The dynamic servo error of heavy-duty vertical machining centres is one of the decisive factors affecting the machining accuracy of large and complex parts. Due to the characteristics of large mass, large load, and the large travel distance of the machine tool, non-linear factors such as friction, backlash, and lateral shift are more likely to cause unstable behaviours such as stick-slip and oscillation of the servo feed system of the machine tool, and reduce the performance and servo accuracy of the motion axis. In this paper, to consider the influence of non-linear factors such as friction, backlash, and lateral shift, an appropriately simplified representation of the mechanical transmission system of the ball screw has been used. According to the control structure of the Siemens 840D numerical control system, a theoretical model of the servo feed system for the heavy-duty vertical machining centre was established based on three-loop control. Then, the single-axis and double-axis closed-loop simulation models of the servo feed system were built in Simulink, and the influence pattern of control parameters and nonlinear factors on the dynamic servo error was obtained through simulation analysis. Finally, the validity of the theoretical model for the servo feed system was verified through a comprehensive comparison of simulation and experimental outcomes. This encompasses an analysis of the control system Bode plots, critical stick-slip velocity, and tracking errors in the X-axis with linear motion. The validation provides theoretical guidance for parameter design and mechanical adjustments of the servo feed system in heavy-duty vertical machining centres.

Due to the large size and large span of heavy-duty machine tools, the structural deformation errors caused by gravity account for a large proportion of the static errors, and the influence of gravity deformation must thus be considered in the machine tool precision design. This paper proposes a precision design method for heavy-duty vertical machining centers based on gravity deformation error modelling. By abstracting the machine tool into a multibody system topology, the static error model of the machine tool is established based on the multibody system theory and a homogeneous coordinate transformation. Assuming that the static error of each motion axis is composed of two parts, i.e., the manufacturing-induced geometric error and the gravity deformation error, the machine tool stiffness model of the relationship between gravity and deformation error is developed using the spatial beam elements. In the modelling process, the stiffness coefficients and volume coefficients of the components are introduced to fully consider the influences of structural parameters on machine tool precision. Taking the machine tool static precision, the component stiffness coefficients and the volume coefficients as the design variables, based on the use of the worst condition method, error sensitivity analysis and global optimization algorithm, the optimal allocation of the static error budget of the machine tool and the structural design requirements of each component are determined, providing a valuable guide for the detailed structure design and manufacture processing of the machine tool components.

Diverse model factories have been established in universities and enterprises to support practical education across various fields. Increasingly stringent health and safety regulations have made practical equipment more complex and costlier. With the advancement of digital infrastructure, virtual reality (VR) technology has been widely adopted in education to simulate real-world environments. This study explores the application of VR technology in enhancing manufacturing process education. To achieve this, an interaction methodology based on the OPC UA standard is proposed to enable data exchange between virtual and physical environments. Additionally, a detailed workflow of the practice course, conducted in a physical model factory at North China University of Technology, is presented. This approach is particularly noteworthy because it allows students to validate simulated results using a physical system, rather than relying solely on virtual scenes to mimic real-world settings. Students were divided into two groups: a practice group using the proposed digital method, and a control group without digital tools. The number of mistakes from the practice group was 37% less than that of the control group. Statistical analysis of students’ grades and questionnaire responses concludes that the proposed methodology is valuable to improve students’ engagement and practical skills. The presented course is replicable for other training institutions.

A growing demand for cheap, strong, and lightweight structures has resulted in an increasing need for materials incorporating macroscopic structures such as surface textures in the form of dimples or internal non-uniformities such as porosity. This has highlighted the potential for misleading results when applying the current standards for the determination of yield strength to materials incorporating such non-uniformities. In the present study, discontinuous, continuous, and severely continuous (departure from linearity significantly prior to macroscopic yield) yield behaviours during tensile loading have been explored with respect to the determination of yield strength. This has clearly shown the limitations of standard measures as well as the incompatibility of different measures, making the comparison of yield strengths deceptive. Therefore, a novel derivative yield method has been proposed. Based on the second derivative of stress with respect to strain, this method is independent of both yield type and the presence or lack of macroscopic structures, and it correctly identifies the upper yield for discontinuous yield as well as the first significant departure from linearity for continuous yield. Furthermore, the derivative yield method is shown to more accurately characterise the behaviour of dimpled steel, non-arbitrarily quantifying the yield strength for severely continuous yielding. This wide applicability, in many cases, eliminates the need for the comparison of results produced by mutually incompatible yield criteria, e.g., when quantifying strengthening due to dimpling.

This work presents a systematic literature review of powder-gas jet stream (PGJS) characterisation techniques for coaxial nozzles in the laser directed energy deposition process (L-DEDp). The analysis includes thirty-four camera-based and four weight-based techniques. In weight-based techniques, the mapping of powder concentration is made by measuring the powder flow rate in certain areas within the PGJS. Despite being cost-effective, these methods are time-consuming, invasive, and less suitable for real-time monitoring. Camera-based techniques use laser light and a camera to capture particle intensities, allowing for the non-intrusive measurement of powder distribution. Despite its advantage, limitations are reported in the literature regarding the techniques. Detecting dense or fine powder flows accurately is challenging. Two-dimensional images cannot fully represent the jet’s three-dimensional structure, relying on image processing algorithms for the results. However, the non-existence of a common standard metric for evaluating and comparing results across various setups is a significant gap, as each characterisation often needs to be performed on a case-by-case basis. To address these challenges, a basic reporting structure is suggested to enable a standardised assessment of PGJS measurements, thereby supporting process control and quality assurance in L-DEDp applications.

In recently years, diverse education platforms have been progressively established across various disciplines to support engineering practice. In addition, the teaching method to improve students’ practical ability is equally important. This paper presents a novel education platform from NCUT (North China University of Technology) and introduces corresponding teaching methods based on the platform to promote the practical ability in engineering students. Taking the manufacturing process of a rotary part as an example, this paper explains the virtual reality integrated method, which is an innovative approach to enhance students’ engagement during the practice sessions. Students are divided into several groups and collaborate to complete the practice. The study concludes that the virtual environment simulated by CAD (computer-aided design) software, serve as an excellent complement to the real-world equipment, enabling students to complete operations repeatedly without the constraints of time and space. The proposed virtual reality integrated education platform and corresponding teaching method significantly enhance students' engagement and practical skills.