Mechanical Assembly Research Articles

A survey of offline precision calibration of industrial robots

Abstract. As the need for precision and efficiency grows in industrial manufacturing, the accuracy of industrial robots assumes paramount importance. Nevertheless, factors, such as mechanical structures and assembly processes often introduce errors, compromising robots' positioning and repeatability accuracy. Consequently, precise calibration and compensation of these errors are paramount for optimizing robots performance. A thorough analysis of error sources and the establishment of error models in industrial robots are conducted in the present study, with special attention paid to offline calibration methods. This paper reviews the robot error model building methods and offline accuracy calibration techniques, summarizes the technical difficulties of the calibration task, and proposes the future development direction for the difficulties such as the complexity of error modeling, the difficulty of non-motor calibration calculation, and the traditional stiffness compensation that does not meet the needs of the robot's operation process. The importance of this research lies in its potential to improve the accuracy and reliability of industrial robots, thus contributing to the development of industrial automation.

Optimised rotational-spring component-based modelling strategy for seismic resistant steel-concrete composite joints and frames with continuous or isolated slab

Joints and frames in steel-concrete composite systems represent complex mechanical assemblies that require specific calculation procedures to optimise their detailing and structural capacity, particularly under seismic loads. To this aim, component-based modelling approaches should be able to account for the most relevant mechanisms and resistance/stiffness behaviours of individual members, and their mutual interaction. In this paper, two different simplified non-linear approaches are considered for steel-concrete composite beam-to-column joints, and are specifically applied to a seismic resistant case-study frame with X-concentric bracings. Both beam-to-column joints with or continuous (“JA” joint) or fully isolated (“JB” joint) slab are examined. First, non-linear axial springs are assembled and calibrated on the base of a previous study (“Type 1″ model (“T1″)), according to force-displacement relationships proposed in the DPC-ReLUIS Italian guidelines. Successively, a novel modelling approach based on non-linear rotational springs is presented (“Type 2″ model (“T2″)), to further simplify the computational cost of T1 strategy, and allow to efficiently account for the moment-rotation behaviour of the examined joints. The preliminary numerical validation is carried out based on past literature experiments. Moreover, the optimized T2 approach is used to explore the in-plane lateral, seismic performance of a 2D steel-concrete composite frame, which is specifically designed with X-concentric bracings. The seismic capacity of the frame (and the associated interaction of components, especially the joint zone with the bracing system) is addressed on the base of pushover analyses.

Influence of re-melting rate on the dry sliding wear characteristics of LPBFed Cu–Cr–Zr alloy

For the past few decades, Copper alloys have made significant contributions to a variety of industrial applications due to their efficient electrical and thermal conductivity. However, moving mechanical assemblies continues to raise concerns about wear-related mechanical breakdowns on a worldwide scale. Hence, this research focuses on examining the wear parameters such as load, sliding velocity and distance based on the re-melting strategy of the (Laser Powder Bed Fusion) LPBF process. The sliding tests were carried out over a wide range load (15, 25, 35 and 45 N), sliding velocity (1, 1.5, 2 and 2.5 m/s) and sliding distance (1500, 2500, 3500 and 4500 m) with a pin-on-disc configuration. The LPBFed Cu–Cr–Zr alloy coupon was printed with four different re-melting ranges (5, 15, 30 and 45%) and it was explored to minimise the occurrence of un-melted particles and inter-particle gaps. The wear results show that the wear parameters have a positive correlation with the Wear Rate (WR) and co-efficient of friction (COF) and also witnessed that the WR and COF decrease with increasing the re-melting rate. The nano-hardness analysis was compared on the un-melted and spattered particles and the re-melted surface. The results show that the spattered particles possess 35.8% more nano-hardness than the other surface on the Cu alloy coupon printed with a 45% re-melting range. The FE-SEM images of the worn-out surface reveal that un-melted and spattered particles have a major contribution in reducing the wear resistance of the printed Cu alloy coupons.

