Special Issue “Feature Review Papers in Mechanical Engineering”

1. Introduction

The study and advancement of crank-slide actuating mechanisms based on four-link structural groups are promising for the development of new designs of crank presses and other stamping and forging machines [1,2]. These mechanisms address existing limitations such as slider distortion during forging compression and design restrictions for implementing slider dwells. Press rigidity is a crucial factor affecting the loading and unloading phases, especially in hot stamping processes, but increased rigidity may lead to higher metal consumption. To address dwell requirements, six-link mechanisms like crank-knee mechanisms are utilized. Hybrid presses with multiple degrees of freedom (DOF) are designed for specific applications, employing adjustable electric motors and servo motors for trajectory and cyclogram control. Various studies explore the synthesis, modeling, and kinematic analysis of hybrid mechanisms with five to seven rods, aiming to optimize stamping efficiency and energy distribution while minimizing manufacturing complexity and cost [3].

Industry 4.0 (I4.0) has revolutionized various industrial sectors by promoting digital and cyber-physical technologies, reshaping manufacturing plants to produce parts efficiently and adaptively [4]. The customization of products and coping with market changes necessitate automation equipment and intelligent machines capable of task reconfiguration and collaboration. However, adapting to engineering changes while supporting different platforms poses challenges in maintaining robustness, safety, and reliability. Industrial Robots (IRs), pivotal in modern smart factories, perform diverse tasks but face limitations due to closed architecture and rigid programming [5]. Overcoming these limitations requires flexible, modular, and open architecture solutions. The advent of Industry 4.0, IoT, big data, and cloud computing has revolutionized manufacturing systems, enabling enhanced adaptability to internal and external changes. However, classical systems like dedicated manufacturing systems (DMSs), flexible manufacturing systems (FMSs), and cellular manufacturing systems (CMSs) have limitations in adjusting to modern industrial trends [6]. CMSs, employing group technology, organize machines and resources into cells for efficient production of part families, balancing flexibility and efficiency. Recent research focuses on improving CMS responsiveness to dynamic changes through dynamic designs, virtual models, reconfigurable machines, and robust approaches. Sustainability efforts aim to reduce energy consumption and emissions, aligning with EU targets and UN Sustainable Development Goals. These recent trends highlight the enhancement of CMS responsiveness and sustainability efforts to ensure efficient energy use amidst dynamic manufacturing landscapes [7].

Research on smart materials, especially shape memory alloys (SMAs), has surged since the late 1980s. SMAs regain their original shape when heated after deformation, offering advantages like compact size and high actuation force. Various review papers have explored SMA applications, including linear and rotary actuators, bi-directional motion, and robotic and morphing wing applications [8,9]. These works focus uniquely on SMA actuators for structural systems, covering the vibration and stiffness control of flexible structures and shape control in aerospace engineering. It summarizes research from the past decade, detailing system characteristics, control methods, and potential applications. While magnetic shape memory alloys are excluded, the review offers insights into SMAs’ roles in advancing structural control systems, omitting detailed modeling techniques to concentrate on practical applications and control algorithms [10].

Constructal theory emphasizes the significance of flow system configuration in their efficiency and survival. It proposes Constructal Design, where flow architecture is a design input, highlighting Svelteness (Sv) as a parameter to characterize the system’s geometry [11]. Sv compares external and internal length scales, representing a global property independent of flow conditions [12]. Higher Sv values indicate better performance and originality in conveying meaning. While Sv’s application has been limited to fluid flow, it holds potential for broader engineering contexts. Research explores Sv’s role in various flow configurations, like parallel, tree, and radial tree flows, emphasizing its impact on system design and evolution. Understanding Sv’s significance can guide engineers in optimizing flow architectures for enhanced performance and longevity.

2. An Overview of Published Articles

Contribution 1 focuses on enhancing the functionality of crank presses by introducing actuators with dwell in which the output link remains stationary during part of the work cycle. By utilizing a fourth-class structural group, the study expands the capabilities of the crank press, allowing for precise control over the dwell duration. Numerical experiments led to the design of four variants of crank-knee press actuators, optimizing dimensions for improved performance, and the methodology involved kinematic analysis and the development of numerical algorithms and modeling programs. The results demonstrate the ability to regulate dwell duration based on slider guide eccentricity and rack coordinates. The findings provide insights into designing crank-knee presses with specific stroke and dwell requirements, offering potential solutions for precise mechanism synthesis.

