Assembly Clearance Research Articles

A study of the compression stability of a coupler under initial asymmetric conditions

In practice, due to the influence of assembly deviation, clearance, vibration and other objective factors, the coupler will inevitably work under asymmetrical conditions in the buffing state. However, the existing theoretical studies on the compression stability of couplers did not pay enough attention to this condition, and most of the studies are based on the premise of ideal symmetry conditions. In this paper, the initial lateral deviation between the ends of a coupling coupler is taken as a typical asymmetrical condition, and the influence of the initial asymmetrical condition on the compression stability of the coupler is analysed by theoretical analysis and dynamic simulation. The results show that with the increase of the initial lateral deviation, the rotation angle of the coupler will also increase when it reaches the self-stabilizing equilibrium point. Therefore, the initial asymmetry will reduce the stability margin of the coupler, and then weaken the self-stabilizing ability and compression stability of the coupler. Improving the symmetry of the coupler is also one of the effective methods to guarantee the compression stability of the coupler and the running safety of the locomotive. When the static friction coefficient of the coupler tail can reach 0.3, the initial lateral deviation of the coupler should be limited to less than 7 mm, and the smaller the static friction coefficient, the higher the requirements for the initial lateral deviation.

On the tribo-dynamic interactions between piston skirt-liner system and pin assembly in a gasoline engine

Piston Skirt-Liner (PSL) system and Piston Pin Bearing (PPB), two key friction pairs in piston-assembly, interact with each other via impact and friction when transmitting the combustion load to crank train. Literature reporting such an interaction behavior in terms of tribology and dynamics is still rare, due to the complexity in a systematic modeling way. This paper proposed an efficient numerical model that fully couples these two friction pairs to investigate tribo-dynamic interactions between them. The model is built by coupling Reynolds-based mixed lubrication models for the friction pairs with Lagrange multibody motion equations for the piston-connecting rod-crank mechanism. Coupling effects between the piston skirt-liner system and the pin assembly are explored by comparing the cases contain the two friction pairs and one of them. Based on the above analyses, some design parameters including pin assembly clearance and pin offset, are further studied to disclose their influences on the tribo-dynamic performance of these two friction pairs. This work has a guiding significance for the systematic design of piston-assembly aiming to improve the dynamic property, economical efficiency and environmental-friendliness of engines.

Design and Analysis of a Series-Parallel Compliant Manipulator

Because of friction and assembly clearance, the accuracy of traditional rigid parallel mechanism cannot be maintained for a long time. Compliant mechanism has the advantages of light weight, high precision and low wear. Combining the characteristics of the two mechanisms, this paper designs a series-parallel compliant manipulator structure, and studies its forward and backward kinematics. Finally, it uses MATLAB software to study its workspace. Motion analysis was carried out.

Experimental study on performance characterization of bolted joint under transverse loading

Threaded fasteners are widely used in a variety of engineering applications. The quality of threaded connections directly affects the service performance. By aiming to acquiring a deeper understanding of the performance characteristics, the mechanical behavior of bolted joint was examined using transverse tensile test. The force–displacement curves of bolted joints exhibit linear characteristics during the first stage, while subsequently the curves exhibit various shapes due to assembly clearance. The tangential stiffness of the bolted joint decreases rapidly when the connected plate slips. And the transverse load threshold between various stages is positively correlated with the clamping force of threaded fastener. The experimental data was fitted to obtain a piecewise function that characterizes the entire slip curve of bolted joints under transverse loading. Main characterization parameters in various stages were analyzed and discussed based on the experimental results, which can aid in the design and using of bolted joints.

