Clearance Fit Research Articles

Probing fretting wear behavior of gauge-changeable spline axle under rotational bending loads

The latest generation of gauge-changeable trains in China feature designs with their wheels and axles connected by spline couples and cylindrical fits. In comparison to the interference fitted wheelset, the spline axle with clearance fit is more prone to fretting damage. In this study, the stress distribution of spline axle was analyzed using finite element method. Then, a rotatory bending test on scaled wheel/axle samples was conducted to reveal the fretting wear behavior of the gauge-changeable axle. During traction, the contact stress of the spline peaks at 311 MPa on the tooth’s root side, with a corresponding relative slip of 14 μm. Fretting wear is observed in the spline axle, the damage zone of the wheel seat can be categorized into five bands (A–E), and severely damaged areas are covered with red-brown debris. Moreover, the main damage mechanism of untreated spline axle and surface-modified spline axle is delamination accompanied with oxidation. The improved properties of plasma nitriding and grease lubricant are attributed to the high surface hardness and residual compressive stress, as well as low frictional stress.

Vibration characteristics investigation of a dual rotor-bearing outer ring–pedestal-casing system with clearance fit

Vibration characteristics investigation of a dual rotor-bearing outer ring–pedestal-casing system with clearance fit

Accuracy of FDM PLA Polymer 3D Printing Technology Based on Tolerance Fields

Fused deposition modelling (FDM) 3D printers have the highest annual growth of 21.15% in the field of 3D printing. FDM desktop 3D printers account for 23.69% of FDM printers. The major drawback of FDM desktop printers is product accuracy, which is particularly pronounced when dimensionally inaccurate and multi-part printed products need to be fit together into a functional assembly. The research presented in this paper aims to determine the accuracy limits of FDM 3D printers when producing elements for assembly using a 3D printer in a tolerance-fit system. A novel method of computer-aided design (CAD) based on ISO 286 and the systematic calibration procedure of 3D printers were presented to achieve the dimensional accuracy of 3D printed parts. For this purpose, a set of nominal dimensions within the clearance fit was selected, and various CAD models were created according to the ISO 286 system of limits and fits. The CAD Slicer software–3D printer interaction was systematically examined for the best hardware and software features. It was found that the Horizontal Expansion parameter should be 0.0 mm and the Hole Horizontal Expansion parameter should be 0.13 mm. The Linear Advance factor was found to be 25. The measurement results showed that the desired tolerance ranges, system, and type of clearance fit could be achieved with a desktop 3D printer. The roundness tolerance for all clearance fits and shaft tolerance ranges in the hole base system was determined to join the parts into a clearance fit.

Dynamic characteristics of spindle-bearing with tilted pedestal and clearance fit

Spindle-bearing systems are widely used in machine tools, aero engines, and other industrial equipment. The vibration characteristics of the spindle system may be affected by the pedestal tilt due to assembly errors. Considering the radial and axial clearance fit between the bearing outer ring and the pedestal, the six-degree-of-freedom (6-DOF) frictional contact relationship between the outer ring and the pedestal is described, and a novel clearance fit model is proposed. In addition, the quasi-static models of deep groove ball bearings (DGBBs), angular contact ball bearings (ACBBs), and cylindrical roller bearings (CRBs) are established with the effects of rotational speed. The clearance fit model, quasi-static models of the bearings, and finite element (FE) model of the spindle are coupled to develop a dynamic model of a spindle-bearing system with pedestal tilt error. The contact performances of the DGBB and the vibration behaviors of the system with pedestal tilt errors are analyzed by simulation and experiment. The results show that the amplitude of the time-domain acceleration response decreases first and then increases with the increase of the pedestal tilt degree. The pedestal tilt error increases the contact angle of the DGBB, so the varying compliance (VC) vibration frequency value and its error also increase.

