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Additively Manufactured Polymer Tooling for Rubber Compression Molding

Description:

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials

 

OBJECTIVE: Develop an additive manufacturing (AM) technology to rapidly create high strength, high temperature, and low-cost polymer tooling for use in rubber compression molding applications.

 

DESCRIPTION: Compression molding is a common manufacturing process for making rubber products. During this process, uncured rubber stock is placed within a heated mold before the mold is closed. The rubber cures and conforms to the mold cavity before the mold is opened and the finished part is removed. Within the Navy, numerous undersea sensor components, such as cable plugs and connectors, are fabricated using rubber compression molding. The molding process typically uses tooling made from steel due to the high temperatures and pressures required. However, steel tooling can have high costs and lead times. Advances in AM (also known as 3D printing) and new high-temperature polymers may allow these steel molds to be replaced with AM polymer molds, which could significantly reduce costs and lead times and open up new workload capabilities.

 

Limited research has been done to adapt AM technology and polymer materials to rubber compression molding. Some commercial AM systems have the capability to print room-temperature silicone molds or low-volume injection mold inserts, but the materials used in these systems do not translate well to the high continuous use temperature of the compression molding environment. The Navy is seeking the development of an additive manufacturing process that can rapidly create high strength, high temperature, and low-cost polymer tooling for use in rubber compression molding applications.

 

Polymer AM was chosen as the preferred process due to its speed, low cost, easy implementation within existing spaces, geometry flexibility, and safety. Metal AM processes will not be considered due to relatively high investment and post-processing costs. Several challenges exist for bringing polymer tools close to parity with traditional steel tools. Surface roughness, dimensional accuracy and precision, durability, and longevity are key focus areas to consider. Surface treatments, coatings, machining, and other post processing techniques may be used, but should be minimized to reduce overall costs. Polymer materials may be thermoplastics, thermosets, composite reinforced, photopolymer, or other novel material and must be non-hazardous. Companies may develop a new material, machine, or process; or adapt a commercial material, machine, or process to meet the Navy’s needs. All printed inserts will be used in a metal master unit die (MUD) frame.

 

The new AM solution will be utilized in a production setting to enable the rapid turnaround time for time- or cost- sensitive tasking, reduce project costs, and develop new products. Proposed concepts should meet the following thresholds:

1. Process:

a. Process: additively manufactured

b. Material: Polymer or composite; surface coatings, treatments, or other post-processing permissible but should be minimized; non-hazardous

c. Build size: 6 in x 3 in x 3 in Threshold, 12 in x 12 in x 6 in Objective

2. Tool:

a. Inserts will sit in metal MUD frame

b. Continuous use temperature: 300°F

c. Typical clamping force: 15 tons

d. Duty cycle: 1 hour minimum cycle time under required temperature and pressure

e. Reusability: 100x minimum, molded part must meet requirements

f. Mating face flatness: 0.010 in Threshold, 0.005 in Objective

g. Chemical resistance: no special considerations

3. Molded part:

a. Dimensional tolerance: 0.010 in Threshold, 0.005 in Objective; or 0.05 in/in Threshold, 0.002 in/in Objective; whichever is greater

b. Surface Roughness: 250 microinch Threshold, 125 microinch Objective

c. No physical defects, bumps, or voids > 0.030 in

 

PHASE I: Develop a concept for an AM process to create rapid, low-cost polymer tooling for use in rubber compression molding as detailed in the Description. The concept shall include proposed material(s), machine(s), and post-processing technique(s) needed to meet the Navy’s requirements and how they address the challenges of high temperature, high pressure, surface finish, dimensional accuracy, and durability. Demonstrate the feasibility through modeling, simulation, analysis, or other formal methods. The Phase I Option, if exercised, will include the initial design specifications and capabilities description to build a prototype solution in Phase II.

 

PHASE II: Develop, demonstrate, and deliver an AM prototype to create mold inserts that meet the Navy’s requirements. The proposed material(s), machine(s), and post-processing technique(s) will be evaluated to determine their capability and feasibility. Perform detailed testing and analysis addressing required performance. Deliver a minimum of five prototype mold inserts for rubber parts chosen by the Navy for evaluation and demonstrate the flexibility of their concept to apply to various rubber part shapes and sizes.

 

PHASE III DUAL USE APPLICATIONS: Apply the knowledge gained in Phase II to further develop a complete turnkey AM system capable of producing polymer inserts suitable for rubber compression molding and assist the Navy in transitioning the technology for use. The AM system may include commercial-off-the-shelf (COTS) parts or equipment, and need not include equipment for typical or readily available post-processing steps such as machining. Support the Navy in implementation of the system within Navy production spaces and qualifying the system for production use. The complete AM solution will be used to support production of undersea sensors components aboard various surface ships and submarines.

 

Explore the potential to apply the solution to other military or commercial rubber molding shops or do further research to apply advancements to similar molding applications, such as injection or composite layup molding.

 

REFERENCES:

  1. Tuteski, Ognen and Kocov, Atanas. “Mold Design and Production by Using Additive Manufacturing (AM) – Present Status and Future Perspectives.” International Scientific Journal of Scientific Technical Union of Mechanical Engineering Industry 4.0, Vol. 3, Issue 2, 2018.https://stumejournals.com/journals/i4/2018/2/82
  2. Gohn, Anne M.; Brown, Dylan; Mendis, Gamini; Forster, Seth; Rudd, Nathan; and Giles, Morgan. “Mold Inserts for Injection Molding Prototype Applications via Material Extrusion Additive Manufacturing.” Additive Manufacturing, Volume 51, 2022. https://doi.org/10.1016/j.addma.2022.102595

 

KEYWORDS: Additive manufacturing; rubber compression molding; high temperature polymers; composite reinforced plastics; master unit die; undersea sensors.

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