Shrink Fitting Process Research Articles

Calculation of Iron Loss with Stress in Stator Core by Shrinkage Tolerance

This paper presents a method for calculating the iron loss of the stator core of an electric motor owing to the stress generated by shrink fit tolerance in the production process. Shrink fit is used to fix the frame and stator core, shaft, and rotor core in a motor, and the corresponding condition varies depending on the material. Three finite element analysis steps were performed to reduce the iron loss owing to stress during shrinking of a frame and stator core. In step 1, the shrink fit process was applied to a frame and stator core, considering the manufacturing tolerances through three-dimensional modeling. Thermal-structure finite element analysis was performed to apply the same conditions as those in the shrink fit process. The shrink fit was expanded by applying heat to the frame, followed by natural cooling to calculate the contact stress between the frame and the stator core. In step 2, the same contact stress as that in step 1 was derived using structural analysis through two-dimensional modeling of the frame and stator core without tolerances. The contact stress was calculated by applying the equivalent thermal expansion coefficient of the frame, and it was confirmed that the manufacturing tolerance and maximum stress intensity are linearly related. In step 3, electromagnetic analysis was performed at the rated operating point of the 2.2-kW induction motor using the model obtained in step 2. The magnetic flux density distribution of the stator core was derived via electromagnetic analysis and the iron loss, including the stress distribution, realized in step 2. The iron losses obtained under different conditions, including the stress of the stator core owing to the shrink fit tolerance, were compared, and the effectiveness of the shrink fit tolerance required to achieve a motor with high efficiency was evaluated.

Development of smart cold forging die life cycle management system based on real-time forging load monitoring

Cold forging dies are manufactured through the shrink fit process to withstand high pressure loads, but fatigue failure eventually occurs due to repeated compressive stresses. The life cycle until fatigue failure was defined as the limit life, and attempts were made to predict the die life based on finite element method. However, accurate prediction was impossible owing to uncontrollable environmental variables. Consequently, it is impossible to clearly determine the die replacement cycle, resulting in negative consequences such as poor quality, production delay, and cost increase. Various environmental factors affecting the prediction of die life cycle result in the increase or decrease of the forming load, which is an important variable that determines the die life cycle. In this study, a system for monitoring load data generated from forging facilities was developed based on a piezo sensor. In addition, the die life cycle was more accurately predicted by using the forming load data measured in real time, and a die life management system that can determine the die replacement cycle was applied to the automobile steering parts production line.

Increasing of Working Pressure and Life Span for Homogenizers

Currently, when a high-pressure homogenizer is operated at internal pressure of 200 MPa, fatigue failure occurs in the cylinder after about 1 million operations, which is much shorter than the expected lifetime. The fatigue cracks caused by fatigue failure are parallel to the axial direction and propagate from the inner surface of the cylinder. This suggests that the fatigue failure was caused by periodic circumferential stresses applied to the microscopic scratches on the inner surface of the cylinder during operation. Therefore, we adopted Shrink-Fit Process and Autofrettage Process. It was found that the circumferential stress generated on the inner surface of the cylinder could be reduced by 267 MPa by applying the Shrink-Fit. It was found that the circumferential stress on the inner surface of the cylinder could be reduced by 510 MPa by applying the Autofrettage-Process. The obtained values were used to predict the life time of the specimens based on S-N diagrams. It was found that the target life of 10 million cycles could be achieved by Shrink-Fit and Autofrettage.

Stress analysis of shrink fitting process of ultra-thin reactor coolant pump rotor-can

This paper aims to accurately predict the stress evolution and stress distribution during shrink fitting process. The hoop stress on rotor-can after shrink fitting process was calculated using Lame’s equation. Then finite element (FE) method was used to calculate the stress evolution on rotor-can during shrink fitting process. The effects of manufacture defects on stress distribution on rotor-can after shrink fitting process was analyzed. Finally, a shrink fitting experiment was carried out, and the residual stress on rotor-can after shrink fitting was measured by hole-drilling strain-gauge method. The results show that during shrink fitting process, thermal stress would occur on rotor-can along axial direction and hoop direction. After shrink fitting process, the fitting stress was along hoop direction. When there were ring-shaped defects on rotor-can, there would be axial stress in the defective area. The theoretical calculation results, simulation results and experimental results are in good agreement with each other.

