Fabrication of hydrodynamic torque converter impellers by using the selective laser sintering method Jaroslaw Kotlinski, Marcin Migus and Zbigniew Kesy Technical University of Radom, Radom, Poland Andrzej Kesy Kazimierz Pulaski University of Technology and Humanities, Radom, Poland, and Philip Hugo, Brent Deez, Kristian Schreve and Dimitri Dimitrov University of Stellenbosch, Stellenbosch, South Africa Abstract Purpose The main aim of the paper is the application of the selective laser sintering (SLS) method for fabrication of hydrodynamic torque converter (HTC) impellers Design/methodology/approach Establishing of assumptions for the impeller design process based on the HTC characteristics analysis, creation of the virtual solid model of HTC impellers, fabrication of HTC impellers by using the SLS method, investigation of the performance of HTC with fabricated impellers by using a test rig Findings The test results show that the SLS method can be successfully used for the fabrication of HTC impellers with 3D and flat blades Research limitations/implications The method application is limited to small diameters of HTC impellers depending on working area dimensions of SLS machine Practical implications The method can decrease the time and cost of fabrication of HTC impellers by using the SLS method Originality/value The application of the SLS method for fabrication of HTC impellers with 3D and flat blades Keywords Selective laser sintering, Hydrodynamic torque converter, Hydrodynamic torque converter impellers, Solid model of impellers Paper type Case study 1 Introduction Hydrodynamic torque converters (HTCs) are widely applied in technical devices Their main advantages is the ability to adapt to the load and damping of torsion vibrations A typical HTC consists of three impellers: pump, turbine, stator and a casing filled with working fluid The pump is connected to the input shaft, the turbine is connected to the output shaft and the stator is locked The power is transferred from the pump to the turbine using the working fluid that fills the channels of the impellers which are equipped with blades The axial intersection of the HTC working area (meridional intersection) is appointed by the peculiar flat curve Blades of the HTC impellers have a complicated three-dimensional (3D) shape Characteristics of an HTC are mainly determined by the impellers channel flow which depends on the working area geometry Because of the complicated geometry of the working area, fabrication of HTC impellers is difficult At present centrifugal casting is the main method for HTC impellers production A weakness of this method involves errors in copying impellers The current issue and full text archive of this journal is available at wwwemeraldinsightcom/1355-2546htm working area geometry These errors lower the quality of the received product As a result a real HTC characteristics are difficult to predict and are always worse than assumed This has a negative influence on HTC application in vehicles and transmission systems Simplifying the HTC working area geometry by using flat blades can be a method to fabricate better and more efficient HTCs (Kesy, 1999) Thanks to simplification of the working area geometry it would be possible to obtain more accurate HTC design Also the characteristics of such an HTC should be more predictable Simplifying an HTC working area geometry could decrease the cost of fabrication both in the prototype phase and during mass production In order to simplify the HTC working area geometry three variants of the HTC design were examined: 1 flat blades in all HTC impellers; 2 flat blades in the pump and turbine but cylindrical blades in the stator; and 3 flat blades in the pump and turbine but 3D blades in the stator Figure 1 shows the above variants of the blade shapes For all variants of the shape of the HTC blades theoretical calculations of the steady-state characteristics were carried out and the characteristics obtained were compared with the characteristics of existing HTCs The characteristics of the 19/6 (2013) 430 436 q Emerald Group Publishing Limited [ISSN 1355-2546] [DOI 101108/RPJ-04-2011-0043] Received: 29 April 2011 Revised: 16 December 2011, 1 January 2013 Accepted: 4 January 2013 430
Jaroslaw Kotlinski et al Figure 1 Variants of the blade shape in the HTC with flat blades HTC with flat blades differ from the characteristics for the HTC 3D blades The most simplified HTC configuration with flat blades in all impellers was least beneficial However, in spite of the worst parameters in this group the HTC meet requirements for application in vehicles and machines On account of time and accuracy, layer manufacturing methods were chosen for fabrication of the HTC impellers The methods allow for the fabrication of impellers with good accuracy (equal to the thickness of a layer) and in a short time (24 h) on the basis of the computer solid model of the created object (Narbut et al, 1995; Grimm, 2004) 2 Design process of typical impellers The idea of using layer manufacturing methods supported by numerical methods and CAD software for the fabrication of HTC impellers was first introduced in Kai and Fai (1997) In this work a numerical model of the HTC working area was established Next, the results of calculations of HTC working area geometrical parameters were transferred to the 3D solid model using AutoCAD In the HTC design process described in Shieh et al (2000) more advanced numerical methods were used For the analysis of the flow the computational fluid dynamics (CFD) method was applied, for strength analysis the FEA method was used, and for the modeling and production CAD software was used In Yang et al (1999) the strategy for the design of HTCs was described by using computer virtual modeling and the CFD method The fabrication of HTC impellers can be divided into three phases: 1 creation of a virtual solid model and then a computer file for layer manufacturing machines; 2 fabrication of HTC impellers; and 3 investigation of the impellers performance by using a test rig A typical course of the design process of HTC with the CAD software and layer manufacturing methods is realized in the following way: Based on assumed characteristics and technical requirements of a given transmission system, modeling and optimization of HTC impeller working area are carried out A computer programme which applies the mathematical model of the working area is used for the calculations As a result of these calculations a set of point coordinates is created determining the aerofoil blade geometry 431
