Bir ankastre bulaşık makinesinin düşme testinin modellenmesi ve analizi
Bir ankastre bulaşık makinesinin düşme testinin modellenmesi ve analizi
Dosyalar
Tarih
2015
Yazarlar
Eraslan, Sabri
Süreli Yayın başlığı
Süreli Yayın ISSN
Cilt Başlığı
Yayınevi
Fen Bilimleri Enstitüsü
Özet
Beyaz eşya sektöründe, ürünlerin depolanması ve nakliyesi süreçlerinde çarpma ve düşme sonucu hasar görmeleri önemli bir maliyete neden olmaktadır. Düşme ve çarpma gibi olumsuz senaryoların yaşanması neticesinde ürünlerin tamir edilmesi veya kullanılmaz hale gelmesi olasıdır. Ürünlerin üretim hattından çıkıp müşteriye ulaşıncaya kadar birçok taşıma aracına yüklenilip indirilmesi, düşme ve çarpma risklerine neden olmaktadır. Bu nedenle ürünlerde meydana gelebilecek olası hasarları önlemek için, beyaz eşyalar koruyucu paketleme malzemeleri ile muhafaza edilmektedir. Paketleme malzemesi olarak basma durumundaki enerji yutumlama özellikleri yüksek, polimer köpük malzemeler tercih edilmektedir. Ürünün düşme ve çarpması sonucunda, paketleme malzemesinin yeterli performansı gösterip göstermediğinin belirlenmesi amacıyla, fabrika ortamında fiziksel düşme testleri yapılmaktadır. Fabrika ortamında yapılan bu fiziksel düşme testleri önemli bir maliyet ve zaman kaybına neden olmaktadır. Fiziksel düşme testlerinde ortaya çıkan bu maliyet ve zaman kaybı, endüstride çalışmakta olan mühendislerin alternatif metotlar araştırmalarına neden olmuştur. Günümüzde gelişen ve hala büyük bir hızla gelişmekte olan bilgisayar teknolojisi ile birlikte, bilgisayar destekli mühendislik araçları kullanılarak gerçekleştirilen çalışmaların önemi artmıştır. Endüstride de kullanımı oldukça yaygın olan bu bilgisayar destekli mühendislik araçlarından biri de sonlu elemanlar yazılımlarıdır. Sonlu elemanlar yazılımları ile karmaşık mühendislik problemleri basitleştirilerek, kabul edilebilir bir yaklaşım ile sayısal olarak çözümlenebilmektedir. Tasarım süreci ile birlikte eş zamanlı olarak kullanılan sonlu eleman yazılımları, optimum tasarımın en kısa sürede gerçekleştirilebilmesini sağlamaktadır. Geliştirilen mühendislik yazılımları kullanılarak gerçekleştirilen simülasyonlarla, endüstride yapılan çalışmalarda daha hızlı ve etkin sonuçlara ulaşılmaktadır. Sonlu eleman yazılımları kullanılarak yapılan çalışmaların güvenilirliği, kurulan sonlu elemanlar modeli ve malzeme özelliklerinin doğru bir biçimde modellenmesi ile mümkün olmaktadır. Bu nedenle beyaz eşyalarda uygulanan düşme testi simülasyonlarında enerji yutumlayıcı paketleme malzemelerinin malzeme özelliklerinin doğru bir biçimde modellenmesi gerekmektedir. Beyaz eşya sektöründe paketleme malzemesi olarak çoğunlukla genleştirilmiş polistren tercih edilmektedir. Endüstride strafor veya polimer köpük olarak da adlandırılan genleştirilmiş polistren, petrolden elde edilen ve basma durumunda enerji yutumlama özelliği yüksek bir malzemedir. Paketleme performansının artırılması ve optimum paketleme yapılması strafor malzemenin mekanik özelliklerinin bilinmesi ile mümkün olmaktadır. Paketleme performansının artırılması ile ürünler darbelere karşı daha korunaklı hale getirilebilir. Ürünlerin nakliye esnasında düşme ve darbe sonucu hasar görmeleri engellenerek, ekonomik kayıplar önlenebilmektedir. Bu çalışma kapsamında ankastre bulaşık makinasının düşme testi analizleri ve fiziksel düşme testleri yapılmıştır. Ankastre bulaşık makinasının kütlesi dikkate alınarak, Arçelik A.