Investigating the Effect of Design Parameters on the Mechanical Performance of Contact Wave Springs Designed for Additive Manufacturing

Haq M.R., Nazir A., Lin S., Jeng J.

Functionality and design of mechanical springs are simple and limited due to manufacturing constraints of conventional fabrication methods being used for making helical and wave springs. In recent era, design for additive manufacturing has proven its great worth to design and manufacture optimal, complex as well as intricate structures with better mechanical and lightweigting properties. This study aims to investigate the mechanical behavior of functionally gradient wave springs as a function of variation in thickness and morphology of each wave. Functionally gradient wave springs incorporated with different morphology and cross-sections including circular, rectangular and combination of both were designed and printed by keeping mass and height constant to investigate their mechanical properties. Loading–unloading experimentation was conducted within the elastic range (90% of compressible distance) in order to study energy absorption/loss, load-bearing capacity and stiffness of all designs. The experimental results were validated by finite element anaylsis (FEA) by providing the identical boundary conditions of experimental setup. The results revealed that the stiffness of wave spring having rectangular cross-section is increased significantly, while energy absorption is almost 90% increased due to circular cross-section of waves. Overall, the design with combination of round and rectangular cross-sectional waves has better stiffness and energy absorption properties. For further investigation of mechanical properties due to variation in cross-section of waves, more designs including semi-circular and filleted waves were designed, and FEA of those showed that 786 N of load-bearing capacity is achieved in the wave spring having semicircular cross-section of waves which is double than the wave spring having variable circular cross-section of waves.

Blakey-Milner B., Gradl P., Snedden G., Brooks M., Pitot J., Lopez E., Leary M., Berto F., du Plessis A.

• Metal additive manufacturing in aerospace comprehensively reviewed. • Discussion of advantages and benefits of metal additive manufacturing in aerospace. • Limitations and challenges described in context of current technology. • Successful examples of metal additive manufacturing in aerospace demonstrated. • Future growth potential and promising areas discussed. Metal additive manufacturing involves manufacturing techniques that add material to produce metallic components, typically layer by layer. The substantial growth in this technology is partly driven by its opportunity for commercial and performance benefits in the aerospace industry. The fundamental opportunities for metal additive manufacturing in aerospace applications include: significant cost and lead-time reductions, novel materials and unique design solutions, mass reduction of components through highly efficient and lightweight designs, and consolidation of multiple components for performance enhancement or risk management, e.g. through internal cooling features in thermally loaded components or by eliminating traditional joining processes. These opportunities are being commercially applied in a range of high-profile aerospace applications including liquid-fuel rocket engines, propellant tanks, satellite components, heat exchangers, turbomachinery, valves, and sustainment of legacy systems. This paper provides a comprehensive review of metal additive manufacturing in the aerospace industry (from industrial/popular as well as technical literature). This provides a current state of the art, while also summarizing the primary application scenarios and the associated commercial and technical benefits of additive manufacturing in these applications. Based on these observations, challenges and potential opportunities are highlighted for metal additive manufacturing for each application scenario.

Xiong Y., Han Z., Qin J., Dong L., Zhang H., Wang Y., Chen H., Li X.

• A method to regulate the porosity gradient pattern of FGPS was developed. • An equation to calculate the mechanical properties of FGPS was developed. • Lattice with solid core structure has the best mechanical properties in all FGPSs. • Failure mechanisms of the lattice with solid core structure were revealed. • Stress protection effect inside the lattice with solid core structure was proposed. Mechanical performance is crucial for lattice structures used in orthopedic applications because they should simultaneously possess high strength and high porosity. Although the additively manufactured Ti-6Al-4 V functionally graded porous structure (FGPS) has proven to be the most promising material owing to its good mechanical performance, the impact of porosity gradient pattern on their mechanical performance has scarcely been investigated. In this study, FGPSs with varied porosity gradient pattern and same overall porosity were designed by triply periodic minimal surface and fabricated by laser powder bed fusion (L-PBF), and their structural and mechanical properties were analyzed. A semi-empirical equation was derived to predict the mechanical properties of FGPSs. Hence, we discovered that the lattice with solid core exhibited the best mechanical performance among all FGPS designs. X-ray microscopy (XRM) analysis revealed a strong relationship between the internal micro-porosity of the L-PBF-fabricated samples and the dimensions of the manufactured components, further proving the rationale of the lattice with solid core design. In situ compression tests under XRM visualized the different failure mechanisms in the porous and dense portion of the lattice with solid core. The strengthening mechanism of the lattice with solid core was further revealed by finite element analysis.

