机械外文翻译--虚拟制造在齿轮生产中的应用.doc

Application of virtual manufacturing in generation of gearsReceived: 29 November 2004 / Accepted: 5 May 2005 / Published online: 24 November 2005Spfinger-Verlag.London Limited 2005Abstract The manufacturing process of gears 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 spur and helical gears and the corresponding rack form cutter necessary for the manufacturing. Using this information, solid models for the cutter and blank are developed and finally gear-manufacturing processes are simulated in a virtual manufacturing environment. The user has the option to choose between designs and manufacture mode at will. The integrated process may also help to develop an optimized product. For better understanding of the operational principle, an animation facility in the form of a movie is included in the package.Keywords Virtual manufacturing; Animation; Gear generation1 IntroductionA 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 two-dimensional sketch. There may be some components that are not adequately described by the two-dimensional approach. In the 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 models 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 tile motion of the gear blank and the gear cutter. This can be achieved very efficiently with the help of the virtual manufacturing technique. It is a technology to create a 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 real life situations. 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 Baneljee 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 VP, MI, (virtual reality manufacturing language) and 3D Sludio Max. They have developed different parts of an automobile and through the special effect of animation imparted all possible motion to the model. The technology is further enhanced by Kiulera 4, who treated product and process modeling as a kernel for the virtual manufacturing environment. In his work, Kimura has incorporated significant modeling issues like representation, representation language, abstraction, standardization, configuration control, etc. Arangarasau 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 Studio Max and VRML, etc. At .Jadavpur University, research work 6, 7 is being carried out to simulate the gear manufacturing processes using A I Ill)CAD and 31) Studio Max as platforms. 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 tile art and literature review reveal that the scope of virtual manufacturing is wide open for simulating spur gear generation processes. Computer simulation can be very effectively used for viewing along with aiding 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 spur and helical gears from the blank using a rack cutter. The scope of the work includes the generation of design data for the spur and helical gears and the rack form cutter, the generation of solid models for the cutter and blank, and finally to simulate gear-manufacturing process through animation. The main motivation of the work is to simplify the task of designing, and to 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 max-script, an object contained programming language that can be run in 3D Studio Max environment.2 Description of the softwareThe 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. 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 a 3D environment. The modular structure of the entire package is presented in Fig. l. The major modules are: input module, gear design module, virtual manufacturing module and special module. A brief description of these modules is mentioned below.2.1 Input moduleThis module is developed to provide input parameters that are essential for (tie design and development of the spur and helical gears and the corresponding cutters. 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 max-script-language. A sample dialogue box is shown in Fig.2. Some fields have some restrictions like predefined lower or upper limits or predefined steps for increment or decrement. This is done purposively to make the environment more user friendly and to restrict the user from entering invalid data, for example, a user cannot make the number of gear teeth less than 18.2.2 Gear-design moduleBefore going for the generation of the gears, one should evaluate the various design parameters of the gears to be manufactured based on the input parameters. In order to design a gear pair, the following data are essential.I Rpm at which the gear is running2. The power being transmitted3. The transmission ratio of the assembly In addition, users may specify the following operational conditions/parameters:1. Precision of the gear assembly2. Pressure angle of the gear3. Material of the pinion4. Type of shock load required for the pinion to take up5. Helix angle in case of helical gear If the user is not satisfied with the output, he can modify the input to obtain desired output. In this module, the entire design procedure for the gears has been treated. The different aspects of design calculations, for example, dynamic load, static load (fatigue load) and the wear load have been calculated in separate programs, and are displayed through 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.2.2.1 MethodologyVarieties of gear cutting processes are available and are generally being followed in the industries during their manufacturing. In this paper, Focus is given on gear manufacturing through generation. The underlying principle of gear design is based on the fact that the profiles of a pair of gear teeth bear a definite relationship to each other such that the pair of teeth have a predetermined relative motion and contact at every instant. Therefore, if the relative motion of the profiles and the form of one of them is known, the determination of the form of the other may be regarded as tile problem capable of solution by either graphical or analytical means. The actual production of gear tooth represents a solution to the above problem by mechanical means known as generation. The generation is a method that follows the following principles. 1. A cutting edge (basically a gear with cutting edges) is given a motion. As a result, it is caused to sweep out the surface corresponding to the actual teeth surfaces of the known member of a pair of conjugate gears. 2. A blank is mounted at an appropriate relationship to the cutter. It is given a motion that the finished gear must have relative to that of the cutter. As a result of the simultaneous movement and the cutting action of the cutter, teeth are formed on the blank conjugate to that represented by the cutter.In fact due to the addition of the relative motion, the profile given to the work piece is different from that of the cutter. This differentiates the generating from the forming operation. 