# Automatic Evaluation of the Robotic Production Process for an Aircraft Jet Engine Casing
## 1 Introduction  
The jet engines that operate in modern passenger aircrafts are built of many complex structural assemblies whose manufacturing methods vary. To reduce their production costs and weight, which in turn reduces the operating costs of jet engines, the precision casting technology that has been applied so far is often replaced by implementations of complex thin-wall assemblies [1]. These designs are manufactured with advanced methods of joining materials, followed by precision machining of the assemblies. Among the many technologies of thin-wall component joining, welding belongs to the most popular ones. Welded joints mainly replace rivet joints. This applies both to defense and commercial aircraft production. The main reasons for this trend is the reduction in manufacturing costs and the improvement in flight safety, obtaining better structural integrity. Diffusion, laser beam, and electron beam welding is preferred in commercial aircraft designs. Electron beam welding is extremely popular for joining titanium alloys for military aircraft [2]. Laser beam welding is used for joining the components of cases for large commercial aircraft that have been previously riveted. Currently developed and implemented space engineering technologies are used in the production of aviation components. This applies to friction stir welding (FSW) and variable polarity plasma-arc welding (VP-PAW) [2]. These technologies have been applied to the production of mission-critical components for space rockets. It seems that diffusion welding of aluminum alloys is one of the processes that is not yet widely used. This paper focused on robotic TIG (tungsten inert gas) welding of thin-wall workpieces for a jet engine. The welded workpiece was large and very complex in shape. It was the complexity of its shape that prevented the application of modern joining technologies, such as FRW (friction welding) in which metals are joined by mechanical friction. The connection areas between the joined metal workpieces are not melted, so no defects develop from melting and solidification, while the welds could be just as strong as the base material. FRWis capable of joining workpieces with relatively straightforward cross-sections, especially those of a circular shape. It is the technology of choice for joining the components of turbine shafts and casings and is sometimes selected for joining aluminum landing gear parts. Another version of this process is FSW (friction stir welding) [3]. FRW and FSW enable welding of aluminum alloys that have been considered non-weldable [2]. The shape complexity of the mentioned part also eliminated other joining methods such as electron beam welding or laser beam welding. In both processes the beam delivery system is very large. During TIG welding an electrical arc is generated between the material and a non-melting tungsten electrode, shielded by an inert gas (such as argon or helium or mixtures of the two). Materials are joined by melting them and this is considered as a manual and automatic welding processes. A filler material can also be added directly to the weld pool. TIG welding can produce welds of high quality and purity. This process is very good in joining workpieces of stainless steel, aluminum, and aluminum alloys. The advantages of TIG welding include the following: very good weld quality, produced at a good work efficiency; welding of various materials and alloys; the possibility of welding workpieces of various thicknesses, from less than 1 mm to approximately 10 mm; and very good control over welding precision. Disadvantages of this method are the requirement of the use of covers during welding in open areas, lower production speed, and weld quality dependence on the welders' skills in manual welding. A comparative analysis of the work performed by an experienced professional and the work of a beginner welder is discussed in [4]. The benefits made TIG welding the method of choice for the joining of the intermediate case of the PW800 jet engine.