Proceedings of the Korean Society of Machine Tool Engineers Conference (한국공작기계학회:학술대회논문집)
The Korean Society of Manufacturing Technology Engineers
- 기타
1997.10a
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In recent years, grinding techniques for precision machining of astainless steel used in shaft, screw parts and clear value have been improved by using superabrasive wheel and precision grinding machine. The completion of optimum dressing of superabrasive wheel makes possible the effective percision grinding of stainless steel. However, the present dressing system cannot have control of optimum dressing of the superabrabive wheel. In this study, a new system and the grinding mechanism of optimum in-process electrolytic dressing were proposed. This system can carry out optimum in-process dressing of superabrasive wheel. Therefore, the optimum in-process electrolytic dressing is a good method to obtain the efficiency and mirror-like grinding of stainless steel(SUS304).
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Thermal expansion of the ball screw in semi-closed loop type CNC Lathe directly affects the position precision along the travel axis. In this paper, the thermal displacement of the ball screw is estimated by using macro variables. The estimated displacements of the ball screw are managed by calculating the interval of pitch error rate in the NC. The thermal behaviour of the ball screw of the CNC Lathe, under the constant operating conditions, was measured to examine the effectiveness of this compensation method. The results showed that thermal displacement of the ball screw could be maintained its accuracy better than 6
${\mu}{\textrm}{m}$ while applying this method. -
This paper describes result of experiment of parameters affecting the micro hole drilling time, kind of assisting gas and it's pressure. The result reveals that parameter value of 0.08J, 20Hz, dwell time of 300 microseconds can be a good machining condition to make micro hole diameter range of 50-70
${\mu}{\textrm}{m}$ , Assistant gas such air, O2, Ar, N2 was adapted. Assistant gas of air makes heat affected zone enlarge due to burning of material, also it makes hole irregular and damage because of refusion stick to caused by chemical reaction with Al2O3 ceramic material. O2(99.9%) has good characteristic to get good drilling and smooth surface on pressure of 0.2kgf/$\textrm{cm}^2$ , but it is expensive. Ar, N2 makes material burn and crack severely and proved to be an appropriate but, Ar was better than N2. -
Advances in EDM power supplies have made the process competitive in some areas dominated by conventional and numerically controlled machines. This paper will produce more comprehensive data than are presently available and will use this data in applying concepts of optimization based on manufacturer's guide lines utilizing neural networks. A method will be developed for determining the machining parameters of the EDM process considering the conflicting desirability of good surface finish, low tool wear and high rates of metal removal. By the proposed method, one can select machining parameters that can maintain permissible tool wear and obtain maximum machining rates on the system represented by the data.
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The objective of this paper is to present the development and application of interface software between robot and F/T sensor for force control. The interface software for among the robot controller, F/T sensor, and host PC is based on interrupt-driven method. To show the suitability of developed interface software, writing-task is performed in real time using F/T sensor that mounts on the wrist of the robot and Scara type 4-axis robot.
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In this study, study, about Automatic Loader and Unloader system which can directly be used for material handing and tool operating is moving linear transfer system for mainly forming of small electronic unit and other at press line. This system for been installed in a press in order to load and unload a workpiece from a press die. Control method be used Programmable logic control(PLC) unit. other Control equipment of system is Motor drive, Positioning Control and so on. It took data of input from each sensor and send signal of output to actuator by sequence program. We try to Characteristics test of this system has good condition when operating by laser measurement
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This paper investigates the relationship between cutting conditions and Acoustic Emission(AE) signals; AEavg, AErms, AEmode, as the base working to monitor the tool wear with in-process. For this purpose, cutting tests were conducted on a CNC lathe with comprehensive cutting conditions.. It is known that AEavg and AErms are proportionaly increased as the increasing of cutting velocity and depth of cut respectively. It is also known that AEmode among three kinds of AE signals may be applied for in-process monitoring to make the self diagnosis system because of its stability to the variation of cutting condition.
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This paper presents a new approach to the calibration of a SCARA robot orientation with a camera modeling that accounts for major sources of camera distortion, namely, radial, decentering, and thin prism distortion. Radial distortion causes an inward or outward displacement of a given image point from its ideal location. Actual optical systems are subject to various degrees of decentering, that is, the optical centers of lens elements are not strictly collinear. Thin prism distortion arises from imperfection in lens design and manufacturing as well as camera assembly. It is our purpose to develop the vision system for the pattern recognition and the automatic test of parts and to apply the line of manufacturing.