Arshad A.B., Nazir A., Jeng J.

Springs are mechanical devices which are used quite extensively in different industries and mechanisms. Traditionally, springs have been manufactured by wrapping a hot wire around a rotating mandrel. This process has certain limitations because it is difficult to vary the spring parameters such as pitch and wire diameter. However, through the use of AM processes, with the complexity-for-free approach, it is possible to design and manufacture springs with variable spring parameters. Furthermore, it is also possible to create springs with multiple helices as opposed to traditional springs with a single helix. In this study, 32 springs with different numbers of helices, variable pitch profiles, variable wire diameters, and constant mass were designed. The springs were manufactured for experimental validation using HP MJF 520, which is a hybrid AM process. The stiffness of these springs was calculated analytically, through FEA, and experimentally validated. It was observed that increasing the number of helices in a spring leads to an increase in the stiffness of the spring. Furthermore, springs with variable pitch profiles and variable wire diameters have greater stiffness as compared to springs with constant parameters. However, with the increase in stiffness, the fatigue life of the springs decreases exponentially. Improvement in the stiffness of the springs without increasing the mass and therefore cost can lead to new and improved designs. These springs show great potential for industries where weight is an important consideration, such as aerospace and automotive. As these springs have a higher stiffness for the same mass, they can lead to designs with a light weight, and lower package volumes.

Chen K., Teo H.W., Rao W., Kang G., Zhou K., Zeng J., Du H.

The viscoelastic-viscoplastic deformation of Multi Jet Fusion-printed polyamide 12 (MJF PA12) was investigated with experimental and numerical approaches. Multi-loading–unloading–recovery tests were conducted to distinguish between the viscoelastic and viscoplastic deformations. The influence of the void defects on deformation of PA12 was investigated through the micro-computed tomography (μCT) and field emission scanning electron microscope. A finite-strain viscoelastic-viscoplastic constitutive model based on the logarithmic stress rate for the matrix of MJF PA12 was developed within the thermodynamic framework as well as an introduction of the accumulated plastic deformation–induced damage into the proposed model. A representative volume element was modeled based on the μCT results of MJF PA12. The simulated results, such as stress–strain and strain–time curves, agreed with the experimental results. Moreover, the model revealed the mechanism that the low tensile ductility of MJF PA12 is caused by the increase in strain localization and narrowing of the shear band. • The viscoelastic-viscoplastic deformation of MJF PA12 was experimentally investigated. • A finite-strain viscoelastic-viscoplastic constitutive model for the matrix of MJF PA12 was developed. • The model reasonably captured the deformation of PA12 as compared to the experiments. • The model was capable of revealing the mechanism behind the low tensile ductility of PA12.

Joseph A., Mahesh V., Harursampath D.

Auxetic structures are a special class of structural components that exhibit a negative Poisson’s ratio (NPR) because of their constituent materials, internal microstructure, or structural geometry. To realize such structures, specialized manufacturing processes are required to achieve a dimensional accuracy, reduction of material wastage, and a quicker fabrication. Hence, additive manufacturing (AM) techniques play a pivotal role in this context. AM is a layer-wise manufacturing process and builds the structure as per the designed geometry with appreciable precision and accuracy. Hence, it is extremely beneficial to fabricate auxetic structures using AM, which is otherwise a tedious and expensive task. In this study, a detailed discussion of the various AM techniques used in the fabrication of auxetic structures is presented. The advancements and advantages put forward by the AM domain have offered a plethora of opportunities for the fabrication and development of unconventional structures. Therefore, the authors have attempted to provide a meaningful encapsulation and a detailed discussion of the most recent of such advancements pertaining to auxetic structures. The article opens with a brief history of the growth of auxetic materials and later auxetic structures. Subsequently, discussions centering on the different AM techniques employed for the realization of auxetic structures are conducted. The basic principle, advantages, and disadvantages of these processes are discussed to provide an in-depth understanding of the current level of research. Furthermore, the performance of some of the prominent auxetic structures realized through these methods is discussed to compare their benefits and shortcomings. In addition, the influences of geometric and process parameters on such structures are evaluated through a comprehensive review to assess their feasibility for the later-mentioned applications. Finally, valuable insights into the applications, limitations, and prospects of AM for auxetic structures are provided to enable the readers to gauge the vitality of such manufacturing as a production method.

Guo B., Xu Z., Luo X., Bai J.