Analysis and evaluation of temperature field and experiment for magnetorheological fluid testing devices

When a large amount of heat is produced during the operation of a MRF (magnetorheological fluid) testing device, the temperature of the device will increase, which will in turn affect the characteristics of the MRF. Exploring the temperature field characteristics of the MRF yield stress testing device is necessary to improve the accuracy of the device. In this study, first, the yield stress testing device is designed, and then its temperature field model, including enameled wire and assembly gap, is established. Second, simulation software is used to simulate the temperature field change. Finally, a test platform is developed to test the simulation results, especially for two factors, namely, thermal conductivity of the coil winding and assembly gap, which demonstrate considerable influence. Comprehensive thermal conductivity and assembly clearance are determined, and the optimum temperature field of the device for measuring yield stress is resulted.

A Novel Method for Assemblability Evaluation of Non-Ideal Cylindrical Parts Assembly

The assemblability, which is the feasibility and difficulty of assembly, will greatly affect the efficiency and quality of assembly process, so assemblability analysis plays an important role during the design stage of products. Cylindrical parts assembly is a common structure with wide applications, whose assemblability can be affected by surface deviations, especially in some precision assemblies. In this paper, a novel method is proposed for the assemblability evaluation of cylindrical parts assembly considering surface deviations. Firstly, based on the surface deviations modeling of cylindrical parts and assembly clearance calculation, the assembly posture adjustment process is defined and simulated to obtain the assemblable postures without interference between parts. Then, in the proposed six dimensional posture space, a search algorithm is established to obtain the boundary points of assemblable posture space. Afterwards, in order to represent this irregular hyperspace, the largest inscribed generalized cone of which is put forward. Finally, based on the characteristics of generalized cone, two indicators are defined to reflect the adjustable range of assembly posture, which can realize the quantitative evaluation of assemblability. The validity of the proposed method is verified by case studies of cylindrical parts assemblies with different surface deviations.

A new selective assembly model for achieving specified clearance in radial assembly

Manufacturing and assembling of high precision assemblies to achieve the specified clearance pose great challenge to the engineers. A complex assembly of piston, piston ring and cylinder is considered for analysis. In this assembly, the assembly clearance is specified to avoid thin oil film or scuffing. To achieve the specified clearance it is required that the individual component tolerances have to be reduced, which may not be possible due to economic considerations. In this paper, a new selective assembly model using Genetic Algorithm is proposed to achieve specified clearance in radial assembly with minimum surplus parts.

Dynamics characteristics analysis of the oil-free scroll hydrogen recirculating pump based on multibody dynamics simulation

The hydrogen recirculating pump is the key equipment of the hydrogen recirculating system for the fuel cell vehicles. The scroll pump is one of the preferred types of hydrogen recirculating pumps because of its unique advantages of higher efficiency and lower noise. In order to provide valuable basis for improving the reliability and durability of hydrogen pumps under oil-free high-speed conditions, this paper carried out dynamics performance research based on the theoretical method. The gas force, force and torque of moving parts were calculated. Tangential gas force is about 100 N and axial gas force is about 200 N which are much smaller than the traditional scroll compressors due to lower designed pressure ratio of hydrogen pump. Due to the exist of bearing assembly tolerances of sub-crankshafts during practical operation, the actual contact forces and dynamics characteristics were further analyzed based on multibody dynamics simulation. It is found that the rotating speed and the actual assembly tolerance have significant influence on the dynamics characteristics. The radial and tangential forces can reach 3000 N at 6000 r·min−1 which is three times than the value at 3000 r·min−1. Furthermore, the service lives of bearings were analyzed. The contact force considering assembly tolerance presented the high-frequency oscillations. When the size of clearance is increasing, the oscillation frequency is reducing, but the contact force is enlarging. The radial force on a sub-crankshaft was 30 N without assembly tolerances. It increased to 150 N and 330 N, respectively, when the assembly clearances were designed separately as 2~−14 μm and −8~−24 μm, and the corresponding bearing service life decreased by 46% and 83%.

