統計的技法 및 有限要素法에 의한 高速脫水用 드럼洗濯機의 驅動시스템 最適設計 = (The) optimum design on operating system of high speed washing machine by statistical method and F.E.M
저자
발행사항
부산 : 釜山大學校, 2008
학위논문사항
학위논문(박사) -- 釜山大學校 大學院 精密機械工學科 2008
발행연도
2008
작성언어
한국어
KDC
551.15 판사항(4)
DDC
621.815 판사항(21)
발행국(도시)
부산
형태사항
xvi, 213 p. : 삽화, 도표 ; 26 cm
일반주기명
참고문헌수록
DOI식별코드
소장기관
Front loaded washing machines, which operate using its horizontal orientation and the conse-quent gravitational falling of water, were mostly used in Europe for small amounts of laundry. As the lifestyle of people become more westernized and advanced, the trend shows a continuous in-crease in the use of front loaded washing machines. Electronics companies now pursue fierce competition in developing front loaded washing machines that accommodate masses of laundry and they aim at accomplishing higher speed rotation to improve the spin-drying function and con-sequently the spin-drying rate. The recently emerging importance of the environment and energy prefers the number of rinsing to be lowered to decrease the amount of water used and the drying time can be reduced thereby conserving electricity, which requires the rotation velocity to be raised during the spin-drying. Also, as health and hygiene become more crucial in people’s lives, there has been an increase in the size of the laundry to accommodate, for example, blankets, which subsequently requires larger-capacity washing machines. In order to develop such high-speed for spin-drying, enlarged front loaded washing machines, it is crucial to establish a rigid structure for all parts to stand against the increased load and also a low-noise, low-vibration design for in-creased noise and vibration that are generated from the higher-speed motor that provides the core power. However, since the stiffness and strength design of the internal operating parts that possess complex problems such as interaction between parameters, discontinuing dynamic parameter, and the operation environment where the laundry water fall downwards require more than mere im-provements to the existing product based on theories. Rather, professional knowledge and technol-ogy that surpass the limiting processing technique are required, which makes it impossible to de-velop high-speed spin drying washing machines using domestic skills.
In this research, we propose and validate the optimal experiment and analysis method on re-solving the internal stiffness and strength that allows developing the country’s first 10kg-capacity and 1800rpm-speed spin-drying washing machine in order to provide a design standard. This is extremely significant and we aim at setting up a stepping stone for developing better-performing washing machines by systematically establishing the findings. The internal structure of front loaded washing machines is largely composed of a drum assembly, tub assembly, and shafting system. We exclude the tub assembly, which is the least important and has fewer issues as we will only concentrate on enhancing the stiffness and strength of the drum assembly and the shafting system. The purpose of the research is the critical issues where one is the joining strength of the spin drum’s seaming part and the other is designing shafting system that has enough stiffness and strength that can withstand large loads. The scope of research and details are as follows.
1) The drum is assembled through a joining process using the seaming and caulking processes. Although the most important mechanism of mechanical press joining has more advantages over welding in term of the spin drum, the joining strength is lower and its mechanically complex is-sues generate difficulties when actualizing a high joining strength that the high-speed operation requires. In this research, we aim to select the optimal mechanical press joining processing condi-tion by using the Box-Behnken design and through F.E analysis and experiment, with a statistical approach of the design of experiment, of the joining strength according to varying thickness, bend-ing radius, bead shape, and seaming contact area, etc.
2) As washing machines become faster and larger, the power of the motor is delivered to the drum and greater load is applied to the shaft, which acts as the rigid body of the horizontal direc-tion of the shaft, and generates fracture strength and fatigue issues. The stiffness required of large-capacity and high-speed shaft depends on the force or the size of the moment as well as the shape of the elastic body, supporting method, and the elasticity modulus of the material. This research uses the design of experiment and the finite element method to select the design factor that has an impact on the characteristics and uses the central composite design applied multi response surface optimization routine to suggest the optimal shape of the shaft that satisfies all conditions.
