July 1, 2017
To reduce overall weight for airframe manufacturing, a design was produced for an airline seat made of magnesium that was almost half the weight of conventional aluminum seats.
The design was used to create a 3D plastic mold, which would then be coated with high-heat ceramic material. Designers partnered with a foundry to use the mold to fabricate numerous magnesium seat frames. The weight reduction, when scaled across a jet fleet, would result in a significant return on investment that would pay for the initial design and mold development many times over.
Magnesium seat frames demonstrated the capability of using 3D printed molds to assist manufacturing production in a positive way. Using such molds expedited the design time by quickly producing prototypes that could be further tooled up for fabrication. Time was reduced and overall production risk was minimized.
Though 3D mold making does have limitations and is not a fully mature technology, it offers much potential to today’s design community that is forever concerned with expediting the time, cost and benefit with technology for design to fabrication.
The Fruition of 3D Printed Mold Making
3D printing has established a firm footing as a viable solution to support manufacturing. Its utility for making molds, however, does have limitations.
“The rapid manufacture of molds has been pursued for 20+ years with limited success until the last 8 to 10 years, after which it has continued to improve,” says Duane Sawyer, 3DEXPERIENCE technical solutions specialist, Simulation for Designers for Dassault Systèmes.
Sawyer says the cost of a 3D printed mold can be more expensive than a traditional subtractive method, but it takes less time to make 3D printed molds.
“There are two different scenarios for 3D printed molds involving plastic or metal mold materials,” he says. “Typically, only the mold cavity and core inserts are made using 3D printing. The mold cavity and core inserts are placed into pockets in a traditional machined metal mold base. If the exercise is strictly for prototyping purposes, a plastic mold would be the quickest and most cost efficient method. If the need is for short-run production, multiple cavity/core sets may need to be made, depending on the complexity of the mold.”
Uses and Limitations
Hanno van Raalte, product manager for Moldflow products in Autodesk in Boston, believes there’s great potential in 3D printed molds, although he agrees its application has been limited thus far.
“So far, in my experience, 3D printing is used primarily for very specific areas in a mold, rather than a full mold,” says van Raalte. “There are some practical limits of what size parts can be 3D printed on most current machines. And most molds, or mold components, can be manufactured more cost effectively with traditional subtractive mold making techniques. However, over time, you would expect these cost and size barriers to drop and gain market share.”
However, he believes that in the short term there are many cases where 3D printing of a mold core for prototypes makes sense. “I’m thinking for instance of small plastic parts for which the cost of failure of that component is high and the complexity is high,” he says. “In that case it should pay to 3D print a mold component to create a small number of physically molded parts that can be used for physical testing.”
But not everyone is upbeat about the advancement of 3D mold making. Gordon Styles is the founder and president of Star Rapid, a custom prototyping, tooling and low-volume manufacturer in Zhongshan, China. He has seen epoxy molds made using 3D printing going back several years.
“We found that molds made by this method could rarely make more than 20 to 100 moldings of relatively low-quality, poor surface finish, long cycle time and poor mechanical properties,” says Styles. “We were very disappointed with the results. We found at the time that it was quicker and of a similar cost to CNC machine a mold in aluminum.”
He hasn’t changed his belief that 3D printed molds are of limited use. “Nearly 20 years on, not a huge deal has changed in the field of 3D printed plastic molds for plastic injection moldings,” he says. “Some larger manufacturers are making better and more complicated parts, but the quality, surface finish, cycle time and mechanical properties have not improved so greatly in two decades that it is taking hold in mainstream prototype tooling and molding. It does, however, fill an essential niche.”
Machined Mold Alternative
In many cases, 3D mold making supplements a process or a machined mold. It is used to facilitate and supplement rather than serve as a primary mold. For example, 3D printed molds may be used to redesign machined molds that are not performing optimally.
“In some cases a plastic part may have deep pockets where the mold may have a hard time getting the heat out of using conventional mold cooling techniques,” says van Raalte. “This would lead to very long cycle times. You would hope an injection molding analysis would have showed that problem, but truth is that often these long cycle times show up once a mold is on a machine, and there is no way to make meaningful improvements without redesigning and optimizing mold cooling at that point. There are several ways to do this, but one of the methods is using highly optimized, conformal cooling channel layouts. In many cases, the most cost effective way to construct mold cores with these optimized cooling channels is using 3D printed mold cores.”
3D printed metal molds are also available. Dassault’s Sawyer says metal 3D printed molds offer limited mold cavity insert sizes. He adds that for tight tolerance parts or highly polished part surfaces, the molding surfaces may need additional polishing or finishing before they can be used.
Because of the durability of 3D printed metal molds compared with plastic ones, the life of these molds can be in the area of millions of shots, says Sawyer. “The need to rerun the analysis from a prototype mold, if a mold was made with 3D printed metal, would be based on changes made after the evaluation of the prototype parts.”
van Raalte sees 3D metal molds as a promising alternative to conventional machined molds and believes the metal molds may be superior to 3D printed plastic molds.
“I think in time 3D metal printed mold designs may evolve away from what we currently look at as a conventional mold,” he says. “In a conventional mold, we have a tremendous amount of steel, and a great deal of this may not actually serve any purpose other than adding weight. 3D printed molds may be optimized to minimize material use and weight, or may contain cavities that could be filled with high thermal conductivity powder/beads to extract heat more with extra efficiency. 3D printing will tap into the creative juices of some people, I’m sure.”
Moving forward, 3D mold making should prove beneficial. Its advancement will likely follow the progress of 3D printing in general and will offer a means to mold making that was not available in the past.
According to van Raalte, when barriers are overcome, 3D mold making should provide great opportunity: “With efficiency improvements and scale, there will be a point that, when past, should open the floodgates for 3D printing in the molding industry.”
About the Author
Jim Romeo is a freelance writer based in Chesapeake, VA. Send e-mail about this article to [email protected].Follow DE