A review on metallic drilling burrs: geometry, formation and effect on the mechanical strength of metallic assemblies

Abstract Machining processes produce unwanted remainders of material on the free edges which are called burrs. In particular, the drilling process generates an entry burr, and a typically larger exit burr. When drilling stacks of several workpieces, exit and entry burrs are produced simultaneously at the interfaces. The presence of burrs can degrade the static and fatigue strength of the parts and assemblies containing them. An example concerns the burrs formed at the interface during the drilling of multi-stacks in One-Way-Assembly processes, where deburring is not systematically applied. The effect on fatigue can be significant. Reductions of up to 70 % in fatigue life have been reported, even though the explanatory rationale is not clear. This paper reviews existing works on burrs, focusing on drilling burrs. A description of the morphology of different types of burrs and of measurement technologies is given. Burr formation mechanisms and its modelling are reviewed. Burr control strategies and the main deburring technologies are examined. The limited literature on the effects of burrs on the static and fatigue strength of mechanical assemblies is also explored.

ИНФОРМАЦИОННЫЕ ОСНОВАНИЯ СИСТЕМЫ ТЕХНОЛОГИЧЕСКОГО ОБЕСПЕЧЕНИЯ МЕХАНИЧЕСКОЙ СБОРКИ В УСЛОВИЯХ ЦИФРОВОЙ ТРАНСФОРМАЦИИ ПРЕДПРИЯТИЙ АВТОМОБИЛЕСТРОИТЕЛЬНОГО КЛАСТЕРА

Information grounds for supporting decision-making on the optimal formation of automated systems for technological preparation of assembly production are in demand at the automotive cluster enterprises. The paper proposes to develop two databases in the process of forming the optimal set of control and verification equipment and the set of spare equipment and spare parts. This will allow accumulating information due to the feedback on the state of its subsystems in the process of operating automated systems for the technological preparation of assembly production. For this purpose, the paper proposes the database “A set of the system elements for providing mechanical assembly”, as well as the database “Statistical information for forming the stock of assembly equipment and spare parts in the system for ensuring mechanical assembly”. The work presents the information on the registration output, the structure and number of records of two developed databases, calculates the economic effect in the cost of technological preparation of production using the described databases.

IMPROVING ORGANIZATIONAL PROCEDURES TRAINING FOR CNC MACHINE OPERATORS

The article is devoted to the issues of improving methodological tools and procedures for conducting organizational training of workers at primary sites in the conditions of modernization of production processes. The introduction of modern, high-tech equipment, digitalization of production, transition to new work standards, as well as optimization of the technological process create the need for a more rapid response to the requests of performers, in particular operators of numerically controlled machine tools. Based on the analysis of theoretical sources, the features of traditional and learning organizations are considered, their distinctive characteristics are presented, the factors influencing the need to invest in in-house training are studied, the sequence of stages in the implementation of in-house training of production workers is shown, and their brief characteristics are given. The study of the existing in-house training system at the enterprise made it possible to identify its shortcomings and propose a number of measures to improve the procedure and methodological tools. In particular, it is proposed to create a training sector on the basis of a mechanical assembly shop for operators of numerically controlled machine tools, which will minimize existing problems with organizational training for this category of workers and reduce the load on the training center, the personnel service of the enterprise, and also presents draft improved training program. The proposed activities will ultimately contribute to the fact that operators of machine tools with numerical control will receive deeper knowledge and skills related to the specifics of software and machining stages on new type equipment, as well as in the process of work will be able to more fully analyze the situation and select the best machining modes, taking into account the available tools.

Fabrication and dielectric spectroscopy analysis of FeGaInS4/PVA composite materials

AbstractThe control of dielectric permittivity and conductivity is a crucial factor in the development of certain electronic components. Materials based on layered structures and polyvinyl alcohol (PVA) show great potential for applications in supercapacitors. Therefore, the creation of polymer composites based on layered semiconductors and the determination of their physical properties is significant. In this investigation, a composite comprising 1 wt% FeGaInS4 dispersed in PVA was synthesized through mechanical mixing, where the FeGaInS4 crystal was incorporated into the PVA matrix. This study explores the physical characteristics of this composite for the first time. The structure of the composite was analyzed using x‐ray diffraction (XRD). Electrical properties and conductivity mechanisms were examined using a dielectric spectrometer. It was determined that the hopping model conductivity mechanism predominates in the FeGaInS4/PVA nanocomposite. For the 1 wt% FeGaInS4/PVA composite, system parameters were calculated at a temperature of 313 K and a frequency of 5 × 103 Hz. The parameters found are s = 0.814, potential barrier height WM = 0.868 eV, hopping length Rω = 14.7 × 10−10 m, and the concentration of pairs of states between, which charge carriers hop N = 1.396 × 1026 m−3.Highlights 1 wt% FeGaInS4 composite synthesized via mechanical assembly. Small crystals boost dielectric constant by 1.5× via interfacial polarization. The system parameters are defined: s = 0.814, WM = 0.868 eV, Rω = 14.7 × 10−10 m. Electrical conduction is multifaceted; conductance hopping dominates. Loss tangent decreases due to interfacial polarization effects.