Multi jet fusion (MJF) is an emerging powder three-dimensional (3D) printing technology with an ultrafast printing speed, in which polyamide 12 (PA12) is the main material currently utilised. Altho...

Bhuvanesh Kumar M., Sathiya P.

Additive Manufacturing (AM) is the significantly progressing field in terms of methods, materials, and performance of fabricated parts. Periodical evaluation on the understanding of AM processes and its evolution is needed since the field is growing rapidly. To address this requirement, this paper presents a detailed review of the Additive Manufacturing (AM) methods, materials used, and challenges associated with them. A critical review of the state of art materials in the categories such as metals and alloys, polymers, ceramics, and biomaterials are presented along with their applications, benefits, and the problems associated with the formation of microstructures, mechanical properties, and controlling process parameters. The perspectives and the status of different materials on the fabrication of thin-walled structures using AM techniques have also been discussed. Additionally, the main challenges with AM techniques such as inaccuracy, surface quality, reinforcement distribution, and other common problems identified from the literature are presented. On the whole, this paper provides a comprehensive outlook on AM techniques, challenges, and future research directions. • A review on the basic and recent practices in additive manufacturing techniques is presented. • Use of metallic materials, ceramics, polymers, biomaterials and composites in additive manufacturing are reviewed. • Additive manufacturing in the fabrication of thin-walled structures and scaffolds are discussed. • The challenges in additive manufacturing found in literature and the scopes for future research works also detailed.

Cai C., Tey W.S., Chen J., Zhu W., Liu X., Liu T., Zhao L., Zhou K.

Selective laser sintering (SLS) and Multi Jet Fusion (MJF) are two of the most developed powder bed fusion additive manufacturing techniques for the manufacture of polymeric components. In this work, a systematic benchmark and comparison of polyamide 12 (PA12) parts printed by SLS and MJF was conducted on the physicochemical characterization of raw powder materials (EOS PA2200 and HP 3D HR PA12) and their printed specimens, as well as the mechanical performance and printing characteristics of printed objects. Both designated-supply PA12 powders for each technique possessed almost identical thermal features, phase constitutions, functional groups, and chemical states. The mechanical strength of the MJF-printed specimens was slightly stronger than that of SLS-printed counterparts due to the synergistic effect of an area fusion mode and carbon black additive in the MJF process. The SLS-printed specimens had a better surface finish on the top surface, but the MJF-printed specimens showed much smoother front and side surfaces. Scaled-down merlions were printed by both processes for the printing accuracy assessment. The results show that the SLS-printed merlion presented higher profile deviations than those of the MJF-printed counterpart, especially in areas with sharp contours. These fundamental experimental results can provide a comprehensive understanding of SLS and MJF processes and serve as a valuable guideline for their industrial applications.

Najafi M., Ahmadi H., Liaghat G.

The human being has always been looking for optimal use of his surrounding materials and over the years, has managed to invent various structures with special properties. Lattice structures are widely used in various applications due to their lower weight and desirable compressive strength. An example of these structures is the honeycomb that is very popular and many studies have been done about it. A new type of lattice structures is auxetic structure that has negative Poisson’s ratio due to its geometry. This characteristic has caused auxetic structures to have unique properties such as high shear strength, indentation resistance and energy absorption. Investigation of energy absorption of auxetic structures is a subject that has not been studied in researches. In this study, the ability of some auxetic structure for absorbing energy is investigated at quasi-static and low velocity impact transverse loading. Specimens with three types of geometries (re-entrant, arrowhead and anti-tetra chiral) are fabricated using additive manufacturing method (3D printing). Discussion about energy absorption and failure mechanisms of all three structures were carried out and compared in both types of loading.

Ali M., Nazir A., Jeng J.

The mechanical properties such as energy absorption, crushing behavior, and strength-to-weight ratio of graded density structures are significantly better when compared with uniform density counterparts. Graded density structures have been widely investigated due to recent developments in additive manufacturing (AM) technology, which can easily manufacture complex geometries. The study explores the significance of variable-dimension helical spring (VDS) to be used in shoe midsole to improve the stiffness, energy absorption, and energy return. Two novel shoe midsoles are designed using the variable-dimension helical springs and their performance was compared with a third shoe midsole designed using uniform-dimension helical spring (UDS). Variable-dimension shoe midsoles were designed according to the actual pressure distribution applied by the human foot on the midsole. The Multijet fusion AM process was employed for the fabrication of all shoe midsole samples. It is revealed that despite the same mass and bounding box, variable-dimension midsoles have significantly improved mechanical properties compared to uniform-dimension midsole. It is found that the VDS midsole has sixfolds higher force-bearing capacity, and has a lower permanent material setting phenomena when compared to UDS midsole. Moreover, a higher (45%) distortion was found in the UDS midsole after the loading-unloading experiment when compared to the VDS midsole (24%) distortion. A further comparison of the VDS midsole was carried out with the commercially available wave spring-based midsole. Despite about 2-fold higher weight of the wave spring–based midsole, the VDS polymer midsole has higher mechanical properties found in terms of flexibility and force-bearing capacity. Finally, it is concluded that the VDS structure of the midsole can enhance the mechanical properties such as force-bearing capacity, flexibility, and stability with a higher strength-to-weight ratio. This study also proves the feasibility of design and AM of customer-specific shoe midsole.

