Researcher works to make 3D-printed metals stronger, customizable

WPI engineer's work involves printing with semi-solid metals, instead of limited powders

diran apelian wpi
Sharon Gaudin/Computerworld

A scientist at Worcester Polytechnic Institute is working on a way to change metal 3D printing that could revolutionize the way products are customized.

Diran Apelian, a professor of mechanical engineering at WPI, is researching the use of so-called semi-solid metals, instead of powdered metals, in additive manufacturing. His work could give manufacturers more metals to work with and ultimately create 3D-printed products that are stronger and longer lasting.

Apelian's work also could enable manufacturers to create specialized parts for medical devices, as well as automobiles and aeronautics.

"There are problems with the powders," said Apelian, director of WPI's Metal Processing Institute. "This will revolutionize the way we make things."

Apelian is collaborating with researchers at Lawrence Livermore National Laboratory and Viridis 3D LLC, a Woburn, Mass., company that makes 3D printing machines and software.

Together, they're working on metals that are semi-solid, or half liquid and half solid, and have a gooey or mushy consistency. Using this materials would be a change for the additive industry, which uses powdered metal for 3D metal printing. Powders, however, have been found to have problems.

Powdered metals contain oxides, which not only make the metal more apt to rust, but also act like holes in Swiss cheese or bubbles in dough, and weaken the final product.

"That's a very bad thing," Apelian said. "It would be like having little pin holes in a glass pane, adding lots of places where the glass could break. The powders for these high-temperature melting alloys are difficult to make and they have a lot of oxides, so it may not be as strong and may lead to failures."

It's also difficult for manufacturers to get a wide variety of powdered metals.

"There are only a few alloys that you can get sufficient quantities of," said James Bredt, a co-founder of Viridis 3D. "It's a small market. The manufacturers of these metal powders are huge companies making the powders for different industries. Most [powders] don't really work on these laser [3D printing] machines. They're not set up to produce stuff of purity as high as you need for a laser sintering process."

Joe Kempton, an analyst with market research firm Canalys, said this is the first he's heard of research on semi-solid metals for 3D printing, and said the material could get around the problems that come with powders.

"It's quite interesting," Kempton said. "Perhaps one of the biggest obstacles for 3D printing itself is the limited amount of materials you can print with… What they really want is a wide range of high-performance alloys or superalloys. The reason these industries are looking for superalloys is because they often have extreme durability and high performance under pressure. They're resistant to oxidation and corrosion."

The ability to print with a variety of superalloys, added Kempton, would be a huge advance in terms of the types of objects that could be produced, as well as their strength and durability.

"3D printing with these metals is highly sought after, especially in the aerospace and automotive industry," he said. "The less oxidization the better. Obviously corrosion means that you have parts that are degenerating at a faster pace and need replacement more frequently. And in the automotive, and particularly the aerospace area, if you have an object that fails, especially midflight, the results are catastrophic."

Using a semi-solid metal, instead of a powder, also would mean lower energy costs for the manufacturer since the processing temperatures needed to print with semi-solids is much lower.

"If you're using lasers [and powders], you have to get the material up to white heat to get the materials to fuse together," explained Viridis' Bredt. "A lower temperature means less energy is needed to make the part and that's a significant part of the cost… One of the significant costs of the process now isn't significant anymore."

Apelian noted that being able to use a wide range of metals – specifically the superalloys – would enable medical device companies to use 3D printing to make customized pieces.

"Everyone has different-sized knees," Apelian said. "If they could print a new knee for someone – customize that knee -- then it would fit just right ... and there would be less pain and less physical therapy."

His work could revolutionize the ability to customize pieces, whether they're replacements for knees and hips, or automotive parts for a military vehicle being used in the desert.

"There are a lot of applications where you're not making 100,000 parts for automobiles," said Apelian. "You may be making customized pieces where it's maybe one or two or four of them. These are high-integrity applications, like jet engine parts or legacy parts that nobody makes anymore. It will revolutionize the way we make things that are customized."

To make that happen, though, he needs to figure out how to control the semi-solids in the manufacturing process.

"How do you control gooey, mushy metals so you have high precision when you make the deposit?" he asked. "I have to control the thixotropy or how the flow changes under the application of a force. I have to make sure it's flowing in a controlled manner."

Robert Parker, an analyst with research firm IDC, said there is a lot of activity going on to expand the variety of materials that can be used in 3D metal printing, but Apelian's group may be the only one looking at using "goo." That means there's a lot of work ahead to make these semi-solids work.

"It largely comes down to the economics," Parker said. "What are the economics of the goo? Does it create maintenance issues in the printer? How expensive is it to create? This is the first step to commercialization – proving the concept. But then you need to produce it economically. It breeds well in captivity, but how does it do in the wild?

Apelian said they are probably a year-and-a-half away from actually using semi-solids in a testing environment.

"We're not doing any printing yet until we know what we're doing," he added. "When I understand what's going on, then I'll print. I want to know what the issues are and figure it out and then I'll go work on it. It's all the prep work ahead of time."

Copyright © 2014 IDG Communications, Inc.

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