Mechanical Design, Assembly and Strain Measurement Results of a 13-T Superconducting Dipole Magnet

Mechanical Design, Assembly and Strain Measurement Results of a 13-T Superconducting Dipole Magnet

Towards direct superlubricity and superlow wear via amino modification of polyhydroxy alcohol solutions

Friction remains as the primary mode of energy dissipation and components wear, and achieving superlubricity shows high promise in energy conservation and lifetime wear protection. The results in this work demonstrate that direct superlubricity combined with superlow wear can be realized for steel/Si3N4 contacts on engineering scale when polyhydroxy alcohol solution was selectively modified by amino group. Macroscopic direct superlubricity occurs because 3-amino-1,2-propanediol molecules at the friction interface could be induced to rotate and adsorb vertically on the friction surface, forming in-situ thick and dense molecular films to passivate the asperity contacts. Furthermore, amino modification is also conducive to improving the lubrication state from boundary to mixed lubrication regime by strengthening the intermolecular hydrogen bonding interaction, presenting enhanced load-bearing capability and reduced direct solid asperity contacts. Thus, direct superlow average friction of 0.01 combined with superlow wear are achieved simultaneously. The design principle of direct superlubricity and superlow wear in this work indeed offers an effective strategy to fundamentally improve energy efficiency and provide lifetime wear protection for moving mechanical assemblies.

Error analysis of self-compensated ultrasound measurements of the thickness loss due to corrosion in pipe walls

The ultrasonic pulse-echo technique is widely employed to measure the wall thickness reduction due to corrosion in pipelines. Ultrasonic monitoring is noninvasive and can be performed online to evaluate the structural health of pipelines. Although ultrasound is a robust technique, it presents two main difficulties arising from the temperature variation in the medium being monitored: the mechanical assembly must have high stability and the ultrasonic propagation velocity must take into account the temperature variation. In this paper, a detailed strategy is presented to compensate for changes in the propagation velocity whenever the temperature changes. The method is considered self-compensated because the calibration data is obtained from the ultrasonic signals captured using the pipe under evaluation. The analysis of systematic errors in the temperature compensation is presented, first considering that a reference initial pipe thickness is given, and second when a reference sound velocity is given. The technique was evaluated under laboratory conditions using a closed loop with accelerated corrosion through the use of continuous flow saline water containing sand. In this test, the ultrasonic results were compared with the traditional coupon method used to determine corrosion loss. The results show that the self-compensated method was able to compensate for temperature fluctuations, and the total thickness loss measured by the ultrasound technique was close to the value measured by the coupons. Finally, the measurement system was tested in a production pipeline exposed to sunlight. The results show that the self-compensated method can reduce the oscillations in the thickness loss readings, caused by temperature swings, but large temperature variations cannot be completely compensated for. This experiment also shows the effects of low mechanical stability, which caused completely invalid results.

Interfacial Heterogeneous Microstructure and Subsequent Machinability of 316L/CuSn10 Bimetallic Structure Manufactured by Laser Powder Bed Fusion

Additively manufactured bimetallic structures combine the advantages of dissimilar materials and can achieve localized properties through a customized composition distribution. However, additively manufactured parts may still lack the dimensional accuracy and surface integrity essential for precision mechanical assemblies that the post-machining process can address. Therefore, this study aims to systematically investigate the microstructure and machinability of 316L/CuSn10 bimetallic structures fabricated using laser powder bed fusion. The results show that the fusion zone of the bimetallic structure had refined grains of microscale size owing to the mixture of the primary elements of the bimetals, which resulted in the highest microhardness of 3.4 GPa. The difference in microstructure and microhardness between the single-material and fusion zones also causes significant differences in the cutting response during the ultraprecision process. The 316L stainless steel side exhibited the highest cutting force and more severe material accumulation in the chips. The cutting force drops when cutting through the fusion zone, with an observable fracture in the chips and separation of dissimilar materials on the machined grooves, indicating that the heterogeneous properties of additively manufactured 316L/CuSn10 bimetallic structures pose challenges to the improvement of surface quality. The simulation results also showed that stress accumulation occurred in the tool path through the fusion zone owing to the higher yield strength and hardness of stainless steel, indicating that lower cutting speeds and depths of cut are favorable for reducing cutting force and improving surface quality. This study provides deep insight into the microstructure evolution mechanism and a theoretical basis for improving the surface quality of additively manufactured bimetallic structures using an ultraprecision machining process.

