Digital Twin for Smart Manufacturing: The Practitioner’s Perspective

The manufacturing sector is experiencing a technological paradigm shift, where new information technology (IT) concepts can help digitize product design, production systems, and manufacturing processes. One of such concepts is Digital Twin and researchers have made some advancement on both its conceptual development and technological implementations. However, in practice, there are many different definitions of the digital-twin concept. These different definitions have created a lot of confusion for practitioners, especially small- and medium-sized enterprises (SMEs). Therefore, the adoption and implementation of the digital-twin concept in manufacturing have been difficult and slow. In this paper, we report our findings from a survey of companies (both large and small) regarding their understanding and acceptance of the digital-twin concept. Five supply-chain companies from discrete manufacturing and one trade organization representing suppliers in the automotive business were interviewed. Their operations have been studied to understand their current digital maturity levels and articulate their needs for digital solutions to stay competitive. This paper presents the results of the research including the viewpoints of these companies in terms of opportunities and challenges for implementing digital twins.

Development of Analytical Force Model for End Milling of Magnesium Matrix Composites

An analytical approach to predict the cutting forces in end milling of magnesium metal matrix composite is presented in this study. The model was developed by identifying three events that occur when the cutting edge encounters the composite, when an element of the cutting edge encounters just the particles, it may fracture the particle, when the element encounters pure ductile matrix, plastic deformation occurs and when the element is in contact with both the particle and matrix, particle debonding occurs due to mismatch in coefficient of thermal expansion. The probability of these events was estimated using the particle concentration and the distribution in the matrix. A cutting force model is developed by considering the stresses and forces experienced by the cutting edge contributed by these events. The predicted feed forces and the measured forces are in good agreement for most of the cutting conditions. While, the predictive thrust forces were found to diverge at higher feed of 1 mm/rev.

Design, Modelling and Simulation of a Rotational Robotic Arm

In this paper, a rotational robotic arm is designed, modelled and optimized. The 3D model design and optimization are conducted by using SolidWorks. Forward kinematics are derived so as to determine the position vector of the end effector with respect to the base, and subsequently being able to calculate the angular velocity and torque of each joint. For the goal positioning problem, the PD control law is typically used in industry. It is employed in this application by using virtual torsional springs and frictions to generate the torques and to keep the system stable.

Investigation of Drilling Temperature in Relation to Machining Conditions and Cutting Time

Controlling drilling temperature and thrust forces play a significant role in reducing tool wear and improving machining efficiency. In this work, drilling experiments are set up to measure flank surface temperature via thermocouple sensor wires passed through the coolant holes of 10mm twist drill and brazed to the drill flank surface. The testing setup is an inverted drilling jig where the workpiece (Aluminum 6061-T6 rod) is chucked into the spindle of a vertical machining center. Thrust forces are co-measured using Kistler type 3-component plate dynamometer attached to the table. A design of experiment (DOE) using JMP-SAS/STAT® was adopted for selecting combinations of cutting speed and feed values that cover a wide range. Drilling temperature rise and thrust forces are found to correlate with cutting conditions of feed (f), maximum cutting speed (V), and drilling depth (Dp). Nonlinear regression analysis produced correlating equations of flank temperature rise and thrust forces to conditions and follow a mechanistic power law of the form a1fa2Va3Dpa4 where a1, a2, a3 and a4 are identified via regression fitting.

