The Honeycomb structure is one of the most common natural structures used in sandwich panel cores. The Enamel structure’s mechanical properties were compared to the Honeycomb structure’s mechanical properties to investigate if the Enamel structure can improve the compressive strength, stiffness and energy absorption capabilities of sandwich panel cores and potentially replace the common Honeycomb structure. Also, the optimal cellular configurations for the Honeycomb and Enamel structures were explored. Indeed, it was found the Enamel structure can potentially replace the Honeycomb structure and a wall thickness of 1.2 mm and a wall length/cell radius of 8.14 mm will maximize the natural structures mechanical properties. Furthermore, it was found that both the natural structures have good compressive strength. Therefore, the natural structures with their optimal cellular configurations were integrated into a novel automobile floor mat to ensure the mat possesses good compressive strength to resist failure or permanent deformation. Moreover, the novel automobile floor mat has a design feature that offers an efficient debris capturing and removal system that adds value to the automobile floor mat.

Tubular structures of hydrogel are used in a variety of applications such as 3D cell culturing for delivery of nutrient supplies. The wall thickness of the tube determines the speed of diffusion or delivery rate. In this study, we aimed to fabricate tubular structures with varying of wall thicknesses using a thermal-crosslinking hydrogel, gellan gum, with the coaxial needle approach. The wall thickness is controlled by changing the flow rate ratio between the inner (phosphate-buffered saline) and outer needles (gellan gum). A simulation model was developed to estimate the proper extrusion speed to allow the gellan gum to be extruded around its glass transition temperature. While keeping the extrusion rate of gellan gum fixed, different PBS extrusion rates were tested to investigate the printability to form continuous tubular structures, range of printable wall thickness, and possibility to form tubes with closed ends to encapsulate fluid or drug inside the tube. The ranges of printable wall thickness with two pairs of coaxial needle were identified. It was found that at about 200% of the baseline PBS extrusion speed, a maximum of 20% difference in wall thickness can be achieved, while a close end can still be formed.

Cellular structures are broadly applicable to lightweight design and multifunctional applications. Especially, with unprecedented fabrication freedom provided by additive manufacturing (AM), design and optimization of nonuniform cellular structures have recently attracted great research interests. Topology optimization is one of the most powerful tools to obtain the optimized material distribution, and much research have been conducted to optimize cellular structures with the help of this optimization technique. In general, the optimized cellular structure is generated based on a predefined ground structure, and thickness of each strut is then decided based on the optimization result. However, many existing studies did not consider the constraints of AM processes, such as some generated struts may be too thin to be manufactured. Besides, only load support structure was considered in these studies. Other applications, such as heat dissipation or energy absorption, were rarely researched. In this paper, a novel cellular structure design method, which considered both functionality and manufacturability, is proposed. Different from other methods, wall thickness of the structure was set as a constant. To get the optimized material distribution, variable cell sizes were applied. Because of uniform wall thickness, the smaller the unit cell is, the higher its volume fraction will be. By mapping small unit cells to high density area and large cell to low density area, the final optimized cellular structure can be generated. In addition, because smaller unit cells have higher surface-to-volume ratio, this method can also be applied to solve heat transfer problem. Two examples, minimum compliance design of a cantilever beam and maximum heat dissipation efficiency design of a CPU heat sink, were conducted to validate the proposed method.

During an induction hardening process, the electromagnetic field generated by the inductor creates eddy currents that heat a surface layer of the part, followed by spray quenching to convert the austenitized layer to martensite. The critical process parameters include the power and frequency of the inductor, the heating time, the quench delay time, the quench rate, and the quench time, etc. These parameters may significantly affect case depth, hardness, distortion, residual stresses, and cracking possibility. Compared to a traditional hardening process, induction hardening has the advantages of low energy consumption, better process consistency, clean environment, low distortion and formation of beneficial residual stresses. However, the temperature gradient in the part during induction hardening is steep due to the faster heating rate of the surface and the aggressive spray quench rate, which leads to a high phase transformation gradient and high magnitude of internal stresses. Quench cracks and high magnitude of residual stresses are more common in induction hardened parts than those of conventional quench hardening processes. In this study, a scanning induction hardening process of a large part made of AISI 4340 with varying wall thickness is modeled using DANTE. The modeling results have successfully shown the cause of cracking. Based on the modeling results, a preheat method is proposed prior to induction heating to reduce the in-process stresses and eliminate the cracking possibility. This process modification not only reduces the magnitude of the in-process tensile stress, but also converts the surface residual stresses from tension to compression at the critical inner corner of the part, which improves the service life of the part. The modified process has been successfully validated by modeling and implemented in the heat treating plant.

