Reverse Engineering and 3D Printing of Turbine Housing for Tank Diesel Turbo Engine

Abstract

The tank uses a twin turbo diesel engine equipped with two turbocharger systems for high output. The main component of the turbocharger system is the turbine housing through which the exhaust flows. Turbine housing is manufactured through a sand casting process, taking into account the shape and material characteristics according to the environmental conditions in which it is used. Currently, turbine housing is imported, and local production is necessary. In this study, basic research was conducted to localize the turbine housing of a tank diesel turbo engine. Reverse engineering and finite element analysis of the imported turbine housing were performed. The prototype of the turbine housing was printed using FDM and PBF 3D printers. The prototype of the turbine housing printed with an FDM 3D printer has an overall appearance similar to 3D modeling, but the printed surface of the whorl part is rough. The prototype printed with the PBF 3D printer is completely identical to the 3D modeling, including the whorl part.

1. Introduction

The tank Leopard 2 developed in Germany is equipped with a liquid-cooled four cycles V12 twin-turbo diesel engine. Engine capacity is 47,600 cc and output is 1,500 HP. It is a twin turbo diesel engine equipped with two turbocharger systems for high engine output[1,2]. The turbocharger system converts the pressure energy of the exhaust discharged from the engine into the rotational power of the turbine, and the rotational power is transmitted to the compressor, which injects compressed air into the engine combustion chamber, thereby improving the engine's output[3-5].

The driving principle of the turbocharger system is as follows. The engine's exhaust is transmitted to the turbine through the manifold, and the turbine wheel rotates due to the exhaust pressure. Since the turbine wheel and compressor wheel are connected by a shaft, the rotational force of the turbine wheel acts as the rotational force of the compressor wheel, and the outside air is compressed. Compressed air's temperature rises due to heat transfer and high pressure, but it cools down again as it passes through the intercooler device. Cooled compressed air enters the engine through the throttle valve. The air sucked in for the engine's piston movement is compressed air with a higher density than atmospheric pressure, so complete combustion is induced. This causes the engine's explosion power to increase. Therefore,

high output and high torque are produced. It is known that turbo engines improve engine output by about 60% compared to naturally aspirated engines[5-7].

As the national security environment around the world reaches a major turning point, European and Middle Eastern countries are becoming more active in order to appropriately respond to potential future risks. Defense spending is expected to increase significantly to strengthen national defense capabilities, and exports from defense companies are expected to continue to increase in the future[8]. Therefore, research and production activities for domestic production and export of defense components must be actively carried out.

The main components of the turbocharger system are the turbine housing through which the exhaust flows. Turbine housing is manufactured through a sand casting process, taking into account the shape and material characteristics according to the environmental conditions in which it is used. Currently, turbine housing is imported, and local production is necessary.

In this study, basic research was conducted to localize the turbine housing of imported tank diesel engines. As work prior to producing the turbine housing through the sand casting process, reverse engineering, finite element analysis, and prototype production of the imported turbine housing were performed. The turbine housing of an imported tank diesel engine was reverse engineered. Finite element analysis of thermal stress and thermal

deformation was conducted under the conditions of diesel engine exhaust temperature. A prototype of the turbine housing was printed with Polylactic Acid (PLA) filament using a Fused Deposition Modeling (FDM) 3D printer. And the prototype of the turbine housing was printed using SUS316L powder by a Powder Bed Fusion (PBF) 3D printer.

2. Reverse Engineering

A turbocharger system is a device that combines a turbine and a compressor, and its main components are turbine housing, compressor housing, center housing, shaft, turbine wheel, and compressor wheel.

A turbine wheel is connected to one end of the shaft, and a compressor wheel is connected to the other end. When the turbine wheel rotates, the compressor wheel rotates at the same time. The engine's exhaust flows into the inlet of the turbine housing and exits again through the outlet. Therefore, the engine's exhaust does not flow into the center housing or compressor housing.

Fig. 1 3D shape of the turbo housing

Reverse engineering of the turbine housing of a tank diesel engine was performed. After performing a 3D scan, 3D modeling was conducted from the scan data. Fig. 1 shows the 3D shape modeling of the reverse engineered turbine housing. The shape of the turbine housing is a shell structure similar to that of a centrifugal pump housing[9]. The turbine housing and centrifugal pump housing have opposite inlets and outlets for fluid to enter and exit. The inlet of the turbine housing is the outlet of the centrifugal pump housing, and the outlet of the turbine housing is the inlet of the centrifugal pump housing. The width (y-axis) of the turbine housing is 183.5 mm, the height (x-axis) is 203.6 mm, and the thickness (z-axis) is 135.9 mm. The volume of the turbine housing is 986,660.6 mm3, and the weight applying the density of iron is 7.74 kg.

3. Thermal Stress Analysis

The exhaust temperature of a diesel engine is 200 to 500 ℃[10]. The inlet of the turbine housing is connected to the engine manifold, so the engine's exhaust flows into the turbine housing. Therefore, gray cast iron or stainless steel is used as the material for the turbine housing. Since the center housing is connected to the turbine housing, the same material as the turbine housing is used in consideration of heat transfer phenomenon,

and the compressor housing is made of aluminum alloy material[11].