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This paper proposes a new approach to the design of fuzzy-neuro control for track vehicle system using fuzzy logic based on neural network. The proposed control scheme uses a Gaussian function as a unit function in the neural network-fuzzy, and back propagation algorithm to train the fuzzy-neural network controller in the framework of the specialized learning architecture. It is proposed a learning controller consisting of two neural network-fuzzy based of independent reasoning and a connection net with fixed weights to simply the neural networks-fuzzy. The performance of the proposed controller is illustrated by simulation for trajectory tracking of track vehicle speed.
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In the past polyester was usually used as the matrix of all fiber-reinforced plastic (FRP). Nowadays, however, epoxy resin has taken the place of polyester due to its superior properties. If the cutting properties of epoxy resin are unknown, It is difficult to find the optimum cutting conditions of all fiber-reinforced plastic such as CFRP. AFRP. GFRP. In this paper, I will study the cutting properties of epoxy resin by testing surface roughness.
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This paper presents a new approach to the design of cruise control system of a mobile robot with two drive wheel. The proposed control scheme uses a Gaussian function as a unit function in the fuzzy-neural network, and back propagation algorithm to train the fuzzy-neural network controller in the framework of the specialized learning architecture. It is proposed a learning controller consisting of two neural network-fuzzy based on independent reasoning and a connection net with fixed weights to simply the neural networks-fuzzy. The performance of the proposed controller is shown by performing the computer simulation for trajectory tracking of the speed and azimuth of a mobile robot driven by two independent wheels.
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Ball-end milling process is widely used in the die and mold manufacturing because of suitable for the machining of free-form surface. Pencil cutting can eliminate overload in uncut area caused by large diameter of ball-end mill before finish cutting. As the ball-end mill for pencil cutting is long and thin, it is easily deflected by cutting force. The tool deflection when pencil cutting is one of the main reason of the machining errors on a free-from surface. The purpose of the research is to find out the characteristics of deflected cutter trajectory by eddy-current sensor.
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The purpose of this study is to investigate the effects of operation factors of a typical main spindle system on its efficiency. Among important factors, material type of ball-bearing, bearing-lubricant type and main spindle bearing preload are taken into considered.
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Development on the mechanical properties of steel sheet for the automobile body panel is very important in the BAF(Batch annealing furnace) annealing process. Because of the heat treatment method in the BAF, mechanical properties was decided on the heat treatment method of the coil. So, we tested on the development of mechanical properties according to heat treatment method at the annealing furnace using the Ax atmospheric gas and the HNx atmospheric gas. As a result of several investigations. We confirmed the following characteristics ; mechanical properties was changed under the influence of the annealing cycle, the heat treatment method and the atmospheric gas. And, elongation in the HNx BAF was better than the Ax BAF. Finally, most important thing in the BAF is using proper annealing cycle in order to get a good quality.
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In these days, customers require high-quality, high-performance, high-ride comfort for Automobile and then the automotive manufacturers concentrated on study of electrical, high-performance, low-cost of parts and sub-parts. In this paper, for ride comfort estimation PSD(Power Spectral Density) of acceleration at eight test point are measured, and then are calculated with new index of ride comfort. The new index of ride comfort developed for optimal design, real test, applied the actual. It can apply for various fields.
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Natural vibration of the rotor system having multi-step cross-sections is analyzed. The rotary inertia and the shear deformation are considered. Torque is also included in order to simulate the power transmission system. The complex displacement and the variable separation are introduced. The exact solutions in uniform cross-section segment and the boundary conditions are used. Natural frequencies and mode shapes are obtained, especially the mode shapes are countinuous.
