Differences in Performance Between 3D Printing And Traditional Process Materials And Lattice Structures

Differences in performance between 3D printing and traditional process materials and lattice structures
The metal three-dimensional lattice structure has excellent mechanical properties such as high specific strength, high mechanical efficiency, and strong energy absorption capacity, and has broad application prospects in various engineering fields such as light aerospace, transportation structures, and impact protection devices. In fact, the metal lattice structure has been maturely used in my country's spacecraft structure products.

Lattice structure properties and energy absorption capacity

      One of the most important properties of lattice materials is energy absorption capacity, which is characterized by the ability to absorb or dissipate mechanical energy during compression. It has been confirmed that most lattice structures, such as pyramid lattices, three-dimensional Kagome lattices, tetrahedral lattices, and diamond lattices, can achieve very good energy absorption performance by changing geometric parameters such as aspect ratio or unit cell size.

      In addition, designable sandwich panels with lattice structures have also been demonstrated to exhibit excellent energy absorption properties. In addition to geometric parameters, the energy absorption performance can also be tuned by complex structures such as gradient structures, metal foam filled structures, multilayer structures, and different unit cell structures, which have been shown to be more efficient in energy absorption than single lattice structures efficient.

3D printed gradient lattice structures

     Another way to improve the mechanical properties or energy absorption capacity is to modify the nodal structure connecting the struts. When subjected to compressive or shock loads, stress concentration usually occurs. This method is relatively simple, but it can improve the energy absorption capacity of the metal lattice structure. Aspects are very effective.

Preparation scheme of lattice structure

Traditional craftsmanship and 3D printing have their own limitations

      To date, there have been several techniques for fabricating metal lattice structures, including stamping forming, extrusion-bonded wire cutting, expansion sheet folding, and investment casting. In addition to casting, these techniques must use bonding or welding techniques to assemble the struts to form the lattice structure. During processing, junctions are often sensitive to defects, such as bubbles and microcracks, leading to a weakening of the overall mechanical properties of the lattice structure. For investment casting technology, the electrolyzer configuration cannot be too complicated due to the limitations of the technology itself.

     The advent of 3D printing technology has made the manufacture of lattice structures less difficult, and it does not require the combination of traditional processes. However, due to the limited materials that can be formed, this technology still has shortcomings in fabricating lattice structures.

     To overcome the limitations of additive manufacturing and investment casting, a new technology that combines 3D printing with investment casting has been developed in recent years. In this technology, a low-melting resin-based lattice structure is first fabricated by 3D printing, and then used to make a ceramic shell mold. Finally, the molten metal penetrates into the mold cavity under the action of compressed air, and after the metal solidifies, the outer shell is removed to obtain a metal lattice structure. Apart from being able to generate any complex configuration, the method has few restrictions on the choice of materials.
3D printing and investment casting to fabricate lattice structures

Cast aluminum lattice structure made by 3D printing + casting

      In order to further compare the differences in mechanical properties and energy absorption caused by different preparation methods of lattice structures, the Key Laboratory of Materials Physics, Institute of Solid State Physics, Hefei Institute of Physical Science, Chinese Academy of Sciences, in cooperation with the Graduate School of the University of Science and Technology of China, combined 3D printing with investment casting. And direct metal additive manufacturing, the reinforced pyramid lattice structure of three pillar materials was prepared, and the compression behavior and energy absorption characteristics were theoretically analyzed and experimentally verified by finite element simulation.

Differences in performance of lattice structures fabricated by different processes

 The lattice structure samples were prepared by two techniques, direct 3D printing and 3D printing combined with investment casting. The former uses a BLT-A300 printer, and the material selects AlSi10Mg powder suitable for 3D printing; the latter uses as-cast AlSi10Mg alloy and 7005 aluminum alloy.