DESIGN AND THEORETICAL ANALYSIS OF A PROTOTYPE TILTING-PAD RADIAL BEARING WITH ADJUSTABLE CLEARANCE

The article introduces a design and analysis results of a prototype ORC (organic Rankine cycle) turbo generator rotor assembly of 300kW power, supported by tilting-pad bearings of original design. The calculations were performed for a prototype turbo generator rotor. The shaft of this machine is supported with two radial bearings, lubricated with an unusual lubricant – a low-boiling-point agent. The main objective of the presented research was to perform calculations verifying the feasibility of using hydrodynamic tilting-pad radial bearings with a low-viscosity lubricant to support a rather massive and high-speed rotor of the developed turbo generator and to determine the geometry and design of the bearings which would ensure optimal kinetostatic and dynamic properties of the rotating system, while simultaneously providing ease of assembly and smooth clearance adjustment.

Analysis of the brazing joints of tubular zirconia ceramics and 06Cr19Ni10 stainless steel tubes

ABSTRACT The gas-tight joining between yttrium-stabilised semi-closed zirconia ceramic tube and 06Cr19Ni10 stainless steel tube was achieved by using a self-made Ag–27Cu–4Ti paste filler material, where the joint form was an outer sleeve joint. After brazing, the samples were subjected to thermal shock (−50°C to 150°C) and thermal cycling tests (room temperature to 600°C), respectively. The sealing tightness of samples with different assembly clearances was investigated. Microstructure and phase composition of the joint with good performance was analysed. The results showed that the sealing performance of samples with the clearances of 0.03∼0.04 mm was best, and their tightness could still be less than 5 × 10−10 Pa·m3 s−1 after a series of heat treatment; microstructure of the joint with good sealing was dense and there were no obvious defects; the joining layer adjacent to ceramic was mainly comprised of three continuous reaction layers, the composition phase of which included Ti3Cu3O, TiO and ZrTiO4.

A Novel Double Chamber Rotary Sleeve Air Compressor- Part III: Leakage Losses Model

This paper presents comprehensive leakage model of a novel double chamber rotary sleeve air compressor (DCRSC). The compressor mechanism is that of a rotary motion whereby the novelty lies in the usage of two rotating sleeves and a secured vane that has one end fixed to an outer sleeve and the other end to a rotor, respectively. The thermodynamic model and friction model of the DCRSC are respectively presented in Part I and Part II of this paper series. The main goal of this study is to formulate and analyse the internal leakage losses at different rotational speed. Dynamic clearance at the contact regions between the high-pressure and low-pressure chambers were made clear. The variations of the internal leakage rate and volumetric efficiency for three compression approaches namely: adiabatic, polytropic and isothermal compression processes were evaluated. At maximum rotational speed of 1500 rpm, the DCRSC volumetric efficiencies are 53.1%, 69.4% and 98% when air undergoes adiabatic, polytropic and isothermal compression process, respectively. The internal leakage losses can effectively be minimized by selecting the right lubricant and reducing the assembly clearances of the rotating parts that defines the compression chambers.

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In the gas turbine, the clearance between the blade tip of the rotor and the inside of the stationary casing varies depending on the rotation of the rotor and the heat output of the combustor. Accordingly, the assembly clearance is determined, and the leakage of the gas occurs because of the gap during operation, affecting the efficiency of the system. Thus, designers use a variety of techniques to optimize this clearance, a typical method that reduces the relative variation of the clearance using heating and cooling mechanisms. In this study, we developed a method to control the blade tip clearance through the axial movement of the inclined blade without using heating and cooling mechanisms. Recently, we designed an advanced blade tip clearance control system that can control multi-step, not on-off control, to apply to large gas turbines developed by Doosan. The designed system is hydraulic and can be used with a maximum thrust of 100 tons, and the desired displacement can be moved in multiple stages as required. We have completed the reliability verification of the entire lifecycle level and applied it to the newly developed gas turbine.

