Complex metal parts are frequently created by a molding process known as casting.

Instruments like coordinate measuring machines, X-ray imagers, and ultrasonic testers can all be used to find defects in the finished metal component, including unintended flaws like rough surfaces, cooling deformations, or cracks.

Do the same inspection methods work for metal 3D printing? How do you test the strength and design limitations of a 3D-printed part?

In a live Tech Briefs presentation titled Testing and Inspecting 3D-Printed Parts, readers had questions for industry expert Kevin Brigden, an Applications Engineer at the U.K.-based engineering company Renishaw.

photo of Kevin Brigden, applications engineer from Renishaw
Kevin Brigden, Applications Engineer, Renishaw

Read Brigden's edited responses below.

"How does a 3D-printed part compare to a forged or cast one when it comes to test to evaluating fatigue?"

Kevin Brigden: This is the elephant in the room when you talk about metal printing fatigue...

Off the bat, the one thing I can say definitely is that there’s not enough fatigue data out in the wild. The amount or volume of that data is nowhere near the same as it is for conventional processes such as forging and casting.

What I can say, more speculatively, is that tensile properties, particularly in the case of casting, generally meet or exceed cast-equivalent materials. When you’re talking AlSi10Mg aluminum or TI64 titanium, [materials used in 3D printing], however, the application of anticipating fatigue is somewhat more difficult.

Often times the data that is generated is treated as proprietary, and people are reluctant to put it out into the wild. There are a number of official groups – ASTM being one of them  – that are working on developing standards and frameworks where this data can be published collectively as a group, particularly with metals and the laser powder bed fusion technologies.

Over the next five to ten years, I would anticipate seeing that data coming out in spades. Certainly, in the shorter term it is unfortunately quite sparse; it’s something that Renishaw is always keen to push the ball forward on. We’re in the habit of publishing white papers on the topic where we can.

"How mature is the simulation of items created by additive manufacturing/3D printing vs. items created by casting?"

Kevin Brigden: I guess it depends on which stage of the process you’re trying to simulate.

At the design stage, if you’re trying to understand design limitations of the product, the material properties, as I alluded to earlier for fatigue, are relatively limited. For tensile properties, they are significantly better developed.

There is the question of anisotropic properties in metal processes — this idea that mechanical properties may vary slightly depending on the direction of the print and the orientation of the part with respect to the print. However, generally speaking, most people that we work with tend to use the worst-case scenario, which is they build tensile bars in a range of orientations, find the one that is the least befitting to what they’re after, and use the worst case.

The second part of the answer is a lot shorter, which is the idea of actually simulating the print process itself. That is somewhat less mature at the moment. Most of these models are using an inherent, strain-based simulation approach, which has limitations in terms of accuracy and precision, but ultimately, it’s down to the resolution.

It’s this idea that clearly we are micro-welding at the smallest scale and building that up to a macroscale part, so trying to effectively model residual stresses and effects, such as surface burning, is considerably more difficult. Whilst a number of companies are working on developing print simulation technology, it still has quite some way to go to be an effective tool in day-to-day use.

What are your questions about metal 3D printing vs. casting? Share your comments about inspection and simulation methods below.