LPW Case Study Examines Porosity in Metal 3D Printing, Helps Users Optimize New System

UK-based LPW Technology, with headquarters in Pittsburgh also, specializes in creating and distributing metal powder for 3D printing and additive manufacturing. This includes a full lineup of powders made for selective laser melting, laser metal deposition, and electron beam melting. Customers have access to standard powders, as well as custom alloys. LPW also offers a number of other services for the industry in relevant development and support.

Now, to help clients and those interested in learning more about metal powders, LPW has released a case study which they shared with 3DPrint.com. In ‘Porosity – Powder or Process Derived?‘ their team takes on a topic highly relevant to 3D printing and additive manufacturing, as porosity has been under close examination for some time as it relates to metal 3D printing.

“When porosity causes issues in a built part, it’s important to understand the root cause. Porosity might originate from the metal powder or the AM process. This case study explores the different types of porosity, how they are identified, and follows LPW’s experienced applications engineers as they analyse an Inconel 718 AM component failure. Identifying porosity as the source enabled the manufacturer to quickly resolve the issue,” says Dr. Rob Deffley, LPW’s Research & Development Manager.

Figure 1 shows the cross-section of gas atomised LPW-718 powder.

With the elimination of porosity in mind, the LPW team points out that their key focus is optimizing material builds, and helping others to figure out where the problems occur.

Metal powder derived porosity/gas atomization commonly causes inherent porosity, but LPW states that it generally happens in particles over 45 μm in diameter. In the sizes relevant to additive manufacturing, the ‘occurrence is considered negligible for most materials when powder production is optimised.’

Parameter derived porosity is usually seen in three different ways. Lack of fusion causes erratically shaped pores. Gas entrapment is a common issue with part porosity, and is a result of insufficient hatching. Vaporization causes large, irregular pores, caused from ‘excessive energy absorption.’In their case study, the LPW team began studying why one part in particular was cracking. It was fabricated with a new batch of powder so they began examining whether that was the cause.

“No anomalies were discovered. Subsequent metallographic analysis was conducted on the solid part to find the crack initiation point and establish the root cause of the cracking,” states LPW in the case study. “In addition to the cracks, lines of porosity were observed. Across the larger block, there were four distinct lines of porosity orientated in the build direction, whilst the smaller tensile piece had two.”

Extensive study showed that the porosity was caused by a problem in the laser scan—with a deficiency in the hatching. Furthermore, as the team delved into the issue with hatching, they found that the parts were produced on a system that had only recently been installed.

“The user was able to focus on optimising the process parameters for the new system, saving time, and eliminating associated problems and additional delays further into the build process,” stated LPW.

To read the whole case study, or to find out more about other case studies produced by LPW, check out their library. Discuss in the LPW forum at 3DPB.com.

[Source / Images: LPW]