely complex shapes with almost no subsequent processing at a more constant temperature and lower deformation resistance. At the same time, computer simulation technology is being widely used to predict metal flow, temperature changes and tissue evolution during the forging process, so that this "taming" journey is on the right path from the beginning. It can be said that every successful forging of titanium alloy is a perfect dialogue between human intelligence and material nature.