This work reports the development of robust and efficient algorithms for optimum process planning of Additive Manufacturing (AM) processes needing support structures during fabrication. In particular, it addresses issues like part hollowing, support structure generation and optimum part orientation. Input to the system is a CAD model in STL format which is voxelized and hollowed using the 2D Hollowing strategy. A novel approach to design external as well as internal support structures for the hollowed model is developed considering the wall thickness and material properties. Optimum orientation of the hollowed part model is computed using Genetic Algorithm (GA). The Fitness Function for optimization is the weighted average of process performance parameters like build time, part quality and material utilization. A new performance measure has been proposed to choose the weightages for performance parameters to obtain overall optimum performance. The paper presents, in detail, the design and development of algorithms with results for typical case studies. The proposed methodology will significantly contribute to improving part quality, productivity and material utilization for AM processes.

Three-dimensional (3D) printing of microscale structures with high resolution (sub-micron) and low cost is still a challenging work for the existing 3D printing techniques. Here we report a direct writing process via near-field melt electrospinning to achieve microscale printing of single filament wall structures. The process allows continuous direct writing due to the linear and stable jet trajectory in the electric near-field. The layer-by-later stacking of fibers, or self-assembly effect, is attributed to the attraction force from the molten deposited fibers and accumulated negative charges. We demonstrated successful printing of various 3D thin wall structures (freestanding single walls, double walls, annular walls, star-shaped structures, and curved wall structures) with a minimal wall thickness less than 5 μm. By optimizing the process parameters of near-field melt electrospinning (electric field strength, collector moving speed, and needle-to-collector distance), ultrafine poly (ε-caprolactone) (PCL) fibers have been stably generated and precisely stacked and fused into 3D thin-wall structures with an aspect ratio of more than 60. It is envisioned that the near-field melt electrospinning can be transformed into a viable high-resolution and low-cost microscale 3D printing technology.

Incremental sheet forming is a flexible manufacturing process that does not require dedicated dies nor custom tooling. Hole-flanging via the ISF process is rapid and cost-effective, especially in prototyping and low-volume production. In this study, a double-sided incremental hole-flanging method was considered where the top and bottom tools were used as the forming tool and supporting tool respectively. Utilization of these generic, stylus tools provides enhanced flexibility and replaces the need for specific blank holders. The double-sided incremental hole-flanging method was experimentally studied with various toolpath techniques for the forming and supporting tools. Two toolpath strategies were determined that developed a successful symmetric hole-flange. The measured wall thickness was found to be comparatively uniform along the wall of the flange, while in-plane strains demonstrate excellent material formability. Additionally, the optimum strategy was trialed on a self-designed complex profile with shrink flange and stretch flange occur alternatively in an effort to demonstrate the flexibility and generality of the proposed double-sided incremental hole-flanging method. Possible future work in this area is also discussed.

A hollow R.R. Moore rotation fatigue sample made of AISI 9310 is processed using vacuum carburization and high pressure gas quenching. The vacuum carburization schedule is designed to through carburize the thin wall section of the fatigue sample to 0.7% wt.% carbon, followed by 10 bar nitrogen quench. Some samples showed significant bow distortion after quench hardening, and further investigations indicated that the unbalanced wall thickness from machining is the main cause of the bow distortion. In this paper, DANTE, a commercial heat treatment software is used to study the cooling, phase transformation, and stress evolution during quenching. The effect of unbalance wall thickness on distortion is also investigated. Residual stress state in the quench hardened sample is critical to the fatigue performance during rotational bending fatigue tests. In this study, the unbalanced geometry has insignificant effect on the residual stresses after quench hardening. However, the unbalanced geometry will affect the applied stress significantly during a rotation fatigue test.

Roll bonding of aluminum sheets is a technology with actual and potential applications in several fields, such as the production of special materials or all-aluminum channeled products. The strength of the rolled bonds clearly depends on the main process parameters, including the rolling conditions (entry temperature, reduction, speed, etc.) and the pre-rolling treatment conditions (annealing temperature and time, surface preparation technique, etc.). The purpose of this paper is to further investigate, experimentally, the effect of additional parameters that have been generally neglected by the scientific literature, such as the initial wall thickness of the sheets and the post-rolling heat treatment. An extensive plan of experiments has been designed for evaluating the simultaneous effect of several process variables. The results have been analyzed with a statistical approach, using the strength of the bond as the main response variable, evaluated though peel tests. The analysis demonstrated that thicker sheets are easier to weld than thin sheets. The study also proved that a prolonged post-rolling heat treatment is useful to enhance the bond strength (by solid state diffusion), but only if a good mechanical bond has already been obtained by rolling. Furthermore, the surface quality of the rolled products has been measured and correlated to the strength of the bond.