Ş. bünyesinde yer alan standartlar incelendiğinde, makinanın 25 cm yükseklikten düşme durumunda hasar almaması gerekmektedir. Standartta belirtilen durumda makine, 25 cm'den düz ve kenarları üzerine 10o açılı olarak düşürülmektedir. Henüz prototip aşamasında bulunan bu ürünün üretim onayı alması için bu testlerden hasarsız olarak geçmesi gerekmektedir. Ayrıca, çalışma kapsamında zorlayıcı koşul olarak makinanın 40 cm yükseklikten düşme testleri de yapılmıştır. Sonlu elemanlar analizleri yapılarak gerçekleştirilen düşme analizleri ele alındığında literatürde strafor malzemesinin yüksek gerinim hızlarındaki mekanik özellikleri araştırılmıştır. Fakat literatürde yapılan çalışmalar incelendiğinde Arçelik A.Ş. bünyesinde kullanılan strafor malzemelere ait özellikler bulunmamaktadır. Bu nedenle öncül bir çalışma olarak öncelikle beyaz eşya sektöründeki uygulamalarda kullanılmakta olan strafora ait mekanik özelliklerin belirlenmesi amaçlanmıştır. Literatürde polimer köpük malzemelerin mekanik özelliklerinin belirlenmesi ile ilgili yapılan çalışmalardan strafor malzemesinin mekanik özelliklerini etkileyen parametreler ve mekanik özelliklerin belirmesi için yapılan test çalışmaları elde edilmiştir. Polimer köpük malzemelerin mekanik özellikleri yoğunluk, gerinim hızı ve ortam sıcaklığına bağlı olarak değişmektedir. Düşme testlerinde strafor malzemenin yüksek gerinim hızlarında deformasyona uğradığı bilindiğinden, bu hızlardaki mekanik özelliklerin bilinmesi gerekmektedir. Ülkemizde polimer köpük malzemelerin yüksek gerinim hızlarındaki mekanik özelliklerini belirlemek için uygun test cihazlarına sahip araştırma merkezleri ve üniversiteler bulunmaktadır. Fakat bu araştırma merkezlerinde yer alan test cihazlarının köpük numunelerin test edilmesi için uygun vurucu kafaya sahip olmaması nedeniyle straforun mekanik özelliklerinin belirlenmesi için basit düşme testi düzeneği tasarlanmıştır. Basit düşme testi düzeneğinde 25 cm, 40 cm ve 70 cm yükseklikten serbest düşmeye bırakılan kütlenin, strafor numunesine çarpması sağlanarak, çarpma anındaki veriler toplanmıştır. Düşme testi düzeneğine ivmeölçer, kuvvet ve lazer deplasman sensörleri yerleştirilmiştir. Kurulan düşme testi düzeneği ile 20, 24, 26 ve 30 kg/m3 yoğunluklarda, 50x50x50 mm3 boyutlarındaki strafor numunelerinin yüksek gerinim hızlarındaki mekanik özellikleri belirlenmiştir. Ayrıca gerinim hızının malzemelerin mekanik özelliklerine olan etkisini belirlemek için Zwick standart çekme testi cihazı ile de testler yapılmıştır. Zwick test cihazı