Learn what factors to consider when choosing the right nozzle size for 3D printing, and what to ensure in autoclave tooling in large-format 3D printing.
If you are 3D printing autoclave tooling, it is key to know the fundamentals of CTE values of the used materials. Knowing this will help you better understand how the 3D printed part will behave in the autoclave and what to expect.
Autoclave tooling is typically used in the manufacturing of composite parts in the aerospace or high-end automotive industry. The tooling must be able to withstand high temperatures and pressures during the curing process of the composite material. large format 3D printing is a cost-efficient method for producing autoclave tooling due to its ability to create complex shapes quickly and accurately.
One of the challenges with autoclave tooling in general is the thermal expansion of the tooling material. If you heat up any material it will expand. If it cools down, it will contract again. This is also for 3D printed tooling.
Coefficient of Thermal Expansion (CTE)The Coefficient of Thermal Expansion (CTE) is a measurement of how much a material expands or contracts in response to changes in temperature. If the CTE of the tooling material is significantly different from the CTE of the composite material being cured, it can lead to distortion and defects in the composite part. Therefore, it is important to carefully select the material for the 3D printed autoclave tooling and to take into account its CTE. Some materials that are commonly used for autoclave tooling include invar or epoxy foam with a low CTE value.
In an ideal world, the CTE value of the composite material and the material for large format 3D printing being used for the tooling would be the same. In that case, the expansion of both materials in the autoclave is the same as well.
LFAM versus traditional molds and toolingThe big difference between traditional tooling material and 3D printed autoclave tooling material is the way it behaves in the autoclave. On paper, the traditional materials have a CTE that is isotropic. This means that the expansion is the same in every direction of the material.
3D printed material will behave differently, due to the production process of the tool. In the X and Y directions of the layers, the CTE will be lower than in the Z direction. This means that the 3D printed tool will expand more in the Z orientation of the tool than it does in the X and Y directions. For this reason, it is always best to keep the amount of layers of the tool as minimal as possible, if the print strategy allows for it.
A general misconception about epoxy foam is that this has an isotropic CTE value, meaning that the expansion of the material is the same in every direction. This is only theoretically the case. In practice, the epoxy foam acts as an isolation. The foam will not heat up evenly, resulting in uneven expansion throughout the tooling. So in fact, the epoxy expansion foam will act as an anisotropic material. Even though on paper it is an isotropic material.
CTE in Large Format Additive ManufacturingPlease always refer to the datasheets provided by the material supplier, the CTE values will be stated in these datasheets. On the customer portal of CEAD, there is an online tool that can calculate the thermal expansion of your 3D printed tool in the autoclave. You only have to provide the temperatures for the curing cycle in the autoclave and the CTE values of the material in every direction.