Study on Non-linear Contact Stress and Prognosis Analysis of Lug Joints With Misfits

Components of aircraft and other large scale structures are generally made in parts in order to facilitate easy manufacturing, assembly and dis-assembly. Lug joints with fasteners are preferred in several aerospace applications where their purpose is to connect primary load carrying members. Study on structural integrity of these types of joints becomes mandatory from the safety point of view. This requires in-depth understanding of science and technology of Structural Health Monitoring (SHM) at these joints. Analysis presented here deals with the critical locations of interference and clearance fit lug joints which continuously operate under fatigue loading. Both interference and clearance fits exhibit non-linear contact-stress variation above certain load level and this effect needs to be addressed for both fatigue and monotonic loading. The maximum Pull or Push loads causes high stress concentrations at critical locations along the pin-hole interface. With continuous usage of the component, crack like damages initiate at these locations and they grow till failure of the component. The non-linear prognosis analysis is carried out to generate the data required for SHM at any stage which can be used to estimate remaining life of the component.

Fluid-solid coupling simulation study on fuel leakage and deformation characteristics of precision coupling component in common rail injector and influence of pressure equalizing structure

In the foreseeable future, the use of fossil energy is still irreplaceable, makes efficient use of fossil energy and reduce emissions became important topics. Diesel engines have a very high share in the transportation field, and high-pressure common rail system has highly improved the performance of diesel engines. As the most important component of common rail system, the performance of common rail injector directly affects the engine. Precision coupling components are composed of moving parts with very precise clearance fit in the injector. With the wear of parts, fuel leakage of precision coupling components may reach the same level as injection quantity, which will seriously affect the injection pressure actually established, and then affect the power, efficiency, and emission performance of diesel engine. Many researchers have studied fuel leakage of precision coupling components, and put forward different methods to reduce fuel leakage, including improving the machining accuracy and machining annular grooves on parts. However, the wear of parts makes it a high-cost and low-effective method to improve machining accuracy. Besides, researchers have not fully considered the deformation of parts. In this work, fluid-solid coupling simulations were performed to analyze deformation and static fuel leakage characteristics, and to investigate effects of pressure equalizing structure on deformation and leakage of precision coupling component in common-rail injector. Different from the previous researches, the influence of machining the annular groove on the plunger sleeve instead of on the plunger, and influence of coexistence of annular groove and deformation were considered. The results show the deformation characteristics of the parts, the fuel flow characteristics in the gap, and the influence of the annular groove on the fuel leakage. The connection between the deformation of parts and fuel leakage, and potential methods to reduce the leakage are also discussed.

Dynamic behaviors and contact characteristics of ball bearings in a multi-supported rotor system under the effects of 3D clearance fit

Clearance fit is a common assembly method for bearings in rotor systems, which leads to a certain clearance between the outer ring of the bearing and the bearing pedestal, that is, the fit clearance. The nonlinear factors caused by the fit clearance may affect the mechanical properties of the bearing and rotor system. Considering the fillet and six-degree-of-freedom (6-DOF) motion of the outer ring, a three-dimensional (3D) clearance fit model is proposed. In addition, considering the interference fit between the inner ring and spindle, an analytical stiffness model of ball bearings is developed. By coupling the clearance fit model and the analytical bearing stiffness model with a finite element (FE) model of a spindle, a dynamic model of a multi-supported rotor system is established and verified by the experiment, which fully considers the nonlinear factors of ball-raceway contact and outer ring-bearing pedestal contact. The effects of fit clearance, radial force, and axial force on the vibration behaviors and contact characteristics of the ball bearing in the system are analyzed. The results indicate that the larger fit clearance of the unilateral bearing may lead to misalignment of the bearing and reduce the bearing force. Under radial force, the bearing clearance and fit clearance are eliminated, which improves the stability of the system. At this time, further application of axial force causes the load-bearing area to become larger and weakens the variable compliance (VC) characteristics of the bearing. This investigation can provide technical support for the assembly and design of the bearing-rotor system.