In today’s manufacturing landscape, the need for flexibility to swiftly respond to customer demands while maintaining operational efficiency is paramount. Industrial Robots (IRs) have emerged as primary resources for modern factories due to their versatility in executing flexible, reconfigurable, and zero-defect manufacturing tasks. However, the effective implementation of IRs is hindered by limitations in control and programming, especially in dynamic production environments or for complex applications. To address these challenges, new technologies supporting more efficient methods for robot control and programming have been developed. Contribution 2 aims to identify and evaluate the main approaches proposed in scientific papers and by the robotics industry in recent decades. Following a critical review of the standard IR control schematic, the paper discusses available control alternatives, summarizing their characteristics, range of applications, and remaining limitations.

Cellular manufacturing systems are widely embraced for their ability to combine the flexibility of job-shop setups with the productivity of flow-shop arrangements. Recent trends such as shortened product life cycles, demand variations, and new technologies have prompted manufacturing companies to enhance responsiveness and streamline cellular manufacturing life cycles through cell redesign. Sustainability concerns, particularly regarding energy costs, are also driving efforts to develop models supporting the sustainability of cellular manufacturing systems. Contribution 3 provides an overview of recent works on design approaches to enhance responsiveness and sustainability in cellular manufacturing systems, highlighting key findings and suggesting future research directions.

Contribution 4 comprehensively reviews effective control applications using shape memory alloy (SMA) actuators, with a focus on vibration and stiffness control in flexible structures and shape control in aerospace engineering. Various vibration control methods and strategies are discussed, along with control strategies like neuro-fuzzy controllers and the inherent hysteretic behavior of SMAs. Additionally, the applications of SMA actuators in morphing wings in aerospace engineering are reviewed, emphasizing control logics and geometrical parameters. A summary table of the study’s contributions is provided, aiming to facilitate the development of advanced vibration and morphing control techniques using SMA actuators.

The application of Constructal theory to flow design in engineering connects channel architecture with their morphing freedom. Svelteness emerges as a crucial parameter in assessing flow architecture evolution, despite its limited use in engineering applications. Contribution 5 explores the application of Svelteness, understanding its impact and evolution over time, and its relevance in explaining freedom to morph in a flow. Using two configurations, the review illustrates the relevance of using the configuration area for the external length scale, offering insights into its potential as an engineering design tool.

3. Conclusions

In conclusion, the research on crank-slide actuating mechanisms collated in this Special Issue offers promising avenues for the development of more efficient crank presses and forging machines. Overcoming limitations such as slider distortion and design constraints, these mechanisms, especially those employing higher-class structural groups, show potential for improved performance and versatility. However, balancing press rigidity with metal consumption remains a challenge, necessitating innovative solutions like hybrid presses with multiple degrees of freedom.

Meanwhile, the advent of Industry 4.0 has transformed manufacturing, emphasizing adaptability and collaboration among automation equipment and intelligent machines. Yet, challenges persist in maintaining robustness and interoperability. Industrial Robots (IRs), crucial in modern factories, face limitations due to closed architectures, highlighting the need for flexible and open solutions.

Similarly, classical manufacturing systems like DMSs, FMSs, and CMSs confront challenges in adapting to modern trends. CMSs, incorporating group technology, aim to balance flexibility and efficiency but require further enhancements to cope with dynamic changes. Sustainability efforts in manufacturing systems align with global targets, emphasizing energy efficiency and emissions reduction.

Furthermore, research on smart materials, particularly SMA actuators, holds promise for structural systems, offering control over vibration, stiffness, and shape. Although research has predominantly focused on fluid flow, the application of Constructal theory and Svelteness in engineering contexts presents opportunities for optimizing system design and performance. Understanding and leveraging Sv’s significance can guide engineers in developing more efficient flow architectures for various applications.