Finite element analysis of the turbine housing was performed using ANSYS Workbench. Gray cast iron was selected from engineering data as the material for the turbine housing. The density of gray cast iron is 7.2 g/cm3, and the young’s modulus and Poisson's ratio are 110 GPa and 0.28, respectively. And the thermal expansion coefficient of gray cast iron is 1.1×10-5 1/℃. Young’s modulus, Poisson’s ratio, and thermal expansion coefficient were set to isotropic conditions. The mesh was created with tetrahedron, and the sizing functions of resolution and span angle center were applied. The part connected to the center housing was created with fine mesh by applying the refinement meshing option. The number of nodes created is 607,628, and the number of meshes is 408,431. As for the boundary support condition, the square surface of the turbine housing connected to the manifold was set as a fixed support condition. The surface where the turbine housing is connected to the center housing was set to not move in the vertical direction of the surface as a displacement condition.

Fig. 2 FEM results - equivalent stress in turbo housing

 As the boundary load condition, 0.157 MPa, which is the boost pressure of the turbo engine, was applied to the inner surface of the turbine housing. And considering the temperature of the engine exhaust, the temperature of all areas of the turbine housing was set to 500 ℃.

Fig. 2 shows the equivalent stress occurring in the turbine housing analyzed with ANSYS Workbench. The equivalent stress around the inlet connected to the manifold is 131∼144 MPa, which is relatively higher than other locations.

Fig. 3 FEM results - safety factor in turbo housing

Fig. 4 FEM results - total deformation in turbo housing

Equivalent stress in the whorl part is 21∼28 MPa. The inlet is completely fixed, and because the engine's exhaust is directly sucked in, the equivalent stress around the inlet is relatively high. Fig. 3 shows the analysis results for the safety factor. Since the tensile yield strength of gray cast iron is 300 MPa, the safety factor at the most vulnerable location is about 2.0. Fig. 4 shows the analysis results for total deformation. It can be seen that the amount of deformation increases as the distance from the inlet increases. Since the inlet is completely fixed, the amount of deformation is relatively small, about 0.25 mm. The amount of deformation in the lower part of the whorl is about 1.45 mm, which is relatively large compared to other locations. This is an analysis result conducted under the condition that all areas of the turbine housing are at 500 ℃, so the amount of deformation is large.

4. Prototype of 3D Printing

4.1 FDM 3D Printing

FDM 3D printing is a method of heating and melting the filament of thermosoftening plastic and then extruding it through a nozzle to build up the layers one by one. PLA filament was used to print the turbine housing with an FDM 3D printer. PLA filament is mainly used in FDM 3D printers and is an eco-friendly polymer resin[12].

Fig. 5 Turbo housing printed by FDM 3D printer

The turbine housing is a shape with a somewhat high level of difficulty because it has many circular and curved parts. The printing conditions were set as follows. A nozzle with a diameter of Ø0.3 mm was used, and the printing speed was set to 80 mm/s. Then, the nozzle temperature was set to 205 ℃ and the bed temperature was set to 60 ℃. Estimated printing time is approximately 15 hours.

Fig. 5 shows the turbine housing that has been printed using an FDM 3D printer. The shape of the printed prototype is almost similar to the shape modeling in Figure 1. However, it can be seen that the printing surface is uneven in the whorl part. In particular, the exterior of the exhaust outlet, which is an area with a large curvature, was formed with an even larger surface because the filaments were not stacked evenly.

4.2 PBF 3D Printing

PBF 3D printer is a printing technology that stacks metal powder in a thin layer and melts it with a laser. It creates a stacked

Fig. 6 Turbo housing printed by PBF 3D printer

surface by stacking a thin layer of metal powder on the laminated surface and melting it. From the precise melting technology of the ultra-precision laser, it is possible to output a product that is not only identical to the modeling shape but also sturdy. From the precise melting technology of precision laser, it is possible to print products that are not only identical to the modeling shape but also have soundness. Recently, the PBF method has been widely used in the aerospace, medical, and defense fields[13].

3D SYSTEMS' Direct Metal Printer (DMP) Flex 350 equipment was used. The printing conditions were set as follows. The laser power was set to 215 W, the scan speed was 900 mm/s, and the jump speed was set to 15,000 mm/s. Minimum feature size is 0.1 mm. For printing the turbine housing, SUS 316L powder consisting of particles with a size of 40 to 60 μm was used.

Fig. 6 shows the turbine housing that has been printed with a PBF 3D printer. The shape of the printed prototype is completely similar to the shape modeling in Figure 1. Unlike the prototype printed by FDM, the

shape of the whorl part can be seen to be perfect. The FDM 3D printer has a nozzle diameter of Ø0.3 mm and the spacing between layers is 0.3 mm, but the PBF 3D printer has a minimum feature size of 0.1 mm. Therefore, it can be said that PBF has a precision that is more than 3 times higher than FDM.

5. Conclusions

In this study, basic research was conducted to localize the turbine housing of a tank diesel turbo engine. Reverse engineering and finite element analysis of the imported turbine housing were performed, and a prototype of the turbine housing was printed using two types of 3D printers.

(1) From the finite element analysis results, it was found that equivalent stress was generated relatively high around the inlet of the turbine housing. On the other hand, the amount of deformation is small around the inlet and increases in size as you move away from the inlet.

(2) The prototype of the turbine housing printed with an FDM 3D printer has an overall appearance similar to 3D modeling, but the printed surface of the whorl part is rough. The prototype produced by the PBF 3D printer is completely identical to the 3D modeling, including the whorl part.