Çamaşır makinesi körüğünün dinamik özelliklerinin belirlenmesi ve makinenin dinamiğine etkisi

Abstract

Beyaz eşya gibi yüksek üretim adetlerine sahip olan bir sektörün ürünlerinden biri de çamaşır makinesidir. Bu sektörde, her komponentten gelecek olan artı ve eksiler kritiktir. Bir parçanın etkisi birkaç parçada veya tüm makine üzerinde görülebilirken aynı zamanda bu parça algı, kalite, ömür gibi parametrelere de etki etmektedir. Çamaşır makinesinin hem görsel hem de dinamik bir eleman olan körük de sistemde hareketli ve hareketsiz parçaları bağlayan bir unsur olarak kritiktir. Körüğün gerek fonksiyonları gerekse sınır koşulları nedeniyle, tasarımı ve malzeme konusu büyük öneme sahiptir. Körüğün etkin olduğu yapısal konulardan biri tahrik grubu deplasmanlarıdır. Tahrik grubu deplasmanlarının bilinmesi, çamaşır makinesinin genel tasarımı anlamında en etkin konular arasındadır. Bu nedenle tasarım aşamasında çamaşır makinesinin bir yazılım kullanılarak modellenmesi ve tahrik grubu deplasmanlarının elde edilmesi, yeni ürün veya ürün geliştirme çalışmalarına yön vereci olacaktır. Körüğün böyle bir modele dahil edilmesi ise, viskoelastik yapısı kaynaklı zorlayıcı bir mühendislik problemidir. Çamaşır makinesi tahrik grubuna dahil olan körüğün dinamik özelliklerinin belirlenmesi ise bu problemi çözmenin gereğidir.Tez çalışmasında, karşılaşılan problemin öncelikli olarak literatürde mevcut bir çözüme veya yaklaşıma sahip olup olmadığı araştırılmıştır. Viskoelastik malzemelerin dinamik özelliklerinin test veya sonlu elemanlar yöntemleri ile belirlenmesi ile ilgili çalışmalar yapılmış, tezlerde test düzenekleri geliştirilmiştir. Fakat istenilen tüm adımlara körüğün dahil olduğu, özelliklerin belirlenip, dinamik bir modelin kurulduğu bir çalışma yapılmamıştır. Daha sonraki bölümde ise çalışmanın temel bilgisinin toplanması adına titreşim, titreşim yalıtımı, körük malzemesi ve modellenmesi, viskoelastik malzeme test yöntemleri ve mekanik altyapının oluşturulduğu teori bölümü sunulmuştur. Birinci ve ikinci bölümde yapılan çalışmalar tezin amacı doğrultusunda hangi test-analiz yöntemlerinin ve teorik alt yapının kullanılması ile ilgili belirleyici olmuştur. Üçüncü bölümde ise körük malzemesi olan EPDM' in dinamik özelliklerinin elde edilmesi amaçlanmıştır. Önce statik bir test olan çekme testi, daha sonra dinamik test yöntemleri olan Oberst Testi ve Dinamik Mekanik Analiz çalışmaları yapılmıştır. Bu yöntemler eksi ve artı yönleriyle ile değerlendirilmiş, malzeme için dinamik elastiklik modülü ve kayıp faktörü değer aralığı frekansa bağlı elde edilmiştir. İlgilenilen frekans aralığındaki veriler sonraki sonlu eleman analizleri bölümünde malzeme kartında kullanılmıştır. Bir sonraki bölümde, körüğün dinamik özelliklerinin belirlenmesi amacıyla körük test düzeneği geliştirilmiştir. Düzenek geliştirilmeden önce alternatif tasarım çalışmaları yapılmış, düzeneğin planlanan testleri yapmaya uygunluğu sağlanmış ve daha sonra imal edilen düzenekte testler yapılmıştır. Test düzeneğinden toplanan veriler, logaritmik azalma yöntemi ile değerlendirilmiş ve dinamik direngenlik ve kayıp faktörü verileri genliğe bağlı elde edilmiştir. Test düzeneğinin ve körüğün sonlu elemanlar yazılımında modellemesi ve analizi yapıldıktan sonra, test ile model korelasyonu karşılaştırılmıştır. Beşinci bölümde ise tezin başlangıçta belirtilen amacına son adım olan çoklu cisim dinamiği yazılımı olan MSC Adams'ta bir çamaşır makinası modeli kurulmuş; bu model analizleri körüksüz ve körüklü durumda tahrik grubu üzerinden elde edilmiştir. Bu model kurulurken ve öncesinde test ile korelasyonu yapılmış güvenilir bir model elde etmek amacıyla körüklü ve körüksüz durumda çamaşır makinesi tahrik grubuna titreşim testi yapılmıştır. Çoklu cisim dinamiği modeli ve test sonuçları karşılaştırılmış; yaklaşımlar yapışmış ve korele bir modele yaklaşılmıştır. Son olarak altıncı bölümde tezin genel değerlendirilmesi yapılmış, tez çalışmasında önemli noktalar vurgulanmıştır. Sonuçlar hakkında yorumlar yapılmış, ileride bu konuda yapılabilecek çalışmalar hakkında fikirler öne sürülmüştür.

