Review on Powder-Bed Laser Additive Manufacturing of Inconel 718 Parts

This study presents a thorough literature review on the powder-bed laser additive manufacturing processes such as selective laser melting (SLM) of Inconel 718 parts. The paper first introduces the general aspects of powder-bed laser additive manufacturing and then discusses the unique characteristics and advantages of SLM. Moreover, the bulk of this study includes extensive discussions of microstructures and mechanical properties, together with the application ranges, of Inconel 718 parts fabricated by SLM.

On Modeling and Simulation of the Discharging Activity in Electrochemical Discharge Machining

Electrochemical discharge machining (ECDM) is a promising machining technology to process non-conducing and brittle materials, featuring high throughput and good accuracy in meso and micro scale machining of hard-to-machine materials. Currently ECDM has not yet attracted wide interest from the industry because of the low controllability and repeatability. There is a huge gap in process optimization to make ECDM viable in industry. A good process model is essential to achieve an improved and optimized process. The fundamental of ECDM is the discharging activity, which triggers various mechanisms to remove material. Therefore characterization of sparks from the aspects of electrical and thermal properties is the premise of process modeling. In this paper, experimental investigation and modeling of discharging activity was presented. The spark releasing process was studied in terms of discharge energy, intensity distribution, and material removal. Conic tool electrodes were fabricated to achieve more consistent discharging. The material removal mechanism was revealed by analytical derivation and simulated with numerical methods.

Effect of Thermal Assistance on the Joining of Al6063 During Flow Drill Screwdriving

An increase in fuel economy standards has affected automakers’ decision toward designing lightweight vehicles and therefore transitioning from steel-based bodies to ones predominantly composed of aluminum. An introduction to lightweight materials couples that of lightweight joining with a thermo-mechanical process, Flow Drill Screwdriving (FDS). This process is favored in terms of robustness, short installation time, and only requiring access to one side. The most significant challenge of this process is reducing the material sheet separation to minimize any possibility of corrosion buildup. Warm forming of aluminum has been shown to increase ductility and formability of the material and thus the process benefits from a reduced cycle time that leads to cost reduction. In this study, the effect of an auxiliary heat source on the flow of Al6063 is investigated for the FDS application. In order to accomplish this task, a conduction-heating ring is implemented into the FDS process to raise the material temperature and thus reduce the total cycle time. Different preprocess material temperatures are studied to determine the effect of material temperature on the process time, installation torque, and sheet separation. As a result, with the thermal assistance, a reduction in the process time up to 52%, the maximum installation torque by 20%, and sheet separation by 11% were attained, indicating better quality joints at a lower cost.

Fabrication of Electroplated CBN End-Mill for High-Efficiency Face Milling of Carbon Fiber Reinforced Plastic

Carbon fiber reinforced plastic (CFRP) was developed in the 1960s. Since then, it has been used in various fields. Accordingly, the number of studies related to machining of CFRP has been increasing (e.g. cutting, laser processing, or abrasive water jet machining). However, these studies have been focusing on the trimming of surplus portions or drilling. In addition, the degradation of mechanical properties due to the heat induced during machining has not been sufficiently considered. Furthermore, another issue is the cost involved, such as tool and equipment costs. This makes several of these proposed methods tremendously expensive. Therefore, in this study, electroplated end-mills with electrodeposited cBN or diamond grains of different grit sizes (the mesh size are #600, #1000, #1500 and #2000) are fabricated. As a result, the cost of the electroplated tool will decrease by 2/3 compared to general diamond-coated tools. Moreover, the flat cutting of CFRP is often carried out with these fabricated tools and with general diamond-coated tools. In cases where the fabricated tools are used, the machined CFRP products are burr-free or nap-free. Additionally, the induced CFRP temperature during cutting decreases compared to the case of diamond-coated tools. From these results, the optimum grit size was determined to be #1000. On the other hand, end-mills with deposited cBN or diamond grains, fixed on the tip of the fabricated tool, occasionally dropped out after a few paths. Therefore, efforts are presented to improve the tool tip shape and minimize its grain dropout rate. Based on such improved characteristics, the electrodeposited end-mill is expected to be able to machine CFRP more effectively.

A Review of Bone Graft Substitutes Made From HA-Polymer Composite Scaffolds and Fabrication Potential With Laser-Based Additive Manufacturing Processes

Hydroxyapatite, a bioactive ceramic, has been combined with biodegradable polymers to create composite three-dimensional interconnected porous scaffolds for bone graft substitutes. The materials and fabrication methods of these composite scaffolds are reviewed. The resulting mechanical and biological properties of scaffolds produced from the combination of certain materials and fabrication methods are analyzed. Requirements for a bone graft substitute and third generation scaffolds with the addition of osteoinductive and osteogenic features to composite scaffolds including biomolecule delivery and cell seeding are also introduced. Finally, the benefits of using additive manufacturing technologies to enable high level of control over the design of interconnected pore structure are discussed.