Zhang J., Lu G., You Z.

Different from conventional materials, materials with negative Poisson's ratios expand laterally when stretched longitudinally. Known as ‘auxetic’ materials, the effect means they possess particularly fascinating properties, which have recently attracted considerable attention in the literature. A range of auxetic materials has been discovered, theoretically designed and fabricated. Developments in additive manufacturing (AM) techniques enable fabrication of materials with intricate cellular architectures. This paper outlines recent progress in the development of auxetic materials and structures, and their mechanical properties under quasi-static and dynamic loading are analysed and summarised. Limited experimental studies on 3D printed auxetic materials and structures are given more attention, ahead of extensively finite element (FE) simulations. A special focus is dedicated to their large, plastic deformation behaviour and energy absorption performance, which should be stressed in their engineering applications; no review paper has yet been found regarding this. Finally, this paper provides an overview of current study limitations, and some future research is envisaged in terms of auxetic materials and structures, nano-auxetics and additive manufacturing.

Nazir A., Ali M., Hsieh C., Jeng J.

Recent advances in additive manufacturing (AM) have made the direct manufacturing of intricate shapes such as metamaterials and complex geometries easier, more efficient, faster, and optimally functional, as compared with the manufacturing of simple solid blocks. In this study, the authors conducted experimental investigations and simulations on the energy absorption, stiffness, and deflection of various variable dimension helical springs fabricated by a recently developed high-speed AM technology, namely, the multijet fusion (MJF) system. The variable dimension helical springs were designed by defining various parameters such as the pitch, diameter of the spring wire and spring coil, and total height of the spring. For comparison, the total masses, bounding boxes, and total heights of all samples were kept constant. The results show that the variable parameters (e.g., shape) significantly affect the properties of helical springs; therefore, the stiffness and deformation can be controlled by varying them for a particular application. Furthermore, in designing variable dimension helical springs, nonlinear force–displacement behaviors and stiffness, along with reductions in weight and maximum stresses, can be obtained. Finally, it was concluded that by optimally defining the above parameters, a spring with an ideal geometry can be designed, thereby realizing comfort, stability, and reliability, along with other application-specific benefits (e.g., lightweight).

Nazir A., Jeng J.

Lattice structures have been used in a variety of engineering applications in aerospace, automobile and biomedical applications. In this study, the buckling analysis of additively manufactured cellular columns was conducted. The effect of unit cell size and height of the column on the critical buckling load and post-bucking behavior of compressive columns constructed with periodic cubic structure was investigated using experimental and simulation-based studies. The results exhibited that the unit cell size and cellular column height significantly affect the critical buckling load while the total mass, volume fraction, and column dimensions remain the same. The critical buckling load increases with the increase of unit cell size or decrease of cellular column height. The largest unit cell size (8.72 mm) has the maximum critical buckling load, followed by unit cell sizes of 4.74 mm and 2.5 mm, respectively. Moreover, the failure of cellular columns having larger height-to-width (h/w) ratio, happens due to global buckling, whereas, local bucking dominates for smaller h/w ratios. Additionally, it was found that the unit cell size significantly affects on the post-buckling behavior; the samples of larger unit cells failed in a brittle manner and this trend continuously changed from brittle to ductile as the unit cell size reduces.

Han S.C., Kang D.S., Kang K.

We introduce a new type of auxetic material with ultrahigh strength and ductility that mimics the crystal structures of two natural solids: α-cristobalite and LaNiO 3 /SrTiO 3 superlattice (or ABO 3 perovskite). The fabrication method is based on wire-woven metals. Namely, this new auxetic material is fabricated by forming helical wires, assembling them into a wire-woven structure, and then filling the tetrahedron or octahedron cells with another solid. The structure is then transformed similar to the crystal structure of one of the two natural auxetic solids, mentioned above. We evaluate the mechanical and auxetic properties of the material through compression tests on the specimens made of aluminum, followed by numerical analyses. Unlike previous auxetic materials, this material can be mass produced and can absorb ultrahigh energy, needed for heavy duty applications such as a sandwich core of military amour, because the raw material is metallic wire and the fabrication process is uncomplicated, merely comprising conventional metal forming and heat treatment.