Rotational behavior and modeling of bolted glulam beam-to-column connections with slotted-in steel plate

In this article, the rotational behavior of typical bolted glulam beam-to-column connections with slotted-in steel plate was studied in the numerical method. In order to describe the complicated behavior of wood more closely, an elastic–plastic damage constitutive law combining the Hill yielding criterion and a modified Hashin failure criterion was embedded in the commercial ABAQUS software in the form of a VUMAT subroutine. Subsequently, a three-dimensional finite element model based on the constitutive law proposed was established, with the failure mode and moment–rotation curve compared to some similar experiments. Based on this finite element model, a parametric study concentrating on the influence of the width of the beam, bolt diameter, and assembly clearance was carried out. It was found that the numerical method using the proposed constitutive law showed a good capacity to study the rotational behavior of the connections. Besides, the initial rotational stiffness increased with the increase in beam width and bolt diameter, and the assembly clearances between bolts and bolt holes would affect the initial rotational stiffness while the assembly clearance between beam and column affected little.

Finite Element Simulation of NiTiNb Shape Memory Alloy Pipe‐Joint Subjected to Coupled Transformation and Plastic Deformation

The assembling process of Ni47Ti44Nb9 alloy pipe joints considering the phase transformation and plasticity was numerically simulated for the first time with a developed constitutive model. The simulated process was based on the experimental material parameters, which were determined with the experimental tensile results of Ni47Ti44Nb9 shape memory alloy (SMA) and steel bars. The results showed that, after assembly, the Mises stress distributed uniformly along the longitudinal direction of the NiTiNb joint, but nonuniformly along the radial direction. The maximum σeq does not appear at the inner wall of the joints due to the coupling effect of the plastic deformation and the recoverable transformation. The contact pressure distributed uniformly along the circumferential direction, but nonuniformly along the longitudinal direction. The sizes of the SMA joint and the pipe should be properly matched to ensure contact during the stage of the rapid reverse phase transformation to obtain stable connection performance. The pull‐out force was also computed, and the results were in good agreement with the experimental results. The results obtained can provide available information for the optimization of the design parameters of the high‐performance SMA pipe‐joint, such as inner diameter and assembly clearance.

Tolerance analysis of slider-crank mechanism for assembly functionality check

The purpose of functionality check is to analyse the stack-up of geometric deviation of part/feature whether it meets geometrical requirement and is it in the range of assembly tolerance. However, usual tolerance analysis model does not include assembly clearance. Aiming at this problem, we have done some research. Firstly, a nominal geometrical transfer model and a stackup model are established based on small displacement torsor (SDT) and homogeneous transformation matrix (HTM). Secondly, HTM expression of tolerance loop is constructed. Next, assembly tolerance matrix model is established and a new tolerance analysis method for assembling feasibility check is put forward. At last, taking a slider-crank mechanism as example, the contrastive study of tolerance analysis for functionality check is done. The results show that it is prone to lead to misjudge when analysing only dimension tolerance. And, it is more restrictively when considering dimension tolerance, geometric tolerance and assembly clearance.

Tolerance analysis of slider-crank mechanism for assembly functionality check

The purpose of functionality check is to analyse the stack-up of geometric deviation of part/feature whether it meets geometrical requirement and is it in the range of assembly tolerance. However, usual tolerance analysis model does not include assembly clearance. Aiming at this problem, we have done some research. Firstly, a nominal geometrical transfer model and a stackup model are established based on small displacement torsor (SDT) and homogeneous transformation matrix (HTM). Secondly, HTM expression of tolerance loop is constructed. Next, assembly tolerance matrix model is established and a new tolerance analysis method for assembling feasibility check is put forward. At last, taking a slider-crank mechanism as example, the contrastive study of tolerance analysis for functionality check is done. The results show that it is prone to lead to misjudge when analysing only dimension tolerance. And, it is more restrictively when considering dimension tolerance, geometric tolerance and assembly clearance.

