Small to mid-sized businesses like Built-Rite Tool & Die, a mold-making and design firm, face increasing pressure from international and domestic competitors in the area of quick-turn mold services. Overseas manufacturers offer lower prices and domestic prototyping shops offer quick turnaround times for small quantities of parts. But 3D-printing gives Built-Rite an opportunity to compete with shorter lead times and reduced costs.

The Massachusetts based mold-making and design firm specializes in the production of molds for plastic injection molding. These molds have complex designs, requiring extensive planning and precise execution.

To meet customer demands, Built-Rite selected Desktop Metal’s Studio System to make quick-turn mold assembly components. The Studio System involves a process that is less labor-intensive than other equipment in the machine shop and more cost competitive than a third-party prototyping firm. The Studio printer uses closed-cell infill to lightweight parts and minimize material usage without affecting the wear resistance required for tooling applications.

Plastic injection molding is a manufacturing process for producing parts in high volume. It works by injecting molten plastic material under high pressure into cavities within the mold to shape a part. For mass production, injection molding offers low cost-per-part, repeatable outcomes, and minimal waste of the injected material. About 32% of all processed plastics go through injection molding processes, making it a dominant manufacturing method.

A mold can be made up of many complex cavities, inserts, and cooling channels. Mold tools must withstand repeated impact and exposure to high-temperature polymers—making wear-resistance a critical feature. Challenges include high tooling costs and long lead times. Design changes can have a significant impact on time and cost, so the ability to iterate quickly is critical to overall process efficiency.

The Studio System uses a technology called Bound Metal Deposition where metal rods—metal powder and polymer binders—are heated and extruded onto the build plate, shaping a green part layer-by-layer. The part is immersed in proprietary debind fluid in the debinder, and then sintered in the office-friendly furnace. The three-part system is designed as an end-to-end solution for in-house metal 3D printing.

Built-Rite identified an existing mold cavity insert for initial testing with the Studio System. Compared to a third-party prototyping shop, the Studio System reduced cost and lead time, as well as part weight and amount of material used.

Injection molding tools require tight tolerances to fit the assembly, as well as a polished finish on surfaces that make contact with the injected plastic so that the part can be easily ejected from the mold. In its as-sintered state, part performance was evaluated based on two post-processing stages to observe variation on process parameters and material behavior, and then functional testing to observe the part in use.

Built-Rite’s machinists ground the surface of the 3D-printed mold inserts to achieve tolerances and surface finish. They assessed whether any special handling was required and determined that the parts heated similarly to other tool steels and did not present any issue in sizing or fitting the inserts into the mold assembly.

Machinists used EDM to achieve the required surface finish on the cavity surfaces of the insert. They assessed the need for varying the parameter setup, electrode wear, and resulting surface finish. They determined that it was not necessary to vary the EDM parameters for the printed parts and the electrode wear was comparable to non-printed inserts. There were no notable differences in surface finish.

After post-machining, the insert was installed in the mold assembly and used to produce plastic parts made of acetal—a non-abrasive, low-friction plastic material. The temperature of the plastic when injected into the mold is about 205°C (401°F), and the mold itself is kept at approximately 82° to 121°C. A test run of about 100 cycles showed no flaw in the plastic parts produced and the 3D-printed insert showed no sign of wear.

The success of the initial evaluation indicated the potential of the Studio System for injection molding applications. The system enables injection mold manufacturers to improve operations and realize the benefits of additive manufacturing without relying on third-party vendors. This includes reduced material usage and printing with closed-cell infill, for lower costs and the ability to lightweight parts while retaining the wear resistance required for tooling applications. In response to unexpected design changes or short turnaround times, the Studio System allows mold-makers to iterate on designs faster and at a lower cost than outsourcing to a third-party mold service.

Follow-up testing will include leveraging design flexibility of the Studio System to produce mold inserts with conformal cooling channels that follow the shape of the mold cavity. This allows for uniform cooling of the plastic part immediately after injection to reduce “hot spots” and optimize part quality beyond traditional manufacturing methods. Additional testing will also include printing with H13 tool steel, a material commonly used in this application.

Desktop Metal
www.desktopmetal.com