Study on tightening characteristics of flareless pipe joint assembly process

AbstractThe assembly process of flareless pipe joints is very important for the sealing performance of hydraulic pipeline system. Based on the theory of contact mechanics, a theoretical model of the assembly process of pipe joints is established to simulate the extrusion moulding process of flareless pipe joints. It is found that tightening torque is an important factor affecting the sealing performance of pipe joints. By comparing the changes of the contact stress between the sleeve and the pipe joint under different tightening tortures, combined with the mechanical transfer and deformation results of the contact surface, the results show that the fitting situation of the sleeve and the pipe is good when the expansion pressure is 180 MPa, and the sealing performance of the pipe joint is good when the tightening tortures are between 15 and 18 N·m. Considering that the contact surface is a clearance fit, the mean value error of contact stress obtained by simulation verifies that the accuracy of the torsional relationship formula is very high.

Influence of Key Process Parameters on Vibration Characteristics of Centrifugal Pump

The low-noise operation of ships will be affected by the vibration of centrifugal pumps, which are widely implemented in vessels. Available papers mainly focused on the structural optimization of pump components with less concentration on their assembly process, which include coaxiality, circle-runout and clearance fit, etc. The clearance between the impeller and wear ring, which is named wear-ring clearance, is influenced by the manufacturing and assembly process and has an impact on vibration. An investigation of the influence of key process parameters on the vibration characteristics of the pump based on wear-ring clearance is presented. A numerical model of the internal flow field of the pump is presented. The dynamic behavior in the frequency domain is obtained for fluid-solid interaction. The vibration is found to be more pronounced at some frequencies. A closed-loop dimensional chain system is constructed targeting the wear-ring clearance, and the circle-runout and coaxiality of some parts are found to have a prominent influence on it. A relationship between the key process parameters of the pump and vibration characteristics is established.

Influence of assembly clearance on vibration characteristics of angular contact ball bearings in the thermal environment

Assembly clearance has a great influence on the vibration characteristics of angular contact ball bearings. In this paper, the effect of assembly clearance variation on bearing vibration characteristics was investigated by establishing a vibration analysis model and accounting for thermal effects. The model calculation results show that when the assembly of the bearing housing and outer ring is in a clearance fit, the bearing has a high-frequency resonance with the outer ring, but this phenomenon does not occur with an interference fit. The vibration characteristics of the bearing under three different assembly clearances were investigated by experiments and the correctness of the established model was proved.

Analysis of output performance of all-metal progressive cavity motor

At present, the traditional progressive cavity motor is usually a rubber stator and metal rotor, and an interference fit is set. When it encounters the high-temperature formation of 180 °C and above, the carbonization of the rubber stator causes motor failure. Therefore, the all-metal progressive cavity motor adopts a metal stator and metal rotor, and the clearance fit is installed, which has good high temperature and corrosion resistance. The leakage caused by the clearance fit is the main reason for its performance output loss. Therefore, this paper is based on the leakage mechanism of all-metal progressive cavity motor and relies on the Couette flow, Poiseuille flow, and Bernoulli's theorem. Then the mathematical model of leakage and output performance of ∅95mm all-metal progressive cavity motor is established in this paper. The 3D-surface nephogram of the model about the effects of differential pressure, density, viscosity, and clearance on motor leakage was calculated numerically and iteratively by Matlab software. At the same time, through the calculation of the motor power loss of the structure design in this paper, the power loss is smaller in the clearance range, which provides a reference for the clearance selection of this kind of motor manufacturing. Finally, according to the mathematical model of the optimal clearance of 0.3 mm in the actual working conditions, the performance curve of the numerical calculation of the motor is demonstrated through the fluid simulation. Then the performance curve is compared and verified by the experiment of the InFocus company, which provides theoretical guidance for reducing leakage of motor and improving output performance.

Investigation on cage motions in high speed angular contact ball bearing with clearance fit between the outer ring and housing

As one of the bearing vibration sources, cage motions were often investigated for distinguishing the bearing performance. However, when the ball bearing works under complex conditions, there may be clearance fit between outer ring and housing, cage motions are affected seriously, which is less considered in previous studies. Thus, a dynamic model for the ball bearing with clearance fit was proposed, and effects of clearance fit on the cage motions were studied. The constructed model is verified by the experiment in the literature. In the obtained results, the whirl orbit, poincare map, cage velocity deviation ratio were given for defining the whirl stability of cage motions. The cage whirl stability declined with the enlargement of clearance fit and initial contact angle. Whereas, the cage whirl stability enhanced with the increasing guiding clearance. The above results may offer some advice for the design and using of angular contact ball bearing.