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This paper examines the crack growth behavior of 7075-T651 aluminum alloy under high-low block loading condition. The cantilever beam type specimen with a chevron notch is used in this study. The crack growth and closure are investgated by compliance method. The applied initial stress ratios are R=-0.5, R=0.0 and R=0.25 Crack length(
$\alpha$ ), effective stress intensity factor range(ΔKeff), ratio of effective stress intensity factor range(U) and crack growth rate(d$\alpha$ /dN) etc. are inspected fracture mechanics estimate. -
In systematic and orderly estimation of fatigue strength of the spot welded lap joints, because the influence of residual stress of fatigue crach initiation and growth is not negligible, there need to estimate fatigue strength considered residual stress at near spot weld part of the lap joints. Therefore, in this thesis, peformed stress distribution and residual stress analysis at near the spot weld part by F.E.M and X-ray diffraction method, and obtained the maximum principal stress considered residual stress at nugget edge by superposing residual stress at nugget edge by superposing their results. From the results obtained above, we could find that fatigue strength of the IB-type spot welded lap joints was rearranged by the maximum principal stress considered residual stress at nugget edge and was entirely low about 13 percents compare with that neglected residual stress.
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The strengthening mechanism of short fiber or whisker reinforced metal matrix composites has been studied by a continuum mechanics treatment utilizing finite element analysis (FEM). To assess the tensile and compressive constitutive responses, a constraint-unconstraint comparative study based on stree-strain hysteresis loop has been performed. For analysis procedures, the aligned axisymmetric single fiber model and the stress grouping technique have been implemented to evaluate the domain-based field quantities. Results indicated that the development of significant triaxial stresses within the matrix both for the tensile and compressive loading, due to the constraint imposed by reinforcements, provides and important contribution to strengthening. It was also found that fiber stresses are not only sensitive to the fiber/fiber interaction effects but also substantially contribute to the composite strengthening both for the tensile and compressive loading.
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In case of spot-welded joints, the fatigue cracks generally originate from the weld interfaces of the neighborhood nugget tips, and propagate toward the outer surfaces of the sheets. Generally, because fatigue crack was observed in nugget around, strain gage was attached at nugget zone. Accordingly, it was very difficult to detect the generation time of fatigue crack in spot-welded joints and to measure the propagation speed of fatigue crack. We developed the non-destructive method, according to which th fatigue crack propagation rate can be quantitatively estimated by utilizing information obtained from strain gages bonded on the electrode indentations of spot welds. The results measured by real crack were compared with the data which was measured by strain gauge method in fatigue testing. And so fatigue strength was evaluated by stress intensity factor. In this study behavior of fatigue crack propagation under repeated load were considered.
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In this paper, We have analyzed dynamic characteristics of cutting force. Test materials are used martensitic heat resisting steel, STS420J2. The obtained results are as follows: 1. Cutting force is smaller make small feed when feed speed make a change. 2. Principal cutting force is smaller make small cutting speed when feed speed make a change.
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The purpose of this study is to analyze how tools, guide bush type and the change of cutting speed have effects on the diameter of cutting hole, surface roughness of workpiece and roundness during the deep hole machining of SM55C with solid BTA drill by using BTA drilling system through experiment. Conclusion reached is as follows. (1) The diameter was expanded for 25
${\mu}{\textrm}{m}$ at the first section and then was reduced 0${\mu}{\textrm}{m}$ and 15${\mu}{\textrm}{m}$ respectively at the 10m and 20m section comparing to the diameter of tool with respect to the variation of cutting length. (2) It was proved that roughness was below 12S for the whole section of cutting length. (3) The roundness has been below 12${\mu}{\textrm}{m}$ . Regarding the polygon phenomenon, it has bee proved that not only uneven number of angle but also even number (quadrilateral, elliptical) of angle were made. (4) Variation of diameter, surface roughness of workpiece and roundness turned out to ve the best at 70m/min of cutting speed, 0.15mm/rev of feed. -
This research is a experimental study for the machining conditions of E. D. M. They were used Cu electrode and the various amplitude of current waves for the machining by E.D.M. By the analyse the characteristics of current, voltage, roughness of surface and over cut, the next results were obtained. E.D.M. machining time become to be more longer by the increasing the tensile stress. In case of NAK 55 as the composite resin, the machining time was more faster without the relationship for the tensile stress. And if it was more increased the amplitude of Ip, it has been more faster in the machining time and more poor in the surface roughness. But it was increased Ip with 5A, it has been increased 0.3 time in over cut. So, if we want to be the precision machining, the diameter of the electrode should be more smaller than the diameter of machined hole in workpiece with E.D.M.