An integrated hybrid approach for assembly tolerance transfer and allocation

PurposeThis study aims to develop an optimal tolerance allocation strategy involves integrating the unique transfer (UT) approach and the difficulty coefficient evaluation (DCE) routine in an interactive hybrid method. This method combines the strengths of both UT and DCE, ensuring simultaneous utilization for enhanced performance. The proposed tolerancing model manifests an integrated computer-aided design (CAD) tool.Design/methodology/approachBy combining UT and DCE based on failure mode, effects and criticality analysis (FMECA) tool and the Ishikawa diagram, the proposed collaborative hybrid tool ensures an efficient and optimal tolerance allocation approach. The integration of these methodologies not only addresses specific transfer challenges through UT but also conducts a thorough evaluation of difficulty coefficients via DCE routine using reliability analysis tools as FMECA tool and the Ishikawa diagram. This comprehensive framework contributes to a robust and informed decision-making process in tolerance allocation, ultimately optimizing the design and manufacturing processes.FindingsThe presented methodology is implemented with the aim of generating allocated tolerances that align with specific difficulty requirements, facilitating the creation of a mechanical assembly characterized by high quality and low cost. To substantiate and validate the conceptual framework and methods, an integrated tool has been developed, featuring a graphical user interface (GUI) designed in MATLAB. This interface serves as a platform to showcase various interactive and integrated tolerance allocation approaches that adhere to both functional and manufacturing prerequisites. The proposed integrated tool, designed with a GUI in MATLAB, offers the capability to execute various examples that effectively demonstrate the benefits of the developed tolerance transfer and allocation methodology.Originality/valueThe originality of the proposed approach is the twining between the UT and DCE simultaneous in an integrated and concurrent tolerance transfer and allocation model. Therefore, the proposed approach is named an integrated CAD/tolerance model based on the manufacturing difficulty tool. The obtained results underscore the tangible advantages stemming from the integration of this innovative tolerance transfer and allocation approach. These benefits include a notable reduction in total cost and a concurrent enhancement in product quality.

A New Approach for Synthesis of 3D Tolerances with Consideration of Flatness Defects in Mechanical Assembly Using Jacobian Torsor Model

A New Approach for Synthesis of 3D Tolerances with Consideration of Flatness Defects in Mechanical Assembly Using Jacobian Torsor Model

Measurement and optimization of writing light field uniformity in dual-galvanometer laser scanning lithography system

The light field uniformity (LFU) in lithography system is a key factor in defining the resolution across the entire micro/nano structures. In this work, a cost-effective and straightforward method based on the focused laser marking on heat-mode resist is proposed for measuring and optimizing the LFU. The factors affecting the LFU are analyzed from the perspectives of optical system aberrations and mechanical assembly error. Subsequently, marking patterns with special structures are designed based on the properties of the heat-mode resist. By analyzing the marked patterns, the LFU of the system is obtained with uniformity coefficient is 42.24%. After optimization achieved by dynamic laser power adjustment, the uniformity coefficient was notably enhanced to 96.11%. This work provides an effective method for measuring and optimizing the LFU in dual-galvanometer laser scanning lithography system.

