Hot form dies (HFD), also known as Hot Size Dies (HSD), are a tool used to form metal utilizing intense heat and pressure. It is most commonly used to form titanium and nickel aerospace components.


HFD’s can be made of various types of tooling materials, however for titanium forming they are most commonly made of 304 stainless steel. Other tooling materials may be used depending on the material’s required forming temperature and press conditions. Stainless steel offers high heat resistance, oxidation resistance, and strength, though it has a tendency to be brittle at high temperatures. This means it is very important that tool designers limit stress concentrators and mitigate such conditions. Trap beads may also be incorporated into the tool design in order to aid in the forming process. Another important consideration that must be incorporated into the tooling design for accuracy is material shrinkage, which is a combination of the thermal expansion of the die under heat and the retraction of the part material when cooled.


The part is generally formed using a simple, open and close, punch and die concept. To form a part a heated piece of material, which may or may not be pre-formed to an approximation of the final shape, is placed in the die and aligned utilizing tooling pins. The die is then closed and held under pressure for a prescribed amount of time to form the part. Pre-forms are used on complex parts and those that may be more likely to suffer from spring back, or the tendency to return to the unformed state. Once cooled the part may be trimmed along with any other secondary operations.


The advantages of HFD’s are a reduction in tearing or shearing of material during forming and decreased spring back and higher dimensional accuracy compared to cold forming, lower cost and less thinning when compared to superplastic forming. Another advantage of the process is its speed, as parts can be formed relatively quickly. The main disadvantage is the high temperatures required.


To learn more about hot form dies or about how we can help you with your tooling needs please contact us.