The debate over the use of 3D printing to create molds for various tooling needs continues. 3D printing is a viable option for making molds for tooling, but, as with everything, there are trade-offs on speed, finish, cost, and so on.

Recently we held a webinar on developing tooling with 3D printing. Derek Roedel, Advanced Tooling Program Manager at FATHOM, was one of the presenters and he offered guidance on 3D printed molds for tooling.

One of the reasons you might choose to 3D print a mold is because it’s fast–you can often produce a finished mold in less than a day. Such speed enables designers to test and validate a design quickly, iterating multiple times and improving the design at each step.

“We have customers all the time tell us they need a part ‘tomorrow,’ and we can meet that need with 3D printed tooling,” said Roedel.

Speed enables this technology to fit a gap in the production of short runs, where all you need is a couple hundred parts, for example. Other methods like CNC machining and casting can produce small quantities, but the cost can be high. Whereas with 3D printing, you can prototype and produce small quantities at reasonable prices.

One of the limitations of 3D printing molds, though, is texture. The resolution of the 3D-printed material will determine the final texture. You can alter texture through various finishing methods, such as sanding or machining. But finishing requirements will have to be balanced against needed tolerances and features, such as thin walls. The wrong finishing method can eliminate desired features or negatively affect the needed tolerance. In addition, various finishing methods add cost to the project.

At Fathom, 3D printing is typically done on a Stratasys PolyJet printer with an ABS-like resin. But another option is direct metal laser sintering (DMLS) technology.

DMLS technology delivers molds made from metal material, usually steel or aluminum, enabling these molds to handle larger part runs. One possible drawback, though, is that DMLS printed tooling will need more finish processing. Noted Roedel, some printed parts will need machining to make the surface finish better suited to the final part, or to release molded parts.

For short runs, such as 50 to 100 parts, resin-based molds are an option. Heat, though, is a factor in tool longevity. The resin choice dictates the life of the tool. Lower melt points will help plastic tools produce for a longer time.

“We’ve experimented and done a lot of research on exactly how far we can push the plastic to get the customers everything that they need,” said Roedel. “We can do higher-temperature polycarbonates. But tool life will be a bit shorter. If we do a thermoplastic elastomer or a lower-temperature, softer resin, we can get more out of the tool life.”

When designing molds to be built on a 3D printer, be sure to consider how the molded part will be removed from the mold. Noted Roedel, “For ejection, we can use large ejection blocks or peel the part by hand versus other standard methods like ejection pins.” Manual removal is fine for small part runs and keeps costs down.

If you plan on using a resin material for your mold, the standing plastic needs to be thick–a millimeter to a millimeter and a half or more, depending on the aspect ratio of walls or standing items in the tool. Otherwise the pressures of the injection molding will blow them away or break them. Draft often needs to be a bit bigger too for 3D printed molds than for traditionally made molds. The reason is the resolution available on the 3D printer.

“Some things, such as very thin walls, cannot be made as exactly as with metal tools, but we’re getting closer,” said Roedel.

Leslie Langnau
llangnau@wtwhmedia.com