Simulation study on modified coil configuration used for shrink fitting of semi-built-up crankshaft and parameters influencing the thermal distribution.

Semi-built-up crankshafts are universally manufactured by shrink-fitting process with induction heating device. The configurations of induction coil have a great impact on the distributions of eddy current and temperature of crankthrows. Most induction devices are apt to cause some undesirable phenomena such as uneven temperature distribution and irregular deformation after induction heating. This article proposes a modified configuration of induction heating coil according to the crankthrow geometry. By combining the heat conduction equation and the heat boundary conditions, a three-dimensional finite element model, which takes into account the nonlinearity of the material's electromagnetic and thermal physical properties in the heating process, was developed. The influence of several parameters, such as position and curvature of the arc coil, the current frequency and density, coaxiality of crankweb hole and coil, influencing the temperature distribution inside the crankthrow was also analyzed. The comparison with the numerical simulation results of the original configuration indicates that the modified configuration has better adaptability to the crankthrow. Also, it can help to improve the temperature distribution, and reduce the deformation of the shrink-fitting hole. This exploration provide an effective way for the enterprise to further enhance the shrink-fitting quality of crankshaft.

Design optimization for a three-layers shrink-fitted pressure vessel exposed to very high pressure

In this paper, design optimization for a different materials three layers shrink-fitted cylinder subjected to very high pressure has been investigated. The optimum design of the cylinder has been brought into being by upsurge the advantageous compressive residual stresses, thus increasing the carrying load capacity of the cylinder as well as its fatigue life. A finite element model has been established to estimate the residual hoop stress, the equivalent von-Misses stress and the equivalent plastic strain. In this optimization problem, the design parameters have been taken as the thicknesses of the layers and the diametral interference between them. Also, the major constraint is that the equivalent von-misses stress for each layer does not exceed the yield strength of each layer material during the shrink-fitting process and when subjected to 750 MPa inner working pressure. Design of Experiment (DOE) and the Response Surface Method (RSM) have been joined together to obtain an effective objective function to be used in the optimization formulation. Two optimization techniques have been sequentially used to obtain accurate global optimum parameters, Multi Objective Genetic Algorithm (MOGA) and Lagrange’s Multiplier (LM). The hoop and von-Mises stresses distributions along the thickness as well as the mechanical fatigue life have been calculated for the cylinder before and after optimization. It was found that the residual hoop stress has been enhanced at the near bore area by 31 %, also the fatigue life for the cylinder is better than that before optimization by 10900 cycles.

Experimental and numerical evaluation of influencing parameters on the manufacturing of lined pipes

The amount of residual contact stress between an inner corrosion-resistant alloy pipe and its external carbon steel counterpart is the main challenge when manufacturing lined pipes. This study outlines the experimental and numerical evaluation of the manufacturing parameters of mechanically bonded double-walled pipes, produced by the thermo hydraulic shrink fit process. The measurements indicate that the gripping force between the outer 4-inch carbon steel and inner 3-inch stainless steel pipes was 33.94 MPa when processed at 350 °C with a hydraulic pressure of 30 MPa. The experimental results correlate with those of finite element method simulations for gripping force. The magnitudes of the measured gripping forces in the experiment are sufficiently high for most scenarios. The cross-sections of the final lined pipes were inspected for possible defects with the most common being the lamination-type defect for this production process.

Optimization of Shrink Fitting Process of Rotor Shaft for Motor Applying High Frequency Induction Heating

This research is collaborative investigation with the general-purpose motor manufacturer. In order to review construction method in production process, we applied the parameter design method of quality engineering and tried to approach the optimization of construction method. Conventionally, press fitting method has been adopted in process of fitting rotor core and shaft which is main component of motor, but quality defects such as core shaft deflection occurred at the time of press fitting. In this research, as a result of optimization design of shrink fitting method by high frequency induction heating devised as a new construction method, its construction method was feasible, and it was possible to extract the optimum processing condition.

