Havacılık sektöründe kullanılan döküm malzemelere uygulanan talaşlı imalat yöntemlerinin geliştirilmesi
Development of mechanic manufacturing methods applied to casting materials used in the aviation sector
Yazar: BURAK ALPEREN TUNÇ
Danışman: PROF. DR. LEVENT TRABZON
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Malzeme ve İmalat Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Bu çalışmanın amacı, havacılık sektöründe kullanılan döküm ham malzemeli parçaların işlenmesi sırasında yeni metotlar geliştirilerek, imal edilecek parçaların teknik resimlerine daha uygun imalat yapılabilmesine katkıda bulunmaktır. Bu amaca yönelik olarak, çalışmada kullanmak için faydalanılan alanlarda araştırmalar yapılıp, sonrasında hedeflenen amaca uygun deney çalışması yapılmıştır.
Uygulanmaya başlanması çok eski yıllara dayanan döküm imalat teknolojisi günümüzde birçok alanda yaygın olarak kullanılmaktadır. Döküm imalatının bu derece yaygın olarak kullanılması, yöntemin her geçen gün geliştirilmesine ve farklı metotlarla uygulanmasına katkı sağlamıştır. Çoğu sektörde olduğu gibi havacılık sektöründe de önemli bir yer tutan döküm teknolojisi, farklı çeşitleri ile havacılık sektörüne hizmet etmektedir. Bu çalışmada, döküm imalatın nasıl yapıldığı; döküm imalat çeşitleri; bu çeşitlerin birbirlerine göre üstünlükleri ve zayıflıkları; ve havacılıkta nasıl ve neden kullanıldıkları irdelenmiştir. Yine havacılık sektöründe kullanılan hassas döküm yöntemi detayları ile araştırılmış, hangi parçalarda daha yaygın kullanıldıkları belirtilmiştir. Bununla birlikte döküm imalatında sık karşılaşılan problemler araştırılmıştır.
Ülkemizde son yıllarda öneminin arttığını gördüğümüz savunma ve havacılık sektörü, gelişmeye ve büyümeye açık bir sektördür. Çalışmamızda gaz türbinli motorların çalışma prensipleri, çeşitleri, birbirlerine göre olan farklılıkları ve kullanım alanları araştırılmıştır. Bunlarla birlikte motorların yine birbirlerine karşı üstünlükleri detaylandırılmıştır. Barındırdıkları modüllerin görevlerini, diyagramlarını anlatan çalışmamız farklı kaynaklardan bulunan kritik parçaların görevlerini ve yapılarını barındırmaktadır. Bununla birlikte deney parçası olan Nozzle Guide Vane (NGV) parçasının detaylı görevi ve yapısı araştırılmıştır.
İmalat yapılırken göz önüne alınan en önemli kriter kalite isterlerinin sağlanmasıdır. İmalatın kalite isterlerinin belirtildiği teknik resim bizlere imalat yöntemleri için yol gösterirken, bir yandan da kalite kontrolünün sağlanması için gerekli olan ölçüm yolları hakkında fikir vermektedir. Yaygın olarak kullanılan Koordinat Ölçme Makinesi (CMM) yerine deneyimizde kullanılan 3D Metroloji yöntemi araştırılmış olup, diğer yöntemlere göre avantajları ve dezavantajları belirtilmiştir.
İki adet döküm ham malzemenin farklı iki yol ile imalatının yapıldığı ve düzeltme metodunda 3D metroloji sisteminden ve geleneksel talaşlı imalat yöntemlerinden faydalanılan deneylerin sonuçları değerlendirildiğinde, çalışmanın hipotezini doğrular şekilde düzeltme prosesinin uygulandığı parçanın, düzeltme prosesinin uygulanmamış parçaya göre kanatçık konumlarının teknik resim değerlerine daha uygun olduğu görülmüştür.