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The requirement of precision products about difficult-to-cut materials such as Cu and Aluminum alloy is becoming more and more. Because of soft materials, the exist narrow groves on surface are difficult to gotten off even on the polishing stage. It has been proved that Magnetic-Electrolytic-Abrasive Polishing (MEAP) is a efficient method to resolve this problem by using the nonwoven-abrasive pads together [1, 2]. In this study, through the experiments, their machining properties of newly developer polishing material of SiC, Al2O3 and diamond nonwoven abrasive pads have been proved. Through the experiments, the optimal machining conditions on larger cylinder shape workpiece of Cu and Aluminium alloy have been found, through the Taguchi[3] method the optimal machining conditions can be selected.
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The biggest challenge facing today's manufacturing industry is better quality and high productivit. From an economic point of view, productivity is the most important parameter, as high productivity will reduce the cost. However, the customers of today are not only cost concerned, but also quality conscious. So high accuracy levels should also be achieved in the manufacturing process. The aim of this paper is to get a comprehensive understanding of its machinability properties and to investigate the relationship between cutting conditions and surface roughness for Ball End Mill cutting process so as to enhance its practical application.
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항공기 부품, 터빈형 임펠라나 브레이드, 자동차나 가전제품용의 대형금형류의 정밀가공과 생산성 향상에는 5축의 NC가공이 기존 3축의 NC 가공보다 많은 이점을 갖고 있다. 제1차 선도기술개발사업을 통해 C 형의 5축머시닝센터를 성공적으로 개발한 실적을 바탕으로 제2차 선도기술개발사업을 통해 작업이송거리 12,000*3,500*1,500(X*Y*Z), 위치정밀도
$\pm0.005mm/M$ , 주축동력 30/45Kw의 대형, 강력, 정밀형의 문형5축머시닝센터 개불을 목표로 추진하고 있다. -
The purpose of this study is the development of CAM system which can cut and measure any shape by machining center and coordinate measuring machine. The overall goal of the CAM system is to achieve the CNC machining, from digitizing through to final cutting. The hardware of the system comprises PC and machining center, CMM. There are three steps in the CNC machining, (1) workpiece measuring on the CMM, (2) geometric modeling by the CAD system, (3) NC commands generation by the tool path compensated for tool nose radius. It is developed a software package, with which can conduct a micro CAM system in the PC without economical burden.
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Thermal deformation of machine origin of machine tools due to internal and external heat sources has been the most important problem to fabricate products with higher accuracy and performance. In order to solve this problem, GMDH models were constructed to estimate thermal deformation of machine origin for a vertical machining ceneter through measurement of temperature data of specific points on the machine tool. These models are nonlinear equations with high-order polynomials and implemented in a multilayered perceptron type network structure. Input variables and orders are automatically selected by correlation and optimization procedure. Sensors with small influence are deleted automatically in this algorithm. It was shown that the points of temperature measurement can be reduced without sacrificing the estimation accuracy of
$\pm$ 5${\mu}{\textrm}{m}$ . From the experimental result, it was confirmed that GMDH methodology was superior to least square models to estimate the thermal behavior of machine tools. -
In surface grinding, the contact between the grinding wheel and the workpiece introduces heat and resistance, which restrict the self-dressing of the grits and result in burrs and cracks on the workpiece. Therefore, before or during th grinding wheel for more accurate performance. In order to determine the dressing time monitoring method of grinding wheel in surface grinding, a three-dimensional computer simulation of the grinding operation has been attempted based on the contact mechanism and surface-shaping system between the grinding wheel and the workpiece. The optimal dressing time is determined based on the amount of the grain wear and work surface roughness.
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This paper describes the camera calibration based-neural network with a camera modeling that accounts for major sources of camera distortion, namely, radial, decentering, and thin prism distortion. Radial distortion causes and inward or outward displacement of a given image point from its ideal location. Actual optical systems are subject to various degrees of decentering, that is, the optical centers of lens elements are not strictly collinear. Thin prism distortion arises from imperfection in lens design and manufacturing as well as camera assembly. It is our purpose to develop the vision system for the pattern recognition and the automatic test of parts and to apply the line of manufacturing. The performance of proposed camera calibration is illustrated by simulation and experiment.
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Reverse engineering involves digitizing a three-dimensional model or part converting the data to a CAD database description and manufacturing by CNC. Currently, the digitization is done through measurements taken manually by a CMM or touch probe mounted on a CNC machinetool. Some reverse engineering techniques require close integration between the data collection method and the surface-fitting algorithms. Accurate surface data are collected by input to the surface fitting method. This study has been found that both the smoothness of surfaces and accuracy of surface fitting are related with the degree of the interpolated surfaces.
