Mechanical Design Practice Teaching Based on Romax Designer

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1 Mechanical Design Practice Teaching Based on Romax Designer Ying Sun 1, *, Jiabing Hu, Gongfa Li 1,, Guozhang Jiang 1, and Hegen Xiong 1, 1 Key Laboratory of Metallurgical Equipment and Control Technology, Wuhan University of Science and Technology, Ministry of Education, Wuhan , Hubei, China Hubei Key Laboratory of Mechanical Transmission and Manufacturing Engineering, Wuhan University of Science and Technology, Ministry of Education, Wuhan , Hubei, China *Corresponding author( sunying65@wust.edu.cn) Abstract In order to enhance the connection between computer aided design and mechanical industry in practice, this paper takes Romax Designer software as an example to analyze the problems in practical application. In view of these problems, this paper presents a practical application of counter-aided design, the Romax Designer software used in mechanical design. Through the establishment of the rigid and flexible hybrid model of the carrier, and then the finite element static stress analysis is carried out. Finally, the finite element modal analysis of the planetary carrier is carried out to determine whether the structural strength is appropriate and the structural design is reasonable. In the form of point to the surface, through the planetary carrier analysis as an example to guide mechanical practitioners how to use the software to achieve the design of parts and meet the requirements, so as to enhance the connection between computer aided design and mechanical industry in practice. Using the Romax Designer software in practice, it will be effective to solute the problem that computer-aided design is not linked to practice. So that mechanical practitioners can achieve the integration of software knowledge and practical ability. Key words: Romax Designer, Mechanical Design, Innovative Practice, Planetary Carrier Analysis 1. INTRODUCTION With the progress and development of society, the national manufacturing industry as the main body of the national economy is developing more and more rapidly. For this country put forward the China Smart Manufacturing 05 plan. The gap in manufacturing talent has gradually become larger. But at the same time, the demand for talent for society is also rising. As an important part of higher education in our country, college students are becoming more and more important (Kang, 016; Zhou, 015). Mechanical subject is a traditional specialty that generally exists in engineering colleges. However, the content of mechanical courses covers a wide range and had strong interrelationships. So the students learning it become difficult. Mechanical design is the basic course of mechanical discipline. In the existing teaching methods, the practice teaching is not enough that the theory and practice teaching are carried out separately. The pre-class teaching focuses on the establishment of the knowledge points and the theoretical system.when the theoretical course ends, practice class will be carried out. This traditional teaching model leads to the lack of students' ability and knowledge integration. In addition, students practice time is too short that the ability to enhance cannot meet the social needs. Therefore, the Mechanical Design of practical teaching is urgent need to reform which strengthen the integration of Mechanical Design knowledge and ability and improve students' practical ability. Romax Designer is one of computer software whom used to build a virtual prototype model for a gear drive system (Sun, 014; Park, 014). It not only includes detailed component intensity and reliability analysis but also vibration and noise analysis of the drive system. Using it s able to determine the design of the components of its structure and strength is reasonable. In addition, it will be greatly accelerating the transmission system design and development process, so that saving time and material costs. And it based on Romax Designer to establishment practical learning links not only strengthen the students practical and design ability but also made the student s steady classroom learning result that is able to meet the needs of enterprises and society (Li, 016; Le, 016).. SOFTWARE APPLICATION PRESENT SITUATIONS The main purpose of the practice teaching reform is making students more using, more understanding, and more experience. This requires teachers to set more innovative practice links, so that they teach the contents of the correct and rapid understanding. So as to improve the teaching efficiency and attract the students taking the initiative to learn, so that mechanical design courses to achieve the best teaching practice. How to teach students the basic principles, thinking habits, behavioral characteristics and psychological characteristics of teaching, so 191

