Using composite structures is a great way to reduce weight and gain strength. However, creating these structures is labor intensive and costly. As a result, manufacturers must often compromise on innovation, design functionality, and number of iterations to meet strict deadlines and stay within budget.
One of the biggest challenges involves making hollow composite structures like tubes, manifolds and vessels. Fabricating these complex parts is sometimes impossible, because the geometry affords no way to remove the lay-up core, or it mandates design compromises to accommodate less-optimal production methods. For example, some designs rely on a “clamshell” mold technique to fabricate two halves of the part separately, then combine them together, post-cure, to form the hollow structure.
However, this method can leave a weaker overall design, as the composite fibers do not bridge the mating line around the part. It also adds another step to the fabrication process. 3D printed sacrificial cores using ST-130 soluble material provide a solution to these challenges. They eliminate “trapped tool” configurations and allow single-piece composite lay-ups for stronger structures that require fewer processing steps. Another use includes metal plating purposes, where the soluble cores are plated and then dissolved, leaving behind a metallic structure.
Sacrificial Tooling Application
ST-130 material combined with FDM® printing enables unparalleled, single-step production of complex dissolvable cores for both lay-up and plating applications. The sacrificial cores are first created in CAD. Once a final CAD design has been developed, it is imported into advanced Insight™ slicing software. Insight software permits the generation of a sparse permeable infill, with extra exterior contour layers. These additional layers give the part structural integrity and rigidity for vacuum bagging, while the sparse infill allows for rapid core removal, post-cure. This build style has been optimized for sacrificial cores, enabling part processing with a single button press in the software. Insight also allows for any further slice modifications as needed. Once the CAD design has been finalized with Insight, fabrication can begin.
3D printing these cores dramatically reduces tool production time. In some circumstances multiple iterations can be built and tested in a single day, achieving faster design optimization. Once the sacrificial core has finished printing, several minimal post processing steps are required. Often, a soluble core requires some support material and must be manually removed after printing. Another post-processing requirement is to seal the core. This includes sanding with multiple grades followed by an epoxy or gel goat. This is a highly important step as it prevents resin from embedding in the core, providing an ultra-smooth finish to the internal surfaces of the final composite structure.
Creating Composite Tools
In this unique “how to” video, Stratasys visit Swift Engineering’s Kerry Dang as he takes us through the step by step process of creating a sacrificial tool for a complex, hollow inlet duct.
Once post-processed, the sacrificial core is ready to be wrapped or plated. Composite wrapping can be done with various methods, including wrapping the entire core, creating a seamless structure. The part is then consolidated using traditional vacuum bagging. While ST-130 can be autoclaved, pressures should not exceed 80 psi and temps of 100 °C unless prior testing is done, as core deformation can occur. In some cases, temperatures in the autoclave have reached 120 °C, but with reduced pressures.
Once cured, the core is removed. Unlike traditional processes, removal of the core tool is completely automated. Using a detergent solution, the composite part and core are submerged for a few hours. It is important to check with the composite resin manufacturer to verify the solution will not degrade the resin. The solution automatically dissolves the printed core tool from the composite structure. This process dramatically reduces manhours spent manually removing the core, allowing much tighter and complex geometries to be achieved.
Sacrificial tooling application is a best fit for:
- Strong and lightweight parts
- Complex hollow composite geometries with a high quality internal surface finish
- Low-quantity production
Benefits over traditional methods:
- Seamless hollow composite structures
- Reduced manual labor – automated core removal process
- Shorter design-to-part time – large lead time savings
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