International Journal of Precision Engineering and Manufacturing最新文献

This study investigates the impact of contralateral cane placement on the decrease in external knee adduction moment (KAM) and explores the underlying mechanisms. Ten healthy adults participated in a study to test three different lateral cane placements. The “Natural” placement corresponded to the participants’ comfortable position, while the “Wide” and “Wider” placements were 10 cm and 20 cm further laterally outward, respectively. Results from repeated measures ANOVA indicated a significant decrease in KAM peaks with more lateral cane placements (p < 0.01). This reduction was primarily due to a decreased moment arm, particularly at the second peak of KAM. The reduction in walking speed associated with more lateral cane placement had a negligible effect on KAM reduction. The decrease in the lever arm was caused by the displacement of knee joint to the medial side, which outweighed the medial rotation of the ground reaction force vector.

Rotate vector (RV) reducers are typical deceleration elements with the outstanding characteristics of small size, compacted structure, strong load-bearing capacity, and low transmission error, which are widely applied in the fields of industrial robots, aerospace, and measurement instruments. The cycloidal gear, as the core component in the second-stage drive of RV reducer, its tooth profile directly determines the general performance of RV reducer such as meshing precision, load-bearing capacity, and riding stability. Therefore, it is necessary to explore the feasible methods and parameters for modification of cycloidal tooth profile. In this paper, taking the CRV-20E reducer as an object, firstly, a mathematical model for analyzing contact stress and load distribution on meshing surface was established. Secondly, based on genetic algorithm, a multi-objective optimization for cycloidal profile was applied with maximum contact stress and load distribution coefficient as objective functions, the optimal combination of modification parameters was obtained. Then, with the idea of piecewise modification and spline interpolation method, the cycloidal profile was separated into three segments of dedendum, working, and addendum, which ensures conjugated meshing in working segment, and the reserved gaps in dedendum and addendum can also be remained flexibility according to the specific requirements. The mechanism performance with cycloidal profiles modified by two proposed methods were systematically compared and discussed. Finally, the finite element simulation verification was carried out. The results indicated that both modification methods have specific advantages. This study provides a theoretical reference for designers in the field of gear profile optimization and underscores the critical implications for improving the overall efficiency and reliability of RV reducers in applications.

The measuring accuracy of coordinate measuring machines (CMMs) will be affected by the different geometrical and dynamic errors, including the deviations associated to the axis displacement, the working table and the part to be measured. This work is focused on the analysis of the influence of the position errors, repeatability errors and reversibility errors in 3-axis FXYZ coordinate measuring machines, and it will be developed by a numerical model that is known as EE-based stochastic model. This model implements a new error index that is named equivalent error (EE), which will integrate the totality of machine errors of the CMMs and will allow a global description of all these error sources by means of a unique error parameter. The results obtained by this numerical model have been compared with the application of a traditional method, and it was probed that the EE-based model makes possible an increase of a 13.29% in the linear modelling of the performance of CMMs from the machine errors considered in this work, which implies a relevant improvement for the analysis and description of the effect of the distinct error sources on the achievable measuring accuracy of CMMs. For this reason, the EE-based model will be of special interest for industrial applications such as the quality control to be applied inside the production systems dedicated to manufacture mechanical components of high dimensional accuracy.

With the development of the clean energy industry, higher requirements are put forward for the forming mode and service performance of bipolar plates, a key component of hydrogen fuel cells. The nickel-based alloy with corrosion and high-temperature resistance, as the potential material for bipolar plate, has the problem of insufficient plasticity. This paper proposes the superplastic forming method as a new attempt to prepare the Inconel 718 bipolar plate. The sheet with fine crystal structure exhibits excellent superplasticity at high temperatures and slow compression rate, thus forming bipolar plates with deep flow channels (~ 0.6 mm) and flat surfaces. The microscopic observation of the channel section shows that the straight channel at the edge is more filled due to the easier feeding of the material. Moreover, the corner channel exhibits more obvious local thinning and stress concentration than the straight channel, especially at the rounded corner of the inner turning. Increasing the billet thickness or adjusting the compression rate can improve the thickness distribution and filling effect for the product to a certain extent. Thicker sheets exhibit a lower proportion of high-stress regions during superplastic forming. Moreover, the moderate compression rate of 2 × 10^–3 mm s⁻¹ suppresses dislocation proliferation while avoiding grain growth in local areas, which improves the superplastic flow of the alloy and the quality of the final product.

Computerized numerical control (CNC) machine tools are typically repairable products. Reliability indicators should be combined with maintenance and availability indicators to fully reflect the level of operational reliability of the machine tools. At present, most of the methods for the comprehensive evaluation of the generalized reliability of CNC machine tools are based on a specific indicators system, the model has a strong subjectivity and can not be changed in a timely manner when the indicators change. This paper proposes a generalized reliability evaluation method for CNC machine tools based on improved entropy weight extensible matter-element model. Introducing contrast intensity and conflict intensity to consider the interrelationships between indicators to improve the entropy weighting method. Meanwhile, the grading method of the extensible matter-element model is improved to replace the scoring grading with the adaptive grading of the indicator data. This makes the methodology not only more objective and independent of the type of indicators, but also able to make timely and accurate changes when the indicators change. The method of this paper is applied to a five-axis CNC machine to conduct a generalized comprehensive reliability evaluation and compared with the traditional method. The results show that this method is more integrated and practical.