2 that the mechanical design course practice teaching really become a student favorite life, life-long benefit of the course, which is long-term troubled many college teachers a problem (Ng, 015; Jiao, 015). The teaching content of the Mechanical Design course mainly includes the design theory and design method of various common parts components. Through the teaching of this course, it makes the students master the specific method of design and calculation of common parts in machinery. But more importantly, it causes the students to know how to use a relatively simple theoretical formula to deal with more complex engineering problems. The course is an important professional basic course for mechanical students that covering a wide range of knowledge and requires a good grasp of their knowledge (Wang, 01). This has an important role in cultivating mechanical students' ability to analyze and deal with practical problems. However, there are still some problems in the teaching of the existing Mechanical Design courses (Cheng, 015; Yue, 014): 1) The time of practice teaching is short and practice equipment is not perfect; ) The students cannot link the theoretical knowledge and practice, so they are poor practical ability; 3) For gears, shafts and other parts of the design, the students understanding is not very well, resulting in lack of design capacity. 3. PRACTICE TEACHING BASED ON ROMAX DESIGNER 3.1. Introduction to Romax Designer Romax Designer is a product developed and simulated CAE software which research and development by the British Romax company and used to specializing in the development of the gear transmission system. It is used for the design and analysis of the whole gear drive system. Romax Company integrates software development and transmission project consulting in one that in the field of transmission has more than 10 years of experience. In 1995, the company released Romax Designer that has turn into standard tools in the field of gear transmission industry today. It widely used in automotive gearbox, wind power Energy and other fields. Romax Designer covers the whole drive system design content that from conceptual model building, component strength analysis, reliability estimation, etc. to system vibration noise (NVH) prediction which makes up the closed-loop solution mechanism of the whole gear transmission system. It provides a variety of complex gear drive system modeling, analysis and optimization functions. 3.. Practical Teaching Reform Engineering is a subject that needs practice. It needs strong logical thinking ability and spatial imagination ability (Wang, 016). But these are not enough, and they need to be supplemented by a wealth of theoretical knowledge. With the popularization of information technology, the teaching mode of flipped classroom has been gradually introduced into teaching. Through the flip classroom teaching model, students can vividly understand all kinds of components and so on and build a good knowledge of the map. It has a great effect on students' theoretical knowledge. But at present students often cannot practice the theory of knowledge. For example, all types of shafts, gears and other component which the calculation of strength, life and so on. Because of the more abstract, students are difficult to master that resulting in poor ability to practice. Taking the course of Mechanical Design as an example, we add the practice learning part based on Romax Designer simulation software in practice teaching. Through establish the model of gear, shaft and bearing, and then carry on the strength analysis and life calculation, etc (Gonzalez, 015). So that classroom and practice synchronization teaching which to strengthen cultivates the practice of practical ability, and deepening the students' classroom learning ability. When the students in the classroom to learn the book knowledge and combined with the practice of links, operation the entity by simulation will be take exercise practical ability at the same time more deepen the understanding of knowledge. This way of teaching will be synchronized with classroom teaching and practice teaching, which will enable students to constantly reflect on the corresponding relationship between knowledge point learning and design ability promotion. While strengthening the knowledge, we should enhance the corresponding design ability to achieve the integration of knowledge and ability. Taking the planetary carrier of reducer as an example, this paper introduces how to analyze components through Romax Designer. That shows how to improve students' practical ability (Yang, 017) Planetary Carrier Rigid and Flexible Mixing Model Established For the reducer, the planetary carrier can be regarded as the flexible body of the parts of the finite element model of the introduction and assembly. It s establishment of rigid and flexible multi-body dynamic model. And the flexible body modeling process is shown in Fig.1. 19

3 Figure 1. Flexible body modeling flow chart Taking the planetary shelf as an example, the modeling process of flexible body in Romax Designer environment is described in detail: (1) 3D modeling of the planetary carrier using CAD software (such as Pro / E, UG, etc.), this paper uses Pro / E for 3D modeling of the planetary carrier, as shown in Fig.. Figure. Geomechanical model of the planetary carrier () The 3D solid model of the planetary carrier is imported into the HyperMesh in IGES format or STEP format. Then use Tetra mesh method to automatically generate tetrahedral mesh, the grid size control is 5mm. And division of the planetary carrier generation unit number is 3340; the number of nodes is At this point the material properties are defined and the planetary shelf material is ZG40Mn. Its performance parameters are elastic modulus 180Gpa, Poisson's ratio 0.3 and density 7.9e3Kg/m 3. The definition is complete When are save it as a *.dat file. As shown in Fig.3. Figure 3. Finite element model of planetary carrier (3) In Romax Designer, it define the Stiffness Components component and obtain the three-dimensional model of the carrier in the form of a node which is call the (*.dat) file in the previous step. As shown in Fig.4, here node is the node in the finite element mesh. 193