3) The bending stiffness of the flange is determined by the sectional form and is increased by designing large in moment of inertia of a plane area. Design time and cost can be reduced by de-termining the factors for only the shapes suggested after considering the simplicity of molding and formability among the so many cross-section. In this research, we use the design of experiment to select the design factor of the many surfaces that impacts the stress and we propose the cross-section of the optimal flange that minimizes the load by using the response surface optimization routine.
4) Although the shaft and the flange become a single unit when the serration formed at the end of the shaft is inserted in the process of producing the flange by die casting process, since two dif-ferent objects come in direct contact with each other, the die casting material and the shaft material induce flow issues when applied with torque and momentum during operation. In this research, we use the design of experiment and the finite element method to identify the impact of serration shape design factor on the flow of contact surface when inserting die casting in the case of static and dynamic loads and we suggest the optimal shape of the serration that can minimize the liquid-ity using the optimized routine.
5) In order to evaluate the static and dynamic characteristics of the entire drum assembly, this research built an initial product based on the proposed optimal configuration and shape data and we determined whether or not the conditions comply with the requirements of high-speed spin-drying washing machine that we would like to develop by comparing actual experimental values with analysis results based on the theory through joining strength, fracture, and fatigue tests so that we can revalidate the usefulness of the design method using finite element method and design of experiment.
In this research, we select, through correlation analysis and regression analysis, the design fac-tor that have a significant impact on the target function for the shaft, serration of the shaft, flange of the shafting system, and the spin drum, which are the operating system, of washing machines by jointly using the finite element method and the design of experiment using MINITAB that can considerably improve the design time and cost that the verification through creating the design model has in order to develop a high-speed and large-capacity spin-drying washing machine. We use the selected design factor as input to perform main effect, interaction effect based on statistics and we assess a regression model function, which is the relationship between the input and the output, to use it as the response surface optimized routine in order to propose the optimal process-ing conditions and shape through experiments and analysis. Such method of combining the statis-tical method and the finite element method is an extremely useful processing design method for configuring the default value for designs when there are many free-variables in determining condi-tions or shapes and it also helps select the required shape and processing condition with less time and cost. Also, through the telemetry system and fatigue test, torsion strength, and bending strength tests on the first product of the operating system that includes the proposed shafting sys-tem, we were able to validate the reliability of our optimal design and we systematically estab-lished a design standard for such operation system. This research is summarized as follows.
1) The optimal configuration of the seaming processing finalized by the DEFORM analysis and Box-Behnken design is TH=0.75mm, BR=0.56mm, SW=7.01mm, PW=2.2mm and the joining strength was 112.8N/mm2, which satisfied the joining strength of 103N/mm2 that is required dur-ing the 1800rpm operation.
2) The configuration of the shaft determined by the optimized design using NASTRAN and the central composite design is D1=39.5mm, D2=25mm, L1=50mm, L2=61.1mm and the mode analysis result using ANSYS shows that the natural frequency is fully optimal for stable operation at 547Hz.
3) The optimal configuration of the main serration determined by the Box-Behnken design and ANSYS analysis is DS1=30mm, DS2=43.7mm, TNO=36ea with the serration equivalent stress at SS=45.1Mpa and the die casting equivalent stress at SF=17.4MPa.
4) The flange cross-sectional form finalized through the central composite design is type II with F1=39.9mm, F2=40.3mm, F3=40mm, H=26.4mm, T=4.6mm, STRESS=43.3MPa, and AREA=1400mm2.
5) After evaluating the operating system, fracture occurred where the drum pulley is connected at the back of the smallest bearing with the diameter, which is the weakest point on the shaft and the fracture torque at this moment was about 83610Ncm, approximately 50% of the fracture torque.
6) As the result of the bending fracture test of shafting system, fracture occurs at the cross sec-tion of flange and the average fracture load was 44650N, which was 4 times as larger than the cen-trifugal force of 10648N derived by assuming a 10kg and 1800rpm operation.
7) According to the result of the fatigue test, the bending load due to the unbalanced centrifugal force when shifting from mid-speed to high-speed increases by 1.27 times whereas the fatigue strength of the model designed in the research shown in the 106 cycle increased by approximately 1.3 times.
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