     To understand the mechanical properties of the different aluminum alloys used in this study, tensile experiments were carried out. The relevant stress-strain curves show that the direct metal 3D printed AlSi10Mg has the highest strength and stiffness, but the lowest ductility; in contrast, the as-cast AlSi10Mg alloy has the highest ductility but the lowest strength, and the 7005 aluminum alloy has medium strength and ductility, only intermediate between the other two materials.

Tensile tests of different aluminum alloys: (a) geometrical dimensions of tensile specimens; (b) stress-strain curves

     The mechanical properties of the lattice structure can be enhanced by nodal enhancement. In this study, the preparation method and the influence of the pillar material are the focus of attention. By comparing the reinforced pyramid lattice structure with the usual structure, it can be seen that the reinforcement is achieved by gradually increasing the diameter of the pillars towards the nodes.
Features of the pyramid lattice structure: ordinary stars on the left, enhanced stars on the right

     The relevant geometric parameters of the lattice structure are defined as follows: de and dm represent the diameter of the end and the middle of the pillar, respectively; L, H, and θ represent the width of the bottom surface, the height of the unit cell, and the angle between the pillar and the bottom surface, respectively; Le and Lc, respectively are the effective length and equal diameter length of the strut. To investigate the effect of geometric parameters, the values of de ranged from 1.4 mm to 1.8 mm at 0.1 mm intervals, where 1.4 mm is also the diameter of the commonly used pyramid structures used for comparison. When de increases, dm decreases to keep the relative density of the lattice structure unchanged. Theta values vary from 35° to 55° in 10° intervals.
Four sets of samples, A, B, C and D, node-enhanced pyramid lattice structure
Deformation process and simulation results of EP lattice structures in groups A, B, and C

     The reinforced lattice structures in the three pillar materials were prepared by two preparation methods. The effects of the preparation methods, pillar materials and geometric parameters on the compression behavior and energy absorption were systematically investigated by finite element analysis and compression experiments. The main conclusions are summarized as follows:


     (1) Compared with metal additive manufacturing, the manufacturing method of 3D printing combined with investment casting eliminates the stress fluctuation at the plateau stage of the stress-strain curve of the pyramid lattice structure, and even increases the energy absorption at large inclination angles. However, the compressive strength decreases at the same time.


     (2) Increasing the inclination angle of the reinforced pyramid lattice structure can narrow the gap in bearing capacity and improve energy absorption. For the as-cast 7005 aluminum alloy lattice structure, brittle fracture occurs during compression, resulting in energy loss.


     (3) The end diameter of the reinforced pyramid lattice structure is critical for the compressive strength and energy absorption. Thickening the end diameter reduces the stress concentration near the nodes to some extent.


     (4) The envelope of the shoulder point relative to the dip angle in the energy absorption diagram is a straight line. The energy absorption map shows that for AlSi10Mg, when σ/ES<1.48×10, 3D printing combined with investment casting is a better choice, and metal additive manufacturing can be considered instead. When σ/ES>6.84×10, the use of as-cast 7005 aluminum alloy is a compromise.



      (5) The theoretical equations and finite element analysis are consistent with the experimental results, and can be used to predict the mechanical and energy absorption properties of the nodal-enhanced pyramidal lattice structure.

     Honeycomb lattice materials have become important structural and functional materials due to their low density, high specific strength and porosity. Conventional honeycomb materials are mainly foams, sponges and honeycombs, which are often used for functional purposes such as sound barriers, anti-vibration devices and impact protection devices. For metal foams and sponges, the pore structures such as the shape, size, number, and distribution of pores are inherently random, in other words, they are almost uncontrollable, while for honeycomb, the pore distribution and mechanical properties are strongly anisotropic opposite sex. These characteristics limit the application of traditional metal honeycomb materials to a certain extent.

     3D printing lattice structures would be one of the most ideal solutions to these problems. They have precisely engineered lattice structures, virtually unlimited matrix materials, optimized properties, and can be fabricated by many industrial-scale techniques, making them important applications in many engineering fields in aerospace.