Multiple Chapters: NC System This Study Focuses

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[. . .] 5-D (two5D_manufacturing_feature). Every working step included contains sub-features (such as pocket, step, planar_face, round_hole slot, general_outside_profile, etc.) along with cutting condition data or information (Calabrese and Celentano, 2007).

The complete and thorough explanation related to the working steps is enclosed in the technology description. This full explanation includes information with respect to machining strategies, tools, definitions of the work pieces and the things of similar nature. For instance, an entire technology description contains depth of hole that is required to be machined, diameter of the tool, rotational speed, and feed rate, etc. (Calabrese and Celentano, 2007). The geometry data employed in different components is explained by employing the ISO 10303 structure (Calabrese and Celentano, 2007).

Every STEP-NC program has a PROJECT and a WORK PLAN unit. The former is a top-level unit, which tells the user about the beginning of a program. It also helps in identifying the work plan that needs to be placed on work along with the work piece used for conducting various operations. The latter entity explains the geometry and the materials that would be used for the operation (Calabrese and Celentano, 2007).

Two different versions of the STEP-NC which are in the making include the following: Application Interpreted Model (AIM) of ISO14649 (also known as ISO 10303 AP-238) (ISO, 2003c) and Application Reference Model (ARM) (also known as ISO14649) (ISO, 2003a and 2003b; Calabrese and Celentano, 2007).

A CAD Manager John Gray, who works at International TechneGroup Inc. (ITI), located in the region of Milford, Ohio points out the difficulty associated with translation when using dissimilar CAD systems. This is due to the fact that both the systems may use separate mathematical representations for similar geometry. Two translators, made by the firm, namely IGES and STEP are being used by many powerful programs currently. IGES, for example, categorizes surfaces such as Nubs surfaces and cylinders are categorized to be exclusive. If a postprocessor is unable to recognize an entity that has been sustained by the preprocessor it simply pays no heed to it. This undetected entity could be the cause for the breakdown on the post processor as pointed out by John Gray (Laguionie et al., 2009).

Problems may also arise because of complicated making of the 3D components and then transferring IGES files to CAM systems. The final model could be infected with huge gaps amongst surfaces if the final user doesn't choose the right translator. This problem can be solved on the basis of their understanding. Gray points out this problem when he says that majority of the people who use CAD depend on the default settings. Most blunders related to translation are a result of the users least participation in data exchange until it becomes problematic. Those who make IGES files of their drawing have to choose from over 50 variables when choosing the right flavor. A few may be related to geometry while the rest may be related to annotation (Laguionie et al., 2009).

Gray explains this concept further by relating it to the locks in a house. If the locks are from one brand then one key would be enough to serve the purpose but if on the contrary they are from more than one brand then a solitary key wouldn't be enough. A CAD interoperability consultant, Doug Cheney at ITI points out the difficulty involved in transferring models amongst various MCAD systems. He explains that each of models may use separate ways for modeling. Catia 4, an old system, works by first making the surfaces and then combining them to built 3D models by using steps with the features and parameters. Recent systems make solid models and have a history tree that constitutes of the tabs of all the steps. In this case, an IGES solid part can also become a surface part mainly due to the fact that surfaces have been divided when translation was done (Laguionie et al., 2009).

Because of the fact that history-based systems employ inferential modeling technique in which a component of the software explains the geometry as opposed to the IGES and STEP. The fact is that IGES and STEP make use of specific geometry based on mathematical equations, and if these are used then transferring models between history and non-history-based systems could be problematic as pointed out by Cheney. Hence higher-order geometries should be altered to lower-order geometries when files are transferred to IGES from an inferential system, which in itself can be a source of difficulty. These conversions can give way to gaps in volumes if they are not done properly (Weck, 2003).

Chapter 2: Literature Review

Because STEP-NC is an improvement of STEP when handling NC processes, it greatly adheres to the standard set by STEP. It therefore implies that all the ways employed (ISO, 1994, 1998, 2000a, 2000b, 2001, 2002, 2004a, 2004b) that are explained by STEP for making and transferring of the product models are applicable. The interface mechanism, Part 21 physical le, is the most widely accepted one. The HEADER, for instance, in a STEP-NC consists of the more common type of information about the part of the program which includes the name, author, data and also the organization (OMG, 2003). The major part of the program is the DATA section which consists of all the information of work related to manufacturing and geometries. The data is separated into three major chunks, first being the work plan and executables, second being the description related to the technology and finally the third part is the description of geometry. Also constituting this section is the PROJECT entity that makes up the specific reference required for beginning of the manufacturing work. It consists of a work plan that is essential for creating a series of manufacturing objectives or commands ready to be put to work and the order for this is provided by the order of executables. If an amendment has to be made in the order it is done by altering this segment of the program. The work plan is also responsible for mixing the various executables. The mixing is usually done in a linear format and/or relies on the given situation if the conditional controls are being put to use (Xu, 2006).

The G-code tells the system how exactly to go about the making process. STEP-NC, on the other hand, deals with the problem of what-to-make by specifying individual tasks that depend upon the machining components. Tasks may include pre-drilling, noshing, drilling and even roughing. The purpose of this is to enable the part program to provide the shop with the equipment or by providing data about the machining task and also about the technological data that may be required over authentic geometrical and topological information; this may also be referred to as higher-level information. Consequently, any changes or alteration at the shop can be easily saved and sent back to the department related to the planning stage and would facilitate an enhanced exchange and conservation of experience and the knowledge (Xu, 2006).

To prevent the information from being displaced when moving across various stages, STEP-NC supplies data models, which are complete and structured, connected with the geometrical, as well as technological information. To equal the performance of a specific CAM shop, programming (SEP) or even an NC, the data model can further be used for newer scalable that contain the conformance classes or for newer technology. A need for a postprocessor methodology will be finished because the interface no longer needs to be provided with the machine-specific information. Saving any alterations at the shop and then sending them back to the design division to allow the accomplishment of the bidirectional information from CAD/CAM to CNC machines (Feeney et al., 2003).

Recently a couple of varieties of STEP-NC are being structured which include namely the application reference model (ARM) (ISO, 2003b, 2003c and 2003d) as well as the application interpreted model (AIM). Containing a comprehensive analysis of the standards required for CNC applications, the ARM, ISO 14-649 contains the particular objects that are precisely determined in addition to the connections among them. EXPRESS, a modeling language is used to develop the structure (ISO, 2003b, 2003c and 2003d). The AIM model, on the contrary, allows the user to draft the application requirement data determined within the ARM (ISO 14-649) in a combined ISO 10-303 application protocol. This is done by following predetermined sets of STEP concepts which are known as a "generic resources." Based on the same principles as some of the other STEP application protocols, AP-238 can exchange information smoothly. Readers should go through studies done by Wolf (2003) and (Feeney et al., 2003) in order to obtain more information on the usage and differences (Xu, 2006).

Research in the field of STEP-NC can be observed worldwide where many important projects have been conducted with the combined efforts of many countries living in either the same region or living overseas (Xu et al., 2005). Three kinds of projects are conducted which constitute the following: first one being… [END OF PREVIEW]

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