Deney sonuçları incelendiğinde, hipotez olarak iddia edilen, kanatçıkların parçanın diğer bölgelerine göre konumlarının daha dar toleranslarda imal edilmesinin, iddia edilen hipotezin bu deney parçaları için doğru olduğu kanısına varılmıştır. Kanatçıkların konumları, düzeltme yapılan deney parçasında daha uygun olduğu analiz edildikten sonra, döküm olarak kalan diğer yüzeylerin farklılıklarının ise dökümün kendisinden gelen varyasyonlar olduğu tespit edilmiştir. Son olarak 14 adet parçada deney uygulanmış olup 12 adet parçanın deneyleri başarı ile sonuçlanmıştır. Deneyin başarı yüzdesi %85.7 dir. Parça başına 2.5 saat talaşlı işleme süresinden kazanım sağlanmıştır. Bir adet motorda 12 adet NGV parçasının kullanıldığı düşünüldüğünde motor başına 25 saatlik bir kazanç elde edilmiştir. Hurda parça oranında ise %2 lik bir azalmaya gidilmiştir.

Abstract:
The goal of the study is to develop new methods during the processing of parts with cast raw materials used in the aviation industry, and to manufacture more suitable for the technical drawings of the parts to be manufactured. In order to use it in the study for this purpose, researches were made in the fields that were used, and then an experimental study was carried out in accordance with the targeted purpose.
Nowadays, Application of Casting manufacturing technology which dates back to old years is vastly used in many areas. The widespread use of casting production has supported the development of the method day by day and its application with different methods. Casting technology, which has an important place in the aviation sector as in every sector, serves the aviation sector with its different varieties. The main reasons for its widespread use in aviation are that it can produce parts close to the final parts, achieve high performance and are more cost-effective than other methods. In this study, the types of molds in casting production and the differences of these molds from each other, the advantages and disadvantages of the casting method compared to other production methods are explained. In addition to these, the advantage when considering the mounting conditions and the advantage of lower total weight are explained with examples. The advantages and weaknesses of the sand mold casting method, plaster mold casting method, ceramic mold casting method, metal mold casting method, pressure casting method, centrifugal casting method relative to each other are basically investigated. The maximum surface qualities that can occur in each casting method are shared in a table. The rate of manufacturing with zero error is very low.
 As in every production, certain problems are encountered during casting production. The quality control process is also applied for the casting process before, during and after each manufacturing method. It is important to detect the errors that may occur before production, both to prevent loss of time and to prevent economic loss. In the study, the basic faults originating from the casting process and making the production difficult were investigated. The main causes of these are parts and design errors, core errors, runner and feeder system errors. These situations leave basic damages such as the formation of fractures or cracks in the parts, and the crushing of the parts by the molds.
The last subject of the research on casting manufacturing is the casting manufacturing in the aviation industry and the precision casting method, which also constitutes the manufacturing method of the test piece. In the researches, 82% of the raw materials used in the GE CF6 engine are forged materials, while 6% are cast materials. In our study, a table showing which casting method some basic aviation parts are produced is shared. The precision casting method, which is one of the most important advantages of its sensitivity and surface quality, is the casting method used in the manufacturing methods of parts such as vane and blade, which are shown as critical parts of the engine. Similarly, the replicast casting method has been developed for the precision production of thin-profile parts. The only difference in the replica casting method compared to the precision casting method is the use of foam models. In our study, the history of precision casting method in aviation was investigated. The main reason why investment casting has been preferred over forged material in recent years, the cooling holes can be removed as castings are detailed. Thus, both cost savings and non-heat effected zones can be obtained. In the study, all the advantages and disadvantages of investment casting have been stated, and the types of investment casting method have been investigated in detail. Finally, the comparison of the investment casting method with other casting methods is presented with a detailed table.
Another research subject of the study is gas turbine engines. The defense and aerospace sector, whose importance we have seen has increased in our country in recent years; It is a sector open to development and growth. Working principles of gas turbine engines in our study; Brighton cycle has been tried to be explained in detail. In this section, which includes P-V and T-S diagrams, the shapes of pressure, volume, temperature and entropy changes in the modules are shown. Along with these, the types of gas turbine engines; turbojet, turbofan; The differences, usage areas and features of turboprop and turboshaft engines are tried to be explained by supporting them with figures. What is the critical by-pass ratio in turbofan engines, its importance and for what purpose the ratio is determined are detailed. The differences between low and high by-pass ratio turbofan engines are explained by supporting with figures. The turboshaft engine, including the test piece, is based on the principle of obtaining shaft power, instead of generating thrust, unlike other engines. In the turboshaft engine, the gases that expand in the high pressure turbine are used to generate power in the free power turbine. Basically, these are turboshaft engines consisting of two parts; The gas generator containing the air intake, compressor, combustion chamber and high pressure turbine, and the power section containing the power turbines, shaft and gears. In our country, the turboshaft engine was first produced by TEI after obtaining the license of the T700 engine produced by GE. Apart from this, the TEI TS1400 engine produced by TEI company was also produced as a prototype and completed its tests. In this study, in which the types and differences of gas turbine engines are explained, the processes that need to be done to increase engine efficiency are also mentioned.
