Are 3D printed molds ready for prime time?

By Clare Goldsberry
Published: November 8th, 2013

With the additive manufacturing (AM) or 3D printing process, there's almost nothing that can't be printed from human ears to end-use aircraft components thanks to an ever increasing range of materials, both polymers and metals. So what's been holding back the 3D printing of molds cores and cavities?

Primarily, cores and cavities for the injection molding process need to hold up under the heats and pressures of that environment. Additionally, the surface finish of 3D printed cores and cavities typically is not suitable for the parts and requires some finishing work. So, for years prototype parts have been built using the various 3D processes to evaluate the geometry, look and feel prior to a one- or two-cavity pilot mold being built in which to run actual pre-production parts.

That is changing however, with an announcement from Stratasys Ltd. with headquarters in Minneapolis, MN, and Rehovot, Israel, that Robert Seuffer, GmbH & Co. KG (Seuffer), a German supplier of parts for household appliances and commercial vehicles, is using Stratasys 3D printing to manufacture cores and cavities to produce injection molded sample parts.

This may be a game-changer for mold manufacturers, whose customers typically require prototype parts to evaluate part design for performance and fit before making the production mold. Even the fastest machined cores and cavities for a "pilot" mold can take up to two weeks to make. That means the ability to dramatically streamline the tool creation process for producing these prototype parts is another concrete example of how Stratasys 3D printing is revolutionizing manufacturing.

 "Working with the automotive industry, sample parts need to be tested in the environment of moving mechanical parts as well as in high temperature environments," explained Andreas Buchholz, Head of R&D at Seuffer. "With Stratasys 3D printing, we can design first drafts of the injection mold within a few days and 3D print them in less than 24 hours for part evaluation. Traditionally, it would take eight weeks to manufacture the tool in metal using the conventional CNC process. And while the conventional tool costs us about 40,000 euros, the 3D printed tool is less than 1000 euros, a saving of 97%."

Using Stratasys 3D printing technology, Sueffer also produces 3D printed molds for its hot melt process. These molds, which are used to overmold low melting point polyamide over electronic circuit boards, are created with Stratasys' rigid, opaque Vero materials.

Rob Winkler, supervisor for FDM (Fused Deposition Modeling) applications for Stratasys, provided an interesting technical presentation at the SPE Thermoforming Conference in September. "Thermoforming is possible using an FDM-built tool with pressures up to 10,000 psi and for most sheet thicknesses," Winkler said. "FDM tooling success is dependent on forming pressures and those are dependent on the type of sheet being formed, the thickness, and the bend radii, draft and draw depth.

The most common material used that provides optimum tool life is ABS, which is also easiest to finish and bond. Polycarbonate is preferred for low-volume manufacturing, because it has a higher heat deflection temperature (HDT) and the sheet material doesn't stick to a warm tool. Ultem is the preferred material for a tool that will form thicker gauge material, and it also has the highest mechanical properties and the best HDT, Winkler noted. Tool life for an FDM tool is typically 500-1000 cycles without wear, which means it's best suited for prototype and low volume manufacturing.

Winkler also stated that FDM tooling's benefit is not labor savings but rather "it's for process improvements for low-volume manufacturing to reduce or remove product design and/or tooling manufacturing time from the critical path. It allows for multiple iterations to improve the final product."

With 3D printing becoming more and more a major part of new-product development, mold development can't be far behind as mold manufacturers seek to provide more up-front support to their OEM customers. Nadav Sella, Stratasys Solution Manager, told PlasticsToday from the K Show, "We are definitely seeing an increasing demand and interest from companies to use 3D printed molds to cut time and cost whenever possible. It also means that they make fewer changes to the production tool. There is a lot of interest here at the K Show."

ABS is used to make the cores and cavities, and the most common materials used for injection molding parts are PP, PE, PS, TPEs, POM, ABS, and PA and other materials with similar processing parameters. Sella also noted that the typical number of shots from a 3D printed mold depends mainly on the geometry of the part and the material being injected.

Andy Middleton, general manager of Stratasys EMEA at Stratasys, added, "Companies worldwide are looking to introduce significant efficiencies to their manufacturing processes when introducing new products, and are discovering the many benefits of additive manufacturing, also known as 3D printing. More and more manufacturers are adopting 3D printed tools as a complimentary injection molding solution - not only to cost effectively test products before mass production, but also to produce customized parts."

DMLS would be an alternative, but where's the demand?

Direct Metal Laser Sintering (DMLS), a process developed by EOS GmbH, uses powdered metal for its 3D metal printing systems. With metal materials improving and evolving to the point that companies like Linear Mold & Engineering in Livonia, MI, can made actual end-use parts for customers in the aerospace industry, DMLS and a similar technology - Selected Laser Melting - would seem to be a natural for building cores and cavities for injection molds.

With five EOSINT machines and one Selected Laser Melting system from SLM Solutions GmbH, Linear is able to meet demand for end-use parts from its customers. However, when it comes to demand for cores and cavities for injection molds, it's just not there yet, according to Linear's Manager for DMLS, Brandy Badami.

"I do get a lot of interest in DMLS cores and cavities," she told PlasticsToday. "Unfortunately, a lot of them are 'undoable' because of the size constraints of the machines, or the cost is too high for the bigger cores and cavities. It's no cost-efficient to 3D print large blocks (cores/cavities), versus smaller inserts like we do with our DMLS conformal cooling lines."

Badami noted that Linear has done a few projects that have had smaller cores/cavities 3D printed, including one for plastic material that was hand-injected, and another core/cavity set for a small injection mold.

"3D printing is a great way to take advantage of being able to conformally cool a core/cavity, but it is not always cost-efficient for an entire mold," Badami explained. "Usually what happens is a prospect wants the entire mold 3D printed, but we talk them down to just 3D printing the [conformal cooling] inserts so that they can chase the hot spots in the mold."

Badami commented that the mold core/cavity demand might increase, as the build beds get larger. Linear's SLM system has a larger build bed, 280mm x 280mm x 350mm, and a higher laser power, 400/1000 Watts fiber laser. "Once the machines allow for larger build envelopes, I anticipate companies wanting to take advantage of the ability to lift the design limitations with water lines and start 3D printing entire molds."  

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