A Domain-Adaptive Segmentation Method Based on Segment Anything Model for Mechanical Assembly

Semantic segmentation of assembly images can effectively identify and prevent non-standard behaviors such as wrong assembly and missing assembly in the assembly process. However, supervised methods require massive training samples and are time-consuming to label. Unsupervised domain adaptation methods can address this issue without labeling the target data. Recently, the large-scale Segment Anything Model (SAM) has achieved significant success in semantic segmentation owing to its powerful feature extraction and instant interaction capabilities. Based on this, this paper proposed a new framework called U-SAM for unsupervised domain-adaptive semantic segmentation. Compared to other frameworks, U-SAM can obtain more segmented features while maintaining shallower features. Meanwhile, this study proposed an iterative loop strategy for the prompt module in U-SAM. This strategy gradually improves the accuracy of target prompt labels and solves the problem of no prompt labels in the target data. Additionally, a novel method of using oblique boxes instead of regular boxes was developed to achieve higher box prompt quality. Finally, a line discriminator module and a trainable line-guided filtering module were designed to improve the quality of edge segmentation. The experimental results indicate that the U-SAM network framework achieves a Dice accuracy of 84.4% for semantic segmentation on the mechanical assembly image dataset. This confirmed that our proposed method can be applied to the assembly monitoring process of target data.

Growth Substrate Geometry Optimization for the Productive Mechanical Dry Transfer of Carbon Nanotubes

The selection of growth substrate geometries for the mechanical dry transfer of carbon nanotubes to device substrates depends on the precision of the assembly equipment. Since these geometries play a decisive role in the overall efficiency of the process, an investigation of the most important geometry parameters is carried out. The substrate geometry affects the number of carbon nanotubes suspended during the growth process and the speed of mechanical assembly at the same time. Since those two criteria are interlinked and affect productivity, a meta-model for the growth and selection of the nanotubes is simulated and a time study of the resulting assembly motions is subsequently performed. The geometry parameters are then evaluated based on the total number of suspended carbon nanotubes and the throughput rate, measured in transfers per hour. The accuracy specifications are then taken into account. Depending on the overall accuracy that can be achieved, different offset angles and overlaps between the growth and receiving substrate can be reached, which affect productivity differently for different substrate geometries. To increase the overall productivity, growth substrate designs are adapted to allow fully automated operation. This measure also reduces the frequency of substrate exchanges once all carbon nanotubes have been harvested. The introduction of substrates with multiple, polygonally arranged edges increases the total number of nanotubes that can be harvested. The inclusion of polygonally arranged edges in the initial analysis shows a significant increase in overall productivity.

Improving the Principles of Identifying Critical Requirements for the Assembly of High-Precision Products

Introduction. The problem of improving the manufacturing of high-precision products is currently becoming a key one, since the requirements for them are constantly being tightened. Maintaining assembly quality and accuracy is an important aspect of manufacturing precision products. Standard approaches to this process do not always have sufficient versatility. Existing studies that aim to develop universal approaches, such as end-to-end production design or the application of parallel engineering principles, also have a number of shortcomings. These include the fact that the given approaches do not fully take into account information about the technology capabilities of a particular production when making design decisions, and do not consider the relationship between the manufacturing preparation of machining and mechanical assembly industries. That is why studies aimed at developing such universal approaches have high applicability. To solve these problems, the authors conceptually developed a set of formalized design procedures for a system of accounting requirements for the assembly of high-precision products in the design of machining processes. However, to effectively identify the numerous requirements for the assembly of high-precision products (output parameters) and select those that cannot be provided by the method of complete interchangeability (critical elements), additional research is needed. The research objective is to develop principles for identifying the output parameters of high-precision products and detecting critical elements. To achieve this goal, it is required to solve the following problems: to formulate principles for constructing generalized surface graphs of high-precision products; to develop standards for classifying output parameters and identifying critical ones.Materials and Methods. To conduct the research, a high-precision assembly unit was selected — “Stator Package 2”. The research was carried out under real conditions of the existing multiproduct manufacture. For this assembly, a generalized surface graph was constructed, including information about the nature and sequence of surfaces, requirements for the assembly, dimensional tolerances and tolerances of shape and location, with its subsequent analysis.Results. This paper presents the results of research on improving the enlarged block of design procedures for analyzing requirements for the assembly of high-precision products of the designed system. The paper established the relationship between the accuracy of dimensional tolerances and the tolerances of the shape and location of the surfaces of the product to which these dimensions belonged. Based on the relationship obtained, an order was determined for the unambiguous identification of critical elements.Discussion and Conclusion. The application of this technique makes it possible to increase the reliability of the source information obtained during the implementation of an enlarged block of design procedures, as well as the validity and efficiency of identifying rational manufacturing technologies at subsequent stages of the system implementation, while providing the specified quality, accuracy of products, and reducing the complexity and cost of their manufacture.

