Page 24 - 3D Metal Printing Fall 2019

3D
AM INSIGHTS
By Mark Barfoot
AM Parts:
From Inception to Inspection
Creating production parts using metal additive manufacturing (AM) requires consideration of the entire process chain during product development. This journey involves several important steps.
The first step: design phase. Typically it is not cost-effective or appropriate to take an existing CNC-machined or cast part and convert it direct-
ly to an additive part. Those parts were designed
to meet specific machining or molding rules, and
those same rules do not apply to AM. To get the
most out of AM, the part should utilize the bene-
fits of additive such as lightweighting and creat-
ing topology-optimized models that include
material only where needed. AM also enables the
integration of several traditionally manufactured
part components into the build of one single part,
which eliminates assembly time. In addition, fea-
tures within traditional parts require support
structures (i.e., round holes). The removal of these support structures can be a challenge and one of the highest cost driv- ers of AM parts. A change in design from the outset eliminates the need for support structures. A round hole converted to a teardrop shape requires no support.
The second step: optimize part build. To achieve this, con- sider adjusting build parameters to ensure optimum part prop- erties for your specific geometry. By maximizing the number of related parts built together on a tray as opposed to building just a single type of part, costs decrease.
The third step: post-processing. Here it is important to ask questions such as, “How should you go about removing the support structures?” “How do you remove trapped powder inside small channels or crevices in your part?” and “Do you need to apply any post finishing (i.e.: sand blasting, vapor pol- ishing) to the part to improve surface finish to meet the end
Mark Barfoot (mbarfoot@ewi.org), as director of additive manufacturing (AM) programs for EWI, oversees AM initiatives and helps develop new AM technology opportunities. He also directs the Additive Manufacturing Consortium, a national consortium of industry, government, academic and non-profit research organizations operated by EWI; manages EWI’s interest in ASTM International’s AM Center of Excellence, focused on AM standards development, projects, education and training; and remains an active member of the Additive Manufacturing Users Group after having served as president of the group.
Unlike the traditional CNC-machined part shown on the right, these three 3D printed parts were designed to utilize the benefits of additive manufacturing, such as lightweighting and topology-optimized models that include material only where needed.
use needs?” For post-processing, consider stress relieving, heat treating and/or hot isostatic pressing (HIP) for reducing resid- ual stresses, improving strength properties and reducing inter- nal porosity. Developing the correct processing parameters for each of these steps is crucial for ensuring that parts do not deform or have less-desirable properties.
Another area often not considered: removal from the build plate. If parts can be built with minimal build-plate contact, removal could be an easy twist off of the plate, though this typ- ically is not practical. More often, bandsaw or wire EDM is needed to remove parts from a build plate. Each method has its pros and cons.
An important part of post-processing to consider: machin- ing to clean up surfaces or dial in tolerances. Most metal AM parts require some level of subtractive machining to ensure that the final parts meet final tolerances and part require- ments. Often, grip points, data and more are ignored when developing the original part design. However, inclusion of such factors in the design ensures rigid holds in the CNC while pro- cessing the part.
The final consideration: post-build analysis. What nonde- structive evaluation (NDE) technique are you going to use to evaluate and certify the part quality? One main NDE technique is x-ray computed tomography (CT), employs x-ray attenua- tion through a sample to reveal information regarding its inner
22 | 3D METAL PRINTING • FALL 2019
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