Zhang Z., He L., Ni J., Cui Z., Sun J., Zhu Z.

The spring system functions as a pivotal element of the check valve, with its compression performance significantly influencing the valve's time, flow stability, and other characteristics. Taking cues from conventional springs, a refined rectangular helical spring with integrated support features was thoroughly evaluated for its compression performance. The design approach for this spring was elucidated, encompassing the utilization of the Finite Element Method (FEM) to model its compression behavior. Additionally, a laboratory configuration was implemented to authenticate the findings derived from the FEM simulation. Subsequently, a comparative investigation was carried out between an engineered spring and a conventional spring subjected to analogous processing. The comparative analysis unveiled that the support-featured spring exhibited a diminished lateral offset of 2.84 mm (equivalent to a reduction of 10.1 %) and a force-displacement curve with narrower vibration intervals and smaller amplitudes. Moreover, it exhibited an enhanced force feedback of 17.5 % under identical compression displacement conditions.

Shah G.J., Haq M.R., Lin S., Jeng J.

Additive manufacturing (AM), often known as 3D printing, is a fast-growing fabrication technology that is rapidly displacing traditional manufacturing due to its capacity to manufacture complex geometries with ease of customization, such as in the case of wave spring designs. Such springs have prospective uses in a variety of industries, including aerospace, automotive, oil and gas, and biomedical where researchers/engineers are interested in the mechanical properties of such springs. Slippage of coils is one of the significant phenomena that was noted during axial compression of additively manufactured wave springs. This study aims to investigate the effect of variable frictional contacts between the coils of wave spring on energy absorption, stiffness, load-bearing capacity, and compression behavior during loading- unloading. Nine contact wave springs with different profiles, i.e., sine, square, concave, convex, V, and mixed profiles on the surface of coils, were designed and fabricated using HP MultiJet fusion printer. Compression testing was performed up to ten cycles to analyze the mechanical performance and compression behavior of each design. The sine profiled coils showed the highest energy absorption, with the minimum energy loss from the first to the tenth cycle while having the lowest stiffness among all the designs for this study. Furthermore, the results demonstrated that these variable fictional contacts improved the stability of the designs as the coil’s slippage resistance increased and has a significant impact on mechanical properties, allowing the researchers to design wave springs for different applications based on load/stiffness requirements having variable dimensions. Experimental results were compared with finite element analysis (FEA), which was performed using the identical boundary conditions of experimental testing and showed minimum variation in terms of load-bearing capacity and compression behavior.

Haq M.R., Nazir A., Azam H., Jeng J.

Design for additive manufacturing (DfAM) enables the design and fabrication of intricate but application-based functionally optimized geometries by reducing the manufacturing time. It also gave unlimited design freedom to alter any specific parameter and regenerate the design with improved mechanical properties. However, designing a complex and application-specific component needs comprehensive knowledge of drawing, intended usage, high expertise, and command of designing software with ample time. Mechanical springs, e.g., wave springs of uniform/complex shaped designs, consume a significant amount of manual hard work. A new design tool, WSdesign, is developed for constructing wave springs of different morphologies with uniform or varying design parameters or a combination of both. A graphical user interface (GUI) was developed in which the user can select the type of wave spring, which can be either uniform, functional gradient, or hybrid with parametric variation defined through Python code. The code is directly run in Autodesk Fusion 360 software which is used to transform that code into a 3D model with all defined features and can be saved in different formats or can be directly printed. Two designs, i.e., rectangular and variable thickness wave springs, were designed each using WSdesign and SolidWorks (manual method), manufactured, and analyzed by performing uniaxial compression testing. The results were compared with each other which were further validated by finite element analysis and found that both design strategies have negligible variations. Furthermore, several designs of complex-shaped wave springs were successfully designed and manufactured using fused deposition modeling (FDM), stereolithography (SLA), and powder bed fusion (MJF) technology with different materials, resulting in a good surface finish, smooth printability, and less dimensional variation, which proves the versatility of WSdesign. In addition, this methodology also enables to design of application-based wave springs for research and industrial usage as per load requirements without having in-depth design expertise and spending much less time.