SCIENTIFIC AND METHODOLOGICAL ENSURING THE PROCESS FORMATION OF THE EMPLOYEE COMPETENCE MODEL

The article outlines the expediency of application and the main problematic issues of implementing the principles of the competency approach in personnel management of current enterprises, in particular, related to the process of formation and practical use of its main tool - the model of employee competencies. A scientific survey of the significant assets of scientists and practitioners on this topic was carried out, as a result of which it was established that there is a need to finalize currently unresolved tasks regarding the clarification of the sequence and the development of scientific and methodological support and practical recommendations for the construction of such models, since the given processes are mostly abstract, difficult for practical application due to the lack of clear instructions and tools for the implementation of each stage. The main goal of the article is to improve the process of forming the model of employee competencies by clarifying the sequence of its development, specifying actions at each stage and developing methodological tools for practical application. The process of forming the model of employee competencies was compiled, presented in the form of a logical sequence of specific ac­tions and decisions with the use of a specially developed toolkit, based on the choice of a certain approach and involves the construction of a model of competencies for employees of diffe­rent categories with a different number of constituent elements. For example, for employees in managerial posi­tions there are 4 constituent elements; for specialists and workers in labourer’s positions - 3 constituent elements etc. A scientific-methodical toolkit and relevant recommendations for its implementation were developed, an approbation was carried out on an example (a model of the competences of fitters in mechanical assembly works was developed). Competences of mechanical assembly fitters included in the developed model were assessed using the "360° method"; taking into account the weight factor of each competence, the general level of their competence is determined. The results of scientific research are the basis for making recommendations for improving the level of employees’ competence.

Wear Reduction on the Roller–Shoe Mechanism at High Operation Loads

The roller–shoe mechanism is a classic mechanical assembly with an essential role in motion transmission. Common rail high-pressure pumps are an example of a complex assembly that uses such a mechanism to transform the rotation motion into a translation one. The rolling element of the mechanism is represented by a cylindrical roller. Although it can carry heavy loads due to its design, a proper surface profile could significantly increase the life of the entire mechanism. A better solution can be achieved using a logarithmic profile. The shoe is the second base element of the mechanism. It is a part with an inner cylindrical surface and it is separated from the roller by a thin lubricant film. Considering this, increasing the hardness of the roller–shoe contact surface can be obtained using a suitable coating. The positive results of this coating are highlighted using endurance tests to which high-pressure pumps are subjected. Therefore, the roller profile and the shoe coating represent two directions for improving the contact between the mechanism transmission elements, in terms of wear reduction. The purpose of this paper is to identify a suitable roller profile and to highlight its impact on the shoe coating.

Design and construction of a refrigerator-cooled adiabatic calorimeter for heat capacity measurement in liquid helium temperature region.

Heat capacity is a fundamental thermodynamic property of a substance. Although heat capacity values and related thermodynamic functions are available for many materials, low-temperature heat capacity measurements, especially for novel materials, can still provide valuable insights for research in physics, chemistry, thermodynamics, and other fields. Reliable low-temperature heat capacity data are typically measured using classical adiabatic calorimeters, which use liquid helium as the refrigerant to provide a cryogenic environment for heat capacity measurements. However, liquid helium is not only expensive but also not easy to obtain, which greatly limits the application of adiabatic calorimetry. In this work, an accurate adiabatic calorimeter equipped with a Gifford-MacMahon refrigerator was designed and constructed for measuring the heat capacity of condensed matter in the temperature range from 4 to 100K. The Gifford-MacMahon refrigerator was utilized to provide a stable liquid helium-free cryogenic environment. A simple mechanical thermal switch assembly was designed to facilitate switching between the refrigeration mode and the adiabatic measurement mode of the calorimeter. Based on the measurement results of standard reference materials, the optimized repeatability and accuracy of heat capacity measurements were determined to be within 0.8% and 1.5%, respectively. The heat capacity of α-Fe2O3 nanoparticles was also investigated with this device. Furthermore, this adiabatic calorimeter only requires electricity to operate in the liquid helium temperature range, which may significantly advance the research on low-temperature heat capacity based on adiabatic calorimetry.