Nowadays the use of thermoplastic materials has been increasing steadily, especially in automotive industries because of its positive effects on vehicle weight which is directly related to fuel consumption. These materials also provide a cost reduction for companies comparing with the steel or other similar materials. The other benefits of the thermoplastic materials are their high stiffness, excellent crashworthiness due to their energy-absorption characteristics, strength-to-weight ratios, fatigue and optimum design. Through their structure occurred by the polymer resins, thermoplastic materials can physically become a homogenized liquid when heated and hard when cooled. The thermoplastic materials are able to reheat, remolded and have good thermal and chemical stability. Also, these materials can be easily recycled which provides a lower environmental impact on the automotive industry. Due to the advantages of the thermoplastic materials, automotive industries have been using these technology in vehicle parts such as door panels, seat backs, load floor, engine cover, front end module, airbag housing, crash boxes, bumpers, instrument panel, air intake manifold, air duck, cross car beam, pedal brackets, gas tank carrier, etc. In order to produce the thermoplastic materials, a number of different methods (i.e. mechanical fastenings, ultrasonic assembly, metal inserts, snap fits, electromagnetic and heat welding, solvent/adhesive bonding) are proposed in the literature and most of them are successfully carried out in industrial applications. However, the identifying the joining technique according to the application area is an important issue to obtain appropriate material. Therefore, this paper presents a literature review of joining methods for thermoplastic materials and classifies the methods according to the structure of the joining technique. Within this context, more than 50 studies about joining techniques for thermoplastic materials are considered the methods are grouped into three main categories: chemical joining techniques, mechanical joining techniques, and thermal joining techniques. Chemical joining methods melt the surfaces of the materials by using a chemical solvent. By using the solvent, one plastic material is joined to itself or the material is joined to another type plastic that dissolves in the same solvent. In mechanical joining techniques, the materials are bonded by using some physical methods such as clipping, clamping, screwing, riveting, etc. Similarly, in thermal joining techniques the surface of the materials to be joined are heated and a pressure is applied until the thermoplastic material is formed. As a result of the review, the differences and efficiency of the joining methods are pointed out in the study with paired comparisons. Moreover, the real life applications of joining methods for thermoplastic materials in the automotive industry are presented. In this paper, effects of the joining techniques on pedestrian and occupant safety are also reviewed by taking into account the high-stress concentration factor, the inconvenient manufacturing process and, the reaction force peaks. Finally, the future challenges of the three categorized are summarized.
Öz: Otomotiv endüstrisindeki araç aydınlatma sistemlerinde kullanılan termoplastik malzemelerin birleştirilmesinde lazer iletim kaynağı üstün özellikleri nedeni ile öne çıkmaktadır. Ancak, proses parametreleri kaynak kalitesini doğrudan etkilediği için etkilerinin tespit edilmesi oldukça önemlidir. Bu çalışmada 2,7 mm kalınlığındaki Akrilonitril bütadien stiren (ABS) ve şeffaf Polimetil metakrilat (PMMA) malzemeler LPKF Twinweld 3D 6000 lazer cihazı ile birleştirilmiştir. Lazer iletim kaynağındaki önemli parametreler olan lazer gücü, baskı kuvveti ve ilerleme hızının etkileri incelenmiştir. Yapılan çalışmada lazer gücü 20-50 W aralığında, ilerleme hızı 30-150 mm/s aralığında ve baskı kuvveti 55-85 N aralığına çalışılmıştır. Farklı parametre kombinasyonlarında birleştirilen numuneler çekme testlerine tabi tutularak mekanik dayanımları incelenmiş ve parametreler ile ilişkilendirilmiştir. Yapılan testler sonucunda en yüksek ortalama mekanik dayanım ve ortalama kopma uzaması 30 W, 70 mm/s ve 70 N parametre kombinasyonunda elde edilmiştir. Diğer tüm parametrelerin sabit tutulduğu durumda mekanik dayanım üzerindeki en etkili parametrenin lazer gücü olduğu görülmüştür.
Emisyon standartlarının sürekli geliştirilmesinden dolayı ağırlık azaltma bu standartları yakalama açısından önem kazanmıştır. Yakıt tüketimi ve performans iyileştirmeleri için maliyetleri kontrol altında tutarken tüm araç bileşenlerinin ağırlığını azaltmak, araç ağırlık azaltması için yenilikçi çözümlere yol açmıştır. Araç ağırlık azaltma çalışmalarında çelik yerine çelik kullanımını azaltmak için polimer kompozit malzemelerin kullanılması dikkat çekicidir. Farklı sektörlerde yaygın olarak kullanılan termoset malzeme bazlı kompozitler, üretim kısıtlamaları ve geri dönüşüm eksikliği nedeniyle binek araçların üretiminde yer bulamamıştır. Seri üretime uygun olarak üretilen ve aynı mekanik performanslarla geri dönüştürülen sürekli elyaf takviyeli termoplastik kompozitler, otomotiv sektöründe artan uygulamalar bulmaktadır. Bu çalışmada, araçlarda metal akü taşıyıcı kısmı yerine sürekli elyaf takviyeli termoplastik kompozit akü taşıyıcı geliştirilmiştir. Bu çalışmada; yapısal olan taşıyıcı çelik bir akü taşıyıcı, hafifletme amaçlı sürekli elyaf takviyeli termoplastik kompozit malzemelere uygun olarak tasarlanmış, sanal analizleri yapılarak üretilmiş ve araç başına 0.5 kg ağırlık azaltımı sağlanmıştır. Tasarım aşamasından itibaren parça için detaylı güvenlik, doğal frekans ve aşırı yükleme analizleri yapılarak meydana gelen yüksek gerinim değerlerini azaltmak için iyileştirmeler yapılmıştır.
In today's competitive business environment the automotive industries aim to increase the usage of the plastic materials in automobile components in order to reduce the weight of the vehicles. Although the plastic materials provide a considerable savings on vehicle weight, these materials have some problems to be solved. One of the difficult problems encountered in the production of plastics is the flow lines on surfaces because of its unpredictable behavior. As a result, the considered problem faced by automobile companies often spend plenty of time and money is an issue to resolve. In this study "the source of plastic flow lines on automotive external aesthetical parts'' is investigated by using material flow analysis tool of Autodesk Simulation Moldflow 2016®. According to conventional methodologies; weld lines, temperature differences, filling times, clamping forces, shrinkages parameters are examined deeply before tooling phase especially to eliminate aesthetical problems. Considering these conventional methodologies, an unordinary situation was observed, such as flow lines on visible surfaces in the front bumper after the tool stage. Therefore, the flow analysis tool is used simulate these flow lines on the material. Flow directions and flow velocity are comprehensively examined step by step during filling analysis. As a result of the analyzes, the geometric factors that affect the balance of flow and brings turbulence are detected. After the root cause analysis for plastic deformation, different design proposals are analyzed to find the best solution. Analyzes are repeated in the same conditions that are considered to be made for all geometric changes. The experiment results are comparatively analyzed and the solution that has the best flow balance is selected.
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