4 Figure 4. Three-dimensional model of the form of the carrier (4) The three-dimensional model in the form of nodes through the condensing node and rigid parts connected, as shown in Fig.5. In the process of fitting the finite element model, the binding characteristic of the connection is the key factor of the whole system simulation. The number and type of nodes in the joint can be set according to the actual working conditions, so that the joint stiffness more close to the actual working condition. The connection between the planet carrier and the planetary axle requires 6 cohesive nodes, and the type of connection is fixed. Figure 5. Planar model connected to rigid parts (5) Select the planet carrier component. Use the Condense FE Model function in the Analysis function menu to calculate the stiffness matrix and mass matrix of the carrier, as shown in Fig.6. Figure 6. Finite element run interface (6) Finally, after the operation of the file after the import is completed. In the properties under the static data under the import ax matrix select Romax FE solver into the import interface, as shown in Fig.7. Figure 7. Import interface At this point, the planet carrier assembly is treated as a multi-body dynamics model of the rigid and flexible mix, as shown in Fig

5 Figure 8. System model after importing the planet carrier finite element Through the detailed modeling process of the planetary carrier, it laid the foundation for the follow-up analysis and optimization Finite Element Static Stress Analysis of Planetary Carrier The definition of the geometric model of the planetary carrier, the division of the mesh, the definition of the material properties and the introduction of the finite element model has been described in detail. Here, the static analysis of the planetary carrier will be carried out directly. In the Analysis function menu, call the Static Deflection of FE Model function to solve the static stress intensity of the planetary carrier. The analysis results are shown in Fig.9. Figure 9. Planetary carrier displacement map It can be seen from Figure.9, the maximum deformation of the carrier occurred in the edge of the site. And the maximum deformation is 0.17mm, so we can see that the deformation of the carrier is very small and it meets the stiffness requirements. Figure 10. Equivalent stress cloud diagram of planetary carrier It can be seen from Fig.10 that the maximum stress experienced by the planetary carrier occurs at the connection with the output shaft. The stress of other parts is smaller and the maximum stress is. In addition, the material of this planetary carrier is ZG40Mn, the yield strength is 95Mpa and the safety factor is 3, which fully meets the requirement of use Finite Element Static Stress Analysis of Planetary Carrier In the actual work, the mechanical structure will inevitably have an impact due to vibration. In order to ensure that it has good dynamic performance and relatively high reliability at work, it is necessary to study the 195

6 dynamic characteristics of mechanical structure, and modal analysis is the basis of all dynamic characteristic analysis. Modal analysis is a modern method used to analyze the dynamic characteristics of the structure which is the system identification method in the field of engineering vibration applications. Through the modal analysis, the natural frequency and the natural mode of the structure can be obtained, which can provide a reliable scientific basis for the design and improvement of the dynamic characteristics of the mechanical structure. 1) Structural Modal Analysis Theory Structural modal analysis process, that a complete mechanical structure is a linear vibration system with n-degrees of freedom. For a linear system with n degrees of freedom, the differential equation of motion is: [ M ]{ x } [ C]{ x } [ K]{ x} { F} (1) Which [M] [C] [K] respectively are the system's mass, damping and stiffness matrix; and {x }, {x },{x} for the system's acceleration, velocity and displacement response. In the micro vibration of the general vibration system, the damping system is very small, and its influence on the dynamic characteristics of the system is small and negligible. The differential equation of the system without damped free vibration is: [ M ]{ x } [ K]{ x} {0} () Since the free vibration of the structure can be decomposed into a certain number of simple harmonic vibration superposition, therefore, can be set () solution is: { x } { X}sin( t ) (3) Substituting (3) into () yields: ([ K] [ M ]){ X} 0 (4) Equation (4) is a generalized feature problem. It is a n-valued linear homogeneous system of equations. The necessary and sufficient condition for the non-zero solution of the system is that the determinant of the coefficient matrix is zero: [ K] [ M] 0 (5) It can be seen that the equation (5) is an n sub algebraic equation of. In the theory of vibration, it is called the frequency equation, and the determinant is called the characteristic determinant. It is assumed that the mass matrix and the stiffness matrix of the system are positive definite real symmetric matrices. By the theorem in algebra, we can prove that under this condition, we solve n prime algebra (5) to obtain n real roots not less than zero which corresponding to the n natural frequencies of the system. According to their size, from small to large arranged as: The obtained ( i 1 n) i 0 1 n is substituted into equation (4) to find the corresponding } { i X is the mode vector or modal vector of the system. ) Finite Element Method for Structural Modal Analysis The basic idea of the finite element method is to divide the studied structure into a number of basic units and specify a certain number of nodes on each base unit. The units are connected to each other through these nodes to form a unit assembly to simulate the physical structure of the analysis. Finite element analysis process mainly has 3 steps: (1) The discretization of the structure: The structure is divided into finite elements that also called mesh generation. In general, the size of the unit should be chosen according to the actual calculation. () Unit characteristic analysis: Firstly, the function matrix of the element shape is assumed to approximate its displacement distribution rule, and the stiffness matrix [ k e ], the damping matrix [ c e ] and the mass matrix e [ m ] of the element are obtained according to the variation principle. (3) Synthesis of the structure: The stiffness matrix, damping matrix and mass matrix of the unit are integrated into the overall stiffness matrix [k], damping matrix [c] and mass matrix [m] of the whole system according to the boundary condition of the structure and the continuous condition between the units. The differential equation of motion for the system is as follows: [ m]{ q( t)} [ c]{ q ( t)} [ k]{ q( t)} { Q( t)} (6) 196

