Design, Additive Manufacturing, and Characterization of a Symmetric 3-Way Wilkinson Power Divider/Combiner

Metal additive manufacturing (AM) has been intensively advanced due to numerous industrial applications such as automobiles, aerospace, consumer electronics, and medical devices. The dynamics of the melt pool via laser sintering for metal AM has been studied by means of the thermodynamic phase change model known as Stefan problem. In this paper, we develop a control design for the laser power to drive the depth of the melt pool to a desired setpoint. The governing equation is described by a partial differential equation (PDE) defined on a time-varying spatial domain which is dependent on the PDE state, and the optical penetration of the laser energy affects the PDE dynamics in domain as well as at surface boundary. The control design is derived via the backstepping method for moving boundary PDEs. The closed loop system is proven to satisfy some conditions to validate the physical model, and its origin is shown to be exponentially stable using Lyapunov method. Numerical simulation illustrates a desired performance of the proposed control law.

Metal additive manufacturing (AM) has been intensively advanced due to numerous industrial applications, such as automobiles, aerospace, consumer electronics, and medical devices. The dynamics of the melt pool via laser sintering for metal AM has been studied by means of the thermodynamic phase change model known as the "Stefan problem". In this article, we develop a control design for the laser power to drive the depth of the melt pool to the desired set point. The governing equation is described by a partial differential equation (PDE) defined on a time-varying spatial domain, which is dependent on the PDE state, and the optical penetration of the laser energy affects the PDE dynamics in the domain as well as at the surface boundary. First, we design the full-state feedback control law utilizing the entire spatial profile of the temperature in the melt pool and the moving interface position. The closed-loop system is proven to satisfy some conditions to validate the physical model, and its origin is shown to be exponentially stable. Next, we propose an observer-based output feedback control law by reconstructing the temperature profile with the availability of only the measured interface position and prove the analogous properties of the closed-loop system. Numerical simulation for a controller designed on a single-phase Stefan model is conducted on a more complex and realistic two-phase Stefan model, which incorporates the cooling effect from the solid phase. In addition, a bias in the interface location measurement is considered. The numerical results illustrate the robustness of the proposed feedback. By lowering the initial temperature in the solid and by increasing the interface sensor bias to more extreme levels, which leads to the controller's failure (where the failure is exhibited through the entire metal freezing and the melt pool disappearing), we explore the limits of how much uncertainty our control law can handle.

Injection moulding of carbon-fibrereinforced polycarbonate

Optimization of 3D printed liquid cooled heat sink designs using a micro-genetic algorithm with bit array representation

Mechanical Properties of Reused Nylon Feedstock for Powder-bed Additive Manufacturing in Orthopedics

Additive manufacturing (AM) can open up the design space for tight integration of electrical machines, thermal management systems as well as power electronics. It can be adopted in integrated modular machines and drives (IMMD) to improve the system integration and performance. This paper investigates an additively-manufactured permanent magnet (PM) machine with modular stator and tooth winding design. Leveraging the capability of AM in terms of building complex 3D structure, two design approaches are explored separately: (i) Encapsulated end winding with stator and rotor overhang, in which the end windings of the stator are encapsulated by soft magnetic material (SMC) cores to improve stator heat dissipation in the end region while keeping core loss due to end leakage flux at a low level; (ii) Direct cooling through heat pipes integrated with conductors, in which the cross section of the conductors is customized to increase slot fill factor as well as minimize AC losses. The results show that both approaches can benefit thermal management of the PM machine, which is promising for the pursuit of high specific power.

In this paper design of an innovative compact broadband millimetre-wave 32-way inline power divider/combiner network is presented for high-power Monolithic Microwave Integrated Circuit (MMIC) amplifiers used in 5G small cell base station. This power combining design produced up to 16-W maximum output power within the frequency band 65-87 GHz by using 32 GaAs MMIC power amplifiers combined with the power combiner network. A design technique is discussed for the oversized axially symmetric coaxial waveguide power combiner/divider network. The electromagnetic field strength simulation of the structure at 75 GHz shows that the maximum electric field that occurs on the sharp edges is two times lower than the air-dielectric breakdown voltage. A 29% 10dB return loss bandwidth is obtained from 65 to 87 GHz.

This paper presents the thermal analysis of a novel laser sintering machine for additive manufacturing of continuous carbon fibre-reinforced polymer parts. The core element of this machine is a fibre integration unit with a heated fibre nozzle. With the help of an additional heat source, which is mounted on the bottom side of the fibre integration unit, the temperature of the powder bed surface is kept within the sintering window of the PA12 material used in the investigations. Different heat source variants differing in shape and material were analysed experimentally concerning the heat distribution achieved within the powder bed surface using an infrared camera. Based on the best-rated variant showing the most homogeneous heat distribution, operating points for successful continuous fibre integration were experimentally identified. An aluminium plate with a closed fibre nozzle slot and symmetrical surface heating power has proven to keep the powder bed surface reliably warm. Compared to the initial state, the resulting increased uniformity of heat-affected zones created by the heated fibre nozzle HAZ was evaluated by fabricating a horseshoe part made of PA12. Furthermore, a CCFRP flat pedal for mountain bikes demonstrated roving integration's process reliability and reproducibility.

This paper presents the analysis and design of a novel millimeter-wave power combining circuit. This combing circuit is composed of a new style 3-dB combiner, which achieves low-loss, wide-band, and symmetric power division. Different from conventional Wilkinson hybrid, the proposed combiner requires no isolating resistor, and is easier fabricated and more suitable for millimeter integrate circuits. Analytical and experimental work on a two-way combining circuit with wave-guide ports in Ka-band shows the combiner has an insertion loss of 0.2dB, and a power-combining efficiency above 80% in 32–33GHz is obtained.

Simulation-guided variable laser power design for melt pool depth control in directed energy deposition

One of the most prevalent additive manufacturing processes, the powder bed fusion process, is driven by a moving heat source that melts metals to build a part. This moving heat source, and the subsequent formation and moving of a melt pool, plays an important role in determining both the geometric and mechanical properties of the printed components. The ability to control the melt pool during the build process is a sought after mechanism for improving quality control and optimizing manufacturing parameters. For this reason, efficient models that can predict melt pool size based on the process input (i.e., laser power, scan speed, spot size and scan path) offer a path to improved process control. Towards improved process control, a data-driven melt pool prediction model is built with a neighborhood-based neural network and trained using experimental data from the National Institute of Standards and Technology (NIST). The model considers the influence of both manufacturing parameters and laser scan paths. The scan path information is encoded using two novel neighborhood features of the neural network through locality. The neural network is used to generate a surrogate model, and we demonstrate how the performance of the resulting surrogate model can be further improved by using several ensemble methods. We then demonstrate how the trained surrogate model can be used as a forward solver for developing novel laser power design algorithms. The resulting laser power plan is designed to keep melt pool size as constant as possible for any given scan pattern. The algorithm is implemented and validated with numerical experiments.