Mechanical Calculation Method

Additive manufacturing processes with metals are always complex time-dependent thermo-mechanical processes that require a correspondingly high simulation effort. In order to achieve practical results more quickly, we transferred the "inherent strain" method to additive production in the powder bed when developing the software.

The method of the inherent strains originates from welding technology and should also be used here to simplify and accelerate the calculation of complex welding processes. The basic idea behind this is that the complex thermo-mechanical history of the process ultimately introduces a typical non-elastic (i.e. non-reducing) strain into the component, the so-called inherent strain. If this strain is now known, the time-consuming time-dependent thermo-mechanical calculation can be omitted and the purely mechanical calculation is much faster.

This method has been proven to achieve excellent results in terms of distortion behaviour and also loading due to internal stresses. It is, therefore, the first choice for achieving practical results quickly, i.e. within minutes or a few hours.

Calibration with Cantilevers

The challenge of the mechanical method is now to achieve the typical inherent elongations of the process under consideration as elegantly as possible, i.e. quickly and reliably. One possibility would be to determine this again by a small-scale simulation of the exposure process. In addition to the time required, however, there are considerable uncertainties regarding the possible result quality, since the nominal but not the actual conditions of the real process are fully known and can also fluctuate. The calibration of the inherent strains on test specimens has therefore proven to be the best approach. No simulation, however good, can completely replace the result of a physical test.

A fast optimization algorithm calibrates the inherent strain values so that they lead to the deformations measured in the test in the simulation. These strain values represent the (individual) machine used, the material and also the process parameters used. This enables reliable and fast simulation even for complex additive components.

Fast optimization algorithm calibrates the inherent strain values

Simufact Additive offers for the first time the possibility not only to use a set of inherent strains for the entire build space but also to define a location-dependent matrix. This allows, for example, different ratios to be mapped on the sides and in the corners of the build space, but also in height.

This makes it possible to further improve the quality of earnings, especially in the case of heavily utilised build space.

The inherent strains can be calibrated automatically for a constant height in the x-y plane.

Thermal Calculation Method

The purely mechanical method of the inherent strains has at least one possible disadvantage with all its advantages - it is no longer possible to gain an insight into the thermal processes, which, however, are decisive for the additive development process. Specific manufacturing problems may require an insight into the temperature processes, e.g. to set heat dissipating support structures or to evaluate the effect of a build plate heating system.

To enable this effect on the component level if required, we have developed a novel thermal calculation model on the element layer level in Simufact Additive. With knowledge of the essential machine parameters such as laser power, speed, and exposure strategy, the global temperature curve can be simulated during the construction process. Since the real efficiency of the melting process is generally unknown, it can be easily calibrated against a specified peak temperature. A physical test is not necessary.

The results are, for example, the peak temperatures reached, which enable the identification and evaluation of overheated and underheated areas. The user also can evaluate temporal heating and cooling rates, local temperature gradients and heat flows.

Efficient use of metallic parts made by additive manufacturing requires the prediction of the part’s performance under various loading condition which is highly sensitive to the inherently heterogeneous location-specific properties of the underlying material. Accurate prediction and control of location specific material properties necessitates accurate knowledge of the underlying microstructure with robust integration with finite element tools.

For the prediction of the microstructures, Simufact will add further functionality to Simufact Additive allowing for transient simulation with linked microstructure. Simufact is collaborating with Materials Resources LLC (MRL), a leader in materials informatics. This collaboration brings to designers and manufacturers the location-specific microstructure effects via an integrated computational microstructure-informed response laboratory (ICMRL) developed by MRL that is used for calibrating and validated Simufact Additive. The insertion of the continuously growing processing, microstructure, and property databases for additively manufactured metals provides Simufact customers with a microstructure-informed modeling tool from powder processing to mechanical performance of a finished part.