Feature-Based Compliance Control for Precise Peg-in-Hole Assembly

This article focuses on solving the problem of precise peg-in-hole assembly. The main contribution of this article is to propose a control method to improve the assembly precision. The method is capable to realize the precise insertion assembly tasks of cylindrical or prismatic objects with clearance or interference fit. In this article, a feature space and a response space are first constructed according to the relative pose and equivalent forces and moments. Then, the contact states are segmented in the feature space and the segmentation boundaries are mapped into the response space. Furthermore, a feature-based compliance control (FBCC) method is proposed based on boundary mapping. In FBCC method, a direction matrix is designed to execute accurate adjustment and an integral element is applied to eliminate residual responses. Finally, the simulations and experiments demonstrate the superiority and robustness of FBCC method.

Optimizing the Clearance Fit of a Progressive Cavity Pump for the Thermal Recovery of Petroleum Using Fluid-Structure Thermal Coupling.

It is important to incorporate the effects of fluid–structure thermal coupling and the boundary conditions when calculating the thermal dynamics and response of progressive cavity pumps. This study develops a fluid–structure thermal coupling model of the progressive cavity pump to improve the accuracy of its measured field of deformation and the temperature field of the stator. A function for the macroscopic motion of a rigid body is written in a typical fluid domain, and the user-defined function (UDF) in FLUENT is used to load the boundary of the rotor to realize its planetary motion. Local remeshing is used to update the moving grid, and the viscoelastic hysteretic heat of the stator is treated as the internal source of heat. One-way decoupling is used based on tire slip theory, and heat flux on the surface of the stator is calculated by the ANSYS Parametric Design Language (APDL). The sequential fluid–structure thermal coupling of the progressive cavity pump is calculated by using the ANSYS workbench. A scheme for optimizing the fit clearance of the stator and rotor is given to improve the volumetric efficiency of the progressive cavity pump and prevent the stator from being stuck owing to a large deformation, and the calculations are verified by experiments on volumetric efficiency. The average deviation in the calculated volumetric efficiency was less than 5% compared with the experimental values. The proposed scheme provides a theoretical basis for the optimal design of the progressive cavity pump for the thermal production of petroleum.

Влияние заходности резьбы ведущей гайки планетарного роликовинтового привода на КПД механизма

Planetary roller screw mechanisms are designed to smoothly convert the rotational movement of the nut into the translational movement of the screw due to the presence of threaded rollers located between the internal thread of the drive nut and the external thread of the driven screw. The position of the rollers around the circumference is determined by two separators located at the ends of the rollers. Smooth cylindrical holes in separators are matched by clearance fit. Both ends of the threaded rollers have gears that mate with the gears at the ends of the screw. Thus, rotating rollers are located between the screw and the nut, and the sliding friction of the threads of the ordinary screw and nut in the planetary roller-screw mechanism is replaced by rolling friction. Friction losses during the operation of the mechanism are significantly reduced. Bearing capacity of the mechanism is increased due to a significant number of contact points in the threads of the nut, screw and rollers. By varying the pitch and setting the thread number of starts on the screw and nut the speed of the axial movement of the screw relative to the nut of the mechanism is regulated. Increasing the thread number of starts on the nut and screw increases the efficiency of the mechanism under study. Increasing a number of starts of the thread on the nut and screw increases the efficiency of the mechanism under study.