Expanding the applicable duration for shrink fitting of the ultrathin-walled reactor coolant pump rotor-can

The rotor-can of reactor coolant pump (RCP) is generally assembled on the rotor using shrink fitting technique. The rotor-can is characterized by large height and ultrathin-walled cylinder, thus, its rigidity is weak and heat capacity is quite limited. The shrink fitting process has to be completed within a short limited-time, which makes it difficult for rotor to insert in the rotor-can completely. In order to solve this problem, a new method was proposed to extend the limited time by using a heat capacity added layer (HCAL) during the shrink fitting process. A thermal-mechanical coupled finite element (FE) model was developed to simulate the whole process. The transient heat exchange with a narrow gap between rotor and rotor-can during the shrink fitting process was taken into consideration. The limited time was predicted by calculating and analyzing the evolutions of temperature field and radial displacement field of the rotor-can. The simulation results indicate that the limited time of the shrink fitting process can be significantly extended with the increase of HCAL in thickness. Then, shrink fitting experiments were performed to confirm the extending effect of the HCAL. The experimental results of limited time show good agreement with the predicted values. The current results will certainly help the designer to improve the shrink fitting technique.

Mu2e Transport Solenoid Prototype Design and Manufacturing

The Mu2e Transport Solenoid consists of fifty-two coils arranged in twenty-seven coil modules that form the S- shaped cold mass. Each coil is wound from Al-stabilized NbTi superconductor. The coils are supported by an external structural aluminum shell machined from a forged billet. Most of the coil modules house two coils with the axis of each coil oriented at an angle of approximately five degrees with respect to each other. The coils are indirectly cooled with LHe circulating in tubes welded on the shell. In order to enhance the cooling capacity, pure aluminum sheets connect the inner bore of the coils to the cooling tubes. The coils are placed inside the shell by the means of a shrink fit procedure. A full-size prototype, with all the features of the full assembly, was successfully manufactured in a collaboration between INFN-Genoa and Fermilab. In order to ensure an optimal mechanical pre-stress at the coil-shell interface, the coils are inserted into the shell through a shrink fitting process. We present the details of the prototype with the design choices as validated by the structural analysis. The fabrication steps are described as well.  Index Terms—Superconducting Magnets, Solenoids, Accelerator Magnets

Coupled Thermomechanical Analysis of Autofrettaged and Shrink-Fitted Compound Cylindrical Shells

In this study, different configurations of compound multilayer cylinders subjected to autofrettage and shrink-fit processes and under combined cyclic thermal and pressure loads have been investigated and their fatigue life has been evaluated and compared. Fully coupled thermo-elastic analysis is taken into consideration during the calculation of the temperature profile through the wall thickness. Finite element model for the compound two-layer cylinder has been constructed and then validated with previous work in the literature and experimental work. In the experimental work, the temperature has been measured at different locations through the thickness of a two-layer shrink-fitted cylinder (SFC), subjected to internal quasi-static and dynamic thermal loads. Besides, the hoop strain at the outer surface of the cylinder has been measured for the same thermal loads. Using the developed finite element model, the hoop stress distributions through the thickness of different configurations of the compound cylinder have been calculated under different loading conditions, including internal static pressure, internal cyclic thermal loads, and combination of these loads. The mechanical fatigue life has been calculated using ASME codes due to the internal cyclic pressure. Moreover, the stress intensity factor (SIF) has been calculated for these configurations under cyclic thermal loads or cyclic thermomechanical loads, considering thermal accumulation. The stress intensity factors for different configurations have been compared with the critical SIF which is the fracture toughness of the material. The number of stress cycles required until the SIF reaches the critical SIF has been considered as the fatigue life for each configuration. It has been found that for the cases of cyclic thermal loads and combined cyclic pressure and thermal loads, the shrink-fitting of two layers followed by the autofrettage of the assembly is the best configuration to enhance the fatigue life of the two-layer cylinder.

Alternative manufacturing process of die carring hook for reducing material loss

To develop a green manufacturing process is very important to minimize material loss, energy consumption and so on. In this study, a shrink fitting process for producing die carring hook of stamping die set was developed through alternative process for sustainable production. Die carring hook is usually manufactured by machining process. Machining process is very common and easy process. However, this process has some disadvantages such as excessive material loss, low productivity, and relatively low mechanical properties. Especially, the excessive material loss and the low productivity are the most serious problems. In order to overcome these problem, the shrink fitting process was applied to manufacture die carring hook for achieving less material loss and higher productivity. In this study, after manufacturing the head ring and body of die carry hook, the two parts was tighten through shrink fitting process. In order to apply the shrink fitting process, the shrink fitting process was analyzed by using FEM. Through FE analysis, heating and cooling process of shrink fitting was analyzed. And after cooling process, the clamping force between head ring and body was predicted to evaluate the quality of die carring hook. The result of FE analysis was verified through experiment. As a result, when the shrink fitting process was applied, not only material utilization but also productivity can be improved approximately 32% and 40%, respectively.

