Challenges in Titanium Hot Forming and How to Overcome Them

The Importance of Hot Forming for Titanium

Hot forming is essential because it is the only way to work with titanium for complex shapes, which comprise a significant portion of the titanium parts used in aerospace. Basic titanium shapes can be formed in a cold state, but more complicated shapes with tighter tolerances require the hot forming process. When working with titanium, it is important to understand that as the temperature increases, the yield curve lowers to a point where the material can stretch without cracking or becoming more brittle.

Understanding the Hot Forming Process

A hot-forming press forms materials such as titanium, precisely as the name suggests, by applying heat. A blank is placed in the machine, which then has to come up to temperature, usually between 1100°F and 1350°F. Once the machine has heated to the proper temperature, it presses the material into the desired shape. Then, it holds it in that position for a set length of time, determined by the complexity of the shape. Once the press has been released, an operator removes the blank, allowing the shape to begin the cooldown process.

Material Difficulties

Titanium is prone to springback, which refers to the tendency of a formed titanium part to partially return to its original shape after the forming forces are released, resulting in a loss of dimensional accuracy due to the material’s elastic properties. The effects of springback can be eliminated by heating the material to 1100°F or higher. When the machine holds the part in that compressed state for several minutes, it sets the material to the precise shape of the tooling surface.

Complexities of Temperature Control

Precision temperature control is critical for titanium hot forming, as the material’s high strength and limited formability require precise heating to achieve the desired complex shapes without compromising mechanical properties. Inconsistent or incorrect temperatures can lead to excessive springback and material fatigue. To overcome these challenges, we employ advanced heating methods such as resistive heating and real-time temperature monitoring to ensure uniform heat distribution and repeatable forming conditions to improve overall part quality.

Resistive Heating

Resistive heating is a method of heat generation where electrical energy converts to heat through friction. This process occurs when an electric current flows through a conductive material, causing electrons to collide with atoms, thereby generating heat.

In titanium hot forming, resistive heating offers precise temperature control, making it an effective alternative to methods like convection or induction heating. Additionally, this method allows for real-time temperature adjustments, ensuring that the material reaches and maintains optimal forming conditions.

Real Time Temperature Monitoring

Precise temperature control is critical in titanium hot forming, where even slight deviations can impact material properties and final part quality. Our press is equipped with nine thermocouples beneath the bottom platen and nine above the upper platen, continuously feeding real-time temperature data to the controller.

By leveraging this data, the system cycles fire rods on and off at optimal intervals, maintaining a consistent thermal environment throughout the process. This precise control enhances part quality and repeatability, reduces thermal stress, improves material properties, and extends tool life.

Tooling Considerations

Effective tooling is essential for a successful hot-forming process, but it comes with its own set of challenges. Over time, tools can wear down, leading to surface degradation, reduced precision, and inconsistencies in formed parts. Additionally, tool growth must be carefully accounted for, as high temperatures can cause the tooling to expand, potentially altering critical dimensions and affecting part quality. Addressing these challenges requires careful material selection, robust tool design, and real-time monitoring to maintain accuracy and extend tool life.

Tool Wear

As with any advanced manufacturing process, tool degradation is a genuine concern. This is particularly true with Titanium due to its high reactivity at elevated temperatures and the fact that it tends to bond with common tooling materials chemically, causing adhesive wear or galling, where material from the tool transfers onto the Titanium, damaging both the part and the tool. Over time, this reaction degrades the tool surface, reducing its lifespan and potentially affecting part quality. At Re:Build Cutting Dynamics, we use stainless steel tooling because the material has a higher yield point than Titanium at elevated temperatures, thus helping to prevent tool wear.

To further mitigate tool wear and galling, we apply a graphite coating to the tooling surface, which serves as a lubricant, reducing friction between the tool and the heated titanium. At elevated temperatures, titanium becomes highly susceptible to scratches and surface damage, which can compromise part integrity. The graphite coating helps protect both the tooling and the formed part, ensuring a smoother forming process and extending the life of the tooling.

Tool Growth

Accounting for tool growth is a critical part of the hot-forming equation. Traditional tool materials will thermally grow when they reach the high temperatures required for this process. Therefore, when our team develops appropriate tooling for a part, the final design is a percentage smaller than the desired part to account for the growth.

Surface Quality Obstacles

Titanium parts that have been hot-formed are prone to surface imperfections. An oxidation layer called an alpha case begins to form when the temperature of the metal rises above 900 degrees. This alpha case layer is a very brittle coating that allows cracks to propagate throughout the material. To remove this oxidation layer, Re:Build Cutting Dynamics sends the newly formed parts to one of our trusted partners to be etched. This etching process relies on a specialized acid bath to remove the outer layer, leaving behind the formed titanium part.

Titanium hot forming is a complex but essential process for producing high-performance aerospace components. While titanium’s exceptional strength-to-weight ratio and resistance to extreme conditions make it an ideal material for aerospace applications, achieving precise and repeatable results requires overcoming significant challenges. From managing temperature control and tooling durability to mitigating springback and ensuring surface quality, each step in the process demands careful consideration and advanced engineering solutions.

Re:Build Cutting Dynamics Should Be Your Partner for Hot-Formed Titanium

Our team’s expertise, combined with our diverse machining capabilities, makes us a reliable aerospace partner. In addition to our advanced engineering and manufacturing capabilities, we design and produce tooling and parts that meet the highest industry standards, all in alignment with our AS9100 certification. Trust us to bring your most critical projects to life with unmatched quality and reliability. Contact our team today to discuss your needs.