Stability Analysis of Rotor with a Spline Coupling

Abstract The spline coupling is widely used in aero-engines. Once the spline coupling fails, it will cause great damage to the engine. In this paper, the stability of a rotor with a spline coupling was studied. The internal damping instability model of the rotor with spline coupling is deduced, and the instability mechanism is explored. The stability boundary is analyzed by using the R-H criterion. The mechanism of rotor instability is analyzed by simulation. An experimental system of rotors with different structural parameters of spline coupling was built. The influence of the positioning surface clearance on the stability was analyzed. The modeling results show that the internal friction of the spline coupling will introduce additional damping and anti-symmetrical cross stiffness to the rotor, the additional damping will reduce the vibration response, and the anti-symmetrical cross stiffness will cause the rotor to become unstable. The simulation and experimental results show that the rotor system will not be unstable when the two positioning surfaces of the spline coupling are in an interference fit. When one of the positioning surfaces is a clearance fit and the other is an interference fit, the internal friction will cause the rotor to become unstable. The instability threshold speed is higher than the first-order critical speed. At the same time, due to the additional damping introduced by the sleeve tooth structure, there will be a transition stage of instability. At this time, the rotor will vibrate with sub-harmonic components, but the vibration amplitude of the rotor will decrease. When the two positioning surfaces are clearance fit, the rotor is unstable and the amplitude increases suddenly. The obtained instability characteristics of the rotor with spline coupling have important value for the instability fault diagnosis, and provide help for the stability control.

Analysis of the lunar regolith sample obstruction in the Chang’E-5 drill and its improvement

The drilling and coring process of the Chang’E-5 mission was terminated at a depth of 1 m due to an extreme lunar regolith profile state. One possible reason for termination was a lunar regolith particle obstructing the sampling entry of the hollow drill tool. This obstruction was caused by particles inside the clearance fit of the coring mechanism. A simulation was carried out using the discrete element method, which verified the particle flow state of the obstruction. A load test-bed was developed to separate the pulling force of the flexible coring tube of the obstruction from the entire drilling and coring process. A sealing device, a sealing ring with a sheath, was designed by isolating the original clearance fit of the coring mechanism toward the obstruction. Based on drilling and coring experiments, the sealing device solved the problem of the high value of the pulling force, which represented good sealing performance and could be used for future planetary penetrating drills like the Chang’E-5 drill.

Test and Improvement of a Fuze MEMS Setback Arming Device Based on the EDM Process.

This paper introduces the working principle of a MEMS safety and arming (S&A) device for a fuze that is installed perpendicular to the axis of the projectile. Additionally, the application of low-speed wire electrical discharge machining (EDM) in the fabrication of the device is proposed. Microsprings are susceptible to flexural deformation and secondary deformation in the EDM process, a problem that is solved by designing the auxiliary support beam, using multiple cuts, destress annealing and optimizing the processing parameters. The difficult problem of setback slider deformation in the principle prototype test is properly solved by establishing V-shaped grooves at both ends of the setback slider. The connection mode between the microspring and the frame is changed to a clearance fit connection. The improved setback arming device can guarantee service process safety and launch reliability. The maximum overload that can be withstood in service processing is 20,000 g, and the minimum overload for safety release during launch is 12,000 g. The results show that the EDM process can greatly reduce the machining cost while improving the machining precision and machining speed, which can compensate for the defects of the current manufacturing technology.

Clearance Fit Design of a Hydraulic Cylinder with Particle Polluted by Hydraulic Oil

In hydraulic cylinder systems, oil pollution results in wear and leakage of hydraulic cylinder components. In accordance with the actual working conditions of a certain type of hydraulic cylinder, the technology of fluid–solid thermal coupling and multiphase flow analysis is applied to analyze the heat–fluid–solid coupling of hydraulic cylinder under the condition of particle polluted by hydraulic oil. The distribution law of the heat field of hydraulic cylinder was obtained through analysis. The results show the effect of heat flow on the partial load effect. The distribution rules of particles in the hydraulic cylinder were obtained under the influence of different gaps and particle pollutants. The damage rate of the hydraulic cylinder under these working conditions was analyzed by optimizing the plunger and cylinder clearance fit and providing important technical support to solve the problem of hydraulic oil leakage in hydraulic cylinders.

Optimizing Clearance Fit of Screw Pump for Thermal Recovery of Petroleum Using Fluid–Structure Thermal Coupling

Optimizing Clearance Fit of Screw Pump for Thermal Recovery of Petroleum Using Fluid–Structure Thermal Coupling