Hydraulic manifold for aerospace redesigned for additive manufacturing with MTC, part-1

Gen3D and the Manufacturing Technology Center (MTC) recently collaborated on a hydraulic manifold for aerospace redesigned for additive manufacturing. Hydraulic manifolds are ideal for additive manufacturing (AM) because there’s huge potential for mass reduction and flow improvement. The project demonstrated that AM could provide a significant mass reduction of the hydraulic manifold while ensuring that the AM process was suitable to deliver the mechanical properties that were required.

This case study describes part-1 where the initial design focused on a component-level redesign. In part-2, we will explore the second iteration of this design project that considered a systems-level redesign approach.

Design brief for the new manifold

The original steel hydraulic manifold, shown below, weighed 28.5kg. The maximum working pressure of the manifold is 250bar and during testing it must undergo a burst pressure test of 450bar.

The new manifold in this case study was printed at the MTC using the Arcam Q20 machine, using the Electron Beam Melting (EBM) process with the titanium alloy Ti-6Al-4V.

We decided that for the first design iteration (part-1) the inlets and outlets of the manifold would remain in the same position because this represents a common use case, where the sub-assembly cannot be redesigned.
 

Component-level redesign option

This scenario represents the component-level redesign option. This is the plug and play solution, where you simply swap out the old manifold for the AM manifold and all the parts seamlessly fit back into place. While this offers the ability to use techniques such as topology optimisation and generative design to significantly reduce the mass, we were still constrained by the overall positions of the components.

This method will almost always cause limits to the AM design when the inlets and outlets of the manifold remain in the same position as the original. The figure below shows the commitment to the potential benefits of being able to change the layout of the manifold.

Designing the fluid channels in Gen3D

Based on the hydraulic circuit diagram, the fluid channel network was designed using our software. The click-and-drag user interface inside of Gen3D’s software makes this process extremely quick and easy. The external components were downloaded from the relevant company catalogues and imported into the software at the coordinates that they are assembled into the original manifold.

The fluid channels for the manifold

The fluid channels were designed with the maximum horizontal circle size in mind. The maximum horizontal circle size is determined by both the material and the AM process itself. One of the benefits of using the EBM process compared to, say, laser powder bed, is the greater freedom of circular channel sizes that can be produced without the requirement for support structure.

For the larger channels, Gen3D’s automatic support compensation tool was used to modify the geometry of the circular channel to a teardrop shape ensuring that the channels could be printed without the need for internal support structures. Additionally, the fluid channels were smoothed to reduce sharp bends and reduce the angles at junctions thus improving the fluid flow characteristics.

The channels were connected in the same locations, however, the blanking plugs were removed as these are a by-product of the original drilling process.

The improved fluid characteristics by smoothing the 90° corners can be seen in the CFD velocity profile results below.

These structures were easily exported from Gen3D’s software as a STEP file and imported back into CAD software in order to continue the design process and prepare the design for printing.

Generative design for optimisation

Once the fluid channels were exported from Gen3D into the traditional CAD software we used Autodesk’s Generative Design solution to optimise the overall structure of the manifold.

To achieve this, we considered the internal fluid pressure of the component in use as well as any machining forces that occur during the post-processing stage. Autodesk’s Generative Design solution like many other topology optimisation programs requires preserve geometry, areas where material must be kept (shown in green in the image below).

These are the STEP fluid channels that are exported from Gen3D and also keep out zones (shown in red) that areas where material cannot be placed as well as the applied loading conditions and a design objective.

A safety factor of 2 was used within the loading to ensure that the part could withstand the burst pressure testing procedure.

No support constraints

Although the option to add manufacturing constraints is available in the generative design software, it was decided to generate the design without any support constraints in order to maximise the search space available.

After the best design was selected, further detail was added including additional webs and fixturing to aid in the post-machining stage.

Additionally, the part was rerun through a secondary FEA analysis to ensure that these additional features did not introduce any stress concentrations into the part that could compromise the part strength.

Printing of the hydraulic manifold

Once the part had been through the generative design program and the additional design features were added, it was sent to print. Additional stock material was added to the interfacing regions that would subsequently be machined in order to achieve the required assembly tolerances.

Inspection and analysis

The post-processing stages included build plate removal, and then manual powder removal. Due to the sinter cake created from the EBM process, this requires both vibrational and physical agitation of the powder. Since some of the channels didn’t have line of site access, a CT scan was undertaken to determine whether all of the powder had been removed from the channels.

Although it can be challenging to interpret the scan data, the results showed that some trapped powder remained in the channels.

Chemical etching to displace the trapped powder

One method that was explored to remove the trapped powder was chemical etching. This removed most of the trapped powder and also significantly improved the surface finish. However, some trapped powder still remained inside of the manifold.

What we have learned in part-1 of this case study

The objective of the first stage of this project (part-1) was to determine the most efficient and effective workflow for redesigning an optimised aerospace hydraulic manifold for additive manufacturing.

The initial design focused on a component-level redesign. In this case, the length of the fluid channels and lack of line of sight features meant that additional material was used for support structures and also trapped powder remained a problem.

In the next post, we will explore the second iteration of this design project that considered a systems-level redesign approach whereby the locations of the inlet and outlet ports could be modified.

This work was carried out as part of DRAMA which was led by the UK’s National Centre for Additive Manufacturing in partnership with leading technology providers, research organisations and the Midlands Aerospace Alliance. DRAMA was funded by UK Research and Innovation through the Industrial Strategy Challenge Fund (UKRI) and was supported by the Aerospace Technology Institute.  Read more about DRAMA via our article.