FIELD OF THE DISCLOSURE

The present invention relates generally to sacrificial tooling, and method for making the same.

BACKGROUND OF THE DISCLOSURE

Tooling is the process of designing and engineering the tools that are necessary to manufacture parts or components. The metal machining for mold represents an excellent example of tooling. Such tools include those for vacuum, stretch, and thermal forming as well as autoclaved composite layups. These tools are often utilized to form components of transportation industry, which requires ducting products, including engine intake and exhaust, as well as cabin air conditioning systems. Most ducting is made of solid plastic or metal components, but there is opportunity to remove weight from ducting by using components with carbon fiber composites and removing the weight of tooling to create hollow structures. Unfortunately, due to the complex shapes required of this tooling, traditional methods for composite layup that use a permanent manifold cannot be used. Conventional methods have been developed for creating one-time use tooling necessary for complex manifolds that can be “washed out” by rinsing the tool with water. Specifically, by using binder jetting of ceramic powders including sands, highly structural tooling can be created at much higher volumes than other additive manufacturing processes.

Tools for composite forming can be made from essentially any material such as fiberglass reinforced plastic, high-density foams, machinable epoxy boards, or clay. However, these materials can only apply to produce parts in low quantities, parts cured at ambient or low temperature, or for prototype parts which does not require concise dimensional accuracy. To create more dimensionally accurate parts in high-quantities at high temperature, high-performance steel-and-nickel alloys, such as Invar are typically utilized, but they are also more costly. Ceramics are particularly well-suited for each of these tooling applications because of their very low coefficient of thermal expansion (CTE). When combined with a right binder, infiltrants, and coatings, the ceramic parts can have properties that exceed concrete. These attributes combined with the low cost of many ceramic powders and the low cost of the binder jetting process make the manufacturing of large, strong tooling a real possibility at a fraction of current tooling prices.

The introduction of the latest manufacturing process, i.e. 3D printing, has the ability to greatly increase the throughput of tooling production. Furthermore, the capability to fabricate complex part geometries using layer-by-layer deposition as opposed to traditional manufacturing now enables production of tools that would be otherwise impossible to create without 3D printing. For example, binder jetting is an additive manufacturing process in which a printhead strategically drops a liquid binding agent to selectively join powder particles within a layer. The job box lowers, and another layer of powder is then spread, and more binder is spread. Over time, the part develops through the layering of powder and binder. Binder jetting is well-suited for the tooling industry due to high production rates, high resolution, and the ability to process low-cost feedstocks. The binder jet machines can print sand artifacts on the order of several feet in size.

The washout tooling process of 3D printing hollow objects is faster and more affordable than traditional methods of manufacturing multi-piece metal breakdown tooling. In addition, because the sand cores can be printed in more complex designs, washout tooling formed using binder jetting also eliminates the need for the multi-piece molds used to make castable washout tooling media for a faster and more streamlined process. Water soluble binder for washout tooling eliminates the expenses and lead time associated with traditional manufacturing of composite parts with trapped geometries. Washout tooling by binder jetting leverages soluble support material for 3D printing hollow objects.

With printed sand tools, a hermetic barrier between the sand and the epoxy in the composite layup must be created to prevent any sand particles from being bonded to the final geometry. The currently used process requires manually covering the printed tools with a tape, which is effective but labor intensive and difficult to scale. In addition, a typical hydrophobic coating including taping on the sand tooling surface greatly decreases the washout property.

Teflon wrapping on the printed tool is the most widely used technique. The wrapping shows good properties including high temperature resistance, non-sticky surface. However, Teflon is not water soluble which decrease the washout property and application of Teflon is a labor intensive and time-consuming process. Silicone is another widely used material to prevent any sand particles from being bonded to the final geometry. Silicone coatings show high elongation and tear strength. However, silicone coatings is not water soluble which decrease the washout property. Urethane is another widely used material. The urethane coating shows good property including electrostatic discharge safe. However, urethane coating is not water soluble.

SUMMARY OF THE DISCLOSURE

In one embodiment, a washout tooling for a composite layup is provided. The washout tooling comprises a casting mold having an exterior surface. The casting mold comprises a particulate material and a water-soluble binder. The casting mold is adapted to break down in the presence of an aqueous solution. The washout tooling further comprises a water-soluble coating layer overlying the exterior surface. The water-soluble coating layer is adapted to break down in the presence of an aqueous solution. The washout tooling further comprises a curable composite layer overlying the water-soluble coating layer. The water-soluble coating layer minimizes contact between the particulate material and the curable composite layer.

In another embodiment, a method for forming the composite layup is provided. The method comprises combining a particulate material and a water-soluble binder to form a casting mold having an exterior surface. The method further comprises applying a water-soluble coating material to overly the exterior surface to form a water-soluble coating layer. The method further comprises applying a curable composite material to overly the water-soluble coating layer to form a curable composite layer. The method further comprises exposing the casting mold and the water-soluble coating layer to an aqueous solution to form the composite layup.

In an exemplary embodiment, the water-soluble binder is deposited through inkjet nozzles to the particulate material to form a casting mold. The water-soluble binder that is ink jetted provides the initial strength/shape of the preform through chemical bonding with the particulate material, and the strength of that bond depends on the characteristics of each feedstock. An infiltrating polymer may be applied to the casting mold to infiltrated therethrough. The infiltrating polymer may provide mechanical strength and also the bonding surface for coatings, and its effectiveness depends highly on the chemistry between the particulate material, the water-soluble binder, and the water-soluble coating material. The water-soluble coating material is applied to the casting mold form a barrier between the particulate material and the curable composite layer. The water-soluble coating material serves as a functional barrier. In washout tooling, this is final coating between the sand print and the adhesive used in the carbon fiber layup functions such that no sand attaches to the final composite structure.

In certain embodiments, the water-soluble coating material comprises water soluble polymers or swellable polymers in water, so that the coating can be effectively removed after forming the composite layup. The water-soluble coating material may include a high glass transition temperature, such that the polymer will not flow during the curing process for the curable composite layer. The water-soluble coating material may include an inorganic filler for adjusting the rheology property of the water-soluble coating material and tuning surface finish.

A new polymer coating method was successfully developed for wash-out tooling that prevents sand from remaining in the carbon fiber layup after curing. A consecutive dip-coating method was developed for sand tooling utilizing polyethylenimine (PEI) binder, which significantly improves the barrier between the carbon fiber surface and the sand tool. Non-limiting examples of suitable PEI binders are disclosed in U.S. Pat. Pub. No. US 2020/0216363, the entire disclosure of which, except for disclaimers, disavowals, and inconsistencies, is hereby incorporated by reference herein. The PEI binder may be more suitable for use in the consecutive coating method relative to other binders having high water solubility. A spray coating method with a water-soluble coating layer formed from a poly(vinylsulfonic acid, sodium salt) (PVS-Na) 30% water solution may be used with printed sand tools to improve geometric accuracy while minimizing loose sand on the surface of the carbon fiber layup.

These and other features and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the appended claims.