2.2.2 Spur gear Generation of spur gear by means of cutter corresponding in form to the mating gear is well known. Cutter may be in the form of a rack. For an involute system of tooth profiles, the cutter corresponding to the rack will have straight sides. The arrangement of such a cutter relative to the blank is shown in Fig. 3. 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 is 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. For such a process to be continuous, The length of the cutter should be somewhat longer than the pitch circumference of the work；since this is usually impracticableThe cutter is withdrawn from the work after it has advanced a distance equal to all integral number of pitches and return to its starting point，the blank in the meantime remains stationaryThis is repeated until all the teeth are cut 2.2.3 Helical gear It is well known that a helical involute gear is conjugate to a straight rack having inclined teethTherefore，the same method described above can be employed to manufacture a helical gearHowever, the direction of reciprocation of the rack cutter must be inclined to the axis of the blank at all angle equal to the helix angle of the gearThe cutter must roll over the blank in a direction similar to that described earlierThe simultaneous motion involved and the orientation of the cutter relative to the blank during the cutting operation is shown in Fig.4 2.3 Virtual manufacturing module This module has been divided into two sub sections：(a) cutter generation，and (b) gear generation 2.3.1 Cutter generation In this section of the virtual manufacturing，a 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 providedFigure 5 exhibits a 3D solid model view of the cutter developed by the software 2.3.2 Gear generation This module is further subdivided into two parts，namely, (i) spur gear generation module，and (ii) helical gear generation module.(i) Spur gear generation In this sub module, spur gear is generated. In order to simulate the 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 be ready for the machining purpose. The cutter is positioned at a desired location. Afterwards, the cutter is given requisite motion to generate involute profile tooth. 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, 6. The kinematics of the gear shaping process involve the following motions.1. Reciprocation of the cutter2. Tangential feed of the cutter and rolling of the gear blank3. The advanced and reliving motion of the gear-blank4. Radial feed of the cutter5. Indexing of the gear-blank All of the above input parameters can be entered through tile input dialog box. 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 a virtual environment created in 3D.(ii) Helical gear generation In the case of helical gears, as the cutter reciprocates up and down over the gear blank. It makes a definite angle with the vertical, equal to the helix angle of the cutter (Fig. 7). As a result, a few teeth that are inclined to the axis of the blank will be partially generated on the gear blank at one time. None of the teeth will be complete in first phase following the principle of gear generation.2.4 Special moduleOne of the major objectives of the software is to simulate the various simultaneous movements involved in a gear generation process. 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.2.4.1 Camera views (snap shot)The software provides the facility to place the camera at different coordinate positions and thus display different camera views of the cutting process. These are the still pictures taken in render form at successive intervals of the machining process. Still pictures of the partially cut pinion along with that of the cutter at every step of cutting is recorded and enable the user to feel the reality in a virtual environment,2.4.2 Animation and movieAnimation is the backbone of virtual manufacturing as it gives life to already created stationary objects, in other words, it simulates the dynamic behavior of different components. In order to create the effect of animation, a series of still pictures are first generated with a little change of position of the objects from the previous one. When these pictures are displayed in proper sequence at successive interval, they create the impression of moving objects. Each of these pictures is known as flame. For the animation, time interval between successive frames is very important. Generally, the human eye can perceive a frame rate between 60 frames per sec (fps) and I0 fps. The illusion of continuous motion as opposed to a fast paced slide show starts to break down under 1 2 fps. So, frame rate is to be kept above this limit. Generally the frame rate for films becomes standardized at 24 fps. In addition, the animator has to decide whether a given motion has to be shot on ones or on twos. For simple motion it is better to shoot on twos in which case each frames would be shot twice, making the effective playback rate 12 fps. For a very swift or intricate motion, the frames of shooting on ones are generally recommended to keep continuity. The cutter and the gear blank occupy different positions in each of the frames depending on the kinematics relationship of the cutting process. This is achieved through the max-script programming environment of 3D Studio Max. They are stored in the hard disk as rendered views of the objects so that whenever necessary they can be run efficiently with the help of Windows media player:2.4.3 Animated camera viewThe software has the additional facility to pan the camera as the gear generation process is in progress. The procedure is quite simple and is described below in brief. As mentioned in the earlier section, a first snap shot of the machining process is taken with the camera situated at a particular position. The next frame is taken with the camera position shifted a little bit from its original location. This process continues until the camera comes to the pre-determined end position. The number of frames to be created within the interval is decided as per the visual requirement. Each of the frames captures the progressive development of the cutting process, while the camera moves along definite path. When these frames are projected on the screen successively, it creates the effect of panning the camera. This facility is very useful to understand the complex mechanism of the gear generation process. However, setting of camera locations requires a thorough understanding of 3D co-ordinate systems. 3 Results and discussions It is not possible to present all the feature of the software. Some of the salient features are highlighted below. As the cutter reciprocates 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 the case of gear, it has an involute profile. In order to create the impression of cutting, a large number of frames are generated, each one exhibiting a diff