APPLICATION OF SOLID MODELING IN VIRTUAL MANUFACTURING OF SPUR GEAR R. K. Pattanayak, G. Pohit and K. N. Saha Department of Mechanical Engineering Jadavpur University, Kolkata - 700 032 Email : [email protected]; [email protected] ABSTRACT Manufacturing process of gear is fairly complicated due to the presence of various simultaneous motions of the cutter and the job. In this paper, an attempt is made to generate meaningful design data for a spur gear and the corresponding rack form cutter necessary for the manufacturing process. Using these information, solid models for the cutter and blank are developed and finally gear-manufacturing process is simulated in a virtual manufacturing environment. The user can switch between design and manufacture mode at will. The integrated process may also help to develop an optimized product. For better understanding of the operational principle, the animation facility is also included in the package.

INTRODUCTION Gear is a very common machine element in mechanical engineering applications. However, manufacturing of the gear seems to be fairly complicated even to the person having thorough technical knowledge in the related field. The conventional gear generation processes like forming, shaping, hobbing, etc. are usually represented in twodimensional sketch. There may have some component that is not adequately described by the two-dimensional approach. In case of gear generation, it may be difficult to understand the complex geometries and the manufacturing arrangement with the help of 2D models. These limitations can be partially overcome and understanding will be more meaningful if one uses 3D solid model instead. However the development of the models using 3D solids may not always ensure the clarity of the complex gear generation process unless one uses animation to represent the motion of the gear blank and the gear cutter. This can be achieved very efficiently with the help of Virtual Manufacturing technique. It is a technology to create virtual environment on the computer screen to simulate the physical world. The knowledge base and expertise gained from the work in the virtual environment enables the user to apply them more meaningfully in the real life situation. A host of literature is available on Virtual Manufacturing in different areas among which some of the recent and important works are referred below. Tesic and Banerjee [1] have worked in the area of rapid prototyping, which is a new technology for design,

visualization and verification. Graphical user interfaces, Virtual Reality technologies, distillation, segregation and auto interpretation are some of the important features of their work. Balyliss et. al [2] dealt with the development of models in a virtual environment using the virtual reality technologies providing an outstanding 3D visualization of the object. In 1994, G.M.Balyliss et. al [3] presented theoretic solid modeling techniques using the VM tools, like VRML (Virtual Reality Manufacturing Language) and 3DSTUDIO MAX. They have developed different parts of an automobile and through the special effect of animation imparted all possible motion to the model. The modeling technology is further enhanced by Kimera [4], who treated product and process modeling as a kernel for virtual manufacturing environment. In his work, Kimura has incorporated significant modeling issues like representation, representation language, abstraction, standardization, configuration control, etc. Arangarasan and Gadh [5] contributed towards the virtual prototyping that are constructed using simulation of the planned production process using virtual manufacturing on a platform of MAYA, 3D- STUIDOMAX and VRML, etc. At Jadavpur University, research work [6] is carried out to simulate the gear manufacturing processes using AUTOCAD as the platform. A software has been developed that helps the design engineers to understand the problems related to spur gear operation and its manufacturing process. A study of the state of the art and literature review reveal that the scope of virtual manufacturing is wide open for spur gear generation. Computer simulation can be very effectively used to view and subsequent analysis of different complicated manufacturing processes using the concept of design centered virtual manufacturing. With this objective in mind, an attempt is made to virtually manufacture a spur gear from the blank using a rack cutter. The scope of the work includes the generation of design data for the spur pinion and the rack form cutter, the generation of solid models for the cutter and blank and finally simulate gear-manufacturing process through animation. The main motivation of the work is to simplify the task of designing and study the gear generation process that can be understood by a layman and to present a realistic view of it. All the processes are developed on the platform of the 3D-STUDIO-MAX, which is one of the most important virtual tools. The software is developed using Maxscript, an object contained programming language that can be run in 3D-STUDIO-MAX environment. DESCRIPTION OF THE SOFTWARE The max-script language, is basically an image processor that creates the visual effects in 3D-Studio-Max. In addition, it can be used for design calculation and subsequent checking also. An attempt is made to develop the entire package in modular form so that any further improvement can be implemented easily without affecting the others. The entire work is carried out in 3D environment. The modular structure of the entire package is presented in Fig. 1. The major modules are: Input Module, Gear Design Module and Virtual Manufacturing Module. A brief description of these modules is mentioned below.

