Orientation Tech Brief

May 15, 2017


What is it?

exaSIM™ is a predictive simulation tool that enables Additive Manufacturing (AM) practitioners to rapidly understand how to optimize part orientation for AM fabrication without the need to perform multiple trial and error iterations of a physical build. In short, exaSIM saves time and money when selecting part orientation.

What is the hurdle?

The success of an AM build is highly dependent on the orientation for which the part is fabricated. Skilled designers and machine operators take into account the interplay between anisotropic material properties,
distortion, residual stress, surface finish, build time, and material consumption when selecting part orientation. Without predictive simulation, AM practitioners rely on experience and intuition to make
these determinations. The geometric complexity of many AM components makes the consideration of these tradeoffs difficult. A commonly used solution is to build several prototypes in different
orientations to determine the best orientation for a quality build. This increases time, cost, and powder consumption.

Figure 1: V-22 link fabricated in Ti64

Figure 1: V-22 link fabricated in Ti64

This Tech Brief reviews the process undertaken to determine optimal part orientation for a NAVAIR V‐22 Osprey linkage. These components required multiple physical build iterations to achieve a successful build. The challenge was to demonstrate if simulation could improve that process.

How was simulation used to clear the hurdle?

The exaSIM user selected four orientations for evaluation (see Figure 2) and simulated the part in each orientation to collect on‐plate (before removal from the baseplate) distortion and stress data. exaSIM‐generated support structures were simultaneously generated and evaluated as part of the decision matrix to determine the best orientation for these parts.

Figure 2: Link file in four different orientations used for evaluation

Figure 2: Link file in four different orientations used for evaluation

Figure 3: On-plate distortion

Figure 3: On-plate distortion

As‐built, on‐plate distortion (see Figure 3) is an important consideration for orientation selection, even if the part will undergo post‐process heat treatment before removal from the baseplate. In comparing orientations it is important to consider not only the magnitude of the distortion, but also the distribution and location of high displacement regions. In this case, the circularity of the holes in each end of the link are critical, since they mate with pressfit bearings. The best orientation for the holes would be those with low and uniform distortion.

When possible, eliminating post‐processing steps saves time and money. Parts with low residual stress may not need to be heat treated, since they will not change dimensions significantly after removal from the baseplate. Parts with high residual stress require heat treatment to maintain part accuracy. On plate residual stress predictions (see Figure 4) show that residual stress for this part is significantly different for different orientations.

Figure 4: On plate residual stress

Figure 4: On plate residual stress

 

exaSIM supports were generated for each of the selected orientations. Orientations with more
supports result in greater material usage. Supports in difficult‐to‐machine regions require extra expense during post‐processing. exaSIM support structures (see Figure 5) are generated based upon residual stress predictions to provide users with a support structure that will fixture the part to the baseplate without support failure – giving the user confidence they can select the ideal orientation without the fear of support structure failure.

Figure 5: exaSIM Auto-generated Support Structures

Figure 5: exaSIM Auto-generated Support Structures

Every part has different requirements. Thus, the trade‐off between, build time, material consumption, residual stress, post‐processing cost and part accuracy will be different based upon part‐specific priorities. In this case, the exaSIM user normalized each element of evaluation and weighted them to create the chart shown in Figure 6. As can be seen in the chart, the best orientation at equal weighting is the flat XY orientation. The user selected this orientation as well as the minimum stress X45 Y30 Z10 orientation for fabrication to evaluate the potential for eliminating the heat treatment step.

Figure 6: Comparison of the four evaluation criteria for this scenario using normalized values

Figure 6: Comparison of the four evaluation criteria for this scenario using normalized values

Did the exaSIM orientation evaluation lead to a successful build?

exaSIM auto‐generated supports were utilized to produce both orientations successfully. This illustrates how exaSIM users can perform orientation evaluation and directly use the exaSIM‐generated output files to improve the success rate of metal AM builds, reducing trial and error iterations. After the first build was fabricated, additional parts were fabricated in the XY orientation to fulfill a complete order with appropriate post‐processing.

Figure 7: Link parts in two orientations on baseplate after a successful build.

Figure 7: Link parts in two orientations on baseplate after a successful build.

Conclusion?

AM practitioners can quickly select the best orientation for their part using exaSIM. A NAVAIR component was simulated in four potential orientations to determine the best orientation based upon part‐specific selection criteria. exaSIM‐generated supports were utilized in the build process and resulted in successful linkage fabrication for a geometry that had been problematic to build prior to utilizing exaSIM.

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