Saint-Gobain SEVA’s “Alloys & Transformation” industrial Business Unit includes a specialized foundry and a wide range of machining capabilities. Thanks to these industrial capabilities and our expertise in designing and building special tooling for high-temperature environments, we entered the aircraft industry several years ago. We supply Hot-Forming & Super-Plastic-Forming toolings as a first-tier and second-tier supplier. SEVA offers a complete service, coordinating and performing most of the steps internally to design and build such tooling.

Everything starts with the customer’s data and technical specifications, where the customer precisely defines the part’s design, its position on the aircraft, and the requirements for the tooling itself, as well as its conditions of use, which are crucial to be considered. Of course, if it is just to duplicate an existing tooling, we can rely on the complete tooling file provided by the customer. However, the customer’s data, technical specifications, and conditions of use become even more critical when creating a completely new tooling. This includes starting from the aircraft part design and designing the corresponding tool by taking all relevant parameters into account. Depending on the level of details provided, we will speak of a “Build to print” or a “Build to spec.” project…

During the design phase, after receiving the 3D CAD data from the customer, our design office will need to:

• Check the part balancing within the tooling to ensure it can be unmolded without deformation after the SPF process. If any draft angles are discovered, rebalancing the part within the tooling (or even redesigning it) may be necessary. This point must be discussed with the customer.

• Define the parting lines: This is the surface that connects the aircraft part to be formed with the general tooling design. The parting line must also be validated by the customer (possibly through a forming simulation) to ensure the most efficient forming process.

Once the parting-line surfaces are created, the general tooling design can begin, taking into account:

• Customer specifications and conditions of use: This includes press specifications, forming process parameters, the relative homothety between the tooling and the titanium part (as they do not have the same expansion coefficients), the target yield depending on the number of parts to be produced, and the titanium sheets throughput.

• Tooling production parameters such as:

• Casting parameters: Total weight of the tooling, required homogeneity of wall thicknesses, tooling handling, etc.

• Machining parameters: Accessibility of cutting tools, minimum radius, etc.

Finally, the 2D drawings will also be created and validated with the customer. They will be used as references for realization and controls.

                              Feeding                                                             Feeder                                                           Solidification

Next comes the casting study itself, including simulations. This is an absolutely essential step before launching the complete casting process. The foundry methods department will design the tooling casting process by adjusting and optimizing several parameters such as:

• Tooling design: This includes the tooling’s radius, surface thicknesses and possible addition of structural reinforcements.

• Casting yield: The ratio between the weight of liquid metal used and the weight of the obtained raw casting.

• Dimensions and design of casting auxiliaries: This includes the “feeders,” which are liquid metal reserves added to the mold to compensate for metal shrinkage during solidification. Feeders help prevent internal defects in the cast part by avoiding shrinkage porosities and locating them in the feeders instead of the tooling.

The tooling design will be optimized and validated through various successive steps of simulations (using MagmaSoft software or other) until the best simulation results are achieved for:

• Feeding : This allows validation of the general tooling design.

• Solidification: This defines and confirms the optimal sizing of feeders and checks the metal behavior during solidification.

Finally, based on the defined tooling design, the corresponding pattern will be designed and built. This pattern will then be used to create the sand mold in which the liquid metal will be poured to cast the required tooling.

As you can see, these are dynamic and multiphysical simulations (including material flow, physical, chemical and thermal behavior according to the time).

Such simulations are quite complexe. Based on industry specific software, they are progressively made more and more efficient and reliable by defining our own parameters and enriching our own database with values adapted to our alloys based on our observations.

Comparison of the main components ratios included into the HF & SPF toolings

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During this phase, an important parameter to consider in the tooling design (and to discuss with the customer) is the choice of alloy grade. Several possible grades for casting tooling exist, but they do not all have the same characteristics or performance. Here again, some compromises may need to be made.

For hot-forming, austenitic refractory steels are most frequently used.

However, SPF processing at higher temperatures, more advanced materials such as Nickel-based superalloys are required.

Finally, in special cases, we even already used some of our in-house Cobalt-based alloys which are even more resistant (more in particular considering creep resistance at higher temperatures) and which could even be an opportunity for future hybrid HF-SPF process ?

As we can see in the graph above comparing each grade’s composition, the Nickel content primarily drives the alloy’s thermal performance, but it also affects the final price of the tooling.

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The Nickel content also influences the mechanical characteristics at high temperatures. So, based on our experience, the choice of the alloy grade the tooling will be made of is a very important step, not to be negliged and to be discussed with the customer. Also considering its conditions of use, this will greatly impact the tooling lifetime.

Indeed, the higher the machining crests, the faster the machining operation will be. However, this will also result in a longer polishing phase. This compromise needs to be defined during programming, depending on the surface typologies and the customer’s expectations. These choices can also significantly impact the final cost of the tooling.

Cutting tool used for the roughing phase

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Of course, the final check will also include dimensional results, particularly focusing on the molding surfaces and the parting lines. This will be conducted using:

• 3D dimensional control: Utilizing contact probes or scanning.

• Surface state control.