Washing machine is one of the products in white goods industry and, in this sector, every pros and cons of components are critical due to very high production volume and cost multiplication. While a part can affect another part or the whole machine, it might also affect the other parameters such as sense, quality and machine life. Washing machine gaskets mainly used for sealing purpose, which is a dynamic part of a washing machine for connecting moving and static parts. Springs and dampers are other parts connecting dynamical tub to the panels of the washing machine. There are many different types of washing machine gasket for different brands and these differences are associated with design, color or material. The design and material topic aspects of gasket have high importance as they affect the performance of the gasket directly. Gasket affects the dynamic of the washing machine, including the displacement of dynamic group of washing machines. In this thesis, displacement of tub group of the washing machine is mentioned as displacement of dynamic group or oscillating group. The displacements, or vibrations, of a dynamic group is one of the most important design criteria for washing machine. Therefore, it is very impartant to model, analyse the washing mashine in order to predict the displacements of dynamic group accurately during the design stage. Early stage design parameters will lead to new feasible designs which is very important for competition. Since gasket is a viscoelastic material, including a gasket into a mathematical model is a challenging engineering problem due to nonlineer behaviour of the material and the contacts beween the gasket and the other parts of the machine. To solve this problem, the dynamic characteristics of a gasket of washing machine should be determined.In this study, firstly the literature was searched to find out related work done by others. Similar unknown parameters for different materials have been found to be an issue for engineering studies since 1930s and Kerwin's sandwich model is a milestone for viscoelastic material modelling and testing. After this, very important study for viscoelastic material testing method was developed by Oberst. Oberst was developed a testing method based on beam theory and composite structures. There are examples of studies which include determination of a viscoelastic material dynamic properties by testing or finite element analysis. The studies are limited as focusing on material analyzing or finite element modelling only. There are also limited dynamical model studies for washing machines with different assumptions. However, there is no study covering the objectives of this thesis as determination of gasket properties and building up a dynamic model. After the literature survey presented in this thesis, the relevant theory was summarised comprising vibration, vibration isolation, gasket material and its modelling theory, and viscoelastic material testing methods. The studies presented in the first and second chapters have been critical to decide which test and analysis methods to be to meet the objectives of this thesis. In the third chapter, determination of the gasket material dynamic properties is aimed. The material of the gaskets is EPDM for almost all brands with different additive rates, colors and designs. EPDM is syntetic rubber which is a type of viscoelastic material. It is widely used in electrical insulation and sealing for different sectors. Although common usage of EPDM in different industrial areas, non-linear material characteristics examination is a challenging topic. Firstly, a tensile test is performed to identify the static behaviour of the gasket material. The standard tensile test data was evaluated for different elongation rates and the lineer zone is shown to be up to %300 elongation with 3 to 5 MPa elasticity modulus. This test is performed to identify brief information for beginning. After this, dynamical material testing methods which are Oberst Beam Method and Dynamic Mechanical Analysis are performed. Oberst Beam Method is applied to two types of gasket materials with two different types of adhesives which are double sided tape and loctite. Advantages and limitations of these methods are evaluated and minuses and ranges of dynamical elasticity modulus and loss factor value are determined as a function of frequency. For the test with loctite, there were problems such as non-homogenous bonding, leakage of loctite from the edges and split of gasket samples from the beam after a time. Double sided tape results were found to be more reliable since matching viscoelastic material behaviour in the literature and these results are used in finite element analysis explained in the third chapter.After the Oberst Method, Dynamic Mechanical Analyzing(DMA) method is also used to identify the dynamic characteristics of gasket in order to have increase the reliability of the estimated material properties. DMA is executed by a testing machine at different frequency and temperatures. There are different types of DMA for different materials and the shear mode is suggested for viscoelastic material samples. An approximation between shear and elastic modulus is used for parameter transformation. A DMA was performed both for variable frequency and temperatures for two types, namely gasket1 and gasket2. For the variable frequency test, the