ile yapılan testler 200 mm/dak, 500 mm/dak ve 1000 mm/dak düşük yükleme hızlarında gerçekleştirilmiştir. Daha sonra aynı yoğunluktaki numuneler için düşük ve yüksek hızlardaki mekanik özellikler karşılaştırılmıştır. Ankastre bulaşık makinasında paketleme malzemesi olarak 20 kg/m3 yoğunluktaki strafor malzeme kullanılmaktadır. Çalışma kapsamında sonlu eleman paket programı olarak kullanılan Hyperworks programı içerisinde, straforun modellenmesi için kullanılabilecek olası malzeme kartları araştırılmıştır. Straforun modellenmesi için Visko-Elasto-Plastik malzeme kartı kullanılmıştır. Hyperworks programı içerisinde yer alan Radioss eksplisit çözücüsü kullanılarak düşme test düzeneğinin analizleri yapılmıştır. Buradan elde edilen sonuçlar incelendiğinde strafora ait deneysel veriler ile sonlu elemanlar analiz sonuçlarının uyumlu olduğu görülmüştür. Straforun malzeme modeli oluşturulduktan sonra ankastre bulaşık makinasının düşme analizi için sonlu elemanlar modeli kurulmuştur. Ardından ankastre bulaşık makinasında yer alan komponentlerin malzeme özellikleri tanımlanmıştır. Hyperworks programı içerisinde bulunan Radioss çözücüsüne ait malzeme kartları incelenmiştir. Buna göre ankastre bulaşık makinasında yer alan sac parçalar için Johnson-Cook malzeme kartı kullanılmıştır. Öte yandan bulaşık makinasında yer alan plastik komponentler için ise elasto-plastik malzeme kartı kullanılmıştır. Son olarak bulaşık makinasında yer alan ve düşme anında kütlesel özelliklerinden dolayı atalet kuvvetlerine neden olan motor, kompresör ve evaporatör için elastik malzeme kartı kullanılmıştır. Bu komponentlerin sadece kütlesel olarak modellenmesi sağlanmıştır. Ankastre bulaşık makinasının sonlu elemanlar modeli kurulduktan sonra, standartta belirtilen 25 cm ve zorlayıcı koşul olarak belirlenen 40 cm yükseklikten düşme analizleri yapılmıştır. Makinanın 25 cm yükseklikten düşmesi sonucu herhangi bir hasar riski görülmemiştir. Fakat 40 cm yükseklikten düşme durumlarında makinanın alt kısmında yer alan şasinin kompresör bağlantı bölgesinde plastik deformasyonlar görülmektedir. Son olarak makinanın Ankara Bulaşık Makinası İşletmesi'nde bulunan düşme testi düzeneği ile fiziksel düşme testleri gerçekleştirilmiştir. Çalışma henüz prototip aşamasında olduğundan dolayı testler aynı makina kullanılarak yapılmıştır. Gerçek durumdaki fiziksel düşme testlerinde, her bir senaryo için farklı makina kullanılmaktadır. Bu durumda da test maliyeti artmaktadır. Yapılan testlerde her bir düşme senaryosunun ardından paketleme malzemesi çıkarılarak makinanın hasar durumu incelenmiştir. Ayrıca her testten önce makina kullanılmamış paketleme malzemesi ile kaplanarak testler yapılmıştır. Sonuçta makinanın 25 cm yükseklikten düşmesi sonucu makine üzerinde herhangi bir hasar gözlenmemiştir. Öte yandan 40 cm yükseklikten düşme sonucunda makine üzerinde yer alan komponentlerde hasar meydana gelmiştir. Fiziksel düşme test sonuçları ile analiz sonuçları uyumluluk göstermiştir.
