DfAM, design for additive manufacturing

Introducing design for Additive Manufacturing

by Srikanth Purli, Design Engineer at AMEXCI

Design for Additive Manufacturing (DfAM) is a collective industrial term referring to the components which are newly designed or redesigned for Additive Manufacturing (AM).

Unlike subtractive manufacturing, Additive Manufacturing processes showcase additional design capabilities, some of the key characteristics are – designing complex internal channels, customization of end use parts, functional integration, material distribution, designing bionic / cellular structures, etc. show the actual value add of Additive Manufacturing.

But given the nature of the process it does have certain limitations, in which designing the components for a specific Additive Manufacturing technology is a crucial aspect. These design restrictions / guidelines are to be addressed during the early stages of the development process to make it an effective usecase.     

Role of software tools in Additive Manufacturing

Software tools play an important role in realising applications for AM. Currently there are several software houses across the digital thread of AM as shown in the fig.1. The main aspects to be considered, while choosing or working with a specific tool, would be its maturity and the key characteristics that help you realize a good application.

To start with, any commercially available CAD tools should help you address the generic design limitations / guidelines. However, designing lattices / bionic structures, design for light weighting, or compliance for instance, are provided as separate bundles from these software houses as shown in the fig.1. DfAM tools like nTopology or Carbon would surely complement the existing CAD tools to go above and beyond the horizon.

Fig. 1: Additive Manufacturing software landscape

At AMEXCI, we initially identify the usecases and evaluate the potential value add. Then we guide and assist you in several aspects on how to realise it for AM, and make a good business case both on the technical and the economic aspects.

Key things to keep in mind

File conversion to stl is crucial to maintain the quality and the tolerances of the manufactured parts. The digital file exported from the CAD tools should maintain the minimum thresholds with chordal lengths and tolerances to especially maintain the parts resolution. But the triangle count in a stl should be always kept in mind, as heavy files might not be easy to handle in the tools used further for file preparation and slicing. Hence a compromise is to be found between the resolution and the triangle count of the exported stl.

For example, in the below fig.2, the sphere is exported with various parameters (chordal length and tolerances), and it is explanatory that the resolution of the sphere is directly proportional to the number of triangles.

Fig.2: Sphere with variable resolutions post conversion

Material distribution is an aspect of DfAM which must be realized during the initial stages of part identification. The key thing to ask yourself after the part identification is:

Whether the volume of the material is completely necessary for this application?

  • If yes, it is straight forward to choose the orientation, support profile (if any) and go ahead with the build.
  • If no (this is where things would be interesting), then the approach would be to realise it with topology optimization / generative design, or with any bionic / lattices, to generate light weight structures with better compliances and functionalities.

For instance, the fig.3 illustrates the material distribution along the internal channels of a heat exchanger for an optimum flow and an effective heat dissipation via optimization.

Fig.3 Heat Exchanger – 2D [1]
 

Note: In general, prior and post this step a proper FE analysis should be performed to understand and evaluate the component from a structural / thermal standpoint with a good safety factor.

Functional integration is to consolidate several components – like Internal channels, connection joints could be redesigned into a single component and can be realised with AM.

Optimum part orientation is necessary to yield better nesting ( = how many parts can be placed on a build plate), better quality with higher tolerances, optimum support profile and post processing times. Hence it is to be kept in mind to decide and design on an orientation from the very initial stage.

The below 2D wedge structure in fig.4 can be oriented in different ways as shown to avoid the supports completely and to improvise the packing density and reduce the cost per part.


Fig.4: Wedge structure – 2D

Reduce support structures is a key aspect to make a cost-effective business case. Supports are mainly used to anchor the parts to the build plates to transfer the heat of the melted area to the platform for efficient cooling and avoid deformation. With proper design for Additive Manufacturing and with an optimum part orientation these support structures should be reduced as much as one can. Saying that, this is highly AM technology dependent and varies among different materials too.

Technology dependency on DfAM

There are 7 sub technologies / categories in Additive Manufacturing and each technology is different in its own way. To best utilize the capabilities and the freedom of design which comes with these technologies, it is in the best practice to design for these technologies accordingly.

For instance, L-PBF metal would need support structures to realize the parts on the build. In contrast, Metal binder jetting process does not need supports (during the printing process), and the parts could be tightly packed and nested in the build envelope.

Your challenge: How would you make it a good case for AM?

Demonstrator: Topology Optimized Bracket (you can access the CAD from this link)

  • Material: AlSi10Mg, dimensions: 32 x 71 x 121 mm, volume: 21,7cm3

Technology & machine manufacturer: L-PBF, SLM 500 (build chamber: 500 x 280 x 365 mm)

Topology Optimized Bracket

Criterion:

  • Suggest an optimum orientation for the best cost per part
  • Showcase the influence of orientation on nesting density – numbers possible to build
  • Effect of part orientation on the support profile / volume

Deliverables: Come up with an optimum solution addressing all the above criterions. Either you can use the software tool of choice to realize the solution or answer back to the below email with your suggestions or thoughts.

Timeline: Please provide your answers by the end of May 2022. The solution will be presented in the tech watch newsletter for June 2022.

The participant with the best solution will have a more in-depth discussion with our Design Engineer, Srikanth Purli, about this case, and other interesting topics related to DfAM.

Please send your answers to srikanth.purli@amexci.com. Looking forward to your answers!


About Srikanth Purli

Srikanth works as a Design Engineer with a major focus on Design for Additive Manufacturing. He specialises in bringing the value add with applications via AM.

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