Methods for design of additively manufactured multi-material parts and characterization of bonding strength

• Applicants: Professor Dr. Sven Hartwig; Professor Dr.-Ing. Thomas Vietor
• Subject Area: Engineering Design, Machine Elements, Product Development ; Joining and Separation Technology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 467577506

Through the process principle of layer by layer material application additive manufacturing (AM) offers new design freedom as opposed to tool based or subtractive processes. Material extrusion for instance offers the possibility for combination of different materials within the same part without the need for additional assembly or joining steps. A local variation of material can achieve a purposeful integration of hinges by using a combination of a stiff and an elastic material. The usage of the potential of multi-material design (MMD) for functional integration is mainly determined by the bonding between the two compound materials.Adhesion is based on the underlying physical mechanisms of diffusion, polarity and wetting. The resulting adhesion is, in addition to the used materials, mainly dependent on process parameters and surface topology. Additional influencing factors are thermally induced stresses due to differing thermal expansion coefficients. Owing to insufficient knowledge about these dependencies, the bonding strength cannot be predicted, thereby restricting goal-driven application of additive MMD. Additionally, AM specific geometrical design flexibility can be used to increase bonding strength especially for incompatible material combinations by utilization of interlocking features. In order to use the potential of integration of material specific functions systematically, a methodical design of material bonding is necessary. For this goal, in addition to researching bonding strength enhancing measures (e.g. variation of process parameters, interlocking features, and measures of pretreatment) new methods of characterization and testing for quantification of influencing factors on bonding strength as well as attribution to underlying effect mechanisms are necessary.For that reason, this research project aims to clarify the main influencing factors together with the underlying mechanisms on resulting bonding strength of additively manufactured MMD. This achieves the material and load type dependent quantification of influencing factors through development of suitable test specimens and methods of characterization, thereby making possible a methodical design of material. For this purpose, process and design measures for enhancement of bonding strength are identified. Moreover, in situ plasma treatment is to be realized. From the clarified relationships design principles and rules are derived, that allow for purposeful consideration of material bond design in product development even regarding the use of incompatible materials. Through this, the potential of AM for the integration of material specific functions can be utilized specifically.

• DFG Programme: Research Grants