Build Time Analysis of Additive Manufacturing for Next Generation SLS Systems

With the recent advances in the additive manufacturing (AM) production technologies, AM is becoming more common in today’s industry, nowadays is a normal practice to use this solution either to test a new prototype or to manufacture a functional product. The increase application is mainly due to significant developments in the production solutions of the AM. These recent developments are resulting in an increase search for new and more efficient production solutions. This search is always focused in producing more efficiently, with a greater variety of materials and produce part with better quality and proprieties. From an industrial point of view, one of the types of additive manufacturing that is increasing the percentage of use is the selective laser sintering (SLS) technologies. Although this process was first used in the mid-80’s, it has shown great developments in the recent years. This evolution of the process allowed it to become a solid solution even if it is highly time consuming, especially when compared with other types of addictive manufacturing. From the several aspects that make the SLS a robust solution is the fact that it offers a consistent solution to produce high complex part with good mechanical properties, and also the ability to use many core materials, from polymers, metal alloy, ceramics or even composites materials. Due to the fact that the production of part using SLS technologies takes a long time, shows the relevance to study the entire process in order to quantify the time spent in each stage a very important step. This study can be conducted with two major goals, in one hand to be able to predict the build time needed to complete a predetermined task, and in other hand, to improve the overall efficiency of the process based on the knowledge acquired in the previous analysis. These two aspects are important because they allow the machine operator to choose the production plan more carefully and also to know all the parameters of the process to make it more efficient. In this paper will be presented a survey of the major stages of a SLS process in order to quantify the time consumed in each one of the stages, and if possible, determine solution to reduce the time spent. To better understand the topic the paper will be divided according to the proprieties and time consumed in each of the elements of the process. In other words, it will be divided accordingly to a machine, laser and material point of view. Furthermore, this paper will be focused in the SLS process and the productions based in a polymeric powder, therefore also containing aspects related to the power source used.

Complex Fastener Model for Simulation of Airframe Assembly Process

The complex model of fastener for the global modeling of aircraft assembly with regard to compliance and contact interaction of parts is introduced in the paper. The presented complex fastener model incorporates such effects as the stiffness of fastening elements; the loosening of fasteners and also the failure of fasteners (if the load exceeds the maximal value that fastener can hold). This model can be implemented for all types of fastening elements in variation simulation and assembly optimization analysis. It provides more realistic simulation results at expense of higher model dimension. The fastener is modeled as having an additional stretching stiffness. The option of fastener loosening is included by implementation of additional contact node in each fastening element. This option allows taking into account the pre-tension in fasteners and also enables the modeling of installation and removal of fasteners without change of stiffness matrix.

A New Kinematic Error Modelling and Identification Method of the Parallel Manipulator

Parallel manipulators have broad application prospects on hybrid machine tools. Kinematic error modelling and identification are two key processes to improve the accuracy of parallel manipulators. The traditional kinematic error modelling method adopts the partial differentiation of the ideal kinematic model. However, the partial differentiation method is pure mathematical calculation, which ignores physical meaning of error terms corresponding to each link. In the process of error identification, the Jacobian matrix obtained from the partial differentiation method is usually ill-conditioned, which leads to non-convergence of the identification process. In order to solve the above problems, this paper proposes a new kinematic error modelling method and an error identification model. Firstly, the basic error terms for single link are analyzed. Based on basic error terms, the kinematic error model is established by using the practical connection point of two adjacent links. Then, a new error identification model is derived from the kinematic error model. Finally, as a study case, a 3-DOF parallel tool head is used to verify the correctness of the proposed method. The numerical results show that the proposed method is effective and the accuracy of the 3-DOF parallel tool head improves significantly after compensation of error terms.

A Creative Vibration Energy Harvesting System to Support a Self-Powered Internet of Thing (IoT) Network in Smart Bridge Monitoring

This paper presents a creative energy harvesting system using a bimorph piezoelectric cantilever-beam to power wireless sensors in an IoT network for the Sunshine Skyway Bridge. The bimorph piezoelectric energy harvester (BPEH) comprises a cantilever beam as a substrate sandwiched between two piezoelectric layers to remarkably harness ambient vibrations of an inclined stay cable and convert them into electrical energy when the cable is subjected to a harmonic acceleration. To investigate and design the bridge energy harvesting system, a field measurement was required for collecting cable vibration data. The results of a non-contact laser vibrometer is used to remotely measure the dynamic characteristics of the inclined cables. A finite element study is employed to simulate a 3-D model of the proposed BPEH by COMSOL Multiphasics. The FE modelling results showed that the average power generated by the BPEH excited by a harmonic acceleration of 1 m/s2 at 1 Hz is up to 614 μW which satisfies the minimum electric power required for the sensor node in the proposed IoT network. In this research a LoRaWAN architecture is also developed to utilize the BPEH as a sustainable and sufficient power resource for an IoT platform which uses wireless sensor networks installed on the bridge stay cables to collect and remotely transfer bridge health monitoring data over the bridge in a low-power manner.