INPUT MODULE: This module is developed to provide input parameters that are essential for the design and development of the spur pinion and the cutter. In order to make the software user friendly, the process of inputting the data is specifically done through an input dialogue-box created by the maxscript-language. A sample dialogue box is shown in Fig.2.

Fig. 2b: Warning message due to wrong input data Fig. 2a: Dialog box for input parameter GEAR-DESIGN MODULE: Before going for the generation of the spur pinion, one should evaluate the various design parameters and the dimensions of the spur gear to be manufactured based on the input parameters. If the user is not satisfied with the output, he can modify the input to obtain the desired output. In this module, the entire design procedure for the spur pinion has been treated. The different aspects of design calculations, for examples, dynamic load, static load (fatigue load) and the wear load have been calculated in separate programs, and are displayed in the output dialog box. While designing the gear, it has been kept in mind that the gear has to form mesh with that of the rack, so care has been taken to avoid the interference of the mating pair. VIRTUAL MANUFACTURING MODULE: This module has been divided into two sub sections: (a) Cutter Generation and (b) Spur gear Generation

Cutter generation: In this section of the virtual manufacturing, solid model of the rack form cutter is developed. This cutter is used in the later stage to animate the gear generation process in the virtual environment. The cutter with all its cutting geometry such as rack and clearance angles have been provided. Figure 3 exhibits a 3D solid model view of the cutter developed by the software. Spur gear Generation: In this sub module, spur gear is generated. In order to simulate actual machining operation, the blank, which is to be used for the generation of spur gear, is bolted on the movable tabletop. The required washer and back-plate are also tied with the same so that it will have a firm support and ready for the machining purpose. The cutter is positioned at a desired location. Afterwards the cutter is given motion to cut the pre-positioned blank to generate involute profile tooth on it. Generation by means of such a tool is called Copy-generation. The arrangement of such a cutter relative to the blank is illustrated in the Fig. 4. Creation of the cutter: The gear is generated from the gear blank. For the generation of the gear, various input parameters for the cutting motion of the rack cutter are provided through input dialog box. In order to start the cutting process, the blank should be properly fastened on a tabletop as shown in Fig. 4.

Fig. 3 Rack form cutter

Fig. 4 Uncut gear blank

The cutter is adjusted radially with respect to the axis of the work. It is reciprocated so that its edges may sweep out the surface of the teeth of the imaginary rack forming the basis of the design of the tooth profile of the blank. In addition to this reciprocation, the cutter is advanced in the direction of the pitch line and at the same time the work is rotated about its axis at a speed such that it’s pitch point has the same linear velocity as that of the rack. In other words, the pitch circle of the blank and the pitch line of the rack roll together. In consequence the straight cuttings edges generate the involute profile in the blank. The simultaneous motion of the cutter and the blank are shown in Fig. 5. SPECIAL MODULE In the special module, additional features are provided for better understanding of the gear generation process. They are a) Camera Views (snap shot), b) Camera Views (Animated) and c) Movie Files.

Cutter Pitch line

P

Pitch circle

O Gear Blank

Fig. 5 Simultaneous motion of the cutter relative to the blank

For such a process to be continuous, the length of the cutter would supposed to be somewhat longer than the pitch circumference of the work; since this is usually impracticable, the cutter is withdrawn from the work after it has advanced a distance equal to an integral number of pitches and return to its starting point, the blank in the meantime remaining stationary. This is repeated until all the teeth are cut. In the software, provision is made to display the following motions of the system in the animation mode so that the users have the feeling of virtual environment created in 3D. a) Reciprocation of the cutter b) Tangential feed of the cutter and rolling of the gear-blank c) The advanced and reliving motion of the gear-blank d) Radial feed of the cutter e) Indexing of the gear-blank RESULTS AND DISCUSSIONS It is not possible to present all the features of the software due to space limitation. Some of the salient features are highlighted below. As the cutter reciprocating up and down over the gear blank, a few teeth will be partially generated on the gear blank at a time. None of the teeth will be in complete shape in the first cut following the principle of gear generation. It should be noted that the cutter teeth profile is straight edge whereas in case of gear, it is having involute profile.