Tuning the Mechanical Properties of High-Density Polyethylene by ECAE Process

This paper investigates the ability of the equal channel angular extrusion (ECAE) process to induce morphological changes and hence tune the mechanical properties of high-density polyethylene (HDPE). In this study, differential scanning calorimetry (DSC), compression and cylindrical macro-indentation tests have been used to investigate the evolution of the mechanical properties of HDPE processed by ECAE up to four passes via route BC, i.e. counter clockwise 90° billet rotation about its longitudinal axis. It was found that the ECAE process induces significant plastic deformations with changes in the crystalline structure. The ECAE process increased the HDPE crystallinity by 10 to 15%. The number of ECAE passes has a significant effect on the magnitude of the mechanical properties especially on the elastic modulus and yield stress. Young’s modulus and yield strength decreased with increasing the number of ECAE passes and reached a stationary state after the third pass.

Finite Element Study of the Cutting Mechanics of the Three Dimensional Rock Turning Process

The unceasing improvements of polycrystalline diamond compact (PDC) cutters have pushed the limits of tool life and cutting efficiency in the oil and gas drilling industry. However, the still limited understanding of the cutting mechanics involved in rock cutting/drilling processes leads to unsatisfactory performance in the drilling of hard/abrasive rock formations. The Finite Element Method (FEM) holds the promise to advance the in-depth understanding of the interactions between rock and cutters. This paper presents a finite element (FE) model of three-dimensional face turning of rock representing one of the most frequent testing methods in the PDC cutter industry. The pressure-dependent Drucker-Prager plastic model with a plastic damage law was utilized to describe the elastic-plastic failure behavior of rock. A newly developed face turning testbed was introduced and utilized to provide experimental results for the calibration and validation of the formulated FE model. Force responses were compared between simulations and experiments. The relationship between process parameters and force responses and the mechanics of the process were discussed and a close correlation between numerical and experimental results was shown.

Dual-Tree Wavelet Packet Transform for Ultrasonic Data Transmission Through Metal Structures

Data communication through metallic structures is generally encountered in manufacturing equipment and process monitoring and control. This paper presents a signal processing technique for enhancing the signal-to-noise ratio and high-bit data transmission rate in ultrasound-based wireless data transmission through metallic structures. A multi-carrier coded-ultrasonic wave modulation scheme is firstly investigated to achieve high-bit data rate communication while reducing inter-symbol inference and data loss, due to the inherent signal attenuation, wave diffraction and reflection in metallic structures. To improve the signal-to-noise ratio, dual-tree wavelet packet transform (DT-WPT) has been investigated to separate multi-carrier signals under noise contamination, given its properties of shift-invariance and flexible time frequency partitioning. A new envelope extraction and threshold setting strategy for selected wavelet coefficients is then introduced to retrieve the coded digital information. Experimental studies are performed to evaluate the effectiveness of the developed signal processing method for manufacturing.

Mechanical Properties of Densified Untwisted Carbon Nanotube Yarn / Epoxy Composites

Carbon nanotubes (CNTs) have very high specific strength and stiffness. The excellent properties make it possible to enhance the mechanical properties of polymer matrix composites. However, it is difficult to use CNTs as the reinforcement of long fibers because of the limitation of CNT growth. In recent years, a method to spin yarns from CNT forests has developed. We have succeeded in manufacturing the unidirectional composites reinforced with the densified untwisted CNT yarns. The untwisted CNT yarns have been manufactured by drawing CNTs through a die from vertically aligned CNT arrays. In this study, the densified untwisted CNT yarns with a polymer treatment were fabricated. The tensile strength and the elastic modulus of the yarns were improved significantly by the treatment, and they were 1.9 GPa and 140 GPa, respectively. Moreover, the polymer treatment prevented the CNT yarns from swelling due to impregnation of the matrix resin. Finally, the high strength CNT yarn composites which have higher volume fraction than a conventional method were successfully fabricated.

Shape Memory Composite Hands for Space Applications

Shape memory composites combine structural properties of continuous-fiber polymer-matrix composites with functional behavior of shape memory polymers. In this study, the production of shape memory composite structures for aerospace applications is described. Small-scale grabbing systems were prototyped as they could be used for space cleaning operations. Composite hands were manufactured by using two carbon fiber composite layers with a shape memory polymer interlayer. They were produced in the closed-hand configuration and subsequently opened in the memorizing step. Due to heating, composites tended to recover the initial closed configuration, allowing to grab small objects. Two different shapes (cylindrical and cubic) were considered for composite hands. In the first case, the shape memory behavior was given to the entire structure whereas, in the second case, shape memory properties were provided only to folding zones. As a result, a good shape recovery was observed in both cases but part weight was already not negligible also in these small-scale systems.