With the recent advances in metal additive manufacturing (AM), many industries are turning to AM for creating more complex components with enhanced performance. A major area of focus for researchers is the hierarchical complexity (macro-, meso-, and microscale) that can be included in components through the idea of free complexity. Free complexity is the idea that complexity of a component does not directly influence the manufacturing cost. Whether for lightweighting a structure, improving energy absorption capabilities, or improving biocompatibility, the mesostructure of a component is often modified with lattice structures.
Lattice structures are one of the primary methods used to design the mesostructural level of a component. Within a lattice structure, the smallest repeating unit is called the unit cell, see Figure 1. There is an infinite set of repeating unit cells that are possible for population within a lattice. Traditionally, researchers started with structures that mimic those found in nature such as the honeycomb. Until recently, manufacturing of lattice structures was limited to simple geometries. Now with metal AM, the type and topologies of the lattices that can be created are nearly limitless. However, with the increased ability to manufacture lattice structures, numerous types of unit cells are possible and it is not well understood when a specific unit cell should be used over another. Commercial software for AM make it all too easy to lightweight a part by simply adding a lattice without any guidance for which lattice will be most beneficial for the component.
The purpose of this project is to develop a systematic design optimization method for generating unique lattice structures with application specific bulk material properties such as minimum compliance, matching the constitutive matrix for desired material properties, generating compliant mechanism-like lattices, mimicking pore size of biomaterials, or impact absorption characteristics. This systematic optimization will use structural and thermal distortion feedback in a ground structure optimization to develop unit cells while incorporating design for additive manufacturing (DfAM) considerations. The intent of such a systematic method will be to provide the ability for designers to determine an appropriate lattice structure for a specific application in order to optimize performance.
A DfAM workflow has been proposed for considering structural and thermal distortion feedback in unit cell design. A manual implementation of the workflow has been detailed for modification of a contact-aided compliant mechanism for energy absorption. The unit cell thermal distortion was reduced by 20% at the cost of an 8% reduction in energy absorption (see Figure 2) [1].
Figure 1 A lattice structure is commonly used to replace a solid section of a component in order to reduce weight while maintaining structural performance. The most basic repeating pattern in a lattice structure is the unit cell. With an infinite set of unit cells that can be created, there is a need for a systematic generation method that account for AM constraints.
Figure 2 In a manual implementation of the workflow for unit cell design, the structural and thermal distortion performance were used to develop trends based on geometric variables. With these trends, a modified unit cell design was simulated resulting in a 20.2% decrease in thermal distortion at the cost of an 8% reduction in energy absorption.
Team Members
Brad Hanks
Daniel Duenas
Joseph Berthel
References
[1] Khurana, J., Hanks, B., and Frecker, M., 2018, “Design for Additive Manufacturing of Cellular Compliant Mechanism Using Thermal History Feedback,” ASME International Design Engineering Technical Conferences and Comp, pp. 1–15.