Design of lightweight parts made by wire and arc additive manufacturing – BeShape

The pattern bank approach requires a methodology for developing this pattern bank. It must meet the manufacturability constraints of the WAAM process, which raises several issues. 1: Since current knowledge does not allow for the validation of this manufacturability numerically, it is necessary to define methods and validate them through tests to be implemented for each pattern. 2: The trajectories associated with these patterns must also be validated, both through simulation and by implementing them on the planned WAAM methods. 3: The patterns must be configurable to adapt them to the material densities envisaged for the designed part.

Regarding the shapes to be obtained on the part, a topological optimization approach is considered. This approach is well-established at the G-SCOP laboratory. The challenge lies in the association of the patterns and their parameters with the material densities generated by topological optimization. A first approach of this type has already been initiated within the framework of EBM technology, but it will require significant changes for WAAM technology.

A third challenge concerns the generation of trajectories on the complete part, based on the elementary trajectories of each pattern, subject to the constraints of the WAAM process. This approach will require a combination of simulations and experimental validations.

The final challenge will involve the construction of a realistic virtual mock-up, representative of the part that will actually be manufactured. This involves the experimental development of a deposited bead model based on the anticipated processing parameters.

Removing these challenges should allow us to validate the proposed lightweight part design approach, based on the assembly of manufacturable patterns for which the WAAM process parameters and associated trajectories have been clearly identified. We will thus be able to verify the following scientific hypotheses: 1: There is a method for intelligently combining manufacturable patterns to obtain a manufacturable part. 2: It is possible, based on topology optimization results, to design a manufacturable part that meets the designer's expectations through intelligent selection and combination of patterns.

The patterns selected for the project are two TPMS (Triply Periodic Minimal Surface) patterns: primitive and gyroid patterns. A functionally graded cellular material based on these patterns has been developed. The objective is to replace a homogeneous material with a variable density material in order to adapt the material characteristics to the functional requirements of the product, while ensuring manufacturability by a WAAM process. The proposed material consists of an assembly of TPMS patterns and the density variation is ensured by the variation of the length and/or thickness of the patterns. The evaluations of the relative density as a function of the geometric parameters of the structures as well as the mechanical properties of the material as a function of the relative density of the structure were carried out. A product design methodology based on the linear variation of the developed material density was proposed. A plug-in to apply this method with the Rhinoceros CAD software was developed. The manufacturability of the patterns by WAAM is made possible by the generation of trajectories at constant layer height. The proposed method allows these trajectories to be generated from a mathematically parameterized pattern or from an STL file. A primitive pattern was produced in multi-axis WAAM.

The work carried out as part of the project enabled the creation of TPMS structures with varying relative density for the design of lightweight parts using pattern assemblies.

The project partners were able to develop a methodology for generating deposition trajectories. This methodology was applied to the fabrication of a unit cell, a primitive-type pattern, with a bead of constant thickness, using multi-axis WAAM. The fabrication of a complete part, consisting of a set of primitive-type patterns, is a potential future for the project.

Variable-density structures are at the heart of the project: the proposed product design methodology is based on the linear variation of material density. As part of the project, we identified that patterns of varying thickness could be achieved by controlling the robot torch feed speeds and wire feed rates during fabrication. However, for now, the fabrication of variable-density structures remains a possibility.

One of the tools developed within the project (the Rhinoceros CAD software plugin) can be used to extract local density, thickness, and length values ??from an arbitrary point on a trajectory. However, developing a tool to link real-world manufacturing conditions to TPMS design parameters is also a prospect.

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Ramírez, E.; Béraud, N.; Montemurro, M.; Pourroy, F.; Villeneuve, F. Effective elastic and strength properties of triply periodic minimal surfaces lattice structures by numerical homogenization. Mech. Adv. Mater. Struct. 2023, 1-13.

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Ramírez, E.; Béraud, N.; Pourroy, F.; Villeneuve, F.; Museau, M. Conception des surfaces minimales triplement périodiques à densité variable pour la fabrication additive. In Proceedings of the 18th Colloque national S.mart, Apr 2023; Carry-le-Rouet, France.

WAAM manufacturing processes using an electric arc to fuse a filler metal in wire form. The 3D part is thus generated by stacking welding beads from any type of weldable material. WAAM processes have the advantage of being more productive and less expensive than other Additive Manufacturing (AM) technologies.
The AM processes are able to deposit the material locally in the right place for making lighter parts by removing some under constrained areas. However, this opportunity remains today little used in WAAM type AM. On one hand because the results from shape optimization in Design For Additive Manufacturing are not manageable as such with this technologies. On the other hand, the existing CAMs for these technologies currently use only parallel plane-based slicing and contour and hatch-based filling strategies.
The project objective is to provide a process for designing lightweight parts by an assembly of predefined patterns manufacturable by a process WAAM. These parameterized patterns are proposed taking into account the manufacturing constraints. The assembly and configuration of the patterns are designed with the objective of designing a part with a minimum of material. We assume that the manufacturability of the part is ensured by the intelligent assembly of individually manufacturable patterns and by using the opportunities offered by the generation of 3D trajectories.
The partnership is composed of 2 laboratories, G-SCOP (conducting researches activities on AM since 2012) and COSMER (leading work on the trajectory generation for AM since 2015) and 3 companies, DRPI (Additive manufacturing CAM software provider), PRODWAYS (WAAM machine builder) and SAFRAN AE as end user (an international high-technology group and tier-1 supplier of systems and equipment in the Aerospace and Defense markets).