In order to create the impression of cutting, a large number of frames are generated; each one exhibiting different amount of material removal from the gear blank. The downward motion of the cutter is assumed to be the cutting stroke. The requisite depth of cut is introduced by bringing the cutter to the predetermined position above the blank. The gear blank below the cutter is not yet cut. This is one frame and is shown to the viewer. The next frame shows the sequence when the cutter just finishes the cutting motion and a few partial teeth are developed on the blank. The successive frames illustrate the withdrawal of the cutter, its backward movement, indexing of the gear blank and positioning of the cutter for the next cutting action. When all these frames are shown one after another, observer will have the impression of virtual manufacturing of the gear. This process continues until all the teeth successively passes on the pitch circumference of the gear-blank. Figure 6 shows a few of the frames during cutting process mentioned above.

Fig. 6 Different frames created by the software for virtual manufacturing The software has the facility of creating movie files in which user can control projection of frame rates. Therefore, it is very useful for demonstration purpose as well. The user can change the camera view as per his requirement for better understanding of the operational principal. Generally the frame rate varies from 60 frames per second (fps) to 10 frames per second. The upper limit corresponds to what a human eye can perceive, and the lower limit is governed by the requirement of continuous motion. Generally the frame rate for films became standardized at 24 fps.

CONCLUSION A user friendly software package has been developed that can tackle the problem of gear design and subsequent visualization of the gear generation process in a virtual environment. It also focuses the development of a rack form cutter, which in the later stage being used for the generation of the gear. All the models are developed in 3D environment. Additional features like camera views, movie files, etc. are incorporated for better understanding of a fairly difficult subject. Provisions are made to enter the input data through dialog box. If there is any incorrect data, warning message is given by the software indicating what should be done next. The results of all the design calculation are indicated in the output dialog box. For a designer these values are very useful information. Using the above output, a designer may have an overall idea about the gear to be manufactured. Once the designer is sure about the output results of the design calculation, he can proceed forward for subsequent Virtual Manufacturing operation. He can also switch between design module and manufacture module at will thus leading to an optimized product. ACKNOWLEDGEMENT This work has been carried out under the financial support of AICTE, Ref.: R&D Project, File No. 8019/RDII/R&D/COM(167)/2000-01 dated 20.12.2000. REFERENCES 1. 2. 3. 4. 5. 6.

Tesic, R. and Banerjee; P., Design of Virtual Objects for Exact Collision Detection in Virtual Reality Modeling of Manufacturing Processes, Proceedings of International Conference on Robotics and Automation, Detroit, 1999. Balyliss, G. M., Bowlyer, A., Talyor, R. I. and Willis, P.G., Virtual Manufacturing, Proceedings of International Workshop on Graphics and Robotics; 1993. Balyliss, G. M., Bowlyer, A., Talyor, R. I. and Willis, P.G., Theoretic Solid Modeling Techniques and Application Using the Virtual Manufacturing; Proceedings of CSG-94, 1994. Kimura, F., Product and Process Modeling as a Kernel for Virtual Manufacturing Environment; CIRP Annals, 42: 147-150,1993. Arangarasan, R. and Gadh; R., Geometric Modelling and Collaborative Design in Multimodel, Virtual Environment; Proceedings of ASME, IDETC/CIE Conference, Sept. 10-13, 2000. Roy, S., Pohit, G. and Saha, K.N., Computer Aided Design of Spur Gear, Proceedings of 20th AIMTDR Conference, BIT Mesra, Ranchi, India, 13-15 Dec., 2003.