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The purpose of this study was to determine the effects of various cutting conditions on the cutting resistance and surface roughness of material in turning operation using a carbide tool. The workpiece materials were the carbon steel SM20C and SM45C. The results of this study are summarized as follows: The cutting force decreases as the feeding amount and cutting depth decrease and the cutting speed increases. In order to obtain a proper surface roughness to each material, it is desirable to set the feeding amount as 0.059mm/rev, the cutting depth as 0.4mm and the cutting speed as 270m/min for SM20C, while setting the feeding as 0.059mm/rev, the cutting depth as 0.6mm and the cutting speed as 270m/min for SM45C.
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기존의 복합 Turning Center 보다 비구심상태에서의 가공, 3축밀링가공 및 3축/4축 동시 Milling가공 등의 특징을 갖고 복잡한 형상과 기능을 갖도 있는 부품 생산용 각형 FMS/C의 기본기계가 될 다기능 복합가공기[최대가공경 310mm *최대가공길이600mm, 6축제어(4축동시가공), ATC Magazine 20개, 주축18.5KW, 제2주축 15KW 회전수36-1,600RPM의 강력, 고속, 정밀 다기능 복합가공기]를 제2차 선도기술개발사업을 통해 개발을 추진하고 있다.
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The ideal surface roughness is obtained by tool geometry and feed rate in face milling. however actual surface roughness is affected by various factors such as cutting conditions. vibration and used tool. To improve the quality and productivity of the machining parts, lots of research on the evaluation of tool life and control of surface roughness has been required. Therefore, the width of flank wear, cutting force, and surface roughness are monitored to analyse the characteristics of surface roughness. This experimental investigation is mainly focused on the characteristics of surface roughness in multi-insert milling using TiN coated tool.
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The measurement of surface roughness and waviness by means of noncontact method is an important area to be developed for GAC(Geometrical Adaptive Control) system. This paper deal with the design of noncontact in-process measurement system which measures the surface roughness and waviness during cylindrical grinding. This measuring system is simple and the apparatus proposed is composed of a laser unit, photodetector and optical system. During operation, the surface of a workpiece is continuously scanned by a laser beam. This method makes it possible to detect the surface roughness and waviness along the feed direction by control the spot diameter of laser beam. The experimental results show that the presence of chattering, loading and glazing can be detected sensitively along the feed directions.
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The experimental and numerical results of buckling loads for symmetrically laminated composite plates are compared. Boundary conditions are all fixed supports. Experiments were conducted for plates with fiber angles
$\theta$ =30$^{\circ}$ , 45$^{\circ}$ , 60$^{\circ}$ and aspect ratios a/b=0.8. Experimental results were obtained from load-deflection curves. Numerical methods were presented to evaluate buckling loads, using structural analysis results from ANSYS. -
Helical gear system is utilized to transmit motion between parallel shafts. The axial thrust loads on the shafts are existed. On each of the support shafts, at least one of the bearings should be able to support the axial loads. The reliability and life analysis are based on the two-parameter Weibull distribution lives of the component gears and bearings. The computer calculates the system lives and dynamic capacities of the components and their system. The system life is defined as the life of the component or the helical gear system at an output torque at which the probability of survival is ninety percent.
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The important parts of the developing AGV model are fabrication of each part and design technology of the body frame. In present day, design of the body frame is depend on the experience of the industry place and the systematic data and the optimal design technology of the frame for the case of model change is insufficient. In this study, the strengths of the AGV(Automatic guided vehicle)are examined with the 3-dimensional Finite Element method. In order to verify the FE results, the computed results are compared with the experimental results are compared with the experimental data from the strain-gage output data. New model designed by removing some parts of the initial model and choosing the thickness change of the rectangular-pipes.
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This paper proposes a systematic design method for axial(or thrust) magnetic bearings using optimal design methodology. The objective of the optimal design is to minimize bearing volume. The constraints include the bearing load capacity, linearized bearing stiffness and damping, the magnetic flux density, and geometric relations. In order to obtain design values which can be applied to fabrication of bearings, branch and bound method was introduced in the postprocessing procedure of optimal design results. Verification of the proposed design methodology was perfomed by an example.
