Additive manufacturing (3D printing) can be a cost-effective way of producing parts, especially when making use of the design freedoms the manufacturing process enables, such as topological complexity and the ability to print assemblies in one step.

Metal additive manufacturing is used to produce parts for aerospace, automotive, medical and other industries. These are high-value parts that require careful design and manufacturing, and simulation has long been used to validate the as-built part performance.

The additive process for metals introduces inherent complexities and challenges, however, such that the process itself requires simulation to successfully produce the parts.

Additive Manufacturing Processes

Additive manufacturing (AM) is classified into a number of processes, most of which are applicable to polymers. Two are the primary processes for fully-dense (no porosity) production of metal parts: laser powder bed fusion (LPBF) and directed energy deposition (DED). Our focus is on modeling these two processes.

In a laser powder bed fusion process – also known as direct metal laser melting (DMLM), direct metal laser sintering (DMLS), or selective laser melting (SLM) – a thin layer of metal powder is deposited and a highly focused laser beam of energy is moved over its surface in order to melt the metal powder composing the current cross section and fuse it to the preceding layer. A solid part emerges as successive layers are deposited and processed. The initial layer is deposited on a build plate or substrate.

In a directed energy process (DED) – also known as laser engineered net shaping (LENS), electron beam additive manufacturing (EBAM®), or laser deposition technology (LDT) – a laser or electron beam creates a melt pool on previously solidified material where blown powder or fed wire is introduced to add material.

Both of these processes produce high temperatures and severe thermal gradients, leading to significant distortion and buildup of residual stresses as the layers are deposited. The distortion can be high enough to interfere with the application of the next layer, and the residual stresses high enough to break the part off the build plate or off its supports, or crack the part itself. Additionally, the residual stresses will produce more distortion when the part is removed from the build plate and its supports removed leading to an undesirable final shape.

How Simulation Can Assist with AM Challenges

Being able to simulate these distortions and stresses during the design of the part will help prevent failed builds and lead to better designs for additive manufacturing.

Supports are generally needed to anchor and support overhangs and other horizontal (and nearly horizontal) surfaces such as the tops of holes. They are also used to control distortions and provide heat transfer routes during the build. Supports add cost – material, build time, and removal effort – so their use should be minimized. Simulation can be used to determine the best build orientation for a part, best locations for supports, and support sizing requirements. Simulation is particularly powerful when used with topology optimization to minimize overhang regions requiring supports.