The most important usage of the element birth technique is to simulate the process of adding material for welding and additive manufacturing. Thus, before starting it is better to know more about these two processes.
Details of Additive Manufacturing and Welding:
Here we provide a brief description of additive manufacturing and welding to have a better understanding of the process.
Many metallic structures in the industry are assembled through some kind of welding process which is composed of heating, melting and solidification using a heat source such as arc, laser, torch or electron beam. The highly localized transient heat and strongly nonlinear temperature fields in both heating and cooling processes cause non-uniform thermal expansion and contraction and thus result in plastic deformation in the weld and surrounding areas. As a result, residual stress, strain and distortion are permanently produced in the welded structures:
High tensile residual stresses are known to promote fracture and fatigue, while compressive residual stresses may induce undesired, and often unpredictable, global or local buckling during or after the welding. It is particularly evident with large and thin panels, as used in the construction of automobile bodies and ships. These adversely affect the fabrication, assembly, and service life of the structures. Therefore, prediction and control of residual stresses and distortion from the welding process are extremely important in the shipbuilding and automotive industry :
Additive manufacturing and WAAM:
Additive manufacturing (AM) of large-scale components requires an insight into the complicated microstructural features. Wire + arc additive manufacturing (WAAM) is by far the most efficient AM process with a relatively higher deposition rate (1-4 kg/h). This enables the manufacturing of large parts up to several metres. This manufacturing process incorporates either gas metal arc welding (GMAW), plasma arc welding or gas tungsten arc welding techniques for metal deposition. Compared to its counterpart powder-based AM techniques, such as selective laser melting (SLM), the WAAM process offers a lower
production cost due to its relatively high deposition rate .
A wide range of weldable metals and alloys such as steel nickel and titanium alloys can be employed in this technology. WAAM facilitates the efficient manufacturing of Ti alloys such as Ti-6Al-4V alloy, which is extensively important in the aerospace industry. A substantial reduction in the buy-to-fly ratio from around 10-20 for a conventionally machined component to 1 could be achieved using this process. WAAM incorporates a multi-pass arc welding process, resulting in the efficient manufacturing of
large-scale parts with acceptable mechanical properties at a lower production cost .
More details about the element birth technique:
An example of the element birth technique by using Python in Abaqus is provided. The element birth technique is useful for adding material for welding and additive manufacturing processes. In the newer version of Abaqus, there are more options to simulate the process of adding material but still, this technique is one of the best tools. Another common method to use is the Hyper technique which is the combination of element birth technique and the Quite element. This approach is useful for modelling powder in selective laser melting/ sintering (SLM/SLS).
The Quite element process requires the USDFLD or any other subroutine code to change the material properties during the process. This approach might cause more errors compared to the element birth technique but it is faster. In fact, this process doesn’t change the material matrix during the simulation which reduces computational time.
There are several python codes that can be used to select elements. Here is a list of them [Abaqus documentation]:
- getSequenceFromMask(…) “This method returns identified using the specified mask. This command is generated when the JournalOptions are set to COMPRESSEDINDEX. When a large number of objects are involved, this method is highly efficient.”
- getByBoundingBox(…) “This method returns within the specified bounding box.”
- getByBoundingCylinder(…) “This method returns within the specified bounding cylinder.”
- getByBoundingSphere(…) “This method returns within the specified bounding sphere.”
The blank space means it can return nesh, node, part and etc.
In this tutorial (element birth technique):
Using Python in this approach helps you create bigger models. At first, we build the models with Abaqus CAE and then we show you how to use Python code to select the elements and deactivate the elements by coding. We explain the “getByBoundingBox” method to select the elements for activating and deactivating the material. The video is short so you can learn this in less than 15 minutes and you will have the output and Abaqus CAE file. In the PowerPoint file, you can find the introduction of this method. If you think you need more background it might be a good idea to see the other video about the subroutine (Please click here).
In this video, we avoid giving too many details so you can easily use the products. Here, you can find the following files:
Abaqus files: CAE, ODB, INP, Python, and JNL
PowerPoint files which contain more details.
Video files: How to create this model, PowerPoint presentation.
For more information please send me an Email:
 Zhu, X. K., and Y. J. Chao. “Effects of temperature-dependent material properties on welding simulation.” Computers & Structures 80.11 (2002): 967-976.
 Tangestani, Reza, et al. “Effects of Vertical and Pinch Rolling on Residual Stress Distributions in Wire and Arc Additively Manufactured Components.” Journal of Materials Engineering and Performance (2020): 1-12.