Miniaturization boosts demand for small 3D-printed parts

This 4-mm-diameter gear, 3D-printed on a Nanogrande MPL-1, is made of 25 5-micron-thick layers of powder metal. Nanogrande

With so many industries clamoring for ever-smaller parts, it’s no surprise that 3D microprinting is growing in popularity. Today, a variety of microprinting technologies turn out parts with feature sizes measured in microns. And for more demanding applications, advanced printing systems can build even smaller features.

Microprinting isn’t the only option for making extremely small parts, of course. Alternatives include microscale machining and injection molding.

But these processes can be costlier than additive manufacturing, according to Juan Schneider, CEO of Montreal-based Nanogrande Inc., developer of a 3D printing system for small parts.

Microprinting Edge

Consider rapid injection molding. Prototyping tools for this process are normally made of aluminum. Micromolding, however, requires costly high-precision steel tools that take several months to produce, noted Pierre Viaud-Murat, founder of Qualified3D, a Southfield, Mich., service bureau that prints small components.

With microprinting, on the other hand, there’s no wait for pricey production tools to be made, said Viaud-Murat. Using microprinting in the prototyping process allows testing of the actual part geometry, though not the correct part material.

He also reported growing interest in microprinting for applications with low part volumes. This trend is partly being driven by small companies introducing new products. These firms usually have limited funding available for trials and testing and don’t know how big demand will be, Viaud-Murat said. “It’s a big step to invest several hundred thousand dollars in a set of production tools.”

In addition, microprinting is catching on with companies that know they will only need limited quantities of certain parts. For them, microprinting makes more sense because there is no upfront tooling investment. “You pay as you go,” Viaud-Murat said.

For some applications he has seen, microprinting was judged a better production option than micromolding for part volumes as high as several hundred thousand per year.

Then there are cases involving complex product designs for which microprinting is the only option because of the limitations of conventional manufacturing methods. As an example, Viaud-Murat points to work his company does for the microfluidics industry, which has historically been limited to 2D component geometries. Microprinting allows the industry to produce 3D geometries, opening up additional design possibilities for microfluidic chips.

This fiber connector was produced on a BMF Precision P140 nanoArch printer. BMF Precision

Work in Progress

Along with impressive capabilities, microprinting has had to overcome a number of challenges. In the past, for example, the resolution produced by microprinters was far inferior to that offered by micromolding, according to Viaud-Murat. Today, though, there are printers on the market designed to go down to the nanoscale range.

Among the most accurate printers currently available are those based on two-photon technology, which involves firing a laser at photosensitive material. According to Schneider, the two-photon process can produce parts with dimensions smaller than a millimeter and resolution of less than a micron. Examples include optical parts like waveguides and lenses, as well as connectors and scaffold components for cell growth.

On the downside, two-photon printers are very slow and expensive, Viaud-Murat said. “The upfront investment is at least five times the cost of the printers we use, and some parts can take weeks to print.”

Instead of trying to achieve the highest possible resolution—and thereby drive up printing time and costs—Viaud-Murat decided that a good compromise is to print at a 10-micron X-Y resolution and a 20-micron layer thickness.

These metrics are achieved by nanoArch™ printers from BMF Precision Technology (www.bmftec.com). According to Viaud-Murat, the printers employ the same digital-light-processing technology as those used to print larger parts, except that the software, optics, and motion controls have been coordinated to boost accuracy.

Typical parts made by these printers for Qualified3D are roughly 10 by 15 by 5 millimeters, with smaller feature sizes in the 40- to 50-micron range. In addition to microfluidic chips, commonly printed parts include either small medical device components having geometries that can’t be made by injection molding or parts made in such low volumes that the cost of the mold can’t be justified.

To limit vibration that can ruin small parts, the BMF printers weigh around 300 kilograms and are mounted on a damping table. Viaud-Murat recommends that all printing of small parts be done in a climate-controlled room that minimizes the impact of temperature and humidity on the print material’s mechanical behavior.

Sticky Situation

Another major microprinting challenge is dealing with the special properties of small material particles. For powders with particle sizes of 20 microns and smaller, cohesive forces have a bigger effect on the process than gravity. In fact, Schneider said cohesive forces acting on 17-micron particles are 100 times stronger than the gravitational forces on the particles.

A 3D-printed microfluidic chip. Qualified3D

It’s “very difficult” to create uniform layers with these sticky particles, he said. In response, Nanogrande developed an approach based on fluid interaction and chemical properties that masks cohesive forces during the layering process. The technology allows those forces to re-exert themselves a few seconds later so the particles become very sticky again. Schneider said this re-emergent stickiness eliminates the need for support structures common to 3D printing, which account for up to 60% of the cost of printed parts in the metals industry.

Nanogrande’s MPL-1 printer can produce single-particle layers as thin as 1 nanometer, according to Schneider. At present, however, the MPL-1 is not printing nanometer-thick layers for customers and works mainly at the 1-micron scale.

Examples of parts made with the MPL-1 include watch faces, gears, and inserts, as well as electronic connectors, fasteners, and cellphone and medical components. Part lengths are 1 mm to 1 centimeter, with thicknesses down to 300 microns and features as small as 20 microns.

Materials currently 3D-printed by the MPL-1 include stainless steel, titanium, and copper. In all, Schneider said, the process has been tested with more than 50 materials, including exotic ones such as graphene, carbon nanotubes, and nanodiamonds.

Postprinting Challenges

Some of the biggest challenges faced by those involved with microprinting come after the printing process. “We are still learning about postprinting operations,” Viaud-Murat said.

Key questions that must be answered about postprocessing include:

• What are the customer’s expectations regarding adequate part inspection?

• How can these expectations be met despite the difficulties involved in precisely inspecting such small parts?

• How should diminutive and delicate parts be packaged and transported to prevent damage?

“These types of questions require discussions with customers,” Viaud-Murat said.

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