In white appliances sector, the process of storage and transportation of products, impact and the falling damage to products lead to significant cost. The products may become unusable or may need a costly repair as a result of the possible dropping and impact cases. After the products are out of the production line, there is always a risk that the product may be subjected to drops and impacts. Therefore, to avoid this possible damage during transportation, white appliances are packaged using protective materials. Polymer foam materials that have high energy absorbing capability under compression are preferred in the white appliances industry. In order to guarentee that the packaged products have sufficient level of protection againist possible dropping or impacts, these products are subjected to so-called dropping tests. Such tests may become quite expensive if the tests are to be repeated many times in case the prototype does not meet the requirements of the standards. Thus, engineers who work in the industry are searching for alternative methods to minimize such costs. Nowadays, the importance of computer aided engineering tools is becoming more important as computer technology is advancing. Finite elements software, which is one of main computer aided engineering tools, is commonly used in the industry. This means that complex engineering problems can be modeled and solved numerically by using computer aided engineering tools. Finite element software are being used during design process, helping the engineers optimise their design in the shortest time. Projects are being completed faster and more effective by using advanced enginnering tools in industry. However, accuracy and reliability of the numerical simulations depend on many factors including the material properties of parts comparing a product. Therefore, mechanical properties of the packaging materials used in the white appliances industry must be modelled accurately for drop test simulations. Expanded polystrene is mostly preferred as a packaging material in household industry. Expanded polystrene, also named as styropor or polymer foam, is obtained from petroleum and has a high energy absorbing property under compression. Mechanical properties of styropor materials must be known for numerical simulations aiming to optimise the performance of the packaging. Optimized protection of goods against impact during transportation can save very significant amount of cost to the industry. In this study, physical drop tests and drop tests analysis of built-in dish washer are carried out. Associated drop test standarts required that built-in dish washer should have no damage when product is dropped from 25 cm height. As specified in the standard, drop tests should be carried out as free falling tests with 0o and 10o inclination angles with respect to the edges of the product. The built-in dish washer machine should not be damaged during these tests to get. On the other hand, drop tests from higher levels are also carried in practise to assess the impact resistance of products. For instance, built-in dish washer was dropped from 40 cm height to evaluate the impact resistance. In this thesis, firstly, mechanical properties of expanded polystrene materials at high strain rates are invastigated in the literature for drop test analysis. However, when studies available in the literature are rewieved, it is not possible to find the properties of packaging foam materials used in Arçelik. Therefore, determination of the mechanical properties of the foam material became one of the main tasks in this thesis. It was found in the literature that mechanical properties of polymer materials mainly depend on density, strain rate and ambient temperature. It was therefore necessary to obtain the material properties at appropriate strain rates for drop tests described in the standards. There are available research centers and universities having test equipments and devices suitable for the determination of the mechanical properties of polymer materials at various strain rates. However, available test equipments were found to be not capable of carrying out the tests at the desired strain rates. Therefore, a drop test rig was designed and developed in this thesis to determine the mechanical properties of polymer foam material used in white appliances industry at desired strain rates. After free falling mass is dropped from 25 cm, 40 cm and 70 cm heights on a styropor specimen, the appropriate data are collected using appropriate sensors of the drop test rig. Force sensor, laser displacement sensor and accelerometer are utilised in the drop test rig. A cubic specimens with dimensions 50 x 50 x 50 mm3 with variying densities (20, 24, 26 and 30 kg/m3) were tested at high strain rates using the test rig developed in the thesis. Also, the same specimens were tested using Zwick standart tensile test machine under uniaxial compression at low strain rates so as to compare strain rate effects on mechanical properties of foam materials. After all tests were carried out, mechanical properties of the foam materials were compared at low and high various strain rates. 