Manipulation of small parts being assembled on a horizontally vibrating plate

The article proposes a new method of manipulating parts on a horizontal plane, when the plane is excited in two perpendicular directions by a harmonic law with different frequencies and a phase shift. To determine motion patterns which are most suitable for automatic assembly, a mathematical model of movement of parts on the horizontal plane was developed. The results demonstrated that by changing the excitation parameters and the coefficient of friction between the part and the plane, the part can be easily moved along prescribed trajectory ensuring a necessary positioning precision and alignment for the assembly operation. The most suitable trajectories for connecting surfaces matching as well as the most suitable excitation parameters for automatic assembling process were obtained. The proposed method can be efficiently applied in automatic assembly to match the surfaces of small parts with a small assembly clearance.

Influencing Factors on Rotate Vector Reducer Dynamic Transmission Error

The factors influencing rotate vector (RV) reducer dynamic transmission error were studied using virtual prototyping technology, which contained the elastic deformation, working load, part manufacturing error, and assembly clearance. According to the error transmission relationship of the RV reducer, 15 influencing factors were selected to design an orthogonal simulation test. The virtual prototype of the RV reducer was built using CREO and ANSYS, and imported into ADAMS for multi-body dynamics simulation. The simulation method reliability was verified via experiments. The results show that the circle center radius error of the pin gear, the amount of equidistant modification of the cycloid gear, the amount of radial-moving modification of the cycloid gear, the clearance between the support bushing and planet carrier, and the clearance between the crankshaft and the support bushing were positively correlated with the RV reducer dynamic transmission error. Among these, the circle center radius error of the pin gear has the greatest influence on the dynamic transmission error of the RV reducer followed by the amount of equidistant modification of the cycloid gear. The elastic deformation of the part and the load fluctuation show a certain gain effect on the transmission error, the elastic deformation of the cycloid gear has a great influence, and the elastic deformation of the pin gear has the least.

Effect of stamping dimensional deviations on residual stresses and deformation of resistance spot welded steel sheets

Direct finite element analysis that takes stamping dimensional deviations into account was achieved based on coupled electro-thermo-mechanical method and reverse engineering in the current research. The two continuous resistance spot welding processes of the reverse established back side panel were simulated. Its residual stresses and deformation were compared with those of the ideal back side panel. Large distortion presents in the reverse back side panel while only slight deformation exists in the ideal one. The former is validated to be closer to the deformation of the actual welded back side panel. The peak residual stresses after processes 1 and 2 remain almost unchanged in the reverse back side panel while those in the ideal one show an increasing trend. The final residual stresses of the reverse and the ideal back side panel are both high but the former is lower than the later. The stamping dimensional deviations are responsible for these differences. They lead to obvious attenuation of geometric features and large assembly clearances in the reverse back side panel. These assembly clearances allow large deformations of the stamping parts during the welding process. Meanwhile, these clearances make it relatively freer for the heated sheet metal to expand thermally in the thickness direction, resulting in less or even no residual stress in this direction. These clearances also promote the release of the thickness-direction component of the tensile residual stress in the extension direction of sheet by allowing deformation in the thickness direction.

Decision-Making Method based on Mixed Integer Linear Programming and Rough Set: A Case Study of Diesel Engine Quality and Assembly Clearance Data

The purpose of this paper is to establish a decision-making system for assembly clearance parameters and machine quality level by analyzing the data of assembly clearance parameters of diesel engine. Accordingly, we present an extension of the rough set theory based on mixed-integer linear programming (MILP) for rough set-based classification (MILP-FRST). Traditional rough set theory has two shortcomings. First, it is sensitive to noise data, resulting in a low accuracy of decision systems based on rough sets. Second, in the classification problem based on rough sets, the attributes cannot be automatically determined. MILP-FRST has the advantages of MILP in resisting noisy data and has the ability to select attributes flexibly and automatically. In order to prove the validity and advantages of the proposed model, we used the machine quality data and assembly clearance data of 29 diesel engines of a certain type to validate the proposed model. Experiments show that the proposed decision-making method based on MILP-FRST model can accurately determine the quality level of the whole machine according to the assembly clearance parameters.