Jaroslaw Kotlinski et al This set of point coordinates is transformed into the 3D impeller model by using one of the available CAD systems The 3D model is then processed by the CAD system and transformed into a data file for the layer manufacturing machine Such data is stored in stereo lithography file format STL Based on the data recorded in the STL file an impeller prototype is fabricated by a layer manufacturing machine These impellers are installed on a test rig and a test is initiated according to a computer programme Test results are recorded by a computer and compared with assumed characteristics In case of significant differences between the modeled and actual characteristics a corrective action is performed by the computer (based on a special corrective computer programme) and another cycle of the HTC working area modeling is performed These design steps are repeated until an acceptable agreement of assumed and actual characteristics is obtained 3 Creation of solid model of impellers with flat blades The stages of the design process of impellers with flat blades are the same as during the design of typical impellers In order to make prototypes of HTC impellers an assumption was made that the HTC active impeller diameter is D ¼ 150 mm The active diameter of HTCs applied in earth moving machines is from 280 up to 440 mm Because of the limited working area of the layer manufacturing machines a small active diameter will allow fabrication of the impellers as one piece The materials applied for object fabrication in layer manufacturing methods in most cases are plastics Therefore, because of plastic material endurance it is essential during the design process of the impellers to apply lower rate forces during test rig investigations so that significant deformation of blades and casings do not appear In an HTC the value of the impeller torque is proportional to the fifth power of the active diameter, and therefore the influence of the impeller s active diameter on blade straining is large On the basis of published analysis (Kesy, 1999) an assumption was made that the blades in all impellers should be flat Moreover, it was assumed that (Figure 2): for the pump the blade lies on the meridional plane; for the turbine the blade plane is drawn aside from the meridional plane at an angle of 458; and for the stator the blade plane is drawn aside from the meridional plane at an angle of 198 Moreover, additional assumptions were made that: inlet and outlet impeller surfaces are surfaces of the ring; and inlet and outlet surfaces lie on the same plane Such assumption force the formation of transitional channels without blades between the outlet of the pump and the inlet of turbine (Figure 3) The channel wall is a part of the pump For the HTC impellers the numbers of blades were established as follows: for the pump 30; for the turbine 22; and for the stator 15 Figure 2 Positioning of HTC impeller blades Note: u tangential velocity Figure 3 Design of HTC working area The solid models of impellers with flat blades can be created by using a CAD programme AutoDesk Inventor As an example, the creation of a solid model is described based on the pump impeller The creation of the solid model begins by determining the shape (flat) and external dimensions of a blade of the pump (Figure 4) Next a draft of the impellers is created by marking outlines of: a core and a shell; walls of core and shell; and faces of transitional channel obtaining the sketch of the impeller on a plane (Figure 5) The draft of the impeller on a plane is changed to a 3D model by rotating it around the HTC axis (Figure 6) The next task is adding aerofoil shapes of the inlet and outlet edges of the blade (in the plane perpendicular to the surface of the blade) (Figure 7) The last step in the construction of the solid model of the pump is arranging the blades on the circumference of the 432
Jaroslaw Kotlinski et al Figure 4 Determination of shape and size of HTC impeller blade pump by their rotation around the HTC axis (Figure 8) The rotation angle of each blade is equal to 3608/30 ¼ 128 Finally, when the solid model of the pump is designed it is written and transformed into a data file for the layer manufacturing system in the STL format Figure 5 Shape of the blade on a meridional plane 4 Fabrication of impellers using selective laser sintering method Different layer manufacturing methods are available on the commercial market To fabricate HTC impellers, selective laser sintering (SLS) method was used This technology is currently one of the most commonly used A CO 2 laser selectively sinters a layer of a part being produced from the powder material After a layer has been sintered, a new material layer is added The process is repeated and this continues until the entire part is completed The HTC impellers discussed in the paper were fabricated on the Vanguard SI type machine In this machine the power of the laser was 11 W and the thickness of the powder layer was 01 mm Nylon polymer powder (Durafon PA) with a particle size of 58 mm was used to fabricate the impellers The fabricated impellers are shown in Figure 9 5 Experimental investigation of impellers Theoretical calculations of the HTC steady-state characteristics require an experimental confirmation by tests Here, the non-dimensional steady-state characteristic of HTC is a curve determining a torque ratio (TR), as a function of a speed ratio (SR): SR ¼ v 2 v 1 ; TR ¼ M 2 M 1 ; ð1þ Figure 6 3D model of the pump 433
