Welding Digest

Changes driven by rapid innovation in 3D printing (3DP) technologies are afoot. Direct metal laser sintering (DMLS) has allowed an impressive list of metals to be built with additive manufacturing.

When 3DP became something beyond science fiction in the 1980s, people said it would be the death knell for welding. They believed individual small parts would no longer have to be manufactured and assembled and instead those multiple parts could be made as one piece, eliminating the need for weldments. Forty years later, welding is alive and well, but 3DP’s future looks bright.

Early 3DP processes relied on plastics such as nylon, acrylonitrile butadiene styrene (ABS), and polypropylene. Over time, new technologies emerged that enabled companies to print metal parts. In particular, the DMLS process uses laser power to fuse layers of powdered metal into specific geometries dictated by a computer-aided design (CAD) model.

The Technology behind DMLS

DMLS works by digitally slicing CAD models into paper-thin layers and then drawing them with a laser, or multiple lasers, into a bed of powdered aluminum, Inconel®, titanium, stainless steel, cobalt-chrome, or other metals. Starting from the bottom layer and working up, the DMLS process uses a powerful laser to melt metal particles and fuse them to their neighbors, building one layer at a time until the part is complete.

The result is a fully dense metal component with mechanical strength and fatigue characteristics that are very similar to — and in some cases exceed — products machined from comparable wrought, forged, or cast material. However, the DMLS product is produced with minimal tooling costs, significantly reducing setup times and waste.

DMLS Printing Advantages and Considerations

With any 3D-printed part, and compared to assemblies of welded parts, the primary advantage is geometric flexibility. Pretty much any shape you might want to create is possible, although rules need to be followed to ensure part inspection and postprocessing operations can be performed. Other advantages of additive manufacturing include the capability to produce one-piece parts and the ability to overcome the limitations of machining or forming.

There are also some critical design rules to consider. Optimally, geometric transitions need to be properly graded to eliminate abrupt shifts or transitions in the design. Incorporating radii, ensuring all overhangs are less than 45 deg, and modifying circles to teardrop shapes can help with this. Additionally, sudden changes in geometry can increase the number of support structures required, and that will ultimately increase the machine time and cost of additively manufactured parts.

Despite these design considerations, 3DP offers the ability to do quick iterations of a design to refine and test geometries. Because of the ubiquity of 3D desktop printers, engineers have discovered they can quickly adjust models before sending them to a manufacturer. Consequently, the 3DP process has become more common, allowing for many to take full advantage of the process’s capabilities.

The Future Is Now

One major change over the past few years that makes 3DP more attractive is the build volume of today’s printers. For example, the GE Additive X Line 2000R has a massive 31.5 x 15.7 x 19.7-in. (800 x 400 x 500-mm) build volume. Protolabs, a provider of custom prototypes and low-volume production parts, uses two of these machines, one that prints in Inconel 718 and another that prints in AlSi10Mg. Building parts of this size takes considerable time, so manufacturing at production levels requires financial resources and some patience.

Two of the most highly regulated industries — aerospace and medical devices — embraced the flexibility of 3DP. They are paving the way for other major industries, like automotive and industrial equipment, to incorporate 3DP technology.

One concern holding back some companies from jumping into 3DP is understanding return on investment. DMLS can be expensive for parts not well designed for the process. But even that is becoming old news as design tools, printers, and postprocessing advancements redefine what’s possible with 3DP and at what price point.

Additive manufacturing will never be a do-it-all process for all applications. For high quantities of standard parts, it will be incredibly difficult to match the economics of injection molding or die casting. But 3DP will become a mainstay in the manufacturing of end-use production parts sooner than you may think.

This article was written by David Bentley (senior manufacturing engineer at Protolabs, Raleigh, N.C.) for the American Welding Society.