20 kg/m3 density styropor is used as a packaging material for packaging the built-in dish washer in this study. Hyperworks finite element software was used to model and simulate the drop test rig. Hexahedral elements are commonly used in literature to model foam materials. However, tetrahedral elements were used to model packaging materials in built-in dish washer because of complex geometry of packaging materials. Therefore, finite element model of polymer foam must be verified not only hexahedral elements but also tetrahedral elements to obtain accurately results from drop test simulations of the built-in dish washer. On the other hand, various material models were researched in Hyperworks finite element software to model accurately for polymer foam materials and visco-elasto-plastic model was chosen to model styropor. Radioss explicit solver in Hyperworks was utilised for the numerical simulation of the drop test rig. Then, the results obtained from the transient simulations were compared with the drop test results. It is found that the results obtained from measurements and simulations agree very well both hexahedral and tetrahedral elements. After material model of styropor was verified, a finite element model suitable for transient non-lineer analysis for the built-in dish washer was created. Built-in dish washer components can be divided into four groups that are sheet metals, plastic components, auxillary components and packaging materials. After all components of the machine were created, material properties of individual components were defined. For sheet metal components of machine, Johnson-Cook material model was used. Johnson-Cook material model is commonly used in literature for isotropic materials such as sheet metals. On the other hand, elasto-plastic material model was selected to define properties of plastic components such as chassis, air channel, salt cellar. Finally, auxillary components such as motor, compressor and evaporator whose inertia properties are very important during impact are defined using elastic material model. After the finite element model of built-in dish washer machine was ready, drop test simulations were carried out for 25 cm and 40 cm height cases. The results of the drop test simulations showed that there was no risk of any damage to the machine when it was dropped from 25 cm height that is specified in standard. However, drop test simulations for 40 cm height revealed that some plastic deformations could occur, at the plastic bottom chassis where the compressor is assembled to the machine. Physical drop tests were also carried out in Ankara Dish Washer Plant using a prototype built-in dish washer. Only one prototype was available for physical drop tests. Therefore, the same built-in dish washer prototype was used in tests with varying drop tests heights. After each drop test, packaging material was removed from built-in dish washer and the possible damage to the machine was inspected. Also, before each test, built-in dish washer was packed using unused packaging material. As predicted using numerical simulation, physical drop test from 25 cm height also showed no sign of any damage on machine, confirming that the product has sufficient resistance to drop damage. However, some damage occurred when the machine was dropped from 40 cm height. This result is also in agreement with numerical simulations.
In white appliances sector, the process of storage and transportation of products, impact and the falling damage to products lead to significant cost. The products may become unusable or may need a costly repair as a result of the possible dropping and impact cases. After the products are out of the production line, there is always a risk that the product may be subjected to drops and impacts. Therefore, to avoid this possible damage during transportation, white appliances are packaged using protective materials. Polymer foam materials that have high energy absorbing capability under compression are preferred in the white appliances industry. In order to guarentee that the packaged products have sufficient level of protection againist possible dropping or impacts, these products are subjected to so-called dropping tests. Such tests may become quite expensive if the tests are to be repeated many times in case the prototype does not meet the requirements of the standards. Thus, engineers who work in the industry are searching for alternative methods to minimize such costs. Nowadays, the importance of computer aided engineering tools is becoming more important as computer technology is advancing. Finite elements software, which is one of main computer aided engineering tools, is commonly used in the industry. This means that complex engineering problems can be modeled and solved numerically by using computer aided engineering tools. Finite element software are being used during design process, helping the engineers optimise their design in the shortest time. Projects are being completed faster and more effective by using advanced enginnering tools in industry. However, accuracy and reliability of the numerical simulations depend on many factors including the material properties of parts comparing a product. Therefore, mechanical properties of the packaging materials used in the white appliances industry must be modelled accurately for drop test simulations. Expanded polystrene is mostly preferred as a packaging material in household industry. Expanded polystrene, also named as styropor or polymer foam, is obtained from petroleum and has a high energy absorbing property under compression. Mechanical properties of styropor materials must be known for numerical simulations aiming to optimise the performance of the packaging. Optimized protection of goods against impact during transportation can save very significant amount of cost to the industry. In this study, physical drop tests and drop tests analysis of built-in dish washer are carried out. Associated drop test standarts required that built-in dish washer should have no damage when product is dropped from 25 cm height. As specified in the standard, drop tests should be carried out as free falling tests with 0o and 10o inclination angles with respect to the edges of the product. The built-in dish washer machine should not be damaged during these tests to get. On the other hand, drop tests from higher levels