Structural Stability of Magnetic Tunnel Junction Based Molecular Spintronics Devices (MTJMSD)

Harnessing the exotic properties of molecular level nanostructures to produce novel sensors, metamaterials, and futuristic computer devices can be technologically transformative. In addition, connecting the molecular nanostructures to ferromagnetic electrodes bring the unprecedented opportunity of making spin property based molecular devices. We have demonstrated that magnetic tunnel junction based molecular spintronics device (MTJMSD) approach to address numerous technological hurdles that have been inhibiting this field for decades (P. Tyagi, J. Mater. Chem., Vol. 21, 4733). MTJMSD approach is based on producing a capacitor like a testbed where two metal electrodes are separated by an ultrathin insulator and subsequently bridging the molecule nanostructure across the insulator to transform a capacitor into a molecular device. Our prior work showed that MTJMSDs produced extremely intriguing phenomenon such as room temperature current suppression by six orders, spin photovoltaic effect, and evolution of new forms of magnetic metamaterials arising due to the interaction of the magnetic a molecule with two ferromagnetic thin films. However, making robust and reproducible electrical connections with exotic molecules with ferromagnetic electrodes is full of challenges and requires attention to MTJMSD structural stability. This paper focuses on MTJMSD stability by describing the overall fabrication protocol and the associated potential threat to reliability. MTJMSD is based on microfabrication methods such as (a) photolithography for patterning the ferromagnetic electrodes, (b) sputtering of metallic thin films and insulator, and (c) at the end electrochemical process for bridging the molecules between two ferromagnetic films separated by ∼ 2nm insulating gap. For the successful MTJMSD fabrication, the selection of ferromagnetic metal electrodes and thickness was found to be a deterministic factor in designing the photolithography, thin film deposition strategy, and molecular bridging process. We mainly used isotropic NiFe soft magnetic material and anisotropic Cobalt (Co) with significant magnetic hardness. We found Co was susceptible to chemical etching when directly exposed to photoresist developer and aged molecular solution. However, NiFe was very stable against the chemicals we used in the MTJMSD fabrication. As compared to NiFe, the Co films with > 10nm thickness were susceptible to mechanical stress-induced nanoscale deformities. However, cobalt was essential to produce (a) low leakage current before transforming the capacitor from the magnetic tunnel junction into molecular devices and (b) tailoring the magnetic properties of the ferromagnetic electrodes. This paper describes our overall MTJMSD fabrication scheme and process optimization to overcome various challenges to produce stable and reliable MTJMSDs. We also discuss the role of mechanical stresses arising during the sputtering of the ultrathin insulator and how to overcome that challenge by optimizing the insulator growth process. This paper will benefit researchers striving to make nanoscale spintronics devices for solving grand challenges in developing advanced sensors, magnetic metamaterials, and computer devices.

Metal Forming With Laser Origami: Parameter Analysis and Optimization

Laser origami is a metal forming process where an initially planar sheet is transformed into a target three-dimensional (3D) form through cutting and folding operations executed by a laser beam. A key challenge in laser origami is to determine the locations of the cuts and folds required to transform the planar sheet into the 3D target shape. The region of the planar sheet that can be transformed into the target shape through these cuts and folds is denoted as the net. This paper presents a method to determine optimal net(s) for laser origami based on criteria including minimum energy usage, minimum fabrication time, minimum error in the fold angles, and minimum material usage. The 3D target shape is given as a polygonal mesh. To generate a net, each edge in the mesh must be classified as a cut or a fold. The energy, time, and other parameters associated with cutting or folding each edge are determined using experimentally calibrated formulas. A search algorithm is subsequently implemented to find combinations of cut and folded edges that provide an optimal set of nets for the given 3D target shape based on a cost function. Nets that are disconnected or have overlapping regions are discarded since they are invalid for laser origami. The method is demonstrated by applying it to different target shapes and cost functions.