7 Where { ( t)} undamped free vibration equation: q is the displacement of unit nodes. In equation (6), if c 0, ( t) 0 [ m]{ q ( t)} [ k]{ q( t)} 0 Q,which is the (7) Equation (7) and () are exactly the same. The frequency and mode of the undamped free vibration of the structure can be obtained. While solve the Equation (4), generalized feature problem, there are many methods in mathematics. Based on the finite element method, the most representative solution is subspace iterative method and Lanczos method. 3) Finite Element Modal Analysis Assuming the geometrical modeling, meshing, constraint definition, and assembly process of the planetary carrier are already processed in the previous way. At this time using Romax Designer directly on the planetary plane modal solution while extract the first 8-order mode to get the natural frequency of each order as shown in Table 1, the various modes shown in Fig.11. Table 1. Natural frequency of planetary carrier Modal order Natural frequency (a)first order natural frequency (b) Second order natural frequency (c) Third order natural frequency (d) Fourth order natural frequency 197

8 (e) Fifth order natural frequency (f) Sixth order natural frequency (g) Seventh order natural frequency (h) Eighth order natural frequency Figure 11. The first eight steps of the planetary carrier By analyzing the 8th order mode of the planetary carrier, it can be seen that the maximum amplitude occurs at the edge of the planet carrier whom mainly for the translation and twist of the edge of the carrier. The non-zero modal frequency of the planetary carrier is between and 07.7 Hz. Through the above analysis, the natural frequency of the planetary carrier is completely avoiding the resonant frequency, which proves that the structural design of the planetary carrier is reasonable Design Conclusion Through the establishment of the rigid and flexible hybrid model of the planetary carrier, the finite element static stress analysis of the carrier is carried out. Finally, finite element modal analysis is carried out on the planetary carrier. Through the analysis we can see that the structure of the planetary carrier is reasonable, available, and its strength to meet the requirements. Through the above design and analysis to ensure that the planets in the use of the strength of the process to meet the requirements and the structural design is also very reasonable. It can be seen, through the Romax Designer can be very convenient to determine whether the structure of the design is reasonable, its strength and other factors to meet the requirements. So the introduction of Romax Designer into practice teaching, students can not only easily complete the design of a mechanical parts, but also to ensure that the design of the structure of the rationality. In this case, students can complete the design of parts through Romax Designer that will be increase the practical experience of students. This experience in the future work plays a very important role which is improving the practical ability of students and comprehensive quality is very useful. 4. THE INFLUENCE OF SOFTWARE COMBINED WITH PRACTICE By combining Romax Designer software with the practical teaching of Mechanical Design, a new teaching scheme is obtained. The program uses Romax Designer to guide students in the Mechanical Design practice, which effectively solves the problem of insufficient experimental equipment. Students can design qualified parts without real equipment. Second, through the software simulation exercises greatly enhance the students' design ability and practical ability. In the country or the province's mechanical competition, there are more than 40 students won the award. Using the software, students have a deeper understanding of Mechanical Design and know how to apply the theory in practice. And understand how to solve practical engineering problems, while fully stimulating their ability to innovate. It raises the interest of the students and creates a lot of high quality graduates who are more able to adapt to their jobs after they go out to work. In short, it strengthens the potential for sustainable development and enhances their core competencies. 5. CONCLUSIONS This paper discusses the application of the software in practice teaching through Romax Designer software. The new practice teaching model effectively compensates the shortcomings of the current Mechanical Design practice teaching mode. Firstly, the rigid and flexible mixing model is established for the planetary carrier of the reducer, and then the static stress analysis of the carrier is carried out to ensure that the structural strength of the planetary carrier can met the requirements. Finally, the finite element model of the planetary carrier is analyzed. By analyzing the 8 order vibration modes of the planet carrier, the weakest link of the planet carrier is determined. Then it compares the natural frequency and the resonance frequency to judge whether the structure is reasonable or not. By taking the planetary design as an example, it reflects the role of Romax Designer in Mechanical 198