Nickel-based superalloys, including CM247LC, fabricated using laser powder bed fusion (LPBF) are prone to cracking. These induced cracks significantly reduce a manufacturability of the LPBF fabricated components; therefore, selecting appropriate process parameters is critical. Standard sample-scale LPBF parameters often lead to cracking in large-scale applications due to thermal energy accumulation and low thermal conductivity. Thus, it is important to explore industrial-scale parameters and post-processing methods, such as hot isostatic pressing (HIP), to mitigate cracking. However, the effectiveness of HIP can be reduced in samples fabricated under high volumetric energy density (VED) conditions. This study examines the impact of HIP on CM247LC samples fabricated under various VED conditions (43.65–159.72 J/mm³). Two distinct crack modes were identified, namely, solidification and liquation cracks at high and low VED conditions, respectively. A comparison of the pre- and post-HIP crack densities revealed that the crack healing effect of HIP under low and high VED conditions was approximately 90 and 47%, respectively. The mechanisms behind the healing of closed cracks, mostly liquation cracks, were analyzed. This study provides novel insight for selecting LPBF process parameters in the low VED range to mitigate cracks, with a quantitative analysis of HIP treatment for healing two types of cracks. These findings are crucial for practical applications in engineering fields such as the energy, aerospace, and automotive industries.

Cracks often develop under complex loading conditions in practical applications, frequently leading to mixed-mode fracture scenarios. Therefore, accurately predicting fracture conditions, specifically the mixed-mode stress intensity factor (SIF) values and their influences, is crucial for assessing structural integrity. Based on preliminary empirical findings from a literature review of the fracture responses of various materials during small punch (SP) tests under different environmental conditions, we propose a model featuring a circular crack positioned on the bottom surface of the SP specimen to evaluate the I/II mixed-mode SIF. Preliminary results from experimental tests using the proposed model demonstrate its feasibility for replicating fracture behavior and determining mixed-mode SIF values. An analytical estimation of the SIF equation for mode-I and mode-II loading will be conducted using elastic finite element analysis. The effects of crack geometry parameters, including the crack ratio (a/t) and the radius of the circular crack, on the mixed-mode fracture parameter were investigated.

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Machining accuracy of the electrochemical micro machining with pulse voltage mainly depends on pulse width of the voltage signals. To give nanometer level machining resolution, an expensive picoseconds pulse power supply is required. In this paper, a quadratic differential feedback method for electrochemical micro machining is proposed. With the method, nanometer level machining resolution can be obtained easily by tuning feedback loop gain under micro second pulse width. Here, the circuits of the machining system are designed and analyzed, and the circuit equation and transfer function of the system are deduced. By the equation, the basic principle of the machining method is revealed and the equation of the machining resolution for the method is also given. By micro hole machining experiments, effects of the feedback gain on the resolution are investigated and compared with the calculated ones. Good agreement is obtained which illustrates the proposed machining method. Besides it, some micro structures are produced and nanometer level machining resolution is obtained.

The arrival of Industry 4.0 has caused manufacturers to search for ways to achieve efficiency and production. This study aims to optimize the manufacturing process parameters in the CNC machining of an aluminium alloy, Aluminium Alloy 7071, with the L27 orthogonal array designed by Taguchi and the response surface design. The factors that directly affect the rate of material removal, surface roughness, and cutting force are the following: spindle speed (1000, 1400, and 1800 rpm), traverse feed (0.20, 0.25, and 0.30) mm/rev), and cutting depth (.5, 1.0, and 1.5 mm). To accomplish this experiment, 27 samples were fabricated using the array model of Al7071 alloy. A wide range of touch sensors (directly tactile and indirectly measured) are employed to study the associated responses. The L27 array of the Taguchi method is used to enhance the optimization process by providing such improvements as minimized surface roughness, the maximum removal rate of material, and reduced cutting force. The response surface contour plots exhibiting reactions for different parameter sets mirrored by significant effects diagrams demonstrating signal-to-noise ratios are used to analyze the outcomes. This result is a key that tells how process factors cope with each other to get the output. Finally, the research done here is used to optimize the machining operations by obtaining the most influential turning of Aluminium Alloy 7071. As one of the principle goals of the Industry 4.0 concept, the methods applied demonstrate a capacity to increase the efficiency, quality, and productivity of modern manufacturing.

As the aviation industry continues to expand, increasing demands are being placed on aviation engines to withstand extreme temperatures, making it essential to effectively disperse heat from turbine blades. Studies have shown that film cooling holes coated with thermal barrier materials can endure high temperatures and significantly increase engine operating temperatures, thereby enabling higher thrust-to-weight ratios. But, the structure of this insulating ceramic layer adhered to the metal surface presents a significant processing challenge. Consequently, a focal point of manufacturing research now centers on developing effective and high-quality methods for processing film cooling holes with thermal barrier coatings. Accordingly, this paper compares the advantages and disadvantages of various specialized machining techniques and reviews the research progress in processing film cooling holes with thermal barrier coatings, considering both single and composite techniques. Finally, it provides an overview of the future directions for film cooling hole machining methods with thermal barrier coatings. This advancement is crucial for enhancing the standards of aero engine manufacturing.

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