After being used to create prototypes, tools or presentation models, Additive Manufacturing (AM) is now more and more being adopted to manufacture functional parts.

And, indeed, AM has a lot of benefits, whether it be to build custom parts, to replace complex assemblies by a single 3D-printed part or to create organic shapes – lighter but still robust parts that would be near-impossible to manufacture with classical means.

It is also now possible to 3D-print a wide variety of metal parts in aluminum, high-grade steel, titanium as well as nickel and cobalt alloys. So why are additively manufactured parts still rare in the industry, in spite of a few spectacular announcements (such as GE Aviation’s 3D-printed fuel nozzles for the LEAP jet engine)?

Well, there is a long way to go from prototypes to mission-critical industrial parts. Get ready to discover the dark side of Additive Manufacturing and learn how the industry could answer its challenges!

1.  Printing a part with the right shape

When printing a metal part using the widespread powder-bed fusion technology, it is necessary to print support structures along with the part itself, otherwise part distortion will occur.

Video showing the printing of a metal part (accelerated). Notice how the part bends at its ends.

 

Support structures may look like this:

A 3D-printed rocket engine prototype, with part of its lattice support structure still in place.  Source: Lawrence Livermore Laboratory

 

But where to place these support structures, knowing that they will need to be removed afterwards, which has a cost?

How to ensure that there will be no distortion during the build or once the support structures are removed (springback effect)?

Software solutions can help ensure that the part is manufactured as it was designed. Such a solution should combine:

• An interactive or automated placement of parts on the build tray
• An automatic generation of relevant support structures
• A realistic simulation of residual stress and distortion; this function is essential to decide whether the support structures or the part design should be reconsidered

2.  Ensuring part qualification

In regulated industries such as Aerospace & Defense, one of the most serious hurdles to the expansion of AM for metal parts is the question of part qualification.

Beside distortion and shrinkage (see above), many other quality issues can occur, such as porosity (some applications require parts with a density greater than 99%), delamination of layers, poor surface finish and thermal stresses.  X-ray Computed Tomography can be used to check the internal structure of the parts.

 

Hydrogen pores in a 3D-printed aluminum alloy (source: Inside Metal Additive Manufacturing)

 

Physics-based models and realistic simulations once again can help avoid some of these issues, such as thermal stress.

Predictive analytics offer a complementary approach to hard science and simulations. By applying machine learning algorithms to simulation results or actual build data, patterns for good and failed parts are discovered. This in turn allows finding appropriate machine settings, which today are typically found using a trial-and-error method. The Lawrence Livermore Research Laboratory has tested this approach for metal parts printed with a Selective Laser-Melting[1] process. They found out that the laser power and scanning speed were the most crucial parameters.

It is also critical for the industry to agree on standard methods and test data for the qualification of materials and processes, which will in turn lead to the certification of the final products.

3.  Which raw materials and machines for which results?

Manufacturers have precise objectives in terms of part characteristics, such as hardness, density, and rigidity—which machine, raw material and AM process parameters could be used to meet these objectives? There is a lack of information related to material properties, and we have much less experience and scientific knowledge of AM processes than, say, molding or casting.

A company called Senvol has decided to address this challenge. They allow querying a database of AM machines and raw materials using criteria such as the required size of the build envelope or the material type.

Most importantly, they have built an empirical database of test results on AM parts built in certified facilities. Tested material properties include such attributes as tensile strength, hardness, compression, coefficient of thermal expansion, etc.  In addition, the AM machine used, the raw materials and the set of process parameters are fully documented for each test. Customers can then purchase test results.

Example of material characteristics obtained from a Senvol test (see full example)

 

Another initiative came from the National Institute of Standard Technologies (NIST), an agency of the US department of commerce. Considering the difficulty for the private industry to develop a consensus on material property data for AM, NIST has the goal of developing new standard material characterization methods, especially for metal parts and the A&D industry (see the project statement).

Summary

During this article we’ve focused primarily on metal part fabrication and covered three aspects of Additive Manufacturing: Printing parts with the correct shape, ensuring part qualification and tying in raw materials with the correct machines to meet the desired results. As we see an increase in manufacturers adopting Additive Manufacturing methods, we expect this growth to continue yet at a conservative rate.

Part 2 of this article will continue with four additional challenges associated with adopting additive manufacturing. Learn more about the economic advantages, risks to operators, challenges and opportunities for traceability, as well as size and material limitations associated with additive manufacturing.

 

If you liked this article, here are others you might also find interesting:

• The Coming Revolution in Additive Manufacturing
• 5 Ways 3D Printing Is Changing the Manufacturing Industry
• 5 Manufacturing Practices that will be Outdated within the Decade

 

[1] A technique of the family of powder-bed fusion processes that creates metal parts by fusing metal powder layers using high-power laser beams.