9 Design and how the theory can be applied in Romax Designer. And through the analysis process of the planetary carrier can made students understand the design of a component and analysis of how to operate, so as to enhance the practical ability of students. This new teaching model allows students to better grasp the mechanical parts of the design and understanding. It strengthens the students' practical ability and enhances the ability of theory to practice, so that students know how the theory can be used in practical projects. In this new model, teaching has achieved more significant results. Most of the students' practical ability and comprehensive quality significantly improved, for the professional knowledge is also more thorough grasp. And finally improve the quality of personnel training. ACKNOWLEDGEMENTS This research was supported by the Higher Education Teaching Reformation Project of Hubei Province of China (01630) and Graduate Teaching Reformation Project of Wuhan University of Science and Technology (Yig01610, Yig01714). REFERENCES Kang H., Lee J., Choi S., et al. (016). Smart manufacturing: Past research, present findings, and future directions. International Journal of Precision Engineering and Manufacturing-Green Technology, 3(1), pp Zhou, J. (015) Intelligent manufacturing - "China made 05" the main direction. China Mechanical Engineering. China Mechanical Engineering, 6(17), pp Sun Y., Jiang G., Li G., et al. (014) Application of modern simulation technology in a mechanical design course for outstanding engineers. World Transactions on Engineering and Technology Education, 1(3), pp Park Y., Kim J., Lee G. (016) Characteristic Analysis of Planetary Gear Set of Hydromechanical Transmission System of Agricultural Tractors. Journal of Biosystems Engineering, 41(3), pp Li G., Liu Z., Sun Y., et al. (016) Reform and effects of a training mode for outstanding mechanical engineers. World Transactions on Engineering and Technology Education, 14(1), pp Le Y., Wang K. (016) Design and Optimization Method of Magnetic Bearing for High-Speed Motor Considering Eddy Current Effects. IEEE/ASME Transactions on Mechatronics, 1(4), pp Ng L., Ong S., Nee A., et al. (015). Conceptual design using functional 3D models in augmented reality. International Journal on Interactive Design and Manufacturing, 9, (), pp Jiao W., Yang J., Ma F., et al. (015). Equal strength optimal design of planetary gear transmission. Transactions of the Chinese Society for Agricultural Machinery, 46(1), pp Wang G., Zhang, H., Zhang L. (01). A study on the fatigue life of hub bearings in front steering axle of a heavy duty truck. Automotive Engineering, 34(8), pp Cheng Z., Wei Y., Niu H., et al. (015). Design and kinematic analysis of differential-balance mechanism for planetary exploration rover. Journal of Astronautics, 36(5), pp Yue H., Liu Y., Xu X., et al. (014). Study on vibration characteristics and tooth profile modification of a plus planetary gear set. Journal of Vibroengineering, 16(),pp Wang Y., Yang J., Guo D., et al. (016) Vibration and sound radiation analysis of the final drive assembly considering the gear-shaft coupling dynamics. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 30(7), pp Gonzalez P., Roda C., Fuentes A. (015) Modified geometry of spur gear drives for compensation of shaft deflections. Meccanica, 50(7), pp Yang H., Ding L., Gao H., et al. (017) Experimental Study and Modeling of Wheel s Steering Sinkage for Planetary Exploration Rovers. Journal of Mechanical Engineering, 53(8), pp