Jaroslaw Kotlinski et al Figure 7 Shapes of the inlet and outlet edges (a) (b) Notes: (a) Blade shape in the plane perpendicular to the inlet and outlet surface; (b) view of the blade Figure 8 Final model of the pump where: v 1, v 2, are angular velocities of a pump and a turbine and M 1, M 2 are the torques of a pump and a turbine (Figure 10) In order to create the characteristic curve, values of v 1, v 2, M 1 and M 2 have to be known for the considered value of TR To determine the experimental non-dimensional steady-state characteristic the HTC was tested on the test rig shown in Figure 11 The shafts of the tested HTC were connected with three-phase induction motors working as an engine and as a brake The motors were powered by a frequency inverter enabling easy and fluent speed regulation from 0 to 300 rad/s The frequency inverter was controlled with a PC The software for the PC had been written in Turbo Pascal programming language Torque and angular velocity meters were connected with the PC by a measuring system containing analog-digital converters, amplifiers and the computer interface The measured quantities ware shown on the PC screen During the testing, the angular velocity of the HTC input shaft was fixed at 100 rad/s Then the angular velocity of the 434
Jaroslaw Kotlinski et al Figure 9 View of the HTC impellers with flat blades Figure 10 Scheme of an HTC Figure 11 Test rig 435
HTC output shaft was changed in order to obtain the desired SR (15 values of SR in the range of 0-096) For the each point on the curve, the measurement data of the angular velocities and torque for the input and output shafts of the HTC were recorded Then, based on this data, the non-dimensional steady-state characteristic of the HTC was obtained according to the equation (1) The characteristic for the HTC with 3D blades in all the impellers and the diameter of the pump equal to 150 mm, is shown in Figure 12 The curve of the HTC characteristic (TR versus SR) shown in Figure 12 has the maximum value TR for SR ¼ 0 In Figure 13 maximum values of TR for different HTC are presented The first bar refers to a typical HTC with 3D blades in all impellers and the diameter of the pump equal to 330 mm This HTC is used in fork lift vehicles It is a standard commercial Figure 12 The non-dimensional steady-state characteristic of the tested HTC with the 3D blades TR 25 2 15 1 05 0 0 02 04 06 08 1 SR Figure 13 Values of maximum values of TR for different HTCs TRmax 25 2 15 1 05 0 SLS method for fabrication Jaroslaw Kotlinski et al 1 2 3 4 HTC with impellers made of aluminium The second bar concerns an HTC with 3D blades in all the impellers and the diameter of the pump equal to 150 mm This HTC was manufactured by the SLS method from nylon This model is a scaled model of the aluminium model The next two bars of maximum values of TR are variants of the HTC with flat blades and the diameter of the pump equal to 150 mm, that have been presented in this paper Here, flat blades are in the pump and the turbine impellers and in the stator there are 3D, and flat blades, respectively All these parts were manufactured by the SLS method from nylon 6 Conclusions Using CAD software for creating the solid model and the SLS method for fabrication of impellers enabled to manufacture of HTC impellers with a good accuracy in a short time and with a low cost The method application is limited to small diameters of HTC impellers It depends on dimensions of SLS machine working area The experimental investigation have confirmed the appropriateness of the new design and the possibility of flat blades application only The tests of impellers with the nylon blades showed satisfactory results, demonstrating that this was a viable manufacturing option in HTC development Moreover, the initial tests showed that there is some movement of the blades with high torque, but the final test results are comparable with HTC with the aluminium impellers References Grimm, T (2004), User s Guide to Rapid Prototyping, Society of Manufacturing Engineers, Dearborn, MI Kai, CC and Fai, LK (1997), Rapid Prototyping: Principles and Applications in Manufacturing, Wiley, New York, NY Kesy, A (1999), Development of bladed wheels with optimal parameters for hydrodynamic transmission systems of transportation means, DSc thesis, MADI Technical State University, Moscow (in Russian) Narbut, AN, Szczepaniak, C and Zielinski, L (1995), Hydrodynamic torque converter with new form of working area, Sterowanie i Naped Hydrauliczny, No 4, pp 3-6 (in Polish) Shieh, T, Perng, C, Chu, D and Makim, S (2000), Torque converter analytical program for blade design process, Society of Automotive Engineers Technical Paper No 2000-11-145, pp 1646-1652 Yang, S, Shin, S, Bae, I and Lee, T (1999), A computer-integrated design strategy for torque converters using virtual modeling and computational flow analysis, SAE Technical Paper Series No 1999-01-1046, pp 1-5 Corresponding author Jaroslaw Kotlinski can be contacted at: jaroslaw kotlinski@prradompl To purchase reprints of this article please e-mail: reprints@emeraldinsightcom Or visit our web site for further details: wwwemeraldinsightcom/reprints 436