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Many papers have been conducted on the applications of honeycomb sandwich maintenance, and to improve the high speed and light weight in rolling stocks, aircrafts and so on. The end door of rolling stock is generally made of rolled steel or stainless steel. Thus, the weight of these materials are heavier than of nonferrous metals and thermal deformation by welding or complexity of manufacturing process is occurred. Therefore, this paper is aimed to develop the light weight by application of end door which is made of aluminum honeycomb sandwich panels in rolling stocks and to propose the standards of design and evaluation for its adhesively bonded strength.
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The rattle noise is the most significant in many kinds of manual gearbox noises, which is generated at the idle stage of the engine operation. The main torsional vibration source of the driveline is the fluctuation of the engine torque. The gear rattle is impacts generating in the backlash of the free gear due to this torsional vibration. Many researchers reported the clutch torsional characteristic optimization method to reduce the idle gear rattle but only few of them give sufficient consideration to the system parameters like gear backlash, drag torque, system inertia, inertia distribution, engine torque fluctuation, idle engine rotation speed, and accessory load. This paper pays attention to the gear impact mechanism and system design parameters to reduce the idle gear rattle with computer simulation.
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Over the last few year, there has been a growing interest in quantitative representation of heat transfer phenomena in weld pools in order to relate the processing conditions to the quality of the weldment produced and to use this information for the optimisation and robotization of the welding process. Normally, a theoretical model offers a powerful alternative to check out the physical concepts of the welding process and to calculate the effects of varying any of parameters. To solve this problem, a transient 2D(two-dimensional) heat conduction were developed for determining bead geometry and temperature distribution for the GMA welding process. The equation was solved using a general thermofluid-mechanics computer program, PHOENICS code, which is based on the SIMPLE algorithm. The simulation results showed that the calculated bead geometry from the developed models reasonablely agree with the experiment results.
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Elastic elements, at first, were extensively used in suspensions as vibration isolators at joints. Nowadays they are used to improve stability and handling. The design of these elements has become a very important matter since the loading condition of the mechanism gives a mew suspension geometry without any modification. This paper presents an analysis of forces and moments of joints with elastic elements in the McPherson suspension mechanism to evaluate accurately the elastic deformation using the displacement matrix method in conjunction with the equilibrium equations. First the suspension is modeled as a multi-loop spatial rigid-body guidance mechanism which has elastic elements at the hardpoints of the suspension. Then a method and design euqations are developed to analyze the suspension characteristics by the various tire load. Also the displacement matrices and constraint equations for links are appllied to determine the sensitivity of the suspension mechanism. Finally this approach may conduct a realistic design of suspension mechanisms with elastic elements to improve the performance of the automobile under various driving conditions.
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An extensive corrosion study was initiated by galvalume steel sheet manufacturing company to clarify the corrosion behavior of zinc and zinc and zinc-alloy coated automotive sheet steel in out panel and electrical application. Since the early 1980's the use of zinc and aluminum alloy coated steel for vehicular corrosion protection has increased drastically. This paper describes the evaluation of formability, weldability and painted corrosion performance of galvalume steel sheet. This paper presents an overview of the program and some initial test results on the weldability, lifetime of the electrode tip shape of the spot welding and corrosion protection. Galvalume steel sheet improved corrosion performance and spot weldability of galvalume steel has no problem for the variation of welding current. And tip lifetime was changed according to the influence of shape.
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The purpose of this study is to reduce the vibration noise of differential gear by reducing torque fluctuation of drive pinion shaft which causes vibration noise of differential gear in rear wheel drive vehicles. For this we developed multi-degree of freedom analysis model in which mass moment of inertia and torsional spring combined, the validity of the simulation model was checked by the field test and we examined the influence of torsional vibration of driveline elements by performing forced vibration analysis of engine excitation torque. We studied the methods for reducing torsional vibration of driveline according to the design factor of propeller shaft and examined the effects reducing vibration differential gear by applying flexible coupling.
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This paper investigates the effects of shot peening on mechanical properties of SAE 9254, which is a spring steel used for the suspension system of automobiles. Rotary Bending Fatigue test is accomplished and the results are summarized as fellows : 1. The tensile strength and the hardness do not change so much. 2. The layer of highly residual stress is obtained by multi-stage shot peening. 3. The fatigue strength seems to be improved by residual stress. 4. The fatigue strength of un-peened and multistage shot peened material are 425 MPa and 756 MPa, respectively.