After explaining the types of gas turbine engines, the research is detailed by explaining the engine parts. In the section where the tasks of the air intake module are explained, it is mentioned how the module design should be. This section, which also affects the engine efficiency, is the first module where the air meets the engine. A separate paragraph is reserved for the compressor module where the air coming out of the air intake encounters. In this section, the duties of the compressor module and the reason for the connection with the turbine shaft are explained. In addition to these, the differences, advantages and weaknesses of two different compressor types compared to each other are explained in detail with values. Apart from these, the types of materials preferred in the compressor module are explained with their reasons. The tasks and material types of the combustion chamber module after the compressor are explained. How the air is burned in the combustion chamber module has been investigated. It is explained how the air coming out of the combustion chamber is converted to work in the turbine module. In addition, the functions and cooling types of the vane and blade parts, which are the critical parts of the turbine module containing the test piece, are investigated in this section. The last research topic of gas turbine engines is the structure and functions of exhausts. The exhaust module is explained with the figures.
The most important criterion taken into consideration while manufacturing is to meet the quality requirements. The technical drawing, in which the quality requirements of the manufacturing are specified, not only guides us for manufacturing methods, but also gives an idea about the measurement ways necessary to ensure quality control. Along with Industry 4.0, computer aided measurement methods needed after CAD and CAM have also been developed. Instead of the generally used CMM (Coordinate Measuring Machine), the 3D Metrology method used in our experiment has been researched, and its advantages and disadvantages compared to other methods have been specified. The advantages of the 3D Metrology method are detailed with sample measurement shapes.
For the purpose of the study, the previous studies that were brought to the literature were searched and the details of the studies were examined. The methods used in 2 different studies are explained in detail, supported by figures. In the study, different from the researches made for our purpose, the subjects that will be included in the literature are mentioned.
After the necessary literature research was done, some experiments were carried out in order to confirm the said hypothesis. In the experiment, two identical casting raw materials were produced in two different ways and the results of these two productions were evaluated. In the correction method used in the experiment, the 3D metrology system and traditional machining methods were used. The methods and experimental steps used in the experiment were supported with detailed figures, and the importance and purpose of each step were explained. The methods of attaching the parts used in the experiment to the fixture and the bench are shown with sample figures. Experiment results were taken together with their outputs and the differences between the two results were explained in detail.
At the end of the experiments, the same measurements were made on both test pieces in order to meet the quality requirements according to the final model, and these measurements are shown with figures. The 3D Metrology method was used to measure the final models. While making these measurements, the kissing method was not made as a best fit, but by making them kiss from the datum surfaces. It is explained that the reason for this is that the datums in the part technical drawing are given from the surfaces to be mounted. The positions of the fins were analyzed with numerical values that were more appropriate in the corrected test piece. Apart from these, the similarities in the processed areas were supported by numerical and visual data. The reasons for the similarities are explained by considering the manufacturing logic. The differences between the regions, except for the fins, which remain in the form of casting, are explained with numerical and visual figures. It has been explained that these differences are the differences arising from the casting method itself and have nothing to do with the machining.
At the end of the experiment, it was determined that the hypothesis claimed before the experiment was confirmed for these parts. In particular, the test process was successful for these parts. Except that the fins, which is the purpose of the experiment, are suitable, it has been observed that both parts are produced in accordance with the part technical drawing. Although the test piece without the Qualify method is in accordance with the part technical drawing, it is thought that it will not be preferred due to the motor assembly and efficiency. The qualifying process, which is carried out in accordance with the purpose of the experiment, is a method open to development. It is thought that the process applied to cast parts can also be applied to parts produced with metal additive manufacturing in the future. Finally, experiments were applied on 14 pieces and the experiments on 12 pieces were successfully concluded. The success rate of the experiments is 85.7%. 2.5 hours time reduction per piece has been gained. Considering that 12 NGV parts are used in one engine, a gain of 25 hours per engine is obtained. There was a 2% reduction in the scrap rate.