Design Optimization of Compound Cylinders Subjected to Autofrettage and Shrink-Fitting Processes

The autofrettage and shrink-fit processes are used to increase the load bearing capacity and fatigue life of the pressure vessels under thermomechanical loads. In this paper, a design optimization methodology has been proposed to identify optimal configurations of a two-layer cylinder subjected to different combinations of shrink-fit and autofrettage processes. The objective is to find the optimal thickness of each layer, autofrettage pressure and radial interference for each shrink-fit, and autofrettage combination in order to increase the fatigue life of the compound cylinder by maximizing the beneficial and minimizing the detrimental residual stresses induced by these processes. A finite element model has been developed in ansys environment to accurately evaluate the tangential stress profile through the thickness of the cylinder. The finite element model is then utilized in combination with design of experiment (DOE) and the response surface method (RSM) to develop a smooth response function which can be effectively used in the design optimization formulation. Finally, genetic algorithm (GA) combined with sequential quadratic programming (SQP) has been used to find global optimum configuration for each combination of autofrettage and shrink-fit processes. The residual stress distributions and the mechanical fatigue life based on the ASME code for high pressure vessels have been calculated for the optimal configurations and then compared. It is found that the combination of shrink-fitting of two base layers then performing double autofrettage (exterior autofrettage prior to interior autofrettage) on the whole assembly can provide higher fatigue life time for both inner and outer layers of the cylinder.

An experimental investigation of thermal contact conductance of Hastelloy C-276 based on steady-state heat flux method

In this study, measurements of the thermal contact conductance (TCC) at the interfaces of Hastelloy C-276/Hastelloy C-276 and Hastelloy C-276/SS302 test pairs were conducted by a self-developed experimental setup based on the steady-state heat flux method. The reliability of experimental setup and method was validated by the repeated measurement of the thermal contact conductance between Hastelloy C-276 and Hastelloy C-276. In addition, the effects of contact pressure and interfacial temperature on thermal contact conductance were also discussed. This study not only provides a necessary database for the accurate numerical simulation but also lays a foundation for the optimal design of the shrink fitting process of rotor can.

AN ANALYTICAL SOLUTION FOR OPTIMUM DESIGN OF SHRINK-FIT MULTI-LAYER COMPOUND CYLINDERS

In this paper, employing an analytical method, optimum design of multi-layer compound cylinders is investigated. To this end, considering Tresca criterion, maximum shear stress in each layer is minimized. Analytical relations for optimum values of a layer dimension, residual pressures and radial interferences are derived. A technique for shrink-fitting of layers is also proposed and relationships for radial interferences, residual pressures and required temperature differences during the shrink-fitting process are derived. Three different examples are presented to show the effectiveness of the proposed method. It is shown that increasing the number of layers makes shear stress distribution near to uniform. As a result, with specified maximum shear stress and inner radius, the weight of compound cylinder is decreased when the number of layers is increased. Moreover, compound cylinders with more layers have lower maximum shear stress for a specified weight. It is also concluded that if the ratio of outer to inner radii be larger, increasing the number of layers is more effective.

Experimental investigation of transient heat transfer between Hastelloy C-276/narrow air gap/silicon steel

The heat transfer between rotor can/narrow air gap/silicon steel sheet has an important influence on the shrink fit process of reactor coolant pump rotor can. The accurate thermal conductance data are needed for the optimal design and numerical simulation of the shrink fit process of rotor can. Consequently, in this study, a set of new experimental apparatus and relevant procedure were developed to measure the thermal conductance at the interface between Hastelloy C-276/narrow air gap/silicon steel based on the transient method. The effects of the initial temperature of the Hastelloy C-276 specimen and the dimension of the air gap between the two test specimens on the thermal conductance were evaluated.

