xxxx機(jī)械設(shè)計制造及自動化畢業(yè)設(shè)計英文翻譯資料-全文預(yù)覽
【正文】 constructed by the reverse engineering technique. RE is a methodology for constructing CAD models of physical parts by digitizing an existing part, creating a digital model and then using it to manufacture ponents. RE can reduce the development cycle when redesigns bee necessary for improved product quality. Preexisting parts with features for improved performance can be readily incorporated into the desired part design. Therefore, it is very useful in creating the CAD model of an existing part when the engineering design is lost or has gone through many design changes. When a designer creates a new design using mockup, it is also necessary to construct the CAD model of the mockup for further use of the design data in analysis and manufacturing. The three primary steps in RE process are part digitization, features extraction, and CAD modelling. Part digitization is acplished by a variety of contact or noncontact digitizers. There are various mercial systems available for part digitization. These systems range from coordinate measuring machine (CMM), laser scanners to ultrasonic digitizers. They can be classified into two broad categories: contact and noncontact. Laser triangulation scanner (LTS), magnetic resonance images (MRI), and puter tomography (CT) are monly used as noncontact devices. Contact digitizers mainly have CMM and crosssectional imaging measurement (CIM). Feature extraction is normally achieved by segmenting the digitized data and capturing surface features such as edges. Part modelling is fulfiled through fitting a variety of surfaces to the segmented data points.In order to reduce the iterations of designprototypetest cycles, increase the product process and manufacturing reliability, it is necessary to guide in optimizing the product design and manufacturing process through virtual prototype (VP). VP is a process of using 3D CAD model, in lieu of a physical prototype, for testing and evaluation of specific characteristics of a product or a manufacturing process. It is often carried out by CAE and virtual manufacturing system. Computer aided engineering (CAE) analysis is an integral part of timepression technologies. Various software tools available (. ANSYS, MARC, IDEAS, AUTOFORM, DYNAFORM, etc.) can speed up the development of new products by initiating design optimization before physical prototypes are built. The CAD models can be transferred to a CAE environment for an analysis of the product functional performance and of the manufacturing processes for producing the product’s ponents. It has also proven to be of great value in the design optimization of part geometry, to determine its dimensions and to control warpage and shrinkage while minimizing processinduced residual stresses and deformations. Virtual manufacturing system (VM) is the natural extension of CAE. It simulates the product functionality and the processes for producing it prior to the development of physical prototypes. VM enables a designer to visualize and optimize a product process with a set of process parameters. The visualization of a virtually simulated part prior to physical fabrication helps to reduce unwanted prototype iterations. Therefore, a product virtual manufacturing system may result in accurate determination of the process parameters, and reduce the number of costly physical prototype iterations. 3D CAD model and VP allow most problems with unfitting to bee obvious early in the product development process. Assemblies can be verified for interference as VP can be exercised through a range of tasks. Structure and thermal analysis can be performed on the same model employing CAE applications as well as simulating downstream manufacturing processes. It is clear that VP increases process and product reliability. Although VP is intended to ensure that unsuitable designs are rejected or modified, in many cases, a visual and physical evaluation of the real pon
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