range between 1 Hz to 100 Hz was scanned at constant tempature, 30°C. For the variable temperature test, the range is between 2°C to 95°C which was performed only on gasket2. The results of both dynamical material testing method was evaluated for dynamic elastic modulus and loss factor. Since the DMA tests are performed using the material gasket only, the effect of beam and adhesive used in Oberst Test Method was eliminated. The loss factor range provided from DMA is proper according to the literature. A comparison between temperature and frequency analysis is performed for accuracy. Material properties identifed from tests are used in the finite element analyse as a material card with covering values of both method.In the next chapter, the design and construction of a gasket testing setup are described. This test rig is then used for determination of the dynamical properties of gaskets. Simultaneously, finite element modelling is performed in Hypermesh software. The finite element model is symmetrical shell model which extracted from 3D SolidWorks data with different thickness values. The gasket is modelled as an axisymmetric. Before the development of experimental setup, alternative design studies were carried out and it was checked whether the setup was appropriate to perform the planned. Then the gasket test setup is built and impact tests are perfomed. The vibration signals in time domain are collected from the test setup with PULSE software. These datas were evaluated by logarithmic decrement method and the dynamic stiffness as well as loss factor values are obtained. After modelling and analyzing the test setup and gasket, the test results of the test and finite element model predictions are compared and correlated.In the fifth chapter, dynamic model of a washing machine is described. The model is created using multibody dynamics software, MSC Adams. Before and during the modelling on MSC Adams, a vibration test is performed on the washing machine dynamic group to provide some experimental data for the purpose of creating a reliable model. For the testing purpose, a washing machine is picked from the production line and a vibration test is performed on the dynamic group of the washing machine on the pre-determined locations. This test was repeated three times to avoid measurement errors. These tests were carried out with a gasket and without a gasket. The multibody model preparation covers colleting 3D design data of the all related parts of the machine.Since it is not possible to model every part of the machine in the Adams software,the parts to be modelled are selected. This solid body data was exported from UG NX software to MSC Adams and the material data for each component was defined in the model. The springs and dry friction dampers were tested to checkthe expected stiffness and force respectively. After this, electrical motor of the washing machine including its time-speed algorithm is defined in the model. This data is an input for rotational velocity of the system which affects the displacements considerably. The model included many details of a wahing machine, including two counter weights, front and back tub, drum, three drum wings, flange, shaft, housing, pulley, electric motor, two springs and two dampers. These components were assembled were assembled using appropriate tools in the software. The electric motor gives an excitation to its shaft, it is transferred to belt and pulley, then it rotates the shaft and shaft rotates the flange which is connected to the drum with screws. The flange rotates with the drum and in this way rinsing and spinning occurs. The results of the first Adams model results wasn't close to test results, which required updating the bushing elements used for defining the joints. As one might expect, one of the most important components affecting the resonance vibration levels results was found to be the friction dampers. Since there is no readily available model or library on the for these dampers, a dry friction damper is explicitly modelled at the end of a lot of pre-damper studies. The washing machine model was created without a gasket first, and in this condition motor algorithm is applied as rotational velocity and displacement results were collected from Adams Postprocessor along three orthogonal directions x, y and z. It should be considered that the algortihm of electric motor is very important for behaviour of vibration data and vibration levels. The electric motor algortihm is not shared due to company restrictions. For the purpose of modelling the damper properties of the gasket, the experimentally identified logarithmic decrement results were utilised and equivalent viscous dampers are defined in the model via related equations. Then, the dynamics of the machine is simulated using the washing model with the gasket. The results of the multibody dynamics model and test results were compared and correlated. For the accurate parameters, so many iterations are performed in Adams. Results are assessed so as to determine a gasket yielding lower vibration levels.Finally, the work done in this thesis is evaluated and the critical points are highlighted for every chapter briefly. All assesments and comparison studies are summarized and directed for topics that should be focused. Furthermore, some ideas for future work and new methods for developing this process has outlined.