are also carried in practise to assess the impact resistance of products. For instance, built-in dish washer was dropped from 40 cm height to evaluate the impact resistance. In this thesis, firstly, mechanical properties of expanded polystrene materials at high strain rates are invastigated in the literature for drop test analysis. However, when studies available in the literature are rewieved, it is not possible to find the properties of packaging foam materials used in Arçelik. Therefore, determination of the mechanical properties of the foam material became one of the main tasks in this thesis. It was found in the literature that mechanical properties of polymer materials mainly depend on density, strain rate and ambient temperature. It was therefore necessary to obtain the material properties at appropriate strain rates for drop tests described in the standards. There are available research centers and universities having test equipments and devices suitable for the determination of the mechanical properties of polymer materials at various strain rates. However, available test equipments were found to be not capable of carrying out the tests at the desired strain rates. Therefore, a drop test rig was designed and developed in this thesis to determine the mechanical properties of polymer foam material used in white appliances industry at desired strain rates. After free falling mass is dropped from 25 cm, 40 cm and 70 cm heights on a styropor specimen, the appropriate data are collected using appropriate sensors of the drop test rig. Force sensor, laser displacement sensor and accelerometer are utilised in the drop test rig. A cubic specimens with dimensions 50 x 50 x 50 mm3 with variying densities (20, 24, 26 and 30 kg/m3) were tested at high strain rates using the test rig developed in the thesis. Also, the same specimens were tested using Zwick standart tensile test machine under uniaxial compression at low strain rates so as to compare strain rate effects on mechanical properties of foam materials. After all tests were carried out, mechanical properties of the foam materials were compared at low and high various strain rates. 20 kg/m3 density styropor is used as a packaging material for packaging the built-in dish washer in this study. Hyperworks finite element software was used to model and simulate the drop test rig. Hexahedral elements are commonly used in literature to model foam materials. However, tetrahedral elements were used to model packaging materials in built-in dish washer because of complex geometry of packaging materials. Therefore, finite element model of polymer foam must be verified not only hexahedral elements but also tetrahedral elements to obtain accurately results from drop test simulations of the built-in dish washer. On the other hand, various material models were researched in Hyperworks finite element software to model accurately for polymer foam materials and visco-elasto-plastic model was chosen to model styropor. Radioss explicit solver in Hyperworks was utilised for the numerical simulation of the drop test rig. Then, the results obtained from the transient simulations were compared with the drop test results. It is found that the results obtained from measurements and simulations agree very well both hexahedral and tetrahedral elements. After material model of styropor was verified, a finite element model suitable for transient non-lineer analysis for the built-in dish washer was created. Built-in dish washer components can be divided into four groups that are sheet metals, plastic components, auxillary components and packaging materials. After all components of the machine were created, material properties of individual components were defined. For sheet metal components of machine, Johnson-Cook material model was used. Johnson-Cook material model is commonly used in literature for isotropic materials such as sheet metals. On the other hand, elasto-plastic material model was selected to define properties of plastic components such as chassis, air channel, salt cellar. Finally, auxillary components such as motor, compressor and evaporator whose inertia properties are very important during impact are defined using elastic material model. After the finite element model of built-in dish washer machine was ready, drop test simulations were carried out for 25 cm and 40 cm height cases. The results of the drop test simulations showed that there was no risk of any damage to the machine when it was dropped from 25 cm height that is specified in standard. However, drop test simulations for 40 cm height revealed that some plastic deformations could occur, at the plastic bottom chassis where the compressor is assembled to the machine. Physical drop tests were also carried out in Ankara Dish Washer Plant using a prototype built-in dish washer. Only one prototype was available for physical drop tests. Therefore, the same built-in dish washer prototype was used in tests with varying drop tests heights. After each drop test, packaging material was removed from built-in dish washer and the possible damage to the machine was inspected. Also, before each test, built-in dish washer was packed using unused packaging material. As predicted using numerical simulation, physical drop test from 25 cm height also showed no sign of any damage on machine, confirming that the product has sufficient resistance to drop damage. However, some damage occurred when the machine was dropped from 40 cm height. This result is also in agreement with numerical simulations.
Açıklama
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2015
Anahtar kelimeler
ağırlık düşürme yöntemi,
polistiren köpük,
sonlu elemanlar analizi,
drop-weight test method,
polystyrene foam,
finite element analysis