In modern lightweight concepts, for example in automotive engineering, structures are increasingly composed of several dissimilar materials. Due to the different material properties of the joining partners, conventional and widely used joining techniques often reach their technological limits when applied in the manufacturing of such multi-material structures. This leads to an increasing demand for appropriate joining technologies, like joining by die-less hydroforming (DHF) for connecting tubular workpieces. The present work introduces an analytical model to determine the achievable joint strength of this connection type. This approach, taking into account the material parameters as well as the groove and tube geometry, is based on a membrane analysis with constant wall thickness. Additionally, bending stresses and friction are considered locally. Besides a fundamental understanding of the load transfer mechanism, this analytic approach allows a reliable joining zone design. To validate the model, experimental investigations using aluminum specimens were performed.

Wall thickness eccentricity is a major dimensional deviation problem in seamless steel tube production. Although eccentricity is mainly caused by abnormal process conditions in the cross-roll piercing mill, most seamless tube plants lack the monitoring at the hot piercing stage but only inspect the quality of finished tubes using ultrasonic testing at the end of all manufacturing processes. This paper develops an online monitoring technique to detect abnormal conditions in the cross-roll piercing mill. Based on an image-sensing technique, process operation condition can be extracted from the vibration signals. Optimal frequency features that are sensitive to tube wall thickness variation are then selected through the formulation and solution of a set-covering optimization problem. Hotelling T 2 control charts are constructed using the selected features for online monitoring. The developed monitoring technique enables early detection of eccentricity problems at the hot piercing stage, which can facilitate timely adjustment and defect prevention. The monitoring technique developed in this paper is generic and can be widely applied to the hot piercing process of various products. This paper also provides a general framework for effectively analyzing image-based sensing data and establishing the linkage between product quality information and process information.

A new bending technique was presented for forming very thin metal tubes, which is characterized by ball filler in the tube as force-transferring media during bending process. Due to the good flow capacity and non-uniform pressure, ball filler is considered as an alternative filler to bend very thin tubes. The experiments of ball filler push bending were carried out for very thin copper tubes. The results indicate that the back pressure and lubrication condition have great effects on the forming quality of the tubes. As the back pressure increases and/or lubrication condition improves, the tube surface quality is improved. The ovality of the bent tube is small, and the intrados and extrados wall thickness are both thickened and changed uniformly, which indicates that the new process applied to form the very thin tubes is feasible.

Aiming at the difficulty of straightening the distorted monolithic components, residual stress redistribution and deformation compensation method based on rolling process is put forward. Finite element Model is established to investigate the rolling process. Based on the FEM analysis, the relationship curve among rolling position, component wall thickness and deformation after rolling is established. The curve is used as a guideline for rolling parameters selection in actual manufacturing process. Straightening experiment for a scaled frame part is design. The validation of rolling parameters selection based on the straightening curve is verified.

Recent advances in high temperature and high pressure applications have made significant increase in industrial applications of square and rectangular seamless tubes. In this work, a reshaping process is presented with cold rolling of a circular thick tube into a square cross section between four flat rolls in different passes. The influence of the amount of roll gap reduction in each pass on the final rolled product was investigated. In order to verify the simulation results, several experimental tests were performed. Quantities such as separated force energy, wall thickness, and corner radius of the tube were observed and measured. Obtained results of simulation showed good agreements with the experiment results.

In this research, numerical approach for modeling the behavior of honeycomb seal material is studied. Also, the optimal forming process of the honeycomb core is developed and the rolling process is analyzed. The part of the honeycomb is modeled using the commercial S/W, CATIA. And the rolling process is simulated using finite element code, DEFORM™-3D. The standard honeycomb has a uniform hexagonal structure defined by the material, cell size, cell wall thickness and bulk density. The simulation results are reflected to the forming process design for the honeycomb core.

The flow of polymers in micromolding applications is dominated by shear stresses. At high flow velocities and small wall thicknesses, the shear rates can exceed the typical characterization scheme of 10,000 reciprocal seconds. Yet, the effective design of micromolded parts and micromolding processes requires a correct understanding of the flow dynamics. In this paper, analytical models assuming power law fluid behavior are developed and experimentally validated for wall thicknesses of 10, 20, and 100 micro meters. A design of experiments is conducted to consider the effect of wall thickness, channel width, melt temperature, and pressure on flow rate in an isothermal molding process. The results indicate that the power law model is a valid representation for viscous polymer flow in very thin gaps under isothermal conditions, though further work is required to validate the non-isothermal dynamics.