An Analytical Solution of Residual Stresses for Shrink-Fit Two-Layer Cylinders After Autofrettage Based on Actual Material Behavior

To enhance the pressure capacity and the life of a pressure vessel, different processes such as shrink-fit and autofrettage are usually employed. For autofrettaged and shrink-fit multilayer cylinders, numerical solutions for determining the residual stress distribution have been reported. However, few studies about the analytical method are available. In this study, an analytical solution was presented for shrink-fit two-layer cylinders after autofrettage based on the actual tensile-compressive stress–strain curve of material. The new analytical method accurately predicted a residual stress distribution, and it could be used to design two-layer compound cylinders. In this method, unloading and shrink-fitting were considered as a simultaneous operation for an inner cylinder, allowing for a simple and accurate analysis. Some significant factors were taken into account, including the nonlinear behavior of an original autofrettaged inner layer in the shrink-fitting process and a material’s different unloading behavior at different maximum tensile affects back-yielding. The results of the proposed method were in excellent agreement with the results from the simulation performed by ansys. The results indicated that an increased shrink-fit pressure expanded the back-yielding zone of the inner cylinders, and did not affect the back-yielding zone of the outer cylinders. The optimum percentages overstrain depend on the working pressure when the shrink-fit pressure, cylinder size, and material are defined, and inner and outer cylinders have different optimum percentages overstrain.

Evaluation of the Iron Loss Distribution of the Actual Stator Core Using Small Excitation Inner Cores

To obtain the basic data to manufacture the highly effective rotating machine, the axial iron loss distribution of an actual stator core of the complex structure was evaluated by using the small excitation inner core. The laminated thickness of this small excitation inner core is approximately 1/6 of the thickness of the stator core. Therefore, the circumferential iron loss distribution of the stator core and the axial iron loss distribution of a stator core can be measured by using this small excitation inner core. Then, to compare the difference of the axial iron loss distribution in the stator core, we investigated the axial iron loss distribution in the actual stator core after two manufacturing processes, the laminating process and the shrink fitting process. The iron losses were measured in three places (the edge, the quarter part, and the center) of two stator cores. As a result of our investigation, the axial iron loss distribution in the actual stator core clearly changed. This paper reports on the axial iron loss distribution in two manufacturing processes in two actual stator cores measured by using the small excitation inner core.

Prediction of the dimensional deformation of the addendum and dedendum after the warm shrink fitting process using a correction coefficient

The warm shrink fitting process is generally used to assemble automobile transmission parts (shafts/gears). However, this process causes a deformation in the addendum and dedendum of the gear depending on the fitting interference and gear profile, and this deformation causes additional noise and vibration between the gears. To address these problems, the warm shrink fitting process is analyzed by considering the error in the dimensional deformation of the addendum and dedendum found when comparing the results of a theoretical analysis and finite element analysis (FEA). A correction coefficient that reduces this error is derived through an analysis of the difference in the cross-sectional area between the shapes used for the theoretical analysis and that of the actual gear, and a closed-form equation to predict the dimensional deformation of the addendum and dedendum is proposed. The FEA method is proposed to analyze the thermal-structural-thermal coupled field analysis of the warm shrink fitting process (heating-fitting-cooling process). To verify the closed-form equation using the correction coefficient, measurements are made of actual helical gears used in automobile transmissions. The results are in good agreement with those given by the closed-form equation.

Three-dimensional finite element method simulation and optimization of shrink fitting process for a large marine crankshaft

Shrink fit is an important method used to connect mechanical parts but less studied by three-dimensional finite element method. Through a finite element method study, here we have simulated the crankshaft shrink fitting process by focusing on four main aspects: the optimization of heating method before shrink fit, the contact behavior on the interface in shrink fit process, and the structural distortion after shrink fit, as well as the evaluation of the bonding strength. Our results have demonstrated: (1) an extended bore with a satisfied radius can be obtained by imposing temperature gradient around the bore during the heating process. (2) In the beginning of the shrink fit, the journal tends to be absorbed into the shrink fit bore until the interfaces are fully contacted. The journal is then squeezed in radius and extended in axial as the heat transfer becomes stable through the interface. (3) The upper crankweb bends upward when heated, while downward after shrink fitted. The shrink fit distortion leads to the journal’ offset and rotation in an individual shrink fit process, and the stacking offset of each journal aggregates the distortion in an integrated crankshaft as compared with the expected shape in an ideal state. (4) The interfacial bonding strength reaches a relative constant in a time that much shorter than expected. The final distribution of the contact pressure on the interface is not uniform but the maximum transmitted torque evaluated by finite element method agrees with that obtained via the proposed analytical method. In terms of these simulated results, a series of practical measurements have been performed with an aim of efficiently enhancing the bonding strength and preventing the shrink fit distortion.