Insights in Metal Printing


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Designing for Additive Manufacturing Brings with It Design Freedom

By: Rutuja Samant

Monday, October 29, 2018
 

In conventional manufacturing, well-established practices such as design for manufacturability (DFM) and design for assembly (DFA)—design parts for ease of fabrication, reduce total number of parts in an assembly, design multi-functional parts, avoid tooling, etc.—are easier said than done. Each principle has its own manufacturability limitations when it comes to complex part designs.

Today, however, additive manufacturing (AM) enables industry to overcome manufacturing limitations that curtail design freedom using AM processes to build complex, optimized geometries one layer at a time, without having to think about fabrication.

New Design Possibilities

AM aerospace brackets
Fig. 1—These AM aerospace brackets demonstrate the advantages of topology optimization.
AM has enabled a paradigm shift in design practices. Designers can base their designs purely on functional requirements of the application without worrying about process constraints. To leverage the potential of AM technologies, designers must think beyond the conventional and constrained possibilities that traditional CAD tools enabled. One could categorize the design enablement of AM processes into these groups:

  • Topology-optimized design. Topology optimization identifies the minimal material requirement in a design space to satisfy the defined boundary conditions. AM processes make it possible to build topology-optimized components. Many conventionally designed parts, now being topology-optimized and redesigned to reduce weight and material consumption (Fig. 1), point to the growing popularity of topology optimization. As a result, many CAD-software companies are launching commercial topology-optimization software packages.
  • Part consolidation. Designing consolidated parts by eliminating the need for large, multicomponent assemblies leads to faster overall turnaround times by eliminating individual-part lead times as well as their logistics and assembly costs. Multiple studies have discussed that fasteners needed for component assembly account for 5 percent of material costs, yet contribute to 70 percent of labor costs. AM enables new designs that potentially eliminate these costs. One of the best-known applications of this concept is General Electric’s fuel-nozzle test case for the next-generation LEAP jet engine, in which 18 parts are combined into a single assembly. Utilizing design strategies that harness the benefits of consolidation is just one way to justify the transition from traditional manufacturing techniques to AM.
  • Functionally graded part design. The ability to build functionally graded component designs is another outcome of AM design not possible through any other manufacturing process. This can be achieved by designing a part made of dissimilar materials with varying strength properties for different sections of the part, but printed through one continuous AM process. The other method to achieve similar functionally graded material properties would be to design a part using lattice structures of varying thicknesses in different locations that control the varying strength requirements of the part. Also, today it is possible to build complex, intricate shapes such as naturally optimized cellular structures that offer high strength-to-weight ratios, objects with varying material density, and mechanical metamaterials wherein the mechanical properties of the part are determined by its shape rather than the composition of the material used.
  • Customized part designs. AM makes customized part design and production a viable, cost-effective option, as one does not have to consider tooling or other such auxiliary costs when making changes. The biggest market for custom part designs is the consumer-goods industry. Other industries benefitting from the ability to fabricate custom part designs include the medical and the maintenance, repair and overhaul industries. One now can design patient-specific implants and reverse-engineer and print legacy parts no longer in production.

Making the Case for AM

key characteristics and factors related to design of AM parts
Fig. 2—Key characteristics and factors related to design of AM parts.
The possibilities of what can be fabricated using AM are unlimited. However, not every part is meant to be additively manufactured. Instead, AM must be viewed as another tool in the manufacturing tool kit of any organization. The technology enables new and efficient design, but does not necessarily replace well-established traditional manufacturing processes. To really make a business case for additive, one must identify niche applications that leverage the unique capabilities that AM has to offer. Material, complexity, size, assembly, tolerances, cost, tooling, logistics and production time are a few of the things to be considered before identifying potential applications for AM.

Important questions to ask before starting the AM journey:

  • Do current manufacturing-process constraints limit part performance?
  • Can subcomponents be merged to avoid assembly?
  • Can the quantity of joints be minimized?
  • Can we save weight and material while achieving the same functionality?
  • Do we need extensive tooling to manufacture the part?
  • Can new material combinations increase part performance?
  • Can part durability be maximized?

Once an application has been identified as a potential AM candidate, one consider a few more things before redesigning the part (Fig. 2). Seven different ASTM-identified AM factors each have their separate characteristics. A designer must be aware of what each offers, while also being cognizant of the post-fabrication processes that apply to the component before it arrives at its destination. While AM is way beyond only a rapid-prototyping tool, one must look at the bigger picture before making a business case for its use.

Challenges and Potential

While AM processes enable the creation of never-before-seen innovations, many designers remain fixated on conventional designs and traditional DFM/DFA practices, not on designing AM-friendly parts.

Every AM process offers its own set of unique capabilities, but manufacturers must creatively design components to see the benefits of these processes. For example, metal powder-bed fusion (PBF) processes enable easily manufactured conformal channels, which would be difficult, if not impossible, using conventional subtractive methods. However, designers must understand that support structures are not required during a PBF build. Designing for AM requires an understanding of the complete manufacturing cycle, including post-processing as well as post-process inspection of parts. Currently, few guidelines exist to help designers make informed AM-design decisions.

Even so, there’s no denying that AM continues to gain momentum. While available CAD-software packages are not yet fully equipped for AM design, some conventional CAD providers are working toward providing robust AM design tools. Most have topology-optimization capabilities that go beyond being mere guidelines for designers. Meanwhile, AM process-simulation packages are becoming more reliable. Perhaps most importantly, 3D-printing programs at schools and colleges are producing a new generation of engineers with a new design mindset.

The potential of AM technologies is just beginning to be uncovered, and designers have an important role to play in bringing this technology into the mainstream. 3DMP

 

See also: EWI


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